Parking brake control device

Abstract

Provided is a parking brake control device that reduces discomfort to passengers even when a parking switch is operated and braking is performed. The parking brake control device (a control unit 100) controls both of a hydraulic unit (10) for performing braking of wheels (3) by means of hydraulic pressure and a parking brake device (200) whereby power from an electric motor (210) is mechanically transmitted to the wheels (3) and braking is performed. The parking brake control device comprises: a hydraulic braking unit (150) capable of executing hydraulic braking control in which braking of the wheels (3) is performed by the hydraulic unit (10) on the condition that a signal from an activation switch (a parking switch 92) for activating the parking brake device (200) is input during vehicle travel; and a pressure reduction rate setting unit (153) that sets a pressure reduction rate (R) in accordance with an end condition of the hydraulic braking control satisfied at the end of the hydraulic braking control when pressure reduction control is performed at the end of the hydraulic braking control.

Description

[Technical Field]

[0001] The present disclosure relates to a parking brake control device. [Background technology]

[0002] Conventionally, a parking brake control device is known that controls a hydraulic unit that brakes the wheels using hydraulic pressure and a parking brake device that brakes the wheels by mechanically transmitting the power of an electric motor to the wheels (see Japanese Patent Laid-Open No. 10-76931). Summary of the Invention

[0003] In a conventional parking brake control device capable of controlling both hydraulic and mechanical brakes, hydraulic brake control can be initiated when a driver operates a parking switch while the vehicle is moving. However, because various situations are conceivable in which hydraulic brake control initiated in this manner may be terminated, various problems may arise if the pressure reduction rate at the end of hydraulic brake control is constant. For example, if a driver operates the parking switch while the vehicle is moving and then wishes to accelerate the vehicle again by operating the accelerator, the hydraulic brake control must be terminated. However, if the pressure reduction rate at the end of hydraulic brake control is set small, the braking force does not decrease quickly, which may result in the driver not experiencing a desirable acceleration feeling and feeling a so-called dragging sensation. Furthermore, if the driver operates the parking switch while the vehicle is moving and then stops, the hydraulic brake control may be terminated and switched to mechanical brake control. However, if the pressure reduction rate at the end of hydraulic brake control is set large, the hydraulic pressure may drop to zero before the braking force of the mechanical brake control is fully applied. In this case, the vehicle may move slightly while stopped, causing discomfort to the occupants.

[0004] Even when braking by operating a parking switch, it is desirable to minimize discomfort felt by the occupants.

[0005] In view of the above background, a parking brake control device is disclosed that controls a hydraulic unit that brakes wheels by hydraulic pressure and a parking brake device that brakes the wheels by mechanically transmitting power from an electric motor to the wheels. In one aspect, the parking brake control device includes a hydraulic braking unit that can execute hydraulic braking control that brakes the wheels by the hydraulic unit on the condition that a signal is input from an activation switch for activating the parking brake device while the vehicle is traveling, and a pressure reduction rate setting unit that, when pressure reduction control is performed at the end of the hydraulic braking control, sets a pressure reduction rate in accordance with a termination condition of the hydraulic braking control that is satisfied at the end of the hydraulic braking control.

[0006] According to this configuration, the pressure reduction rate is set according to the termination conditions of the hydraulic braking control, so that discomfort to the occupants can be reduced even when braking is performed using an activation switch for activating the parking brake device.

[0007] In addition, when the termination condition is a request to cancel the hydraulic braking control by an operation of the driver while the vehicle is traveling, the pressure reduction rate setting unit may set the pressure reduction rate to a first pressure reduction rate that is greater than a minimum value.

[0008] According to this, when pressure reduction control is performed based on a request to cancel hydraulic braking control, pressure reduction control is performed at a first pressure reduction rate that is greater than the minimum value, so that the dragging sensation can be reduced compared to when pressure reduction control is performed at, for example, the minimum pressure reduction rate.

[0009] Furthermore, the parking brake control device may include a switching unit that switches from the hydraulic braking control to mechanical braking control that brakes the wheels using the electric motor of the parking brake device, and when the switching unit switches from the hydraulic braking control to the mechanical braking control when the vehicle stops, the pressure reduction rate setting unit may set the pressure reduction rate to a second pressure reduction rate that is smaller than the first pressure reduction rate when the termination condition is that the vehicle has stopped.

[0010] According to this, when pressure reduction control is performed based on the vehicle being stopped, pressure reduction control is performed at a second pressure reduction rate that is smaller than the first pressure reduction rate. Therefore, compared to when pressure reduction control is performed at the first pressure reduction rate when the vehicle is stopped, for example, the braking force can be maintained when switching from hydraulic braking control to mechanical braking control, and the vehicle can be kept stopped in a good state.

[0011] Furthermore, when the switching unit switches from the hydraulic braking control to the mechanical braking control when the hydraulic unit is abnormal, the pressure reduction rate setting unit may set the pressure reduction rate to a third pressure reduction rate that is smaller than the first pressure reduction rate and greater than the second pressure reduction rate when the termination condition is an abnormality in the hydraulic unit.

[0012] According to this, when pressure reduction control is performed based on an abnormality in the hydraulic unit, pressure reduction control is executed at a third pressure reduction rate that is smaller than the first pressure reduction rate and larger than the second pressure reduction rate, so that when an abnormality occurs in the hydraulic unit, hydraulic braking control can be smoothly switched to mechanical braking control.

