Electric mechanic power split PTO for implements

Abstract

In standard tractors, the mechanical PTO is used to drive high power demanding implements. Its current design as a mechanic, manually switchable transmission enables efficient power transmission, but does not provide the variability needed for automated optimization of the operating points of the engine and the implement. In this paper the development and testing of an electro-mechanic power spilt transmission as PTO drive for agricultural machinery is being presented. This transmission offers variable speed control with efficiencies of 90% in the main operating range. Introduction The mechanical power take-off shaft has established itself in standard tractors for driving agricultural implements. Two nominal speeds, 540 and 1000 rpm, are mainly used for power transmission. Up to two additional stages offer these speeds at reduced engine speed in order to reduce fuel consumption and noise emission during partial load operation [1]. However, in order to adapt the attachment speed continuously and automatically to changing environmental conditions during operation or to stop it during the turning manoeuvres on the headland an infinitely variable transmission is required. Due to the mechanical coupling between PTO and engine, the speed adaption can only be met by actively adjusting the engine speed of the tractor [2]. This is not only less practicable, but also prevents the optimisation of the whole working combination’s operating point. Variable-speed drive concepts for attachments offer great potential for improvement with regard to the efficiency and quality of the working process. As an alternative to the established mechanical drives, hybrid and fully electric drive concepts for implements are being tested increasingly. Due to the good controllability of electric drives, this drive technology is suitable for various applications such as fertilizer spreaders, VDI-Berichte Nr. 2361, 2019 119 https://doi.org/10.51202/9783181023617-119 Generiert durch IP '54.70.40.11', am 24.05.2021, 02:44:44. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. sowing machines or potato harvesters. Since established standard tractors do not have the correspondingly powerful electrical energy sources and are therefore not suitable for the conversion-free operation of electrical attachments, only a few electrical attachments exist so far [3]. Approach In order to both eliminate the speed coupling of the combustion engine to the implement and to offer a retrofittable electrical power source for tractors, a joint research project carried out by Müthing GmbH & Co. KG and Pulsgetriebe GmbH & Co. KG with the Professorship for Natural Materials Technology of TU Dresden and the Institute for Machine Elements and Systems Engineering of RWTH Aachen University developed an electric power-split transmission for the power take-off drivetrain. The aim of the project is to develop a variable and easily controllable implement drive, which allows to operate the implement at optimum speed without changing the speed of the engine of the tractor. For this purpose, the transmission is equipped with two electric machines, which are used as a generator-motor combination for continuously variable speed transmission. Both can also be used as generators to power electrically driven implements or as a drive motor for the attachment. The power-split transmission structure reduces the electrical machine power to be installed, so that smaller and more cost-effective units can be used. Furthermore, compact high-speed machines with operating speeds above 10.000 rpm are used to allow a compact design and competitive cost. As seen in Fig. 1, four operating modes are provided. The infinitely variable PTO allows the PTO speed to be controlled independently of the tractor engine speed between 0 and 1090 rpm. The main operating range of the PTO of the tractor is 800 to 1000 rpm, which allows the optimization of the operating point of the engine. The Generator mode can be used to equip current tractors with an electrical power interface. The Hybrid mode offers a variable PTO and an electrical interface simultaneously. In order to drive a mechanical implement locally emission-free the unit can also be used as an electric motor using external power supply.