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A Review on Tribological Investigations for Automotive Applications
Published in Jitendra Kumar Katiyar, Alessandro Ruggiero, T.V.V.L.N. Rao, J. Paulo Davim, Industrial Tribology, 2023
Vipin Goyal, Pankaj Kumar, Pradyumn Kumar Arya, Dan Sathiaraj, Girish Verma
The primary purpose of the valve train is to transform rotational camshaft movement into linear valve movement so that airflow into the combustion chamber can be controlled. Friction is an essential factor when selecting a valve train for an IC engine. Typically, two types of followers are used: roller follower and sliding follower. Roller follower is the optimum arrangement for valve train compared to sliding follower because roller contact gives a smaller coefficient of friction. Friction losses in the valve system are approximately 5–10% of mechanical losses, which is less than piston assembly. The inclusion of friction modifier chemicals like molybdenum dithiocarbonate into the lubricating oil reduces the friction coefficient in the valve train [31]. The wear of valve seats and their grooves seems to be a significant issue in the valve train that influences engine performance. So, materials for valve seats are chosen that are resistant to wear and corrosion and have high-temperature strength. The materials used for the inlet valves are hardened low alloy steel. Still, the materials used for the exhaust valves are hot hardened stainless steel because they require more excellent corrosion resistance and high-temperature strength.
Introduction to Kinematics
Published in Kevin Russell, Qiong Shen, Raj S. Sodhi, Kinematics and Dynamics of Mechanical Systems Implementation in MATLAB® and Simmechanics®, 2018
Kevin Russell, Qiong Shen, Raj S. Sodhi
Several of the noted linear and circular input–output motion combinations appear in the valve train assembly illustrated in Figure 1.6.† The valve train assembly is comprised of four major components: the cam, rod, rocker, and valve (Figure 1.6a). Figure 1.6b includes the motion produced by these four components. The initial input in this assembly is produced by the cam.‡ The constantly rotating cam produces an oscillating translational rod motion. The oscillating translational rod motion produces an oscillating rotational rocker motion (as the name “rocker” implies). Lastly, the oscillating rotational rocker motion produces an oscillating translational valve motion. It is the oscillating valve motion that governs the timing in which air and fuel are brought into an internal combustion engine and exhaust products are removed from the engine.
Engine Tribology
Published in Peerawatt Nunthavarawong, Sanjay Mavinkere Rangappa, Suchart Siengchin, Kuniaki Dohda, Diamond-Like Carbon Coatings, 2023
H. H. Masjuki, M. Gulzar, M. A. Kalam, N. W. M. Zulkifli, M. A. Maleque, M. S. S. Malik, A. Arslan
The valvetrain system in an IC engine has components which include the cylinder head, intake and exhaust valves, and the actuation mechanism. For a conventional IC engine, this subsystem would include the camshafts, intake and exhaust poppet valves, rocker arms, valve springs, and cam followers (James, 2012). There are four types of contacts and friction sources in the different configurations of valvetrains (Wong & Tung, 2016). The relevant lubrication regimes include hydrodynamic to boundary lubrication and mixed lubrication. The major contact and friction sources are: The camshaft bearingsThe cam/follower interfaceThe rocker arm pivot/shaftLinearly oscillatory components Valvetrain architecture in IC engines can be categorized in five different types. However, two types of valvetrain architectures are mostly used in modern engines including roller finger followers and direct acting mechanical bucket (Gangopadhyay, 2017). Considering the direct-acting mechanical bucket architecture type, the cam lobe-tappet interaction is responsible for major frictional losses. For the roller finger follower type, the cam and tappet interface experiences comparatively very low friction. The reason for low friction is the mixed lubrication regime in which this tribo-pair operates and, thus, offers various options for friction reduction through lubricating oils, surface engineering and low friction coatings.
Sensitivity of light duty vehicle tailpipe emission rates from simplified portable emission measurement systems to variation in engine volumetric efficiency
Published in Journal of the Air & Waste Management Association, 2021
Tongchuan Wei, H. Christopher Frey
VE is also affected by inter-vehicle variability in engine characteristics, such as VHP, FI, VPC, VVT, VT, CD, and CR (Chen et al. 2011; Heywood 2018; Hong, Parvate-Patil, and Gordon 2004; Pulkrabek 2003; Turner et al. 2004). VE tends to be higher for engines with larger VHP (Pulkrabek 2003). FI includes port fuel injection (PFI) and GDI for the current U.S. LDGV fleet (EPA 2021). GDI engines tend to have higher VE than PFI engines (Chen et al. 2011). An engine with more VPC tends to have higher VE (Heywood 2018). VVT is a process of changing the timing of valve opening and closing. Engines that have VVT have a higher VE than engines that do not (Hong, Parvate-Patil, and Gordon 2004). An engine valvetrain is a mechanical system that controls the operation of cylinder valves. VTs include overhead valves (OHV), single overhead camshafts (SOHC), and dual overhead camshafts (DOHC). VE tends to increase from OHV to SOHC and from SOHC to DOHC (Turner et al. 2004). VE is affected by a derived term based on Cylinder Displacement and Compression Ratio (CDCR). CDCR is the reciprocal of CD minus the reciprocal of the product of CD and CR, or . Larger CDCR indicates an engine with smaller CD and higher CR. VE is larger for smaller CD and for higher CR; thus, VE tends to increase as CDCR increases (Heywood 2018; Pulkrabek 2003). Details about the physics that explain these trends are described in Section SM.1 in the SM.