JP7165598B2 - brake device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking device that applies braking force to a vehicle such as an automobile.

Patent Literature 1 discloses a braking device that includes a braking mechanism that generates braking force for a vehicle by driving an electric motor that is controlled by a pulse width modulation method, and a control device that controls the electric motor based on a braking request. .

JP-A-2000-168545

By the way, in order to control the electric motor, it is necessary to switch the U-phase, V-phase, and W-phase of the inverter circuit. Since switching noise is generated during control of the electric motor, radiation noise (emission) of EMC (electromagnetic compatibility) is a concern. In order to comply with EMC standards, it is necessary to lengthen the rise time and fall time during switching and reduce the slew rate. If the rise time and fall time during switching are lengthened, there is a problem that the switching loss of the drive element (FET) of the inverter circuit increases, and the temperature also increases at the same time.

In addition, in the brake device described in Patent Document 1, the frequency of switching is reduced by lowering the PWM frequency during switching in order to reduce loss during a sudden braking request. As a result, switching occurs within the audible frequency range, so magnetostrictive noise generated according to the PWM frequency falls within the audible range, causing the problem of unpleasant noise that echoes in the ears of the user (driver) while driving. ,A large impact.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a brake device capable of reducing loss while keeping magnetostrictive noise out of the audible range and suppressing heat generation of a control device.

In order to solve the above-described problems, the present invention provides a brake mechanism that generates braking force for a vehicle by driving an electric motor controlled by a pulse width modulation method, and a control device that controls the electric motor based on a braking request. In the brake device having the control device, the control device reduces the rise time and rise time of the drive signal for controlling the electric motor when there is a braking request for emergency braking, compared to when there is a braking request other than for emergency braking. The descending time is shortened , and the PWM frequency of the drive signal is set to a value higher than the maximum audible frequency during emergency braking and during normal times other than emergency braking, and is set to the same value .

According to the present invention, loss can be reduced while magnetostrictive sound is kept outside the audible range, and heat generation of the control device can be suppressed.

1 is a diagram showing a system configuration of a vehicle to which an electric brake device according to an embodiment of the invention is applied; FIG. FIG. 2 is a schematic diagram showing an electric brake device in FIG. 1; FIG. 3 is a block diagram showing the configuration of a rear electric brake ECU; Fig. 3 is a flow chart showing slew rate control; FIG. 4 is a characteristic diagram showing changes over time in drive voltage, drive current, and loss during normal operation; FIG. 5 is a characteristic diagram showing temporal changes in drive voltage, drive current, and loss during emergency braking;

Hereinafter, a case where an electric brake device as a brake device according to an embodiment is applied to a four-wheeled vehicle will be described as an example with reference to the accompanying drawings.

FIG. 1 is a diagram showing a system configuration of a vehicle 1 to which an electric brake device 20 according to an embodiment is applied. The brake device 2 mounted on the vehicle 1 includes a hydraulic brake 4 (front braking mechanism) provided corresponding to the left front wheel 3L and the right front wheel 3R, and a left rear wheel 5L and a right rear wheel 5R. An electric brake 21 (rear braking mechanism) as an electric caliper provided correspondingly is provided. A main ECU 9 is connected to a hydraulic pressure sensor 7 and a pedal stroke sensor 8 that measure the amount of operation of the brake pedal 6 by the driver. The main ECU 9 receives signals from the hydraulic pressure sensor 7 and the pedal stroke sensor 8 and calculates a target braking force for each wheel (four wheels) according to a predetermined control program. Based on the calculated braking force, the main ECU 9 transmits a braking command for each of the two front wheels to the front hydraulic device ECU 10 via a CAN 11 (Controller area network). Based on the calculated braking force, the main ECU 9 transmits a braking command for each of the two rear wheels to the rear electric brake ECU 31 via the CAN 11 . The main ECU 9 is also connected to wheel speed sensors 13 provided in the vicinity of the front wheels 3L, 3R and the rear wheels 5L, 5R to detect the wheel speed of each wheel. The electric brake 21 and the rear electric brake ECU 31 constitute an electric brake device 20 .

Next, a specific configuration of the electric brake device 20 will be described with reference to FIGS. 1 to 3. FIG.

