Patent Publication Number: US-2022219661-A1

Title: Brake System of Vehicle, Vehicle, and Control Method for Brake System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2020/113986, filed on Sep. 8, 2020, which claims priority to Chinese Patent Application No. 201910940787.2, filed on Sep. 30, 2019. The disclosures of the aforementioned applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This application relates to the vehicle field, and more specifically, to a brake system of a vehicle, a vehicle, and a control method for a brake system. 
     BACKGROUND 
     A brake system of a vehicle is a system that forcibly brakes the vehicle to some extent by applying specific brake force to wheels of the vehicle. The brake system is used to force a traveling vehicle to decelerate or even stop based on a requirement of a driver or a controller, or to enable a stopped vehicle to park stably under various road conditions (for example, on a rampway), or to enable a vehicle that goes downhill to keep a stable speed. With electrification and intelligentization development of vehicles, the vehicle has an increasingly high requirement for a brake system. For example, with improvement of an automated driving level, dependence of running of the brake system on a driver is reduced, and therefore a requirement for redundancy performance of the brake system is increasingly high, and the vehicle is required to still have a braking function even after one or more parts of the brake system fail. 
     To improve the redundancy performance of the brake system, as a popular brake system, an electro-hydraulic brake (EHB) system generally includes two levels of brake sub-systems. In a first-level brake system, a controller controls, in a wire-controlled manner, a hydraulic cylinder to provide brake force for a wheel, and in a second-level brake sub-system, a master brake cylinder provides brake force for a wheel. 
     In both the first-level brake sub-system and the second-level brake sub-system, the master brake cylinder and the hydraulic cylinder separately adjust brake force of four wheels of the vehicle by controlling pressure of brake fluid in two independent brake pipes. Specifically, pressure of brake fluid in a first brake pipe is controlled to adjust brake force of a first group of wheels, and pressure of brake fluid in a second brake pipe is controlled to adjust brake force of a second group of wheels. In this way, after one of the brake pipes is faulty, the vehicle may further control brake force of a corresponding wheel by using the other brake pipe, so that brake performance of the electro-hydraulic brake system does not entirely fail. However, in the foregoing electro-hydraulic brake system, after a pressure providing apparatus (a pressure boosting apparatus and a master brake cylinder) on one brake pipe fails, the vehicle loses half of the brake force, and a current requirement of automated driving for redundancy performance of the brake system cannot be met. 
     SUMMARY 
     This application provides a brake system of a vehicle, a vehicle, and a control method for a brake system, to improve redundancy performance of the brake system. 
     According to a first aspect, this application provides a brake system of a vehicle, and the brake system includes a first pressure boosting apparatus, a second pressure boosting apparatus, and a first control valve. The first pressure boosting apparatus is configured to adjust pressure of brake fluid in a first brake pipe, to control brake force applied to a first group of wheels of the vehicle. The second pressure boosting apparatus is configured to adjust pressure of brake fluid in a second brake pipe, to control brake force applied to a second group of wheels of the vehicle, where the first group of wheels are different from the second group of wheels. The first control valve is configured to connect the first brake pipe to the second brake pipe, where if the first control valve is in a closed state, the first brake pipe is connected to the second brake pipe, and if the first control valve is in an open state, the first brake pipe is disconnected from the second brake pipe. 
     In this embodiment of this application, the first control valve is used to connect the first brake pipe and the second brake pipe, so that when the first control valve is in a closed state, the first brake pipe is connected to the second brake pipe, and brake fluid in the two brake pipes can flow in the two brake pipes, thereby helping improve redundancy performance of the brake system, and avoiding a problem in an existing brake system that the first brake pipe and the second brake pipe are two mutually independent brake pipes, and after a pressure providing apparatus (a pressure boosting apparatus and a master brake cylinder) on one brake pipe fails, the vehicle loses half of brake force. 
     In another aspect, after a pressure providing apparatus on a target brake pipe is faulty, a controller may control the first control valve to be in a closed state, so that the first brake pipe is connected to the second brake pipe, and pressure of brake fluid in the two brake pipes is balanced, to improve traveling stability. 
     In a possible implementation, if the first control valve is in a closed state, the first pressure boosting apparatus is configured to adjust the pressure of the brake fluid in the first brake pipe, to adjust the pressure of the brake fluid in the second brake pipe; and/or if the first control valve is in a closed state, the second pressure boosting apparatus is configured to adjust the pressure of the brake fluid in the second brake pipe, to adjust the pressure of the brake fluid in the first brake pipe. 
     In this embodiment of this application, if the first control valve is in a closed state, the first pressure boosting apparatus may boost the pressure of the brake fluid in the second brake pipe, to control the brake force applied to the second group of wheels. Accordingly, the second pressure boosting apparatus may also boost the pressure of the brake fluid in the first brake pipe, to control the brake force applied to the first group of wheels. In this way, redundancy performance of the brake system is improved. 
     In a possible implementation, the brake system further includes a tandem master brake cylinder. A first chamber of the master brake cylinder communicates with the first brake pipe, and is configured to adjust the pressure of the brake fluid in the first brake pipe, to control the brake force applied to the first group of wheels. A second chamber of the master brake cylinder communicates with the second brake pipe, and is configured to adjust the pressure of the brake fluid in the second brake pipe, to control the brake force applied to the second group of wheels. 
     In this embodiment of this application, if the first control valve is in a closed state, the first chamber may boost the pressure of the brake fluid in the second brake pipe, to control the brake force applied to the second group of wheels. Accordingly, the second pressure boosting apparatus may also boost the pressure of the brake fluid in the first brake pipe, to control the brake force applied to the first group of wheels. In this way, redundancy performance of the brake system is improved. 
     Optionally, if the first control valve is in a closed state, the master brake cylinder adjusts the pressure of the brake fluid in the first brake pipe by using the first chamber, to adjust the pressure of the brake fluid in the second brake pipe; and/or if the first control valve is in a closed state, the master brake cylinder adjusts the pressure of the brake fluid in the second brake pipe by using the second chamber, to adjust the pressure of the brake fluid in the first brake pipe. 
     In a possible implementation, the brake system further includes a fluid storage apparatus for storing brake fluid, a plurality of fluid outlet valves, and a second control valve. Pressure outlet ports of the plurality of fluid outlet valves are connected to a pressure inlet port of a fluid outlet pipe, a pressure outlet port of the fluid outlet pipe is connected to an inlet port of the fluid storage apparatus, and the second control valve is located on a fluid outlet pipe between the pressure inlet port of the fluid outlet pipe and the inlet port of the fluid storage apparatus. 
     In this embodiment of this application, the second control valve is disposed on the fluid outlet pipe between the pressure inlet port of the fluid outlet pipe and the inlet port of the fluid storage apparatus. When the second control valve is in an open state, a fluid outlet pipe between the pressure inlet port of the fluid outlet pipe and the second control valve may be used as a brake pipe that provides brake force for a brake wheel cylinder, to improve redundancy performance of the brake system. 
     In a possible implementation, if the second control valve is in an open state and the plurality of fluid outlet valves are in a closed state, a target pressure boosting apparatus is configured to adjust pressure of brake fluid in a first segment of pipe of the fluid outlet pipe, to control the brake force applied to the first group of wheels and/or the second group of wheels; and the target pressure boosting apparatus is the master brake cylinder, the first pressure boosting apparatus, or the second pressure boosting apparatus, and the first segment of pipe is a fluid outlet pipe between the pressure inlet port of the fluid outlet pipe and the second control valve. 
     In this embodiment of this application, if the second control valve is in an open state and the plurality of fluid outlet valves are in a closed state, the target pressure boosting apparatus may adjust the pressure of the brake fluid in the first segment of pipe, to control the brake force applied to the first group of wheels and/or the second group of wheels, thereby helping improve redundancy performance of the brake system. 
     In a possible implementation, the brake system further includes a controller. The controller is configured to send first control information to the first pressure boosting apparatus, to control the brake force applied by the first pressure boosting apparatus to the first group of wheels; and/or the controller is further configured to send second control information to the second pressure boosting apparatus, to control the brake force applied by the second pressure boosting apparatus to the second group of wheels. 
     In this embodiment of this application, the controller may directly control the first pressure boosting apparatus and the second pressure boosting apparatus to respectively provide brake force for the first group of wheels and the second group of wheels, thereby helping improve diversity of a working mode of the brake system. 
     In a possible implementation, the brake system further includes a pressure sensor, and the pressure sensor is located on the first brake pipe between a pressure outlet port of the master brake cylinder and a pressure outlet port of the first pressure boosting apparatus; the pressure sensor is configured to detect the pressure that is of the brake fluid in the first brake pipe and that is adjusted by the master brake cylinder; and the pressure sensor is further configured to send pressure information indicating the pressure to the controller, so that the controller determines, based on the pressure, brake force applied to the wheel of the vehicle. 
     In this embodiment of this application, the controller may determine the pressure of the brake fluid in the first brake pipe based on the pressure sensor, to determine, based on the pressure, the brake force applied to the wheel of the vehicle, thereby helping improve diversity of a working mode of the brake system. 
     In a possible implementation, the brake system further includes a pedal travel sensor; the pedal travel sensor is configured to detect a pedal traveling distance of a brake pedal of the vehicle; and the pedal travel sensor is further configured to send traveling distance information indicating the pedal traveling distance to the controller, so that the controller determines, based on the traveling distance, the brake force applied to the wheel of the vehicle. 
     In this embodiment of this application, the controller may determine the pedal traveling distance of the brake pedal based on the pedal travel sensor, to determine, based on the pedal traveling distance, the brake force applied to the wheel of the vehicle, thereby helping improve diversity of a working mode of the brake system. 
     In another aspect, when the pedal travel sensor and the pressure sensor are applied to a same brake system, the controller may determine, based on either of the foregoing two types of information (the pedal traveling distance and the pressure of the brake fluid), the brake force applied to the wheel of the vehicle, thereby helping improve redundancy performance of the brake system. 
     According to a second aspect, a vehicle is provided and includes a first group of wheels, a second group of wheels, a first pressure boosting apparatus, a second pressure boosting apparatus, and a first control valve, where the first group of wheels are different from the second group of wheels. The first pressure boosting apparatus is configured to adjust pressure of brake fluid in a first brake pipe, to apply brake force to the first group of wheels. The second pressure boosting apparatus is configured to adjust pressure of brake fluid in a second brake pipe, to apply brake force to the second group of wheels, where the first group of wheels are different from the second group of wheels. The first control valve is configured to connect the first brake pipe to the second brake pipe, where if the first control valve is in a closed state, the first brake pipe is connected to the second brake pipe, and if the first control valve is in an open state, the first brake pipe is disconnected from the second brake pipe. 
     In this embodiment of this application, the first control valve is used to connect the first brake pipe and the second brake pipe, so that when the first control valve is in a closed state, the first brake pipe is connected to the second brake pipe, and brake fluid in the two brake pipes can flow in the two brake pipes, thereby helping improve redundancy performance of the brake system, and avoiding a problem in an existing brake system that the first brake pipe and the second brake pipe are two mutually independent brake pipes, and after a pressure providing apparatus (a pressure boosting apparatus and a master brake cylinder) on one brake pipe fails, the vehicle loses half of brake force. 
