This paper delves into the research of an intelligent tightening unit for diesel engine connecting rod bolts. It begins by highlighting the importance of proper connecting rod bolt tightening in diesel engine assembly and the drawbacks of traditional assembly methods. Then, it details the overall solution analysis and determination, including key technical points such as torque – angle control to ensure reliable tightening. The main structure, technical principles, and working processes of the tightening unit are described in depth, along with its three working modes. Additionally, the market prospects and application value of this unit are explored, demonstrating its significance in the manufacturing industry.
1. Introduction
Diesel engines play a crucial role in various industries, especially in transportation and power generation. The connecting rod assembly in a diesel engine is a vital moving part, and the quality of the connecting rod bolt tightening directly impacts the reliability and operational safety of the diesel engine. In the past, the 刻线把对法 (a traditional marking – alignment method) was commonly used in railway diesel engine production and maintenance. However, this method is labor – intensive, inefficient, and difficult to ensure the required precision of bolt elongation, as shown in Table 1.
Steps of Traditional Assembly Method | Description | Problems |
---|---|---|
Step 1 | Measure the elongation of a special process bolt in the assembly process bushing with a special dial gauge, and mark lines on the bolt and bushing when the elongation is 0.58 ± 0.02 | Complicated operation, high labor intensity |
Step 2 | Replace the process bolt with the bolt to be assembled, measure its elongation, and transfer the mark from the process bushing to the bolt | Difficulty in ensuring accurate elongation due to multiple transfer operations |
Step 3 | Install the process bolt in the connecting rod, measure its elongation, and transfer the mark to the connecting rod cover | |
Step 4 | Install the marked bolt in the connecting rod and align the marks | Low assembly efficiency |
With the development of modern control and measurement technologies, it is necessary to explore a new and more efficient assembly method. The intelligent tightening unit for diesel engine connecting rod bolts emerges as a solution to address these issues.
2. Overall Solution Analysis and Determination
2.1 Failure Analysis of Bolt Connections
Connecting rod bolts are often subjected to axial variable loads. Common failure forms include bolt rod breakage and thread damage. These failures usually occur because the pre – tightening force on the bolt decreases, causing relative sliding between the bolt and the connected parts. The working tension of the thread connection is related to the pre – tightening force. Therefore, controlling the pre – tightening force is the key to ensuring the reliability of the thread connection.
2.2 Relationship between Tightening Methods, Parameters, and Pre – Tightening Force
Using different tightening methods and calculating or detecting certain parameters during the tightening process can improve the reliability of bolt connections. The torque – controlled tightening tool is a new type of tool that can enhance the assembly process level. However, simply using torque to judge the tightness of the connection has limitations. Although torque is related to the clamping force, not all torque is converted into clamping force. There is a phenomenon called “false torque,” where the workpiece may not reach the expected clamping state even when the torque seems to be sufficient. This is actually a “false clamping force” situation. So, when discussing tightening problems, the starting point should be the clamping force rather than just the torque, as shown in Table 2.
Tightening Parameter | Relationship with Clamping Force | Limitations |
---|---|---|
Torque | Indirectly related. Torque is used to estimate clamping force in practice | Torque does not fully convert to clamping force, affected by friction and other factors |
Clamping Force | The direct factor determining the connection tightness | Difficult to measure directly in production |
2.3 Key Technical Solutions
In the development of the intelligent tightening unit for diesel engine connecting rod bolts, in addition to controlling and monitoring the tightening torque based on advanced micro – electronic technology, torque – angle control is adopted. This method can eliminate the influence of friction on tightening. By setting a torque value as the starting point and rotating a certain angle, the bolt generates a specific tensile force to clamp the workpiece. Since the controlled angle corresponds to the required bolt elongation deformation after tightening, it can effectively eliminate the influence of “false torque.” The control and monitoring of the starting and ending points of the torque – angle ensure the reliability of the tightening process.
3. Main Structure and Technical Principles of the Diesel Engine Connecting Rod Intelligent Tightening Unit
3.1 Main Structure
The intelligent tightening unit mainly consists of a frame, connecting rod mounting seats, a transverse moving frame, a longitudinal moving frame, a tightening motor, a multi – stage reducer, a two – stage gear transmission mechanism, a spline – driven lifting mechanism, a torque measurement system, an angle measurement system, a tightening control system, and a torque – angle self – calibration system, as shown in Figure 1.
[Insert Figure 1: Schematic Diagram of the Main Structure of the Intelligent Tightening Unit]
The frame is equipped with transverse moving guides, allowing the tightening head to move transversely and operate on four workstations on one side. After completing the operations on one – side workstations, the transverse moving frame can be rotated 180 degrees to operate on the other – side workstations. The transverse moving frame, longitudinal moving frame, and spline – driven lifting mechanism together form the tightening head.
3.2 Working Principle
The tightening unit uses a tightening motor as the power source. After passing through a multi – stage reducer, it obtains sufficient tightening torque. A torque sensor is installed at the output end of the motor to continuously detect the change in tightening torque, providing control parameters for tightening control. An angle sensor is installed at the input end of the two – stage gear transmission mechanism, which is mainly used to measure the elongation of the bolt and complete the entire tightening process.
