Browse Topic: Camshafts
The cam mechanism, as an extremely important transmission method in mechanical transmission, is widely used in automatic machinery and automatic control devices. In small and medium-sized high-speed automatic guns, high-speed camshafts are often used to achieve intermittent movement of the supply and transport of ammunition during high-speed shooting. Due to the possible vibrations, wear, and instability that may occur during the movement of high-speed camshafts, the design of camshafts needs to meet the requirements of continuous third-order derivatives of the curve, while minimizing angular acceleration as much as possible. This article focuses on the design requirements of a high-speed intermittent motion mechanism, with continuous angular velocity and angular acceleration as design constraints. It establishes segmented function motion equations for the acceleration, deceleration, and uniform speed sections of a high-speed conjugate parallel indexing cam while ensuring that the design cam curve does not have knots. The theoretical profile and the actual profile of the cam, considering roller radius offset, are calculated. Based on this, dynamic simulations are carried out on the acceleration and deceleration sections of the cam roller, and the structural response considering structural elastic deformation and contact collision conditions is obtained. The calculations show that the cam and roller meet the structural strength requirements during high-speed motion. Experimental verification shows that the structure is stable and reliable during high-speed motion.
A computational investigation was carried out using SimericsMP+ to analyze oil distribution and aeration behavior in a V6 engine oil pan during severe vehicle maneuvers. The model accounted for the crankshaft/camshaft rotations and piston motions, which allows for capturing realistic oil distribution in cylinder head drainbacks, engine bay and sump after initializing the crankcase with prescribed oil levels to establish baseline aeration prior to applying dynamic maneuver profiles. Of particular interest was the response of the main oil gallery (MOG) pressure and the exposure of the oil pickup tube during kickoff conditions at multiple fill levels. Both a baseline configuration and a modified sump featuring a containment “doghouse” were examined. Results obtained from the kickoff maneuver show complete uncovering of the pickup tube in the baseline design, leading to unstable lubrication. The first doghouse design only delayed pickup tube uncovering briefly, as oil pooled at the rear gap and air ingestion still occurred. Full fill avoids air ingestion; however, high interaction with the crank shaft results in higher oil aeration longer term after kickoff maneuver ends. The findings highlight the complexity of oil behavior in engine environments, where unpredictable interactions during dynamic maneuvers can easily lead to ingestion and aeration. Despite this complexity, the computational strategy developed in this study was able to accurately reproduce and predict these events which were seen in the test scenario as well in the form of pressure readings at the pump inlet. Since these high-aeration events were validated against experimental measurements, this simulation approach proves to be highly valuable for guiding product design and optimization, allowing engineers to identify risks early and improve lubrication performance in the engines before physical testing.
During a recent Bosch tech showcase, we spoke with Joe Dear, engineering manager for electric propulsion systems at Linamar. The Guelph, Ontario-based parts manufacturer is no stranger to building unsung components for the auto industry, including gears, camshafts, connecting rods, and cylinder heads. The Linamar team was demonstrating a modified Ram 2500, a collaboration between Bosch and Linamar, that was outfitted with a prototype electric powertrain and new e-axles: a rigid axle on the rear (with a Bosch motor and inverter) and a steering axle up front.
To improve the fuel efficiency and satisfy the strict emission regulations, the development of internal combustion engine gets more complicated in both hardware and software perspectives, and the margins for durability and NVH quality become narrower, which could result in poor NVH robustness in harsh engine operating conditions. In this paper, we investigate experimentally the camshaft impact noise mechanism relating the valve train and timing chain forces to detailed motion of the camshaft and the chain tensioner. After the initial investigation of identifying the impact timings and specific engine operating points when the noise occurs, the camshaft orbital motion inside of the sliding bearing is measured and visualized with the proximity sensors with calibration after sensor mounting, in addition to the chain tensioner movements. It is shown that the impact noise occurs at the event of the abrupt change of camshaft orbital motion, which results from the combined resultant force of valve train and timing chain forces. As the valve timing has significant effects on the breathing and combustion efficiency sequentially, only the timing chain force on the camshaft is modified in a way to reduce the abrupt change of movement of the camshaft. In conclusion, the mechanism of camshaft impact has been identified with the proper visualization of the camshaft movement together with the tensioner force-displacement diagram in problematic engine operation condition.
