Literature review on stabilizing high speed valve- and drivetrain concepts for racing applications

Roodink, T. (2016) Literature review on stabilizing high speed valve- and drivetrain concepts for racing applications.

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Abstract:The Deutsche Tourenwagen-Masters (DTM) will be moving towards more fuel economic and CO2-engine concepts in the near future. Stefan Ziegler mentioned in 2015 that smaller two liter turbocharged engines with 600 horsepower will become the new standard in 2018. Where engine speeds can increase up to 9500 rpm, which can cause issues with the engine’s valve- and drivetrain. A literature review is carried out to get an overview of the currently available valvetrain concepts. The focus hereby lies on increasing the valve- and drivetrain’s stability and reducing friction and wear. It can be said that the Overhead valve concepts (OHV) needs less components to overcome the distance between the cam- and crankshaft. However, the additional flexibility inside the components and rotating/translating mass that come with the OHV principle make it an unsuitable concept for high speed (race) engines. Therefore only Overhead camshaft (OHC) engines are being considered (Ballard, 2002) (Trzesniowski, 2014). Fingers or rockerarms are, commonly seen in racing engines. Mainly, since the reciprocating weight is reduced and it allows for higher valve lifts with equal or even smaller camshaft lobes, due to the lever arm. A valvetrain including rockerarms also has an advantage over direct-driven systems in terms of friction (Carley, 2011). According to Trzesniowski (2014) Diamond Like Carbon (DLC) coatings are applied on the valve fingers of many racing engines, minimizing both wear and friction. Bamsez (2013) from Cosworth states that finger followers have a friction and stiffness advantage over bucket tappets. Valves in racing engines are exposed to even higher temperatures, reciprocating accelerations and cylinder pressures than those in production cars. Moreover, there is a risk of having floating valves when operating engines at higher speeds (Ajay, 2014). Multiple solutions to the floating valve problem are mentioned in literature (Trzesniowski, 2014) (Bamsez, 2013) (Ballard, 2002). Decreasing the valve’s weight may prevent floating valves. This is more advantageous than increasing the spring constant regarding friction and inertia. This can be done by changing the design, the material and the production technique, since they all are strongly related. Varying the valve spring’s shape, surface treatment, inclination or wire- and coil diameter over the length are commonly used solutions to the floating valve problem in motorsport engines (Youd, 2011). Moreover, the number of springs is varied to cope with oscillations. To maintain control over the valvetrain even in harsh high speed conditions engine engineers were forced to develop different concepts, like the Pneumatic Valve Return System (PVRS), that can be found in the F1 and MotoGP series. Moreover, a hydraulic valve system and a Desmotromic valve actuation proved to be solutions as well. The camshafts are driven by gears, a chain or belt. These driving mechanisms can lead to fluctuations in the angular velocity of the camshaft, caused by vibrations. Spur gears are more durable, accurate and efficient than roller chain and belt mechanisms, especially for high revving engines (Trzesniowski, 2014). Nonetheless, gears are sensitive to torsional vibrations and produce sound. To minimize these viscous dampers, additional gears, masses and quill drives are being designed (Hayakawa, 2009). Sakurahara (2009) states that a stiffer car has a better performance on the track. Being part of the carrying chassis means that the stiffness of the cylinder head and actually of the whole engine have to be as high as possible. A major part of the research capacity goes into developing valvetrain models (Hayakawa, 2009). Besides being cheaper than testing it is also faster, allowing for a shorter responding time on regulation changes. Whereas G. Blair stated in 2006: “There is no such thing as cam design, there is only valve lift profile design which requires the creation of a cam and follower mechanism to reliably provide this designed valve lift profile.”
Item Type:Internship Report (Master)
Audi Sport, Germany
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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