CN205440327U - Electronic helping hand braking system with complex function - Google Patents

Abstract

The utility model relates to the field of vehicle engineering, and discloses an electric power-assisted braking system with compound functions, which includes a brake pedal displacement sensor, a brake pedal, a pedal stroke simulator, an electric power-assisted assembly, a master cylinder, a wheel cylinder, Hydraulic control unit, liquid storage tank, motor, deceleration and torque increasing mechanism, electronic control unit, normally open solenoid valve, normally closed solenoid valve, and other sensors on the vehicle. By designing a pedal stroke simulator, the friction braking force and regenerative braking force can be achieved. Decoupling, providing continuously variable foot feel, the motor assist device can be integrated with the brake anti-lock braking system and the hydraulic control unit to realize the active braking function, there is no interference between the motor input and the driver input, the motor can realize active braking, It can be used as a brake actuator for smart cars and driverless cars.

Description

An electric power-assisted braking system with composite functions

technical field

The utility model relates to the field of vehicle engineering, in particular to an electric power-assisted braking system with composite functions.

Background technique

With the development of electric vehicles and smart vehicles, new requirements are put forward for the braking system, such as the ability to independently generate the required braking force (active braking), to realize the function of braking energy recovery, and to be able to match the active safety system of the chassis. Functions, for example, anti-lock braking system (ABS, Anti-lockBrakingSystem) anti-skid control (ASR, AccelerationSkidcontrolsystem), vehicle stability control system (ESC, ElectronicStabilitycontroller) and adaptive cruise control (ACC, AdaptiveCruiseControl), etc.

The traditional hydraulic braking system uses a vacuum booster and a master cylinder and wheel cylinder system. Among them, the vacuum booster needs to draw vacuum through the engine. However, the electric vehicle cancels the traditional engine structure and uses the electric motor as the driving device, which makes the vacuum booster of the traditional hydraulic brake lose its function; at the same time, due to the regenerative braking function requirements of the electric vehicle, it is required In the process, try to use the regenerative braking force generated by the reverse drag of the motor, and at the same time do not want the frictional braking force generated by the driver to actuate the wheel cylinder to clamp the brake disc by stepping on the pedal to participate in the braking process, which requires the braking system to be able to achieve Decoupling of friction braking force and regenerative braking force.

Therefore, it can be seen that the traditional braking system can no longer meet the development needs of electric vehicles and smart vehicles. The vacuum pump system has a large volume and single function, and cannot be integrated and controlled with ABS/ESC, ACC (or similar products).

In recent years, many electric vehicles use vacuum pumps to replace the engine to extract the vacuum of the vacuum booster to ensure the boosting function of the braking system. However, the vacuum pump solution requires the motor to work in stages in order to ensure the vacuum degree, that is, the motor also needs to work when the driver does not brake; and when the system brakes continuously, the brake pressure will gradually decay, which may cause to safety hazards. At the same time, the volume of the vacuum pump system is large, which is not conducive to saving space, and it cannot be integrated with other control systems of the chassis.

In addition, there are also a small number of cars that use other forms of power assist devices such as electric power assist and hydraulic power assist, such as Nissan's e-ACT braking system. However, electric power assist or hydraulic power assist systems cannot realize the decoupling of frictional braking force and regenerative braking force, which greatly affects the regenerative braking function of electric vehicles.

Brake-by-wire systems, such as the electro-hydraulic brake system EHB and the electro-mechanical brake system EMB, can well meet the above needs of electric vehicles. However, the structure of the brake-by-wire system is complicated and the manufacturing cost is high. Composed of simulators, motors, pumps, high-pressure accumulators, and 10 solenoid valves, the hydraulic circuit is very complex. The EMB system consists of four sets of motors, deceleration mechanisms, and motion conversion mechanisms. If failure backup is considered, four sets of traditional hydraulic braking systems are required, and the cost is relatively high.

