RICERCA ITALIANA     

Research program

THE ENHANCEMENT OF MECHANICAL TRANSMISSIONS FOR THE REDUCTION OF THE ENERGY CONSUMPTION

University Co-ordinator

Università degli Studi di PALERMO - MECCANICA - PALERMO(PA)

Research Unit Leader

Francesco SORGE

Description

Our research unit aims at improving the performances of continuously variable transmissions in terms of transmissible power, matching of the speed variogram with the vehicle demands, efficiency, pollution reduction and fuel saving. All performances are to be analysed in the two chief operative conditions, the steady working and the speed ratio shifting.
Since some time, our research unit addressed the analysis and the experimentation of two-mode split-way drive systems including one V-belt variator and one epicyclic gear. The idea is to realize the first mode in the split-way configuration in order to cover the range "reverse-first gear" and provide a higher torque, and the second one in the simple way configuration for a faster movement of the vehicle. Such a two-mode configuration permits overcoming the main drawback of the one-mode version, that is the increase of the variator class and the whole efficiency worsening due to the widening of the drive aperture. In view of this, the cooperation to be estabilished with other units of the same project appears very important, in particular with the ones of Turin and Florence as regards the simulation of the transmission behaviour on their hardware-in-the-loop test benches
Some two-mode drive systems were already reported in the literature, sometimes with negative aperture (i. e. including the reverse speed). These proposals indicate the interest of the researchers on the multi-mode solutions.
Our research unit has already carried out a close examination of the wide range of possible solutions and a particular attention is also addressed to the analysis and the design of the automatic actuators for the control of the speed ratio and of the axial thrust. In practice, the idea is to modify the actuator geometry for a better match with the desired characteristics of the drive and for the improvement of performance and efficiency.
Therefore, our research unit aims firstly at validating the theoretical analyses regarding the mechanical behaviour of the actuator by measuring torque, speed and closure force. Then, new actuator geometries wil be designed and realized in order to adjust the functional variogram to the engine characteristic map, contain the closure force and prevent unnecessary overloads for the belt.
At the same time, the experimental equipment will permit veryfying the theoretical models of the previous Sect. 2.4 regarding the mechanical behaviour of V-belt variators during the transient phases of speed ratio shifting, which are the most frequent ones in the usual working condition of common vehicles. Obviously, two main categories of V-belt variators must be distinguished, with different mechanical behaviour from each other: the rubber belt variators, where the elastic deformation of the belt exerts an essential role in conjunction with the overall outward/inward motion due to the closing/opening of the pulley, and the metal belt variators, where the belt configuration is strictly dependent on the plate deflection. In the case of rubber belt in particular, since the angle of friction is generally larger than the groove angle, atypical belt configurations arise for the closing pulleys, with wide spiral-shaped adhesive arcs developing toward the inside in the motion direction. Similar arcs of spiral are found for the opening pulleys as well, but with a much smaller extent and with outward penetration. Of course, these two different categories involve different mathematical models and different experimental approaches.
Only very few papers are reported in the literature on these subjects and a suitable experimentation on the transient condition could offer very important developments in case of agreement with the theory, as the model validity could be extended to analyse the variable behaviour of a real vehicle on the road.
This investigation will benefit from the synergetic advantage of the collaboration with the research unit of Bari, which is engaged in analogous researches.

The course of our research project could roghly be divided into five phases.
The first phase schedules a further refinement of all previous theoretical analyses, in order to select new ameliorative solutions as regards the two-mode CVT scheme and the optimized design of the actuators, with the aim at containing the variator class and the power losses. All possible problems relative to their practical construction will be examined (about 4-6 months).
The second phase, to be developed in practice simultaneously with the first one, is devoted to refine the theoretical models for the ratio shift transient, for cases of both rubber belt and metal belt variators (about 4-6 months).
The third phase schedules a general comparison with the base researches in course in the other centres, together with the exchange of information and results, in order to introduce eventual corrections or modification into the experimental research to be carried out, and the planning of the experimental tests in cooperation with the other units. As regards in particular the research unit of Bari, the information exchange will concern the transient behaviour of CVT's and the viscoelastic characteristics of the rubber belt response (about 2-3 months).
The fourth phase will be devoted to the construction of a test bench for mechanical transmissions and of new actuators for the control of the speed ratio and of the closure force. Extensive experimental tests will follow, regarding the two-mode split-way drive on the one hand, and the transient variator behaviour on the other hand. The drive prototype will be proposed to the units of Turin and Florence for the tests on their HIL benches (about 6-10 months).
The fifth phase schedules the publication of the final results, together with meetings and discussions with all the other fellows of the present research project, in order to compare and mutually integrate all results and data (about 4-6 months).
It is estimated that the experimental part of the research will require a remarkable set of instruments, considering the great number of measures to be carried out on the various components. The equipment of our laboratory has then to be potentiated (torque-meters, speed-meters, brakes, software, etc.).
At last, it is to be pointed out that, in parallel with the research on the split-way drives and on the transient operation, the theoretical studies on the other themes concerning the mechanics of the belt drives will go on without interruptions (viscoelastic behaviour of rubber belt, boundary region, tribological properties of the belt pulley contact, etc.).