     In another aspect, after a pressure providing apparatus on a target brake pipe is faulty, a controller may control the first control valve to be in a closed state, so that the first brake pipe is connected to the second brake pipe, and pressure of brake fluid in the two brake pipes is balanced, to improve traveling stability. 
     In a possible implementation, if the first control valve is in a closed state, the first pressure boosting apparatus is configured to adjust the pressure of the brake fluid in the first brake pipe, to adjust the pressure of the brake fluid in the second brake pipe; and/or if the first control valve is in a closed state, the second pressure boosting apparatus is configured to adjust the pressure of the brake fluid in the second brake pipe, to adjust the pressure of the brake fluid in the first brake pipe. 
     In this embodiment of this application, if the first control valve is in a closed state, the first pressure boosting apparatus may boost the pressure of the brake fluid in the second brake pipe, to control the brake force applied to the second group of wheels. Accordingly, the second pressure boosting apparatus may also boost the pressure of the brake fluid in the first brake pipe, to control the brake force applied to the first group of wheels. In this way, redundancy performance of the brake system is improved. 
     In a possible implementation, the vehicle further includes a tandem master brake cylinder. A first chamber of the master brake cylinder communicates with the first brake pipe, and is configured to adjust the pressure of the brake fluid in the first brake pipe, to control the brake force applied to the first group of wheels. A second chamber of the master brake cylinder communicates with the second brake pipe, and is configured to adjust the pressure of the brake fluid in the second brake pipe, to control the brake force applied to the second group of wheels. 
     In this embodiment of this application, if the first control valve is in a closed state, the first chamber may boost the pressure of the brake fluid in the second brake pipe, to control the brake force applied to the second group of wheels. Accordingly, the second pressure boosting apparatus may also boost the pressure of the brake fluid in the first brake pipe, to control the brake force applied to the first group of wheels. In this way, redundancy performance of the brake system is improved. 
     Optionally, if the first control valve is in a closed state, the master brake cylinder adjusts the pressure of the brake fluid in the first brake pipe by using the first chamber, to adjust the pressure of the brake fluid in the second brake pipe; and/or if the first control valve is in a closed state, the master brake cylinder adjusts the pressure of the brake fluid in the second brake pipe by using the second chamber, to adjust the pressure of the brake fluid in the first brake pipe. 
     In a possible implementation, the vehicle further includes a fluid storage apparatus for storing brake fluid, a plurality of fluid outlet valves, and a second control valve. Pressure outlet ports of the plurality of fluid outlet valves are connected to a pressure inlet port of a fluid outlet pipe, a pressure outlet port of the fluid outlet pipe is connected to an inlet port of the fluid storage apparatus, and the second control valve is located on a fluid outlet pipe between the pressure inlet port of the fluid outlet pipe and the inlet port of the fluid storage apparatus. 
     In this embodiment of this application, the second control valve is disposed on the fluid outlet pipe between the pressure inlet port of the fluid outlet pipe and the inlet port of the fluid storage apparatus. When the second control valve is in an open state, a fluid outlet pipe between the pressure inlet port of the fluid outlet pipe and the second control valve may be used as a brake pipe that provides brake force for a brake wheel cylinder, to improve redundancy performance of the brake system. 
     In a possible implementation, if the second control valve is in an open state and the plurality of fluid outlet valves are in a closed state, a target pressure boosting apparatus is configured to adjust pressure of brake fluid in a first segment of pipe of the fluid outlet pipe, to control the brake force applied to the first group of wheels and/or the second group of wheels; and the target pressure boosting apparatus is the master brake cylinder, the first pressure boosting apparatus, or the second pressure boosting apparatus, and the first segment of pipe is a fluid outlet pipe between the pressure inlet port of the fluid outlet pipe and the second control valve. 
     In this embodiment of this application, if the second control valve is in an open state and the plurality of fluid outlet valves are in a closed state, the target pressure boosting apparatus may adjust the pressure of the brake fluid in the first segment of pipe, to control the brake force applied to the first group of wheels and/or the second group of wheels, thereby helping improve redundancy performance of the brake system. 
     In a possible implementation, the vehicle further includes a controller. The controller is configured to send first control information to the first pressure boosting apparatus, to control the brake force applied by the first pressure boosting apparatus to the first group of wheels; and/or the controller is further configured to send second control information to the second pressure boosting apparatus, to control the brake force applied by the second pressure boosting apparatus to the second group of wheels. 
     In this embodiment of this application, the controller may directly control the first pressure boosting apparatus and the second pressure boosting apparatus to respectively provide brake force for the first group of wheels and the second group of wheels, thereby helping improve diversity of a working mode of the brake system. 
     In a possible implementation, the vehicle further includes a pressure sensor, and the pressure sensor is located on the first brake pipe between a pressure outlet port of the master brake cylinder and a pressure outlet port of the first pressure boosting apparatus; the pressure sensor is configured to detect the pressure that is of the brake fluid in the first brake pipe and that is adjusted by the master brake cylinder; and the pressure sensor is further configured to send pressure information indicating the pressure to the controller, so that the controller determines, based on the pressure, brake force applied to the wheel of the vehicle. 
     In this embodiment of this application, the controller may determine the pressure of the brake fluid in the first brake pipe based on the pressure sensor, to determine, based on the pressure, the brake force applied to the wheel of the vehicle, thereby helping improve diversity of a working mode of the brake system. 
     In a possible implementation, the vehicle further includes a pedal travel sensor; the pedal travel sensor is configured to detect a pedal traveling distance of a brake pedal of the vehicle; and the pedal travel sensor is further configured to send traveling distance information indicating the pedal traveling distance to the controller, so that the controller determines, based on the traveling distance, the brake force applied to the wheel of the vehicle. 
     In a possible implementation, the first group of wheels include a right front wheel and a left front wheel, and the second group of wheels include a right rear wheel and a left rear wheel; or the first group of wheels include a right front wheel and a left rear wheel, and the second group of wheels include a left front wheel and a left rear wheel. 
     In this embodiment of this application, the controller may determine the pedal traveling distance of the brake pedal based on the pedal travel sensor, to determine, based on the pedal traveling distance, the brake force applied to the wheel of the vehicle, thereby helping improve diversity of a working mode of the brake system. 
     In another aspect, when the pedal travel sensor and the pressure sensor are applied to a same brake system, the controller may determine, based on either of the foregoing two types of information (the pedal traveling distance and the pressure of the brake fluid), the brake force applied to the wheel of the vehicle, thereby helping improve redundancy performance of the brake system. 
     According to a third aspect, this application provides a control method for a brake system, and the brake system includes a first pressure boosting apparatus, a second pressure boosting apparatus, and a first control valve. The first pressure boosting apparatus is configured to adjust pressure of brake fluid in a first brake pipe, to control brake force applied to a first group of wheels of a vehicle. The second pressure boosting apparatus is configured to adjust pressure of brake fluid in a second brake pipe, to control brake force applied to a second group of wheels of the vehicle, where the first group of wheels are different from the second group of wheels. The first control valve is configured to connect the first brake pipe to the second brake pipe, and if the first control valve is in an open state, the first brake pipe is disconnected from the second brake pipe. The method includes: if the controller controls the first control valve to be in a closed state, the first brake pipe is connected to the second brake pipe; and if the controller controls the first control valve to be in an open state, the first brake pipe is disconnected from the second brake pipe. 
     In this embodiment of this application, after a pressure providing apparatus on a target brake pipe is faulty, the controller may control the first control valve to be in a closed state, so that the first brake pipe is connected to the second brake pipe, and the brake fluid may flow in the two brake pipes, thereby helping improve redundancy performance of the brake system, and avoiding a problem in an existing brake system that the first brake pipe and the second brake pipe are two mutually independent brake pipes, and after a pressure providing apparatus (a pressure boosting apparatus and a master brake cylinder) on one brake pipe fails, the vehicle loses half of brake force. 
     In a possible implementation, the method includes: the controller determines that a pressure providing apparatus on the target brake pipe is faulty, where the target brake pipe is the first brake pipe or the second brake pipe; and the controller controls the first control valve to be in a closed state, so that the first brake pipe is connected to the second brake pipe. 
     In this embodiment of this application, after the pressure providing apparatus on the target brake pipe is faulty, the controller may control the first control valve to be in a closed state, so that the first brake pipe is connected to the second brake pipe, and pressure of brake fluid in the two brake pipes is balanced, to improve traveling stability. 
     In a possible implementation, the target brake pipe is the first brake pipe, the pressure providing apparatus includes the first pressure boosting apparatus, and the method further includes: the controller controls the second pressure boosting apparatus to adjust the pressure of the brake fluid in the second brake pipe, to adjust the pressure of the brake fluid in the first brake pipe. 
     In this embodiment of this application, after the first pressure boosting apparatus on the first brake pipe is faulty, the controller may control the first control valve to be in a closed state, so that the first brake pipe is connected to the second brake pipe, and the brake fluid may flow in the two brake pipes, thereby helping improve redundancy performance of the brake system. 
     In a possible implementation, the target brake pipe is the second brake pipe, the pressure providing apparatus includes the second pressure boosting apparatus, and the method further includes: the controller controls the first pressure boosting apparatus to adjust the pressure of the brake fluid in the first brake pipe, to adjust the pressure of the brake fluid in the second brake pipe. 
     In this embodiment of this application, after the second pressure boosting apparatus on the second brake pipe is faulty, the controller may control the first control valve to be in a closed state, so that the first brake pipe is connected to the second brake pipe, and the brake fluid may flow in the two brake pipes, thereby helping improve redundancy performance of the brake system. 
     In a possible implementation, the brake system further includes a tandem master brake cylinder. A first chamber of the master brake cylinder communicates with the first brake pipe, and is configured to adjust the pressure of the brake fluid in the first brake pipe, to control the brake force applied to the first group of wheels. A second chamber of the master brake cylinder communicates with the second brake pipe, and is configured to adjust the pressure of the brake fluid in the second brake pipe, to control the brake force applied to the second group of wheels. The method further includes: if the first chamber is faulty, the controller controls the first control valve to be in a closed state, so that the pressure of the brake fluid in the second brake pipe and the pressure of the brake fluid in the first brake pipe are balanced; or if the second chamber is faulty, the controller controls the first control valve to be in a closed state, so that the pressure of the brake fluid in the first brake pipe and the pressure of the brake fluid in the second brake pipe are balanced. 
     In this embodiment of this application, after the first chamber is faulty, the controller may control the first control valve to be in a closed state, so that the first brake pipe is connected to the second brake pipe, and the brake fluid may flow in the two brake pipes, thereby helping improve redundancy performance of the brake system. 
     After the second chamber is faulty, the controller may control the first control valve to be in a closed state, so that the first brake pipe is connected to the second brake pipe, and the brake fluid may flow in the two brake pipes, thereby helping improve redundancy performance of the brake system. 
