Motor drive system and vehicle braking system

Abstract

To reduce the peak value of a short-circuit current when an electric motor is short-circuited.SOLUTION: A motor drive device (100) includes a rotation detection unit (8) that detects that an electric motor (22) is driven by external force due to an induced voltage generated by the electric motor (22) when the torque of the electric motor (22) fails, a short circuit switch (7) that shorts between terminals of the electric motor (22), and a switch control unit (10) that turns on the short circuit switch (7) intermittently in synchronization with the induced voltage when the rotation detection unit (8) detects that the electric motor (22) is driven by external force.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a motor drive device for causing a motor to perform a short - circuit braking operation and a vehicle braking device including the same.

Background Art

[0002] Patent Document 1 describes a braking device that holds an electric braking force when an abnormality in an in - vehicle power supply is detected while an electric braking force is applied to a wheel by an electric brake. Specifically, in this braking device, when an abnormality in which power supply to the electric motor of the electric brake from the in - vehicle power supply is impossible is detected while an electric braking force is being applied to the wheel by the electric brake, the electric motor is short - circuited. As a result, a short - circuit brake operates, and it becomes difficult to rotate the electric motor by an external force, so that the electric braking force applied to the wheel can be held.

[0003] In Patent Document 1, it is premised that power supply to the ECU that controls the electric motor is possible in order to short - circuit the electric motor. However, from the viewpoint of fail - safe, even when power supply to the ECU is unnecessary, it is desirable to short - circuit the electric motor.

[0004] For example, Patent Document 2 describes a device that shorts both ends of two FETs each constituting each phase of a bridge circuit that drives an electromechanical device (electric motor) when the power supply fails. In a state where the FETs are short - circuited by the semiconductor switches, in the bridge circuit, for example, the upper - side FET of the U - phase is turned ON and the lower - side FETs of the V - phase and W - phase are turned ON. As a result, when the electric motor is driven by an external force, a short - circuit current flows through each phase via the turned - ON FETs, and the electric motor operates in a generator mode that generates electricity in the U - phase.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, in the apparatus described in Patent Document 2, the peak value of the short-circuit current that flows when the electric motor operates in generator mode may be excessive.

[0007] One aspect of this invention aims to reduce the peak value of the short-circuit current when an electric motor is short-circuited. [Means for solving the problem]

[0008] To solve the above problems, a motor drive device according to one embodiment of the present invention is a motor drive device for driving an electric motor, comprising: a detection unit that detects when the electric motor is driven by an external force due to an induced voltage generated by the electric motor when the torque of the electric motor is lost; a short-circuit switch that short-circuits the terminals of the electric motor; and a control unit that, when the detection unit detects that the electric motor is driven by an external force, turns on the short-circuit switch intermittently in synchronization with the induced voltage.

[0009] With the above configuration, the short-circuit switch can be intermittently turned on when the electric motor loses torque. This reduces the peak value of the current (short-circuit current) flowing between the terminals of the electric motor via the short-circuit switch. [Effects of the Invention]

[0010] According to one aspect of this invention, the peak value of the short-circuit current can be reduced when an electric motor is short-circuited. [Brief explanation of the drawing]

[0011] [Figure 1]This figure shows the configuration of a vehicle braking system according to one embodiment of this invention. [Figure 2] This is a magnified cross-sectional view showing the electric cylinder in the above-mentioned vehicle braking system. [Figure 3] This is a block diagram showing the configuration of the motor drive unit in the above-mentioned vehicle braking system. [Figure 4] This is a circuit diagram showing the switching elements that constitute the inverter in the motor drive device described above. [Figure 5] This waveform diagram shows the operation of each part of the motor drive unit during short-circuit braking. [Figure 6] This waveform diagram shows the operation of each part of the motor drive device during short-circuit braking in a comparative example. [Modes for carrying out the invention]

[0012] An embodiment of this case will be described below with reference to Figures 1 to 6.

[0013] Figure 1 shows the configuration of a vehicle braking system 1 in a non-energized state according to one embodiment of this invention. Figure 2 is an enlarged cross-sectional view showing the electric cylinder 2 in the vehicle braking system 1.

[0014] As shown in Figure 1, the vehicle braking system 1 comprises an upstream unit 11, a downstream unit 3, a first brake ECU 901, a second brake ECU 902, and a motor drive unit 100. The vehicle braking system 1 is a device that supplies brake fluid to wheel cylinders 81-84 provided on the wheels of the vehicle. The first brake ECU 901 controls at least the upstream unit 11. The second brake ECU 902 controls at least the downstream unit 3.

