The hydraulic cylinder is the executive element of the hydraulic system, which can convert hydraulic energy into mechanical energy of linear reciprocating motion. Because of its simple structure and reliable work, it has been widely used in mechanical systems. At present, there are many manufacturers of hydraulic cylinders. On the one hand, the performance and quality of hydraulic cylinders must meet the requirements of the main engine, and at the same time, they must meet the standard indicators of the hydraulic cylinder itself. According to the GB/T15622-2005 and JB/T10205-2010 standards, the hydraulic cylinder performance test bench has been developed.
1 The composition and working principle of the test bench
The test bench is composed of four parts: bench, hydraulic system, electrical system, and measurement and control software.
1. 1 Bench structure design
In order to meet the requirements of wide loading amplitude and large length variation of the tested hydraulic cylinder, the test platform is equipped with two test benches with the same structure and different parameters. The main technical parameters are shown in Table 1.
The loading hydraulic cylinder and the tested hydraulic cylinder are on the same axis and are fixed inside the closed loading frame. As shown in Figure 2, the closed loading frame consists of a reaction support, a stand, a reaction rod, a reaction rod bracket, and a lock. Composed of tight nuts. During the loading test of the test bench, the loading hydraulic cylinder transmits the force to the tested hydraulic cylinder through the transition piece assembly. The guide rail assembly bears the lateral force caused by the installation error, and at the same time plays a guiding role. The transition piece assembly (where a force sensor is installed to measure the force between the tested hydraulic cylinder and the loading hydraulic cylinder) slides along the axial direction under the constraint of the guide rail to transmit force. The closed loading frame converts the force between the hydraulic cylinders into the internal force of the system. Hydraulic cylinders of different lengths can be tested by adjusting the length of the transition piece; hydraulic cylinders of different interface types can be connected by changing the tooling of the test piece.
1. 2 Hydraulic system
The hydraulic system is mainly composed of large-diameter cartridge valves, electro-hydraulic directional valves and proportional valves. Through the precise adjustable performance of the proportional valve, the flow and pressure of the hydraulic cylinder test bench can be easily and accurately controlled to test different types of hydraulic cylinders. The hydraulic schematic diagram is shown in Figure 3.
The loading hydraulic cylinder and the tested hydraulic cylinder are on the same axis and are fixed inside the closed loading frame. As shown in Figure 2, the closed loading frame consists of a reaction support, a stand, a reaction rod, a reaction rod bracket, and a lock. Composed of tight nuts. During the loading test of the test bench, the loading hydraulic cylinder transmits the force to the tested hydraulic cylinder through the transition piece assembly. The guide rail assembly bears the lateral force caused by the installation error, and at the same time plays a guiding role. The transition piece assembly (where a force sensor is installed to measure the force between the tested hydraulic cylinder and the loading hydraulic cylinder) slides along the axial direction under the constraint of the guide rail to transmit force. The closed loading frame converts the force between the hydraulic cylinders into the internal force of the system. Hydraulic cylinders of different lengths can be tested by adjusting the length of the transition piece; hydraulic cylinders of different interface types can be connected by changing the tooling of the test piece.
1. 2 Hydraulic system
The hydraulic system is mainly composed of large-diameter cartridge valves, electro-hydraulic directional valves and proportional valves. Through the precise adjustable performance of the proportional valve, the flow and pressure of the hydraulic cylinder test bench can be easily and accurately controlled to test different types of hydraulic cylinders. The hydraulic schematic diagram is shown in Figure 3.
The pressure and flow into the tested cylinder are adjusted by the proportional flow valve and the proportional relief valve, and the extension and retraction of the tested cylinder are controlled by the electro-hydraulic directional valve. The loading cylinder is loaded by a bridge circuit and a cartridge proportional relief valve. The tested cylinder and the loading cylinder are connected by a sliding trolley, and a force sensor is installed on the trolley to measure the force between the two cylinders during the test.
In order to accurately measure the minimum starting pressure of the tested cylinder, a bypass is deliberately added to the tested cylinder circuit. In a small flow state, the test pressure is controlled by a more accurate proportional relief valve and pressure sensor to achieve the purpose of accurate measurement. In addition, the test bench adds an ultra-high pressure test circuit for the pressure test, which can withstand a pressure of 55 MPa. The test bench is equipped with an oil leakage recovery device. The oil leakage generated during the hydraulic cylinder test and disassembly process is collected through the oil pan. The recovered oil is sent back to the oil tank of the hydraulic source through the gear pump motor unit and the filter. It not only reduces the waste of hydraulic oil, but also prevents the oil from causing pollution to the test environment.
1. 3 electrical system
The electrical system of the hydraulic cylinder test bench mainly includes a task management computer, a measurement and control computer, a signal conditioning box, and a UPS power supply part.
