Comparison of hydrostatic transmission and dynamic pressure transmission of tire loader
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The hydrostatic drive scheme (with the subsequent load shift transmission) has a number of advantages over the hydrodynamic torque converter drive scheme, which has been successfully applied to the production of wheel loaders up to 60 kW. in.
The application of high-power wheel loader hydrostatic transmission is similar to that of a torque converter drive. Due to the large torque range in this type of hydrostatic transmission, an additional shifting transmission is required, resulting in a shifting process. The shortcoming of the interruption of traction. Despite this, in a tire loader with a drive power from 60 kW to 100 kW, the travel system tends to be statically driven.
However, in a tire loader with an engine power of 200 kW, an engine load of 25,000 kg and a maximum travel speed of 45 km/h, more than just a torque converter transmission has been used so far.
The advantages of the hydrostatic transmission relative to the dynamic pressure transmission: on the one hand, its large control range, in the additional shifting transmission, it is possible to achieve stepless or only a small number of shifts. On the other hand, its structural form enables an integrated transmission scheme and allows installation in a modern wheel loader tilted or transverse to the direction of travel. In a closed loop, torque can be transmitted in both directions.
Therefore, during the braking process, a "support" acting on the driving machine can be generated, thereby reducing brake power and brake wear, which will result in a reduction in the operating cost of the tire loader. Operating the hydraulic pressure while braking, the return flow energy can be additionally transmitted to the other hydraulic pump and actuator. The decisive advantage of hydrostatic transmission is that it has a wide 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 optimization design of the tire 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 in the driving drive, the hydraulic traction is normally reduced by approximately 80% of the loader's weight. This traction can not only Meet the requirements, and can avoid the phenomenon that the loader drives the wheels to slip when cutting in the goods. This is typical of wheel loaders and often occurs during the loader's cutting into the stack.
Relative to the dynamic pressure transmission in which the traction force is rapidly rising, at this point, the tire wear of the hydrostatic transmission is significantly reduced. The hydrostatic drive provides maximum traction when operating hydraulic pressure at the same time. Especially when loading large cargo, the hydrostatic transmission loader can improve work efficiency. In the dynamic pressure transmission, only about 50% of the original traction force can be provided due to the decrease in the rotational speed of the drive motor.
The torque bearing capacity of a torque converter is a quadratic equation of speed. This means that the torque converter can accept all the torque at a certain speed, generally at the load speed. At the number of revolutions below this speed, the receiving capacity drops sharply, which causes a drop in traction and speed.
In the application of hydrostatic transmission, it can theoretically cover the entire engine's characteristic curve family because it can freely distribute the speed change and torque conversion. Combined with various open-loop and closed-loop control, noise and energy consumption can also be optimized. In this way, as long as the drive motor speed is regulated at an optimum 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, on the one hand to improve their working conditions, and on the other hand to enable them to concentrate on decisive tasks. In addition to the performance advantages, the modern hydrostatic transmission scheme, which is coordinated with the special drive power, is also very competitive in price relative to the torque converter transmission scheme.