[0015] [Upstream Unit] The upstream unit 11 includes a master cylinder device 4, a stroke simulator 43, a simulator cut-off valve 44, a reservoir 45, a first liquid passage 51, an electric cylinder 2, a second liquid passage 52, a communication passage 53, a reservoir liquid passage 54, a master cut-off valve 62, a communication control valve 61, a stroke sensor 71, pressure sensors 72 and 73, and a level switch 74. The upstream unit 11 is connected to the downstream unit 3 via connection paths 510 and 520.

[0016] The master cylinder device 4 is a device that generates hydraulic pressure in response to a driver operation. The master cylinder device 4 includes a master cylinder 41, a master piston 42, a master chamber 41a, and a biasing member 41b. The master cylinder 41 is a bottomed cylindrical member. The master cylinder 41 has an input port 411 and an output port 412.

[0017] The master piston 42 is a piston member disposed within the master cylinder 41 and is mechanically connected to the brake pedal Z. The master piston 42 slides along the inner wall surface of the master cylinder 41 in response to the operation of the brake pedal Z. A through hole 421 is formed in the master piston 42. The master piston 42 is biased toward its initial position by a biasing member 41b described later. The initial position is the position of the master piston 42 when the volume of the master chamber 41a is at its maximum. When the master piston 42 is at the initial position, the through hole 421 and the input port 411 are in communication.

[0018] The master chamber 41a is formed within the master cylinder 41 by the master cylinder 41 and the master piston 42. In the present embodiment, only one master chamber 41a is formed within the master cylinder 41. The volume of the master chamber 41a changes in response to the movement of the master piston 42. When the master piston 42 moves to one side in the axial direction, the volume of the master chamber 41a decreases and the hydraulic pressure in the master chamber 41a increases.

[0019] The biasing member 41b is a spring member provided in the master chamber 41a. In a state where no force is acting on the master piston 42, the master piston 42 is located at the initial position.

[0020] The stroke simulator 43 is connected to the master cylinder device 4 via the simulator cut-off valve 44. The stroke simulator 43 is a device that generates a reaction force (load) against the operation of the brake pedal Z. The stroke simulator 43 includes a cylinder, a piston, and a biasing member. The stroke simulator 43 is connected to the output port 412 of the master cylinder 41 via the liquid passage 43a.

[0021] The simulator cut-off valve 44 is a normally-closed solenoid valve provided in the liquid passage 43a. When the brake pedal Z is operated in a state where the master cut-off valve 62 described later is closed and the simulator cut-off valve 44 is open, a pedal reaction force is generated by the stroke simulator 43.

[0022] The reservoir 45 stores the brake fluid. The pressure inside the reservoir 45 is maintained at atmospheric pressure. Inside the reservoir 45, two storage chambers 451 and 452 for storing the brake fluid are formed respectively.

[0023] The storage chamber 451 is connected to the master cylinder device 4. Specifically, the storage chamber 451 is connected to the input port 411 of the master cylinder 41. When the master piston 42 is located at the initial position, the storage chamber 451 is hydraulically connected to the master chamber 41a via the input port 411 and the through-hole 421. When the master piston 42 slides a predetermined amount from the initial position, the input port 411 and the through-hole 421 are hydraulically disconnected. In this case, the master chamber 41a and the reservoir 45 are hydraulically disconnected. The storage chamber 452 is connected to the electric cylinder 2 via the reservoir liquid passage 54. The reservoir 45 may be composed of two separate reservoirs instead of two storage chambers.

[0024] The first fluid passage 51 is a fluid passage that connects the master cylinder device 4 and the downstream unit 3. One end of the first fluid passage 51 is connected to the master chamber 41a via the output port 412. The other end of the first fluid passage 51 is connected to the connecting passage 510.

[0025] When the master piston 42 slides in a direction that reduces the size of the master chamber 41a while the master chamber 41a and the reservoir 45 are not hydraulically connected, brake fluid is supplied from the master chamber 41a to the first fluid passage 51 via the output port 412, and hydraulic pressure is generated in the first fluid passage 51. The hydraulic pressure generated in the master chamber 41a is supplied to the downstream unit 3 via the first fluid passage 51. The first fluid passage 51 includes a connection part 50 that is connected to a communication passage 53, which will be described later. The first fluid passage 51 is provided with a master cut valve 62 and a pressure sensor 72.

[0026] The mastercut valve 62 is a normally open type solenoid valve located in the first fluid passage 51, on the master cylinder device 4 side of the connection part 50. When the mastercut valve 62 is closed, the master cylinder device 4 and the downstream unit 3 are hydraulically isolated.

[0027] The pressure sensor 72 is located in the first fluid passage 51, on the master cylinder device 4 side of the master cut valve 62. The pressure sensor 72 detects the pressure in the first fluid passage 51. When the master cut valve 62 is closed, the pressure detected by the pressure sensor 72 corresponds to the fluid pressure in the master chamber 41a.

