CN117657096A - Braking device, control method thereof and vehicle - Google Patents

Abstract

The application provides a braking device, a control method thereof and a vehicle. A control method for a brake device, the control method comprising: a screen flushing step S0, wherein the screen flushing step S0 includes: advancing a slave cylinder piston in the slave cylinder to discharge brake fluid from the slave cylinder chamber; and opening a liquid inlet branch and a liquid inlet valve and a pressure relief valve on a liquid inlet branch and a pressure relief branch of at least one unit in the body stabilization module in fluid communication with the slave cylinder such that brake liquid flushes a filter screen disposed at a port of the reservoir from outside to inside via the liquid inlet branch and the pressure relief branch of the at least one unit, the port being connected to both the pressure relief branch and the slave cylinder chamber. Apparatus and methods according to embodiments of the present application reduce or eliminate false positives in a level self-test step.

Description

Braking device, control method thereof and vehicle

Technical Field

The present application relates to the field of vehicle braking devices, and more particularly, to a braking device, a control method thereof, and a vehicle.

Background

Brake-by-wire systems, and in particular, integrated brakes (Integrated Power Brake, IPB) are a new type of braking system developed from conventional hydraulic systems. Unlike conventional mechanical brake systems in which the brake pedal is mechanically coupled to the master cylinder piston via a connecting rod and the motor is used only to provide assistance, the brake pedal is decoupled to some extent from the hydraulic brake cylinder by a brake-by-wire system such that the braking force is primarily or even entirely dependent on the motor, and the stroke of the brake pedal is detected as a signal to control the motor, thereby making full use of the controllability characteristics of the motor and making the brake system more convenient for integration with systems of electric vehicles, intelligent driving or automatic driving, etc.

For such a brake device, in order to ensure that there is enough brake fluid in the reservoir while verifying the accuracy of the fluid level sensor in the reservoir, it is a challenge how to ensure the accuracy of the fluid level self-test step, which requires to perform the fluid level self-test step periodically.

Disclosure of Invention

The object of the present application is to solve or at least alleviate the problems of the prior art.

According to an aspect of the present application, there is provided a control method for a brake apparatus, the control method including: a screen flushing step S0, wherein the screen flushing step S0 includes: advancing a slave cylinder piston in the slave cylinder to discharge brake fluid from the slave cylinder chamber; and opening a liquid inlet branch and a liquid inlet valve and a pressure relief valve on a pressure relief branch of at least one unit in a body stabilization module in fluid communication with the slave cylinder such that brake liquid flushes a filter screen disposed at a port of the reservoir from outside to inside via the liquid inlet branch and the pressure relief branch, the port being connected to the pressure relief branch and the slave cylinder chamber.

According to another aspect of the present application, there is provided a control method for a brake apparatus, the control method further including a liquid level self-checking step including:

s1, advancing the auxiliary cylinder piston to discharge a first volume of brake fluid from the auxiliary cylinder chamber and monitoring whether the pressure in the auxiliary cylinder chamber is greater than a first threshold value during the advance of the auxiliary cylinder piston, stopping the liquid level self-checking step and reporting when the pressure in the auxiliary cylinder chamber is greater than the first threshold value, and executing step S2 when the pressure in the auxiliary cylinder chamber is not greater than the first threshold value:

s2, cutting off the fluid connection between the auxiliary cylinder and the vehicle body stabilizing module, enabling the auxiliary cylinder piston to continuously move forward to build pressure in the auxiliary cylinder, and calculating first air content V3 in the auxiliary cylinder at the moment based on first forward movement of the auxiliary cylinder piston when the preset pressure is built;

s3, the auxiliary cylinder piston is retracted to extract a second volume of brake fluid from the reservoir through an auxiliary cylinder fluid supplementing flow path from the reservoir to the auxiliary cylinder cavity;

s4, advancing the auxiliary cylinder piston again to build pressure in the auxiliary cylinder, and calculating second air content V5 in the auxiliary cylinder at the moment based on second advanced movement of the auxiliary cylinder piston when the preset pressure is built; and

s5, comparing whether the difference between the first air content V3 and the second air content V5 is larger than a second threshold value.

