The powertrain efficiency deeply affects the performance of off-road vehicles like wheel loaders in terms of fuel economy, load capability, smooth control, etc. The hydrostatic transmission (HST) systems have been widely adopted in off-road vehicles for providing large power density and continuous variable control, yet using relatively low efficiency hydraulic components. This paper presents a hydrostatic-mechanical power split transmission (PST) solution for a 10-ton wheel loader for improving the fuel economy of a wheel loader. A directly-engine-coupled HST solution for the same wheel loader is also presented for comparison. This work introduced a sizing approach for both PST and HST, which helps to make proper selections of key powertrain components. Furthermore, this work also presented a multi-domain modeling approach for the powertrain of a wheel loader, that integrates the modeling of internal combustion (IC) engine, hydraulic systems, mechanical transmission, vehicle(wheel) dynamics, and relevant control systems. In this modeling, an engine torque evaluation method with a throttle position control system was developed to describe the engine dynamics; a method to express the hydraulic loss of the axial piston hydraulic pump/motor was developed for modeling the hydraulic transmission; and a vehicle velocity control system was developed based on altering the displacement of a hydraulic unit. Two powertrain models were developed, respectively, for the PST and HST systems of a wheel loader using MATLAB/Simulink. The simulation on a predefined wheel loader drive cycle was conducted on both powertrain models to evaluate and compare the performance of wheel loader using different systems, including vehicle velocity, hydraulic displacement control, hydraulic torque, powertrain efficiency, and engine power consumption. The simulation results indicate that the vehicle velocity controller developed functions well for both the PST and HST systems; a wheel loader using the proposed PST solution can overall save about 8% energy consumption compared using an HST solution in one drive cycle. The sizing method and simulation models developed in this work should facilitate the development of the powertrains for wheel loaders and other wheeled heavy vehicles.
The 3D bio-printing has been developed as an effective approach to artificially create tubular tissue structures, which have been frequently found in body and organ systems. China Agricultural University (CAU) has developed a laboratory 3D bio-printer that can create tubular structures with the encapsulation of microfluidic channel. In order to create a tubular structure with more effective micro-channel encapsulation for better nutrient delivery and chemical stimulation, this work presents a design optimization of co-axial dispensing nozzle of this 3D bio-printer. In this study, an experimentally validated two-phase flow computational fluid dynamics modeling tool based on ANSYS CFX has been developed to analyze the microfluidic domain of fluid channels inside the nozzle. The simulations on the extrusion and encapsulation process of bio-inks have been conducted. Based on the response surface method, the simulation work has established an equation to predict the volume fraction of the encapsulating layer against a variety of influencing factors including the size of extrusion nozzle, pneumatic pressure condition and the dynamic viscosity of the bio-ink. This equation has been used to recommend optimal solutions of printing parameters for the CAU bio-printer, which is expected to improve the quality of bio-printed tubular structure with an encapsulation.
The high-speed valve with advanced performance, which is expected to possess characteristics of large nominal flow and fast response at the same time, plays an important role in enabling efficient digital hydraulics. In order to solve the tradeoff between a large rated flow and less response time, this paper proposed an novel design of high speed valve actuator called energy coupler actuator(ECA)based on the shear working mode of magnetorheological fluid. The ECA allows a rotary energy source couple/decouple the translational valve spool for fast and long stroke on/off switching. This work developed a multi-physics model of ECA to study its performance and simulation work based on response surface method has been conducted to optimize the ECA design parameters. An ECA prototype using the optimal design solution has been manufactured and experimentally tested. The testing results shows that driven by the power level similar to off-the-shelf solenoid valves, this ECA prototype only took 5ms to achieve 1.5mm stroke, which provide a flow area equivalent to a nominal flow of 100L/min@5bar. This prototype also demonstrated the ECA’s design feature of long stroke with quick response by achieving 7mm stroke in just 16ms.
In many dynamic systems, such as vehicles, engine air and fuel control systems, fluid power systems, industrial robotics, and testing machines, high-speed actuators are necessary to achieve efficient system operation and high bandwidth performance. This article introduces a new actuation mechanism to enable high-speed actuation. The premise for this actuation mechanism is to momentarily couple a moving component (kinetic energy source) with translational components, which is enabled by a coupling/clutch system. The kinetic energy source (flywheel, electric motor, pump or motor shaft, etc.) is intermittently clutched and declutched to produce linear motion. This article presents such an energy coupler actuator using a magneto-rheological fluid clutch, initially focused on an application for high-speed valve actuation. A multi-physics coupled model was developed to evaluate the proposed energy coupler actuator performance. Simulations were conducted to optimize the energy coupler actuator design parameters. A prototype of the magneto-rheological fluid energy coupler actuator based on the optimal design solution was fabricated and experimentally tested, which achieved 1.6-mm stroke in 4.7 ms.
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