Browse Topic: Valvetrains
Oil pressure, the most fundamental to engine's performance and longevity, is not only critical to ensure that the engine components are properly lubricated, cooled, and protected against wear and contamination, but also ultimately contributing to reliable engine performance. Due to several factors of engine such as, rotational fluctuation, aeration, functioning of hydraulic components there are fluctuations in oil pressure. In engines, with a crank-mounted fixed displacement oil pump (FDOP), these inherited pressure fluctuations cannot be eliminated completely. However, it is very necessary to control the abnormal oil pressure fluctuation because abnormal pressure fluctuation may lead to malfunction of hydraulic component functioning like variable valve timing (VVT), hydraulic lash adjuster (HLA) and dynamic chain tensioner which can further cause serious issues like excessive or sudden load drops, unstable engine performance, valve train noise, improper valve lift operation etc. In this paper, engine oil pressure fluctuation in HLA gallery is studied, and its impact was assessed on valve train system. Root cause analysis (RCA) was conducted using high frequency oil pressure measurement to understand the various reasons impacting high oil pressure fluctuations inside HLA galleries. Time domain analysis was performed to understand oil pressure fluctuations with respect to VVT cam phasing. Angle domain analysis was performed to assess the impact of oil pressure fluctuations on valve train behavior. Further findings from this study aim to enhance the understanding of impact of VVT cam phasing in oil pressure fluctuations.
Condition-based monitoring (CBM) has emerged as a transformative approach in predictive maintenance, enabling the proactive identification of potential component failures. It offers numerous advantages like Cost Savings, Increased Equipment Lifespan, RCA of failed parts, Optimized Resource Utilization, Reduced Disruptions, Enhanced Reliability and Safety and many more making it a vital approach for effective maintenance and operational efficiency. This paper presents a comprehensive methodology for monitoring and analyzing vibration trends to predict and prevent the breakdown of critical components in IC Engine in its testing phase. The good part here is that this methodology is not just limited to IC Engine but can be applied across wide range of industries and mechanical systems as from the literature and past vibration data, it was observed that before any such failure engine vibration increases. If the engine is stopped at that moment, it can be preserved, allowing for further investigation to be conducted. During the engine reliability development process, failures in the crank train and valve train can result in damage to multiple components, making it challenging to analyze the sequence of failure and identify the initial cause and root problem. By employing advanced vibration analysis techniques, the study aims to detect anomalies indicative of wear, misalignment, or other precursors to failure. This research contributes to the growing body of knowledge in CBM, offering a scalable and adaptable framework for implementing vibration-based predictive maintenance across diverse industrial applications. The proposed methodology not only enhances reliability but also supports sustainable maintenance practices by minimizing resource wastage and ensuring timely interventions.
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.
Valve train system is one major contributor to engine overall friction loss and is approximately 30% of total engine friction at lower speed and approximately 20 % at higher engine speed. Valve spring loads (preload and working) are proportional to friction loss of valve train. To optimizing the valve spring design main requirement is valve train perform it function safely at maximum engine cutoff RPM with minimum preload and working load. Robustness and frictional power loss are contradicting requirement, robustness demand high stiffness spring for better valve jump and bounce performance with dynamic safe valve spring design, on the other hand low frictional power loss demand for use of low stiffness spring. To optimize the valve spring stiffness for meeting both the requirement we need accurate prediction of valve spring in design stage and good correlation with testing data to reduce the number of iterations. For achieving robust valve spring design with low friction in current work valve Jump, valve bounce, valve spring dynamic stress and valve surging phenomena of valve train predicted from Multi body dynamic analysis is correlated with testing. Testing measurement methodology explained with test rig setup procedure. Good correlation is achieved in analysis and testing. Major evaluation parameters considered for valve spring analysis verification are valve jump, valve bounce, dynamic stresses and fatigue life performance.
