Abstract
The unreasonable shift point will cause a large shift impact, which will affect the engine fuel economy and the service life of the wet clutch. To decrease shift impact on agricultural tractors with HMCVT (Hydromechanical Continuously Variable Transmission) and find the best working point, the following methods are proposed in this paper: firstly, conducting all-factor method and response surface method (RSM) to design and carry out bench test of shift impact; secondly, using the basic linear fitting, RSM, and stepwise regression analysis to establish comprehensive mathematical models and selecting models with high prediction accuracy; thirdly, putting forward the method of determining the weight of variance to match parameters of three quality evaluation indexes with inconsistent correlation; finally, establishing the total shift quality evaluation index and obtaining the optimal shift working point. It is found that oil filling pressure has a significant effect on speed drop, while the engine speed has a significance on the dynamic load and sliding friction. To make the transmission section of the best quality, the oil pressure at this time is 1 MPa and the engine speed is 1040 r/min. The results show that the proposed method can determine the optimal shift point and provide a reference for developing the control strategy.
Highlights
Hydromechanical Continuously Variable Transmission (HMCVT) consists of a hydraulic system and mechanical system
One part goes into the planetary row through the hydraulic system, and the other part goes into the planetary row through the mechanical system. e power of two parts merged into one under the action of the planetary row, and the power goes into the power-output shaft . e transmission ratio of the mechanical system is determined by the gears and it cannot be changed, while the transmission ratio of hydraulic transmission can be changed by changing the displacement of the variable pump. e output speed of HMCVT can achieve continuous change in the segment
HMCVT depends on the opening and closing of wet cutch to realize segment change. e shift quality refers to the ability to realize shift smoothly on the premise of ensuring the power of the tractor. is paper evaluates the shift quality of HMCVT from three aspects: the fluctuation of rotating speed and torque and the friction heat generated by wet clutch during changing section
Summary
Hydromechanical Continuously Variable Transmission (HMCVT) consists of a hydraulic system (pump-motor) and mechanical system (gears). E output speed of HMCVT can achieve continuous change in the segment. E first route (HM0) is controlled by variable pump, constant motor, and wet clutch C0. E second route (HM1) is controlled by gear pairs, planetary row P1, and wet clutch C1. E third route (HM2) is controlled by gear pairs, planetary row P2, and wet clutch C2. When working in HM2 section, some of the engine power goes through i1-i2 gear pairs and hydraulic system and reaches sun gear of planetary row P1. E other part power goes through i3-i5 gear pairs and reaches planet carrier of planetary row P1. When working in HM2 section, some of the engine power goes through i1-i2 gear pairs and hydraulic system and reaches sun gear of planetary row P1. e other part power goes through i3-i5 gear pairs and reaches planet carrier of planetary row P1. rough the confluence of planetary row P1, the power is delivered to the output shaft through gear ring of planetary row P1. is paper studies HM1 segment for HM2
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