The electric brake 21 is a brake mechanism 22 that transmits thrust generated by driving the electric motor 22B to a piston 22E that moves a brake pad 22F (braking member) pressed against a disc rotor D (braking member) based on a braking request. and has. In addition to this, the electric brake 21 has a parking mechanism 23 . In this case, the electric brake 21 includes a rotation angle sensor 24, a thrust sensor 25 as thrust detection means, and a current sensor 26 (see FIG. 2 for all) in order to perform position control and thrust control. .

The brake mechanism 22 is provided for each of the left and right wheels of the vehicle 1, that is, the left rear wheel 5L side and the right rear wheel 5R side. The brake mechanism 22 is configured as an electric brake mechanism. The brake mechanism 22 generates braking force for the vehicle 1 by driving an electric motor 22B (electric motor) controlled by a pulse width modulation method. For example, as shown in FIG. 2, the brake mechanism 22 includes a caliper 22A as a cylinder (wheel cylinder), an electric motor 22B (electric motor) as an electric actuator, a reduction mechanism 22C, a rotation/linear motion conversion mechanism 22D, It has a piston 22E as a pressing member, a brake pad 22F as a member to be braked (pad), and a return spring (not shown). The electric motor 22B is, for example, a brushless motor, and is driven (rotated) by power supply to propel the piston 22E. The electric motor 22B is controlled by the main ECU 9 and the rear electric brake ECU 31 . The deceleration mechanism 22C decelerates the rotation of the electric motor 22B and transmits it to the rotation/linear motion conversion mechanism 22D.

The rotation/linear motion converting mechanism 22D converts the rotation of the electric motor 22B transmitted via the reduction mechanism 22C into axial displacement (linear motion displacement) of the piston 22E. The piston 22E is propelled by driving the electric motor 22B. The brake pad 22F is pressed against a disk rotor D as a member (disk) to be braked by a piston 22E. The disk rotor D rotates together with the wheels (rear wheels 5L, 5R). When braking is applied, the return spring applies a rotational force in the braking release direction to the rotating member of the rotation/linear motion conversion mechanism 22D. In the brake mechanism 22, the piston 22E is propelled to press the brake pad 22F against the disc rotor D by driving the electric motor 22B.

The parking mechanism 23 is provided on the brake mechanism 22 . The parking mechanism 23 maintains the propelling state of the piston 22E of the brake mechanism 22 .

The rotation angle sensor 24 detects the rotation angle (motor rotation angle) of the rotation shaft of the electric motor 22B. The thrust sensor 25 detects a reaction force against the thrust (pressing force) from the piston 22E to the brake pad 22F. The thrust sensor 25 is provided in the brake mechanism 22 and constitutes thrust detection means for detecting the thrust acting on the piston 22E (piston thrust). The current sensor 26 detects the current (motor current) supplied to the electric motor 22B. The rotation angle sensor 24, the thrust sensor 25, and the current sensor 26 are connected to the rear electric brake ECU 31. As shown in FIG.

The rear electric brake ECU 31 is provided corresponding to the brake mechanism 22 . As shown in FIG. 3 , the rear electric brake ECU 31 includes a microcomputer 32 , a motor pre-driver IC 33 and an inverter 34 . The rear electric brake ECU 31 controls the brake mechanism 22 (electric motor 22B) based on a command from the main ECU 9 . At this time, the rear electric brake ECU 31 constitutes a control device (electric brake control device) that controls the electric motor 22B based on a braking request (braking command).

The microcomputer 32 receives braking commands from the main ECU 9 . The microcomputer 32 acquires the rotation angle of the electric motor 22B based on the signal from the rotation angle sensor 24. FIG. The microcomputer 32 acquires the thrust acting on the piston 22E based on the signal from the thrust sensor 25. FIG. The microcomputer 32 acquires the motor current supplied to the electric motor 22B based on the signal from the current sensor 26. FIG. Microcomputer 32 acquires the temperature of inverter 34 (switching element S) based on the signal from temperature sensor 36 . The temperature sensor 36 is arranged near the switching element S (driving element) of the inverter 34 and detects the component temperature. The microcomputer 32 turns on and off the switching element S of the inverter 34 via the motor predriver IC 33 based on the braking command, the rotation angle of the electric motor 22B, the thrust acting on the piston 22E, and the temperature of the inverter 34. (OFF). At this time, the motor predriver IC 33 outputs a gate voltage of a switching element S (drive element) such as a MOSFET according to a control signal from the microcomputer 32 . Further, the microcomputer 32 controls the generation of drive signals by the motor pre-driver IC 33 and the slew rate of the drive signals that can be set in the register inside the motor pre-driver IC 33 . As a result, the rise time and fall time of the drive signal can be temporarily set earlier, or the rise time and fall time can be reset to meet the EMC standards.