According to another aspect of the present application, there is provided a brake device including:

a master cylinder having a master piston and a slave piston therein, the master piston engaging a pushrod connected to a brake pedal, the master piston and the slave piston having a first chamber therebetween, and the slave piston and an end wall of the master cylinder having a second chamber therebetween;

a slave cylinder having a slave cylinder piston and a slave cylinder chamber therein, the slave cylinder piston being drivingly connected to a drive motor; a reservoir in communication with the first chamber and the second chamber through a master cylinder fluid replacement flow path and in communication with the slave cylinder chamber through a slave cylinder fluid replacement flow path;

a body stabilization module including a plurality of units corresponding to the respective wheel cylinders, each unit including a liquid inlet branch provided with a liquid inlet valve and a pressure relief branch provided with a pressure relief valve, a liquid inlet branch of a first portion of the plurality of units being connected to the first chamber of the master cylinder through a first branch provided with a first control valve and to the slave cylinder chamber through a third branch provided with a third control valve, a liquid inlet branch of a second portion of the plurality of units being connected to the second chamber of the master cylinder through a second branch provided with a second control valve and to the slave cylinder chamber through a fourth branch provided with a fourth control valve; and

a controller configured to perform the control method according to various embodiments of the present application.

According to another aspect of the present application, a vehicle is provided, which is configured with a brake device according to various embodiments of the present application.

Apparatus and methods according to embodiments of the present application reduce or eliminate false positives in a level self-test step.

Drawings

The disclosure of the present application will become more readily understood with reference to the accompanying drawings. As will be readily appreciated by those skilled in the art: these drawings are for illustrative purposes only and are not intended to limit the scope of the present application. Moreover, like numerals in the figures are used to designate like parts, wherein:

FIG. 1 illustrates a schematic diagram of a brake-by-wire system according to an embodiment;

fig. 2 shows a partial schematic structural view of a brake device according to an embodiment; and

fig. 3 and 4 show flowcharts of a control method according to an embodiment of the present invention, respectively.

Detailed Description

A brake device according to an embodiment of the present invention is described with reference to fig. 1 and 2. The braking device according to an embodiment of the present application includes: a master cylinder 1 having a master piston 22 and a slave piston 24 therein, the master piston 22 engaging a push rod 21 connected to a brake pedal 20, the master piston 22 and the slave piston 24 defining a first chamber 101 therebetween, the slave piston 24 defining a second chamber 102 therebetween with an end wall 12 of the master cylinder; a slave cylinder 5 having a slave cylinder piston 51 and a slave cylinder chamber 50 in the slave cylinder 5, the slave cylinder piston 51 being drivingly connected to a drive motor 52; a reservoir 3, the reservoir 3 being in communication with the first chamber 101 and the second chamber 102 through the master cylinder fluid-replacement flow paths 31,32, respectively, and with the slave cylinder chamber 50 through the slave cylinder fluid-replacement flow path 33; a body stabilization module 6, said body stabilization module 6 comprising a plurality of units corresponding to respective wheel brake cylinders, in particular in the present embodiment four units comprising brake cylinders 71,72,73,74 corresponding to four wheels 81,82,83,84, each unit comprising a feed branch provided with a feed valve 611,621,631,641 and a relief branch provided with a relief valve 612,622,632,642, the feed branch of a first part of the plurality of units (corresponding to wheels 81, 82) being connected from a first position 61 to a first chamber 101 of the master cylinder by a first branch 181 provided with a first control valve 182 and to said slave cylinder chamber 50 by a third branch 581 provided with a third control valve 582, the feed branch of a second part of the plurality of units (corresponding to wheels 83, 84) being connected from a second position 62 to the second chamber 102 of the master cylinder by a second branch 191 provided with a second control valve 192 and to said slave chamber 50 by a fourth branch 591 provided with a fourth control valve 592. In addition, the driving motor 52, the first control valve 182, the second control valve 192, the third control valve 582, the fourth control valve 592 and the respective intake valves 611,621,631,641 and the relief valve 612,622,632,642 in the system, as well as sensors and other valves to be described later, are connected to a controller which performs the respective control methods as will be described later. The pressure relief branches of the individual units of the body stabilization module 6 are joined together at a third location 63 and then connected to the reservoir 3.