[0028] As shown in Figure 2, the electric cylinder 2 comprises a cylinder 21, an electric motor 22, a piston 23, a hydraulic chamber 24, a biasing member 25, and an anti-rotation member 26. The electric cylinder 2 is a single-type electric cylinder in which a single hydraulic chamber 24 is formed within the cylinder 21. In the following description of the electric cylinder 2, the direction in which the piston 23 reduces the size of the hydraulic chamber 24 will be referred to as the X1 direction, and the direction in which the piston 23 increases the size of the hydraulic chamber 24 will be referred to as the X2 direction.

[0029] The cylinder 21 is a bottomed cylindrical member. The cylinder 21 has a through hole 213 in its side wall. The cylinder 21 has an input port 211 and an output port 212. The input port 211 is formed so as to be connected to the through hole 213 and is an opening formed inside an annular sealing member 214 provided on the cylinder 21. The output port 212 is an opening formed closer to the tip of the cylinder 21 than the input port 211. At least one input port 211 and at least one output port 212 are required.

[0030] The electric motor 22 is connected to the piston 23 via a linear motion mechanism 20 that converts rotational motion into linear motion. The piston 23 is a bottomed cylindrical member and slides along the inner wall surface of the cylinder 21 when driven by the electric motor 22. The piston 23 is held in the cylinder 21 by an anti-rotation member 26 so as not to rotate together with the nut 20b (described later), allowing axial movement (in the X1 and X2 directions) while restricting radial movement. The hydraulic chamber 24 communicates with the input port 211 when the piston 23 is in its initial position. The initial position is near the end of the cylinder 21 on the electric motor 22 side, where the volume of the hydraulic chamber 24 is at its maximum.

[0031] The motor drive device 100 that drives the electric motor 22 will be explained in detail later.

[0032] The hydraulic chamber 24 is partitioned by the cylinder 21 and the piston 23. The volume of the hydraulic chamber 24 changes as the piston 23 moves.

[0033] The hydraulic chamber 24 can communicate with the reservoir 45 via the input port 211. Specifically, when the piston 23 is in its initial position, it is hydraulically connected to the reservoir 45 via the through hole 213 and the input port 211. When the through hole 213 and the input port 211 are blocked by the piston 23, the hydraulic chamber 24 and the reservoir 45 are hydraulically isolated. The hydraulic chamber 24 is connected to the second fluid passage 52 via the output port 212.

[0034] The biasing member 25 is a spring located in the hydraulic chamber 24 that biases the piston 23 toward its initial position. When the electric motor 22 is not driven, the biasing force of the biasing member 25 causes the piston 23 to be in its initial position.

[0035] When the piston 23 is in its initial position, the hydraulic chamber 24 is connected to the reservoir 45 via the through-hole 213, the input port 211, and the reservoir fluid passage 54. As shown in Figure 2, when the piston 23 moves a predetermined amount in the X1 direction from its initial position due to the drive of the electric motor 22, the communication between the input port 211 and the through-hole 213 and the hydraulic chamber 24 is cut off. In this state, the hydraulic chamber 24 is hydraulically disconnected from the reservoir 45. When the hydraulic chamber 24 and the reservoir 45 are hydraulically disconnected, if the piston 23 slides to reduce the size of the hydraulic chamber 24, brake fluid is supplied from the hydraulic chamber 24 to the second fluid passage 52 via the output port 212, and hydraulic pressure is generated in the second fluid passage 52.

[0036] The electric cylinder 2 is configured such that when the relative position of the piston 23 to the cylinder 21 is in a predetermined open position, the input port 211 and the through hole 213 are opened by the piston 23. Furthermore, the electric cylinder 2 is configured such that when the relative position of the piston 23 to the cylinder 21 is in a predetermined closed position, the input port 211 and the through hole 213 are closed by the piston 23. The closed position is set, for example, to the position where the volume of the hydraulic chamber 24 is maximized among the positions where the hydraulic chamber 24 and the reservoir fluid passage 54 are blocked.

[0037] Next, the linear motion mechanism 20 will be described. The linear motion mechanism 20 includes a reduction gear 20a, a nut 20b, a bearing 20c, a screw shaft 20d, and a plurality of balls 20e.

[0038] The reduction gear 20a reduces the rotational speed of the drive shaft 22b of the electric motor 22 and outputs the reduced speed. For example, the reduction gear 20a is composed of a planetary gear mechanism. Specifically, in the planetary gear mechanism, the gear 22c provided on the drive shaft 22b of the electric motor 22 functions as the sun gear. The reduction gear 20a also has a plurality of planetary gears that mesh with the gear 22c and are arranged around the gear 22c, and an internal gear that meshes with the planetary gears. By fixing the internal gear, the planetary gears rotate around the gear 22c while meshing with the internal gear as the gear 22c rotates.

