Alarico Macor

Optimization of components and layouts of hydromechanical transmissions

Abstract In the agricultural and work machine sectors, hydromechanical transmission competes with traditional mechanical transmission. However, the double energy conversion taking place in hydrostatic transmission lowers the efficiency of the entire transmission. Thus, the dimensioning of hydromechanical transmission must not only meet the functional requirements of speed and power to be transmitted, but must also identify the particular combination of layout and the components that leads to the maximum efficiency. In this study, a general answer to this problem will be given. The design is transformed into a mathematical programming problem, whose goal is the optimisation of both the configuration and internal components of the transmission. The structure of the transmissions is described by means of graph theory, and the resolution of the optimisation problem is obtained by means of a ‘direct search’ algorithm based on the swarm method.

Prediction of sound pressure level for a dual-stage hydromechanical transmission

Abstract Hydromechanical continuously variable transmissions are frequently used in high power applications, including agricultural vehicles, buses and heavy vehicles. These offer several operative advantages such as improved driving comfort, better operational management and less fuel consumption if appropriately managed. However, the acoustic impact that they generate in the environment, which should be checked in the early stages of the project, is often neglected. This paper studies the noise emitted by a drive train for urban buses, which comprises a natural gas engine and a hydromechanical input coupled dual-stage transmission. The aim of this study is the evaluation of the noise emitted by the transmission compared with that emitted by the engine, which is considered the main noise source in the vehicle. The study was carried out by means of a model of the entire vehicle that was implemented in an Amesim environment. The mechanical model was integrated with the acoustic models of the engine and of the transmission. The results show that the transmission, despite its two hydraulic machines, produces a sound pressure level lower by about 2 to 15 dBA than that of the engine, whereas its contribution to the total pressure level does not exceed 1 dBA.

Hydrostatic Hybrid System: System Definition and Application

Abstract The use of high efficiency engines is an unavoidable necessity in the transportation field. The reduction of gas emissions and the optimisation of conversion efficiency cannot be entrusted only to engine characteristics, but it is necessary to work with integrated propulsion systems, which have to manage the production and transmission of the energy in an optimal way. In this paper a hybrid propulsion system made of a parallel type hybrid engine and a hydrostatic transmission is presented. The operational flexibility of the hydrostatic transmission allows the thermal engine to operate at a constant speed, hence at maximum efficiency and/or minimum emission conditions. This propulsion system was applied to the case of a “12 m class” bus for passenger transportation. An Italian hybrid vehicle was taken as the reference solution for performance comparison and as a technical database for the vehicle design aid. Starting from the Italian laws regarding buses, the design and sizing of the propulsion group components were performed. Then, in order to verify the ability of the hybrid scheme to satisfy the design targets, a simulation of the system was carried out using a dynamic simulation code. The simulation showed that the combination of the hydrostatic transmission with the hybrid engine leads to energy savings and a pollutant reduction in comparison with the reference vehicle.