It is difficult to realize the decoupling of friction braking force and regenerative braking force with a pure electric power assist system, which greatly affects the regenerative braking function of electric vehicles. The brake-by-wire system has certain advantages in matching electric vehicles and smart vehicles. However, the manufacturing cost of the brake-by-wire system is relatively high, the structure is complex, and the failure protection capability is difficult to gain the trust of automobile manufacturers.

Contents of the invention

The purpose of the utility model is to provide an electric power-assisted braking system with composite functions, which can realize basic power-assisted braking functions, active braking functions, regenerative braking functions, and failure backup functions. At the same time, it can be integrated with brake anti-lock braking system and vehicle stability control system to realize active safety control.

In order to achieve the above-mentioned technical purpose and achieve the above-mentioned technical effect, the utility model discloses an electric power-assisted braking system with composite functions, which includes a brake pedal displacement sensor 1, a brake pedal 2, a pedal stroke simulator 3, an electric power-assisted Assembly 4, master cylinder 5, wheel cylinder 6, hydraulic control unit 7, liquid storage tank 8, motor 9, deceleration and torque increasing mechanism 10, electronic control unit 11, normally open solenoid valve 12, normally closed solenoid valve 13, vehicle-mounted others The brake pedal displacement sensor 1 is installed at the rotating shaft of the brake pedal 2, the pedal stroke simulator 3 is arranged between the brake pedal 2 and the electric power assist assembly 4, and the master cylinder 5 and the hydraulic control unit 7 pass through the brake pedal. The hydraulic control unit 7 is connected to the four wheel cylinders 6 through the brake pipeline, and the liquid storage tank 8 is connected to the pedal stroke simulator 3 through the oil inlet hole through the normally open solenoid valve 12 and the normally closed solenoid valve 13 respectively. The front cavity of the motor is connected to the rear cavity, the motor 9, the brake pedal displacement sensor 1 and other sensors 14 on the vehicle are all connected to the electronic control unit 11 through wires, and the motor 9 is connected to the electric power assist assembly 4 through the deceleration torque increasing mechanism 10.

Wherein, the pedal stroke simulator 3 comprises a pedal stroke simulator housing 301 , a front piston 302 , a front piston return spring 303 , a rear piston 304 , and a rear piston return spring 305 .

Among them, the electric booster assembly 4 includes an electric booster assembly housing 401, a sleeve 402, a rack 403, a booster assembly push rod 404, a push rod return spring 405, a buffer block 406, a reaction disc 407, and a master cylinder push rod. 408, master cylinder push rod return spring 409, master cylinder push rod displacement sensor 410, gear 411 form.

Wherein, the rear end surface of the front piston 302 of the pedal stroke simulator 3 is connected with the brake pedal 1 through a hinge, a spring seat is arranged in the middle of the front piston 302, and the front piston return spring 303 is placed on the spring seat; the rear piston 304 is arranged on the front Between the piston 302 and the front end of the pedal stroke simulator housing 301, the rear piston return spring 305 is arranged between the rear piston 304 and the front end of the pedal stroke simulator housing 301; the rear piston 304 and the pedal stroke simulator housing The cavity enclosed between the front end faces of body 301 is the rear cavity of the pedal simulator, the cavity surrounded between the front piston 302 and the rear piston 304 is called the front cavity of the pedal simulator, the front cavity of the pedal simulator and the rear cavity of the pedal simulator An oil inlet is all opened, and the liquid storage tank 8 is connected to the front cavity of the pedal simulator and the rear cavity of the pedal simulator through the normally open electromagnetic valve 12 and the normally closed electromagnetic valve 13 through the oil inlet respectively.

