Study On Characteristics Of Hydro-Mechanical Continuously Variable Transmission Of Tractor

The hydro-mechanical continuously variable transmission (HMCVT) is a new type transmission device, which consists of a mechanical transmission (MT) combined in parallel with a hydrostatic transmission (HST) featuring a pair of hydraulic units. The HMCVT has a continuously variable shifting ratio by the combination of HST and MT and achieves high efficiency by MT. This device can greatly improve power and fuel economy characteristics and operation automation level of vehicle. Study on the design theory and method of HMCVT drive scheme suited for agricultural tractor, matching theory of engine and transmission system, dynamic characteristic and performance tests of hydro-mechanical continuously variable transmission system (HMCVTS) has important theoretical and engineering value.Based on systematic analysis of the hydro-mechanical continuously variable transmission theory, the characteristic relationship equations of output split power transmission and input split power transmission are gained. Some rules about how the structural parameters affect the performance of output and input split power transmission are analyzed. The analysis results show that the output split power transmission is suitable for vehicle transmission.Combine to the actual working demand of tractor, the general drive scheme for HMCVT is decided. The structural parameters of HMCVT are obtained by optimization design method. The stepless speed regulation characteristic, torque characteristic, power split characteristic, power flow characteristic, efficiency characteristic and tractive characteristic of HMCVT are analyzed. The tractive performance of original tractor and improved tractor are compared. The analysis results show that the tractor assembled with HMCVT can gain a continuously variable speed. Additionally, in any traction force, the engine works near full load. As a result, the tractor with the HMCVT demonstrates greatly improved productivity and fuel economy.Based on engine test results, the engine output torque model and fuel consumption model are established. The engine rotary speed feature denotes the relationship between the engine rotary speed and the throttle opening when engine works in the optimal modes of economic and power operating. According to the different fieldwork, the working conditions of tractor are divided into three operating models. On the basis of the above work, the matching strategy for HMCVTS with the engine is studied; the realization schemes that the HMCVTS matches with the engine are explained in various working models. The matching evaluation index is presented. The power and fuel economy performance of original tractor and improved tractor are compared. The study results show that the power and fuel economy performance of tractor assembled with HMCVT is better than that of original tractor.By the power bond graph theory, a power bond graph model is established and the stateequations of HMCVTS of tractor are derived. A practical fuzzy self-adaptive PID controller isdesigned. The dynamic characteristics of the power and fuel economy performance of tractorHMCVTS in two typical working conditions are simulated.Based on the new type power drive test bench, the performance tests of HMCVTS oftractor in static and dynamic working conditions are completed. The test results show that thehydro-mechanical continuously variable transmission theory is correct.