Speed change and range shift control schedule of the multi-range hydro-mechanical CVT for farm tractors

For the multi-range hydro-mechanical continuously variable transmission (HMCVT) used in the farm tractor, on the purpose of getting the maximum driving capacity and avoiding shift circulation, a speed change and range shift control schedule is presented. An analysis of the pulling characteristics showed that: when engine runs on the maximum power point by governing transmission ratio, maximum pulling efficiency can be got at any polling force; and by means. of the characteristic that the efficiency is different at the range shift point of two neighbor ranges, the changeable range of pulling force and engine speed can be located to avoid shift circulation. Thus a speed change and range shift control schedule that uses the speed control lever position, engine speed and range number as the calculation parameters is presented. This work laid the foundations of the development of the multi-range HMCVT automatic control system.