| The wheel loader is the one among the earthmoving, it is one of the main construction machinery and widely used in the places such as the mining industry, infrastructure, agriculture and disaster relief and so on due to its fast and convenient to use and operate and flexible power-driven, easier to use and maintenance. The wheel loaders have become into the largest construction machinery exports in our country.For the powertrain of wheel loader, studies have not been confined the performance match between the engine and the drive system, but should also include the subsystems supplying power for the transmission system, the implement system, the power steering system, the braking system and the auxiliary unit of the whole vehicle. Due to the presence of these subsystems, it can be assured that the whole machine complete a variety of production operations. As the point of view of the existing product design model, the main focus is the whole dynamic performance. But due to complex and variable load conditions at work, the operating efficiency of the wheel loader will be reduced and the consumed energy will be increased during the practical use under the non-appropriate operating type even if the whole vehicle performance has been optimized during the design procedure. The user must adopt corresponding operating type to work with an optimum operating mode according to various operating environments during the practical operation, reducing energy consumption while raising operating efficiency.This paper aims at the performance characteristics study of the wheel loader powertrain at typical modes based on the mathematical model of it, and obtains a changing law of the performance characteristics when emphasizing on the different external loads, providing a theoretical basis for the optimal combination of the dynamic and economy of the whole vehicle. This is the main significance.In this paper, mathematical models for the power system of 80-type wheel loader have been developed according to its structure characteristics and the load models developed by analyzing the load conditions at its typical operating modes.In this paper, tests have been performed for the transmission, implement, steering oil pump outlet pressures of a "V" loading cycle of the 80-type wheel loader, obtaining the changing characteristics of them and applying the measured data to the characteristics research of it. This means which uses a combination of theoretical and experimental analysis has improved the authenticity and credibility of the analysis result, making the whole analyzing process much closer the actual working condition.Based on the MAP of engine performance, we have studied the performance characteristics of the 80-type wheel loader powertrain during starting. For the full throttle and part throttle of engine, we have analyzed the performance characteristics of the powertrain during the straight start process, the result showed that the powertrain has a better power performance when the former selected, but a relatively lower economy. For the performance characteristics of powertrain during starting at the no-load and full load state, the results showed that when the powertrain load increased, the engine can automatically adjust the power and energy needs to adapt to changes of the external loads. For the powertrain performance characteristics of gear 1 and 2 during starting, the former has a better dynamics as well reducing the power consumption of the engine in the implement and steering oil pump. For the powertrain energy allocation characteristics during starting, the result showed the hydraulic torque converter pump has a greater torque power ratio in the engine power, and the other subsystems have a less proportion. This allocation is little affected by the gears, throttle opening and loadings during starting.Based on engine performance MAP, high-speed driving performance characteristics of the 80-type wheel loader powertrain has been studied using different combinations of gear shift strategy and gears under the same driving distance. The result showed that the powertrain had a better power performance and an better economy when adopting optimum dynamic gear shift strategy and optimum economical gear shift strategy respectively, however the dynamic and the economy are not good when manual gear shift. When adopting the optimum dynamic and economy gear shift strategy, the dynamic and economy of the powertrain during starting at gear 1 and driving at gear 4 has a advantage over the one during starting at gear 2 and driving at gear 4. While adopting manual gear shift strategy, the result is on the contrary. At the present wheel loaders still almost adopt manual way to shift gear, so gear combination of gear 2 starting and gear 4 driving has a greater advantage at high-speed driving. In the process of high-speed driving, hydraulic torque converter has a greater power ratio in the engine power, and the other subsystems have a less ratio. From this, we can get the engine output energy is mainly used in the drive system needs when the wheel loader is at high-speed operating and driving.Based on engine performance MAP, selecting the "KD" and non-"KD" mode, the engine at full throttle and part throttle opening, "V"-type loading cycle powertrain characteristics of 80-type wheel loader has been studied. The results show that, although "KD" mode due to a more one gear shift brings a larger gear shifting impact than non-"KD", but in the traction force, efficiency, operating time and fuel consumption, "KD" way has a better advantage over non-"KD "way. When operating at full throttle the engine torque and power, fuel consumptions, traction forces are all higher than the one operating at part throttle. From this above, we know that the powertrain has a better dynamic operating at full-throttle and the engine has a relatively sufficient power and energy to supply the power system. When operating at part throttle, the traction efficiency is higher the one at full throttle. From this, it can be known that operating at part throttle, the engine energy has a higher utilization but a poor dynamic, as a result the time of steering, movable arm to lift and bucket to trip-over become long and the shovel loading not continuous, the loader speed decreases. A loading cycle of "V" the power split-flow characteristics of the operating oil pump and steering oil pump is more obvious, during driving the torque converter has a greater power ratio, during steering the power ratio of steering oil pump increases. When the movable arm is lifting and bucket flipping, the operating oil pump power increases. From this, it can bee known that when the loads of corresponding subsystems are increased, the engine can reallocate energies according to its loading to meet the energy needs of corresponding subsystems.The results shows that although the theory of general vehicles is also suitable for wheel loaders, but due to their own work characteristics, use of conventional research methods for their powertrain will has certain limitations. The proposed method in the paper against the of powertrain operating characteristics of wheel loaders with typical operating modes and loadings supplied a new direction for the research on the powertrain of the future wheel loaders. At the same time, the developed powertrain mathematical models for wheel loader further expend the scope of application of the powertrain model.
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