Jan-Ove Palmberg

Fast pipeline models for simulation of hydraulic systems

In most cases it is justified to regard pipelines as lumped capacitances when hydraulic systems are simulated. In some cases, however, when the system is widely distributed the wave propagation effects in lines may become important and there exists very good models today to simulate these effects. The price to be paid is that of a much larger computational effort. In this paper, a numerically highly efficient model is presented which is just slightly more demanding than a model to represent a pure capacitance, yet it captures all the essential characteristics of a line, the finite wave propagation speed and the distributed frequency dependent friction. The model only calculates state variables at the ends of a line and not in any internal nodes as most models do. Despite this, the model gives good results both in the time and frequency domain which compared to more elaborate models. If for some reason internal state variables are wanted they can be obtained by representing a line with several line elements. The model is integrated in the library of the HOPSAN simulation package and has been used successfully for simulation of oil hydraulic systems as well as the human cardiovascular system.

Individual metering fluid power systems: challenges and opportunities

A review of recent and current research on individual metering fluid power systems is presented. An overview of different systems and their pros and cons is given. General challenges related to independent metering fluid power systems are discussed. The major choices in the design of these systems are the hardware layout and the control strategy. The evolution of existing independent metering fluid power systems from the 1970s until the present day is also presented.

Modelling and validation of a fast switching valve intended for combustion engine valve trains

Abstract In recent years much research has been done in the area of variable-valve actuation in order to improve the efficiency of combustion engines. Currently, a number of different concepts for variable-valve actuation are under development or at a prototype stage. Hydraulic actuation has been an obvious candidate, but the lack of sufficiently fast switching valves with appropriate flowrates has been the major shortcoming. Design of such highly dynamic systems requires accurate models of the actual included components. In this paper a model of a fast 2/2 switching valve is presented, where both the magnetic path as well as the spool assembly are modelled. The model presented here is primarily aimed at system simulations; therefore it has to be kept simple with the number of parameters low. Some of the parameters are often hard to obtain, especially when it comes to magnetic material properties. In this study, an optimization strategy has been utilized in order to parameterize the model against measured data. However, even for major deviations from the operational point used for the model adaptation, the model predicts the valve response sufficiently accurately.

Dynamic Properties of Load-Sensing Systems With Interacting Complex Mechanical Loads

A load-sensing fluid power system is a feedback system with several types of instability modes. This paper deals with one of them, where load interaction through a mechanical structure and the fluid power system may cause instability, e.g. in a lorry crane. Criteria for instability are evaluated. This paper also proposes some methods how to avoid this type of instability

Noise Reduction by Means of Non-Uniform Placement of Pistons in a Fluid Power Machine

In conventional machines, the pulsations are periodic and originate from the uniform placement of a given number of pistons. This paper discusses the possibilities to introduce non-uniform placemen ...

Efficient Collaborative Modelling and Simulation with Application to Wheel Loader Design

Abstract Technical systems are becoming increasingly integrated, partly because of the intensive use of software due to demands for energy efficiency, performance and customizability. This leads to complicated interactions among the subsystems during operation. The dynamic behaviour of such a system is hard to predict since every sub-system needs to be taken into account. Also, the sub-systems often differ in characteristics between engineering domains, and engineers therefore need to collaborate to make the prediction. A validated model is needed to predict how a change to a system will affect its behaviour. The paper investigates how the modelling, simulation and validation processes can be organized in the described case where several engineers from different disciplines are involved. The application studied is a wheel loader that is complex and represents a large family of machines. In the resulting approach, teams of engineers from the different disciplines create one general-purpose model, each team using the most appropriate modelling environment. The system simulation is realized through coupled simulation, where accurate results are achieved by connecting the simulation environments by so-called bilateral delay lines.

Parking System Demands on the Steering Actuator

This paper describes how a hydraulic power steering system with increased flexibility, Active Pinion, can be applied as the actuator to an automatic parking system, Parking Pilot. The requirements on the actuator from the parking system and how the actuator’s performance translates into parking maneuver performance is studied. The system have been installed in a test rig and in a demonstrator car.Copyright