The traditional traveling device of construction machinery adopts mechanical transmission or hydro mechanical transmission. Mechanical transmission has the advantages of high transmission efficiency and high transmission precision. But it is inconvenient to shift gears and adjust speed, so it is difficult to realize intelligent control. The hydraulic mechanical transmission mode introduces the hydraulic torque converter on the basis of the mechanical transmission mode. The hydraulic torque converter has the advantages of adaptive transmission ratio and load, soft transmission, etc. However, the high efficiency area of the hydraulic torque converter is very narrow, and the low-speed stability is poor. For construction machinery with low driving speed and requiring frequent starting, braking and reversing, the total transmission efficiency is low, resulting in large heating of the system, poor operability and high labor intensity of the driver.
At present, the transmission modes of the driving system of engineering vehicles include mechanical transmission, hydro mechanical transmission, hydraulic transmission and motor drive. Each transmission mode has its own advantages and disadvantages. This article will introduce hydromechanical transmission and its advantages and disadvantages.
Hydro mechanical transmission is the addition of hydraulic torque converter on the basis of mechanical transmission. Hydraulic torque converter is a kind of transmission device that transmits power by hydraulic momentum. The output speed of the hydraulic torque converter can adapt to the load torque. When the external load increases, the output torque automatically increases and the output speed automatically decreases, that is, the transmission ratio of the hydraulic transmission changes with the load. Therefore, the hydro mechanical transmission mode improves the operating performance of the drive system, reduces the operating intensity of the driver, and makes the vehicle more soft and controllable in the process of starting, accelerating and braking. This performance is of great significance for engineering vehicles that frequently start, stop, accelerate and brake. The disadvantages of hydro mechanical transmission are small speed stiffness and low transmission efficiency. Due to the torque adaptive characteristic of the hydraulic torque converter, when the external load increases, the vehicle speed will automatically decrease, which is not allowed on some construction machinery requiring constant speed. In addition, the high efficiency area of the hydraulic torque converter is very narrow, and the efficiency is very low in most speed ranges. This is a big problem for engineering vehicles that start, accelerate and brake frequently. However, the starting and braking time of high-speed vehicles such as automobiles and cars accounts for a small proportion of the total driving time. Therefore, the efficiency of hydraulic torque converter has little impact on energy consumption. Therefore, hydraulic torque converter has been widely used in high-speed vehicles and has great advantages.
