Design of a load cart to reproduce field load conditions on test tracks

摘要

The increase in the competitiveness between tractor manufacturers has forced, as a consequence, an increase in tractor reliability. This increase in reliability can be reached only through the design of the tractor in function of the real loads seen in different components during the actual use of the machine. In the recent years the introduction of CAE software in the design and development phase has contributed greatly to this improvement in reliability, however the final validation of the machine is only completed after physical, experimental tests. These tests to reproduce vehicle load cycles and validate design models can still require a large amount of time and represent a large cost to the manufacturer. In any case the field test of the tractor in real world conditions is difficult due to the reduced acceleration factor and the problems connected with the seasonality of the operations. In the past different procedures have been introduced to reproduce the loads acquired during field test on proving grounds or on 4 post-test rigs. Despite the use of both methods manufactures were only able to accurately reproduce vertical loads and accelerations, these methods were not able to reproduce the longitudinal loads frequently introduced on the tractors by the connection with implements. It is possible to introduce longitudinal loads during proving ground tests by connecting a load cart to the tractor, but the commercially available load carts are not designed to recreate impulsive loads transmitted to the tractor due to the implements interaction with the soil. The goal of the paper is a feasibility study into the design of a load cart able to reproduce longitudinal impulsive loads transmitted by a three point hitch to the tractor. Measurements using different implements on different soil types were performed to define the loads transmitted by the implement to the tractor through the three point hitch. Then a mathematical model to simulate the dynamics of the connection between tractor-implement was defined to allow the design the load cart. A brake on the wheels of the load cart was designed to generate the longitudinal impulsive loads.