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2025
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Automobile basic knowledge (8) These two can be pulled 100 tons
In the previous article: "Automobile Basics (7) What is a Hydraulic Retarder?" ", we talked about the difference between hydraulic retarder, hydraulic torque converter, and hydraulic coupling. It has to be said that due to the excellent cushioning effect of the hydraulic element and the very low wear, it is very suitable for heavy load scenarios. For example, construction vehicles with large loads will use torque converters to transmit power. For larger vehicles with larger loads and more variable transport conditions, more complex accessories are required. At present, the two most commonly used are ZF's WSK system and Voith's VIAB system.
● The particularity of large-scale transportation
Compared with ordinary cargo transportation, the weight that large trucks need to tow is very large, often more than 100 tons, so if you use a conventional friction clutch, very large wear will occur, and the reliability is very low, so fluid transmission is a good choice.
However, the efficiency of hydraulic transmission is lower than that of mechanical transmission, and for construction machinery, the transportation distance is short, and frequent gear shifts are required, and the difference in transmission efficiency will not be very large. However, the transportation distance of large vehicles is relatively long, and the frequency of gear shifting after starting is relatively low, so the energy loss caused by hydraulic transmission will be more obvious.
Therefore, the ideal transmission method for large-scale transportation is to use hydraulic force transmission at the beginning to reduce wear. After starting, it is transferred mechanically to reduce energy loss.
● Voith VIAB system
The Chinese name of this system is "starting the slow clutch", as can be seen from the name, it has two functions, "start" and "slow", and often appears on large cars of Mercedes-Benz, Sinotruk and other brands.
According to the information found, the structure of this VIAB consists mainly of a mechanical clutch and a hydraulic coupling.
1) When starting, the engine power is transmitted to the gearbox through the hydraulic coupler, which plays a buffering role and reduces friction;
2) After starting, the power is transmitted to the gearbox through the mechanical clutch to improve the transmission efficiency;
3) When decelerating, lock one end of the hydraulic coupler, and then the coupling will become a retarder and brake the vehicle.
(As mentioned in the previous article, the basic structure of a hydraulic coupling is the same as that of a hydraulic retarder.)
● ZF WSK system
This system is a bit more complex than Voith's VIAB and is often accompanied by their own gearbox, as is the case with the WSK system on MAN's TGX bulky vehicles.
The WSK system consists of a mechanical clutch, a torque converter and a hydraulic retarder:
1) When starting, the engine is transmitted to the gearbox through the torque converter, which can reduce wear and tear and amplify the torque;
2) After starting, the power is transmitted to the gearbox through the mechanical clutch to improve the transmission efficiency;
3) When decelerating, the WSK system is equipped with a separate hydraulic retarder to brake the vehicle.
● Comparison of the two systems
Through the above description, everyone should be clearer, and here is a more direct comparison for them.
Structurally speaking, both of them use the transmission mode of hydraulic machinery, so they can take into account the starting ability and transmission efficiency in terms of function. But the differences are:
1) VIAB's hydraulic retarder and hydraulic coupling are integrated, and the starting and deceleration rely on the same element, while the WSK starts by the hydraulic torque converter and the deceleration relies on a separate hydraulic retarder;
2) The WSK starts by relying on a torque converter, which has a torque amplification effect. For example, the WSK440 can reach a torque amplification ratio of 1.58, but the VIAB starts with a coupler and does not have a torque amplification function.
In addition to making the vehicle more capable of starting and getting out of trouble, the amplified torque can also make the engine output more torque at lower speeds, reduce engine wear and extend service life.
● Conclusion
Through the above comparison, it can be seen that the WSK system is more powerful, but the structure of VIAB is simpler, and the cost of VIAB is lower for fleets with better transportation road conditions, which is a good choice; For fleets with complex transportation road conditions and high requirements for vehicle extrication capabilities, WSK can make the transportation process more comfortable.
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