Abstract : The transmission is a key component in an automotive system. Achieving online comprehensive performance testing of the transmission on a single test bench is unprecedented in China. This paper introduces a novel test bench system that enables online comprehensive performance testing of transmissions. The system architecture and working principle are described, and the development and implementation of its control software are detailed. Keywords : Transmission; Test bench; System architecture; Control software The automotive transmission is a key component in a vehicle, and its performance directly affects the vehicle's power, economy, and reliability. Testing the comprehensive performance of automotive transmissions is complex. Currently, domestic automotive transmission test benches have low automation levels, unfriendly interfaces, and rely heavily on the tester's experience. Therefore, this test bench system boasts high automation, numerous test items, strong real-time performance, and complete reliability. I. System Introduction Specifically, this test bench system has the following advantages: it can perform performance tests on five different types of transmissions and their extended types; the automatic testing process can be intelligently controlled; comprehensive performance (shifting, loading, synchronizer) tests can be completed in a short time; operating parameters can be displayed in real time; and it can automatically detect, alarm, and handle faults. 1. System Hardware Introduction: This system uses dual-frequency inverter motors to simulate the working conditions of an automotive transmission, thereby achieving realistic testing of transmission performance. Motor control is achieved through Siemens 6SE70 series frequency converters. These frequency converters employ AC vector control technology, enabling precise control of high-power AC motors. Because the number of frequency converters and data transmission volume in this system are relatively small, an RS485 bus is used to achieve communication between the industrial computer and the frequency converters, meeting real-time requirements. Due to the stability and reliability of PLC control, the automatic gear shifting actuator (robotic arm) uses a PLC controller to implement automatic gear shifting actions for different transmission models. 2. System Software Development Environment: Industrial process control software often requires strong communication capabilities, real-time monitoring of field data, a powerful database, and a user-friendly graphical interface. KingSCADA 6.01 adopts a brand-new Chinese Explorer interface and possesses rich drawing tools and a large graphics library (including a large number of industrial standard components). It supports multimedia and ODBC database functions, has powerful controls and control languages, and is flexible and convenient to use, providing users with a convenient integrated development environment that allows developers to quickly construct application systems. It also has strong communication capabilities and good openness. The system control software is based on KingSCADA 6.01 secondary development, realizing the control of the testing process and the real-time display of test data, and shortening the development time. II. System Architecture 1. System Requirements The manufacturer requires the test bench system to be able to test the comprehensive performance of the transmission online, including the following tests: ① Gear shifting test; ② Transmission loading capacity test; ③ Transmission handling (synchronizer) performance test; ④ Gear skipping detection; ⑤ Transmission fatigue life test; ⑥ Transmission efficiency test. The working performance requirements are: (1) The system operates stably, safely and reliably; (2) The test data report and the interface for testing and fault diagnosis are user-friendly; (3) The bench test method is standardized and meets the national standard for bench test methods of automotive mechanical transmissions; (4) The test function can be completed on the same bench for different types of transmissions. 2. System Architecture The overall system structure is shown in Figure 1. The system is divided into three main modules: ① Control part; ② Gear shifting manipulator part; ③ Test bench electromechanical part. The control unit is computer-centric. The control software controls the system's flow, task allocation, command transmission, and fault detection based on field data and current operating status. It sends shift control commands to the PLC robot via board communication and transmits the required speed and load torque signals to the inverter via an RS485 bus. The control unit also includes an inverter, a field data acquisition card (PCL818L), and a PLC controller. The inverter enables stepless speed regulation of a three-phase AC asynchronous motor. A Siemens 6SE70 series inverter is selected, which uses vector control technology for AC motors. Vector control, also known as field-oriented control, uses a dq rotating coordinate transformation to divide the stator current into an excitation current id1 and a torque current iq1. During speed regulation, the rotor flux linkage remains constant, i.e., id1 is constant. In this case, the speed regulation principle of the AC motor is the same as that of the DC motor. The field data acquisition card transmits the data collected from the field to the computer. The PLC controller converts the shift signals into execution commands for the robot based on the instructions sent by the computer. The gear-shifting robotic arm is the actuator of the control unit. It performs precise gear shifts based on shift commands sent by the PLD. The electromechanical part of the test bench is the final actuator of the system, driving the transmission to the corresponding speed and applied torque to achieve specific test conditions. The mechanical part includes two high-power variable frequency motors and the test bench. The performance of the motors in this system has a significant impact on the overall performance; therefore, AC variable frequency motors were selected. These motors can meet the requirements of high-precision torque and speed control, and their power is sufficient to meet the test conditions of this system. During operation, the loading motor operates in generator mode, feeding energy back to the grid, significantly saving energy. The test bench includes a clutch, transmission mechanism, and automotive transmission. Because high speed and high torque are required during testing, the mechanical part must have high precision. The automotive transmission is the test object of this system. To minimize the time required for loading and unloading the transmission, the clamping and releasing operation of the transmission on this test bench is achieved through a four-axis hydraulic cylinder linkage pressure plate. 