Part of the components of the braking device are described with reference to fig. 2. The master cylinder 1 may be substantially cylindrical, having a side wall 11 and an end wall 12, with the outer end of the side wall 11 being open for receiving the piston and the inner end of the side wall 11 being closed by the end wall 12 (hereinafter, the direction approaching the end wall 12 will be referred to as the inner side or the interior). In the master cylinder 1, a master piston 22 and a slave piston 24 are provided, one end of a push rod 21 is for connection with the brake pedal 20, and the other end of the push rod 21 is capable of engaging with the master piston 22 to push the master piston 22. The reservoir 3 communicates with the first chamber 101 through a first fluid-replacement flow path 31 provided with a first valve 311, and the reservoir 3 communicates with the second chamber 102 through a second fluid-replacement flow path 32 not provided with a valve. The first fluid-replacement flow path 31 and the second fluid-replacement flow path 32 are intended to enable the brake fluid in the reservoir 3 to be replenished to the respective chambers, for example, a fluid-replacement condition when a leak occurs in a first-time filling condition, a pedal exhaust condition, or the like. Further, a first return spring 23 is provided between the master piston 22 and the slave piston 24 and a second return spring 25 is provided between the slave piston 24 and the end wall 12 of the master cylinder 1, the first and second return springs 23 and 25 being used to urge the master piston 22 and the slave piston 24 back to the initial positions when the brake pedal is released.

In some embodiments, the primary piston 22 is generally cylindrical with its outer end engaged by the push rod 21 closed and its inner end open near the end wall 12 of the master cylinder 1, and through holes 223 are circumferentially distributed on the circumferential surface of the inner end of the primary piston 22, and similarly, the secondary piston 24 is generally cylindrical with its outer end closed and its inner end open, and through holes 243 are circumferentially distributed on the circumferential surface of the inner end of the secondary piston 24. Further, there are a first seal 221 and a second seal 222 between the master piston 22 and the side wall 11 of the master cylinder 1, the first seal 221 being for isolation from the external environment, the second seal 222 being for sealing with the first chamber 101, the first port 111 of the first fluid-replacement flow path 31 to the first chamber 101 being located between the first seal 221 and the second seal 222. In the initial position where the brake pedal is not depressed, i.e., the master piston 22, the through hole 223 of the peripheral surface of the master piston 22 is also located between the first seal 221 and the second seal 222, so that the first chamber 101 communicates with the first port 111 through the inside of the master piston. During the initial stroke of the master piston 22, no effective pressure will build up in the first chamber 101 until the through-hole 223 in the peripheral surface of the master piston 22 passes the second seal 222, and therefore this stroke is also referred to as an idle stroke, similarly having the third seal 241 and the fourth seal 242 between the slave piston 24 and the end wall 11 of the master cylinder, with the second port 112 of the second fluid-makeup flow path 32 to the second chamber 102 being located between the third seal 241 and the fourth seal 242. In addition, the brake device further includes a pedal feel simulation cylinder 4 connected to the first chamber 101 via the fifth control valve 41, a first sensor 291 that monitors the displacement of the push rod 21, and a second sensor 292 that monitors the pressure of the first chamber 101 or the second chamber 102, and a third sensor 331 that monitors the pressure in the slave cylinder 50, and the controller is further connected to the first sensor 291, the second sensor 292, and the third sensor 331.