The major area in which the automotive manufacturers are working is to produce high-performance vehicles with lighter weight, higher fuel economy and lower emissions. In this regard, hollow camshafts are widely used in modern diesel and gasoline engines due to their inherent advantages of less rotational inertia, less friction, less weight and better design flexibility. However, the dynamic loads of chain system, valve train and fuel injection pump (if applicable) makes it challenging to design over-head hollow camshafts with the required factor of safety (FOS). In the present work, high-fidelity FE model of a hollow camshaft assembly is simulated to evaluate the structural performance for assembly loads, valve train operating loads, fuel injection pump loads and chain system loads. The investigation is carried out in a high power-density (70 kW/lit) 4-cylinder in-line diesel engine. The camshaft is used for operating the intake valves which induce varying stresses in-line with the engine firing order. Moreover, the camshaft is also used to drive the high-pressure fuel injection pump (FIP) at the rear-end which can add significant torsional stresses. Furthermore, the stresses induced by the hub-loads of timing chain is found to be having a significant effect on the bending behavior of the front-end of the camshaft. In addition to these operating stresses, the camshaft is subjected to different kinds of mean stresses induced by the bolt (used to fasten the drive-sprocket) and interference fit of the camshaft child parts (cam and front plug). Hence, the authors propose a robust and reliable evaluation methodology to evaluate the structural performance and factor of safety (FOS). The dynamic bending behavior of the camshaft under press-fit loads of cam lobes and front plug is discussed. The present work also covers the load-path and multi axial stress state induced on the hollow camshaft under varying load conditions apart from estimating the fatigue life. Moreover, the investigation includes the assessment of different parameters influencing the stress multi-axiality on the camshaft to arrive at potential improvements in the camshaft design. Overall, the results arrived using this methodology is found to be having a good correlation with the parts used for durability testing. Thus, the proposed methodology can be used for evaluating hollow camshafts of modern engines subjected to complex and highly dynamic loads.
Scania Power Solutions has launched a new engine platform designed to provide new power outputs, longer service intervals, longer base-engine operational life and reduced carbon dioxide emissions. The engines will be available for industrial, heavy machinery and power generation applications. Series production is due to begin in 2024. The starting point for the new platform is the 12.74-liter inline six-cylinder diesel engine designed for Scania's road-going vehicles, which was launched in late 2021. This engine delivered a claimed reduction in fuel consumption of 8% and thermal efficiency approaching 50%. Design features include dual overhead camshafts and a single cylinder head casting, replacing the individual cylinder heads of the previous engine.
This document describes methodologies to determine the causes blow-by oil consumption caused by the power cylinder.
Hydrogen may be used to feed a fuel cell or directly an internal combustion engine as an alternative to current fossil fuels. The latter option offers the advantages of already existing hydrocarbon fuel engines - autonomy, pre-existing and proven technology, lifetime, controlled cost, existing industrial tools and short time to market - with a very low carbon footprint and high tolerance to low purity hydrogen. Hydrogen is expected to be relevant for light and heavy duty applications as well as for off road applications, but currently most of research focus on small engine and especially spark ignition engine which is easily adaptable. This guided us to select modern high-efficient gasoline-based engines to start the investigation of hydrogen internal combustion engine development. This study aims to access the properties and limitations of hydrogen combustion on a high-efficiency spark ignited single cylinder engine with the support of the 3D-CFD computation. A high efficiency gasoline single cylinder engine was adapted for hydrogen combustion system with a direct injection and a platinum-free cold spark plug. The injection and camshaft phasing ranges were defined to limit the passage of hydrogen in the intake and exhaust manifolds. The experiments were focused on two operating points (2000rpm and 3000rpm at IMEP=10 bar) at various fuel-air equivalent ratios, fuel injection and air intake camshaft timings and in-cylinder charge motion, at high compression ratio (CR=14). 3D-CFD computation was carried out on CONVERGETM to visualize and understand the local mixing in the combustion chamber. The study revealed that the highest indicated efficiency (close to 47%) coupled with low NOX and acceptable unburnt H2 emissions (respectively below 0.5g/kWh and 1% input energy) was obtained at lean mixture, early hydrogen injection and high tumble level. The pre-ignition known as one of the highest challenges in hydrogen combustion is successfully limited by adjusting the injection timing and camshaft phasing. 3D-CFD simulations showed that optimum fuel injection and intake camshaft timings should favor the homogenization of the mixture and avoid the presence of rich zones near hot spots to avoid pre-ignition.
