Comparison between static pressure transmission and dynamic pressure transmission of tyre loaders

Comparison between static pressure transmission and dynamic pressure transmission of tyre loaders

Tyre loaders, as mobile machinery, are widely used in earthwork transfer as well as the loading, lifting and transportation of loose and piled goods. On the one hand, as a tire loader with high traction, it has great maneuverability. On the other hand, it has the characteristic of quickly changing work sites under high-speed driving conditions. Therefore, it is a great combination of power and maneuverability, and this determines its economy and practicality.

The hydrostatic driving transmission scheme (with a subsequent load shift transmission) has numerous advantages over the hydrostatic torque converter transmission scheme and has been successfully applied in the production of wheel loaders with driving power up to 60 kilowatts.

The application of hydrostatic transmission in high-power tire loaders is similar to that of hydraulic torque converter drive devices. However, due to the large torque range required in this type of hydrostatic transmission, an additional shift transmission is needed, which leads to the disadvantage of interrupted traction force during the shift process. Despite this, in tyre loaders with drive power ranging from 60 kilowatts to 100 kilowatts, the traveling system is still gradually tending towards hydrostatic transmission.

However, in tyre loaders with a power range greater than the above, an engine power of 200 kilowatts, an empty load weight of 25,000 kilograms and a maximum traveling speed of 45 kilometers per hour, up to now, almost only hydraulic torque converter transmission devices have been adopted.

The advantages of static pressure transmission over dynamic pressure transmission: On the one hand, it has a wide control range. In an additional shift transmission, it can achieve stepless or only a few levels of gear shifting. On the other hand, its structural form can achieve an integrated transmission scheme and allows it to be installed inclined or laterally in the direction of travel in modern tire loaders. In a closed-loop loop, torque can be transmitted in two directions. Therefore, during the braking process, a "support" that acts on the driving machinery can be generated, thereby reducing braking power and brake wear. These will lead to a decrease in the operating costs of the tire loader. Operating the working hydraulic system while braking can transfer the refluxing energy to another 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 current and future research and development, optimizing the design of the transmission device of tire loaders has become an inevitable trend.

Comparison of the traction force and speed provided by the hydraulic torque converter and the hydrostatic device: When all the available engine power is used for driving transmission, the hydraulic traction force is usually reduced by approximately 80% of the loader's weight. This traction force not only meets the requirements but also avoids the phenomenon of drive wheel slippage when the loader cuts into the cargo. This is a typical working situation of a tire-type loader and often occurs during the process of the loader cutting into the cargo pile. Compared with the dynamic pressure transmission where the traction force rises rapidly, at this point, the tire wear of the static pressure transmission is significantly reduced. When the working hydraulic pressure is operated simultaneously, the hydrostatic transmission can provide the maximum traction force. Especially when loading large goods, the static pressure transmission loader can improve work efficiency. In dynamic pressure transmission, due to the decrease in the rotational speed of the driving motor, only approximately 50% of the original traction force can be provided.

The torque-carrying capacity of a hydraulic torque converter is a quadratic equation of rotational speed. This means that the hydraulic torque converter can only accept the full torque at a certain rotational speed, generally at the load speed. At speeds below this level, the acceptance capacity drops sharply, thus causing a decrease in traction and speed. When applying hydrostatic transmission, as it can freely distribute speed and torque changes, theoretically, it can cover the entire family of engine characteristic curves. And when combined with various open-loop and closed-loop controls, it can also achieve optimization of noise and energy consumption. In this way, as long as the speed of the drive motor is regulated at an optimal operating point, the driver can put forward the required requirements for acceleration, traction or speed only by the position of the accelerator pedal.

The purpose of optimizing the transmission device is to reduce the burden on drivers. On the one hand, it improves their working conditions; on the other hand, it enables them to focus on decisive tasks. In addition to its performance advantages, modern hydrostatic transmission solutions that are coordinated with dedicated drive power are also highly competitive in terms of price compared to torque converter transmission solutions.