Abstract
The article deals with control of process of tractor unit acceleration from the standpoint of meeting the requirements imposed on the dynamics of the tractor: the maximum value of the tractor acceleration and the maximum acceleration growth rate. As in the electro-hydraulic shift control the pressure in the switchable friction clutches is controlled by a feedback effected by proportional hydraulic valves, the pressure change process is considered to be exponential. The time constant of this process is defined. It is established that the simultaneous acceptance of the permissible values of the maximum acceleration of the tractor and the maximum growth rate of the acceleration (jerk) determines the calculated value of the time constant of the process of changing the pressure in the included friction clutch during the acceleration period. There were determined the parameters of the calculated acceleration process and the basic values of the pressures in the friction clutches, which are used in the formation of the program for changing the pressure in the clutches when changing gears. From the positions of dynamics and heat losses in friction clutches the influence of the structural difference in the hydraulic schemes of the pressure supply to the clutches and the progress of the tractor acceleration is estimated. Some variants of forming a pressure change program are considered that allow, with unfavorable design characteristics of the pressure supply to the clutches, to meet the requirements for the dynamics of the tractor when shifting gears. The results of calculations performed with the help of the mathematical model of the dynamics of the tractor in the course of gear shifting, the values of the dynamic parameters and the friction work in friction clutches for various characteristics of hydraulic pressure supply systems, or for various programs of pressure change are presented. The analysis of calculation results is carried out; conclusions are drawn and recommendations are given.
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