Technical Status and Development Trends of Wheel Excavators

Wheel excavators are excavation machinery that use tires as walking components, abbreviated as wheel excavators. The wheel excavator has fast walking speed and does not damage the road surface. It can switch fields remotely and quickly replace various operating devices. The maximum walking speed of foreign wheel excavators is mostly 25-40 km/h, while domestic ones are mostly 20-35 km/h, The high-speed wheel excavator JYL200G produced by Guizhou Zhanyang Power has a walking speed of even 51 km/h The walking speed of walking excavation is only 3-5 km/h. The comparison between wheel excavation and walking excavation of the same level is shown in Table 1. Although the efficiency of wheel excavation is not as high as that of walking excavation of the same level, compared with the expensive transfer fee of walking excavation, wheel excavation has more economic advantages when frequently transitioning. It is precisely because of its distinctive characteristics of mobility, flexibility, and high efficiency that wheel excavation has been widely used in material excavation and moving in municipal maintenance engineering, highway transportation construction, and rapid repair.

According to statistics, in developed Western countries, the demand for rotary excavation accounts for over 12% of the total demand for excavators, with some even reaching 70-80%, making it widely used. However, the proportion of wheel excavation in China is only about 3%, so from a global perspective, the application of wheel excavation in China needs to be explored. It can be said that in the next few years, the continued expansion of domestic demand, the expansion of infrastructure development strategies, and the overall environment of urban and small town construction development strategies have determined the broad prospects of China's rotating mining market.

There are many foreign rotary excavation production enterprises with complete varieties, such as Hitachi, Komatsu, Liebherr, Caterpillar, Volvo, JCB, Hyundai, etc. These companies' products basically reflect the highest level of technological development in wheel excavators in the world today, and many well-known companies have their proprietary key technologies and components. However, domestically produced rotary excavators have less selectivity in terms of brand and variety, which is in stark contrast to the phenomenon of "hundred schools of thought contending" abroad. In recent years, although domestic wheel excavators have made certain progress in terms of production, variety, and technical level, for example, the high-speed wheel excavators developed and produced by Zhanyang Power Heavy Industry have filled the domestic gap and achieved significant breakthroughs in driving speed

Even slightly higher than similar foreign models, the development scale is still very small, and the technical performance and working reliability cannot meet the needs of the domestic market, seriously lacking key technologies. In short, there is a significant difference between domestic rotary excavation and foreign ones, and its development still has a long way to go.

Current Situation of Wheel Excavation Technology Abroad

There are many foreign enterprises producing rotary excavators and their product series are complete. The main enterprises and products of foreign wheel excavation are shown in Table 2. These companies' products basically reflect the highest level of world wheel excavation technology development, and many of them have their own key technologies and components with independent intellectual property rights.

The technical characteristics of foreign wheel excavation mainly include the following:

(1) Hydraulic systems often use load sensing systems or negative control systems. For example, Komatsu's closed center hydraulic system (CLSS) with load sensing and pressure compensation valves, Bosch Rexroth's load independent flow distribution system (LUDV), Linde's load sensing synchronous control system (LSC) and other hydraulic systems with basically the same structure, principle and function have been well applied.

Caterpillar, Liebherr, Volvo, Doosan, JCB and other companies have also adopted load sensing systems. The advantages of load sensing system in hydraulic excavators are obvious, as it can achieve fast and accurate control of multiple executing components with different load pressures simultaneously, and each executing component does not interfere with each other [5]. The negative control technology has the characteristics of good stability, fast response, good reliability and maintainability, but when the starting point is heavy load operation, the flow is related to the load, so the Controllability is poor. Due to mature manufacturing technology and low prices, negative control systems will continue to function, especially in developing countries.

(2) Foreign brands often use independently developed electronic energy-saving and microcomputer control technologies for wheel excavation. JCB's AMS control system balances simple operation with achieving maximum efficiency under various working conditions. The system is designed with several power modes, which can automatically sense and respond to hydraulic requirements according to the movement and usage requirements of the joystick, match engine power with hydraulic power, and activate power boost and automatic engine idle function as needed. The unique new generation electronic power optimization system (e-EPOS) from Doosan, South Korea, is designed to operate in two digging and trenching modes for ease of operation; Liebherr wheel digging adopts all electronic control, and the proprietary technology of LSC electronic limit load adjustment has the functions of pressure compensation and flow compensation to enhance the selection of various working modes such as power gear, high power gear, economic gear, fine gear and ultra precision control switch; LCD display, sound and light alarm, sensor control of engine idle speed without load. These control systems basically have multiple power (working) mode options, instantaneous power increase function, automatic engine idling, automatic engine preheating and overheating protection, real-time electronic monitoring and self-diagnosis functions, thereby improving the production efficiency of excavators, reducing fuel consumption, improving the driver's working environment, and enhancing the automation level of the machine.