[0039] The nut 20b is a cylindrical member and is rotatably attached at one end to the inner circumferential surface of the open end of the cylinder 21 by a bearing 20c. The nut 20b is connected to the axis (planetary carrier) of the planetary gear, and the rotational driving force generated by the rotation of the planetary gear around the gear 22c is transmitted via the planetary carrier. A helical inner groove is formed on the inner circumferential surface of the nut 20b, extending from the end on the hydraulic chamber 24 side of the screw groove 20d to near the center. The inner groove has a semicircular cross-section.

[0040] The screw shaft 20d is a cylindrical shaft member inserted inside the nut 20b. A screw groove is formed on the outer surface of the screw shaft 20d along its entire length. The screw groove has a semicircular cross-section.

[0041] Multiple balls 20e are held between the internal groove of the nut 20b and the thread groove of the screw shaft 20d. The nut 20b is supported by the screw shaft 20d by the balls 20e.

[0042] The nut 20b, screw shaft 20d, and balls 20e constitute a ball screw. In the ball screw, the rotation of the nut 20b causes the balls 20e to roll between the inner groove of the nut 20b and the screw groove of the screw shaft 20d, which in turn propels the screw shaft 20d in its axial direction (X1 or X2). The balls 20e move to one end of the inner groove, are discharged to the outside, move to the other end of the inner groove, and are returned to the inside of the nut 20b, thus creating an endless cycle.

[0043] The second fluid passage 52 is a fluid passage connecting the electric cylinder 2 and the downstream unit 3. One end of the second fluid passage 52 is connected to the electric cylinder 2, and the other end of the second fluid passage 52 is connected to the connecting passage 520. The fluid pressure generated in the hydraulic chamber 24 is supplied to the downstream unit 3 via the second fluid passage 52. A hydraulic pressure sensor 73 is provided in the second fluid passage 52. The first fluid passage 51 and the second fluid passage 52 are the parts of the fluid passage connecting the master cylinder device 4 and the downstream unit 3 that are located within the upstream unit 11.

[0044] The hydraulic pressure sensor 73 is a sensor that detects the pressure in the second fluid passage 52. When the control mode of the vehicle braking system 1 is the brake-by-wire mode (hereinafter referred to as "by-wire mode"), the hydraulic pressure detected by the hydraulic pressure sensor 73 corresponds to the output pressure of the electric cylinder 2.

[0045] The connecting passage 53 is a liquid passage that connects the first liquid passage 51 and the second liquid passage 52. The connecting passage 53 is connected to the first liquid passage 51 at the connection part 50. A communication control valve 61 is provided in the connecting passage 53.

[0046] The communication control valve 61 is a normally closed type solenoid valve. The valve body of the communication control valve 61 is positioned on the first fluid passage 51 side of the valve seat. Therefore, when the pressure on the first fluid passage 51 side in the communication passage 53 is higher than the pressure on the second fluid passage 52 side, a force acts on the communication control valve 61 in the closing direction. As a result, when the communication control valve 61 is closed, even if the hydraulic pressure in the wheel cylinders 81 and 82 is higher than the output pressure of the electric cylinder 2, a force is applied to the valve body in the direction that presses it against the valve seat (self-sealing), and the valve remains closed.

[0047] The stroke sensor 71 detects the stroke of the brake pedal Z. In this embodiment, two stroke sensors 71 are provided. The data detected by the two stroke sensors 71 is transmitted to the first brake ECU 901 and the second brake ECU 902. The brake ECUs 901 and 902 each acquire stroke information from the corresponding stroke sensor 71.

[0048] The level switch 74 is located in the reservoir 45 and detects when the fluid level in the reservoir 45 falls below a predetermined level. When the fluid level in the reservoir 45 falls below a predetermined value, the level switch 74 transmits data indicating that the fluid level has decreased to the first brake ECU 901.

[0049] [Brake ECU] The first brake ECU 901 and the second brake ECU 902 are electronic control units equipped with a CPU and memory, respectively. Each brake ECU 901 and 902 is equipped with one or more processors that perform various controls. The first brake ECU 901 and the second brake ECU 902 are separate ECUs, but are connected to each other so that they can communicate information (control information, etc.).

