Search Results

Valvetrain friction can represent a substantial portion of overall engine friction, especially at low operating speed. This paper describes the methodology for predictive modeling of frictional losses in the direct-acting mechanical bucket tappet-type valvetrain. The proposed modeling technique combines advanced mathematical models based on established theories of Hertzian contact, hydrodynamic and elastohydrodynamic lubrication (EHL), asperity contact of rough surfaces, flash temperature, and lubricant rheology with detailed measurements of lubricant properties and surface finish, driven by a detailed analysis of valvetrain system kinematics and dynamics. The contributions of individual friction components to the overall valvetrain frictional loss were identified and quantified. Calculated valvetrain friction was validated against motored valvetrain friction torque measurements on two engines.

The helical spring is one of fundamental mechanical elements used in various industrial applications such as valves, suspension mechanisms, shock and vibration absorbers, hand levers, etc. In high speed applications, for instance in the internal combustion engine or in reciprocating compressor valves, helical springs are subjected to dynamic and impact loading, which can result in a phenomenon called “surge”. Hence, proper design and selection of helical springs should consider modeling the dynamic and impact response. In order to correctly characterize the physics of a helical spring and its response to dynamic excitations, a comprehensive model of spring elasticity for various spring coil and wire geometries, spring inertial effects as well as contacts between the windings leading to a non-linear spring force behavior is required. In practical applications, such models are utilized in parametric design and optimization studies.

Belt-drive systems are a commonly used for power transmission in automotive applications, notably in engine and vehicle auxiliary subsystem drives. In order to characterize the physics of a belt drive system and its response to speed and load excitations, a comprehensive model of belt elasticity and of belt-pulley contact and friction is required. In practical applications such models are utilized in parametric design and optimization studies, and computational efficiency is therefore also a key requirement. In this paper a belt drive dynamics model is presented, in which the belt is modeled by means of geometrically exact cables that can undergo large rigid body motions but whose strains remain small. The Finite Element approach is used in order to efficiently discretize these elastic components. In addition, a state-of-the-art dynamic friction model (LuGre) is used in order to model the friction loads between the belt and pulleys.

The advantages of Variable Valve Actuation (VVA) in the aspects of improved engine performance, fuel economy and reduced emissions are well known in the industry. However, the design and optimization of such systems is complex and costly. The design process of VVA mechanisms can be greatly accelerated through the use of sophisticated simulation tools. Predictive numerical analysis of systems to address design issues and evaluate design changes can assure the required performance and durability. One notable requirement for the analysis and design of novel mechanically-actuated VVA systems is a general-purpose fast and easy-to-use planar mechanism kinematics analyzer with cam solution/design features, which can be applied to general mechanisms.

There exists a strong interaction between the engine cylinder, intake and exhaust gas flow dynamics and the dynamics of mechanical and hydraulic components constituting the valvetrain system, which controls the engine gas flow. Technologies such as turbo-charging and Diesel particulate filtration (DPF) can significantly increase port gas pressure forces acting on the exhaust valve. When such systems are introduced or undergo design modifications, the operation of valvetrain system can be greatly affected and even compromised, which in turn may lead to degradation of performance of the internal combustion engine. Often, the valvetrain system needs to be retuned. Further, predictive analysis of design issues or evaluation of design changes requires highly coupled simulations, combining models of gas pressure forces and the dynamics of all mechanical and hydro-mechanical parts constituting the valvetrain.

Changing and more stringent emissions norms and fuel economy requirements often call for modifications in the fuel injection system of a Diesel engine. There exists a strong interaction between the injection system hydraulics and the dynamics of mechanical components within the unit injector and the camshaft-driven mechanical system used to pressurize it. Hence, accurate predictive analysis of design issues or evaluation of design changes requires highly coupled and integrated hydro-mechanical simulations, combining analysis of fuel injection hydraulics and the dynamics of all mechanical parts, including the cam-drive system. This paper presents an application of such an integrated model to the study and alleviation of an observed increase in mechanical vibration and related noise levels associated with a proposed design change in unit injectors and valve-train of a 6-cylinder truck diesel engine.