[0013] In addition, the pressure reduction rate setting unit may set the first pressure reduction rate to a first rate when the vehicle speed is a first speed, and may set the first pressure reduction rate to a second rate that is greater than the first rate when the vehicle speed is a second speed that is greater than the first speed.

[0014] According to this, the dragging sensation can be eliminated as the vehicle speed increases, so discomfort to the driver can be further reduced.

[0015] In addition, if the parking brake control device includes a switching unit that switches from the hydraulic braking control to mechanical braking control in which the wheels are braked by the electric motor of the parking brake device when the hydraulic unit is abnormal, the pressure reduction rate setting unit may set the pressure reduction rate to a third pressure reduction rate that is smaller than the first pressure reduction rate when the termination condition is an abnormality in the hydraulic unit.

[0016] According to this, when pressure reduction control is performed based on an abnormality in the hydraulic unit, pressure reduction control is performed at a third pressure reduction rate that is smaller than the first pressure reduction rate, so that when there is an abnormality in the hydraulic unit, hydraulic braking control can be smoothly switched to mechanical braking control.

[0017] In addition, if the parking brake control device includes a switching unit that switches from the hydraulic braking control to mechanical braking control in which the wheels are braked by the electric motor of the parking brake device when the vehicle has stopped or when the hydraulic unit is abnormal, the pressure reduction rate setting unit may set the pressure reduction rate to a second pressure reduction rate when the termination condition is that the vehicle has stopped, and may set the pressure reduction rate to a third pressure reduction rate that is greater than the second pressure reduction rate when the termination condition is that the hydraulic unit is abnormal.

[0018] According to this, when pressure reduction control is performed based on the vehicle being stopped, the pressure reduction control is performed at the second pressure reduction rate which is smaller than the third pressure reduction rate, so that the braking force can be maintained when switching from hydraulic braking control to mechanical braking control and the vehicle can be kept stopped in a good condition, compared to when pressure reduction control is performed at the third pressure reduction rate when the vehicle is stopped. Also, when pressure reduction control is performed based on an abnormality in the hydraulic unit, the pressure reduction control is performed at the third pressure reduction rate which is larger than the second pressure reduction rate, so that the hydraulic braking control can be switched to mechanical braking control in a good condition when the hydraulic unit is abnormal. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a configuration diagram of a vehicle equipped with a parking brake control device according to an embodiment; [Figure 2] FIG. 2 is a diagram showing the configuration of a hydraulic unit. [Figure 3] FIG. 2 is a diagram showing the structure of a rear wheel brake. [Figure 4] FIG. 2 is a block diagram showing the configuration of a control unit. [Figure 5] 10 is a flowchart showing the operation of a control unit. [Figure 6] 10 is a time chart showing pressure reduction control when hydraulic brake control is terminated due to the absence of a braking request. [Figure 7] 6 is a time chart showing pressure reduction control when hydraulic braking control is terminated due to the vehicle coming to a stop. [Figure 8] 6 is a time chart showing pressure reduction control when hydraulic brake control is terminated due to an abnormality in the hydraulic unit. DETAILED DESCRIPTION OF THE INVENTION

[0020] An embodiment of a parking brake control device will be described in detail with reference to the accompanying drawings. As shown in Figure 1, a vehicle 2 is equipped with wheel brakes FR, FL, RR, and RL provided on each of the front, rear, left, and right wheels 3, and a vehicle brake hydraulic pressure control device 1 that transmits hydraulic pressure to each of the wheel brakes FR, FL, RR, and RL to brake each of the wheels 3.

[0021] Each of the front wheel brakes FR, FL includes a brake rotor BR and a wheel cylinder 4. Each of the rear wheel brakes RR, RL includes a brake rotor BR, a wheel cylinder 4, and a parking brake device 200. The wheel cylinder 4 and the parking brake device 200 apply braking force to the wheel 3 by pressing a friction pad 260 (see FIG. 3) against the brake rotor BR, which is a rotating body that rotates integrally with the wheel 3.

[0022] The vehicle brake hydraulic pressure control device 1 mainly comprises a hydraulic unit 10 that brakes the wheels 3 using hydraulic pressure, and a control unit 100. The hydraulic unit 10 is provided with oil passages and various components. The control unit 100 controls the various components in the hydraulic unit 10 as appropriate.

[0023] The hydraulic unit 10 is connected to a master cylinder 5 as a hydraulic pressure source and each wheel cylinder 4. Brake hydraulic pressure generated in the master cylinder 5 according to the depression force on the brake pedal 6 (braking operation by the driver) is supplied to the wheel cylinder 4 after being controlled by the control unit 100 and the hydraulic unit 10.

[0024] The control unit 100 is connected to a wheel speed sensor 91, a parking switch 92, and an accelerator sensor 93. The wheel speed sensor 91 detects the wheel speed of each wheel 3. The parking switch 92 is an example of an activation switch. The parking switch 92 is a switch for activating the parking brake device 200 and is provided near the driver's seat. The parking switch 92 can be configured to turn ON when the driver pulls a parking lever (not shown) operated by the driver, and to turn OFF when the driver releases the parking lever. The accelerator sensor 93 detects the movement of the accelerator pedal 7.

[0025] The control unit 100 includes, for example, a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and an input / output circuit, and performs various arithmetic operations based on inputs from the parking switch 92 and the sensors 91, 93, etc., and on programs and data stored in the ROM, thereby executing control. Details of the control unit 100 will be described later.