The brake device according to the embodiment is capable of operating in a wire control mode and a standby mechanical mode. In the on-line control mode, the first control valve 182 and the second control valve 192 are closed to cut off the connection between the master cylinder 1 and the body stabilization module 6, and the third control valve 582 and the fourth control valve 592 are opened to connect the slave cylinder 5 with the body stabilization module 6. At this time, a corresponding brake pressure is established in the hydraulic cylinder at each brake caliper by the slave cylinder 5 based on the push rod 21 displacement and/or the pressure in the master cylinder. The magnitude of the brake pressure in the slave cylinder 5 is controlled by the slave cylinder motor 52 based on displacement signals sent by the first sensor 291 and/or the second sensor 292, including, for example, the master cylinder pressure and/or the push rod 21. In addition, the fifth control valve 41 is opened such that the pedal feel simulation cylinder 4 is connected with the first chamber 101 to simulate the depression feel of the conventional hydraulic brake system by the pedal feel simulation cylinder 4 when the driver depresses the brake pedal 20. In some embodiments, the slave cylinder motor 52 may also be taken over entirely by the autopilot system or interposed by the emergency braking system. In the on-line mode, in the body stabilization module 6, normally the intake valves 611,621,631,641 remain open while the relief valve 612,622,632,642 remains closed. When the tire is monitored to slip, the ABS function is started, and then the liquid inlet valve of the corresponding unit of the slipping tire is closed and the pressure release valve is intermittently opened to release the brake liquid, and the specific control mode of the vehicle body stabilizing module 6 is not repeated. When the brake device fails, the brake device switches (downgrades) to the standby mechanical mode, at which time the first 182 and second 192 control valves are opened and the third 582, fourth 592 and fifth 41 control valves are closed, the brake device switches to a purely mechanical brake system, and the pressure in the hydraulic cylinders at the respective brake calipers is effected entirely in dependence on the master cylinder 1, i.e. in dependence on the driver depressing the brake pedal 20.

A check valve 332 is provided in the slave cylinder fluid replacement flow path 33 between the slave cylinder chamber 50 and the reservoir 3, and the check valve 332 allows fluid to flow only from the reservoir 3 to the slave cylinder chamber 50. Further, the slave cylinder fluid replacement flow path 33 is also connected to a third sensor 331 that monitors the pressure of the slave cylinder chamber 50. As shown, in some embodiments, the port of the slave cylinder chamber 50 that connects to the reservoir 3 is also the port of the pressure relief branch that connects to the reservoir, where a filter screen 301 is also provided. In addition, the port has an additional fluid-supplementing flow path 34, the additional fluid-supplementing flow path 34 being connected to the vicinity of the initial position of the slave cylinder piston 51 of the slave cylinder chamber 50, and the additional fluid-supplementing flow path 34 being isolated from the slave cylinder chamber 50 by a seal after the initial stroke (idle stroke) of the slave cylinder piston 51. In addition, a liquid level sensor 39 is provided in the reservoir 3.

For the above braking device, in order to ensure that there is sufficient brake fluid in the reservoir 3 and at the same time verify the validity of the level sensor 39 in the reservoir 3, a level self-checking step FLP may be performed. Referring to fig. 3, the steps include: beginning at S10, S1 advances the slave cylinder piston 5 to displace a first volume of brake fluid, e.g. a few milliliters, from the slave cylinder, which may be 8 milliliters depending on the slave cylinder size, and simultaneously monitors whether the pressure in the slave cylinder chamber 50 during the advance of the slave cylinder piston 51 is greater than a first threshold, e.g. 10bar, and when the pressure in the slave cylinder chamber 50 is greater than the first threshold, step S11 is performed to stop the fluid level self-test step and report.