[0050] The first brake ECU 901 is configured to control the upstream unit 11. Specifically, the first brake ECU 901 controls the electric cylinder 2 and each solenoid valve 61, 62, 44 based on data detected by multiple sensors 71, 72, 73, 74 of the upstream unit 11. The first brake ECU 901 calculates each wheel pressure based on the detection results of the pressure sensors 72, 73 and the control status of the downstream unit 3.

[0051] The second brake ECU 902 controls the downstream unit 3 based on the values ​​detected by the stroke sensor 71 and the pressure sensor 75. The second brake ECU 902 also receives values ​​detected by a wheel speed sensor (not shown), an acceleration sensor (not shown), etc., installed in the vehicle.

[0052] The vehicle braking system 1 is configured to perform normal control. Normal control is also called by-wire mode. In normal control, the output pressure of the upstream unit 11 is the hydraulic pressure output by the electric cylinder 2. The downstream unit 3 can output hydraulic pressure to the wheel cylinders 81-84 based on the output pressure of the upstream unit 11. Normal control will be described below.

[0053] [Normal control] The first brake ECU 901 has a control unit 91 that controls the upstream unit 11, which includes an electric motor 22, etc. The unit control unit 91 performs normal control and shut-off control. Normal control is a control that hydraulically shuts off the master cylinder device 4 and the wheel cylinders 81-84, and pressurizes the wheel cylinders 81-84 by at least one of the electric cylinder 2 and the downstream unit 3. Normal control includes preparation control and normal pressurization control.

[0054] Preparation control is a control that forms a so-called by-wire mode. In preparation control, the unit control unit 91 closes the master cut valve 62 and opens the communication control valve 61 and the simulator cut valve 44. Preparation control is performed when a vehicle equipped with the vehicle braking system 1 becomes ready to start. Being ready to start means, for example, when the vehicle's ignition is turned on or when an electric vehicle is started. More specifically, preparation control is performed when the first brake ECU 901 is started (powered on).

[0055] Normal pressurization control is a control method that pressurizes the wheel cylinders 81-84 in by-wire mode (ready control complete state). In normal pressurization control, the unit control unit 91 sets a target output pressure based on the data detected by the stroke sensor 71 and the pressure sensor 72, and controls the electric cylinder 2 based on the set target output pressure. In this way, in normal control, the hydraulic pressure of the wheel cylinders 81-84 can be adjusted by controlling the electric cylinder 2 based on the set target value.

[0056] Specifically, the rotational motion of the electric motor 22 is converted into linear motion via the linear motion mechanism 20 and transmitted to the piston 23. As the linear motion (linear movement) of the piston 23 in the X1 direction increases the hydraulic pressure in the hydraulic chamber 24, the braking fluid is pumped towards the wheel cylinders 81-84. This increases the wheel pressure in the wheel cylinders 81-84.

[0057] [Motor drive device] Figure 3 is a block diagram showing the configuration of the motor drive unit 100. Figure 4 is a circuit diagram showing the switching elements that make up the inverter 6 in the motor drive unit 100.

[0058] As shown in Figure 3, the motor drive device 100 is a device that drives the electric motor 22. The motor drive device 100 includes a motor power supply circuit 5 (power supply), an inverter 6, a short-circuit switch 7, a rotation detection unit 8 (detection unit), an ON voltage determination unit 9, a switch control unit 10, an operation permission unit 12, a motor controller 13, a controller 14, and a capacitor C.

[0059] The electric motor 22 is a three-phase brushless motor, and each of the three coils is a U-phase, V-phase, and W-phase motor. One end of each of the three coils of the electric motor 22 is connected to each other, forming a neutral point.

[0060] The motor power supply circuit 5 is a power supply circuit that converts the battery power supply voltage (+BM) into a voltage supplied to the electric motor 22. The motor power supply circuit 5 is composed of switches such as FETs and supplies the +BM voltage to the inverter 6 at any desired timing.

[0061] The inverter 6 is a drive circuit that drives the electric motor 22 by supplying power from the motor power supply circuit 5 to the U-phase, V-phase, and W-phase coils of the electric motor 22. The inverter 6 has high-side switching elements 61UH, 61VH, and 61WH that are connected to the positive terminal of the motor power supply circuit 5, and low-side switching elements 61UL, 61VL, and 61WL that are connected to the negative terminal (ground) of the motor power supply circuit 5. In Figure 3, the switching elements 61UH, 61VH, 61WH, 61UL, 61VL, and 61WL are each indicated by "SW".

[0062] Switching elements 61UH and 61UL are connected in series, and the connection point of switching elements 61UH and 61UL is connected to the other end of the U-phase coil of the electric motor 22. Switching elements 61VH and 61VL are connected in series, and the connection point of switching elements 61VH and 61VL is connected to the other end of the V-phase coil of the electric motor 22. Switching elements 61WH and 61WL are connected in series, and the connection point of switching elements 61WH and 61WL is connected to the other end of the W-phase coil of the electric motor 22.