The inverter 34 is configured using a plurality of switching elements S (drive elements) such as MOSFETs, for example. Inverter 34 is connected to battery 35 . The inverter 34 switches on (ON) and off (OFF) of the switching element S at a predetermined PWM frequency according to the gate voltage from the motor pre-driver IC 33 . Therefore, the inverter 34 switches ON and OFF of the switching element at the PWM frequency, and controls the pulse width thereof. As a result, the inverter 34 converts the DC power into three-phase AC power, and supplies the drive voltage Vd (drive signal) and the drive current Id to the U-phase, V-phase, and W-phase of the electric motor 22B. As a result, the inverter 34 converts the DC power into three-phase AC power and PWM-controls the electric motor 22B. At this time, the PWM frequency is set to a value (for example, 20 kHz) higher than the maximum audible frequency.

Next, the operation of applying and releasing braking during running by the electric brake device 20 will be described. In the following description, the operation when the driver operates the brake pedal 6 will be described as an example. (not shown) or is substantially the same except that it is output from the main ECU 9 to the rear electric brake ECU 31 .

For example, when the driver depresses the brake pedal 6 while the vehicle 1 is running, the main ECU 9 outputs a command (braking application command) to the rear electric brake ECU 31 . The rear electric brake ECU 31 drives (rotates) the electric motor 22B in the forward direction, that is, in the braking application direction (apply direction) based on a braking request command from the main ECU 9 . The rotation of the electric motor 22B is transmitted to the rotation/linear motion conversion mechanism 22D via the reduction mechanism 22C, and the piston 22E advances toward the brake pad 22F.

As a result, the brake pad 22F is pressed against the disk rotor D and a braking force is applied. At this time, the braking state is established by controlling the drive of the electric motor 22B based on detection signals from the pedal stroke sensor 8, the rotation angle sensor 24, the thrust sensor 25, and the like. During such braking, a return spring (not shown) provided in the brake mechanism 22 applies a force in the direction of releasing the brake to the rotating member of the rotation/linear motion conversion mechanism 22D and to the rotating shaft of the electric motor 22B. .

On the other hand, when the brake pedal 6 is operated to the release side, the main ECU 9 outputs a command (braking release command) corresponding to this operation to the rear electric brake ECU 31 . Based on a command from the main ECU 9, the rear electric brake ECU 31 drives (rotates) the electric motor 22B in the reverse direction, that is, in the braking release direction (release direction). The rotation of the electric motor 22B is transmitted to the rotation/linear motion conversion mechanism 22D via the reduction mechanism 22C, and the piston 22E retreats in the direction away from the brake pad 22F. When the brake pedal 6 is completely released, the brake pad 22F is separated from the disc rotor D, and the braking force is released. In a non-braking state in which braking is released, a return spring (not shown) provided in the brake mechanism 22 returns to its initial state.

By the way, for example, when the driver depresses the brake pedal 6 abruptly and strongly to avoid an obstacle, a braking request for emergency braking from the main ECU 9 is input to the rear electric brake ECU 31 . Also, when the automatic braking is activated, a request for emergency automatic braking is input to the rear electric brake ECU 31 as a braking request for emergency braking. During such an emergency braking, the rear electric brake ECU 31 outputs a drive signal for suddenly braking the vehicle, and operates the electric brake 21 so as to generate a sudden large braking force. Therefore, a large current flows through the electric motor 22B of the electric brake 21 . At this time, inverter 34 and electric motor 22B tend to suffer a large power loss depending on the rise time and fall time (slew rate) of the drive signal. Therefore, the electric brake device 20 according to the present embodiment changes the slew rate of the drive signal depending on whether emergency braking is being performed.

Next, slew rate control for adjusting the slew rate of the drive signal for the electric brake device 20 will be described with reference to FIG. The slew rate control process shown in FIG. 4 is repeatedly executed for each predetermined control period. The steps in the flow chart shown in FIG. 4 use the notation "S", for example, Step 1 is indicated as "S1".

