Automotive drive axle is one of the core components of the car, and its quality is related to the quality of the car and the safety of the whole vehicle. The vehicle drivetrain rotation endurance test system is mainly used to verify the durability and other properties of automotive drive axle components. This article introduces a new vehicle drivetrain rotation endurance test system, describes its system structure and analyzes the core control scheme.
The car drive axle bears complex loads during the driving process of the car, which must transmit both the torque in the system and the load of the car. The transaxle must have sufficient strength, stiffness and lifetime. Therefore, the transaxle assembly and its components must undergo rigorous testing. It is necessary to develop a high-performance, high-precision automotive drivetrain endurance test system.
At present, there are two main types of common transaxle fatigue endurance test benches, one is open type and the other is closed type. The closed test bench is divided into mechanical closed type and electric energy closed type. The open test bench has a simple structure and low technical content, but the input energy is all consumed by the loading device, which consumes great energy and has extremely high operating costs. The mechanical closed test bench seals the torque through the accompanying test pieces, etc., the energy only flows inside the system, basically does not consume externally, and the power of the motor is only to balance the friction loss generated during the operation of the system, which is very energy-saving. However, the structure of the mechanical closed test bench is more complex, the cost is high, and the load is difficult to change during operation, and the torque control is difficult. The electric energy closed test bench is not to recover electrical energy through the mechanical structure, but through the transmission system inside some motors are in the generator, some motors are in different states of the motor to achieve energy recovery, the speed torque of the motor can be adjusted by the electronic control system, the entire system takes into account both the simple cost of the open structure, but also the high efficiency of the mechanical closed structure, low energy consumption. The author has researched and developed a new type of power-blocked test system, and this paper analyzes its core technology.
Composition of the test bench
The test system is mainly composed of drive motor, drive end transmission, drive end test piece torque sensor, drive end test piece speed sensor, drive end bearing temperature sensor, load 1 drive motor, load 1 end transmission, load 1 end specimen torque sensor, load 1 end test device speed sensor, load 1 end bearing temperature sensor, load 2 drive motor, load 2 end transmission, load 2 end test piece torque sensor, load 2 end test device speed sensor, load 2 end bearing temperature sensor, Drive end transmission oil temperature control, load 1 transmission oil temperature control, load 2 transmission oil temperature control, specimen oil temperature control, electrical drive system, automation and acquisition control system, etc. The block diagram of the test bench structure is shown in Figure 1.
Figure 1 Block diagram of a drive train rotation endurance test bench
Control the network
The control network of the electronic control system includes two types of networks: etherCAT network and Modbusrtu network, as shown in Figure 2.
Figure 2 Control network diagram of a drive train rotation endurance test bench
EtherCAT is an open architecture, Ethernet-based fieldbus system with short Cycle Times and all program data handled by the slave controller's hardware. This feature, combined with EtherCAT's functional principles, makes EtherCAT a high-performance decentralized I/O system: program data exchange with a thousand decentralized digital inputs/outputs takes only 30ms, equivalent to transmitting 125B of data over 100Mbit/s Ethernet. Systems that read and write 100 servo axes can be updated at a rate of 10kHz, and the general update rate is about 1 to 30kHz. The EtherCAT network can meet the requirements of torque closed-loop control and system real-time control of the test system.
The equipment in the EtherCAT network mainly includes drive motor inverters, load 1 motor frequency converters, load 2 motor frequency converters, remote I/O stations, acquisition units and host computers. The host computer reads and writes the device data on the above network at high speed through the EtherCAT network to achieve real-time control, and completes the torque closed-loop control according to the torque data measured by the torque sensor and the set torque. The host computer is the core component of the whole system, completing real-time data display, real-time control, data recording, data analysis, historical data query, fault recording and lubrication system temperature control. The frequency converter is responsible for driving the servo motor for speed and torque control. The remote I/O station collects field I/O information, as well as vibration sensor data, and sends it to the host computer. The acquisition unit is specifically responsible for collecting torque data and speed data at the drive and load ends.