[0026] As shown in FIG. 2, the hydraulic unit 10 is disposed between the master cylinder 5 and the wheel brakes FR, FL, RR, and RL.

[0027] The hydraulic unit 10 is configured by arranging hydraulic lines and various electromagnetic valves in a pump body 11, which is a base having hydraulic lines (hydraulic lines) through which brake fluid flows. The output ports 5a and 5b of the master cylinder 5 are connected to an input port 11a of the pump body 11, and the output port 11b of the pump body 11 is connected to each of the wheel brakes FL, RR, RL, and FR. Under normal circumstances, a continuous hydraulic line runs from the input port 11a to the output port 11b in the pump body 11, so that the depression force of the brake pedal 6 is transmitted to each of the wheel brakes FL, RR, RL, and FR. The hydraulic system connected to the output port 5a of the master cylinder 5 is connected to the wheel brakes FL and RR, and the hydraulic system connected to the output port 5b of the master cylinder 5 is connected to the wheel brakes RL and FR, and these systems have substantially the same configuration.

[0028] Each hydraulic system is provided with a pressure regulating valve 12 on the hydraulic line connecting the input port 11a and the output port 11b. The pressure regulating valve 12 is a normally open proportional solenoid valve that can adjust the difference in hydraulic pressure between its upstream and downstream sides according to the supplied current. A check valve 12a that allows flow only to the output port 11b is provided in parallel with the pressure regulating valve 12.

[0029] The hydraulic line on the wheel brakes FL, RR, RL, and FR side of the pressure regulating valve 12 branches off midway and each branch is connected to an output port 11b. An inlet valve 13, which is a normally open proportional solenoid valve, is provided on each hydraulic line corresponding to each output port 11b. A check valve 13a that allows flow only toward the pressure regulating valve 12 is provided in parallel with each inlet valve 13.

[0030] A return hydraulic line 19B is provided from the hydraulic line between each output port 11b and the corresponding inlet valve 13, and connects between the pressure regulating valve 12 and the inlet valve 13 via an outlet valve 14, which is a normally closed solenoid valve.

[0031] On this return hydraulic pressure line 19B, arranged in this order from the outlet valve 14 side are a reservoir 16 that temporarily absorbs excess brake fluid, a check valve 16a, a pump 17, and an orifice 17a. The check valve 16a is positioned so as to allow only a flow between the pressure regulating valve 12 and the inlet valve 13. The pump 17 is driven by a motor 21 and is provided so as to generate pressure between the pressure regulating valve 12 and the inlet valve 13. The orifice 17a damps pressure pulsations of the brake fluid discharged from the pump 17 and pulsations generated by the operation of the pressure regulating valve 12.

[0032] An intake hydraulic pressure line 19C connects an intake hydraulic pressure line 19A connecting the input port 11a and the pressure regulating valve 12 to a portion of the return hydraulic pressure line 19B between the check valve 16a and the pump 17. An intake valve 15, which is a normally closed solenoid valve, is disposed in the intake hydraulic pressure line 19C.

[0033] In the hydraulic unit 10 configured as described above, the solenoid valves are not energized under normal conditions. Brake fluid pressure introduced through the input port 11a passes through the pressure regulator valve 12 and the inlet valve 13 and is output to the output port 11b, where it is directly applied to the wheel brakes FL, RR, RL, and FR. To reduce excess brake fluid pressure in the wheel brakes FL, RR, RL, and FR, such as during antilock brake control, the corresponding inlet valve 13 is closed and the outlet valve 14 is opened, allowing the brake fluid to flow through the return fluid pressure path 19B to the reservoir 16 and drain the brake fluid from the wheel cylinder 4. To pressurize the wheel brakes FL, RR, RL, and FR without the driver's brake pedal 6 being depressed, the intake valve 15 is opened and the motor 21 is driven, allowing the pump 17 to actively supply brake fluid to the wheel brakes FL, RR, RL, and FR. Furthermore, the degree of pressurization of the wheel brakes FL, RR, RL, and FR can be adjusted by adjusting the current flowing through the pressure regulator valve 12.

[0034] 3, the wheel brakes RR, RL include a wheel cylinder 4, a parking brake device 200, a pair of friction pads 260, and a brake rotor BR. The friction pads 260 are arranged to sandwich the brake rotor BR.

[0035] The parking brake device 200 includes an electric motor 210, a reducer 220, and a nut 250. The wheel cylinder 4 includes a housing 230 and a brake piston 240.

[0036] The electric motor 210 is a motor that can rotate forward and backward, and has an output shaft (not shown) connected to a reducer 220 .

[0037] The reducer 220 is a mechanism for reducing the power of the electric motor 210, and includes a plurality of gears therein. An output shaft 221 of the reducer 220 is formed with a male thread portion 222.

[0038] The housing 230 has a cylinder bore 231 that supports the brake piston 240 so that the brake piston 240 can move in the axial direction of the reducer 220. The cylinder bore 231 is formed in a cylindrical shape with a bottom that opens toward the friction pad 260 side.

[0039] The brake piston 240 is formed in a cylindrical shape with a bottom, and is disposed in the cylinder bore 231 with its opening facing the bottom surface of the cylinder bore 231. One of the friction pads 260 is attached to the brake piston 240. Brake fluid is supplied from the hydraulic unit 10 described above to a hydraulic pressure chamber 232 formed by the brake piston 240 and the cylinder bore 231 via an oil passage 233 formed in the housing 230. As a result, the brake piston 240 advances toward the friction pad 260 due to hydraulic pressure applied from the hydraulic unit 10, thereby enabling the friction pad 260 to be pressed against the brake rotor BR. In other words, the wheel brakes RR, RL have the function of pressing the friction pad 260 against the brake rotor BR by hydraulic pressure from the hydraulic unit 10.