In S<b>1 , the microcomputer 32 of the rear electric brake ECU 31 acquires the temperature of the inverter 34 (switching element S) based on the signal from the temperature sensor 36 . In S2, it is determined whether the temperature of the inverter 34 is higher than a predetermined threshold. At this time, the threshold is set to a value higher than the maximum temperature reached by the inverter 34 (switching element S) during normal operation and lower than the minimum temperature reached by the inverter 34 (switching element S) during emergency braking. there is

When the temperature of the inverter 34 is higher than the threshold value, "YES" is determined in step S2, and the process proceeds to step S3. When a high temperature is determined, the slew rate of the drive signal is increased to temporarily shorten the rise time and fall time of the drive signal, thereby reducing switching loss and suppressing temperature rise. Such situations in which the temperature exceeds the threshold and become high are, for example, the timing at which the user wants to make an emergency stop of the vehicle 1, the timing at which the vehicle 1 senses a person or an obstacle and applies sudden braking in preparation for a collision, and the acceleration and acceleration. This is the timing at which the function to prevent the brake from being erroneously pressed is activated and sudden braking is applied. In such a situation, the electric motor 22B needs to generate high torque, so a large current flows through the electric motor 22B. At this time, in step S3, the slew rate of the drive signal is set to a value larger than that in normal times. As a result, the time required for the switching element S to switch between on (ON) and off (OFF) is shortened. As a result, the heat generation of the switching element S can be suppressed, and the absolute maximum rating of the component due to the heat generation can be prevented from being exceeded.

On the other hand, when the temperature of the inverter 34 is lower than the threshold value, "NO" is determined in step S2, and the process proceeds to step S4. In step S4, the slew rate of the drive signal is set to a value smaller than that during emergency braking. Normally, when the temperature of the inverter 34 is lower than the threshold, the slew rate is reduced and the rise time and fall time of the drive signal are set long so as to comply with EMC standards. As a result, the time required for the switching element S to switch between on (ON) and off (OFF) is longer than during emergency braking.

Thus, in the embodiment, the rear electric brake ECU 31 (control device) reduces the electric power when there is a braking request for emergency braking compared to when there is a braking request for other than emergency braking (normal time). The rise time and fall time of the drive signal that controls the motor 22B (electric motor) are shortened.

For example, as shown in FIG. 5, when there is a braking request for normal time other than emergency braking, the rise time ΔT10, fall time ΔT11 and slew rate SR10, SR11 of the drive voltage Vd, which is the drive signal, are , is a preset value in consideration of the EMC standard in order to reduce radiation noise. At this time, the rise slew rate SR10 of the drive voltage Vd is a value obtained by dividing the amplitude .DELTA.V of the drive voltage Vd by the rise time .DELTA.T10 (SR10=.DELTA.V/.DELTA.T10). The falling slew rate SR11 of the drive voltage Vd is a value obtained by dividing the amplitude .DELTA.V of the drive voltage Vd by the fall time .DELTA.T11 (SR11=.DELTA.V/.DELTA.T11).

In this case, when the drive signal is switched between on and off, power loss occurs according to the product of the drive voltage Vd and the drive current Id according to the slew rates SR10 and SR11 (see FIG. 5).

On the other hand, during emergency braking, a large drive current Id flows through the electric motor 22B, so power loss tends to increase. On the other hand, as shown in FIG. 6, during emergency braking, the rear electric brake ECU 31 sets the slew rates SR20, SR21 of the drive signal to larger values (SR20>SR10, SR21>SR11) than those during normal operation. and shorten the rise time ΔT20 and the fall time ΔT21 (ΔT20<ΔT10, ΔT21<ΔT11). At this time, the rising slew rate SR20 of the driving voltage Vd is a value obtained by dividing the amplitude ΔV of the driving voltage Vd by the rising time ΔT20 (SR20=ΔV/ΔT20). The falling slew rate SR21 of the drive voltage Vd is a value obtained by dividing the amplitude ΔV of the drive voltage Vd by the fall time ΔT21 (SR21=ΔV/ΔT21).

As a result, the ON/OFF switching time of the driving voltage Vd during emergency braking becomes shorter than during normal operation. Therefore, the power loss (average power) caused by the switching of the drive voltage Vd can be reduced as compared with the normal time, and the temperature rise of the inverter 34 and the like can be suppressed.

