EASY5 Model of Two Position Solenoid Operated Cartridge Valve

The two position solenoid operated cartridge valve is widely used in the applications, such as process control systems, pavers, agricultural machinery, where response and installed costs are more important than precise control through electronic position feedback. In recent years, the combination of multiple cartridge valves, so called ‘smart valve’ or ‘programmable valve’, which is able to break the mechanical linkage between the meter-in and meter-out orifices and enables high precision control as well as optimal usage of energy, is gaining engineering interests. But the control of such combination is far from trivial. It demands good knowledge of the valve dynamics and nonlinear flow properties. Unlike servo valve or proportional directional control valve, a mathematic model of solenoid operated cartridge valve, or even a thorough understanding of the dynamics and nonlinear performance, are not available. This paper presents an EASY 5 model for the two position solenoid operated cartridge valve. The model, which includes the solenoid force, spring force, damping force, flow force and nonlinear mass flow rate, can be used to analyze cartridge valve as well as simulate system or controller performance. It is also able to connect with Matlab for more complicated simulation.

Some Experimental Considerations of Stage Control in Digital Valves

Because of saturation and hysteresis of magnetic materials, nonlinear characteristics are commonly experienced in servo or proportional valves. These nonlinearities can substantially affect the performance of the valve in practical applications. In the presence of magnetic nonlinearities, the output signal (displacement or force) is dependent on the input current and the sign of its derivative. If the driving current to the electrical-to-mechanical interface device changes for a number of cycles, as in a stepper motor for example, then a series of reset points will occur as the current undergoes cyclic changes. At each reset point the original starting characteristics of the system are re-established. A large number of reset points across the full stroke of the spool results in a significant reduction in the nonlinear behavior; indeed, the characteristics of the valve approach those of a linear system. The approach in creating these multiple reset points has been defined by the authors as “stage control”. In this paper, stage control using variable reluctance and hybrid stepper motors is first discussed. For the variable reluctance stepper motor, the reset point occurs once at each step of the stepper motor, whereas it occurs twice in a single cycle in the hybrid types. Experiments using a spool valve as a load were designed to obtain the characteristics using stage control. It is demonstrated that with the introduction of stage control, nonlinearities, such as saturation and hysteresis, are greatly reduced, system stiffness is increased, and the positioning accuracy and resolution of the spool are improved. The effect of dither due to a “digital fragment” signal is also examined and found to be crucial in reducing the hysteresis and in improving the resolution accuracy.

Accumulator-Charged Drive for a Hydraulic Boom to Save Energy

Improving energy utilization in hydraulic booms has been an important scheme for industries and designers due to energy cost, environmental requirements, etc. This paper presents accumulator-charged drive in a Loglift boom, which is driven by Electro-hydraulic Load-Sensing (ELS) system based a micro-controller. The practical measurement and simulation are carried out for different work situations. The energy transfer process for a typical duty cycle is calculated and compared. The experimental and theoretical results show that this drive can improve energy utilization. The validation of its experiment in an example hydraulic boom will encourage its further research for possible application.

The Effect of Parameter Uncertainty on the Reliability of Pressure Accumulator Simulations

The aim of this study is to demonstrate how the various parameters and the uncertainty associated with them affect the simulation results of a pressure accumulator. The parameters to be studied are related mainly to the pre-charging procedure of a membrane accumulator and cover the constants for the pressure and temperature of the nitrogen gas and the efficient volume of accumulator. These parameters are included in the non-linear model which is suited especially for large amplitude and low frequency transients. The background of the work is related to the fact that simulation is already an important tool in product development work. To be able to design the control of the system and predict the performance of it an estimate of the accuracy of the calculations is needed. The usability of simulation is determined by the fact how reliable the information is. To gain full benefit of simulation more attention has to be paid to the validity of the models, the accuracy of the parameter values needed in the models and the sensitivity of these parameters. The most sensitive parameters have to be recognized and paid special attention to the accuracy of the values given to them. Also the changes of these values in time due to wear or other modification in the system have to be noticed. Numerous factors have an influence on the accumulator operation. The most important of these are the ratio of the operation pressure to the pre-charge pressure, the amplitude of the flow rate disturbances, the temperature of the hydraulic fluid and the gas, the viscosity of the hydraulic fluid, the thermodynamic process of the nitrogen gas in the accumulator and the changes in the speed of sound. Also the mounting of the accumulator, the fittings used and the connecting pipes may have a significant role in the dynamics of an accumulator. The methods used in the study include measurements in time domain, modeling, simulations, and analytical work. The accumulator dynamics may alter due to remarkable changes in operating points like pressure levels. These are possible because of large amplitudes of flow rates particularly at the low frequency area where the presented study is focused on. The results include model analysis and information of the importance of the most fundamental parameters of the models and suggestions for future research work.

Analysis of Electromagnetic Nonlinearities in Stage Control of a Stepper Motor and Spool Valve

In digital valves, stepper motors are often used as the electro-to-mechanical interface. To sustain both high speed of response and good quantitative accuracy, a special algorithm has been designed to control the stepper motor to produce a continuous displacement. Unlike conventional proportional magnets or torque motors, the input current to the stepper motor is cyclic (stage control) which has been shown to reduce magnetic saturation and hysteresis. In this paper a special mathematical formulation is developed to simulate magnetic saturation and hysteresis which can be applied to a generic situation. The mathematical formulation derived is one in which hysteresis and saturation parameters are established; an error rate of both saturation and hysteresis is defined from this. Since the error rates are easily determined experimentally or through manufacturers’ specifications, the parameters can be found from these mathematical formulations. The parameters can then be used to predict the hysteresis and saturation characteristics. Special experiments are designed to obtain the input-output characteristics of a stepper motor/valve system under single and multi-stage control. The model follows the experimental results reasonably well and can be used with confidence to model any system with hysteresis and saturation. The model also predicts very well the effects of using stage control in reducing hysteresis and saturation in a practical valve.