The tests were carried out on an 3D engine model with an unconventional multiple linkage system. Compared to a classic crankset, the mechanism consists of more elements. In this multiple linkage system the camshaft, the piston rod and the main rod are connected to one common element. The camshaft rotating during operation at twice the speed of the crankshaft makes possible to achieve different piston stroke lengths with each revolution. With proper synchronization of the camshaft revolution with the crankshaft, the suction and compression stroke is smaller in relation to the expansion and exhaust strokes. For this reason, the Atkinson cycle was obtained without interfering with the variable valve timing. The thermal cycle is characterized by increased theoretical thermal efficiency. Due to the unique mechanism, the piston movement has different characteristics compared to classic solutions. Therefore, work was undertaken to analyze the distribution of forces in the system. For the needs of the work, a 3D model of the described engine was created. It was used to examine the characteristics of the piston path during operation. Using computer simulation, piston movement and forces occurring in the system were analyzed. Numerical simulations of combustion process were also carried out in a program designed for internal combustion engines. The most important thermodynamic indices such as pressure distributions, temperatures and heat release are presented. Identical tests were also carried out for the engine with a conventional crank system. The results of both engines were combined and analyzed.
Nowadays, the vehicle hybridization and the use of non-conventional fuels for heavy-duty applications brings to a new beginning in the use of spark ignition (SI) engines. For a standard intake system, the premixed fuel/air mixture is controlled by the injection of fuel after the throttle valve. Then, the geometry of the intake system, with the intake duct, the intake valves and the cylinder head shape, influences the characteristics of the flow within the cylinder up to the combustion process. The new technology of fluid-power and electrical actuations gives the opportunity to decouple the intake and exhaust valve actuations with respect to the standard cam shaft distribution. The Variable Valve Actuation (VVA) concept is not new, but its application is now affordable and flexible enough to be applied to partial load conditions. In this work, the intake, compression and combustion processes of an SI engine are studied by means of a three-dimensional numerical approach based on a finite volume approach. In this model, the Unsteady Reynolds-Averaged Navier-Stokes (U-RANS) equations are solved together with a k-ε model for turbulence and an Extended Coherent Flamelet Model (ECFM) for combustion. The 4-valve engine is equipped with two symmetrical intake valves as well as two symmetrical exhaust valves. Two strategies are studied under partial load conditions: a standard valve lift profile for both intake valves, and a single intake valve lift profile, to provide the same overall fresh mass in the cylinder of the 2-valve opening. The valve timing has been kept constant for both strategies, with an Early Intake Valve Closing (EIVC) approach due to the partial load conditions. The intake flow characteristics and their influence on the combustion process are analyzed and a comparison between the two strategies is carried out. The results show flow structures quite different between the single valve opening and the standard 2-valve opening. The asymmetry of the intake flow, induced by the single valve approach, leads to an increase of the swirl ratio with respect to 2-valve opening. The highest swirl ratio of the single valve case is sustained till spark ignition occurs. At spark timing, the Turbulent Kinetic Energy (TKE) is greatly influenced by the valve strategy, leading to higher values for the single valve lift case with respect to the standard two valves lift. Moreover, the results show that single valve opening provides a faster combustion in lean mixture conditions than the standard lift.