In some embodiments, the level self-checking step further includes performing the following steps when the pressure in the slave cylinder chamber 50 is not greater than a first threshold: s2, cutting off the fluid connection of the auxiliary cylinder 5 and the vehicle body stabilization module 6, allowing the auxiliary cylinder piston 51 to continue to advance to build pressure in the auxiliary cylinder 5, and calculating a first air content V3 in the auxiliary cylinder at this time based on a first advance movement of the auxiliary cylinder piston 51 when a predetermined pressure is built up, for example, any value of 8 to 15 bar; s3, retracting the auxiliary cylinder piston 51 to extract a second volume of brake fluid from the reservoir 3 through the auxiliary cylinder fluid-compensating flow path 33 from the reservoir 3 to the auxiliary cylinder chamber 50, for example, the second volume may be 3 milliliters; s4. advancing the slave cylinder piston 51 again to build pressure in the slave cylinder 5, and calculating a second air content V5 in the slave cylinder at this time based on a second advanced displacement of the slave cylinder piston 51 when the predetermined pressure (8 to 15 bar) is built up; and S5, comparing whether the difference between the first air content V3 and the second air content V5 is larger than a second threshold value, such as 1 cubic centimeter. In some embodiments, the method further comprises: in step S5, when the difference is greater than a second threshold value, such as 1 cubic centimeter, step S52 is performed to downgrade the brake device into a mechanical braking mode in which the master cylinder 1 is in fluid communication with the body stabilization module 6 and output a prompt, and when the difference is not greater than a second threshold value, such as 1 cubic centimeter, step S51 is performed to maintain the brake device in a brake-by-wire mode in which the slave cylinder 5 is in fluid communication with the body stabilization module 6 and the current level self-test step is ended. In a specific embodiment, step S2 may be accomplished by closing the third control valve 582 and the fourth control valve 592, and maintaining the valves in a closed state in subsequent steps S3 and S4.

Various problems of the brake module, such as the problem of too low liquid level in the reservoir 3, can be effectively detected through the liquid level self-checking step, wherein step S1 can detect whether the flow path from the slave cylinder to the body stabilizing module to the master cylinder to the reservoir is smooth, and steps S2 to S5 can detect whether the brake liquid pumped from the reservoir 3 contains air to determine whether the reservoir 3 has sufficient brake liquid, and also verify whether the liquid level sensor 39 works normally, i.e. when the liquid level in the reservoir 3 is too low, a larger proportion of air (for example, 1 milliliter) is mixed in the brake liquid of the second volume pumped in step S3, then the detected air volume V5 in step S4 will be significantly larger than the detected air volume V3 in step S2, i.e. when the difference between the two is larger than 1 cubic centimeter, then the liquid level of the reservoir is deemed insufficient, and the brake mode is continuously used in a line control mode, so that a mechanical brake mode is used, otherwise the line control mode is maintained.

In some embodiments, the control method further comprises: step S10 includes starting to execute a liquid level self-checking step on the premise that the vehicle speed reaches a third threshold value after the brake device is started and the brake request is not generated, namely, detecting the liquid level self-checking step after each starting of the brake device, thereby ensuring the normal operation of the brake device.

In some conditions, in the case of normal braking module, there is a false alarm in the above-mentioned liquid level self-checking step, which may be caused by two reasons. The first situation is that in step S1, as brake fluid passes from the slave cylinder chamber 50 through the third branch 581, the first branch 181, the first chamber 101 and the first fluid-filled flow path 31 back to the reservoir, the first valve 311 on the first fluid-filled flow path 31 may exhibit a large flow resistance under extreme conditions, resulting in a pressure build-up in the slave cylinder chamber 50 that is greater than a first threshold, e.g. 10 bar. To avoid this, in some embodiments, in step S1, the fourth control valve 592 on the fourth branch 591 may be controlled to open, the first control valve 192 on the second branch 191, to return brake fluid from the brake fluid to the reservoir 3 via the second chamber 102 of the master cylinder, where there is no valve in the second fluid-compensating flow path 32 connecting the second chamber 102 and the reservoir 3, and the flow resistance in this flow path is small. In addition, based on the structural arrangement of the braking device, the length of the flow path through the second chamber 102 is also smaller than that of the flow path through the first chamber, so the flow resistance in the process of flowing the fluid to the reservoir in the step S1 can be effectively reduced by the control method, and the false alarm in the step S1 can be effectively avoided. In an alternative embodiment, in step S1, the brake fluid may be returned to the reservoir 3 via both the third 581 and fourth 591 branches connecting the slave cylinder with the body stabilization module 6, both the first 181 and second 191 branches connecting the body stabilization module 6 with the first 101 and second 102 chambers of the master cylinder 1, and the master cylinder make-up flow paths 31,32 connecting the first 101 and second 102 chambers of the master cylinder with the reservoir 3, respectively, at which time the brake fluid passes from the first and second chambers simultaneously.

