Comparison of hydrostatic drive and dynamic drive of loader
As a kind of mobile machinery, wheel loader is widely used for earth loading and lifting of loose goods and piles of goods. On the one hand it is a large traction tire loader, with great mobility, on the other hand it has the characteristics of fast change of working location under high speed driving conditions. Therefore, it is a good combination of strength and maneuverability, which determines its economy and practicality.
The hydrostatic drive scheme (and subsequent load shift transmission) offers a number of advantages over the hydrodynamic torque converter drive scheme, which has been successfully used in the production of wheel loaders up to 60 kW. Throughout the year.
The application of hydrostatic drive in high-power wheel loaders is similar to torque converter drive. Due to the wide torque range of this hydrostatic transmission, an additional shift transmission is required, resulting in a shift process. Disadvantages of interrupted traction. Nonetheless, in tire loaders with driving power ranging from 60 kW to 100 kW, the ride system tends to be statically driven.
However, in a tyre loader with an engine power of 200kW, an engine load of 25,000kg and a top driving speed of 45km/h, it is not just the torque converter transmission that has been used so far.
Advantages of hydrostatic transmission over dynamic pressure transmission: on the one hand, its control range is large, in the additional shift transmission, can achieve stepless or only a small amount of shift. On the other hand, its structural form supports integrated transmission solutions and allows installation on modern wheel loaders, tilted or lateral to the driving direction. In a closed loop, torque can be transferred in both directions.
Therefore, during the braking process, the "support" acting on the driving machinery can be generated, which reduces the braking power and brake wear, thus reducing the operating cost of the loader. When the hydraulic pressure is operated during braking, the returned flow energy can be additionally transferred to another hydraulic pump and actuator. The decisive advantage of hydrostatic transmission is that it has a variety of open-loop and closed-loop controls and can accept disposable engine power at any speed. Therefore, in the current and future research and development, the optimal design of loader transmission has become an inevitable trend.
Comparison of traction and speed provided by torque converters and hydrostatic devices: When the total available engine power is used to drive the drive, hydraulic traction typically reduces the weight of the loader by approximately 80%. This traction can not only meet the requirements, but also avoid the phenomenon of wheel skid when the loader cuts into the cargo. This is typical of wheel loaders, and often occurs during loader cuts into stacking.
Compared with the dynamic pressure drive with a rapid rise in traction force, the tire wear of static pressure drive is significantly reduced at this time. The hydrostatic drive provides maximum traction while simultaneously operating the hydraulics. Especially in the loading of large cargo, hydrostatic transmission loader can improve the work efficiency. In dynamic pressure transmission, only about 50% of the original traction force can be provided due to the reduction of the speed of the driving motor.
The torque carrying capacity of torque converter is a quadratic equation of velocity. This means that the torque converter can accept all torque at a certain speed, usually at load speed. At revolutions below this speed, the receiving capacity decreases sharply, resulting in a decrease in traction and speed.
In the application of hydrostatic transmission, the whole engine characteristic curve family can be covered theoretically, because it can freely distribute speed variation and torque conversion. Noise and energy consumption can also be optimized by combining various open-loop and closed-loop controls. Thus, as long as the drive motor speed is adjusted to the optimal operating point, the driver can only request the acceleration, traction, or speed required by the position of the accelerator pedal.
The purpose of optimizing the transmission is to reduce the burden on the driver by improving their working conditions on the one hand and enabling them to concentrate on the decisive tasks on the other. In addition to the performance advantages OF modern hydrostatic transmission solutions that are coordinated with special driving forces, they are also highly competitive in price with respect to torque converter transmission solutions.
