International Journal of Fluid Power

Editorial

2024-10-05T04:01:37+02:00

Welcome to the special issue of the Journal of the International Fluid Power. Most of the papers included here are extended versions of ones presented at the Scandinavian International Conference on Fluid Power (SICFP) conference (Tampere, Finland, 30 May–1 June 2023).

Energy Efficient and Redundant Steer-by-Wire for Articulated Non-road Mobile Machines

2024-03-08T12:39:53+01:00

The electrification of on-road vehicles has got momentum in recent years, but for Non-Road Mobile Machines there are still many barriers to cross. In order to completely eliminate the internal combustion engine or reduce its use, the energy loss in machines needs to be minimised at every possible section. One such part is the steering of heavy non-road mobile machines which has been unchanged to a large extent for decades, especially in articulated machines. The major cause of the industry being cautious in replacing the traditional steering system is its safety. As being a safety-critical system, it requires to comply with the highest safety standards. An articulated steered wheel loader has been selected as a case study in this article to first carry out a detailed hazard analysis to assess the machine performance levels required for steering. Two scenarios are selected for hazard analysis: 1. the wheel loader is on work site; 2. the wheel loader is travelling on road. To achieve the required performance level, the requirements of functional safety and safety integrity level of the steering are analysed. Based on corresponding standards and the required performance level for the steering, a new electro-hydrostatic-based steer-by-wire system is proposed. The proposed steering complies with safety standards for articulated steering and has the potential for energy saving. The simulation of the proposed system is carried out from an energy-efficiency point of view in MATLAB/Simulink. The proposed electro-hydrostatic steering system is compared to the traditional steering of a wheel loader in the Mevea digital twin environment and has been found to be substantially more energy efficient in the primary analysis. The simulations show that in conventional steering, 51% of energy is wasted in the steering valve alone, while in EHA (Electro-hydrostatic actuator) steering only 29% is wasted in the entire steering system.

Dynamic Response Analysis of the Main Plunger in A Two-stage On/Off Poppet Valve for the Digital Hydraulics Field

2024-01-23T12:08:19+01:00

The necessity for greater energy conservation in hydraulic machinery is highlighted by escalating fuel costs and heightened ecological awareness. Utilizing independent metering to enhance the energy utilization of hydraulic actuators is one effective strategy, yet the market is short on efficient reversible proportional valves that can perform this function. For handling modest flow rates up to 150 Liters per minute, the digital hydraulic method utilizing fast direct operated on/off solenoid valves shows promise; however, solutions for managing larger flows remain vague. This research explores the application of pilot-operated solenoid valves in digital hydraulic systems designed for substantial flow volumes. It establishes a model grounded in physical principles to examine how various factors influence the valve reaction speed. A unique valve design was established, derived from an existing valve but with a modified structure.

The findings indicate that the pressure difference, viscosity of the fluid and pilot plunger dynamics are crucial determinants of the valve response time. Incorporating a stroke limiter proves significant in harmonizing the response times across valves with varying flow rates, while the traditional methods of deploying serial orifices is deemed unsuitable. A glance from the results shows that at a Δ
P of 10 bar, the valve with an 8 mm attached serial orifice has an opening response of 65 ms, while the stroke limited valve achieves 40 ms. This significant advantage slightly narrows at higher pressures, stabilizing at 100 bar. During closing, the stroke limiter is remarkably 60% faster at 10bar, and both configurations settle at 40 ms at 200 bar.

Variable-Speed Pump-Controlled Three-chamber Cylinder System for Hydraulic Boom with Feed-Forward LADRC

2024-03-08T18:07:44+01:00

With the increasing fossil fuel crisis and environmental degradation, energy-saving has been one of the fluid power transmissions’ priority research areas. In a conventional hydraulic boom, throttling and potential energy losses result in poor energy efficiency and extra rising of fluid temperature. To boost the energy efficiency of a hydraulic boom, this paper proposed a variable-speed pump-controlled three-chamber cylinder system for hydraulic boom with feed-forward plus linear active disturbance rejection control (LADRC). In the proposed system, chambers A and B of the three-chamber cylinder are controlled by two variable-speed fixed-displacement pumps and the third chamber C is connected to a hydraulic accumulator to balance the weight of the boom. Firstly, the model of the variable-speed pump-controlled three-chamber cylinder system is built in Matlab/Simulink. Further, the mechanical model of a 1-ton excavator is established, and the proposed system is applied to the boom. Secondly, a compound controller combining speed feed-forward and LADRC is designed. Thirdly, simulations were performed under boom up and down while keeping the arm and bucket cylinders fully retracted. The position control performance and energy consumption are analysed and compared. The results show that, compared to the PID and speed feed-forward PID control, the proposed controller has a lower position tracking error (less than 2.66%). Compared with the variable-speed pump-controlled differential cylinder system, the proposed system can save energy by 43.51% when considering energy recovery. Therefore, the proposed system has good position tracking performance and has the potential to be applied to different types of heavy-lifting equipment driven by hydraulic cylinders.

A Study on Design Methodologies for Compact Electric Machines Used in Electrified Mobile Hydraulics

2024-02-09T13:28:03+01:00

Electric Machines (EMs) have gained increasing importance in the mobile hydraulic industry as prime movers for hydraulic actuation systems. Therefore, their design and sizing are important aspects for any system layout architecture. The on-road vehicle industry has exploited EM versatility by proposing different sizes for various applications. However, off-road vehicles cannot borrow designs from on-road applications directly due to their unique challenges pertaining to drive cycle dynamics and limited space availability. Furthermore, considerations of the thermal limitations of EM and their cooling must also be studied to devise an effective methodology for designing prime movers suitable for mobile hydraulic applications.

This paper proposes EM operational sizing strategies based on corner point operation, flux weakening and transient operation that can downsize EMs by carefully selecting sizing points from the operating domain. These strategies can leverage the operational capabilities of EMs and involve trade-offs in terms of EM compactness and efficiency. Therefore, based on a specific requirement, a given strategy can have certain benefits explored in this paper. The paper also examines two other downsizing methods based on switching the ePump architecture to variable displacement pump operation and improving the cooling performance. The paper considers a 5-ton mini excavator’s arm actuator as a reference application. The resulting EMs are compared in terms of size and efficiency to study the effectiveness of each operational sizing strategy. This paper uses a well-established genetic algorithm-based multi-objective algorithm to design a Permanent Magnet Synchronous Machine (PMSM) for each sizing strategy. The effect of cooling technology is considered in terms of limiting winding current density for the EMs, and the impact of cooling technology on the size and efficiency of the EM is also demonstrated. Finally, the effectiveness of the proposed operational sizing strategies in downsizing EMs is combined with, and compared to other methods like variable displacement operation and aggressive cooling to identify the best ways to obtain the most compact EMs for any hydraulic application.