[0040] The nut 250 has a female thread portion 251 that screws onto the male thread portion 222 of the output shaft 221 of the reducer 220. The nut 250 is disposed inside the brake piston 240 and is engaged with the brake piston 240 so as to be non-rotatable relative to the brake piston 240 but movable in the axial direction. As a result, when the electric motor 210 is rotated forward, the nut 250 advances toward the friction pad 260 and can press the friction pad 260 against the brake rotor BR via the brake piston 240. When the electric motor 210 is rotated backward, the nut 250 retreats away from the friction pad 260, thereby releasing the pressing force of the friction pad 260 against the brake rotor BR. In other words, the parking brake device 200 has the function of mechanically transmitting power generated by the forward rotation of the electric motor 210 to the friction pad 260 without using hydraulic pressure, thereby pressing the friction pad 260 against the brake rotor BR.

[0041] Next, the control unit 100 will be described in detail. 4, the control unit 100 includes a wheel speed acquisition unit 110, a vehicle body speed calculation unit 120, a slip amount calculation unit 130, a wheel deceleration calculation unit 140, a hydraulic braking unit 150, a mechanical braking unit 160, and a memory unit 170. The control unit 100 functions as a parking brake control device for controlling the parking brake device 200.

[0042] The wheel speed acquisition unit 110 has a function of acquiring the wheel speed Vw of each wheel 3 from each wheel speed sensor 91. Upon acquiring the wheel speed Vw of each wheel 3, the wheel speed acquisition unit 110 outputs the acquired wheel speed Vw to the vehicle body speed calculation unit 120, the slip amount calculation unit 130, and the wheel deceleration calculation unit 140.

[0043] The vehicle speed calculation unit 120 has a function of calculating (estimating) the vehicle speed Vc by a known calculation method based on the wheel speed Vw output from the wheel speed acquisition unit 110. Various methods can be used to calculate the vehicle speed Vc. One example is a method in which, in principle, the front wheel speed Vw is used as the vehicle speed Vc, and when the magnitude of the acceleration or deceleration of the front wheel speed Vw exceeds a predetermined upper limit, the vehicle speed Vc is converted so that the acceleration or deceleration of the vehicle speed Vc becomes the upper limit. If the vehicle is equipped with an acceleration sensor that detects acceleration in the longitudinal direction, the vehicle speed Vc may be calculated based on the acceleration in the longitudinal direction. After calculating the vehicle speed Vc, the vehicle speed calculation unit 120 outputs the calculated vehicle speed Vc to the slip amount calculation unit 130 and the hydraulic braking unit 150.

[0044] The slip amount calculation unit 130 has a function of calculating the slip amount SL of each wheel 3 based on the wheel speed Vw output from the wheel speed acquisition unit 110 and the vehicle speed Vc output from the vehicle speed calculation unit 120. Specifically, the slip amount SL can be obtained as the difference between the vehicle speed Vc and the wheel speed Vw. After calculating the slip amount SL, the slip amount calculation unit 130 outputs the calculated slip amount SL to the hydraulic braking unit 150 and the mechanical braking unit 160.

[0045] In this embodiment, the slip amount SL is calculated by subtracting the wheel speed Vw from the vehicle speed Vc. Alternatively, the slip ratio expressed as (Vc-Vw) / Vc may be used as the slip amount SL.

[0046] The wheel deceleration calculation unit 140 has a function of calculating the wheel deceleration Dw of each wheel 3 based on the wheel speed Vw of each wheel 3. Here, a positive value of the wheel deceleration Dw indicates deceleration, and a negative value indicates acceleration. The wheel deceleration Dw can be calculated, for example, by subtracting the current value of the wheel speed Vw from the previous value. After calculating the wheel deceleration Dw of each wheel 3, the wheel deceleration calculation unit 140 outputs the calculated wheel deceleration Dw of each wheel 3 to the mechanical braking unit 160.

[0047] The hydraulic braking unit 150 has a function of executing hydraulic braking control in which the hydraulic unit 10 brakes each wheel 3 individually, based on an ON signal output from the parking switch 92 while the vehicle is traveling. More specifically, the hydraulic braking unit 150 executes hydraulic braking control when the following conditions are met: the vehicle speed Vc is equal to or greater than a predetermined value, and the parking switch 92 is in the ON state.

[0048] The hydraulic braking control includes emergency braking control for increasing brake hydraulic pressure by the pump 17, and lock suppression control for suppressing locking of the wheels 3. When the hydraulic braking unit 150 receives an ON signal output from the parking switch 92 while the vehicle is traveling, it starts emergency braking control and then executes lock suppression control.

[0049] In emergency brake control, the hydraulic braking section 150 activates the motor 21 of the hydraulic unit 10 based on an ON signal from the parking switch 92.