The task management computer transmits the input instructions and parameters of the operator to the measurement and control computer; the measurement and control part controls the movement of the tested cylinder and the loading of the loading cylinder according to the input instructions and parameters, collects the input signals of the sensors and sends them to the task management computer for Display and output test report. Signal conditioning box The digital signal conditioning box and the analog signal conditioning box are used to adjust the signal of each sensor into a standard signal and input it into the measurement and control computer, and adjust the output of the measurement and control computer into a signal that can be received by an electro-hydraulic proportional valve and an electromagnetic reversing valve; UPS The power supply part is responsible for the power supply of task management computer, measurement and control computer and signal conditioning box.
The hydraulic cylinder measurement and control system and the central control room computer adopt Ethernet communication, and the central control room computer can remotely monitor and control the test bench control system.
The hydraulic cylinder measurement and control system and the oil source PLC use RS485 communication to collect PLC output signals to understand the operation and status of the oil source, and the oil source can be remotely started, loaded, and stopped.
1. 4 measurement and control software
The measurement and control software is written by LabVIEW software. Through the various controls provided in LabVIEW software, the control software is written according to the test process and data acquisition requirements of the hydraulic cylinder test bench.
Hydraulic cylinder test test system software interface
The software interface is mainly composed of several parts: test bench status monitoring, tested cylinder information, real-time display of test data, manual control, curve display and automatic control item tab bar. The software can realize two control modes of manual test and project automatic test. The data meters in the interface simulate and display the current test data and the state of the hydraulic system. Real-time recording of relevant data in the test process through data recording, and supports automatic generation of test reports.
2 Analysis and optimization design of the platform structure
The closed loading frame is a key component of the testing machine, which consists of a reaction rod, a lock nut, a reaction support and a bench. The hydraulic cylinder is fixed between the reaction rod and the bench. During the loading test, the closed loading frame converts the force between the hydraulic cylinders into the internal force of the system, and the overall coordinated deformation makes the test bench low requirements for the laboratory foundation strength. In order to ensure that the system has sufficient strength and rigidity, finite element analysis and optimized design are carried out. The results of the finite element analysis are shown in Figs. 5-7. The maximum stress is 67 MPa, the maximum deformation in the Y direction is 1.15 mm, and the maximum deformation in the Z direction is 0.05 mm.
3 Features of the test bench
(1) The test bench has strong adaptability. The load capacity is large, and the length of the test piece can be adapted to a wide range. By changing the connection interface of different forms, the test bench can adapt to the test piece of different connection forms.
(2) It has a unique rigid closed frame, which can convert the force between the hydraulic cylinders into the internal force of the system, which reduces the force between the test bench and the foundation, and has low requirements for the strength of the laboratory foundation.
(3) The cartridge valve and electro-hydraulic valve are used as the main components of the system, which can carry out large flow tests.
(4) A proportional pressure valve is used to control the test pressure, and a proportional flow valve and pressure sensor are used to control the flow at the side without a separate oil source.
(5) With ultra-high pressure circuit, the two-cavity pressure test of the hydraulic cylinder can be completed in one installation.
(6) It is equipped with a leaking oil recovery device, which can recover the hydraulic oil that leaked during the disassembly and assembly of the tested cylinder, and return it to the hydraulic source tank after filtering.
(7) The measurement and control cabinet adopts modularization and is divided into 4 modules: task management computer, measurement and control computer, signal conditioning box, and UPS power supply.
(8) The software interface is intuitive and easy to operate, and it is convenient to switch manually and automatically. The software has powerful functions, which can realize various tasks such as data collection and processing, eliminating the need for experimenters to collect and processing data, and improve efficiency and accuracy. The software is writeable, and test functions can be added according to actual test needs. The test report can be generated automatically.
4 Conclusion
The hydraulic cylinder performance test bench developed can test hydraulic cylinders in accordance with GB/T1562-2005, and can test most hydraulic cylinders (maximum output 2800kN, maximum stroke 6000mm) used on construction machinery with different tooling. The successful development of the hydraulic cylinder performance test bench has three implications:
(1) In terms of new product development and basic research on hydraulic cylinders, testing can verify whether the technical performance of hydraulic cylinders meet the expected design goals. Through the analysis of the test data and curves, it can be judged whether the structure of the hydraulic cylinder is reasonable and the material used is the best, so as to solve the problems of the hydraulic cylinder in design, processing, and materials; help analyze the optimal working range of the hydraulic cylinder to facilitate Determine the reasonable working conditions of the hydraulic cylinder and extend the service life of the hydraulic cylinder.
(2) When manufacturing companies perform quality control on batches of products, they will verify the quality stability and reliability of products through regular and random sampling tests, eliminate potential problems, ensure product quality, and increase users’ trust in products, which will help develop and stable
Solid market.
(3) Solve the problem of differences in product performance and quality between hydraulic cylinder manufacturers and users.