     In a possible implementation, the brake system further includes a fluid storage apparatus for storing brake fluid, a plurality of fluid outlet valves, and a second control valve. Pressure outlet ports of the plurality of fluid outlet valves are connected to a pressure inlet port of a fluid outlet pipe, a pressure outlet port of the fluid outlet pipe is connected to an inlet port of the fluid storage apparatus, and the second control valve is located on a fluid outlet pipe between the pressure inlet port of the fluid outlet pipe and the inlet port of the fluid storage apparatus. The method further includes: the controller determines that the first pressure boosting apparatus and the first control valve are faulty; and the controller controls the second control valve to be in an open state, and controls the plurality of fluid outlet valves to be in a closed state, so that brake fluid in a first segment of pipe is pressed into a brake wheel cylinder of a wheel of the vehicle by the second pressure boosting apparatus, to control brake force applied to the wheel of the vehicle, where the first segment of pipe is a pipe between the pressure inlet port of the fluid outlet pipe and the second control valve. 
     In this embodiment of this application, when the first pressure boosting apparatus and the first control valve are faulty, the controller may control the second control valve to be in an open state, and control the plurality of fluid outlet valves to be in a closed state, so that the brake fluid in the first segment of pipe is pressed into a brake wheel cylinder of the vehicle by the second pressure boosting apparatus; in other words, the first segment of pipe is used as a brake pipe that provides brake force for the brake wheel cylinder, to improve redundancy performance of the brake system. 
     In a possible implementation, the method further includes: the controller determines that the second pressure boosting apparatus and the first control valve are faulty; and the controller controls the second control valve to be in an open state, and controls the plurality of fluid outlet valves to be in a closed state, so that brake fluid in the first segment of pipe is pressed into the brake wheel cylinder of the wheel of the vehicle by the first pressure boosting apparatus, to control the brake force applied to the wheel of the vehicle. 
     In this embodiment of this application, when the second pressure boosting apparatus and the first control valve are faulty, the controller may control the second control valve to be in an open state, and control the plurality of fluid outlet valves to be in a closed state, so that the brake fluid in the first segment of pipe is pressed into the brake wheel cylinder of the vehicle by the first pressure boosting apparatus; in other words, the first segment of pipe is used as a brake pipe that provides brake force for the brake wheel cylinder, to improve redundancy performance of the brake system. 
     In a possible implementation, the brake system further includes a pressure sensor and a pedal travel sensor. The pressure sensor is configured to detect the pressure that is of the brake fluid in the first brake pipe and that is adjusted by the master brake cylinder. The pedal travel sensor is configured to detect a pedal traveling distance of a brake pedal of the vehicle. The method further includes: the controller receives pressure information that is sent by the pressure sensor and that is used to indicate the pressure; and if the pedal travel sensor fails, the controller allocates brake force to the first group of wheels and/or the second group of wheels based on the pedal traveling distance. 
     In this embodiment of this application, when the pedal travel sensor and the pressure sensor are applied to a same brake system, the controller may determine, based on either of the foregoing two types of information (the pedal traveling distance and the pressure of the brake fluid), the brake force applied to the wheel of the vehicle, thereby helping improve redundancy performance of the brake system. 
     According to a fourth aspect, a controller is provided, and the controller may be an independent device, or may be a chip in the device. The controller may include a processing unit and a sending unit. When the controller is an independent device, the processing unit may be a processor, and the sending unit may be an input/output interface; the device may further include a storage unit, and the storage unit may be a memory; and the storage unit is configured to store instructions, and the processing unit executes the instructions stored in the storage unit, so that the device is enabled to perform the method in the third aspect. When the controller is a chip in a device, the processing unit may be a processor, and the sending unit may be a pin, a circuit, or the like; and the processing unit executes instructions stored in the storage unit, so that the controller performs the method in the third aspect. The storage unit may be a storage unit (for example, a register or a cache) in the chip, or may be a storage unit (for example, a read-only memory or a random access memory) that is in a terminal device/network device and that is outside the chip. 
     In the fourth aspect, that a memory is coupled to a processor may be understood as that the memory is located in the processor, or the memory is located outside the processor, so that the memory is independent of the processor. 
     According to a fifth aspect, a computer program product is provided. The computer program product includes computer program code, and when the computer program code is run on a computer, the computer is enabled to perform the methods in the foregoing aspects. 
     It should be noted that some or all of the computer program code can be stored in a first storage medium. The first storage medium can be encapsulated with a processor, or encapsulated separately from a processor. This is not specifically limited in this embodiment of this application. 
     According to a sixth aspect, a computer-readable medium is provided. The computer-readable medium stores program code. When the computer program code is run on a computer, the computer is enabled to perform the methods in the foregoing aspects. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an example schematic diagram of a first-level brake sub-system  100  according to an embodiment of this application; 
         FIG. 2  is an example schematic diagram of a second-level brake sub-system  200  according to an embodiment of this application; 
         FIG. 3  is an example schematic diagram of a brake system  300  according to an embodiment of this application; 
         FIG. 4  is an example schematic diagram of a vehicle according to an embodiment of this application; 
         FIG. 5  is an example schematic diagram of a flowing path of brake fluid in a brake system according to an embodiment of this application; 
         FIG. 6  is an example schematic diagram of another flowing path of brake fluid in a brake system according to an embodiment of this application; 
         FIG. 7  is an example schematic diagram of another flowing path of brake fluid in a brake system according to an embodiment of this application; 
         FIG. 8  is an example schematic diagram of another flowing path of brake fluid in a brake system according to an embodiment of this application; 
         FIG. 9  is an example schematic diagram of another flowing path of brake fluid in a brake system according to an embodiment of this application; 
         FIG. 10  is an example schematic diagram of another flowing path of brake fluid in a brake system according to an embodiment of this application; 
         FIG. 11  is an example schematic diagram of another flowing path of brake fluid in a brake system according to an embodiment of this application; 
         FIG. 12  is an example schematic diagram of another flowing path of brake fluid in a brake system according to an embodiment of this application; 
         FIG. 13  is an example flowchart of a control method for a brake system according to an embodiment of this application; and 
         FIG. 14A ,  FIG. 14B , and  FIG. 14C  are example flowcharts of a control method for a brake system according to another embodiment of this application. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The following describes the technical solutions of this application with reference to accompanying drawings. 
     In an existing brake system, as a popular brake system, an EHB usually includes two levels of brake sub-systems. In a first-level brake system, a controller controls, in a wire-controlled manner, a pressure boosting apparatus to provide brake force for a wheel, and in a second-level brake sub-system, a master brake cylinder provides brake force for a wheel. 
     In both the first-level brake sub-system and the second-level brake sub-system, the master brake cylinder and a hydraulic cylinder separately adjust brake force of four wheels of a vehicle by controlling pressure of brake fluid in two independent brake pipes. Specifically, pressure of brake fluid in a first brake pipe is controlled to adjust brake force applied to a first group of wheels, and pressure of brake fluid in a second brake pipe is controlled to adjust brake force of a second group of wheels. In this way, after one of the brake pipes is faulty, the vehicle may further control brake force of a corresponding wheel by using the other brake pipe, so that brake performance of an electro-hydraulic brake system does not entirely fail. However, in the foregoing electro-hydraulic brake system, after a pressure providing apparatus (a pressure boosting apparatus and the master brake cylinder) on one brake pipe fails, the vehicle loses half of the brake force, and a current requirement of automated driving for redundancy performance of the brake system cannot be met. 
     To improve redundancy performance of a brake system, an embodiment of this application provides a new brake system. To be specific, a first brake pipe  111  and a second brake pipe  121  are connected by using a first control valve  130 . Therefore, the first control valve  130  is also referred to as a “connection valve.” When a pressure boosting apparatus on one of the two brake pipes ( 11  and  121 ) is faulty, the first control valve  130  may be controlled to be in a closed state, so that brake fluid in the two brake pipes can flow in the two brake pipes, or pressure of the brake fluid in the two brake pipes is balanced. In this case, the pressure boosting apparatus may adjust, by using the two connected brake pipes, brake force applied to a wheel of a vehicle. A brake system according to an embodiment of this application is described below with reference to  FIG. 1 . 
     It should be noted that, for ease of describing a connection relationship between brake elements in the brake system, terms such as “pressure outlet port” and “pressure inlet port” are used. The “pressure outlet port” may be understood as a port through which brake fluid flows out, and the “pressure inlet port” may be understood as a port through which brake fluid flows in. To be specific, the “pressure outlet port” and the “pressure inlet port” may be understood as functions for limiting ports functionally. The “pressure outlet port” and the “pressure inlet port” may be used to limit a function of a physical port in different working modes. The “pressure outlet port” and the “pressure inlet port” may alternatively correspond to two different physical ports. This is not limited in this embodiment of this application. 
     Generally, in the following descriptions, when a pressure inlet port of a device A and a pressure outlet port of a device B are connected, it may be understood that the pressure inlet port and the pressure outlet port correspond to two physical ports, and are used to describe a connection relationship between the device A and the device B. 
       FIG. 1  is a schematic diagram of a first-level brake sub-system  100  according to an embodiment of this application. The first-level brake sub-system  100  shown in  FIG. 1  includes a first pressure boosting apparatus  110 , a second pressure boosting apparatus  120 , and a first control valve  130 . 
     The first pressure boosting apparatus  110  is configured to adjust pressure of brake fluid in a first brake pipe  111 , to control brake force applied to a first group of wheels  112  of a vehicle. 
     A pressure outlet port of the first pressure boosting apparatus  110  is connected to a pressure inlet port of the first brake pipe  111 , the first brake pipe  111  includes two pressure outlet ports ( 1  and  2 ), and the two pressure outlet ports ( 1  and  2 ) are connected to pressure inlet ports ( 5  and  6 ) of brake wheel cylinders of the first group of wheels  112 . 
     Accordingly, the first pressure boosting apparatus  110  may be configured to boost the pressure of the brake fluid in the first brake pipe  111 , to increase the brake force applied to the first group of wheels  112  of the vehicle. 
     Optionally, the first pressure boosting apparatus  110  includes a motor  113  and a hydraulic cylinder  114 . The motor  113  is configured to drive a piston in the hydraulic cylinder  114  to perform linear reciprocating motion, and press brake fluid in the hydraulic cylinder  114  into the first brake pipe  111 , to boost the pressure of the brake fluid in the first brake pipe  111 . 
     The second pressure boosting apparatus  120  is configured to adjust pressure of brake fluid in a second brake pipe  121 , to control brake force applied to a second group of wheels  122  of the vehicle. 
     A pressure outlet port of the first pressure boosting apparatus  120  is connected to a pressure inlet port of the second brake pipe  121 , the second brake pipe  121  includes two pressure outlet ports ( 3  and  4 ), and the two pressure outlet ports ( 3  and  4 ) are connected to pressure inlet ports ( 7  and  8 ) of brake wheel cylinders of the second group of wheels  122 . 
     Accordingly, the second pressure boosting apparatus  120  may be configured to boost the pressure of the brake fluid in the second brake pipe  121 , to increase the brake force applied to the second group of wheels  122  of the vehicle. 
     Optionally, the second pressure boosting apparatus  120  includes a motor  123  and a hydraulic cylinder  124 . The motor  123  is configured to drive a piston in the hydraulic cylinder  124  to perform linear reciprocating motion, and press brake fluid in the hydraulic cylinder  114  into the second brake pipe  121 , to boost the pressure of the brake fluid in the second brake pipe  121 . 