Another case is that it is detected in step S5 whether the difference of the first air content V3 and the second air content V5 is greater than the second threshold value, however it is actually detected that there is sufficient brake fluid in the reservoir 3. It was found through analysis that this is due to clogging of the filter screen 301 provided at the port of the sub-cylinder fluid-replenishing flow path 33 to the reservoir, resulting in insufficient brake fluid being drawn in (resulting in vacuum being drawn in) in step S3. The function of the filter 301 is to prevent impurities in the reservoir 3 from entering the brake fluid flow path, but accumulation of impurities on the side of the filter 301 facing the reservoir 3 is liable to occur after a long-term use.

In order to avoid such false alarms, there is also provided according to an embodiment of the present invention a control method for a brake device, referring to fig. 4, comprising a screen flushing step S0, said screen flushing step S0 comprising: advancing the slave cylinder piston 51 in the slave cylinder 5 to discharge the brake fluid from the slave cylinder chamber 50; and opening the inlet and outlet valves on the inlet and outlet branches of at least one unit in the body stabilization module 6 in fluid communication with the slave cylinder such that brake fluid flushes (downward upward in fig. 1) the filter screen 301 disposed at the port of the reservoir from outside the reservoir 3 via the inlet and outlet branches of at least one unit. It should be connected that since the pressure relief branch of the body stabilization module 6 is only open in ABS or other specific situations, the brake device will not have a flow from the pressure relief branch back flushing the filter screen 301 in normal use, so that the side of the filter screen 301 facing the reservoir 3 may be blocked by impurities. The filter 301 is periodically backwashed by using a pressure relief circuit to effectively mitigate the accumulation of contaminants at the filter 301, thereby avoiding the occurrence of the false alarm condition described above. The screen flushing step S0 may be performed less frequently than the level self-detection S1-S5, for example, based on a predetermined time interval, such as every half month, a predetermined driving distance, such as every 1000 km, and/or a predetermined number of brake activation times, such as every 50 activations, in step S91, or may be performed based on a weighted combination of a plurality of the above factors. In some embodiments, in the flushing method described above, the slave cylinder piston 51 may be caused to discharge 7 milliliters to 15 milliliters of brake fluid from the slave cylinder chamber 50. It should be appreciated that the above-described backflushing screen flushing step S0 may be performed with any one of the units of the body stabilization module 6 or may be performed with a plurality of units together, and in a particular control step, one or both of the third control valve 582 connected to the third branch 581 between the slave cylinder chamber 50 and the first set of units of the body stabilization module 6, or the fourth control valve 592 connected to the fourth branch 591 between the slave cylinder chamber 50 and the second set of units of the body stabilization module 6 may be opened. For example, as a specific embodiment, the controller is configured to perform in step S0: the third control valve 582 is opened, and the intake valve 621 and the pressure release valve 622 connected to the third control valve 582 in the body stabilization module are opened, and the slave cylinder piston 51 in the slave cylinder 5 is advanced to discharge the brake fluid from the slave cylinder chamber 50, so that the brake fluid flushes the reservoir screen 301 from outside to inside of the reservoir 3 via the intake and pressure release branches in which the intake valve 621 and the pressure release valve 622 are located. According to the method and the device provided by the embodiment of the invention, the liquid level self-detection step can be effectively executed, and false alarm is avoided.