The ever-increasing customer expectations put a lot of pressure on car manufacturers to constantly reduce the noise, vibration, and harshness (NVH) levels. This paper presents the holistic approach used to achieve best-in-class NVH levels in a modern high-power density 1.5 lit 4-cylinder diesel engine. In order to define the NVH targets for the engine, global benchmark engines were analysed with similar cubic capacity, power density, number of cylinders and charging system. Moreover, a benchmark diesel engine (considered as best-in-class in NVH) was measured in a semi-anechoic chamber to define the engine-level NVH targets of the new engine. The architecture selection and design of all the critical components were done giving due consideration to NVH behaviour while keeping a check on the weight and cost. Extensive 1D crank-train simulations were carried out to ensure that the crankshaft torsional amplitude was contained less than the NVH limit of 0.1 degree for higher-order excitations. Similarly, the flywheel-end speed irregularity was confirmed to be within acceptable limits. A complete engine-level simulation was carried out to simulate the surface velocities which could help to identify the areas with high noise radiation. Based on the results, potential improvement areas were identified and modified to reduce surface velocity. Prototype engine testing in the semi-anechoic test chamber identified further potential improvement areas including the camshaft drive gears, injection pump, engine top, and damper pulley. Acoustic holography technique was extensively used to identify high noise radiating areas. With the incorporation of all these optimization measures, a best-in-class value of 65 dB(A) could be achieved as the average 1m engine noise at the low-idle condition. This paper explains the methodology used throughout the design and development of the engine to achieve the above-mentioned NVH levels.
GM Propulsion engineers elevate the evergreen small-block V8 to new heights for its mid-engine Corvette mission. Instead of heaving decades of small-block V8 expertise out the window, GM Propulsion engineers led by chief engineer Jordan Lee leveraged past success to create a new-for-2020 V8. Known as the LT2, the 6.2-L V8 gives Chevy's all-new, eighth-generation 2020 Corvette more power (the most yet in the base Stingray), stirring response, and competitive fuel efficiency compared with the outgoing C7. And the small-block, with its single camshaft in block and two valves per cylinder, remains unmatched versus its rivals in three key metrics: bill of material, package efficiency, and the power-per-dollar quotient. It's the payoff for 65 years of continuously refining (and never giving up on) a brilliant original design.
The development of electric vehicle motors, power controls and batteries tend to dominate today's industry's headlines, but R&D of internal combustion engine technologies in its many forms continues. That is underlined by the U.K.'s Brunel University establishing a new future-powertrain research program centering on “intelligent” valve technology and the eventual replacement of the conventional camshaft by electric actuators. Brunel's Centre for Advanced Powertrain and Fuels (CAPF) has installed Camcon Automotive's SCI (Single Cylinder Intelligent Valve) technology development system, which the company regards as supporting upcoming emissions regulations and reducing ICE costs. CAPF Director, Prof. Hua Zhao, said of the potential for Camcon Automotive's intelligent valve technology: “Its flexibility and superior controllability will enable the development of the next generation powertrain with very high efficiency, low carbon and zero environmental impact emissions.”