     The first group of wheels are different from the second group of wheels. The first group of wheels include a right front wheel and a left front wheel, and the second group of wheels include a right rear wheel and a left rear wheel; in other words, the first-level brake sub-system  100  is disposed in an H-shape. Alternatively, the first group of wheels include a right front wheel and a left rear wheel, and the second group of wheels include a left front wheel and a left rear wheel; in other words, the first-level brake sub-system  100  is arranged in an X-shape. This is not limited in this embodiment of this application. 
     The first control valve  130  is configured to connect the first brake pipe  111  to the second brake pipe  121 . If the first control valve  130  is in a closed state, the first brake pipe  111  is connected to the second brake pipe  121 , and if the first control valve  111  is in an open state, the first brake pipe  111  is disconnected from the second brake pipe  121 . 
     If the first control valve  130  is in an open state, the first brake pipe  111  and the second brake pipe  121  are independent brake pipes, and pressure of the brake fluid in the two brake pipes is respectively controlled by the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120 . If the first control valve  130  is in a closed state, the first brake pipe  111  and the second brake pipe  121  are connected brake pipes, and the brake fluid may flow between the first brake pipe  111  and the second brake pipe  121 , so that the pressure of the brake fluid in the two brake pipes is balanced. 
     Optionally, if the first control valve  130  is in a closed state, the first pressure boosting apparatus  110  is configured to adjust the pressure of the brake fluid in the first brake pipe  111 , to adjust the pressure of the brake fluid in the second brake pipe  121 . If the first control valve  130  is in a closed state, the second pressure boosting apparatus  120  is configured to adjust the pressure of the brake fluid in the second brake pipe  121 , to adjust the pressure of the brake fluid in the first brake pipe  11 . 
     In this way, based on the foregoing brake system described in this application, when the first pressure boosting apparatus  110  is faulty, but brake force needs to be applied to the first group of wheels  112 , the first control valve  130  may be controlled to be in a closed state. In this case, the second pressure boosting apparatus  120  may boost the pressure of the brake fluid in the second brake pipe  121  to transfer the pressure of the brake fluid in the second brake pipe  121  to the first brake pipe in and finally apply the brake force to the first group of wheels  112  by boosting the pressure of the brake fluid in the first brake pipe in. 
     When the second pressure boosting apparatus  120  is faulty, but brake force needs to be applied to the second group of wheels  122 , the first control valve  130  may be controlled to be in a closed state. In this case, the first pressure boosting apparatus no may boost the pressure of the brake fluid in the first brake pipe in to transfer the pressure of the brake fluid in the first brake pipe  111  to the second brake pipe  121  and finally apply the brake force to the second group of wheels  122  by boosting the pressure of the brake fluid in the second brake pipe  121 . 
     Generally, when the first pressure boosting apparatus  110  is faulty, to avoid a case in which the first pressure boosting apparatus  110  intermittently boosts pressure of a brake system, a control valve  119  may be disposed at a pressure outlet port of the first pressure boosting apparatus  110 . After the first pressure boosting apparatus  110  is faulty, the control valve  119  may be controlled to be in an open state, and in this case, the first pressure boosting apparatus  110  is disconnected from the first brake pipe  111 . Accordingly, a control valve  129  may also be disposed at a pressure outlet port of the second pressure boosting apparatus  120 . After the second pressure boosting apparatus  120  is faulty, the control valve  129  may be controlled to be in an open state, and in this case, the second pressure boosting apparatus  120  is disconnected from the second brake pipe  121 . Therefore, the control valve  119  and the control valve  129  are also referred to as “isolation valves.” 
     For the brake system, different brake force usually needs to be applied to different wheels. Therefore, fluid inlet valves ( 9 ,  10 ,  11 , and  12 ) may be controlled to be configured on brake pipes corresponding to brake force of the wheels, to independently manage brake force applied to each wheel. 
     To be specific, a fluid inlet valve corresponding to a wheel to which brake force needs to be applied is controlled to be in a closed state, and a fluid inlet valve corresponding to another wheel to which brake force does not need to be applied is controlled to be in an open state. When the fluid inlet valve is in a closed state, the brake fluid in the brake pipe can flow to a brake wheel cylinder of the wheel through a corresponding brake pipe. When the fluid inlet valve is in an open state, the brake fluid in the brake pipe cannot flow to the brake wheel cylinder of the wheel through the corresponding brake pipe. 
     For example, as shown in  FIG. 1 , the first brake pipe  111  may include a first branch  115  and a second branch  116 , to respectively control brake force on two wheels in the first group of wheels  112 . A pressure outlet port of the first branch  115  is connected to a pressure inlet port  5  of a brake wheel cylinder  17  of the first group of wheels  112 , and a pressure outlet port of the second branch  116  is connected to a pressure inlet port  6  of a brake wheel cylinder  18  of the first group of wheels  112 . A fluid inlet valve  9  is disposed between a pressure inlet port of the first branch  115  and the pressure inlet port  5  of the brake wheel cylinder  17 . When the fluid inlet valve  9  is in a closed state, pressure of brake fluid in the first branch  115  may be boosted, to increase brake force applied to the brake wheel cylinder  17 . A fluid inlet valve  10  is disposed between a pressure inlet port of the second branch  116  and the pressure inlet port  6  of the brake wheel cylinder  18 . When the fluid inlet valve  10  is in a closed state, pressure of brake fluid in the second branch  116  may be boosted, to increase brake force applied to the brake wheel cylinder  18 . 
     It should be noted that the pressure inlet port of the first branch  115  and the pressure inlet port of the second branch  116  may be the pressure inlet port of the first brake pipe  11 . 
     The second brake pipe  121  may include a first branch  125  and a second branch  126 , to respectively control brake force on two wheels in the second group of wheels  122 . A pressure outlet port of the first branch  125  is connected to a pressure inlet port  7  of a brake wheel cylinder  19  of the first group of wheels  122 , and a pressure outlet port of the second branch  126  is connected to a pressure inlet port  8  of a brake wheel cylinder  20  of the first group of wheels  122 . A fluid inlet valve  11  is disposed between a pressure inlet port of the first branch  125  and the pressure inlet port  7  of the brake wheel cylinder  19 . When the fluid inlet valve  11  is in a closed state, pressure of brake fluid in the first branch  125  may be boosted, to increase brake force applied to the brake wheel cylinder  19 . A fluid inlet valve  12  is disposed between the pressure outlet port of the second branch  126  and the pressure inlet port  8  of the brake wheel cylinder  20 . When the fluid inlet valve  12  is in a closed state, pressure of brake fluid in the second branch  126  may be boosted, to increase brake force applied to the brake wheel cylinder  20 . 
     It should be noted that the pressure inlet port of the first branch  125  and the pressure inlet port of the second branch  126  may be the pressure inlet port of the second brake pipe  121 . 
     For the brake system, in some cases, the brake force on the wheel also needs to be decreased. Therefore, a fluid outlet valve ( 140 ) may be controlled to be configured on a brake pipe of each wheel to independently manage decreased brake force on each wheel. To be specific, a fluid outlet valve corresponding to a wheel on which brake force needs to be decreased is controlled to be in a closed state, and a fluid outlet valve corresponding to another wheel on which brake force does not need to be decreased is controlled to be in an open state. When the fluid outlet valve is in a closed state, brake fluid in the brake pipe may flow to a fluid outlet pipe  117  through the fluid outlet valve, and flow to a fluid storage apparatus  118  through the fluid outlet pipe  117 , to facilitate cycling. When the fluid outlet valve is in an open state, the brake fluid in the brake pipe is blocked by the fluid outlet valve, and cannot flow to the fluid storage apparatus. 
     For example, as shown in  FIG. 1 , the first brake pipe  111  may include a first branch  115  and a second branch  116 , to respectively control brake force on two wheels in the first group of wheels  112 . A pressure outlet port of the first branch  115  is connected to a pressure inlet port  5  of a brake wheel cylinder  17  of the first group of wheels  112 , and a pressure outlet port of the second branch  116  is connected to a pressure inlet port  6  of a brake wheel cylinder  18  of the first group of wheels  112 . A fluid outlet valve  13  is disposed between a pressure inlet port of the first branch  115  and the pressure inlet port  5  of the brake wheel cylinder  17 . When the fluid outlet valve  13  is in a closed state, brake fluid in the first branch  115  may flow to the fluid outlet pipe  117  through the fluid outlet valve  13 , and finally flow to the fluid storage apparatus  118 , to avoid boosting pressure of the brake wheel cylinder  17  by using the brake fluid. When the fluid outlet valve  13  is in an open state, the brake fluid in the first branch  115  is blocked by the fluid outlet valve  13 , and cannot flow to the fluid outlet pipe  117 . A fluid outlet valve  14  is disposed between a pressure inlet port  2  of the second branch  116  and the pressure inlet port  6  of the brake wheel cylinder  18 . When the fluid outlet valve  14  is in a closed state, brake fluid in the second branch  116  may flow to the fluid outlet pipe  117  through the fluid outlet valve  14 , and finally flow to the fluid storage apparatus  118 , to avoid boosting pressure of the brake wheel cylinder  18  by using the brake fluid. When the fluid outlet valve  14  is in an open state, the brake fluid in the first branch  116  is blocked by the fluid outlet valve  14 , and cannot flow to the fluid outlet pipe  117 . 
     It should be noted that the pressure inlet port of the first branch  115  and the pressure inlet port of the second branch  116  may be the pressure inlet port of the first brake pipe  11 . 
     The second brake pipe  121  may include a first branch  125  and a second branch  126 , to respectively control brake force on two wheels in the second group of wheels  122 . A pressure outlet port of the first branch  125  is connected to a pressure inlet port  7  of a brake wheel cylinder  19  of the first group of wheels  122 , and a pressure outlet port of the second branch  126  is connected to a pressure inlet port  8  of a brake wheel cylinder  20  of the first group of wheels  122 . A fluid outlet valve  15  is disposed between a pressure inlet port of the first branch  125  and the pressure inlet port  7  of the brake wheel cylinder  19 . When the fluid outlet valve  15  is in a closed state, brake fluid in the first branch  125  may flow to the fluid outlet pipe  117  through the fluid outlet valve  15 , and finally flow to the fluid storage apparatus  118 , to avoid boosting pressure of the brake wheel cylinder  19  by using the brake fluid. When the fluid outlet valve  15  is in an open state, the brake fluid in the first branch  125  is blocked by the fluid outlet valve  15 , and cannot flow to the fluid outlet pipe  117 . A fluid outlet valve  16  is disposed between a pressure inlet port  2  of the second branch  116  and the pressure inlet port  8  of the brake wheel cylinder  20 . When the fluid outlet valve  16  is in a closed state, brake fluid in the second branch  126  may flow to the fluid outlet pipe  117  through the fluid outlet valve  16 , and finally flow to the fluid storage apparatus  118 , to avoid boosting pressure of the brake wheel cylinder  20  by using the brake fluid. When the fluid outlet valve  16  is in an open state, the brake fluid in the second branch  126  is blocked by the fluid outlet valve  16 , and cannot flow to the fluid outlet pipe  117 . 
     It should be noted that the pressure inlet port of the first branch  125  and the pressure inlet port of the second branch  126  may be the pressure inlet port of the second brake pipe  121 . 