(3) Safe, comfortable, and reliable cab. Adopting a cab with a Falling Object Protection Knot (FOPS) and a Rollover Protection Structure (ROPS), installing adjustable elastic seats, and using sound insulation measures to reduce noise interference. For example, McLark adopts ROPS and FOPS cab, Volvo adopts original RPOS

Care cab. The driver's cabin will gradually implement the design methods of ROPS and FOPS, and be equipped with cold and warm air conditioning. A fully sealed and noise reducing "safe and environmentally friendly" cab, with an ergonomically designed driver's seat that can be adjusted in all directions, as well as an integrated joystick, fully automatic gear shifting device, and electronic monitoring and fault diagnosis system, to improve the driver's working environment and improve work efficiency.

(4) Energy conservation and environmental protection. In order to improve the energy-saving effect of products and meet increasingly stringent environmental requirements, foreign wheel excavation enterprises mainly focus on reducing engine emissions, improving hydraulic system efficiency, vibration reduction, noise reduction, and other aspects. The development of foreign engineering machinery diesel engines has reached the level of fully electronic control, using direct injection technology to control the injection amount and injection time of diesel, eliminating traditional mechanical governors and timing gears, and simplifying the structure of diesel engines. At present, manufacturers such as Carter and Komatsu have developed electronic controlled diesel engines around the world. Their characteristic curves can be determined by software, and different characteristics are adopted for different operating conditions to achieve optimal economic, emission, and power performance of the diesel engine. The ZX130W wheeled excavator launched by Hitachi Construction Machinery is equipped with engines that comply with Euro II and Tier II emission standards, and adopts ultra-low noise silencers and other measures to reduce engine noise.

(5) Multifunctionality. Wheel excavation is increasingly inclined towards versatility. In addition to excavation and lifting functions, there are also hydraulic hammers, pliers, scissors, compactors, drilling machines, milling heads, etc., which can be replaced with different working devices according to the working conditions. The use of these supporting devices can reduce costs, reduce manual labor, and improve productivity. Correspondingly, the excavator is equipped with a quick replacement system, which can automatically and quickly replace various devices under normal hydraulic system pressure without leaving the driver's cab. For example, Liebherr's Likufix2 System, which includes a set of combined hydraulic quick assembly device and an automatic conversion coupling device, with which the operator can complete the conversion of the mechanical and hydraulic parts of the tooling in a few seconds; Mcclark is a self-locking clamp quick change device for remote automatic switching.

From the above points, it can be seen that foreign enterprises have conducted extensive research in engine fuel combustion and electronic control, hydraulic control systems, automatic operation, improvement of cab conditions, fault diagnosis and monitoring, energy conservation and environmental protection, and developed many new structures and products, which have increased the high-tech content of wheel excavators and promoted their development

Exhibition.

Current status of domestic wheel excavation technology

There are two main types of domestically produced wheel excavators. One is a 360 ° rotation wheel excavator, which uses a dedicated chassis; The other type is an economical and applicable wheel excavator that can only have a 180 ° angle, mostly modified from small agricultural tractors. At present, the main domestic 360 ° rotary wheel excavators and their products are shown in Table 3 (a). These companies' products basically reflect the highest development level of domestic wheel excavators technology, such as the high-speed wheel excavators developed by Guizhou Zhanyang Power Heavy Industry using our factory's matching kit and unique three section folding arm working device, and the 130W type wheel excavators of Shanhe Intelligent.

Domestic component companies have made technological breakthroughs in working cylinders, slewing bearings, cabs, seats, electrical instruments, and other aspects, and can basically replace imported products. However, there is still room for improvement in craftsmanship and reliability.

The key technologies such as pumps, valves, and motors in engines, electronic control systems, and hydraulic systems are basically mastered by developed countries such as Japan and Germany, so the key technologies and components of domestically produced wheel excavators still need to rely on imports. The comprehensive performance indicators of domestic diesel engines can not meet the needs, so domestic wheel excavators mostly use Cummins, Yangma, Deutz AG, Isuzu, Perkins and other foreign brands; In terms of hydraulic systems and components, domestic enterprises generally do not have the ability to produce various energy-saving multi way valves and hydraulic pumps. Therefore, hydraulic systems are generally sourced from foreign enterprises, mainly including Rexroth in Germany, L Inde in Germany, NACH I and KYB in Japan, Comer in Italy, etc. Walking motors, pumps, and rotary motors are mostly sourced from Germany, South Korea, Japan, etc., while drive axles are mostly sourced from ZF bridges in Germany or DANA bridges in Italy. For example: (1) Shanhe Intelligent Wheel Digging 130W adopts Cummins water-cooled diesel engine, Rexroth's LUDV closed center system [13]; (2) XCG140W28 from Xuzhou Xuzhou uses an ISUZU diesel engine, Rexroth's LUDV, and an Italian DANA company's wheel excavation dedicated bridge.