3. System Working Principle The system employs a dual-motor system to simulate automotive operating conditions. The drive motor uses a frequency converter's speed closed-loop control to simulate the car's drive mechanism, while the loading motor uses a frequency converter's torque closed-loop control to simulate the car's loading. The robotic arm, following instructions from the computer, performs gear shifting actions on different types of transmissions, thus controlling the transmission to shift to designated gears. During testing, the control software records and displays the system's operating parameters in real time, and monitors temperature, speed, torque, current, and full cover positioning signals in real time. It automatically alarms and analyzes faults. III. System Software Development and Implementation The system's control software is based on a secondary development of KingSCADA 6.01, and its functional structure is shown in Figure 2. Functionally, the system completes automatic testing, manual testing, individual gear shifting testing, fatigue testing, and efficiency testing. Computer-controlled automatic testing is the main part of the system. In this mode, the computer controls the transmission testing process, including: test flow, gear shifting sequence during the test, speed setting for each gear, loading torque setting, system coordination, signal detection and processing, etc. Under automatic test control, the shifting and loading alternation process from neutral to the highest gear is completed, followed by downshifting from the highest gear to the lowest gear, and finally the reverse gear test. Manual testing is performed by manually operating the knobs on the control panel; its program mainly performs monitoring and alarm functions. Individual gear shifting is performed on a specific gear as required by the manufacturer. Fatigue testing and efficiency testing respectively test the durability and transmission efficiency of the transmission. KingSCADA 6.01 has a rich screen creation system, supporting unlimited colors and twenty-four filter colors, and has a rich image library and image wizards, as well as rich animation connection wizards. Using the KingSCADA 6.01 interface development system, vivid interfaces can be developed for various control modes, which are very intuitive and aesthetically pleasing. Since the automatic testing process is the key to this software system, only automatic testing will be discussed below. 1. Interface Communication Parameters: Communication between KingSCADA and I/O devices is very convenient, mainly through the following methods: serial communication, DDE, board communication, network node communication, and human-machine interface communication. KingSCADA has a rich variety of data types and is very convenient to use. The interface communication parameters are shown in Figure 3. The computer sends corresponding control commands to the PLC and the frequency converter according to the task planning status by detecting the field data. The field data includes: the current gear position of the transmission, speed, torque, the shifting force measured by the tension and pressure sensor, clutch switch signal, transmission clamping signal, bearing temperature, etc. Among them, the communication with the PLC uses the KingSCADA board communication method, the communication between KingSCADA and the frequency converter uses the KingSCADA serial communication method, and the communication between KingSCADA and the field data is realized through the PCL818L expansion board. The field data is used to detect whether the working status is in place and to detect fault alarms, such as whether the robot arm has shifted to the correct gear, which is determined by whether the speed ratio collected on site is consistent with the speed ratio in the formula, while the temperature, speed and other indicators are the basis for fault alarms. 2. Implementation of automatic shifting process (1) Automatic shifting process flowchart The automatic shifting process flowchart is shown in Figure 4. The automatic shifting process needs to complete the actions of releasing the clutch, shifting gears, closing the clutch, and timed loading, as well as the automatic shifting of gears. Since the release of the clutch, shifting gears, and closing the clutch all work while the motor is running, each action command must first check whether its conditions are strictly met to ensure safety. The conditions for the clutch to be released are: the motor speed must be within the preset range; the conditions for shifting gears are: the clutch must be detected to be released; the conditions for the clutch to be closed are: the gear shift is in place. If the conditions are not met, wait for the conditions to be met, but the waiting time is also limited, so a timer is used to control the waiting time of the sequential actions. When the gear is in place, the test parameters of that gear are loaded, and the loading capacity of the transmission can be measured after a period of loading, so the loading timing is also done using a timer. After the loading timing is completed, the next gear test will be carried out, and the shift preparation process will be entered in the program. During the shift preparation process, the current gear flag is replaced with the flag of the next test gear, and the gear parameters (gear ratio, gear, loading torque, loading speed) are changed to the parameters of the next test gear. (2) Automatic gear shifting process is implemented based on KingSCADA programming. The KingSCADA event command language can specify the program to be executed when the event occurs, exists, and disappears. Discrete variable names or expressions can all serve as events. When an event has just occurred, the program in that unit executes only once; while the event exists, the program in that unit executes repeatedly at set time intervals; when the event disappears, the program in that unit executes only once. The loop execution of the program when the event command language exists is similar to, but not entirely the same as, a while loop in a normal program. The event command language can control and adjust the system's loop execution time under the condition that an event exists, thus facilitating timing operations in process control. The event command language can fulfill the if and while conditions of a normal program, and also achieve timing functions. Moreover, many industrial control processes use discrete state changes to trigger program flows. The KingSCADA command language is well-suited for developing such processes. The automatic gear shifting process establishes multiple working states: "Gear Shift Preparation," "Gear Shift Start," "Gear Shift Successful," "Loading," "Running," "Test Completed," etc. These working states and the field data detected by the computer are combined to form different events, and the logical relationships of mutual triggering and transformation between these different events are used to realize the logical relationships of the automatic gear shifting process. Here, the timing function of the loop execution when an event exists in the KingSCADA event command language is used. When the program enters the timer state, a counter is used for countdown. When an event occurs, other programs in the command language are in a non-activated state. In this state, the timer's timing T (T=n×t) can be set by setting the initial counter value n and the time t for one cycle execution when the event command language occurs. KingSCADA also has a recipe function. In the manufacturing field, a recipe describes the proportional relationship between different ingredients used to produce a product, representing a set of parameter settings corresponding to some variables in the production process. The data structure type of test parameters (speed, loaded torque, etc.) for different models of transmissions and different gears is consistent, only the proportional relationship differs, thus the recipe function is convenient for proportionalization. This software system has networking capabilities, allowing remote monitoring of the on-site working status and integration into the enterprise's CIMS system. This test bench system integrates knowledge from computer science, communication, automation, electronics, electrical engineering, and mechanics, and is an intelligent online mechatronics testing system for comprehensive transmission performance testing. It features a high degree of automation, shortened testing time, significantly reduced operating costs, and improved production efficiency. The brake motor uses regenerative braking, saving energy. The system control method is precise, and the detection sensors have high accuracy, achieving a very high precision. The powerful communication and process control capabilities of KingSCADA have reduced the development time of control programs. The test bench has passed factory acceptance and will soon be put into production, where it will be widely adopted.