Editorial of Special Issue on Power Transmission and Control in Power and Vehicle Machineries

1. Introduction

Power transmission and control include the conversion, transmission, and distribution of power, and the actuating of control in the end implement block; it plays an important part in the power and the vehicle of machines [1], such as automobile and construction machinery [2], airplanes [3], and ships. Power transmission and control has also been widely used in power engineering, such as in wind power generation systems, hydroelectric power systems, solar power systems, compressed air energy storage systems, hybrid energy vehicles, geological mining machinery [4], hydrogen energy vehicles [5], and wind generators [6]. By using advanced sensors and transducers, control theory, modelling and simulation, and optimization methods, the performances of power transmission and control systems in power and vehicle machinery can be significantly improved.

This Special Issue focuses on reporting the new achievements in power and vehicle machines from 2017 to 2018.

2. New Theories and Technological Progresses

In this Special Issue, we have curated a selection of 18 papers that represent cutting-edge research in the fields of hydraulic and pneumatic system technologies. These papers highlight innovative approaches to design, analysis, and control strategies, emphasizing advancements in energy efficiency and precision in industrial applications. When looking back on previous Special Issues, various topics have been addressed, including hydraulic system design and control, pneumatic systems and components, and hydraulic and pneumatic analysis and optimization. In relation to hydraulic system design and control, the published papers mainly focus on novel design methodologies and control strategies for hydraulic systems. The first paper, authored by Pedro Roquet et al. (contribution 1), provides a new simplified methodology to evaluate the design specifications of hydraulic components, in which the method allows for the definition and establishment of the hydraulic cylinder design specifications while taking into account the probabilistic characterization of the load spectrum variability; this method could be extrapolated to other hydraulic or mechanical components. The second paper is authored by Che-Pin Chen and Mao-Hsiung Chiang (contribution 2), developed a novel proportional pressure control valve for an automobile hydraulic braking actuator. In this article, the proposed novel proportional pressure control valve of an automobile hydraulic braking actuator is implemented and verified experimentally. The third paper, authored by Haoling Ren et al. (contribution 3), proposes a novel automatic idle speed control system with a hydraulic accumulator and control strategy for construction machinery. In order to reduce the energy consumption and emissions of the hydraulic excavator, a two-level idle speed control system with a hydraulic accumulator for the construction machinery is proposed to reduce the energy consumption and improve the control performance of the actuator when the idle mode is cancelled. The fourth paper is authored by Qing Guo et al. (contribution 4); a prescribed performance constraint (PPC) control method is adopted in an electro-hydraulic system (EHS) to restrict the tracking position error of the cylinder position to a prescribed accuracy and to guarantee the dynamic and steady position response in a required boundedness under these uncertain nonlinearities. These papers address critical challenges in enhancing the reliability and efficiency of hydraulic systems in various applications.

The second category is pneumatic systems and components; the papers in this category mainly deal with the development and enhancement of pneumatic systems, high-performance valves, and actuators. The fifth paper by by Songlin Nie et al. (contribution 5) focuses on the development of a high-pressure pneumatic on/off valve with high transient performances directly driven by a voice coil motor; this research will have a significant effect on raising the performance of the high-speed pneumatic on/off valve and the development of pneumatic precision motion control. The sixth paper in this Special Issue, which is authored by Yeming Zhang et al. (contribution 6), presents a pneumatic rotary actuator position servo system based on ADE-PD control. The flow state of the gas and the motion state of the pneumatic rotary actuator in the pneumatic rotary actuator position servo system are analyzed in this paper. The seventh paper theoretically analyses the flow ripple of a tandem crescent pump with index angles; it is authored by Hua Zhou (contribution 7) and presents a theoretical approach for lowering the outlet flow ripple of a crescent pump by applying a tandem crescent pump consisting of two gear pairs with an index angle between them. The eighth paper, authored by Fan Yang et al. (contribution 8), proposes a new method for analyzing the pressure response delay in a pneumatic brake system caused by the influence of transmission pipes; the study aims to propose an analysis method for resolving the pressure response of a pneumatic brake circuit considering the effect of a transmission pipe. The ninth paper, written by Fan Yang et al. (contribution 9), analyzed the energy efficiency of a pneumatic booster regulator with energy recovery; it discovers that a recovery chamber helps to improve the performance of the VBA-R, which included a boost ratio improvement of 15–25% and an efficiency improvement of 5–10% compared with a conventional VBA booster regulator. The tenth paper carries on an experimental study on hysteresis characteristics of a pneumatic braking system for a multi-axle heavy vehicle in emergency braking situations, and it is authored by Zhe Wang et al. (contribution 10). In the article, the hysteresis of a pneumatic brake system for an eight-axle vehicle in an emergency braking situation is studied based on a novel test bench. The eleventh paper investigates the effects of internal EGR by variable exhaust valve actuation with post injection on auto-ignited combustion and emission performance and it is authored by Insu Cho et al. (contribution 11). The paper discovers that it is possible to efficiently utilize heat to recompress retardation post injection with a downscaled specification of the exhaust valve rather than the intake valve. These contributions are pivotal in pushing forward the operational capabilities and energy efficiency of pneumatic systems.