The other type is the economical and applicable wheel excavator that can only have a 180 ° angle, which is a modification of the excavation working device on the basis of agricultural four-wheel tractors. Its technical content is low, performance is unstable, and reliability is poor. The main enterprises and product models for domestically produced economical and applicable wheel excavators are shown in Table 3 (b).

Gap and Development Direction of Domestic and Foreign Rotary Excavation

Gap between domestic and international rotation excavation

Looking at domestic wheel excavators, despite significant progress in design and manufacturing, there is still a significant gap compared to foreign products in terms of high reliability, safety and comfort, appearance, especially electronic energy-saving and microcomputer control technology, due to factors such as outdated design methods and serious insufficient investment in development and manufacturing.

The following are important factors that affect the quality and market competitiveness of domestic rotary excavation:

(1) The smoothness and reliability of operation are poor, the work efficiency is not high, the product quality is not high, and the appearance is rough. Compared with advanced foreign excavators in terms of durability and reliability, there is a significant gap. The average time between failures and the first major repair period of domestic excavators are only half of those of advanced foreign products;

(2) The engines, hydraulic systems, and key components in the electronic control system of domestically produced wheel excavators are basically imported, resulting in high production costs and restricting the competitiveness of domestically produced wheel excavators; It cannot meet the needs of the domestic market in terms of intelligence, electronic control, automatic monitoring, mechatronics and hydraulic integration, etc;

(3) There are few available brands and a single variety of wheel excavators, lacking medium and micro products, especially for medium-sized wheel excavators close to 20 tons;

(4) There are deficiencies in the overall structure, pipeline layout, accessory selection, and engine emission standards of excavators. The new product testing cycle is short, resulting in some potential quality hazards of the entire machine, which cannot meet user requirements.

The development direction of wheel excavation

Since the 1990s, the hydraulic system and electronic technology of excavators have undergone unprecedented development, improving overall productivity and economic performance. Undoubtedly, excavators have always been developing towards efficiency, energy conservation, improved comfort, and environmental adaptability.

(1) Intelligent electro-hydraulic proportional control has been applied to engineering machines since the 1980s

Mechanical not only eliminates the complex and massive hydraulic signal transmission pipelines, but also makes the control of the entire excavator power system more flexible and convenient. After entering the 1990s, with the development of computer technology, electro-hydraulic proportional control further became "intelligent", mainly reflected in the following aspects: firstly, the setting parameters of certain hydraulic components will no longer be fixed and can be adjusted, such as the pressure cutoff value, pump torque, and the pressure difference set by the pressure compensator on the load sensing valve; Secondly, the computer can automatically monitor the operating parameters of the hydraulic system and diesel engine, such as pressure and diesel engine speed, and adjust the operating parameters of the hydraulic system automatically based on these parameters, such as engine speed and pump output flow, torque, etc., to control the entire excavator power system to operate in an efficient and energy-saving state; Thirdly, being able to complete general semi-automatic operations such as leveling and slope trimming requires low proficiency from the driver, but the quality of work can be greatly improved

Improve; Fourthly, it is possible to diagnose faults based on the monitored operating parameters, facilitating the maintenance of excavators. The emergence of these functions can significantly improve the performance of excavators.

(2) Diesel electromechanical injection control

In traditional mechanically adjustable speed diesel engines, the circulating fuel supply and injection advance angle of the fuel injection pump are all affected by the speed, making it difficult to further improve the performance of the diesel engine. After applying electronic injection control on diesel engines, the circulating fuel supply and injection advance angle of the pump can no longer be affected by the speed, so that the excavator can always work in the best state and accelerate the response speed. With the help of computer control technology, the matching control between the pump and the engine will further achieve "intelligence", and the combination between the two will be closer to achieve integrated control. In this control, the controller can automatically adjust the hydraulic pump and engine according to changes in working conditions, ensuring that the output power meets the working needs while minimizing fuel consumption, improving the energy-saving and environmental protection of the excavator.

(3) Continued Development of Load Sensing Technology

Load sensing control has emerged since the 1970s, and various manufacturers of hydraulic components in construction machinery have launched a series of related products. This system has good energy-saving and maneuverability, and even inexperienced drivers can quickly adapt. The emergence of proportional flow distribution valves has further promoted the application of load sensing technology in excavators, further improving the maneuverability of excavators and solving the problems caused by the lack of skilled drivers in Western countries. Therefore, the demand for load sensing controlled excavators in developed countries will further increase.

(4) Developing towards hybrid power

In recent years, hybrid hydraulic excavators have received widespread attention in the field of construction machinery. At present, some foreign excavator enterprises, such as Komatsu in Japan, Kobe Steel, Sumitomo and Hitachi Construction Machinery, Liebherr in Germany, and Caterpillar in the United States, have carried out research work on hybrid hydraulic excavators, and energy recovery has also been widely used in the industry