Energy Condition of Gear Shifting under Load in Commercial Vehicles

Abstract

In the fight against global warming, all increase in energy efficiency contributes to reaching the target numbers. This is especially true for agriculture, where a huge number of large vehicles work. Currently, used modern tractors are equipped with powershift transmissions, which allow for shifting underload. In the case of tractors, owing to the large traction force and low speed of tractors, kinetic energy loss during shifting is high, which reduces efficiency. The traction test presented here aimed to analyse the shifting process of a tractor from an energetic perspective. It was a challenging task to select the appropriate measuring devices and to create a measurement system for this purpose, due to the extremely short (0.3-0.5 s) shifting time. In order to be able to analyse the parameter changes and the cause-and-effect relationships between speed and engine revolution, and between traction force and slip in the shifting process. Two scenarios were examined: fixed speed and fixed traction force. Data characterizing shifting while high traction force is exerted was analysed by methods of mathematical statistics. The unit changes of traction force and slip and the required time were analysed. Traction force increased after shifting (+ 5 kN), which indicates that extra traction force is needed to make up for speed lost during shifting, and because of which slip is considerably increased, typically by more than 10%. After shifting, traction force vacillates at a frequency around 2 Hz, similarly to the vacillation of engine revolution. When changing down, the process starts with a decrease in slip. After almost 0.15 s, traction force plummets by 15 kN at the beginning of shifting. At the same time, slip also decreases, for a short time it can also exhibit negative values. The analysis proved that slip continuously causes considerable losses to various degrees during shifting. In order to minimize these losses, recommendations are given both for driving technique and for the parameter settings of the controlling software.