     The foregoing solution of the fluid outlet valve and the solution of the fluid inlet valve may be separately configured in the brake system for use, or may be used in a same brake system in cooperation with each other. With reference to  FIG. 1 , a connection manner between the fluid outlet valve  13  and the fluid inlet valve  9  corresponding to the brake wheel cylinder  17  is used as an example below to describe the connection manner between the fluid outlet valve  13  and the fluid inlet valve  9  in this embodiment of this application. It should be noted that a connection manner of the fluid outlet valve  14  and the fluid inlet valve  10  corresponding to the brake wheel cylinder  18 , a connection manner of the fluid outlet valve  15  and the fluid inlet valve  11  corresponding to the brake wheel cylinder  19 , and a connection manner of the fluid outlet valve  16  and the fluid inlet valve  12  corresponding to the brake wheel cylinder  20  may use a same connection manner. 
     The fluid inlet valve  9  is located on the first branch  115  of the first brake pipe  11 , and is located between the pressure inlet port of the first branch  115  and the pressure inlet port  5  of the brake wheel cylinder  17 . A pressure outlet port of the fluid inlet valve  9  is connected to a pressure inlet port of the fluid outlet valve  13 , and a pressure outlet port of the inlet valve  9  is further connected to the pressure inlet port  5  of the brake wheel cylinder  17 . A pressure outlet port of the fluid outlet valve  13  is connected to the fluid outlet pipe  117 . Generally, to prevent brake fluid from flowing from the brake wheel cylinder  17  to the first pressure boosting apparatus, in other words, to prevent the brake fluid from being refluxed, a one-way valve  119  may be connected in parallel to two ends (the pressure outlet port and the pressure inlet port) of the fluid inlet valve  9 . 
     It should be noted that the fluid inlet valve and the fluid outlet valve may cooperate with each other in a plurality of manners, and only one of the manners is listed above. For example, the first branch  115  may be further divided into two independent branches that are connected in parallel, and the fluid inlet valve and the fluid outlet valve are respectively disposed on the two independent branches. This is not limited in this embodiment of this application. 
     To improve redundancy performance of the brake system, the brake system may further include a second-level brake sub-system  200 . It should be noted that the second-level brake sub-system  200  may be used in combination with the first-level brake sub-system  100 , may be separately used as an independent brake system, or may be separately combined with another form of brake sub-system. This is not specifically limited in this embodiment of this application. A second-level brake sub-system according to an embodiment of this application is first described below with reference to  FIG. 2 , and then a brake system in which a first brake sub-system  100  cooperates with a second brake sub-system  200  is described with reference to  FIG. 3 . 
       FIG. 2  is a schematic diagram of a second-level brake sub-system  200  according to an embodiment of this application. The second-level brake sub-system  200  shown in  FIG. 2  includes a master brake cylinder  210 . The master brake cylinder  210  is configured to convert mechanical energy of a brake pedal into brake fluid pressure, and transmit the brake fluid pressure to a brake wheel cylinder through a brake pipe. It should be understood that parts in  FIG. 2  with a same function as those in  FIG. 1  use a same number. For brevity, for a specific function, refer to the foregoing descriptions. 
     The master brake cylinder  210  is configured to adjust pressure of brake fluid in a first brake pipe  211 , to control brake force applied to a first group of wheels  112 . 
     The master brake cylinder  210  may be a tandem master brake cylinder. To be specific, a front chamber may be connected to a second brake pipe  221 , and a rear chamber may be connected to the first brake pipe  211 . Certainly, the master brake cylinder  210  may alternatively have a single chamber. In this case, the two brake pipes  211  and  221  are one physical pipe. A specific form of the master brake cylinder  210  is not limited in this embodiment of this application. 
     A first pressure outlet port of the master brake cylinder  210  is connected to a pressure inlet port of the first brake pipe  211 , and the pressure of the brake fluid in the first brake pipe  211  may be boosted, to increase the brake force applied to the first group of wheels  112 . 
     Pressure outlet ports ( 1  and  2 ) of the first brake pipe  211  are connected to pressure inlet ports ( 5  and  6 ) of brake wheel cylinders of the first group of wheels. 
     The master brake cylinder  210  is further configured to adjust pressure of brake fluid in the second brake pipe  221 , to control brake force applied to a second group of wheels  122 . 
     A second pressure outlet port of the master brake cylinder  210  is connected to a pressure inlet port of the second brake pipe  221 , and the pressure of the brake fluid in the second brake pipe  211  may be boosted, to increase the brake force applied to the second group of wheels  122 . 
     The first pressure outlet port and the second pressure outlet port may be a same pressure outlet port, or may be two different pressure outlet ports. This is not limited in this embodiment of this application. 
     Pressure outlet ports ( 1  and  2 ) of the first brake pipe  211  are connected to pressure inlet ports ( 5  and  6 ) of brake wheel cylinders of the first group of wheels. 
     Optionally, when the master brake cylinder  210  is a tandem master brake cylinder, the master brake cylinder  210  includes a first chamber  212  and a second chamber  222 . A first piston in the first chamber  212  and a second piston in the second chamber  222  are connected by using a spring. When the first piston is displaced relative to a cylinder body, the spring may push the second piston to be displaced relative to the cylinder body. A pressure outlet port  21  of the first chamber  212  is connected to the pressure inlet port of the first brake pipe  211 , and a pressure outlet port  22  of the second chamber  222  is connected to the pressure inlet port of the second brake pipe  221 . 
     If a first control valve  130  is in an open state, the first brake pipe  211  and the second brake pipe  221  are independent brake pipes, and pressure of brake fluid in the two brake pipes is respectively controlled by the first chamber  212  and the second chamber  222 . If the first control valve  130  is in a closed state, the first brake pipe  211  and the second brake pipe  221  are connected brake pipes, the brake fluid may flow between the first brake pipe  211  and the second brake pipe  221 , so that the pressure of the brake fluid in the two brake pipes is balanced. 
     In this way, when the first chamber  212  is faulty, but brake force needs to be applied to the first group of wheels  112 , the first control valve  130  may be controlled to be in a closed state, and then the second chamber  222  may boost the pressure of the brake fluid in the second brake pipe  221  to transfer the pressure of the brake fluid in the second brake pipe  221  to the first brake pipe  211 , to apply the brake force to the first group of wheels  112  by boosting the pressure of the brake fluid in the first brake pipe  211 . 
     When the second chamber  222  is faulty, but brake force needs to be applied to the second group of wheels  122 , the first control valve  130  may be controlled to be in a closed state, and then the first chamber  212  may boost the pressure of the brake fluid in the first brake pipe  211  to transfer the pressure of the brake fluid in the first brake pipe  111  to the second brake pipe  221 , to apply the brake force to the second group of wheels  122  by boosting the pressure of the brake fluid in the second brake pipe  121 . 
     Generally, when the first chamber  212  is faulty, to avoid a case in which the first chamber  212  intermittently boosts pressure and the like, a control valve  213  may be disposed at a pressure outlet port of the first chamber  212 . After the first chamber  212  is faulty, the control valve  213  may be controlled to be in an open state, and in this case, the first chamber  212  is disconnected from the first brake pipe  211 . Accordingly, a control valve  214  may also be disposed at a pressure outlet port of the second chamber  222 . After the second chamber  222  is faulty, the control valve  214  may be controlled to be in an open state, and in this case, the second chamber  222  is disconnected from the second brake pipe  221 . Therefore, the control valve  213  and the control valve  214  are also referred to as “isolation valves.” 
     It should be noted that the first brake pipe  211  includes a first branch  115  and a second branch  116 , and the second brake pipe may include a first branch  125  and a second branch  126 . For connection manners of the foregoing four branches, and a configuration manner of fluid inlet valves and fluid outlet valves on the four branches, refer to the foregoing descriptions. 
     A brake system according to an embodiment of this application is described below with reference to  FIG. 3 .  FIG. 3  is a schematic diagram of a brake system  300  according to an embodiment of this application. The brake system  300  includes a first-level brake sub-system  100  and a second-level brake sub-system  200 . It should be understood that parts in  FIG. 2  with a same function as those in  FIG. 1  use a same number. For brevity, for a specific function, refer to the foregoing descriptions. 
     In the brake system  300  shown in  FIG. 3 , a first brake pipe  11 in the first-level brake sub-system  100  communicates with a first brake pipe  211  in the second-level brake sub-system  200 , and a second brake pipe  121  in the first-level brake sub-system  100  communicates with a second brake pipe  221  in the second-level brake sub-system  200 . 
     In other words, when a first control valve  130  is in an open state, a first pressure boosting apparatus  110  and a first chamber  212  of a master brake cylinder are disposed on the first brake pipes ( 111  and  211 ) as pressure providing apparatuses. A second pressure boosting apparatus  120  and a second chamber  222  of the master brake cylinder are disposed on the second brake pipes ( 121  and  221 ) as pressure providing apparatuses. When the first control valve  130  is in a closed state, any one of the master brake cylinder  210 , the first pressure boosting apparatus  110 , and the second pressure boosting apparatus  120  may be used as a pressure providing apparatus in the brake system  300 . The first-level brake sub-system  100  and the second-level brake sub-system  200  cooperate with each other, so that redundancy performance of the brake system  300  is improved. 
     In the brake system described above, if the first control valve  130  is faulty, the first brake pipes ( 111  and  211 ) and the second brake pipes ( 121  and  221 ) become independent pipes. In this case, a redundancy rate of the brake system is 2. To further improve redundancy performance of the brake system, a second control valve  310  may be further disposed on a fluid outlet pipe  117 . The second control valve  310  is located on a fluid outlet pipe between a pressure inlet port of the fluid outlet pipe  117  and an inlet port of a fluid storage apparatus  118 , or is located on a fluid outlet pipe between the inlet port of the fluid storage apparatus  118  and pressure outlet ports of a plurality of fluid outlet valves ( 13 ,  14 ,  15 , and  16 ). 
     Accordingly, when the first control valve  130  is faulty or is in an open state, the second control valve  310  may be controlled to be in an open state, the plurality of fluid outlet valves ( 13 ,  14 ,  15 , and  16 ) are controlled to be in a closed state, and a plurality of fluid inlet valves ( 9 ,  10 ,  11 , and  12 ) are controlled to be in a closed state. In this case, pressure of brake fluid in a first segment of pipe ( 320 ) between the second control valve  310  and the pressure outlet ports of the fluid outlet valves ( 13 ,  14 ,  15 , and  16 ) may be boosted, to accordingly boost pressure of a brake wheel cylinder. 
     For example, if brake force on the first group of wheels  112  needs to be boosted when the first control valve  130  is in an open state or the first control valve  130  is faulty, and a pressure providing apparatus on the first brake pipe  111  is faulty, a pressure providing apparatus on the second brake pipe  121  may provide brake force for the first group of wheels  112 . It is assumed that the second pressure boosting apparatus  120  provides brake force for the first group of wheels  112 . In this case, the second control valve  310  may be controlled to be in an open state, the fluid inlet valves ( 11  and  12 ) on the second brake pipe  121  are controlled to be in a closed state, the fluid outlet valves ( 15  and  16 ) on the second brake pipe  121  are controlled to be in a closed state, and the fluid outlet valves ( 13  and  14 ) on the first brake pipe  111  are also controlled to be in a closed state. 
