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This paper presents a response to the question: Simulation - mathematical manipulation or useful design tool? A mathematical model of a modulating valve in a transmission control system was developed to predict clutch pressure modulation characteristics. The transmission control system was previously reported in SAE Paper 850783 - “Electronic/Hydraulic Transmission Control System for Off-Highway Vehicles”. The comparison of simulation predictions with test data illustrates the effectiveness of simulation as a design tool. THE EVOLUTION OF COMPUTER hardware and simulation software has resulted in increased interest and usage of simulation for dynamic analysis of hydraulic systems. Most commercially available software is relatively easy to learn to use. The application of such software and the modeling techniques involved require a longer learning curve.

There has been an ongoing interest in replacing mineral oil with more biodegradable and/or fire-resistant hydraulic fluids in many mobile equipment applications. Although many alternative fluids may be more biodegradable, or fire-resistant, or both than mineral oil, they often suffer from other limitations such as poorer wear, oxidative stability, and yellow metal corrosion which inhibit their performance in high-pressure hydraulic systems, particularly high pressure piston pump applications. From the fluid supplier's viewpoint, the development of a definitive test, or series of tests, that provides sufficient information to determine how a given fluid would perform with various hydraulic components would be of interest because it would minimize extensive testing. This is often too slow or prohibitively expensive. Furthermore, from OEM's (original equipment manufacturer's) point of view, it would be advantageous to develop a more effective, industry accepted fluid analysis screening.

Fluid power systems are widely used in agricultural and construction equipment for power conversion and transmission. Solving dynamic stability problems associated with complex and inherently nonlinear fluid power systems on this equipment is very challenging. In the past ten years, a new technology named SNAS (Symbolic/Numeric Analysis/Synthesis) has been developed and implemented by the author (Jiao Zhang). SNAS has been successfully applied to fluid power engineering area for optimizing system dynamic performance. In this paper the fundamentals of SNAS will be discussed and the successful application of SNAS to solve a hydrostatic drive instability problem will be presented.

Laboratory tests have shown that 40% glass-reinforced PPS is suitable for automotive underhood use where it comes into contact with used engine oil, gasoline/alcohol, gasoline/MTBE, water, water/ethylene glycol, hydraulic fluid, and transmission fluid at elevated temperatures. On exposure to water or water/ethylene glycol at 248° F (120° C) and 257°F (125°C), respectively, there is a sharp decline in mechanical strength in the first few weeks with little change thereafter. The residual strength of the 40% glass-reinforced PPS is comparable to, or better than other materials, such as phenolics, which have proved satisfactory in such usage. These results have been translated to successful applications in heavy duty diesel engines. Piston cooling nozzles and water pump impellers made of 40% glass-reinforced PPS have undergone successful engine component evaluations.

Technical groups worldwide have been actively developing specifications and requirements for biodegradable hydraulic fluids for mobile applications. These groups have recognized that an industry-wide specification is necessary due to the increase in environmental awareness in the agriculture, construction, forestry, and mining industries, and to the increasing number of local regulations primarily throughout Europe. Caterpillar has responded to this need by publishing a requirement, Caterpillar BF-1, that may be used by Caterpillar dealers, customers, and industry to help select high-performance biodegradable hydraulic fluids. This requirement was written with the input of several organizations that are known to be involved with the development of similar types of specifications and requirements.

This paper presents an experimental setup and an equivalent FEM simulation methodology to accurately predict the response of Engine Control Module (ECM) assembly mounted on a commercial vehicle subjected to road vibrations. Comprehensive vibration study is carried out. It involved Modal characteristics determination followed by random vibration characterization of the ECM assembly. A hammer impact experiment is first performed in lab to estimate the natural frequencies and mode shapes of ECM assembly. Mounting conditions in test specimen are kept similar to the actual mounting settings on vehicle. Natural frequencies and mode shapes predicted from free vibration experiment are compared with finite element (FE) based modal analysis. The importance of capturing the assembly stiffness more accurately by incorporating pre-stress effects like bolt-pretension and gravity, is emphasized.