On the other hand, the PWM frequency is set to the same value during emergency braking and during normal braking. Therefore, even during emergency braking, loss can be reduced while magnetostrictive noise is kept out of the audible range, and unpleasant noise is not generated. As a result, it is possible to reduce the time taken to deal with noise and vibration.

Furthermore, when the rise time and fall time are shortened, EMC (emission level) increases, which tends to degrade radio reception quality, for example. However, interference with radio reception occurs only in, for example, remote areas where the received radio waves are weak, so the impact on the user (driver) is small. In addition to this, when activating the emergency brake, it is the timing at which an emergency stop is desired. That is, when the emergency brake is operated, it is the timing at which the user is not affected even if the reception quality of the radio temporarily deteriorates during the emergency brake. Therefore, radio reception quality can be ignored during emergency braking.

Further, when the braking request for emergency braking is the request for emergency automatic braking, when the emergency braking by the automatic braking is activated, the temperature rise of the inverter 34 and the like is suppressed while suppressing the generation of unpleasant noise. be able to.

Further, the rear electric brake ECU 31 has a plurality of switching elements S (driving elements) that are switched in accordance with pulse width modulation (PWM), and the temperature of the switching element S is set in advance to determine whether emergency braking is being performed. determined by whether or not it is higher than the specified threshold. At this time, during emergency braking, a large drive current Id flows through the electric motor 22B, so the temperature of the switching element S rises compared to normal times. Therefore, by monitoring the temperature of the switching element S, it is possible to determine whether or not emergency braking is being performed.

In the above embodiment, the electric brake device 20 is applied to the rear wheels 5L and 5R, but the electric brake device 20 may be applied to the front wheels 3L and 3R, and the electric brake device 20 may be applied to all four wheels. may apply.

In the above-described embodiment, the rear electric brake ECU 31 determines whether or not emergency braking is being performed by determining whether or not the temperature of the switching element S is higher than a preset threshold value. The present invention is not limited to this. For example, it may be determined whether or not emergency braking is being performed based on the magnitude or amount of change of a braking request (braking command) from the main ECU 9 or the like.

In the above embodiment, the electric brake device 20 was described as an example of the brake device. The present invention is not limited to this, and may be applied to a brake device in which a brake mechanism is configured by combining the hydraulic brake 4 with an electric booster or an anti-skid device, for example. In this case, the hydraulic pressure is increased by driving the electric booster or the electric motor of the skid prevention device in response to a braking request during emergency braking, and the hydraulic brake 4 generates a braking force.

As a brake device based on the embodiments described above, for example, the following aspects are conceivable.

A first aspect of the present invention is a brake device having a brake mechanism that generates braking force for a vehicle by driving an electric motor controlled by a pulse width modulation method, and a control device that controls the electric motor based on a braking request, wherein: The control device shortens the rise time and fall time of the drive signal for controlling the electric motor when there is a braking request for emergency braking, compared to when there is a braking request other than for emergency braking. is characterized by

A second aspect is characterized in that, in the first aspect, the braking request for emergency braking is a request for emergency automatic braking.

As a third aspect, in the first or second aspect, the control device has a plurality of drive elements that are switched according to pulse width modulation, and whether or not the emergency brake is being applied is determined by the drive element is higher than a preset threshold.

1 vehicle 20 electric brake device (brake device)
21 electric brake 22 brake mechanism 22B electric motor (electric motor)
31 Rear electric brake ECU (control device)
S Switching element (drive element)

Claims (3)

A braking device having a braking mechanism that generates braking force for a vehicle by driving an electric motor controlled by a pulse width modulation method, and a control device that controls the electric motor based on a braking request,
The control device shortens the rise time and fall time of the drive signal for controlling the electric motor when there is a braking request for emergency braking, compared to when there is a braking request other than for emergency braking. ,
The braking device according to claim 1, wherein the PWM frequency of the drive signal is higher than the maximum audible frequency during emergency braking and during normal times other than emergency braking, and is set to the same value . In claim 1,
The brake device, wherein the braking request for emergency braking is a request for emergency automatic braking. In claim 1 or 2,
the controller having a plurality of drive elements that are switched according to pulse width modulation;
A braking device, wherein whether or not the emergency braking is being performed is determined based on whether or not the temperature of the drive element is higher than a preset threshold value.

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