Wherein, the inner surface of the sleeve 402 is provided with stepped protrusions and the inner surface and the outer surface are welded with limit blocks, the sleeve 402 is installed in the hollow interior of the rack 403, and the top of the rack 403 meshes with the gear 411, and the booster assembly pushes The rear end surface of the rod 404 is in contact with the front end surface of the rear piston 304, the front end surface of the booster assembly push rod 404 is threadedly connected with the buffer block 406, and the middle of the booster assembly push rod 404 is provided with a raised spring seat and a push rod return position spring 405, the inner ring of the reaction disc 407 is in contact with the buffer block 406, the outer ring of the reaction disc 407 is in contact with the stepped protrusion of the sleeve 402, and the master cylinder push rod 408 has a "T" structure and is installed with a master cylinder push rod return. Position spring 409 and master cylinder push rod displacement sensor 410, the front end face of master cylinder push rod 408 links to each other with master cylinder 5, and the rear end face of master cylinder push rod 408 contacts with reaction disk 407, and master cylinder push rod displacement sensor 410 passes circuit and The electronic control unit 11 is connected.

Preferably, the buffer block 406 is made of plastic, and the reaction disc 407 is made of rubber.

The utility model has the following beneficial effects:

1. The electric power-assisted braking system described in this utility model can continue to use the traditional brake master cylinder, brake and hydraulic control unit, and at the same time control the motor to participate in the adjustment of the braking pressure. The motor torque is actively controlled to suppress the impact of the liquid return from the hydraulic control unit on the brake pedal.

2. The electric power-assisted braking system described in the utility model does not need to set up a special brake failure backup device. When the brake fails, the driver can directly actuate the master cylinder to generate part of the braking force by stepping on the pedal, which meets the requirements of regulations and has high reliability. sex.

3. The electric power-assisted braking system described in this utility model, when matched with an electric vehicle, can realize the complete decoupling of the brake pedal and the friction brake, and perform coordinated braking of the regenerative braking force and the frictional braking force, which can maximize recovery braking energy.

4. The electric power-assisted braking system described in this utility model can obtain the driving state of the vehicle through other sensors on the vehicle, so as to implement active braking, and the brake pedal will not be driven during the braking process, which can be well matched with smart cars .

Description of drawings

Fig. 1 is the structural representation of the utility model.

Explanation of main component symbols:

1: Pedal displacement sensor, 2: Brake pedal, 3: Pedal stroke simulator, 4: Electric power assist assembly, 5: Master cylinder, 6: Wheel cylinder, 7: Hydraulic control unit, 8: Fluid storage tank, 9: Motor, 10: deceleration torque increasing mechanism, 11: electronic control unit, 12: normally open solenoid valve, 13: normally closed solenoid valve, 14: other sensors on the vehicle, 301: pedal stroke simulator housing, 302: front piston, 303 : Front piston return spring, 304: Rear piston, 305: Rear piston return spring, 401: Electric power booster assembly housing, 402: Sleeve, 403: Rack, 404: Power booster push rod, 405: Push Rod return spring, 406: buffer block, 407: reaction plate, 408: master cylinder ejector rod, 409: master cylinder ejector rod return spring, 410: master cylinder ejector rod travel sensor, 411: gear

detailed description

In order to make the purpose, technical solution and advantages of the utility model clearer, the utility model will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Example 1

As shown in Figure 1, the utility model discloses an electric power-assisted braking system with composite functions, which includes a brake pedal displacement sensor 1, a brake pedal 2, a pedal stroke simulator 3, an electric power-assisted assembly 4, Master cylinder 5, wheel cylinder 6, hydraulic control unit 7, liquid storage tank 8, motor 9, deceleration and torque increasing mechanism 10, electronic control unit 11, normally open solenoid valve 12, normally closed solenoid valve 13 and other sensors 14 on the vehicle, among which , The pedal stroke simulator 3 includes a pedal stroke simulator housing 301, a front piston 302, a front piston return spring 303, a rear piston 304, and a rear piston return spring 305. Among them, the electric booster assembly 4 includes an electric booster assembly housing 401, a sleeve 402, a rack 403, a booster assembly push rod 404, a push rod return spring 405, a buffer block 406, a reaction disc 407, and a master cylinder push rod. 408, master cylinder push rod return spring 409, master cylinder push rod displacement sensor 410, gear 411 form.

