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The End of Compromise
Published in Patrick Hossay, Automotive Innovation, 2019
In fact, greater capacity for variation and control is possible. Cam profile switching (CPS) typically uses two sets of distinct cam lobes, or otherwise shift between two distinct cam profiles. As a result, both timing and lift can be changed. But once again, only as a choice between two options, typically a close-to-conventional cam for normal operation, and a cam designed for performance operation at high rpm. Manufacturers have defined multiple sophisticated systems that can allow for control of both lift and timing, and can offer incremental or continuous variable valve timing (VVT), variable valve lift (VVL), or both. BMW, for example, uses a sprocket on a helical spline of the camshaft to progressively adjust valve timing; and their Valvetronic variable valve system utilizes an electronically adjusted cam and rocker arm to vary the relationship between the camshaft and the valve stem allowing variation in valve lift from 0.3 to 9.7 mm (Image 2.5). This means valve lift variation can be used to control engine speed, and once again eliminate throttling loss from a conventional throttle.
Lubricant Contribution to Energy Efficiency
Published in Don M. Pirro, Martin Webster, Ekkehard Daschner, Lubrication Fundamentals, 2017
Don M. Pirro, Martin Webster, Ekkehard Daschner
There are a number of approaches that are aimed at varying the exhaust and air intake strategies. In a conventional engine, the valves that control these processes are driven by cam fixed shafts. This sets the sequencing and amount of valve opening and closing to a fixed pattern for all engine operating conditions. A number of systems are designed to provide a means to change valve behavior based on engine operation and include variable valve timing, continuously variable valve timing, variable valve lift (VVL), and valve phasing as examples. Each of these can affect the valve operation in different ways but all aim to provide an extra degree of control of valve operation during different phases of engine operation. This can reduce air pumping losses, help maintain temperatures, manage available power, and reduce emissions. In some cases, it can even adjust the thermodynamic cycle. An example of this is conversion from the normal Otto cycle to the Atkinson cycle that is achieved when the inlet timing is extended, allowing some of the intake air to return into the manifold. Adjustable valve systems require more complex cam and associated drive systems, which are frequently controlled through hydraulically operated mechanisms. This introduces a requirement that the engine oil also needs to perform as a hydraulic fluid with management of air entrainment and separation becoming important attributes.
Internal Combustion Engines
Published in Mehrdad Ehsani, Yimin Gao, Stefano Longo, Kambiz M. Ebrahimi, Modern Electric, Hybrid Electric, and Fuel Cell Vehicles, 2018
Mehrdad Ehsani, Yimin Gao, Stefano Longo, Kambiz M. Ebrahimi
While many engines use only two valves, high-performance engines use three, four, or five valves to increase the intake flow area. Multiple valves provide a significant increase of torque at high engine speed but sacrifice low-speed torque because the larger intake flow area results in slower flows at low speed. Multiple valves imply multiple camshafts, which increases the cost and complexity of the engine. Modern high-performance engines can feature variable valve lift and timing.
Operational feasibility of a spark ignition engine which is subjected to VTEC management strategy
Published in Australian Journal of Mechanical Engineering, 2020
Lucky Anetor, Edward E. Osakue
Research and practical engine operations have shown that various variable valve lift and timing (VVT) technologies can improve idle speed stability, low speed stability, emissions, power and fuel economy of the engine. In view of this, a lot of automobile manufacturers have started incorporating this technology into their products. Some of the automobile companies that have commercialised and incorporated the variable valve lift and timing technology in various forms are Toyota (i-VTEC), BMW (Vanos), Ford (VCT), Delphi (VCP), Nissan (CVVT), Hyundai (VVT) and Kia (CVVT). The mechanics of these variable valve lift and timing systems is based on camshaft phase modulation which adjusts the valve timing by changing the relative phase of the cam shaft and crankshaft. It is worth mentioning that this method of implementing the variable valve lift and timing can only adjust the valve timing over a certain/restricted range of angles. However, when compared with the traditional valve-cam systems, it does improve engine emissions and performance significantly.
Modelling of an electro-hydraulic variable valve actuator for camless engines aimed at controlling valve lift parameters
Published in International Journal of Control, 2021
Alessandro di Gaeta, Carlos Ildefonso Hoyos Velasco, Veniero Giglio
Unlike repetitive control, the cycle-by-cycle control proposed here is based on the idea of tracking arbitrary valve lift trajectories (among all feasible trajectories of the EHVA system) by regulating one or more of its shape parameters. The implementation of advanced combustion concepts requires increased valve control through variable valve timing and variable valve lift: for example, Atkinson and Miller thermodynamic cycles (used for reducing pollutant emissions, improving volumetric efficiency and mitigating knock phenomena) rely on the possibility of varying the timing and lift of the valve trajectory. In this context, we undertook design of a valve lift controller.