Comparison between hydrostatic transmission and dynamic pressure transmission of wheel loader
Jun 09 , 2022
Wheel loaders are widely used as mobile machines for earth moving as well as for the loading, lifting and transport of loose and bulk cargoes. On the one hand, as a large-traction tire loader, it has great maneuverability, and on the other hand, it has the characteristics of quickly changing work sites under high-speed driving conditions. Therefore, it is a good combination of power and maneuverability, and thus determines its economy and practicality.
The hydrostatic travel drive concept (with subsequent duty shift transmission) offers numerous advantages over the hydrodynamic torque converter drive solution and has been successfully used in the production of wheel loaders with drive power up to 60 kW middle.
The application of hydrostatic transmission of high-power tire loaders, similar to the hydraulic torque converter drive
Similarly, due to the large torque range in this type of hydrostatic transmission, an additional
Shifting the transmission, thereby bringing the disadvantage of interruption of tractive effort during the shifting process. Nevertheless, in tire loaders with driving power from 60 kW to 100 kW, the walking system is still gradually tending to hydrostatic transmission.
However, in tire loaders with an engine power of 200 kW, an unladen weight of 25,000 kg and a maximum travel speed of 45 km/h, so far almost exclusively torque converter transmissions have been used.
The advantages of hydrostatic transmission over hydrodynamic transmission: On the one hand, it has a large control range, and in the additional shifting transmission, it is possible to realize continuously variable or only a small number of gear shifts. On the other hand, its structural form enables comprehensive transmission solutions and allows installation in modern tire loaders obliquely or transversely to the direction of travel. In a closed loop, torque can be transmitted in both directions. Therefore, in the braking process, a "support" acting on the driving machine can be generated, which can reduce the braking power and brake wear, which will reduce the operating costs of the tire loader. Operating the working hydraulic pressure while braking, The energy of the return flow can be additionally transmitted to another hydraulic pump and actuator. The decisive advantage of hydrostatic transmission is: it has a variety of open-loop control and
Closed-loop control and take advantage of available engine power at any rpm

Rate. Therefore, in the current and future research and development, it has become an inevitable trend to optimize the design of the tire loader transmission.

Comparison of Traction and Speed Provided by Torque Converter and Hydrostatic Unit: When all available engine power is used for travel transmission, hydraulic traction is typically reduced by approximately 80% of the loader's weight. This traction can not only It meets the requirements and can avoid the phenomenon that the drive wheel slips when the loader is cutting into the cargo. This is a typical wheel loader operation and often occurs as the loader cuts into the pile. At this point, the tire wear of the hydrostatic transmission is significantly reduced compared to the dynamic pressure transmission, which has a rapid increase in traction. The hydrostatic transmission provides maximum traction when operating hydraulic pressure simultaneously. Especially when loading bulky goods, the loader with hydrostatic transmission 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 speed of the drive motor.
The torque capacity of a torque converter is a quadratic equation of rotational speed. This means that the torque converter can only accept full torque at a certain speed, generally at a load speed. At revs below this, acceptance drops sharply, thus causing a drop in traction and speed. In the application of hydrostatic transmission, since it can freely distribute the speed change and torque change, it can theoretically cover the entire engine characteristic curve family. And combined with various open-loop and closed-loop control, it can also achieve optimization of noise and energy consumption. In this way, as long as the rotational speed of the drive motor is regulated at an optimal operating point, the driver can make demands on acceleration, traction or speed only through the position of the accelerator pedal.
The purpose of optimizing the transmission is to lighten the load on the driver, improving their working conditions on the one hand and enabling them to concentrate on decisive work tasks on the other. In addition to the performance advantages, the modern hydrostatic transmission solution coordinated with the specific drive power is also very competitive in price compared to the torque converter transmission solution.

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