The specific embodiments of the present application have been described above merely to provide a more clear description of the principles of the present application, in which individual components are explicitly shown or described so as to provide a more readily understood principles of the present invention. Various modifications or variations of this application may be readily made by those skilled in the art without departing from the scope of this application. It is to be understood that such modifications and variations are intended to be included within the scope of the present application.

Claims (14)

1. A control method for a brake device, the control method comprising: a screen flushing step S0, wherein the screen flushing step S0 includes: advancing a slave cylinder piston (51) in a slave cylinder (5) to discharge brake fluid from a slave cylinder chamber (50); and opening inlet and relief valves on inlet and relief branches of at least one unit in a body stabilization module (6) in fluid communication with the slave cylinder such that brake fluid flushes a filter screen (301) arranged at a port of the reservoir (3) from outside to inside via the inlet and relief branches of the at least one unit, the port being connected to the relief branches and the slave cylinder chamber (50).

2. The control method according to claim 1, characterized in that it comprises performing the screen flushing step S0 based on a combination of one or more of a predetermined time interval, a predetermined driving distance and/or a predetermined number of activations of the braking means.

3. A control method according to claim 1, characterized in that the flushing method comprises letting the slave cylinder piston (51) discharge 7 ml to 15 ml of brake fluid from the slave cylinder chamber (50).

4. The control method according to claim 1, characterized in that it further comprises opening a third control valve (582) connected to a third branch (581) between the slave cylinder chamber (50) and the first set of units of the body stabilization module (6) or opening a fourth control valve (592) connected to a fourth branch (591) between the slave cylinder chamber (50) and the second set of units of the body stabilization module (6).

5. A control method for a brake device, the control method comprising a liquid level self-checking step comprising:

s1, advancing the slave cylinder piston (51) to drain a first volume of brake fluid from the slave cylinder chamber (50) and monitoring whether the pressure in the slave cylinder chamber (50) during the advancement of the slave cylinder piston (51) is greater than a first threshold, stopping the fluid level self-test step and reporting when the pressure in the slave cylinder chamber (50) is greater than the first threshold, and performing step S2 when the pressure in the slave cylinder chamber (50) is not greater than the first threshold:

s2, cutting off the fluid connection of the auxiliary cylinder (5) and the vehicle body stabilizing module (6), enabling the auxiliary cylinder piston (51) to continue to advance so as to build pressure in the auxiliary cylinder (5), and calculating a first air content V3 in the auxiliary cylinder at the moment based on the first advance movement of the auxiliary cylinder piston (51) when the preset pressure is built up;

s3, retracting the auxiliary cylinder piston (51) to extract a second volume of brake fluid from the reservoir (3) through an auxiliary cylinder fluid-supplementing flow path (33) from the reservoir (3) to the auxiliary cylinder containing cavity (50);

s4, advancing the auxiliary cylinder piston (51) again to build pressure in the auxiliary cylinder (5), and calculating a second air content V5 in the auxiliary cylinder at the moment based on a second advanced movement of the auxiliary cylinder piston (51) when the preset pressure is built; and

s5, comparing whether the difference between the first air content V3 and the second air content V5 is larger than a second threshold value.

6. The control method according to claim 5, characterized in that the master cylinder comprises a master piston (22) and a slave piston (24), the master piston (22) being engaged with a push rod (21) connected to a brake pedal, the master piston (22) and the slave piston (24) having a first chamber (101) therebetween, the slave piston (24) having a second chamber (102) therebetween with an end wall (12) of the master cylinder, the control method comprising, in step S1, returning brake fluid to the reservoir (3) via a flow path connecting the slave cylinder with the body stabilization module (6), a flow path connecting the body stabilization module (6) with the second chamber (102) of the master cylinder (1), and a master cylinder fluid make-up flow path (32) connecting the second chamber (102) of the master cylinder with the reservoir (3); or alternatively

The control method includes returning brake fluid to the reservoir (3) via a flow path connecting the slave cylinder and the body stabilization module (6), a flow path connecting the body stabilization module (6) and the first chamber (101) and the second chamber (102) of the master cylinder (1), and master cylinder fluid-supplementing flow paths (31, 32) connecting the first chamber (101) and the second chamber (102) of the master cylinder and the reservoir (3), respectively, in step S1.