A new model of spur gear contact and gear dynamics was developed for use in studies of dynamic response of mechanical systems involving geartrains. The model is general; in this paper it is applied to geartrain dynamics in valvetrain gear drives. The model dynamically uses a gear contact formulation based on exact involute geometries of gear teeth and can therefore account for varying, non-linear mesh stiffness. It can also account for gear torsional stiffness as well as shaft stiffness at gear centers. The paper further proposes an alternative to dynamic calculation of instantaneous gear tooth contact conditions. The proposed method uses a varying effective mesh stiffness pre-computed through static calculation of contact conditions between teeth of a gear pair, for one mesh, or tooth engagement-disengagement, period. The technique is shown to significantly reduce computational time, while closely matching the predictions of the full model.

A model of roller chain and sprocket dynamics was developed, aimed at analyses of dynamic effects of chain drive systems in automotive valvetrains. Each chain link is modeled as a rigid body with planar motion, with three degrees of freedom and connected to adjacent links by means of a springs and dampers. The kinematics of roller-sprocket contacts are modeled in full detail. Sprocket motions in the chain's plane, resulting from torsional and bending motions of attached camshafts are also taken into account. One or two-sided guides can be treated as well as stationary, sliding or pivoting tensioners operated mechanically or hydraulically. The model also takes into account the contact kinematics between chain link rollers and guides or tensioners, allowing for guides/tensioners of arbitrary shape, or simpler (flat and circular) geometries. The model is first applied to study the chain drive and valvetrain of a 1-cylinder motorcycle engine.

An integrated simulation tool has been developed, which is applicable to a wide range of design issues. A key feature introduced for the first time by this new tool is that it is truly a single code, with identical handling of engine, powertrain, vehicle, hydraulics, electrical, thermal and control elements. Further, it contains multiple levels of engine models, so that the user can select the appropriate level for the time scale of the problem (e.g. real-time operation). One possible example of such a combined simulation is the present study of engine block vibration in the mounts. The simulation involved a fully coupled model of performance, thermodynamics and combustion, with the dynamics of the cranktrain, engine block and the driveline. It demonstrated the effect of combustion irregularity on engine shaking in the mounts.

Engine and vehicle development is a multi-step process: from component design, to system integration, to system control. There is a multitude of tools that are currently being used in the industry for these purposes. They include detailed simulations for component design on one hand, and simplified models for system and control applications on the other hand. This introduces one basic problem: these tools are almost totally disconnected, with attendant loss of accuracy and productivity. An integrated simulation tool has been developed, which is applicable to all of the design issues enumerated above. A key feature introduced for the first time by this new tool is that it is truly a single code, with identical handling of engine and powertrain elements. Further, it contains multiple levels of engine and powertrain models, so that the user can select the appropriate level for the project at hand (e.g. depending on the time scale of the problem).

A multi-purpose valvetrain analysis tool has been developed, which is aimed at addressing all design issues arising in various stages of valvetrain development. Its capabilities include polynomial cam design, valvetrain mechanism kinematics, quasi-dynamic analysis, spring design/selection, multi-body elastic analysis of a single valvetrain with cam-follower and bearing tribology, and multi-valvetrain dynamics with camshaft torsional vibrations. The basic architecture of this tool is object-oriented. Its underlying basis is a library of cam design methods, kinematics operators, and dynamics/hydraulics/tribology primitives (masses, dampers, springs, etc.). On top of this basic system lies a higher-level library of valvetrain compound objects, which are pre-programmed sub-assemblies of valvetrain components built from the primitives. These high level objects minimize modeling effort and may be mixed with primitives, allowing construction of models for virtually any valvetrain.

An increasing emphasis is being placed in the vehicle development process on transient operation of engines and vehicles, and of engine/vehicle integration, because of their importance to fuel economy and emissions. Simulations play a large role in this process, complementing the more usual test-oriented hardware development process. This has fueled the development and continued evolution of advanced engine and powertrain simulation tools which can be utilized for this purpose. This paper describes a new tool developed for applications to transient engine and powertrain design and optimization. It contains a detailed engine simulation, specifically focused on transient engine processes, which includes detailed models of engine breathing (with turbocharging), combustion, emissions and thermal warm-up of components. Further, it contains a powertrain and vehicle dynamic simulation.