Impact of Ageing on Tribological Properties of Environmentally Friendly Hydraulic Fluids

Hydraulic systems are used in many technical applications, e.g. in agricultural and forestry machines. Hydrostatic pumps and engines as well as hydraulic fluids are essential components of these systems. Thereof, the hydraulic fluids are of great importance since not only technical but also ecological requirements have to be fulfilled. Apart from fluid power transmission the most important technical function of hydraulic fluids is lubrication and the resulting reduction of friction and wear. In times when saving energy and resources have become environmental matters, lubricants are increasingly attracting public awareness. Important ecological aspects which need to be considered since they have a major impact on the application of technical products and decide about their success are biodegradability, water pollution and ecological toxicity. This is why ester based hydraulic fluids have started to substitute mineral oil based fluids. Additionally, ester based fluids have excellent tribological features due to the polarity of the ester molecules. However, ester based fluids change their physical and chemical properties due to usage. This paper will show that both the total acid number and the viscosity is increased by ageing while the level of additives and the viscosity index is decreased. Therefore, the impact of ageing on the tribological performance of an ester based hydraulic fluid will be analysed by friction and wear investigations. Exemplary, two tribological contacts are chosen: a mixed friction and an elasto-hydrodynamic contact. These are representative conditions for hydrostatic pumps and engines. Analysing the fluid’s behaviour being stressed by mixed friction is performed by using a tribometer. Investigating the ageing impact on elasto-hydrodynamic behaviour of the fluid, a bearing test facility is used. Finally, after having been dealing with tribological contacts used in hydrostatic machines the performance of a hydrostatic machine itself will be analysed. The impact of increased viscosity on friction which is generated within a hydrostatic gear unit at low speed will be discussed.

Infinitely Variable Transmission (IVT) of John Deere 7000 TEN Series Tractors

The John Deere 7000 TEN series tractors represent a significant change in the transmission system compared to previous John Deere tractor models in this category. John Deere 7710 and 7810 series tractors are the first of the 7000 TEN series tractors offering an infinitely variable transmission (IVT). These tractors provide infinite vehicle speeds in the forward mode from 50 meters/hr to 40 km/hr or an optional 50 km/hr. Reverse mode provides infinite vehicle speeds from 50 meters/hr to 17 km/hr. The IVT provides performance improvements in several areas for unmatched operator convenience and control. The new IVT uses an electric signal to control the electro-hydraulic hydrostatic system with mechanical power train. The IVT represents a hydro-mechanical transmission system using electronics, hydraulics and mechanical systems’ integration to achieve the required performance. This paper describes the IVT system configuration, components, operation, characteristics and some of the engineering considerations dealt with in the development process. The overall IVT system truly represents a “drive-by-wire” mechatronic design.

An E/H Control Design for Poppet Valves in Hydraulic Systems

In this paper, an E/H control design is proposed for flow control in hydraulic systems using poppet valves. With the pressures at the valve input and output ports being known, the proposed poppet valve flow control is formulated as tracking the desired poppet displacement xd(t) under the system disturbances. No pilot pressure is required. Using the control pressure at its equilibrium points, the proposed control law largely simplifies the real world implementation with bounded tracking error. Preliminary studies show that the proposed controller is capable of controlling the flow in both directions, with some limitations on the pressure difference between input and output ports while flow is reversed. Simulation results show the effectiveness of the presented control design and experimental validations are scheduled in near future.

Prediction of Swash Plate Moment Using the Simulation Tool CASPAR

The paper presents a new method of prediction of the swash plate moment based on a complex simulation model of the rotating group of swash plate axial piston machines. Due to further important demands within the design of the next generation of displacement machines – the reduction of noise and an increase of efficiency – the optimization of pump and motor control becomes really difficult. The application of the computer aided design tool CASPAR, a simulation tool developed at the Technical University of Hamburg-Harburg for the design and optimization of swash plate axial piston machines, allows the calculation of swash plate moments dependent on time, design and operating parameters of the machine. Especially the valve plate design affects the generated swash plate moment. The paper presents results of a simulation study into the influence of swash plate moments on the valve plate design. The dependency on the instantaneous pressure behaviour in the displacement chamber is explained. The simulation results were compared with experimental results obtained by measurements of the instantaneous pressure behaviour in the displacement chamber for various valve plate designs.

Simulation Model of an Axial Piston Pump Inclusive of Cavitation

A mathematical model of an axial piston pump is presented. The numerical model is based on a finite volume concept. The pump has been divided in different volumes where fluid properties are assumed homogeneous. Since the reduction of the pressure pulsations is one of the most important aims of pump builders, the effects of the port plate relief groove design have been carefully modelled. The gaseous cavitation has been considered in a simplified manner. The pump has been modified in order to measure the fluid pressure inside one of the cylinders; therefore a conduit has been realized to connect the cylinder chamber to a pressure transducer that is placed in a non-rotating position. The fluid pressure inside the conduit has been modelled with a one dimensional scheme for unsteady flow. The code has been tested and calibrated by comparing its numerical results with a set of experimental data. The potentials of the code are presented, spanning over different geometries.