[0050] In lock prevention control, the hydraulic braking unit 150 determines for each wheel 3 whether to reduce, increase, or maintain the brake fluid pressure of the wheel 3 based on the wheel acceleration Aw estimated from the wheel speed Vw and the slip amount SL. More specifically, if the slip amount SL is equal to or greater than a predetermined threshold SLth and the wheel acceleration Aw is equal to or less than 0, the hydraulic braking unit 150 determines that the wheel 3 is about to lock and decides to reduce the brake fluid pressure. Furthermore, if the wheel acceleration Aw is greater than 0, the hydraulic braking unit 150 decides to maintain the brake fluid pressure, and if the slip amount SL is less than the predetermined threshold SLth and the wheel acceleration Aw is equal to or less than 0, the hydraulic braking unit 150 decides to increase the brake fluid pressure.

[0051] When it is determined that the brake fluid pressure is to be reduced, the hydraulic braking unit 150 executes reduction control to control the current to the inlet valve 13 and the outlet valve 14 of the hydraulic unit 10 so as to close the inlet valve 13 and open the outlet valve 14. When it is determined that the brake fluid pressure is to be maintained, the hydraulic braking unit 150 executes maintenance control to control the current to the inlet valve 13 and the outlet valve 14 so as to close both the inlet valve 13 and the outlet valve 14.

[0052] Furthermore, when the hydraulic braking unit 150 determines to increase the brake fluid pressure, it executes pressure increase control by controlling the current to the inlet valve 13 and the outlet valve 14 so that the inlet valve 13 opens and the outlet valve 14 closes.

[0053] The hydraulic braking unit 150 includes an abnormality determination unit 151, a switching unit 152, and a pressure reduction rate setting unit 153. The abnormality determination unit 151 has a function of determining whether or not an abnormality has occurred in the hydraulic unit 10. When the abnormality determination unit 151 determines that an abnormality has occurred in the hydraulic unit 10, it outputs an abnormality signal indicating this to the switching unit 152. Specifically, for example, when the abnormality determination unit 151 determines that an abnormality has occurred in the hydraulic unit 10, it sets an abnormality flag to 1, and when it determines that no abnormality has occurred, it sets the abnormality flag to 0.

[0054] When the switching unit 152 receives an abnormality signal from the abnormality determination unit 151 while the vehicle is traveling, the switching unit 152 has a function of switching from hydraulic braking control to mechanical braking control in which the rear wheels 32 are braked by the electric motor 210 of the parking brake device 200. Specifically, when the switching unit 152 receives an abnormality signal from the abnormality determination unit 151 during hydraulic braking control, the switching unit 152 ends the hydraulic braking control and outputs a signal indicating the ON / OFF state of the parking switch 92 to the mechanical braking unit 160. Note that when the switching unit 152 receives an abnormality signal from the abnormality determination unit 151 before starting hydraulic braking control, the switching unit 152 outputs a signal indicating the ON / OFF state of the parking switch 92 to the mechanical braking unit 160 without starting hydraulic braking control.

[0055] The switching unit 152 also has a function of switching from hydraulic braking control to mechanical braking control when the vehicle 2 stops, more specifically when the vehicle speed Vc becomes a value close to 0 (for example, 0). Specifically, when the vehicle speed Vc becomes a value close to 0, the switching unit 152 ends the hydraulic braking control and outputs a signal indicating the ON / OFF state of the parking switch 92 to the mechanical braking unit 160.

[0056] The hydraulic braking unit 150 has a function of terminating the hydraulic braking control not only when the control is switched by the switching unit 152, but also when a request to cancel the hydraulic braking control is received by the driver while the vehicle is traveling. More specifically, the hydraulic braking unit 150 terminates the hydraulic braking control when it receives no longer an ON signal from the parking switch 92 or a signal from the accelerator sensor 93 as a request to cancel the hydraulic braking control.

[0057] That is, three conditions are set as termination conditions for the hydraulic braking control in this embodiment: a request to cancel the hydraulic braking control is received by the driver while the vehicle is traveling; the vehicle 2 is stopped; and an abnormality occurs in the hydraulic unit 10. The hydraulic braking unit 150 terminates the hydraulic braking control when at least one of the termination conditions is satisfied. More specifically, when at least one of the termination conditions is satisfied, the hydraulic braking unit 150 executes pressure reduction control to terminate the hydraulic braking control. In the following description, the pressure reduction control at the end of the hydraulic braking control is also referred to as "end-time pressure reduction control."

[0058] When performing termination pressure reduction control, the pressure reduction rate setting unit 153 has a function of setting the pressure reduction rate R according to the termination condition of the hydraulic braking control (hereinafter also referred to as the "termination condition") that is satisfied when the hydraulic braking control is terminated. More specifically, when the termination condition is a request to cancel the hydraulic braking control by an operation by the driver while the vehicle is traveling, the pressure reduction rate setting unit 153 sets the pressure reduction rate R to a first pressure reduction rate R1 that is greater than the minimum value.

[0059] When the termination condition is a stop of the vehicle 2, the pressure reduction rate setting unit 153 sets the pressure reduction rate R to a second pressure reduction rate R2 that is smaller than the first pressure reduction rate R1. When the termination condition is an abnormality of the hydraulic unit 10, the pressure reduction rate setting unit 153 sets the pressure reduction rate R to a third pressure reduction rate R3 that is smaller than the first pressure reduction rate R1 and greater than the second pressure reduction rate R2.

[0060] Furthermore, the pressure reduction rate setting unit 153 sets the first pressure reduction rate R1 in accordance with the vehicle body speed Vc. More specifically, the pressure reduction rate setting unit 153 sets the first pressure reduction rate R1 based on the vehicle body speed Vc and a first pressure reduction rate setting map that is set in advance to associate the vehicle body speed Vc with the first pressure reduction rate R1.

