Toward optimal multi-actuator displacement controlled mobile hydraulic systems
Abstract
The research in this thesis is primarily motivated by rising fuel costs and increasingly stringent emissions regulations for diesel engines. These factors increase the cost of operation and the cost of production of mobile hydraulic machine systems, thereby providing large incentives for the discoveries of more efficient hydraulic system solutions. Additionally, sensors and electronics are becoming more openly accepted for use in mobile hydraulic machine systems and they are key enablers to the development of smarter and more efficient system solutions. Displacement controlled (DC) actuation technology is an energy efficient hydraulic actuation technology which could have a substantial impact on energy consumption and emissions of the mobile machine sector if it were to become widely accepted. It has been demonstrated to save 40% fuel compared to a standard load sensing hydraulic system on a compact excavator performing a truck loading cycle. Its lack of acceptance today is due to a combination of unfamiliarity with the system, higher costs due to current low volume production of necessary components, and its reliance on sensors and electronic controllers. DC actuation is a hydraulic actuation technology where the motion of the hydraulic motor or cylinder is controlled directly by the volume of fluid displaced by a servo pump, without the use of metering valves. More specifically, in this work it will refer to the use of a swash plate type axial piston pump to control a hydraulic cylinder, where the cylinder motion is controlled directly by adjusting the swash plate angle. This type of actuation is more efficient than valve controlled actuators because only the exact amount of pressure and flow required for actuator control is generated and therefore the only power losses are those of the pump, the transmission lines, and the cylinder. In addition to this the servo pump will behave as a motor when braking of the actuator is required and this will recover energy to the input shaft which can either be stored or used elsewhere in the system. This thesis will focus on design of multi-actuator DC hydraulic systems. Specifically new circuit architectures will be introduced with goals of overcoming common barriers to the application of basic DC actuators in mobile machine systems. The most notable of these architectures is the DC series-parallel (S-P) hydraulic hybrid system which introduces energy storage into DC actuator systems without requiring an additional pump/motor for energy storage and reuse. Among other benefits this system also has the potential to reduce the number of pumps required for DC actuator systems in multi-actuator mobile machines. A dynamic simulation of this system for an aggressive truck loading cycle of an excavator reveals that the hybrid design would save 20% fuel compared to the non-hybrid DC system while allowing a reduction of 50% for the rated engine power. In addition to new architecture designs static sizing guidelines are given for DC actuators and a multi-body dynamic and hydraulic co-simulation model is derived for multi-actuator DC systems and validated with experimental measurements on a DC excavator. The model is then used to study the effect of component sizing, component performance, and parameter variations on the overall system productivity and efficiency of the non-hybrid DC system. A new static sizing methodology is also introduced for the S-P hybrid system and a dynamic sizing methodology using dynamic programming as a design tool is presented for DC S-P hybrid systems. Finally the improved efficiency of DC hydraulic systems results in lower operating temperatures of the hydraulic oil compared to standard valve controlled systems. For this reason a thermal model for multi-actuator DC mobile machines is introduced. The model is validated with experimental measurements and simulations show that the heat rejection requirement of the hydraulic cooler on the prototype DC excavator could be reduced by as much as 50%.
Degree
Ph.D.
Advisors
Ivantysynova, Purdue University.
Subject Area
Hydrologic sciences|Engineering|Mechanical engineering
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