The hydraulic system of construction machinery mainly includes hydraulic pumps, torque converters, control valves, hydraulic motors and cylinders (actuators), transmissions, and power shift valves. Its faults generally manifest as weak, slow, vibrating, or overheating movements of the walking and actuating mechanisms, poor coupling of hydraulic clutches, and hydraulic pistons not extending or retracting properly. The causes of these faults are mainly due to failures in the hydraulic system or its components. Such failures often manifest as changes in pressure, flow rate, and temperature within the hydraulic system. The fault characteristics of construction machinery hydraulic systems have the following five features:

The so-called monitoring and diagnosis of faults in construction machinery's hydraulic systems involves using modern technological means and instruments to detect basic parameters such as temperature, pressure, flow rate within the hydraulic system as well as oil condition status (including speed noise leakage) for actuators like hydraulic motors and cylinders to comprehensively assess the operational state of the hydraulic system thereby inferring the working state and damage condition of its components.

Depending on different objects involved, there are mainly two types of monitoring and diagnosis technologies for faults in construction machinery's hydraulic systems: one is monitoring and diagnosing oil contamination; the other is monitoring and diagnosing the entire hydraulic system itself. During operation processes within these systems localized oil leaks can occur leading to partial oil contamination which affects operational efficiency even causing faults. Monitoring oil contamination can help diagnose such issues.

The realization of different functions within a construction machinery's hydraulic system requires multiple components to work together; if one or more components fail during operation it will inevitably affect overall performance. By employing fault monitoring and diagnosis technologies on these devices it becomes possible to promptly identify existing issues within a construction machine's hydraulics ensuring reliable operation.

Once a fault occurs within a construction machine's hydraulics field staff can adopt several methods to locate fault points quickly resolving issues: First is observation method which is simplest where staff check parts through listening smelling touching seeing etc., distinguishing normal operational noise from faulty noise along with changes like odor vibration temperature color etc., allowing them to identify issues like deformation loosening leaking ruptures etc.

'Observation method' is simple reliable especially suitable when necessary tools or instruments are lacking at work sites; Second method involves diagnosis through operation adjustments when problems arise experienced personnel can compare equipment’s current state against normal operating conditions determining types locations of faults based on discrepancies observed during operations.

'This diagnostic approach can be performed under no load but requires high skill levels from personnel; Thirdly comparison or replacement inspection method comes into play when equipment fails without testing instruments professionals may compare two identical machines’ working states or replace suspected faulty components identifying problem areas directly though this method faces limitations due finding identical equipment disassembly difficulties etc.

(1) International Status

'Numerous foreign institutions represented by developed countries like those in Europe America have conducted extensive research into information technology intelligence applications for engineering machines already putting them into practice For instance Caterpillar Inc has installed GIS geographic information systems GPS global positioning systems GSM global mobile communication systems METS mining earthmoving transport systems across many pieces of heavy equipment METS consists mainly three parts CAES (Computer-Aided Earthmoving System) VMS (Vital Management System) CAESoffice (CAES proprietary office software) featuring radio communication device detection early warning diagnostics job management automation control capabilities.'

'Caterpillar developed F series G series loaders during1990s equipped with CMS (Computer Monitoring System) replacing their previous generation E series EMS (Electronic Monitoring System).'

'F series G series loaders come equipped with electronic computer systems capable simultaneously monitoring engine fuel levels water temperatures transmission temperatures hydraulics temperatures while also providing diagnostic functions offering three levels alarms.'

'Among them Cat992G loader’s electronic computer system monitors diagnoses various parameters sending data wirelessly back office for recording analysis Cat950G loader features Cat computer monitoring diagnostic providing guidance diagnostic software packages maintenance tools.'

'Cat994D loader installs VMS (Vital Management System) further enhancing its monitoring diagnostics capabilities displaying error messages causes LCD screens while also providing three-level alarm signals indicating engine hydraulics electrical electronic states.'

'Swedish Volvo company produces L series loaders also equipped Matris software based computer technology used monitor analyze engines hydraulics key operational states providing human-machine interaction automatic diagnostics displays.'

(2) Domestic Status

In comparison, the fault detection and diagnosis technology for construction machinery in our country is lagging behind. Since entering the 21st century, many domestic research institutions have increased their theoretical research and practical exploration on electronic monitoring, fault monitoring, and diagnosis of construction machinery. For example, He Lingsong and Yang Shuzi from Huazhong University of Science and Technology have summarized the current research status and key technical issues of internet-based remote diagnosis of equipment faults both domestically and internationally; Xing Songyin from Harbin Institute of Technology introduced the application of CSCW (Computer Supported Cooperative Work) in the field of fault monitoring and diagnosis for construction machinery from aspects such as development background, conceptual connotation, key technologies, application prospects, and development trends.

To improve the reliability of construction machinery, leading domestic design and manufacturing companies (such as LiuGong, XCMG, SANY Heavy Industry, etc.) have begun to attempt to develop electronic monitoring systems for construction machinery to monitor and record the operating status of construction machinery. These systems provide preliminary fault monitoring and diagnostic service functions based on computer and internet technology. Construction machinery equipped with this system can be monitored by experts from the manufacturer at any time as long as users activate the remote service system, regardless of where in the world it is located. They can also provide consultation services for diagnosing faulty machines.

The intelligent remote monitoring platform for construction machinery developed by SANY Heavy Industry based on GPS, GPRS (wireless communication technology), and GIS (geographic information technology) has been widely applied in products such as their positive flow hydraulic excavators, achieving performance indicators that meet international standards.

(1) Virtualization

With continuous advancements in computer technology, related software technologies and microelectronics are also being updated constantly. Virtual instrument technology has gradually been applied to various types of construction machinery as a new type of technology. This technology is flexible and open; users can make appropriate changes to software to realize new functions.

(2) High Precision

For hydraulic systems in construction machinery, signals are often nonlinear, abrupt, and transient. Therefore, traditional time-domain and frequency-domain analyses only apply to steady-state signals and cannot reveal fault information within them. This necessitates a method that can simultaneously represent both time-domain and frequency-domain signals. The continuous development of computer technology and big data technologies meets this requirement well while significantly improving signal processing resolution.

(3) State-based

Introducing sensor technology, computer technology, infrared temperature measurement technology, ultrasonic technology into the monitoring and diagnosis field of hydraulic systems in construction machinery can effectively solve tracking issues related to time-lagged flow signals generated by comprehensive carrier signals such as flow rate, pressure, noise when liquids pass through pipelines. This enables real-time online monitoring of dynamic parameters within hydraulic systems while avoiding issues related to 'disassembly inspections' on hydraulic systems in construction machinery; thus effectively resolving contradictions between 'insufficient maintenance' and 'over-maintenance'.

(4) Intelligentization

The application of artificial intelligence technologies such as knowledge engineering, expert systems, and artificial neural networks in the monitoring and diagnosis field for hydraulic systems in construction machinery can effectively address issues where fault diagnosis heavily relies on practical experience due to hidden faults within hydraulic systems that are diverse with complex causes.

(5) Networking

The structure of modern hydraulic systems for construction machinery is becoming increasingly complex with growing specialization; thus requiring equipment experts to intervene promptly during fault detection and diagnosis processes. Given that construction machinery has high mobility which often prevents manufacturers from dispatching experts quickly on-site to resolve issues; establishing an internet-based real-time online measurement & diagnostic system will become an inevitable choice for monitoring & diagnosing hydraulic systems in construction machinery.

This article is selected from "Engineering Machinery & Maintenance Magazine", Issue No.3 in 2017.

Author: Shen Chunxia