[0063] Specifically, the switching elements 61UH, 61VH, 61WH, 61UL, 61VL, and 61WL are composed of switching element 61, as shown in Figure 4. Switching element 61 has a FET (Field Effect Transistor) 61a and a body diode 61b. The body diode 61b is connected in parallel with the FET 61a. In the following description, unless otherwise specified, the switching elements 61UH, 61VH, 61WH, 61UL, 61VL, and 61WL will be referred to as switching element 61.

[0064] The short-circuit switch 7 is a switch that short-circuits the terminals of the electric motor 22 and is composed of, for example, an FET. The short-circuit switch 7 is provided between the other end (terminal) of one of the three coils in the electric motor 22 and ground. One end of the short-circuit switch 7 is connected to, for example, the other end of the U-phase coil, and the other end of the short-circuit switch 7 is connected to ground. The short-circuit switch 7 short-circuits the terminals of the electric motor 22 by short-circuiting the other end of one phase coil of the electric motor 22 with ground, thereby allowing current to flow to the other ends (terminals) of the other two phase coils via the body diodes 61b of the other two phase switching elements 61.

[0065] Capacitor C is connected between the positive terminal of the motor power supply circuit 5 and ground. Capacitor C smooths the induced voltage generated by the electric motor 22.

[0066] The rotation detection unit 8 detects when the electric motor 22 is driven by an external force. Specifically, the rotation detection unit 8 detects rotation when the smoothed voltage of the V-phase (or W-phase) voltage generated by the electric motor 22 when the torque of the electric motor 22 is lost exceeds a predetermined value. The rotation detection unit 8 also detects that the motor has (almost) stopped when the voltage falls below the predetermined value.

[0067] The rotation detection unit 8 determines, for example, that the electric motor 22 is rotating when the V-phase (W-phase) voltage exceeds a voltage set as a predetermined value. Such a threshold is set as the minimum voltage at which the circuit operating for the transistors that perform the determination operation in the rotation detection unit 8 can operate.

[0068] When the rotation of the electric motor 22 is detected by the rotation detection unit 8, the ON voltage determination unit 9 determines the ON period for turning on the short-circuit switch 7 based on the period during which the three-phase induced voltage, which has been rectified by the body diode 61b in the inverter 6 and further smoothed by the capacitor C, exceeds a threshold. In the example shown in Figure 3, the ON voltage determination unit 9 makes the above determination using the three-phase induced voltage in the inverter 6.

[0069] The ON voltage determination unit 9 uses a Zener diode to quickly turn on the short-circuit switch 7 (FET) when the set voltage is reached, thereby reducing the heat generated by the short-circuit switch 7, which is typically done over a period of time according to the induced voltage. Furthermore, the ON voltage determination unit 9 can suppress unnecessary ON / OFF switching of the switch near the threshold by changing the threshold so that it increases when the induced voltage rises and decreases when the induced voltage falls.

[0070] The switch control unit 10 generates a gate drive signal that intermittently turns on the short-circuit switch 7 during the ON period determined by the ON voltage determination unit 9, in synchronization with the induced voltage used by the ON voltage determination unit 9 to determine the period during which the short-circuit switch 7 is turned ON. Specifically, the switch control unit 10 generates a pulse voltage such that the short-circuit switch 7 is turned ON when the rising portion of the induced voltage exceeds a set threshold, and the short-circuit switch 7 is turned OFF when the falling portion of the induced voltage falls below the threshold, and outputs this pulse voltage as a gate drive signal during the ON period.

[0071] The operation permission unit 12 is provided on the transmission signal line that transmits the gate drive signal between the switch control unit 10 and the short-circuit switch 7. The operation permission unit 12 permits the switch control unit 10 to control the short-circuit switch 7 by conducting on the transmission signal line and prohibits it by blocking the signal line, based on a command from the controller 14.

[0072] The motor controller 13 controls the current supplied to the electric motor 22 by controlling the switching operation of the switching elements 61UH, 61VH, 61WH, 61UL, 61VL, and 61WL of the inverter 6 based on the command from the controller 14.

[0073] The controller 14 consists of a microcomputer and other components, and monitors and controls the motor drive unit 100. When an abnormality occurs in the electric motor 22, such as torque loss, the controller 14 issues an operation permission command to the operation permission unit 12, and when it is functioning normally, it issues an operation prohibition command to the operation permission unit 12. The controller 14 operates using the battery power supply voltage (+BS).