The Modbusrtu network includes a host computer, a drive reducer lubrication temperature controller, a load 1 reducer lubrication temperature controller, a load 2 reducer lubrication temperature controller, and a specimen lubrication temperature controller. The host computer directly controls the above four temperature controllers through the 485 network interface, completes the temperature setting and reads the real-time value of the temperature, the host computer in the network is the master station, and the four temperature controllers are used as slaves.
Drivetrain
When the test system is loaded, the drive motor is in the motor state, the load 1 and load 2 motors are in the generator state, and the DC part of the three frequency converters is connected together, so that the electrical energy generated by the motor of load 1 and load 2 flows to the DC busbar, and the drive motor inverter obtains the electrical energy. In this way, the electrical energy is closed. The electrical energy input of the whole system is mainly used to overcome the friction of mechanical devices such as bearings, and the consumption of some public and auxiliary systems, which greatly reduces energy consumption compared with open test benches.
There are two forms of transmission common DC. The first, as shown in Figure 3, uses three independent frequency converters, each of which is equipped with a DC lead accessory, and the DC parts of the three frequency converters are connected together by the DC lead out attachment. The second type, as shown in Figure 4, adopts a rectifier device and three inverter devices, and when the test system is running, the energy flows through the linear bus line inside the three inverters, and only the insufficient energy is obtained through the rectifier device. The first method is equivalent to three rectifiers in parallel, and there is no essential difference from the second method, but the first method occupies less space and the total cost will be relatively low. This article takes the first form.
Figure 3 Transmission diagram of a drive train rotation endurance test bench 1
Fig. 4 Transmission diagram of a rotary endurance test bench for a drive train 2
There are two main control methods for inverter control three-phase motors: vector control and direct torque control. Vector control theoretically solves the dynamic and static performance of AC motors, but in practice, the motor rotor flux is difficult to observe, and the vector rotation coordinate transformation is complex, resulting in lower actual performance than theory. Direct torque control directly adopts torque model and voltage type flux model, as well as voltage space vector PWM inverter, to achieve speed and flux bang control, which largely solves the problems encountered in space vector control. Direct torque control ensures that ac motor torque is the primary control element, not motor current, which guarantees extremely high torque accuracy, good repeatability and linearity, and very fast torque rise times. In this article, a frequency converter with direct torque control is used.
According to the actual process requirements, the selection of frequency converters is shown in Table 1, and the motor selection is shown in Table 2.
Table 1 Inverter selection
Table 2 Motor selection
Host computer
The host computer includes a real-time control system and a host computer monitoring system. The real-time control system mainly completes the real-time closed-loop control and rapid data acquisition of the controlled amount such as torque speed. The system adopts INTIME real-time system, the real-time system is different from the traditional hardware PLC, it is a software PLC, can make full use of the computer's powerful CPU processing power, to achieve hardware PLC difficult to achieve performance, greatly improve the closed-loop control speed and external IO device communication capabilities. The INTIME real-time system loads a real-time operating system while loading the Windows system, so that they share the same CPU and terminal hardware, but are otherwise independent of each other. Each operating system is encapsulated as a virtual machine that manages its own descriptor table and memory management. When a real-time activity must occur, the computer switches the context to that real-time system, and after the activity ends, the computer switches the context back to the WINDOWS operating system. In this way, INTIME and windows systems are independent of each other, switching only when necessary, and when WINDOWS crashes, INTIME is notified and can run independently, and the corresponding fault handler can be run.
The host computer monitoring system adopts Labview programming software development, data exchange through the interface and INTIME system, completes the test setting and obtains the test data, and the sequence logic control of the entire test. The software flow is shown in Figure 5.
Figure 5 Upper Monitoring Software Flowchart
epilogue
After application in the field, the control system is highly automated and stable, which can effectively check the durability of the drive axle components. However, the system also has some shortcomings, can not achieve remote monitoring, the need for on-site duty engineers on duty, the future can be through the mobile phone App system or other means to achieve remote monitoring unattended function.
Source: AI "Automotive Manufacturing"
Author: Su Quan in Lu Xiaozhou
Work unit: China Automotive Technology and Research Center Co., Ltd. / China Automobile Research Institute Automotive Industry Engineering (Tianjin) Co., Ltd
【Important Statement】This article is an original article and may not be reproduced without permission
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