The third category is hydraulic and pneumatic analysis and optimization, which includes research focused on analytical models and optimization techniques for both hydraulic and pneumatic systems. The 12th paper, written by Dan Jiang et al. (contribution 12), builds a pressure transient model of water–hydraulic pipelines with cavitation. Different from the traditional method of characteristics (MOCs), the present model method is advantageous in terms of its simple and convenient computation. The 13th paper studies the dimensionless energy conversion characteristics of an air-powered hydraulic vehicle, and this paper is authored by Dongkai Shen et al. (contribution 13). The research can be referred to in the performance and design optimization of the HP transformers. The 14th paper in the Special Issue conducts a performance test and internal flow field simulation of a vortex pump; it is authored by Ping Tan et al. (contribution 14). It is revealed that for the vortex pump to have advanced suction and anti-cavitation performance, the lowest pressure in the pump should be −4 × 10⁴ Pa and it should be located at the centre of the vortex chamber cavity. The 15th paper models and dynamically analyses the direct operating solenoid valve for improving the performance of the shifting control system and it is authored by Xiangyang Xu et al. (contribution 15). A numerical approach for solving the multi-domain physical problem of the valve is presented. Moreover, the 16th paper proposed an energy regeneration hydraulic system via a relief valve with an energy regeneration unit; the paper is authored by Tianliang Lin et al. [2] and indicates that the proposed structure of the relief valve with HERU can achieve a better performance and higher regeneration efficiency. The 17th paper, written by Wei Liu et al. (contribution 16), reviewed inlet/outlet oil coordinated control for electro-hydraulic power mechanisms under a sustained negative load and presented the existing problems and future trends in inlet/outlet coordinated control for an electro-hydraulic power mechanism under sustained negative load. The 18th paper, authored by Fangwei Ning et al. (contribution 17), reviewed the research progress of related technologies of electric–pneumatic pressure proportional valves. These studies provide foundational insights into optimizing component design and operational strategies for improved performance and sustainability.

Overall, this Special Issue not only highlights the new advances, but also anticipates the future trajectory for enhancing power transmission and control within power and vehicle machinery systems from 2017 to 2018. The curated selection of papers significantly enriches the field’s knowledge base, focusing on hydraulic and pneumatic system advancements. These contributions offer both practical solutions and theoretical insights that are crucial for refining system integration, thereby fostering more sustainable and efficient technological developments in power transmission and vehicle machinery.

3. Emerging Technologies and Future Prospects

Although electric transmission achieved great technological progresses in the past decade [7,8], fluid power transmission and control still has unique advantages in power machines, construction machinery [1], mining machinery, aircrafts [3], hydro-electric power machines [9], agricultural machines [10], etc. Currently, hybrid power transmission, energy management, and new energy sources are being paid great attention in the field of power transmission and control [11,12]. In the meantime, cybernetic physic systems (CPSs), artificial intelligence, advanced modelling [13,14] and simulation, advanced control theory, and digital twin [15] will provide the innovation and development power for fluid power transmission and control technology.