[0061] In the first pressure reduction rate setting map, the first pressure reduction rate R1 is set to decrease as the vehicle speed Vc increases. That is, when the vehicle speed Vc is a first speed V1, the pressure reduction rate setting unit 153 sets the first pressure reduction rate R1 to a first rate R11, and when the vehicle speed Vc is a second speed V2 that is greater than the first speed V1, the pressure reduction rate setting unit 153 sets the first pressure reduction rate R1 to a second rate R12 that is greater than the first rate R11.

[0062] In the first decompression rate setting map, the range of the first decompression rate R1 can be set, for example, to a range near the maximum value of the decompression rate R. In other words, the first decompression rate R1 may be set to a value equal to or less than the maximum value of the decompression rate R and greater than the third decompression rate R3.

[0063] Furthermore, the second decompression rate R2 can be set to, for example, the minimum value of the decompression rate R. The second decompression rate R2 may be set to a value equal to or greater than the minimum value of the decompression rate R and smaller than the third decompression rate R3. Here, the maximum and minimum values ​​of the decompression rate R are determined by, for example, the capabilities of the electric motor 210 and the reducer 220.

[0064] The mechanical braking unit 160 has a function of executing mechanical braking control when it receives a signal from the switching unit 152. The mechanical braking control includes dynamic actuation control that is performed while the vehicle 2 is traveling, and static actuation control that is performed when the vehicle 2 is stopped. The mechanical braking unit 160 executes dynamic actuation control when the vehicle 2 is traveling, and executes static actuation control when the vehicle 2 is stopped.

[0065] The mechanical braking unit 160 includes an apply control unit 161 capable of performing apply control to increase the braking force of the wheel 3, a stop control unit 162 capable of performing stop control to maintain the braking force of the wheel 3, and a release control unit 163 capable of performing release control to reduce the braking force of the wheel 3.

[0066] Here, the apply control is a control for advancing the nut 250 toward the brake rotor BR at a constant speed by rotating the electric motor 210 in the forward direction. More specifically, the apply control increases the clamping force of the pair of friction pads 260 by supplying a constant current to the electric motor 210.

[0067] The stop control is a control for stopping the rotation of the electric motor 210, thereby stopping the nut 250. The release control is a control for retracting the nut 250 at a constant speed so as to separate from the brake rotor BR, by rotating the electric motor 210 in the reverse direction.

[0068] When performing static actuation control, the mechanical braking unit 160 executes only apply control. When performing dynamic actuation control, the mechanical braking unit 160 appropriately selects and executes apply control, stop control, and release control.

[0069] The apply control unit 161 has a function of executing the apply control when a predetermined start condition (a start condition for mechanical braking control) is satisfied.

[0070] In detail, when the start conditions are met, such as the vehicle speed Vc being close to 0 (for example, 0) and the parking switch 92 being in the ON state, the apply control unit 161 executes apply control in static operation control (i.e., control to rotate the electric motor 210 forward for a predetermined time).

[0071] The apply control unit 161 executes the apply control in the dynamic actuation control when start conditions are satisfied, such as the vehicle speed Vc being equal to or greater than a predetermined value and the parking switch 92 being in the ON state. In other words, the apply control unit 161 executes the apply control when start conditions for actuating the parking brake device 200 are satisfied while the vehicle is traveling.

[0072] The apply control unit 161 ends the apply control when the stop control or the release control described later is started. More specifically, the apply control unit 161 executes the apply control when the wheel deceleration Dw is less than a predetermined threshold value Dth during a period when the release control described later is not executed.

[0073] The stop control unit 162 has a function of executing stop control based on the wheel deceleration Dw output from the wheel deceleration calculation unit 140. Specifically, the stop control unit 162 executes stop control by stopping the supply of current to the electric motor 210 when the wheel deceleration Dw is equal to or greater than a predetermined threshold value Dth at least during the apply control. More specifically, the stop control unit 162 executes stop control when the wheel deceleration Dw is equal to or greater than a predetermined threshold value Dth during a period when the release control, which will be described later, is not being executed. In this embodiment, the threshold value Dth is a fixed value.

[0074] The release control unit 163 has a function of executing release control based on the slip amount SL output from the slip amount calculation unit 130. More specifically, the release control unit 163 executes release control when the slip amount SL becomes equal to or greater than a threshold value SLth.

[0075] That is, in dynamic operation control, the mechanical braking unit 160 executes apply control when SL < SLth and Dw < Dth, executes stop control when SL < SLth and Dw ≥ Dth, and executes release control when SL ≥ SLth.

[0076] The storage unit 170 stores the aforementioned first decompression rate setting map, each threshold value SLth, Dth, etc. The first decompression rate setting map and each threshold value SLth, Dth are appropriately set by experiments, simulations, etc.

[0077] Next, the operation of the end-time decompression control of the control unit 100 will be described in detail. When one of the end conditions of the hydraulic braking control is satisfied, the hydraulic braking unit 150 starts end-time decompression control according to the flowchart shown in FIG. 5 (START).

[0078] In the end-time decompression control, the hydraulic braking unit 150 first sets the first decompression rate R1 according to the vehicle body speed Vc (S1). After step S1, the hydraulic braking unit 150 determines whether the end condition is a cancellation request (S2).