     Accordingly, brake fluid may flow into the second brake pipe  121  from a pressure outlet port of the second pressure boosting apparatus  120 , and flow into the fluid outlet valves ( 15  and  16 ) through two branches ( 125  and  126 ) of the second brake pipe  121 , and then the brake fluid is transmitted to the fluid outlet valves ( 13  and  14 ) through the foregoing first segment of pipe  320 , and is transmitted to brake wheel cylinders ( 17  and  18 ) of the first group of wheels  112  through the fluid outlet valves ( 13  and  14 ) along branches ( 115  and  116 ) of the first brake pipe  11 , to provide brake force for the first group of wheels  112 . 
     It should be noted that pressure of any one of the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) may be boosted by using the first segment of fluid outlet pipe  320 . A specific method is similar to the foregoing process of boosting pressure of the brake wheel cylinders ( 17  and  18 ) by using the first segment of fluid outlet pipe  320 . 
     Optionally, the first control valve  130 , the second control valve  310 , the fluid outlet valves ( 13 ,  14 ,  15 , and  16 ), the fluid inlet valves ( 9 ,  10 ,  11 , and  12 ), isolation valves ( 119 ,  129 ,  213 , and  214 ), and the like involved in the foregoing descriptions may be solenoid valves. After the brake system is powered on, a working status, to be specific, a closed state or an open state, of the solenoid valve may be controlled by using a controller. 
     Optionally, the controller may further control working statuses of the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  in a wire-controlled braking manner. After the isolation valves ( 213  and  214 ) are controlled to be in an open state, the controller may determine, based on an obtained pedal traveling distance, required brake force required by a driver. Then, the controller may send first control information to the first pressure boosting apparatus  110  based on the required brake force, to control the brake force applied by the first pressure boosting apparatus to the first group of wheels; and send second control information to the second pressure boosting apparatus  120 , to control the brake force applied by the second pressure boosting apparatus  120  to the second group of wheels. 
     When the controller controls the first pressure boosting apparatus  110  and/or the second pressure boosting apparatus  120  to provide brake force for the wheel, the controller generally can only sense whether the first pressure boosting apparatus  110  and/or the second pressure boosting apparatus  120  fail/fails, but cannot sense whether the first brake pipe  111  and the second brake pipe  121  are faulty. 
     Therefore, to enable the controller to sense whether the first brake pipe  111  and the second brake pipe  121  are faulty, and to determine a working manner of the brake system in a timely manner, a pressure sensor  1  may be disposed at a pressure outlet port of the first pressure boosting apparatus  110 , and the controller may sense, by using the pressure sensor  1 , whether the first brake pipe in is faulty. Accordingly, a pressure sensor  2  may be disposed at a pressure outlet port of the second pressure boosting apparatus  120 , and the controller may sense, by using the pressure sensor  2 , whether the second brake pipe  121  is faulty. 
     Generally, the controller may detect, by using a pedal travel sensor  420 , displacement of a piston in the master brake cylinder relative to the cylinder body of the master brake cylinder, in other words, a pedal traveling distance of a brake pedal. Specifically, after detecting the foregoing displacement, the pedal travel sensor  420  may send the displacement to the controller, and accordingly, the controller determines, based on the displacement, brake force applied to a wheel of a vehicle. 
     However, in the foregoing solution in which the controller detects the displacement by using the pedal travel sensor  420  to determine the brake force applied to the wheel of the vehicle, if the pedal travel sensor  420  is faulty, the controller cannot determine the brake force. 
     To avoid this case, in the brake system provided in this application, a pressure sensor  330  may be further disposed on the first brake pipe  211  and/or the second brake pipe  222 . In this way, after the pedal travel sensor  420  fails, the controller may further detect pressure of brake fluid in the first brake pipe  211  and/or the second brake pipe  222  by using the pressure sensor  330 , and determine, based on the pressure of the brake fluid, the brake force applied to the wheel of the vehicle. 
     To be specific, the brake system further includes the pressure sensor  330 , the pressure sensor  330  is located on the first brake pipe  211  between the master brake cylinder  210  and the first pressure boosting apparatus  110 , and the pressure sensor  330  is configured to detect the pressure that is of the brake fluid in the first brake pipe  211  and that is adjusted by the master brake cylinder  210 . The pressure sensor  330  is further configured to send pressure information indicating the pressure to the controller. 
     Optionally, the second-level brake sub-system  200  may further include a pedal sense analog spring  223 , and the pedal sense analog spring  223  is located on the second brake pipe  221 . In this way, the brake fluid in the second brake pipe  221  may flow into the pedal sense analog spring  223 , so that the pedal sense analog spring  223  determines displacement of the piston in the master brake cylinder  210  relative to the brake cylinder body by sensing the pressure of the brake fluid in the second brake pipe  221 . In this way, the pedal sense analog spring  223  may send the detected pressure of the brake fluid to the controller, so that the controller determines the brake force on the wheel. 
     Generally, after the second-level brake sub-system  200  is faulty or the brake system enters a wire-controlled braking working mode, the isolation valves  213  and  214  are in an open state. In this case, the pedal sense analog spring  223  may sense the pressure of the brake fluid in the second brake pipe  221 , and send the sensed pressure to the controller. 
     Certainly, a control valve  224  may be further disposed between a pressure inlet port of the pedal sense analog spring  223  and the second brake pipe  221 . When the pedal sense analog spring  223  does not need to work, the control valve  224  may be controlled to be in an open state, to isolate the second brake pipe  221  from the pedal sense analog spring  223 . Therefore, the control valve  224  is also referred to as an “isolation valve.” When the control valve  224  is in a closed state, the second brake pipe  221  communicates with the pedal sense analog spring  223 , and the pedal sense analog spring  223  is in a working state. 
     The brake system according to the embodiments of this application is described below with reference to  FIG. 1  to  FIG. 3 . The brake system provided in this application may be applied to a vehicle. A vehicle that uses the foregoing brake system is described below with reference to  FIG. 4 . 
       FIG. 4  is a schematic diagram of a vehicle according to an embodiment of this application. It should be understood that the vehicle  400  shown in  FIG. 4  includes a first group of wheels  112 , a second group of wheels  122 , and any brake system described above. 
     Optionally, the vehicle  400  further includes a brake pedal  410  and a pedal travel sensor  420 , and the pedal travel sensor  420  is configured to detect displacement that is of a piston in a master brake cylinder relative to a cylinder body of the master brake cylinder and that is generated when the brake pedal pushes the piston, namely, a pedal traveling distance. The pedal travel sensor  420  is further configured to send the displacement to a controller, so that the controller determines, based on the displacement, brake force applied to a wheel of the vehicle. 
     A connection manner between brake elements in the brake system is described with reference to  FIG. 1  to  FIG. 4 . A plurality of working modes of the brake system are described below with reference to  FIG. 5  to  FIG. 12 . It should be noted that priorities of the plurality of working modes are not specifically limited in this application. 
     The vehicle  400  shown in  FIG. 4  may be divided into three working modes: a non-pressure boosting manual braking mode, a wire-controlled braking mode, and an active braking mode. The non-pressure boosting manual braking mode may be understood as that only a second-level brake sub-system  200  provides brake force for the wheel. The active braking mode may be understood as that only a first-level brake sub-system  100  provides brake force for the wheel, and may be applied to a case such as adaptive cruise control or obstacle avoidance controlled by an advanced driving assistant system (advanced driving assistant system). The wire-controlled braking mode may be understood as that the controller controls, based on pedal depressing of a driver, a first pressure boosting apparatus  110  and a second pressure boosting apparatus  120  to provide brake force for the wheel. 
     In the foregoing three working modes, some functions in different modes may be implemented in a same implementation. For example, a same pressure boosting solution may be used in different modes. For another example, a same pedal brake force requirement calculation solution may be used in different modes. For still another example, a same redundant solution may be used in different modes. Therefore, for brevity, functions implemented in the brake system are classified into the following three scenarios for separate descriptions. 
     It is assumed that in the brake system  300 , the isolation valves ( 119  and  129 ) are normally-open valves, the fluid inlet valves ( 9 ,  10 ,  11 , and  12 ) are normally-open valves, the fluid outlet valves ( 13 ,  14 ,  15 , and  16 ) are normally-closed valves, the isolation valves ( 213  and  214 ) are normally-open valves, the first control valve  130  is a normally-closed valve, the second control valve  310  is a normally-open valve, and the control valve  224  is a normally-closed valve. 
     It should be noted that the normally-open valve and the normally-closed valve are default states of a control valve before the control valve is powered on. When the controller needs to adjust a status of the control valve, the control valve whose status is to be adjusted may be powered on, so that the control valve can be controlled to be in an open state or a closed state. 
     Scenario 1: A pedal brake force requirement calculation solution and a redundant solution for pedal brake force requirement calculation in the brake system in the wire-controlled braking mode. 
     In the wire-controlled braking mode, the controller controls the isolation valves ( 213  and  214 ) to be in an open state, and controls the control valve  224  to be in a closed state, so that the pedal sense simulator  223  is connected to the second brake pipe  221 , and another control valve in the brake system maintains the foregoing default state. 
     In this way, a driver depresses the brake pedal  410  to push, by using a push rod, a piston in the master brake cylinder  210  to be displaced relative to the master brake cylinder  210 . Brake fluid in the second chamber  222  is pressed into the second brake pipe  221 , and brake fluid in the first chamber  212  is pressed into the first brake pipe  211 . Because the isolation valves ( 213  and  214 ) are in an open state, the brake fluid in the two brake pipes is blocked at the isolation valves ( 213  and  214 ), and the brake fluid in the second brake pipe  221  is pressed into the pedal sense simulator  223  by using the control valve  224 . Pressure of the brake fluid in the first brake pipe  211  is boosted under an action of the master brake cylinder  210 . 
     A pedal brake force requirement calculation solution in an embodiment of this application is described below based on the foregoing described working status of each brake element in the brake system in the wire-controlled braking mode. 
     The controller calculates required brake force of the driver based on a pedal displacement measured by the pedal travel sensor  420 , and feeds back the required brake force to the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120 . 
     The first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  control, based on the foregoing required brake force, the motors ( 113  and  123 ) to compress brake fluid by using the hydraulic cylinders ( 114  and  124 ) and provide brake force for the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) by using the isolation valves ( 119  and  129 ). 
     As a redundant solution of the pedal brake force requirement calculation solution, when the pedal travel sensor  42031  is faulty, the pressure sensor  330  may be used to measure the pressure of the brake fluid in the first brake pipe  211 , determine brake force required by the driver, and then feed back the brake force to the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120 . 
     Accordingly, the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  control, based on the brake force, the motors ( 113  and  123 ) to compress brake fluid by using the hydraulic cylinders ( 114  and  124 ) and provide brake force for the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) by using the isolation valves ( 119  and  129 ). For a flowing path of the brake fluid in the brake system, refer to  FIG. 5 . 
     It should be noted that neither of the foregoing two solutions for pedal sense simulation directly affects implementation of dynamics functions such as an antilock brake system (ABS), a traction control system (TCS), and an electronic stability system (ESC). To implement dynamics control algorithms such as the TCS, the ABS, and the ESC, a single brake wheel cylinder needs to be controlled. In this case, a single fluid inlet valve and a single fluid outlet valve may be controlled with assistance of the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  to implement pressure boosting, pressure maintenance, and pressure reduction operations for the single brake wheel cylinder. 
