Thread Content
The walking drive system is an important component of construction machinery. Compared to the working system, the walking drive system not only requires the transmission of greater power, demanding higher efficiency and longer lifespan from the components, but also needs to have excellent capabilities in terms of speed regulation, differential drive, changing the rotation direction of the output shaft, and reversing power transmission. Therefore, determining what type of transmission to use and how to better meet the requirements for driving various construction machinery has always been a challenge for the construction machinery industry. Especially in recent years, with the rapid development of infrastructure construction in areas such as transportation and energy in our country, as well as the continuous expansion of construction and resource exploitation activities, construction machinery is faced with not only increasing market demand but also more stringent operating conditions and complex working environments. This further drives research into its driving systems. Here, an attempt is made to explore the development and patterns of hydraulic transmission technology in the walking drive systems of construction machinery from the perspectives of technical composition and performance characteristics. 2. Transmission methods based on a single technology: Initially, the traveling systems of construction machinery mainly used mechanical transmission and hydro-mechanical transmission (except for fully hydraulic excavators). Now, hydraulic and electric drive systems are also being used in the walking drive units of construction machinery, which clearly demonstrates the significant impact of scientific and technological advancements on this field. 2.1 Mechanical Transmission: Engines with pure mechanical transmission have a low average load factor; as a result, they can generally only achieve stepwise gear changes, and their layout is limited. However, due to its advantages in high efficiency under steady-state operation and low manufacturing costs, it still holds a dominant position in the field of general-purpose passenger and freight vehicles with a relatively narrow speed range, as well as in agricultural tractors that require high economic efficiency and operate at constant speeds. 2.2 Hydraulic transmission: The torque converter used in hydraulic transmission replaces the clutch found in mechanical transmissions, and it offers the ability for stepless speed regulation. Its main advantage is its output torque-speed characteristic, which is close to that of a hyperbola; combined with a rear-mounted power-shift mechanical transmission, it enables automatic adjustment to the load and prevents the power transmission system from being overloaded. Its high power density, low load stress, and low mass production costs enable it to be widely used in large and medium-sized earth-moving machinery, lifting and transportation equipment, as well as in high-speed vehicles such as cars and tanks. However, its characteristic matching and layout are limited, the torque range is small, and the power braking capacity is poor, making it unsuitable for applications that require stable speed. 2.3 Hydraulic transmission compared to mechanical transmission. Hydraulic transmission makes it easier to control its motion parameters (flow rate) and power parameters (pressure), and it exhibits better low-speed load characteristics compared to hydrodynamic transmission. Hydraulic transmission is widely used in construction machinery due to its outstanding advantages, such as high transmission efficiency, the ability to achieve constant power output control, efficient use of power, simple system structure, stepless regulation of output speed, the capability to operate in both forward and reverse directions, high speed stability, and easy operation. Hydraulic technology can be found in almost all construction machinery, and it has become the primary method for transmission and control in many of these devices. The development of a closed-loop system for regulating the ultimate load, along with a variable system that combines constant pressure and constant power control for engine speed regulation, offers broad prospects for the application of hydraulic drives in the traveling systems of construction machinery. Compared to purely mechanical and hydraulic transmission systems, the main advantages of hydraulic transmission lie in its ease of adjustment and flexibility in layout. It allows various components such as the engine, drive wheels, and working mechanisms to be placed in appropriate positions depending on the design of the construction equipment and the requirements of its operating conditions. The engine can operate at any desired speed, and the transmission system is capable of delivering high traction forces. Moreover, it maintains high efficiency over a wide range of output speeds, and it is easy to achieve various optimized power transmission characteristics to suit the load conditions of different tasks. The walking hydraulic drive system with a closed oil circuit, used in walking machinery with high speeds, enables stepless speed control, allowing the vehicle to start smoothly, shift gears quickly, and change direction without any shocks. This performance is highly valuable for vehicles that need to start and shift gears frequently during operations, and that often travel back and forth. However, compared to open-loop systems, the design, installation, commissioning, and maintenance of closed-loop systems require higher levels of difficulty and technical expertise.