[0079] If it is determined in step S​​​If it is determined in step S4 that the termination condition is that the vehicle 2 is stopped (Yes), the hydraulic braking unit 150 sets the pressure reduction rate R to the second pressure reduction rate R2 (S5). If it is determined in step S4 that the termination condition is not that the vehicle 2 is stopped (No), the termination condition is the remaining one of the three termination conditions (abnormality in the hydraulic unit 10), so the hydraulic braking unit 150 sets the pressure reduction rate R to the third pressure reduction rate R3 (S6).

[0081] After setting the pressure reduction rate R in steps S3, S5, and S6, the hydraulic braking unit 150 executes the termination pressure reduction control at the set pressure reduction rate R (S7). More specifically, in step S7, the hydraulic braking unit 150 controls the current flowing through the outlet valve 14 so that the pressure reduction rate becomes the set pressure reduction rate R.

[0082] Next, the termination pressure reduction control according to each termination condition will be described in detail with reference to FIGS. As shown in Fig. 6, when the driver turns on the parking switch 92 while the vehicle is running (time t1), the hydraulic braking unit 150 starts hydraulic braking control. When the driver releases the parking lever or depresses the accelerator pedal 7 while the vehicle is running, outputting a release request to the hydraulic braking unit 150, the hydraulic braking unit 150 sets the pressure reduction rate R to a first pressure reduction rate R1 with a large slope, and quickly reduces the brake hydraulic pressure at this first pressure reduction rate R1. This allows the braking force applied to the wheels 3 to be released in an extremely short time (between t2 and t3), thereby reducing the dragging sensation felt by the driver.

[0083] 7, when the hydraulic braking unit 150 determines during hydraulic braking control that the vehicle speed Vc has reached a value close to 0 (for example, 0), that is, that the vehicle 2 has stopped (time t11), it starts the end-time pressure reduction control. On the other hand, when the end-time pressure reduction control is started (time t11), the mechanical braking unit 160 drives the electric motor 210 of the parking brake device 200 to start the mechanical braking control.

[0084] In the termination pressure reduction control, the hydraulic braking unit 150 sets the pressure reduction rate R to a second pressure reduction rate R2 that has a smaller slope than the first pressure reduction rate R1, and gradually reduces the brake hydraulic pressure at this second pressure reduction rate R2. As a result, the time that the brake hydraulic pressure can be applied to the wheels 3 can be set to a relatively long time (t11 to t13) compared to when the brake hydraulic pressure is rapidly reduced at the first pressure reduction rate R1 shown by the two-dot chain line in the figure, for example. Therefore, the braking force can be maintained when switching from hydraulic braking control to mechanical braking control, and the vehicle 2 can be kept stopped in a good condition.

[0085] As shown in the figure, the second pressure reduction rate R2 should be set to a gradient such that the brake fluid pressure becomes 0 after the mechanical braking force (the force with which the nut 250 presses the brake piston 240) that increases due to the mechanical braking control that is started approximately simultaneously with the termination pressure reduction control reaches a target value (for example, a maximum value) (time t12). In other words, the second pressure reduction rate R2 should be set to a gradient such that the total braking force, which is the sum of the braking force caused by the brake fluid pressure and the mechanical braking force, becomes equal to or greater than a predetermined value during the execution period of the termination pressure reduction control.

[0086] 8, when the hydraulic braking section 150 determines that an abnormality has occurred in the hydraulic unit 10 during hydraulic braking control (time t21), it starts the end-time pressure reduction control. On the other hand, when the end-time pressure reduction control is started (time t21), the mechanical braking section 160 starts the mechanical braking control.

[0087] In the termination pressure reduction control, the hydraulic braking unit 150 sets the pressure reduction rate R to a third pressure reduction rate R3 that has a slope smaller than that of the first pressure reduction rate R1 and a slope larger than that of the second pressure reduction rate R2, and reduces the brake hydraulic pressure at this third pressure reduction rate R3. This allows for smooth switching from hydraulic braking control to mechanical braking control when an abnormality occurs in the hydraulic unit 10.

[0088] Here, when switching from hydraulic braking control to mechanical braking control due to an abnormality in the hydraulic unit 10, if the brake hydraulic pressure is rapidly reduced at a large gradient such as the first pressure reduction rate R1, the brake hydraulic pressure may become zero before the mechanical braking force increases sufficiently, which may result in poor braking control. Furthermore, when switching from hydraulic braking control to mechanical braking control due to an abnormality in the hydraulic unit 10, if the brake hydraulic pressure is reduced slowly at a small gradient such as the second pressure reduction rate R2, the total braking force, which is the sum of the braking force due to the brake hydraulic pressure and the mechanical braking force, may become too large, which may result in the wheels 3 locking. To address these problems, in this embodiment, the third pressure reduction rate R3 is set to a gradient between the first pressure reduction rate R1 and the second pressure reduction rate R2, thereby enabling a good switch from hydraulic braking control to mechanical braking control.

[0089] As described above, according to this embodiment, in addition to the effects described above, the following effects can be obtained. Since the pressure reduction rate R is set according to the termination condition, which is the termination condition that is satisfied when the hydraulic braking control is terminated, discomfort to the occupants can be suppressed even when braking is performed using the parking switch 92.

[0090] By setting the first pressure reduction rate R1 to a larger value as the vehicle speed Vc increases, the dragging sensation can be eliminated as the vehicle speed Vc increases, thereby further reducing discomfort to the driver.

[0091] The above-described embodiment can be modified in various ways as exemplified below. In the following description, the same reference numerals are used to designate components and processes that are substantially the same as those in the above-described embodiment, and the description thereof will be omitted.