A single-stage turbocharger turbine is developed with the objective of enabling a gasoline spark-ignition engine to operate under lean-burn conditions with an air-to-fuel ratio of λ=2 in the range of the Worldwide Harmonized Light-Duty Vehicles Test Cycle. For this purpose, extensive 1-D engine simulations are performed using a combination of a simple compressor and simple turbine model as well as a combination of the stock compressor and a simple turbine model. The results show that an isentropic turbine efficiency of more than 70% over a wide operating range is required for the desired engine operation - especially with regard to the low-end-torque. Based on the crank-angle-resolved engine simulation data, turbine requirements are determined. Their evaluation shows that an axial turbine is a reasonable alternative to conventional radial turbines for this application. Next, a preliminary axial turbine is designed using 1-D/2-D design approaches. Then, the corresponding performance map is calculated by 3-D CFD simulations showing isentropic total-to-static turbine efficiencies of up to 77% over a wide operating range. Ultimately, the derived turbine performance map is implemented into the 1-D engine model and the valve train settings are optimized for this configuration to enhance the lean-burn performance further. The simulation results show a significantly extended λ=2 operating range in comparison to the stock turbine.
The introduction of CAFE (Corporate Average Fuel Economy) norms has put a lot of importance on improving the fuel economy of passenger car vehicles. One of the areas to improve the fuel economy is by reducing engine friction. Camshaft drive torque reduction is one such area that helps in engine friction reduction. This paper explains the camshaft drive torque optimization work done on a passenger car Diesel engine with DOHC (double overhead camshaft). The exhaust camshaft of the engine drives the high-pressure Fuel Injection Pump (FIP) in addition to valve actuation. Camshaft drive torque is reduced by reducing the chain load. This is done through optimum phasing of the FIP lobe that drives the fuel injection pump and the cam lobe actuating the exhaust valves. Additional boundary condition for the phasing is ensuring that the FIP lobe is in the fall region of its profile while the piston is at TDC. This helps in avoiding rail pressure fluctuation. This work is done on the BS VI variant of the engine and results are also compared with the BS IV version of the same engine. Changes in the fuel injection system are also explained. CAE simulations were performed to identify the FIP lobe orientation where the addition of FIP load along with valve train loads results in lowest chain load. Finalizing the FIP lobe orientation led to the re-design of FIP housing which was done successfully. Based on the above optimization the finalized design of camshaft with FIP lobe and chain system was validated in both engine testbed and vehicle conditions successfully. Chain loads are also measured on the engine and they are compared against the simulation results.
The present work deals with the 3-D, transient, system level CFD simulation of an automotive coolant system using a 3D CFD solver Simerics MP+®. The system includes actual CAD of radiator, cooling jacket, coolant pump, bypass valve and thermostat valve. This work is in continuation of the work done by Srinivasan et al. [1] where wax melting, conjugate heat transfer, Fluid Structure Interaction (FSI) of the valve had been solved. Thermostat valve was controlled by wax phase change model which also incorporates the hysteresis effect of wax melting and solidification. The previous work dealt with the simulation of complete cycle, opening, and closing of the thermostat valve system. Besides the physics considered in the previous study, the current model also includes the treatment of cavitation to account for the presence of dissolved gases and vaporization of the liquid coolant. A methodology has been developed and implemented where the run-time of such a system has been made considerably faster to be able to simulate complete drive cycle tests. The distributed parallel solver of Simerics-MP+, coupled with the newly developed method made it to successfully simulate an HOUR of drive-cycle of coolant system within a day of simulation time. Various parameters from experimental measurements have been corroborated with the simulation results to validate the developed technology. Further, a few design iterations are performed to showcase the potential of the developed methodology.
In order to meet the challenges of future CAFE regulations & pollutant emission, vehicle fuel efficiency must be improved upon without compromising vehicle performance. Optimization of engine breathing & its impact on vehicle level fuel economy, performance needs balance between conflicting requirements of vehicle Fuel Economy, performance & drivability. In this study a Port Fuel Injection, naturally aspirated small passenger car gasoline engine was selected which was being used in a typical small passenger car. Simulation approach was used to investigate vehicle fuel economy and performance, where-in 1D CFD Engine model was used to investigate and optimize Valve train events (Intake and exhaust valve open and close timings) for best fuel economy. Engine Simulation software is physics based and uses a phenomenological approach 0-D turbulent combustion model to calculate engine performance parameters. Engine simulation model was calibrated within 95% accuracy of test data. This model is sufficient to analyze the change in engine performance with change of valve timings. GT POWER engine model was integrated to a vehicle simulation model of small hatchback car developed using GT Drive and validated for regulatory drive cycle. 1-D simulation model was run for various combination of Intake and exhaust valve timings. Impact of individually changing each valve timing on Fuel Economy was assessed initially via Vehicle simulation model. Optimization of valve timings was carried out and after analysis Atkinson effect was observed at final timing position. Intake valve closing was delayed which reduced compression stroke. This reduced pumping effort at F.E relevant engine operating points and improved fuel consumption. Fuel economy of optimized proposal was validated against test vehicle. It was possible to fix a Non-Variable Valve Timing (VVT) Valve train without extensive hardware trials for desired performance.