Structural design:

The brake pedal displacement sensor 1 is installed at the rotating shaft of the brake pedal 2, the pedal stroke simulator 3 is arranged between the brake pedal 2 and the electric power assist assembly 4, and the master cylinder 5 communicates with the hydraulic control unit 7 through the brake pipeline , the hydraulic control unit 7 is connected to the four wheel cylinders 6 through the brake pipeline, and the liquid storage tank 8 is connected to the front cavity and the front cavity of the pedal stroke simulator 3 through the normally open solenoid valve 12 and the normally closed solenoid valve 13 through the oil inlet hole respectively. The rear cavity is connected, the motor 9, the brake pedal displacement sensor 1 and other sensors 14 on the vehicle are all connected to the electronic control unit 11 through wires, and the motor 9 is connected to the electric power assist assembly 4 through the deceleration torque increasing mechanism 10.

Wherein, the rear end surface of the front piston 302 of the pedal stroke simulator 3 is connected with the brake pedal 1 through a hinge, a spring seat is arranged in the middle of the front piston 302, and the front piston return spring 303 is placed on the spring seat; the rear piston 304 is arranged on the front Between the piston 302 and the front end of the pedal stroke simulator housing 301, the rear piston return spring 305 is arranged between the rear piston 304 and the front end of the pedal stroke simulator housing 301; the rear piston 304 and the pedal stroke simulator housing The cavity enclosed between the front end faces of body 301 is the rear cavity of the pedal simulator, the cavity surrounded between the front piston 302 and the rear piston 304 is called the front cavity of the pedal simulator, the front cavity of the pedal simulator and the rear cavity of the pedal simulator An oil inlet is all opened, and the liquid storage tank 8 is connected to the front cavity of the pedal simulator and the rear cavity of the pedal simulator through the normally open electromagnetic valve 12 and the normally closed electromagnetic valve 13 through the oil inlet respectively.

Wherein, the inner surface of the sleeve 402 is provided with stepped protrusions and the inner surface and the outer surface are welded with limit blocks, the sleeve 402 is installed in the hollow interior of the rack 403, and the top of the rack 403 meshes with the gear 411, and the booster assembly pushes The rear end surface of the rod 404 is in contact with the front end surface of the rear piston 304, the front end surface of the booster assembly push rod 404 is threadedly connected with the buffer block 406, and the middle of the booster assembly push rod 404 is provided with a raised spring seat and a push rod return position spring 405, the inner ring of the reaction disc 407 is in contact with the buffer block 406, the outer ring of the reaction disc 407 is in contact with the stepped protrusion of the sleeve 402, and the master cylinder push rod 408 has a "T" structure and is installed with a master cylinder push rod return. Position spring 409 and master cylinder push rod displacement sensor 410, the front end face of master cylinder push rod 408 links to each other with master cylinder 5, and the rear end face of master cylinder push rod 408 contacts with reaction disk 407, and master cylinder push rod displacement sensor 410 passes circuit and The electronic control unit 11 is connected.

working principle:

Electric power assist function:

Under the electric power assist function, the normally closed solenoid valve 13 and the normally open solenoid valve 12 are not energized, at this time the connection between the front chamber of the pedal stroke simulator 3 and the liquid storage tank 8 is cut off, and the front chamber of the pedal stroke simulator 3 is locked. The back cavity of the pedal stroke simulator 3 is connected with the liquid storage tank 8, and the back cavity of the pedal stroke simulator 3 is in a free state. When the brake pedal 2 is stepped on, the pedal force is transmitted to the front piston 302. Since the front cavity of the pedal stroke simulator 3 is locked, the force is transmitted to the rear piston 304 through hydraulic pressure. During this process, the front piston return spring 303 does not Compressed, the front piston 302 and the rear piston 304 are equivalent to move forward as a whole, and exert force on the push rod 404 of the booster assembly, and apply force to the reaction disk 407 through the buffer block 406. At this time, the reaction disk is deformed. The inner ring is dented due to the force exerted by the push rod 404 of the power booster assembly, thereby generating a deformation amount. The electronic control unit 11 measures the deformation amount X1 through the brake pedal displacement sensor 1, and at the same time measures the master cylinder through the master cylinder push rod displacement sensor 410. Push rod displacement X2, in order to compensate for the concave deformation of the reaction disc 407, the electronic control unit 11 controls the motor 9 to drive the gear 411 to rotate through the deceleration and torque increasing mechanism 10, thereby driving the rack 403 to move in translation, and the rack 403 passes through the outer edge of the sleeve 402 The contact action of the limit block drives the sleeve 402 to move in translation, so that the stepped protrusion of the sleeve 402 contacts the reaction disk 407, so that the outer edge of the reaction disk 407 is stressed, thereby compensating for the concave deformation of the reaction disk 407. Electronic control The unit 11 obtains the control amount X of the motor pushing the sleeve 402 according to the following formula: X=X2-X1, repeating this process repeatedly, the manpower applied to the push rod 404 of the booster assembly and the motor force applied to the sleeve 402 are between The reaction disk 407 is superimposed, so that the reaction disk 407 does not deform macroscopically, and the joint action pushes the master cylinder ejector 408 forward, thereby actuating the master cylinder 5 to generate braking force, realizing the electric power assist function.

2. Regenerative braking function

When the brake pedal 2 is stepped on, the pedal force acts on the front piston 302 of the pedal stroke simulator 3. At this time, the electronic control unit 11 controls the normally open solenoid valve 12 to close, the normally closed solenoid valve 13 to open, and the pedal stroke simulator 3 The rear chamber of the chamber is locked, and the front chamber communicates with the liquid storage tank 8 and is in a free state. At this moment, the front piston 302 advances along with the increase of the driver's stepping on the pedal force. Since the rear cavity is locked at this time, the front piston pushes the front piston return spring 303 of the pedal simulator to compress, and the rear piston 304 remains motionless. The spring 303 now Provide foot feeling, at the same time, the electronic control unit 11 obtains the driver's braking intention through the brake pedal stroke sensor 1, and then controls the electric vehicle drive motor (not shown in the figure) to drag backward and perform regenerative braking. At this time, the pedal force has no It is transmitted to the electric booster mechanism 4, and the booster motor 9 is not working at the same time, so that the decoupling of friction braking and regenerative braking can be realized, and the braking energy can be recovered to the greatest extent. With the increase of the pedal displacement (medium braking intensity), the front piston 302 is constantly moving forward. 0.2g or less), at this time, the front piston 302 blocks the oil inlet hole of the front chamber, and the front chamber is locked at this time; at the same time, the electronic control unit 11 controls to open the normally open solenoid valve 12, so that the rear chamber is connected to the liquid storage tank 8, The rear cavity is unlocked. In this way, as the pedal displacement continues to increase, the front piston 302 transmits force to the rear piston 304 through the oil in the front cavity, and the front and rear pistons move forward together to act on the reaction disc 407 through the push rod 404 of the booster assembly. At the same time, The electronic control unit 11 recognizes the driver's braking intention through the signals of the pedal displacement sensor 1 and the master cylinder pushrod displacement sensor 410, and then controls the booster motor 9 to generate the required booster torque (its specific working process is consistent with the electric booster function). In this stage, friction braking and regenerative braking work simultaneously, which is a hybrid braking stage.

3. Active braking function

When the brake pedal 2 is not depressed, but the electronic control unit 11 judges that active braking needs to be implemented or other control devices issue active braking requests (such as emergency braking, automatic driving, etc.) The braking system works in active braking mode. In this mode, the electronic control unit 11 sends a control signal to the booster motor 9 through the judgment of signals from other sensors 14 on the vehicle, and the booster motor 9 drives the gear 411 to rotate through the deceleration and torque increase mechanism 10, thereby driving the rack 403 to move in translation and driving the sleeve 402 Translational movement, the inner stepped protrusion of the sleeve 402 acts on the outer ring of the reaction disk 407, and the reaction disk 407 is deformed. Since the push rod of the booster assembly does not act on the inner ring of the reaction disk 407 at this time, there is no way to compensate the reaction disk The deformation of 407, because the reaction disc 407 is made of rubber, when it deforms to a certain extent, it will have the characteristics of a rigid body, and move forward as a whole to push the master cylinder ejector 408, and actuate the master cylinder 5 to generate braking force. Since there is no mechanical connection between the rack 403 and the pedal 2, the brake pedal 2 will not produce unnecessary movement during active braking.

