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Analysis of a fluid power system with the use of a mathematical model can provide much useful information for good design and safety of a machine. Analysis of a system may cover flow distribution, component operation, or a combination of both. A method is described in this paper, that allows inclusion of all aspects of a fluid system in a single mathematical model. The method may be used to predict circuit flow division simultaneously with component behavior.

The success of agricultural and construction machinery owes a great deal to the effective use of fluid power. Most fluid power systems are configured with a positive displacement fluid pump that is large enough to meet the flow requirements of many work circuits. Different work functions require a variety of fluid flow and pressure values to provide the desired operation. System branches, therefore, must include specialized flow and pressure regulating valves. The development of a mathematical model of a fluid flow control valve follows.

The success of mobile construction machinery owes a great deal to the proper use of hydraulic power. Hydraulic power systems are usually configured with a positive displacement hydraulic pump. Different work functions require a variety of hydraulic flow and pressure values to provide the desired operations. System branches, therefore, must include a variety of specialized flow and pressure regulating valves. The correct configuration of these valves can be accomplished by building and testing variations of a valve until desired conditions are achieved. However, since machinery build programs are expensive; the use of mathematical modeling of a fluid power component is often well worth the time required to establish the model. Use of the model to study the operation of a component will then lead to fewer hours of shop testing. This example discusses the design and mathematical model of a pressure control valve that provides priority to selected circuits on a mobile machine.

Pressure waves in hydraulic systems can cause control valves to become un-stable during operation and also contribute to vibration and noise. These undesirable pulses must be filter-filtered out or at least reduced in magnitude, in order to optimize the performance of fluid power systems and their controls. Reduction in pressure wave amplitude also reduces wear and damage to system parts [13].* The fluid pump is usually the primary source of pressure pulsations. These waves travel throughout the fluid system. Therefore, it becomes advantageous to reduce the amplitude of the pressure waves as close to the source as possible [16]. A method of reducing the pressure waves by use of a carefully selected volume in the flow line is described. A successful mathematical means of sizing the desired attenuator volume is outlined. The mathematical model can be used with any computer simulation program. Some of these are mentioned by Bowns and others [1,2,3,4,5,6,7,18,19].

A need to vary the wheel base during operation exists for some mobile equipment. This need can be caused by legal considerations or the geometry of the haul road. To meet this need, we consider a hydraulically-operated device used as a fifth wheel. This type of unit is being built and installed on some tractor trailer combinations. Since the apparatus can be operated with the vehicle in motion, the system needs to be analyzed under various dynamic conditions. System pressure peaks and component operation is examined under a variety of conditions involving road surface irregularities and the effect of striking obstructions such as loading docks. Some recommendations for design improvement are included. The analysis was carried out with the use of the IBM-CSMP (Continuous System Modeling Program) (1).* The purpose of the work was to gain preliminary knowledge regarding probable operation of the apparatus.