In the present work, a system approach to the tribological optimization of passenger car engines is demonstrated. Experimental data and simulation results are presented to demonstrate the role of surface specifications, ring pack, and lubricant on the piston/bore tribology. The importance of in-design “pairing” of low-viscosity motor oils with the ring pack and the cylinder bore characteristics in order to achieve maximum reduction in GHG emissions and improvement in fuel economy without sacrificing the endurance is elucidated. Earlier motored friction data for two different gasoline engines - Ford Duratec and Mercedes Benz M133 - using motor oils of different viscosity grades are now rationalized using AVL EXCITE® piston/bore tribology simulations. The main difference between the engines was the cylinder bore surface: honed cast iron vs thermally sprayed, and the valve train type: direct-acting mechanical bucket (DAMB) vs roller finger follower (RFF). The simulation data show that mirror-like bores have very low asperity friction and therefore allow safe deployment of ultralow viscosity oil for improved fuel economy. However bearings may remain vulnerable to wear under high load conditions, calling for higher performance resource conserving lubricants.
Since a significant part of energy losses in the internal combustion engine comes from viscous dissipation, the trend has shifted toward low-viscosity oils from SAE 40 and 50 in the 1960s-1980s to current SAE 20 and lower viscosity grades. Use of low viscosity engine oils significantly reduces energy losses in the main bearing and piston/bore systems, while tribological stresses on the valvetrain - especially in flat-tappet cammed engines - may increase. This makes a strong argument for deploying new classes of friction modifiers and antiwear additives. However, development of a balanced formulation is not as straightforward as it appears, and numerous pitfalls may be encountered due to additive interactions. Another serious problem is that the definition of “fuel-economy engine oil” is rather vague, as it depends on choice of reference oil. Nowadays, the assessment of fuel economy is often based on the Sequence VIE or VIF tests using a 2012 3.6L GM V6 gasoline engine. It is not unexpected that the results of this test turn to be largely misleading when extrapolated to modern heavily boosted low-displacement engines. Hence, many OEM-specific fuel economy tests also exist and different engine designs often produce controversial results. Furthermore, the “fuel economy” performance of the same oil in the same engine may change dramatically depending on the driving cycle. All the aforesaid circumstances are to be taken into account when trying to harmonize normative performance claims with customer expectations.
For the regeneration of the Lean NOx Trap (LNT) a rich air-to-fuel ratio must be generated. This operation is very critical and has low combustion stability, especially in low load operation. A certain minimum engine load is always required for the regeneration phase. In the Real Driving Emissions this minimum engine load can be undercut over a long period of time. Hence, a reliable regeneration phase is not possible. The aim of these investigations is to extend the engine map range in which regeneration is possible towards lower loads. This is done by means of a variable valve train with second exhaust valve lift, which increases the internal residual gas amount. This in turns increases the temperature at start of combustion in the cylinder. Especially at low load and low combustion stability this leads to a stabilization of the combustion process. This advantage in combustion stability can be used for a reduction of the minimum engine load. The approach of this work consists of investigations on the engine test bench and accompanying simulations. The combustion process is thermodynamically examined and evaluated on the engine test bench using pressure trace and gas exchange analysis, including a residual gas model.