4. Down long slope braking function

The regenerative braking force is preferentially used for braking on a long downhill slope. If the energy storage device of the vehicle energy system does not allow energy storage (for example, the SOC is full) in the regenerative braking mode, the system enters the electric power assist mode. At this time, the electronic control unit 11 controls Close the normally closed solenoid valve 13 and open the normally open solenoid valve 12, so that the front piston 302 of the pedal stroke simulator transmits the pedal force to the rear piston 304 to actuate the push rod 404 to act on the reaction disc 407, and at the same time, the electronic control unit 11 passes the pedal The signals of the displacement sensor 1 and the master cylinder pushrod displacement sensor 410 are used to identify the driver's braking intention, and then control the booster motor 9 to generate the required booster torque (the specific working process is consistent with the electric booster function) to push the master cylinder push rod 408, Co-actuating the master cylinders 5 generates braking force. And the locking torque of the motor 9 is used to provide long-time braking force retention.

5. Failure backup braking function

When the electronic control device, actuator or sensor of the braking system breaks down, the normally open solenoid valve 12 is opened, the normally closed solenoid valve 13 is closed, the front chamber of the pedal stroke simulator 3 is locked, and the force of the driver pedaling through the pedal The front piston 302 of the stroke simulator 3 is transmitted to the rear piston 304, thereby actuating the push rod 404 to act on the inner ring of the reaction disc 407, and the reaction disc 407 is deformed. Since the motor is not working at this time, the outer ring of the reaction disc 407 In general, there is no force to compensate for the deformation. Since the reaction disc 407 is made of rubber, when its deformation reaches a certain level, it will have the characteristics of a rigid body and move forward as a whole to push the master cylinder ejector 408 and actuate the master cylinder 5 to generate Braking force, part of the braking force is generated by manpower, which meets the requirements of emergency braking regulations.

6. Active safety function

If an ABS or ESC valve block (hydraulic control unit 7 in the figure) is added between the brake master cylinder 5 and the wheel cylinder 6, the integration with the ABS and ESC control algorithm can be realized. There are two ways of integration: the first way is that E-Booster replaces the traditional hydraulic brake system to generate basic braking force, and the ABS or ESC valve block adjusts the wheel cylinder braking force according to needs. This integration method does not interfere with ABS/ESC, The normal function of ESPhev (or similar products); another way of integration is that the pressure on the four wheel cylinders 6 can not only be adjusted through the hydraulic control unit 7, but also can be adjusted through the electronic control unit 11 to adjust the torque output of the motor ; Thus, the power assist characteristic curve of the motor is adapted to the identified road surface adhesion coefficient, that is, the electric power assist is relatively small under low adhesion conditions, and the electric power assistance is relatively large under high adhesion conditions. At the same time, the electronic control unit 11 can also control the motor to output an additional torque according to the pressure signal collected by the master cylinder pressure sensor (not shown in the figure) to suppress the pressure impact of the liquid return of the HCU7 on the master cylinder 5, thereby achieving good control. Pedal feel.

The above is only a preferred embodiment of the utility model, but the scope of protection of the utility model is not limited thereto, and any person familiar with the technical field can easily think of All changes or replacements should fall within the protection scope of the present utility model.