[0074] Examples of situations in which the electric motor 22 may experience torque loss include a power outage where the motor power supply circuit 5 stops operating, and a state where the motor controller 13 is unable to control the inverter 6. Furthermore, when the controller 14 determines that the system is functioning normally after power is restored, the operation permission unit 12 returns from the operation prohibited state to the operation permitted state.

[0075] [Motor control in case of abnormality] Next, we will explain the control of the electric motor 22 by the motor drive unit 100 when a power outage occurs while the wheel pressure is high. Figure 5 is a waveform diagram showing the operation of each part of the motor drive unit 100 during short-circuit braking. Figure 6 is a waveform diagram showing the operation of each part of a motor drive unit according to a comparative example during short-circuit braking.

[0076] When the power supply is lost and the wheel pressure of the wheel cylinders 81-84 increases, the piston 23 is rapidly retracted by the wheel pressure, causing the electric motor 22 to rotate in the opposite direction to that of normal operation. In this case, the linear motion mechanism 20 has reverse efficiency. The efficiency when rotational motion is converted to linear motion is positive efficiency, and the efficiency when linear motion is converted to rotational motion is reverse efficiency. Therefore, the electric motor 22 can be rotated by the wheel pressure.

[0077] When the electric motor 22 rotates in reverse, it generates a three-phase alternating current induced voltage. These induced voltages are all rectified by the body diode 61b of the switching element 61 in the inverter 6, and then smoothed to an almost DC voltage by the capacitor C, as shown by the dashed line in Figure 5.

[0078] The rotation detection unit 8 determines that the electric motor 22 is rotating when the smoothed voltage exceeds a predetermined value. The ON voltage determination unit 9, upon receiving this determination, determines that if there is a period during which the induced voltage of the V phase in the inverter 6 exceeds a threshold, that period is an ON period. The switch control unit 10 generates and outputs a gate drive signal synchronized with the induced voltage during the ON period.

[0079] When the controller 14 detects a torque loss in the electric motor 22, for example due to a power outage, it reduces the output signal voltage from a high level (e.g., a few volts) to a low level (almost 0 volts), as shown by the thick solid line in Figure 5. The high-level output signal is given to the operation enablement unit 12 as an operation disable command, and the low-level output signal is given to the operation enablement unit 12 as an operation enable command.

[0080] The activation enablement unit 12 receives a low-level output signal, i.e., an activation enablement command, and opens the transmission signal line. As a result, as shown by the thin solid line in Figure 5, a pulse-shaped gate drive signal output from the switch control unit 10 is applied to the gate of the short-circuit switch 7. The short-circuit switch 7 is intermittently turned ON by the gate drive signal.

[0081] In this state, the short-circuit current flowing through the short-circuit switch 7 to the V phase of the electric motor 22 changes as shown by the dashed line in Figure 5. Also, a current flows through the W phase of the electric motor 22 as shown by the dashed line in Figure 5. When the short-circuit current flows through the electric motor 22, the electric motor 22 performs a short-circuit braking action. As a result, the reverse rotation of the electric motor 22 is reduced, so the return distance of the piston 23 can be kept short. In addition, since the short-circuit switch 7 is intermittently turned ON, the heat generated in the switching element 61 (FET) of the inverter 6, the short-circuit switch 7 (FET), and the electric motor 22 in the current path can be reduced.

[0082] Here, a motor drive unit in which the switch control unit 10 is omitted from the motor drive unit 100 is used as a comparative example. In this motor drive unit, as shown by the thin solid line in Figure 6, the short-circuit switch 7 turns ON when the signal indicating the ON period output from the ON voltage determination unit 9 changes from a low level to a high level. As a result, current flows in the W phase of the electric motor 22, as shown by the thick dashed line in Figure 6, and the short-circuit current shown by the dashed line in Figure 6 flows for a longer period than the short-circuit current shown in Figure 5. Therefore, the peak value of the short-circuit current shown in Figure 6 is about 10 percent larger than the example shown in Figure 5 (shown by the dashed line).

[0083] In this way, the motor drive device 100 can reduce the peak value of the short-circuit current by intermittently turning on the short-circuit switch 7, compared to the motor drive device of the comparative example in which the short-circuit switch 7 is continuously turned on.

[0084] [Effects of motor-driven devices] As described above, the motor drive device 100 according to this embodiment includes a short-circuit switch 7, a rotation detection unit 8, and a switch control unit 10. The short-circuit switch 7 short-circuits the terminals of the electric motor 22. The rotation detection unit 8 detects that the electric motor 33 is rotating due to the induced voltage generated by the electric motor 22 when the torque of the electric motor 22 is lost. When the rotation detection unit 8 detects that the electric motor 22 is rotating, the switch control unit 10 intermittently turns on the short-circuit switch 7 in synchronization with the induced voltage.