The JASO GLV-1 standard was introduced in Japan for 0W-8 ultra-low viscosity gasoline engine oil to improve fuel economy. Fuel economy targets are specified for new oil but not for aged oil. In contrast, Sequence VI in the ILSAC GF-6 standard requires fuel economy improvement for both new and aged oils. This test simulates fuel economy improvement after 6400 km (FEI 1) and 16000 km (FEI 2) of driving based on US fuel economy certification testing. Currently, 0W-8 is not included in the ILSAC standard and the fuel-saving durability of 0W-8 has not been investigated. To include ultra-low viscosity oil like 0W-8 in future engine oil standards, it is necessary to know its fuel-saving durability and to examine the evaluation test method. This study focused on the fuel-saving durability of 0W-8 with or without the Mo friction modifier and considered the evaluation method. Sequence VIF tests, JASO M365 MR20DD motored fuel economy tests and actual vehicle fuel economy tests involving 16000 km of driving were conducted to investigate the fuel-saving durability of 0W-8. The results show that (1) fuel-saving durability in the MR20DD motored test using engine oil aged by laboratory oxidation displayed the same tendencies as fuel-saving durability in Sequence VIF tests. This test method shows good potential for evaluating fuel-saving durability. (2) Fuel economy improvement after 16000 km of driving was better than the initial fuel economy improvement with or without the Mo friction modifier. This tendency differed from the results of previous studies of 0W-8 in Sequence VIF tests cited in this paper and the reason is presumed to be differences in the engine valve train system and coatings.
Model-based development (MBD), which makes it possible to study and adjust contradictory requirements between a large number of functions and systems to a high level in a short period of time was implemented within an engine development. In fact, however, elevating engine systems to more advanced levels is a challenge even by satisfying the stand-alone requirements of components. In addition, a still higher level of technology is required for the conflicting relationships between multiple functions, e.g. the power output of an engine and its strength and durability performance, and the reconciliation between the numerous related systems that comprise it. Such reconciling technology requires the consideration of overall optimization that envisions design over a wide range. For present-day development, this would require an extensive period of examination over several years. This presents the issue of requiring an extended period for verification. The valve train, which has multiple functions and is influenced by multiple systems, was therefore taken as the subject of the present research for the purpose of further advancing MBD. The research discussed in this paper conducted a risk analysis in relation to multiple requirements using a design structure matrix (DSM). Quantification of values made it possible to isolate parameters that presented a high risk of rework. Multi-objective design exploration (MODE) was employed to narrow down the design range and satisfy the requested values simultaneously in a short period of time. By this means, the authors sought to create a new MBD process that would reduce development man-hours. The use of a DSM and MODE has increased the efficiency of verification of important parameters, making it possible to realize a new MBD process that reduces the time needed for determination of specifications by 57% against conventional development.
In this contribution, the mechanical torque transmission between the Electric Motor (EM) and the Internal Combustion Engine (ICE) of a P0 architecture hybrid power unit is analysed. In particular, the system is made up of a brand new, single-cylinder 480cc engine developed on the basis of the Ducati 959 Panigale V90 2-cylinders engine. The thermal engine is assisted by a custom electric motor (30 kW), powered by a Li-Ion battery pack. The Ducati 959 Panigale engine is chosen because of its high power-to-weight ratio, and for taking advantage of its V90 2-cylinders layout. In fact, the proposed hybridization process considers to remove the vertical engine head and to replace it by the electric motor directly engaged to the crankshaft using the original valvetrain transmission chain, thus achieving a very compact package. This solution could be suitable for many V-type engines and it aims to obtain a small hybrid power unit for possible motorcycle/small vehicle applications. The original timing chain object of this study is a silent chain, which is commonly employed as a transmission component in hybrid power units because it can operate at high speeds transmitting high loads and ensuring noise reduction. For this reason, the aim of this study is to assess the possibility of using the original chain to couple the EM and the ICE. This investigation allows the replacing of the minimum number of components during the hybridization process leading to a real plug&go solution. Therefore, the mechanical behaviour of the chain is investigated performing a dynamic analysis of the whole crank mechanism. In particular, the original twin cylinders model considering the original valvetrain system is compared with the single cylinder model engaged with the EM. The dynamic analysis provides the maximum load on the single chain link in both configurations, allowing the evaluation of a relative fatigue safety factor.
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