On the Design and Tuning of the Controllers in a Power-Split CVT for High-Power Agricultural Tractors

Savaresi S.M., A. Taroni, F. Previdi, S. Bittanti

In this work, a power-split continuously variable transmission (CVT) used in high-power
tractors is considered. Power-split CVTs are characterized by the combination of a traditional discontinuous mechanical transmission and a continuously variable transmission. This provides, at the same time, smooth variations of the transmission ratio and high eciency of the overall transmission
system. The CVT considered in this paper is a hydrostatic power-split unit conceived for top-power
agricultural tractors. The goal of this paper is to present a case study on the design and tuning of
the control system structure for this type of CVT. This structure consists of three main parts: a servo
controller on the internal current of the valve of the hydraulic transmission; a servo controller on
the hydraulic transmission ratio; a synchronizer which coordinates the hydraulic and the mechanical
parts of the CVT. The design, tuning and testing of this set of automatic controllers is presented.

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