3.3 Working Process
- First, install eight sets of connecting rods into the connecting rod mounting seats on both sides of the frame and lock them (four workstations on each side, a total of eight working positions).
- Move the tightening head to the right – hand end of the frame and rotate it 90 degrees. Press the power button on the control panel and select the torque – angle self – calibration mode. Align the tightening head with the calibration seat and press the tightening start button. The system will calibrate the torque and angle measurement systems.
- After calibration, rotate the tightening head 90 degrees back to its working position. Select the automatic tightening mode by pressing the tightening mode selection button. Move the tightening head to align it with the connecting rod bolt head, turn the sleeve lifting handle to engage the tightening sleeve with the bolt head, and press the tightening start button. The system will automatically complete the entire tightening process.
- After completing the assembly of one set of connecting rod bolts, move the tightening head to the second workstation and repeat the above process. After completing the tightening of the four workstations on one side of the frame, rotate the tightening head 180 degrees and continue to complete the tightening of the four workstations on the other side, thus finishing the tightening work of all eight workstations.
3.4 Tightening Control Process
The unit has three working modes:
- Self – calibration Mode: When in the self – calibration mode, the tightening machine calibrates the process bolt. During the calibration tightening process, the single – chip microcomputer continuously detects the tightening torque. At the same time, a displacement sensor installed on the head of the process bolt is used to detect the elongation of the bolt. When the displacement sensor value starts to increase from 0, the computer automatically records the critical torque value at this time, and the angle sensor starts to measure the angle the process bolt turns. When the displacement sensor reading reaches the expected value, the corresponding angle value is recorded as the relative standard for formally tightening the connecting rod bolts, ensuring the requirements for bolt elongation in the connecting rod assembly.
- Automatic Tightening Mode: In the automatic tightening mode, the tightening machine tightens the connecting rod bolts. The single – chip microcomputer continuously detects the tightening torque. When the torque reaches the critical value, the angle sensor starts to calculate. The tightening machine continues to tighten until the angle value reaches the predetermined value, and then stops tightening. The tightening machine then rotates in the reverse direction by a certain angle under the control of the single – chip microcomputer to disengage the tightening sleeve from the bolt head, completing the automatic tightening assembly work.
- Manual Tightening Mode: In the manual tightening mode, the tightening machine also tightens the connecting rod bolts. The single – chip microcomputer continuously detects the tightening torque. When the torque reaches the critical value, the tightening machine stops tightening. At this time, the operator presses the final – tightening button, and the tightening machine continues to tighten while the angle sensor starts to count. When the angle value reaches the predetermined value, the tightening machine stops tightening and rotates in the reverse direction to disengage the sleeve from the bolt head, completing the manual tightening assembly work. A comparison of these three modes is shown in Table 3.
Working Mode | Tightening Torque Detection | Angle Detection and Control | Operator Intervention |
---|---|---|---|
Self – calibration Mode | Continuously detect during calibration tightening of process bolt | Record critical torque and corresponding angle for calibration | None during calibration process |
Automatic Tightening Mode | Continuously detect, start angle detection when torque reaches critical value | Stop tightening when angle reaches predetermined value | Select mode and start/stop operations |
Manual Tightening Mode | Continuously detect, stop at critical torque and wait for operator to press final – tightening button | Start counting when operator presses final – tightening button, stop when angle reaches predetermined value | Press final – tightening button during tightening |
4. Market Prospects and Application Value
There are hundreds of power machinery factories, such as railway locomotives, automobiles, tractors, and engines, and thousands of parts factories in China. These factories require a large number of assembly tools and systems with different precisions to meet the technological requirements. Considering industries such as compressors, electrical appliances, and engineering installation, the market prospect of this intelligent tightening unit is very promising.
The series of products of this project can meet the requirements of most domestic enterprises due to long – term and systematic research in the field of threaded fasteners and their assembly technologies. It has extensive application value in industries such as railway locomotives, automobiles, and internal combustion engines, as shown in Table 4.
Industry | Application Significance |
---|---|
Railway Locomotives | Improve the reliability of diesel engine connecting rod assembly, ensuring the safe operation of locomotives |
Automobiles | Enhance the quality of engine assembly, improving the performance and durability of vehicles |
Internal Combustion Engines | Ensure the high – quality assembly of connecting rod bolts, promoting the overall development of the internal combustion engine industry |
5. Conclusion
The intelligent tightening unit for diesel engine connecting rod bolts represents a significant improvement over traditional assembly methods. By adopting advanced technologies such as torque – angle control, it can ensure the reliability of bolt connections, improve assembly efficiency, and reduce labor intensity. With broad market prospects and high application value, this unit has the potential to revolutionize the assembly process in relevant industries. Future research can focus on further optimizing the structure and control algorithms of the tightening unit to improve its performance and adaptability to different working conditions.