[0085] According to the above configuration, when the electric motor 22 loses torque, such as when power cannot be supplied to the electric motor from the motor power supply circuit 5, the short-circuit switch 7 is intermittently turned ON. This makes it possible to reduce the peak value of the current (short-circuit current) flowing between the terminals of the electric motor 22 via the short-circuit switch 7.

[0086] Furthermore, in the motor drive unit 100, the short-circuit switch 7 short-circuits the terminals of any one phase of the electric motor 22, which is a three-phase motor, for example, the U phase. In addition, in the motor drive unit 100, the switch control unit 10 may turn on the short-circuit switch during the period from zero to the maximum value of the current of the V phase, which is the next phase after the U phase whose terminals are short-circuited.

[0087] With the above configuration, the short-circuit switch 7 can be turned ON only during periods when a large deceleration torque is generated. This allows the short-circuit current to be interrupted before it reaches its peak.

[0088] Furthermore, in the motor drive unit 100, the switch control unit 10 may be operated by an induced voltage. This allows the short-circuit switch 7 to be driven even in the event of a power outage.

[0089] Furthermore, the motor drive device 100 according to this embodiment is useful for short-circuit braking the electric motor 22 in the event of torque loss (such as power outage or uncontrollable state of the inverter 6). The motor drive device 100 is also useful for causing the electric motor 22 to perform a general short-circuit braking operation, which shortens the stopping time of the motor that maintains rotation by inertia when the power supply is cut off.

[0090] Furthermore, the vehicle braking system 1 according to this embodiment includes an electric cylinder 2 and a motor drive unit 100. The electric cylinder 2 pressurizes the wheel cylinders 81 to 84 with the hydraulic pressure generated when a piston 23 driven by an electric motor 22 moves through a hydraulic chamber 24 inside the cylinder 21.

[0091] According to the above configuration, if a torque loss occurs in the electric motor 22 while the brake fluid pressure (hydraulic pressure in the wheel cylinders 81-84) is increasing, the rotational speed of the electric motor 22 is reduced. This suppresses the impact load caused by the return of the piston 23 that occurs when a power loss occurs while the brake fluid pressure is increasing or while the brake fluid pressure is being maintained.

[0092] Furthermore, the vehicle braking device 1 according to this embodiment includes an electric cylinder 2 having a linear motion mechanism 20. The linear motion mechanism 20 includes a ball screw including a nut 20b, a screw shaft 20d, and a ball 20e, and a planetary gear mechanism that transmits the rotational driving force of the drive shaft 22b of the electric motor 22 in a direction in which the rotation centers of the drive shaft 22b and the nut 20b coincide.

[0093] With the above configuration, the nut 20b and the electric motor 22 can be positioned in the same direction. This reduces the space required for the electric cylinder 2 to be located.

[0094] [Additional Notes] This invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Furthermore, embodiments obtained by appropriately combining the technical means disclosed in each embodiment are also included in the technical scope of this invention. [Explanation of symbols]

[0095] 1. Vehicle braking system 2 Electric Cylinder 5. Motor power supply circuit (power supply) 7 Short-circuit switch 8. Rotation detection unit (detection unit) 10 Switch control unit (control unit) 21 Cylinder 23 pistons 24. Hydraulic chamber 81-84 Wheel Cylinder 100 Motor drive unit

Claims

1. A motor drive device for driving an electric motor, A detection unit that detects when the torque of the electric motor is lost, by the induced voltage generated by the electric motor, that the electric motor is driven by an external force, A short-circuit switch that short-circuits the terminals of the aforementioned electric motor, The system includes a control unit that, when the detection unit detects that the electric motor is being driven by an external force, intermittently turns on the short-circuit switch in synchronization with the induced voltage, The aforementioned electric motor is a three-phase motor. The short-circuit switch short-circuits the terminals of any one phase of the three-phase motor. A motor drive device comprising: a control unit that turns on the short-circuit switch during the period from zero to the maximum value of the current of the phase following the phase in which the terminals are short-circuited, and turns off the short-circuit switch when the current of the phase following the phase in which the terminals are short-circuited reaches its maximum value.

2. The motor drive device according to claim 1, wherein the control unit operates by the induced voltage.

3. An electric cylinder that pressurizes a wheel cylinder with hydraulic pressure generated by the movement of a piston driven by the electric motor within the hydraulic chamber of the cylinder, A vehicle braking device comprising a motor drive device according to claim 1 or 2 for driving the aforementioned electric motor.

4. The vehicle braking device according to claim 3, wherein the external force is generated by an increase in the wheel pressure of the wheel cylinder, which causes the piston to return due to the wheel pressure.

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