Commercial vehicles require continual improvements in order to meet fuel emission standards, improve diesel aftertreatment system performance and optimize vehicle fuel economy. Aftertreatment systems require significant space claim which makes vehicle packaging a challenge. Today’s diesel engines require valvetrain lash adjustment settings at distinct intervals to ensure proper valvetrain performance. This requires removing the engine rocker cover to access the valvetrain rocker arms for setting lash. Setting lash for compact vehicle applications sometimes requires removing the aftertreatment system to provide access to the rocker cover prior to setting lash. Then, the rocker cover is reinstalled followed by the aftertreatment system making the lash setting process time consuming and complex. This paper focuses on the design, development and validation of adapting hydraulic lash adjusters (HLAs) into a type V (camshaft in block) diesel engine thus eliminating the lash adjustment process. The flat mechanical tappets were replaced with roller follower HLAs on both the intake and exhaust valves. The roller was included to reduce valvetrain friction over flat tappets. An anti-rotation design was included to maintain alignment between the roller and the camshaft. A major advantage of using the HLA was reduced engine valvetrain noise. Minor engine block changes were required to accommodate the roller follower HLAs. The HLA design ensured reliable and repeatable valve motion from engine build thru cold start and normal engine operation over the useful life of the engine. Reliability was key for the roller follower HLA as it is embedded inside the block which makes replacement impractical. This paper highlights the major design aspects for including roller follower HLAs in a type V diesel engine.
Knurling joint applied in assembled camshaft has developed rapidly in recent years, which have exhibited great advantages against conventional joint methods in the aspects of automation, joint precision, thermal damage, noise, and near net shape forming. Both quality of assembly process and joint strength are the key requirements for manufacturing a reliable assembled camshaft. In this article, a finite element predictive approach including three subsequent models (knurling, press-fit and torsion strength) has been established. Johnson-Cook material model has been used to simulate the severe plastic deformation of the material. The residual stress field calculated from the knurling process was transferred as initial condition to the press-fit model to predict the press-fit load. The predicted press-fit load, torque strength and displacement of cam profile before failure were calculated. The torque strength of the joint was twice higher than that of a typical passenger vehicle requirement. The torque strength was significantly positive correlated to the press-fit load. Taking the knurling tool dimensions and feed amount as variables, the relationships between them and press-fit as well as joint strength were studied. The predicted press-fit and joining strength using the subsequent modeling ware validated by the experimental measurement with maximum errors less than 11%.
This article presents a comparative study between two camshafts systems adapted to the single cylinder engine of a Supermileage vehicle in a fuel economy perspective. One system is from a Honda AF70E engine and the other is a new design. The new camshaft system was improved for fuel economy by developing a new camshaft that enhances volumetric efficiency while reducing friction losses. The comparison was made by measuring the efficiency of the engine in the speed range where the engine was used by the Supermileage vehicle and a calculation was made to show which configuration is best for the vehicle.
Research on turbocharging for FSAE at the University of Malta, has been ongoing for a number of years. 1D simulations were done to determine best design configuration and determine a lowered compression ratio. A decompression plate was installed on the Kawasaki 600 cc engine. Calibration of the engine was performed on the engine dynamometer. A hot-gas test stand for testing of the turbocharger was developed. The turbocharger speed was measured by a custom built hall-effect sensing setup that is compact enough to be implemented also in the FSAE vehicle. Bespoke camshafts with optimized valve timing determined through WAVE 1D simulations and designed with Valdyn® were machined. The turbocharged setup was used on the University of Malta FSAE vehicle in the FSAE Italy 2017 competition. Knock was investigated through in-cylinder pressure measurements and use of commercial knock sensor on the 600 cc engine. Benchmarking in-cylinder pressure measurement tests were carried out on a 1.4 liter naturally aspirated Ford engine for both ‘masked’ and ‘unmasked’ in-cylinder pressure sensors to assess the possibility and effect of cavity resonance in such experimental tests. High speed data acquisition was performed at 200 kHz per channel and was post-processed using LabVIEW®. Calibration of the knock detection feature on the programmable ECU required the determination of the relevant parameters namely: knock frequency, reference and knock windows and knock to reference window amplitude ratio. Calibration of the ECU knock parameters was aided by playing back recorded engine sensor data to minimize the time of engine knocking.