[0092] In the above embodiment, there are three termination conditions for the hydraulic braking control, but any number of termination conditions may be used. For example, if the termination conditions are set to two conditions, that is, a request to cancel the hydraulic braking control and the vehicle 2 being stopped, the pressure reduction rate R may be set to the first pressure reduction rate R1 or the second pressure reduction rate R2. Also, if the termination conditions are set to two conditions, that is, a request to cancel the hydraulic braking control and an abnormality in the hydraulic unit 10, the pressure reduction rate R may be set to the first pressure reduction rate R1 or the third pressure reduction rate R3. Furthermore, if the termination conditions are set to two conditions, that is, the vehicle 2 being stopped and the hydraulic unit 10 being abnormal, the pressure reduction rate R may be set to the second pressure reduction rate R2 or the third pressure reduction rate R3.

[0093] In the above embodiment, the wheel deceleration Dw is set to a positive value when the vehicle 2 decelerates, but the wheel deceleration may also be set to a positive value when the vehicle accelerates. That is, the wheel deceleration Dw may be calculated by subtracting the previous value of the wheel speed Vw from the current value. In this case, stop control may be executed when the wheel deceleration, which takes a negative value during deceleration, exceeds a negative threshold value on the negative side (in the direction away from 0).

[0094] In the above embodiment, the control unit 100 of the vehicle brake fluid pressure control device 1 is exemplified as the parking brake control device, but the parking brake control device may be, for example, an ECU (Electronic Control Unit) that controls an engine or the like.

[0095] In the above embodiment, the parking brake device 200 is illustrated as including the electric motor 210, the reducer 220, the nut 250, and the brake piston 240. However, any parking brake device that mechanically transmits the power of an electric motor to a friction member may be used. For example, the parking brake device may transmit the power of an electric motor to a friction member via a wire.

[0096] In the above embodiment, the wheel brakes FR, FL, RR, and RL are so-called disc brakes equipped with brake rotors BR, but the wheel brakes may also be drum brakes, for example. In this case, the rotating body may be a drum that rotates integrally with the wheel, and the friction member may be a brake shoe that slides against the inner circumferential surface of the drum.

[0097] Furthermore, the operating switch is not limited to the parking switch 92 that detects the movement of the parking lever as in the above embodiment, but may be, for example, a switch that is turned on when pressed by the driver and turned off when pressed again.

[0098] Furthermore, the elements described in the above-described embodiment and modified examples may be combined in any desired manner.

Claims

1. A parking brake control device that controls a hydraulic unit that brakes wheels by hydraulic pressure and a parking brake device that brakes the wheels by mechanically transmitting power of an electric motor to the wheels, a hydraulic braking unit capable of executing hydraulic braking control to brake the wheels by the hydraulic unit on the condition that a signal is input from an activation switch for activating the parking brake device while the vehicle is traveling; a pressure reduction rate setting unit that sets a pressure reduction rate in accordance with a termination condition of the hydraulic brake control that is satisfied at the time of termination of the hydraulic brake control when pressure reduction control is performed at the time of termination of the hydraulic brake control, and a pressure reduction rate setting unit that sets the pressure reduction rate to a first pressure reduction rate that is greater than a minimum pressure reduction rate that is pre-stored in a memory unit when the termination condition is a request to release the hydraulic braking control by a driver's operation while the vehicle is traveling.

2. a switching unit that switches from the hydraulic braking control to a mechanical braking control that brakes the wheels by the electric motor of the parking brake device, the switching unit switches from the hydraulic brake control to the mechanical brake control when the vehicle stops, 2. The parking brake control device according to claim 1, wherein the pressure reduction rate setting unit sets the pressure reduction rate to a second pressure reduction rate that is smaller than the first pressure reduction rate when the termination condition is a stop of the vehicle.

3. the switching unit switches from the hydraulic brake control to the mechanical brake control when the hydraulic unit is abnormal and the pressure reduction control is possible, 3. The parking brake control device according to claim 2, wherein the pressure reduction rate setting unit sets the pressure reduction rate to a third pressure reduction rate that is smaller than the first pressure reduction rate and greater than the second pressure reduction rate when the termination condition is the abnormality of the hydraulic unit.

4. The pressure reduction rate setting unit When the vehicle speed is a first speed, the first pressure reduction rate is set to a first rate; 4. The parking brake control device according to claim 1, wherein when the vehicle speed is a second speed that is greater than the first speed, the first pressure reduction rate is set to a second rate that is greater than the first rate.

5. a switching unit that switches from the hydraulic braking control to mechanical braking control in which the wheels are braked by the electric motor of the parking brake device when the hydraulic unit has an abnormality that allows the pressure reduction control, 2. The parking brake control device according to claim 1, wherein the pressure reduction rate setting unit sets the pressure reduction rate to a third pressure reduction rate that is smaller than the first pressure reduction rate when the termination condition is the abnormality of the hydraulic unit.

6. a switching unit that switches from the hydraulic braking control to mechanical braking control in which the wheels are braked by the electric motor of the parking brake device when the vehicle stops or when the hydraulic unit has an abnormality that allows the pressure reduction control, the pressure reduction rate setting unit sets the pressure reduction rate to a second pressure reduction rate when the termination condition is a stop of the vehicle; 2. The parking brake control device according to claim 1, wherein, when the termination condition is the abnormality of the hydraulic unit, the pressure reduction rate is set to a third pressure reduction rate that is greater than the second pressure reduction rate.

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