Abstract
In order to improve the shift quality of hydro-mechanical continuously variable transmission, the effect of tangent bulk modulus and different control methods on the shift quality were analyzed. Theoretical analysis and experimental study on the tangent bulk modulus of oil were carried out to obtain the effect law of air content on the tangent bulk modulus of oil. A four-cavity model of a closed hydraulic circuit was established based on a two-stage arithmetic type hydro-mechanical transmission. By means of simulation analysis and experimental study, the effect of the tangent bulk modulus of oil on the shift quality is studied. The lean control method of reasonably controlling displacement ratio and prolonging the reverse time of load torque is put forward. The results show that this method can reduce the fluctuations of the speed of the fixed displacement motor and the oil pressure of the original low-pressure side. This method can also improve the shift quality and provide reference for the study of the shift process of hydro-mechanical continuously variable transmission.
Highlights
When Hydro-mechanical continuously variable transmission (HMT) shifts from the H-range to the HM-range, the speed of the variable displacement pump is 1000 rpm, the oil temperature is 90°C, and the pressure at the low-pressure side of the closed hydraulic circuit is 2.55 MPa. The displacement ratio is constant at 0.98, and the load torque from -147 N Á m step changes to 99 N Á m (Figure 9)
According to the above effect laws, an lean control method of displacement ratio and the flipping time of two brakes is put forward; a mathematical model of displacement ratio of variable displacement pump and a mathematical model of flipping time of two brakes are established; through simulation analysis and experiment verification, the results show that in the shift process of Hydro-mechanical continuously variable transmission (HMT), considering the effect of oil bulk modulus, the lean control of displacement ratio and the shifting time can effectively reduce the fluctuation of oil pressure in closed hydraulic circuit and the fluctuation of speed of fixed displacement motor, eliminate the speed difference of the motor before and after the shift, effectively improve the shift quality
The closed hydraulic circuit of HMT is equivalent to four cavities, and the mathematical model of closed hydraulic circuit shift process considering the air content of oil is established
Summary
When HMT shifts from the H-range to the HM-range, the speed of the variable displacement pump is 1000 rpm, the oil temperature is 90°C, and the pressure at the low-pressure side of the closed hydraulic circuit is 2.55 MPa. The displacement ratio is constant at 0.98, and the load torque from -147 N Á m step changes to 99 N Á m (Figure 9).
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