     When the driver releases the brake pedal  410 , the displacement of the piston in the master brake cylinder relative to the cylinder body is restored to 0. Brake fluid in the pedal sense simulator  223  flows back from the control valve  224  to the second chamber  222  in an opposite direction, and finally flows into the fluid storage apparatus  118 . Hydraulic cylinders ( 114  and  124 ) in the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  work reversely, pressure in the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) is greater than pressure in the hydraulic cylinders ( 114  and  124 ), and the brake fluid is separately returned from the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) to the hydraulic cylinders ( 114  and  124 ) by using respective corresponding fluid inlet valves ( 9 ,  10 ,  11 , and  12 ) and a one-way valve along the brake pipes. 
     Optionally, the isolation valves ( 213  and  214 ) may be further controlled to be in a closed state, so that the brake fluid is returned from the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) to the fluid storage apparatus  118  by using the isolation valves ( 213  and  214 ), the second chamber  222 , and the first chamber  212 . 
     When pressure needs to be reduced rapidly, the fluid outlet valves ( 13 ,  14 ,  15 , and  16 ) may be further turned on, so that brake fluid in the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) flows back to the fluid storage apparatus  118 . 
     Scenario 2: An active pressure boosting solution in the active braking mode and a redundant solution for active pressure boosting. 
     Similar to the active pressure boosting solution in the wire-controlled braking mode described in the scenario 1, the brake system may directly use the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  to perform braking. A difference from the wire-controlled braking mode described in the scenario 1 lies in that the driver does not need to operate the brake pedal  410  in the active braking mode. 
     If the controller determines, by analyzing information such as an environment condition, a vehicle status, an ADAS status, and a driver input, that the vehicle needs to perform the active braking mode, the isolation valves ( 213  and  214 ) are in an open state, and another control valve maintains the foregoing default state. The controller sends required brake force to the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120 . The first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  provide brake pressure for the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) based on the brake force. For a flowing path of the brake fluid in the brake system, refer to  FIG. 6 . 
     When pressure needs to be reduced, a first hydraulic cylinder  114  and a second hydraulic cylinder  124  work reversely under an action of the motors ( 113  and  123 ), pressure in the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) is greater than pressure in the first hydraulic cylinder  114  and the second hydraulic cylinder  124 , and brake fluid is separately returned from the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) to the first hydraulic cylinder  114  and the second hydraulic cylinder  124  by using the respective fluid inlet valves ( 9 ,  10 ,  11 , and  12 ) and a one-way valve along the brake pipes. 
     Optionally, the isolation valves ( 213  and  214 ) may be further controlled to be in a closed state, so that the brake fluid is returned from the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) to the fluid storage apparatus  118  by using the isolation valves ( 213  and  214 ), the second chamber  222 , and the first chamber  212 . 
     When pressure needs to be reduced rapidly, the fluid outlet valves ( 13 ,  14 ,  15 , and  16 ) may be further turned on, so that brake fluid in the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) flows back to the fluid storage apparatus  118 . 
     It should be noted that neither of the foregoing two solutions for pedal sense simulation directly affects implementation of dynamics functions such as an ABS, a TCS, and an ESC. To implement dynamics control algorithms such as the TCS, the ABS, and the ESC, a single brake wheel cylinder needs to be controlled. In this case, a single fluid inlet valve and a single fluid outlet valve may be controlled with assistance of the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  to implement pressure boosting, pressure maintenance, and pressure reduction operations for the single brake wheel cylinder. 
     Four redundant solutions for active pressure boosting in the active braking mode are described below. It should be noted that the redundant solutions for active pressure boosting may be further applied to the wire-controlled braking mode. Because the solutions are essentially the same, for brevity, redundant solutions for active pressure boosting in the wire-controlled braking mode are not specifically described below. 
     Redundant solution 1: When the first pressure boosting apparatus  110  is faulty, the first control valve  130  is controlled to be in a closed state. In this case, the first brake pipe  111  is connected to the second brake pipe  121 , and the second pressure boosting apparatus  120  works and provides brake pressure for the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) based on brake force fed back by the controller. In this case, for a flowing path of the brake fluid in the brake system, refer to  FIG. 7 . 
     Redundant solution 2: When the second pressure boosting apparatus  120  is faulty, the first control valve  130  is controlled to be in a closed state. In this case, the first brake pipe  111  is connected to the second brake pipe  121 , and the first pressure boosting apparatus  110  works and provides brake pressure for the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) based on brake force fed back by the controller. In this case, for a flowing path of the brake fluid in the brake system, refer to  FIG. 8 . 
     It should be noted that neither of the foregoing two solutions for pedal sense simulation directly affects implementation of dynamics functions such as an ABS, a TCS, and an ESC. To implement dynamics control algorithms such as the TCS, the ABS, and the ESC, a single brake wheel cylinder needs to be controlled. In this case, a single fluid inlet valve and a single fluid outlet valve may be controlled with assistance of the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  to implement pressure boosting, pressure maintenance, and pressure reduction operations for the single brake wheel cylinder. 
     Redundant solution 3: When both the first pressure boosting apparatus  110  and the first control valve  130  are faulty, the second control valve  310  is controlled to be in an open state, all fluid outlet valves ( 13 ,  14 ,  15 , and  16 ) are turned on, and another control valve is in the foregoing default state. The second pressure boosting apparatus  120  works and presses brake fluid into the second brake pipe  121  based on brake force fed back by the controller, and the brake fluid flows into the first segment of fluid outlet pipe  320  through the fluid inlet valves ( 11  and  12 ) and the fluid outlet valves ( 15  and  16 ). When the second control valve  310  is blocked, the brake fluid flows into the fluid outlet valves ( 13  and  14 ) through the first segment of fluid outlet pipe  320 . With isolation of the one-way valve, brake fluid flowing out of the fluid outlet valves ( 13  and  14 ) flows into the brake wheel cylinders ( 17  and  18 ) through the first branch  115  and the second branch  116 , and finally provides brake pressure for the brake wheel cylinders ( 17  and  18 ). Accordingly, a part of the brake fluid that is pressed into the second brake pipe  121  may flow into the brake wheel cylinders ( 19  and  20 ) through the first branch  125  and the second branch  126 . For a flowing path of the brake fluid in the brake system, refer to  FIG. 9 . 
     Redundant solution 4: When both the second pressure boosting apparatus  120  and the first control valve  130  are faulty, the second control valve  310  is controlled to be in an open state, all fluid outlet valves ( 13 ,  14 ,  15 , and  16 ) are turned on, and another control valve is in the foregoing default state. The first pressure boosting apparatus  110  works and presses brake fluid into the first brake pipe  111  based on brake force fed back by the controller, and the brake fluid flows into the first segment of fluid outlet pipe  320  through the fluid inlet valves ( 9  and  10 ) and the fluid outlet valves ( 13  and  14 ). When the second control valve  310  is blocked, the brake fluid flows into the fluid outlet valves ( 15  and  16 ) through the first segment of fluid outlet pipe  320 . With isolation of the one-way valve, brake fluid flowing out of the fluid outlet valves ( 15  and  16 ) flows into the brake wheel cylinders ( 19  and  20 ) through the first branch  125  and the second branch  126 , and finally provides brake pressure for the brake wheel cylinders ( 19  and  20 ). Accordingly, a part of the brake fluid that is pressed into the first brake pipe  111  may flow into the brake wheel cylinders ( 17  and  18 ) through the first branch  115  and the second branch  116 . For a flowing path of the brake fluid in the brake system, refer to  FIG. 10 . 
     Scenario 3: Redundant backup solution for manual braking. To be specific, when both the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  fail, mechanical braking can still be implemented if the driver depresses the pedal, so that it is ensured that the vehicle reliably decelerates. 
     All control valves in the brake system are in the default state. The driver depresses the brake pedal  410 , pushes the brake fluid in the second chamber  222  into the second brake pipe  221 , and pushes the brake fluid in the first chamber  212  into the first brake pipe  211 ; and finally, the brake fluid flows into the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) through the fluid inlet valves ( 9 ,  10 ,  11 , and  12 ) along the first brake pipe  211  and the second brake pipe  221 . In this way, manual braking is implemented. For a flowing path of the brake fluid in the brake system, refer to  FIG. 11 . 
     When the driver releases the brake pedal  410 , the piston in the master brake cylinder returns to an initial position under an action of a return spring, and the brake pedal  410  returns to an initial position by using a push rod. In this case, the brake fluid flows back from the brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ) into the second chamber  222  and the first chamber  212  through the fluid inlet valves ( 9 ,  10 ,  11 , and  12 ) and a one-way valve in opposite directions, and finally flows into the fluid storage apparatus  118 . For a flowing path of the brake fluid in the brake system, refer to  FIG. 12 . 
     The brake system and the vehicle according to the embodiments of this application are described above with reference to  FIG. 1  to  FIG. 12 . A control method based on the brake system according to an embodiment of this application is described below with reference to  FIG. 13  and  FIG. 14A ,  FIG. 14B , and  FIG. 14C . It should be noted that the control method shown in  FIG. 13  may be performed by the controller in the brake system. 
       FIG. 13  is a flowchart of a control method for a brake system according to an embodiment of this application. The method shown in  FIG. 13  includes step  1310  and step  1320 . The method shown in  FIG. 13  may be used in combination with the brake system and the vehicle that are described above. Either of the foregoing first brake pipe  111  and second brake pipe  121  is referred to as a “target brake pipe.” 
       1310 : A controller determines that a pressure providing apparatus on a target brake pipe is faulty. 
     The pressure providing apparatus may include a master brake cylinder  210  or a pressure boosting apparatus. If the target brake pipe is a first brake pipe  11 , the pressure providing apparatus may be the master brake cylinder  210  or a first pressure boosting apparatus  110 . If the target brake pipe is a second brake pipe  121 , the pressure providing apparatus may be the master brake cylinder  210  or a second pressure boosting apparatus  120 . 
       1320 : The controller controls a first control valve  130  to be in a closed state, so that the first brake pipe in is connected to the second brake pipe  121 . 
     If the first brake pipe  111  is connected to the second brake pipe  121 , brake fluid may flow in the first brake pipe in and the second brake pipe  121 , and brake force is provided for a brake wheel cylinder by using pressure of the brake fluid. 
     In this embodiment of this application, after the pressure providing apparatus on the target brake pipe is faulty, the controller may control the first control valve  130  to be in a closed state, so that the brake fluid flows in the first brake pipe in and the second brake pipe  121 , and the brake force is provided for the brake wheel cylinder by using the pressure of the brake fluid, thereby avoiding a problem in a conventional brake system that the first brake pipe and the second brake pipe are two mutually independent brake paths, and after a pressure providing apparatus in one brake pipe is faulty, the brake pipe cannot control brake force on a brake wheel cylinder on the brake pipe. This helps improve redundancy performance of a brake system is improved. 
     Optionally, the target brake pipe is the first brake pipe ( 111 ), the pressure providing apparatus includes the first pressure boosting apparatus ( 110 ), and the method further includes: The controller controls the second pressure boosting apparatus ( 120 ) to adjust pressure of brake fluid in the second brake pipe ( 121 ), to adjust pressure of brake fluid in the first brake pipe ( 111 ). 