7. The control method according to claim 5, characterized in that the method further comprises: in the step S5, when the difference is larger than a second threshold value, the braking device is degraded to a mechanical braking mode in which a master cylinder (1) is in fluid communication with the body stabilizing module (6) and a prompt is output, when the difference is not larger than the second threshold value, the braking device is kept in a line control braking mode in which a slave cylinder (5) is in fluid communication with the body stabilizing module (6), and the current liquid level self-checking step is ended.

8. The control method according to claim 5, characterized in that the control method further comprises: and after the braking device is started, the liquid level self-checking step is executed on the premise that the vehicle speed is accelerated for the first time until the vehicle speed reaches a third threshold value and a braking request is not generated.

9. The control method according to claim 5, further comprising performing a screen flushing step S0 according to any one of claims 1-4.

10. A brake apparatus, comprising:

a master cylinder (1) having a master piston (22) and a slave piston (24) therein, the master piston (22) engaging a push rod (21) connected to a brake pedal (20), the master piston (22) and the slave piston (24) having a first chamber (101) therebetween, the slave piston (24) and an end wall (12) of the master cylinder having a second chamber (102) therebetween;

a slave cylinder (5), the slave cylinder (5) having a slave cylinder piston (51) and a slave cylinder chamber (50) therein, the slave cylinder piston (51) being drivingly connected to a drive motor (52);

-a reservoir (3), the reservoir (3) being in communication with the first chamber (101) and the second chamber (102) through a master cylinder fluid-refill flow path (31, 32) and with the slave cylinder chamber (50) through a slave cylinder fluid-refill flow path (33);

a body stabilization module (6), the body stabilization module (6) comprising a plurality of units corresponding to respective wheel brake cylinders, each unit comprising a feed branch provided with a feed valve (611, 621,631, 641) and a relief branch provided with a relief valve (612, 622,632, 642), a feed branch of a first part of the plurality of units being connected to the first chamber (101) of the master cylinder by a first branch (181) provided with a first control valve (182) and to the slave cylinder chamber (50) by a third branch (581) provided with a third control valve (582), a feed branch of a second part of the plurality of units being connected to the second chamber (102) of the master cylinder by a second branch (191) provided with a second control valve (192) and to the slave cylinder chamber (50) by a fourth branch (591) provided with a fourth control valve (592); and

a controller configured to perform the control method of any one of claims 1-9.

11. Brake device according to claim 10, characterized in that the pressure relief branch of the plurality of units is connected to the same port of the reservoir (3) as the auxiliary cylinder fluid-compensating flow path (33), and in that the port is provided with a sieve (301), the controller being configured to perform in step S0: -opening the third control valve (582) or the fourth control valve (592) and opening a feed and relief valve of at least one unit connected thereto in a body stabilization module, and-advancing a slave cylinder piston (51) in the slave cylinder (5) to drain brake fluid from a slave cylinder chamber (50) such that brake fluid flushes the filter screen (301) of the reservoir from outside to inside via a feed and relief branch of the at least one unit.

12. The braking device according to claim 10, wherein the controller is configured to perform in step S1: -closing the third control valve (582) and opening the fourth control valve (592) and the second control valve (192), -advancing a slave cylinder piston (51) in the slave cylinder (5) to expel a first volume of brake fluid from the slave cylinder chamber (50), -returning brake fluid to the reservoir (3) via the third branch (581), the second branch (191) and the second chamber (102) of the master cylinder.

13. The brake apparatus of claim 10, wherein the controller is configured to maintain the third control valve (582) and the fourth control valve (592) in a closed state in steps S2, S3, and S4.

14. A vehicle comprising a braking device according to any one of claims 10-13.