Digital hydraulics is a key part of the continuing applicability of fluid power in the modern world. In order to realize the potential of digital hydraulic circuits, valves which are able to switch at high frequencies whilst retaining high flows are first required. This paper details the development of a valve which is capable of switching in 0.5ms whilst providing a flow rate of over 50L/min at a 10bar pressure drop. Unlike most of the other valves currently in development, position control is used as opposed to the more common bang-bang actuation. This has obvious benefits for valve robustness and offers the possibility of a hybrid control approach which utilizes both throttling and switching control. This paper will detail the design and empirical testing of the valve and benchmark it against published and commercial valves before proceeding to discuss the challenges present in developing the valve further.
Abstract Digital Displacement® pumps are a type of variable displacement, radial piston hydraulic pump currently being developed for use in efficient mobile hydraulic systems. The pump displacement is controlled by selective enabling of solenoid valves at the inlet of each cylinder and since the pump displacement can be controlled directly by software it is possible to use the pump as a flow source with any arbitrary demand. By enabling precise flow control and reducing leakage and throttling losses they can provide a significant improvement in efficiency over conventional pumps; however, this also leads to a decrease in the overall sources of damping in the system and may result in increased transmission of vibration and fluid-borne noise. This paper presents a method for characterising vibration sensitivity of a hydraulic system, using the pump as a frequency generator whose flow output follows a sinusoidal ‘chirp’ demand. Simulation results are presented of the pump open-loop frequency response, which show the control bandwidth and demonstrates that the pump can modulate its output flow at frequencies into the audible range. This enables the possibility of using the pump to identify potential sensitivities in a downstream hydraulic system up to 200 Hz. A method is described for characterising the noise and vibration of the connected system within this frequency range. Test data from a hydraulic excavator are presented and analysed to create a characteristic transfer function for the system, relating pump output flow to pressure ripple and vibration in the downstream system. These system transfer functions can be used to develop control methods to reduce the impact of vibration, either by active damping, filtering of the control signals or choice of cylinder enabling strategy. Test data are presented also showing the effect of some mitigation strategies in the same hydraulic excavator, leading to a reduction of overall vibration in the vehicle cabin.
The transmission line method is a very efficient method for dynamic modelling of flow in pipelines and uses delay elements to represent wave propagation. In this article, an existing transmission line method model is investigated and shown to have some deficiencies. An alternative technique is introduced to enhance the transient and steady-state accuracy. Extremely good agreement is obtained between this new transmission line method and an analytical model. The model has been implemented in simulation of a number of highly dynamic systems and has been found to be robust and reliable.
A novel method for estimation of unsteady flow rate using pressure at two or three points along a pipeline is described in this paper. The pressure data are processed using a wave propagation model to determine the unsteady flow. The comparison and analysis of two-transducer and three-transducer techniques are investigated through simulation. The proposed method is shown to be effective for unsteady flow rate measurement over a high bandwidth. However, if the pressure values from two transducers are used, inaccuracies exist at certain frequencies when the transducer spacing coincides with multiples of half a wavelength. The accuracy can be improved by adding a third transducer with unequal spacing. The three-transducer method has been implemented in experiments and has been found to be robust and reliable.
Whilst Product Development is the basis of engineering, increasingly complex products have a tendency to also increase the complexity of the Product Development process, and in many cases the process is not truly understood. There are many tools that have been developed for managing complexity, but few that are specific to Product Development and fewer still that provide pragmatic analyzes that can be used by decision-makers. This paper develops a methodology to apply a Network-of-Networks approach to data collected from a Product Development organization and provides an accompanying pragmatic analytical framework that can be used by decision-makers on all levels. It then uses an Agent-Based modelling approach to represent the knowledge diffusion within Product Development. This allows a microscopic analysis to complement the macroscopic analysis of the Network-of-Networks approach. This will allow an organization to analyze its current practices on both macro and micro scales, model dynamic changes to the structure of the organization and understand its internal dynamics, with respect to development teams and the design process. This will illuminate the complex system dynamics in Product Development that would otherwise be viewed of as unexpected consequences to a system intervention. This understanding will give greater ability to make suitable, risk-mitigating decisions.
This article reports on theoretical and experimental investigations of a switched inertance device, which is designed to control the flow and pressure of a hydraulic supply. The device basically consists of a switching element, an inductance and a capacitance. It is able to boost the pressure or flow with a corresponding drop in flow or pressure, respectively, analogous to a hydraulic transformer. In this article, an enhanced analytical distributed parameter model in the frequency domain, which includes the effect of switching transition, non-linearity and leakage of the valve, is proposed and validated by simulation and experiments. A flow booster test rig is studied as a typical system. Simulated and experimental results show good performance, and accurate estimation of system pressure and dynamic flowrate can be obtained using the enhanced analytical model. The model is very effective for understanding, analysing and optimising the characteristics and performance of a switched inertance device. It can also be used to aid in the design of a switched inertance hydraulic system.
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