Claims (6)

1. An electric power-assisted braking system with compound functions is characterized in that it comprises a brake pedal displacement sensor (1), a brake pedal (2), a pedal stroke simulator (3), an electric power assist assembly ( 4), master cylinder (5), wheel cylinder (6), hydraulic control unit (7), liquid storage tank (8), motor (9), deceleration torque increasing mechanism (10), electronic control unit (11), normal open solenoid valve (12), normally closed solenoid valve (13), and other vehicle-mounted sensors (14), the brake pedal displacement sensor (1) is installed at the rotating shaft of the brake pedal (2), and the pedal The stroke simulator (3) is set between the brake pedal (2) and the electric booster assembly (4), the master cylinder (5) communicates with the hydraulic control unit (7) through the brake pipeline, and the hydraulic control unit (7) Connect the four wheel cylinders (6) through the brake pipeline, and the liquid storage tank (8) is connected with the oil inlet hole through the normally open solenoid valve (12) and the normally closed solenoid valve (13) respectively. The front chamber of the pedal stroke simulator (3) is connected to the rear chamber, and the motor (9), the brake pedal displacement sensor (1) and other sensors (14) on the vehicle are all connected to each other with the electronic control unit (11) by wires, The motor (9) is connected to the electric power assist assembly (4) through a deceleration and torque increasing mechanism (10). 2. An electric power-assisted braking system with compound functions according to claim 1, characterized in that: said pedal stroke simulator (3) comprises a pedal stroke simulator housing (301), a front piston (302 ), front piston return spring (303), rear piston (304), rear piston return spring (305) and form. 3. An electric power-assisted braking system with composite functions according to claim 1, characterized in that: the electric power-assist assembly (4) comprises an electric power-assist assembly housing (401), a sleeve (402) , rack (403), booster assembly push rod (404), push rod return spring (405), buffer block (406), reaction plate (407), master cylinder push rod (408), master cylinder push rod return Position spring (409), master cylinder push rod displacement sensor (410), gear (411). 4. A kind of electric power-assisted brake system with composite function as claimed in claim 2, is characterized in that: the rear end face of the front piston (302) of described pedal travel simulator (3) is connected with the brake pedal by a hinge (2) connected, a spring seat is provided in the middle of the front piston (302), and the front piston return spring (303) is placed on the spring seat; the rear piston (304) is arranged on the front piston (302) and the pedal stroke simulator Between the front end faces of the housing (301), the rear piston return spring (305) is arranged between the rear piston (304) and the front end face of the pedal stroke simulator housing (301); the rear piston (304) The cavity surrounded by the front end of the pedal stroke simulator housing (301) is the rear cavity of the pedal simulator, and the cavity formed between the front piston (302) and the rear piston (304) is called the front cavity of the pedal simulator , the front chamber of the pedal simulator and the rear chamber of the pedal simulator both have an oil inlet hole, and the liquid storage tank (8) passes through the oil inlet hole and the pedal simulator through the normally open solenoid valve (12) and the normally closed solenoid valve (13) respectively. The front cavity is connected with the rear cavity of the pedal simulator. 5. An electric power-assisted braking system with composite functions as claimed in claim 3, characterized in that: the inner surface of the sleeve (402) is provided with stepped protrusions and the inner and outer surfaces are welded to a limited extent. As a bit block, the sleeve (402) is installed in the hollow inside of the rack (403), the top of the rack (403) meshes with the gear (411), and the rear end surface of the booster assembly push rod (404) is in contact with the rear The front end face of the piston (304) contacts, and the front end face of the booster assembly push rod (404) is threadedly connected with the buffer block (406), and a raised spring seat is provided in the middle of the booster assembly push rod (404) and A push rod return spring (405) is installed, the inner ring of the reaction disc (407) is in contact with the buffer block (406), and the outer ring of the reaction disc (407) is in contact with the stepped protrusion of the sleeve (402), so The master cylinder push rod (408) is a "T" structure and is equipped with a master cylinder push rod return spring (409) and a master cylinder push rod displacement sensor (410). The master cylinder (5) is connected, the rear end surface of the master cylinder push rod (408) is in contact with the reaction disk (407), and the master cylinder push rod displacement sensor (410) is connected with the electronic control unit (11) through a circuit. 6. The electric power-assisted braking system with compound functions according to claim 5, characterized in that: the buffer block (406) is made of plastic, and the reaction disc (407) is made of rubber.