Electronics technology has evolved significantly since the first electronically controlled heavy duty on-highway truck engines were introduced in the mid 1980's. Engine control hardware, software, and sensor designs have been driven by many factors. Emissions regulations, fuel economy, engine performance, operator features, fleet management information, diagnostics, vehicle integration, reliability, and new electronics technology are some of those factors. The latest engine electronics technology is not only found in heavy duty on-highway trucks, but in off-highway applications as well. Track-type tractors, haul trucks, wheel loaders, and agricultural tractors now benefit from the advantages of electronic engines. And, many more new applications are being developed.

A cooperative program between the DOE Office of Heavy Vehicle Technology and Caterpillar is aimed at demonstrating electric turbo compound technology on a Class 8 truck engine. The goal is to demonstrate the level of fuel efficiency improvement attainable with an electric turbocompound system. The system consists of a turbocharger with an electric motor/generator integrated into the turbo shaft. The generator extracts surplus power at the turbine, and the electricity it produces is used to run a motor mounted on the engine crankshaft, recovering otherwise wasted energy in the exhaust gases. The electric turbocompound system also provides more control flexibility in that the amount of power extracted can be varied. This allows for control of engine boost and thus air/fuel ratio. The paper presents the status of development of an electric turbocompound system for a Caterpillar heavy-duty on-highway truck engine.

A key ingredient in the development of the Caterpillar 416 backhoe loader was the development of the hydraulic system. A load sensing, pressure compensated system was selected on the basis of its best being able to meet design goals. The result is a backhoe loader in which the hydraulic system contributes greatly to the vehicle's overall acceptance by operating efficiently and utilizing low lever efforts for ease of control.

A microprocessor based, underspeed draft control has been developed and introduced for use on belted agricultural tractors. This system does not rely on costly, strain sensitive pins for operation. By utilizing engine acceleration and deceleration rates, this system is able to respond quickly to needed changes in implement depth, while remaining stable under all operating conditions. The development process relied heavily on real-time computer simulation, minimizing the amount of actual field operation and substantially reducing the development time and expense.

Off-highway mining and construction equipment typically converts all the power output of the engine to hydraulic power, with this power then used to perform the earth-moving operations, and also to propel the vehicle. This equipment presents significant opportunities for a new type of powerplant designed to deliver hydraulic power directly. An alternative to the conventional engine driven pump is a free-piston engine-pump (FPEP). The FPEP incorporates the functions of both an internal combustion engine and a hydraulic pump into a single, less-complex unit. The design presented in this paper utilizes two double-ended, reciprocating, opposed pistons, with combustion at one end of each piston and pumping at the opposite end. The opposed piston layout provides balance and also facilitates uniflow scavenging through intake and exhaust ports in the combustion section of the engine. An important feature of this FPEP design is the rebound accumulator circuit.

This paper summarizes the successful application of Computational Fluid Dynamics (CFD) analysis to predict and control the cavitation erosion in a hydraulic control valve. The accurate control of different vehicle operations demands very fine spool modulations in a hydraulic valve. The precise spool modulations create very high flow rates and high-pressure drops in the valve. The low local fluid pressure regions create cavitation inside the valve. Due to the explosion of bubbles there is a high erosion damage to the valve body as well as the spool surface. The CFD analysis has been used to predict the location of cavitation origination and also used to control the cavitation by redistributing the flow inside the valve.

There is an ongoing interest in biodegradable hydraulic fluids. Biodegradable fluids are often considered to include only vegetable oils, polyol esters and diester base stocks. However, other fluid base stocks including highly refined mineral oils, poly(alpha olefins) and fire-resistant fluids such as water-glycol hydraulic fluids are also biodegradable fluid alternatives. This paper will provide an overview of the international literature on biodegradable fluids, various international testing protocol, fluid base stocks, effect of oxidative stability, material compatibility and pump performance.