Analysis of powertrain’s workload during the turning process of a high-speed tracked vehicle

Abstract

High-speed tracked vehicles have a great advantage over wheeled vehicles when it comes to overcoming hard condition terrains. In order to maintain high mobility in low adhesion and high moving resistance conditions, these vehicles have robust powertrain components and complex turning mechanisms, which can withstand high torque, while producing a respectful velocity at the same time. This means that the power source, IC engine, has to produce enough power to satisfy all of these requests. Unlike with wheeled vehicles, the selection of the IC engine for a highspeed tracked vehicle is calculated according to the power requirements for the lowest turning radius achieved with the highest vehicle velocity, turning towards the hill of a maximum gradient. To analyze the efficiency of a high-speed tracked vehicle powertrain, it is necessary to understand the powertrain workloads in specific working regimes. Experimental tests are conducted on a specific high-speed tracked vehicle, in various terrain conditions, in order to obtain accurate workload data and isolate the maximum workload regimes. The vehicle is driven on soft soil and in dry conditions, varying turning and rectilinear moving scenarios, with gear and vehicle velocity changes. In order to analyse the power losses during the turning mechanism slip, a scenario where the vehicle is driven with a relatively constant engine input velocity, in specific gear, with field condition change reduced to minimum is selected, varying only the activation pressure of the auxiliary clutch. The turning process of a high-speed tracked vehicle is evidently the most complex moving scenario, influenced by a large number of variables such as vehicle mass and dimensions, construction of the powertrain and turning mechanism, vehicle velocity, engagement state of the powertrain components, adhesion conditions, moving resistance etc. Given that, special attention is given to analysing the results from power balance point of view. The obtained results indicate that the slip of the turning mechanism friction elements greatly influences the character of the power balance change. For 30% of auxiliary clutch maximum activation pressure value, power delivered to the outer track is 25% lower than when the clutch is fully engaged. When the clutch activation pressure is 60% of the maximum value, the power losses are reduced to 10%. It is obvious that, the lower the activation pressure of the auxiliary clutch, the greater the power loss due to slip, so the logical conclusion is to avoid these working regimes and turn the vehicle with auxiliary clutch fully activated. Unfortunately, these vehicles are most commonly driven in such working regimes, where the vehicle is slightly turned just for trajectory correction. Rarely is the vehicle turned with the lowest values of the turning radius (calculated radius). This means that, for the most of the vehicle usage, the vehicle is turned with great power losses in turning mechanism friction elements. The problem of power loss on friction elements can be overcome by modifying the powertrain, in such a way, that the existing turning mechanisms with friction elements are replaced with hydrostatic or electric components, which would provide a continuous trajectory change, with an infinite number of calculated turning radii and no power loss.