     Optionally, the target brake pipe is the second brake pipe ( 121 ), the pressure providing apparatus includes the second pressure boosting apparatus ( 120 ), and the method further includes: The controller controls the first pressure boosting apparatus ( 110 ) to adjust pressure of brake fluid in the first brake pipe ( 111 ), to adjust pressure of brake fluid in the second brake pipe ( 121 ). 
     Optionally, the brake system further includes a tandem master brake cylinder ( 210 ). A first chamber ( 212 ) of the master brake cylinder ( 210 ) communicates with the first brake pipe ( 111 ), and is configured to adjust the pressure of the brake fluid in the first brake pipe ( 111 ), to control brake force applied to a first group of wheels ( 112 ). A second chamber ( 222 ) of the master brake cylinder ( 210 ) communicates with the second brake pipe ( 121 ), and is configured to adjust the pressure of the brake fluid in the second brake pipe ( 121 ), to control brake force applied to a second group of wheels ( 122 ). The method further includes: if the first chamber ( 212 ) is faulty, the controller controls the first control valve ( 130 ) to be in a closed state, so that the pressure of the brake fluid in the second brake pipe ( 121 ) and the pressure of the brake fluid in the first brake pipe ( 111 ) are balanced; or if the second chamber ( 222 ) is faulty, the controller controls the first control valve ( 130 ) to be in a closed state, so that the pressure of the brake fluid in the first brake pipe ( 111 ) and the pressure of the brake fluid in the second brake pipe ( 121 ) are balanced. 
     To further improve redundancy performance of the brake system, a second control valve  310  may be further disposed on a fluid outlet pipe  117 . After the second control valve  310  is in an open state, a first segment of pipe  320  may be configured to provide brake force for brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ). 
     Optionally, the brake system further includes a fluid storage apparatus ( 118 ) for storing brake fluid, a plurality of fluid outlet valves ( 140 ), and a second control valve ( 310 ). Pressure outlet ports of the plurality of fluid outlet valves ( 140 ) are connected to a pressure inlet port of a fluid outlet pipe ( 117 ), a pressure outlet port of the fluid outlet pipe ( 117 ) is connected to an inlet port of the fluid storage apparatus ( 118 ), and the second control valve ( 310 ) is located on a fluid outlet pipe ( 117 ) between the pressure inlet port of the fluid outlet pipe ( 117 ) and the inlet port of the fluid storage apparatus ( 118 ). The method further includes: the controller determines that the first pressure boosting apparatus ( 110 ) and the first control valve ( 130 ) are faulty; and the controller controls the second control valve ( 310 ) to be in an open state, and controls the plurality of fluid outlet valves ( 140 ) to be in a closed state, so that brake fluid in a first segment of pipe ( 320 ) is pressed into a brake wheel cylinder of a wheel of a vehicle by the second pressure boosting apparatus ( 120 ), to control brake force applied to the wheel of the vehicle, where the first segment of pipe ( 320 ) is a pipe between the pressure inlet port of the fluid outlet pipe ( 117 ) and the second control valve ( 310 ). 
     Optionally, the method further includes: the controller determines that the second pressure boosting apparatus ( 120 ) and the first control valve ( 130 ) are faulty; and the controller determines the first control valve ( 310 ) to be in an open state, and controls the plurality of fluid outlet valves ( 140 ) to be in a closed state, so that the brake fluid in the first segment of pipe ( 320 ) is pressed into a brake wheel cylinder of a wheel of a vehicle by the first pressure boosting apparatus ( 110 ), to control brake force applied to the wheel of the vehicle. 
     In a non-pressure boosting manual braking mode and a wire-controlled braking mode of the brake system, the controller generally needs to determine, by using a pedal travel sensor  420 , brake force required by a driver. However, if the pedal travel sensor  420  is faulty, the controller cannot sense the brake force required by the driver. 
     Therefore, to avoid the foregoing case, a pressure sensor  330  is further disposed in the brake system provided in this embodiment of this application, and is located on a first brake pipe  212  and/or a second brake pipe  222 , and is configured to sense pressure that is output from a pressure outlet port of the master brake cylinder  210  and that flows into the first brake pipe  212  and/or the second brake pipe  222 . In this way, after determining pressure of brake fluid in the first brake pipe  212  and/or the second brake pipe  222  by using the pressure controller  330 , the controller may determine, based on the pressure of the brake fluid, the brake force required by the driver. 
     Optionally, the brake system further includes a pressure sensor ( 330 ) and a pedal travel sensor ( 420 ). The pressure sensor ( 330 ) is configured to detect the pressure that is of the brake fluid in the first brake pipe ( 111 ) and that is adjusted by the master brake cylinder ( 210 ). The pedal travel sensor ( 420 ) is configured to detect a pedal traveling distance of a brake pedal of the vehicle. The method further includes: the controller receives pressure information that is sent by the pressure sensor ( 330 ) and that is used to indicate the pressure; and if the pedal travel sensor ( 420 ) fails, the controller allocates brake force to the first group of wheels ( 112 ) and/or the second group of wheels ( 122 ) based on the pedal traveling distance. 
     A control method for a brake system according to another embodiment of this application is described below with reference to  FIG. 14A ,  FIG. 14B , and  FIG. 14C . The control method may be used in combination with the brake system  300  or the vehicle  400 . The method shown in  FIG. 14A ,  FIG. 14B , and  FIG. 14C  includes step  1410  to step  1426 . 
       1410 : A controller determines a working mode of a brake system, and performs step  1411  if it is determined to enter a wire-controlled braking mode, or performs step  1412  if it is determined to enter an active braking mode. 
       1411 : The controller determines whether a pedal travel sensor  420  fails, and performs step  1413  if the pedal travel sensor  420  fails, or performs step  1414  if the pedal travel sensor  420  works normally. 
       1413 : The controller determines whether a pressure sensor  330  fails, and performs step  1415  if the pressure sensor  330  fails, or performs step  1414  if the pressure sensor  330  works normally. 
       1415 : The controller notifies a driver that a brake system enters a manual braking working mode. 
     Specifically, the foregoing notification manner may be presented by using a user interface or in a voice prompt manner. This is not limited in this embodiment of this application. 
       1414 : The controller calculates a total brake force requirement of a pedal, and performs step  1416 . 
       1412 : The controller calculates, by using a self-driving controller (for example, an ADAS), brake force required by a vehicle, and then performs step  1416 . 
       1416 : The controller determines whether both a first pressure boosting apparatus  110  and a second pressure boosting apparatus  120  fail, and performs step  1415  if both the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  fail, or performs step  1417  if not both the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  fail. 
       1417 : The controller calculates pressure boosting brake force, to determine brake force that needs to be provided by a pressure boosting apparatus (the first pressure boosting apparatus  110  and/or the second pressure boosting apparatus  120 ), and performs step  1418 . 
       1418 : The controller determines whether the first pressure boosting apparatus  110  fails, and performs step  1419  if the first pressure boosting apparatus  110  fails, or performs step  1420  if the first pressure boosting apparatus  110  does not fail. 
     It should be noted that step  1418  is performed when not both the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  fail. In this case, when step  1419  is performed, the second pressure boosting apparatus  120  does not fail. 
       1419 : The controller determines whether a first control valve  130  fails, and performs step  1421  if the first control valve  130  fails, or performs step  1422  if the first control valve  130  does not fail. 
       1421 : The controller controls the second pressure boosting apparatus  120  to work, a second control valve  310  to be in an open state, and fluid outlet valves ( 13 ,  14 ,  15 , and  16 ) to be in a closed state. 
       1422 : The controller controls the second pressure boosting apparatus  120  to work and a second control valve  310  to be in a closed state. 
       1420 : The controller determines whether the second pressure boosting apparatus  120  fails, and performs step  1423  if the second pressure boosting apparatus  120  fails, or performs step  1424  if the second pressure boosting apparatus  120  does not fail. 
     It should be noted that step  1424  is performed when not both the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  fail. In this case, when step  1424  is performed, the first pressure boosting apparatus  110  does not fail. 
       1423 : The controller determines that the first pressure boosting apparatus  110  and the second pressure boosting apparatus  120  work simultaneously to provide brake force for brake wheel cylinders ( 17 ,  18 ,  19 , and  20 ). In this case, the first control valve  130  is in an open state. 
       1424 : The controller determines whether a first control valve  130  fails, and performs step  1425  if the first control valve  130  fails, or performs step  1426  if the first control valve  130  does not fail. 
       1425 : The controller controls the first pressure boosting apparatus  110  to work, a second control valve  310  to be in an open state, and fluid outlet valves ( 13 ,  14 ,  15 , and  16 ) to be in a closed state. 
       1426 : The controller controls the first pressure boosting apparatus  110  to work and a second control valve  310  to be in a closed state. 
     It should be understood that in this embodiment of this application, the memory may include a read-only memory and a random access memory, and provide an instruction and data to the processor. A part of the processor may further include a non-volatile random access memory. For example, the processor may further store information of a device type. 
     It should be understood that the term “and/or” in this specification describes only an association relationship for describing associated objects and represents that at least three relationships may exist. For example, A and/or B may represent the following three cases: Only A exists, both A and B exist, and only B exists. In addition, the character “/” in this specification generally represents an “or” relationship between the associated objects. 
     It should be understood that sequence numbers of the foregoing processes do not mean execution sequences in various embodiments of this application. The execution sequences of the processes should be determined based on functions and internal logic of the processes, and should not be construed as any limitation on the implementation processes of the embodiments of this application. 
     A person of ordinary skill in the art may be aware that units and algorithm steps in the examples described with reference to the embodiments disclosed in this specification can be implemented by electronic hardware or a combination of computer software and electronic hardware. Whether the functions are performed by hardware or software depends on particular applications and design constraints of the technical solutions. A person skilled in the art may use different methods to implement the described functions for each particular application, but it should not be considered that the implementation goes beyond the scope of this application. 
     It may be clearly understood by a person skilled in the art that, for the purpose of convenient and brief description, for a detailed working process of the foregoing system, apparatus, and unit, refer to a corresponding process in the method embodiments. 
     In the several embodiments provided in this application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described apparatus embodiments are merely examples. For example, division into units is merely logical function division and may be other division during actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented through some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electrical, mechanical, or another form. 
     The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual requirements to achieve the objectives of the solutions of the embodiments. 
     In addition, functional units in the embodiments of this application may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units may be integrated into one unit. 
     When the functions are implemented in a form of a software functional unit and sold or used as an independent product, the functions may be stored in a computer-readable storage medium. Based on such an understanding, the technical solutions of this application essentially, or the part contributing to the conventional technology, or some of the technical solutions may be implemented in a form of a software product. The computer software product is stored in a storage medium, and includes several instructions for instructing a computer device (which may be a personal computer, a server, or a network device) to perform all or some of the steps of the methods described in the embodiments of this application. The foregoing storage medium includes: any medium that can store program code, such as a USB flash drive, a removable hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disc. 
     The foregoing descriptions are merely specific implementations of this application, but are not intended to limit the protection scope of this application. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in this application shall fall within the protection scope of this application. Therefore, the protection scope of this application shall be subject to the protection scope of the claims.