The demand for improving fuel economy in passenger cars is continuously increasing. Eliminating energy losses within the engine is one method of achieving fuel economy improvement. Frictional energy losses account for a noticeable portion of the overall efficiency of an engine. Valvetrain friction, specifically at the camshaft interface, is one area where potential for friction reduction is evident. Several factors can impact the friction at the camshaft interface. Some examples include: camshaft lobe profile, rocker arm interface geometry, valve spring properties, material properties, oil temperature, and oil pressure. This paper discusses the results of a series of tests that experimented the changes in friction that take place as these factors are altered. The impact of varying testing conditions such as oil pressure and oil temperature was evaluated throughout the duration of the testing and described herein. Test data quantifying the effect of utilizing friction reducing surface treatment methods, specifically diamond-like carbon, is also provided. However, the main focus of the study is on the frictional differences that take place at the camshaft interface for a switching roller finger follower equipped with a roller bearing vs. a switching roller finger follower equipped with a slider pad. An analysis was performed, using brake specific fuel consumption, in order to predict the approximate fuel economy benefit that would result from transitioning from a slider pad design to roller only design for a switching roller finger follower application. Test results suggest that making the switch from a slider-style switching roller finger follower to a roller-style switching roller finger follower has a noticeable improvement on the overall fuel consumption of an engine.
The engine efficacies require the blend of friction reduction approach for optimising the attained output. The research elucidates the scope of friction reduction mechanism to increase engine power and life. The engine components piston and piston rings are coated with the unique composite of graphite, molybdenum disulfide, tantalum layer to reduce friction and wear. The coating on piston minimizes direct contact between piston and cylinder liner, which reduces friction, BSFC and lead to better thermal stability, and engine life. The research also focuses on friction reduction of camshaft bearing by replacing sliding contact bearing with low friction roller bearing. The friction between engine components reduces output power, and the engine oil temperature plays a significant role in it. The research empowers zirconium dioxide coating on oil sump in order to reduce the temperature decay rate so that the optimized engine oil temperature of 100 °C can be retained for longer time. The cars because of traffic gets on and off sporadically, where engine oil temperature role become more prominent, as optimised temperature reduces the problems caused by cooler engine oil temperature which is more viscous and absorbs chamber warmup temperature. The absorption of chamber temperature leads to extra combustion affecting BSFC. The variable flow of oil according to engine RPM reduces oil pump friction by and BSFC by significant amount. The use of lightweight ceramic and sheet metal material in valve train reduces FMEP by 38%. The effect of different engine oils grading on friction have been elucidated on the basis of kinematic viscosity and viscosity index.
In a previous report, it was shown that power transmission through the camshaft reduced the first mode natural frequency of the power train and translated its convergence with dominant engine excitatory harmonics to a lower engine speed resulting in a marked reduction in torsional vibration while achieving 2/1 gear reduction for a 4-stroke 6-cylinder compression ignition (CI) engine for aviation. This report describes a sweep though 2 and 4-stroke engines with differing numbers of cylinders configured as standard gear reduction (SGRE) and with power transmission through the camshaft (CDSE) or an equivalent dedicated internal driveshaft (DISE). Four and 6-cylinder 4-stroke engines were modeled as opposed boxer engines. Four and 6-cylinder 2-stroke engines and 8, 10 and 12-cylinder 2-stroke and 4-stroke engines were modeled as 180° V-engines. All 2-stroke engines were considered to be piston ported and configured as SGRE or DISE. All 4-stroke engines were configured as SGRE or CDSE. Mass-elastic models of the different engine power train configurations were constructed and analyzed using the torsional vibration module in Shaft Designer obtained from SKF (Svenska Kullagerfabriken). Maximum torsional stress at the power train segments was used to discriminate between the different configurations. The best 4-stroke CDSE configuration was the 6-cylinder engine as described previously and provided a significant advantage over the SGRE configuration. The best 2-stroke applications with the analogous DISE configurations were the 8 and 10-cylinder engines although they were inferior to the SGRE configurations. These simulation studies suggest that the 6-cylinder 4-stroke engine is ideally suited for use with the CDSE power train configuration for reduction of torsional vibration and achieving gear reduction compared with SGRE.
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