Research on hardware-in-the-loop testing method for electric vehicle brake-by-wire system

Brake-by-wire system (E-Booster) is an important component to improve energy recovery and vehicle braking stability of electric vehicles. This part has many interactive components and requires high operating precision and accuracy. Therefore, it is necessary to carry out adequate testing on it. This article discusses a method of testing the brake-by-wire system by using hardware-in-the-loop (HIL) simulation test, which can realize all-round control of the brake-by-wire system by building a simulation test environment without real vehicles or actual samples. automated testing.

The braking system of traditional fuel vehicles consists of brake pedals, vacuum booster components (EVP) and anti-skid control components (ESP, ABS), etc., without braking energy recovery function, if used on electric vehicles, a lot of braking energy will be wasted energy. The brake-by-wire system (E-Booster) uses the brake-by-wire system controller and the brake-by-wire actuator (mainly the servo motor system) to replace the vacuum booster components, which will effectively solve the problem that the braking energy of the traditional braking system cannot be recovered. Pain points. When the driver brakes, the controller of the brake-by-wire system controls the motor to implement electric braking according to the working state of the powertrain and the driver's braking demand, and the insufficient braking force of the motor is supplemented by hydraulic braking. During the braking process, the pedal stroke simulator will decouple the pedal force and the wheel cylinder pressure, so that the energy of the electric braking part of the motor can be recovered, which improves the endurance of the vehicle and improves the comfort of the driver during the braking process. In addition, the brake-by-wire system interacts with the intelligent driving (ADAS) components through its controller, which can respond to the braking demand of the intelligent driving components.

The parts directly related to the brake-by-wire system on electric vehicles include vehicle controller (VCU), motor controller (MCU), intelligent driving components (ADAS) and anti-skid control components (ABS, ESC), etc. The working process of braking energy recovery in the brake-by-wire system is as follows: the brake-by-wire system collects the driver's braking demand and sends the braking torque request to the VCU, and the VCU calculates the maximum electric braking capacity of the motor and then sends it to the brake-by-wire system controller, then the brake-by-wire system controller calculates the shortfall in braking force and compensates with hydraulic braking. In this way, the electric brake replaces a considerable part of the mechanical brake, reduces the loss of mechanical friction energy, increases the energy recovery of the motor, and thus increases the mileage of the vehicle.

Hardware-in-the-loop testing uses Matlab Simulink to model and simulate parts (VCU, MCU, ADAS, etc.) system to connect and interact. In this way, the test accuracy can be controlled according to the actual test situation, and the extreme working conditions and fault injection tests can also be completely simulated, and automated tests can also be realized by writing automated test scripts.

The hardware-in-the-loop testing method of the brake-by-wire system proposed in this paper mainly includes:

(1) developing the test model through Matlab Simulink;

(2) using the Configuration Desk software of Dspace Company to perform I/O testing of parts interacting with the brake-by-wire system;

(3) Connect the brake-by-wire system controller with the real-time simulation system through the external wiring harness, and compile the test model;

(4) Import the compiled test model into the upper computer software ControlDesk of Dspace Company, and then The real-time simulation system is controlled by the host computer to realize the interactive test of the controlled components and the brake-by-wire system

3.1-Construction of test model

The hardware-in-the-loop test model of the brake-by-wire system is divided into four modules for construction, namely Simulator, E-booster, BusSystems and MDL. Simulator model building is mainly used to control and monitor the state of the real-time simulation cabinet, such as the power supply voltage of the cabinet, the upper and lower limit values of the current, power-off state release, power output command, cabinet voltage collection, cabinet current collection and power supply status collection and other states ; The Booster module is used to build the hardware interface model. This module will realize the configuration of the interactive hardware pin properties of the real-time simulation system and the brake-by-wire system; BusSystems is the core module for model building. properties of text signals. MDL is also the core module of model building. It is the simulation module of the controlled object of the whole vehicle. For the controlled object of the brake-by-wire system, models of VCU, MCU, ADAS and brake anti-skid parts need to be built in this module.

3.2-I/O interface configuration

The hardware-in-the-loop test of the brake-by-wire system realizes the configuration of the input and output ports of the hardware-in-the-loop test system through the ConfigurationDesk software. The content of the configuration includes: the configuration of the hardware port of the brake-by-wire system, the configuration of the board port of the real-time simulation system and the configuration of the model port.

(1) Hardware port configuration of the brake-by-wire system. First, manage the types of ports in groups, such as digital type ports, analog type ports, and PWM waveform ports, etc., and then define the name, description, and device type of the port, such as defining input and output, port number, and port type, etc., and define these property and drag it to the configuration workspace.

(2) Real-time simulation system hardware port configuration. Select the port corresponding to the hardware port of the brake-by-wire system from the existing hardware resources of the real-time system, drag it to the configuration workspace, and then configure the properties of the port, such as port number, description, potential, and fault injection. Then, according to the attribute number, use the external wiring harness to connect the brake-by-wire system controller with the real-time simulation system. So far, the connection between the brake-by-wire system and the real-time simulation system is completed.

(3) Configuration of the model interface, right click on the hardware port of the real-time simulation system to generate the corresponding model interface, which is a bridge for the interaction between the test model and the real-time simulation system, through which the test model can realize the control of the real-time simulation system .

When the test model and I/O interface configuration are completed, use the Configuration Desk software to compile the entire project, and generate the corresponding SDF file after the compilation is completed.

3.3-Test implementation

The hardware-in-the-loop test of the brake-by-wire system is implemented in the ControlDesk software. Open the ControlDesk software , import the compiled test environment model SDF file described in 2.1.2 of this article and run the model, and use the software to The dynamic system simulates sending control information. Feedback information from the brake-by-wire system can also be displayed in the ControlDesk software.

(1) Brake-by-wire system hardware input signal test: Take the brake pedal stroke input test as an example, find the brake pedal model port configured in 2.1.2 in the ControlDesk software, drag it to the test interface and Associate the relevant plug-ins, and then control the real-time simulation system to simulate and output a brake pedal stroke to the controller of the brake-by-wire system by changing the value of the variable, and then observe the execution results of the brake-by-wire system, which realizes the test of the system hardware input signal .

(2) CAN network input signal test of the brake-by-wire system: Take the analog VCU to send the CAN message signal test of "maximum electric braking allowed by the motor" to the brake-by-wire system as an example, find the BusSystems module VCU "motor Allow the maximum electric braking" signal, drag it to the test interface to associate with the relevant plug-ins, and then change the value of this variable to control the real-time simulation system to output the "motor maximum electric braking" CAN message signal to the wire-controlled brake system, and then observe the execution results of the brake-by-wire system, that is, the test of the input signal of the CAN network of the system is realized.

As for the feedback information of the brake-by-wire system, you only need to find the variable that needs to be observed in the model, and drag it to the test interface to observe the change of the variable. For the test result processing, the feedback obtained from the test can be analyzed according to the prediction result of the VCU test case, combined with the recorded CAN signal data and hard-wire signal data, if the control logic of the brake-by-wire system is satisfied, the test will be passed. Otherwise, it will not pass.

As automobiles develop towards electrification and intelligence, there will be more and more electronic components in automobiles, and the requirements for test accuracy, coverage, and test cycle will also become higher and higher. Therefore, it is necessary to develop hardware-in-the-loop testing. Based on the electric vehicle brake-by-wire system, this paper discusses its implementation process in the hardware-in-the-loop test. After the actual project verification, this method meets the test requirements such as test accuracy and test coverage of the electric vehicle brake-by-wire system, and shortens the project time. The development cycle reduces the actual vehicle verification time.