On the design and tuning of the controllers in a power-split continuously variable transmission for agricultural tractors

Abstract

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 efficiency 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.

Optimization of the transmission characteristics of an HMCVT for a high-powered tractor based on an improved NSGA-II algorithm

“…Because the loss in system efficiency mainly originates from the hydraulic system, the efficiency characteristics of the HMCVT can be improved by decreasing the hydraulic system power split ratio or improving the inherent efficiency of the hydraulic system. 22 Consequently, the efficiency is highest when the HMCVT is operating in a fully mechanical state when e = 0.…”