Author: William E. Tourdot
Publisher:
ISBN:
Category :
Languages : en
Pages : 334

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Author: Mohammad Pournazeri
Publisher:
ISBN:
Category :
Languages : en
Pages :

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The automotive industry has been in a marathon of advancement over the past decades. This is partly due to global environmental concerns about increasing amount of air pollutants such as NOx (oxides of nitrogen), CO (carbon monoxide) and particulate matters (PM) and decreasing fossil fuel resources. Recently due to stringent emission regulations such as US EPA (Environmental Protection Agency) and CARB (California Air Resource Board), improvement in fuel economy and reduction in the exhaust gas emissions have become the two major challenges for engine manufacturers. To fulfill the requirements of these regulations, the IC engines including gasoline and diesel engines have experienced significant modifications during the past decades. Incorporating the fully flexible valvetrains in production IC engines is one of the several ways to improve the performance of these engines. The ultimate goal of this PhD thesis is to conduct feasibility study on development of a reliable fully flexible hydraulic valvetrain for automotive engines. Camless valvetrains such as electro-hydraulic, electro-mechanical and electro-pneumatic valve actuators have been developed and extensively studied by several engine component manufacturers and researchers. Unlike conventional camshaft driven systems and cam-based variable valve timing (VVT) techniques, these systems offer valve timings and lift control that are fully independent of crankshaft position and engine speed. These systems are key technical enablers for HCCI, 2/4 stroke-switching gasoline and air hybrid technologies, each of which is a high fuel efficiency technology. Although the flexibility of the camless valvetrains is limitless, they are generally more complex and expensive than cam-based systems and require more study on areas of reliability, fail safety, durability, repeatability and robustness. On the contrary, the cam-based variable valve timing systems are more reliable, durable, repeatable and robust but much less flexible and much more complex in design. In this research work, a new hydraulic variable valve actuation system (VVA) is proposed, designed, prototyped and tested. The proposed system consists of a two rotary spool valves each of which actuated either by a combination of engine crankshaft and a phase shifter or by a variable speed servo-motor. The proposed actuation system offers the same level of flexibility as camless valvetrains while its reliability, repeatability and robustness are comparable with cam driven systems. In this system, the engine valve opening and closing events can be advanced or retarded without any constraint as well as the final valve lift. Transition from regenerative braking or air motor mode to conventional mode in air hybrid engines can be easily realized using the proposed valvetrain. The proposed VVA system, as a stand-alone unit, is modeled, designed, prototyped and successfully tested. The mathematical model of the system is verified by the experimental data and used as a numerical test bench for evaluating the performance of the designed control systems. The system test setup is equipped with valve timing and lift controllers and it is tested to measure repeatability, flexibility and control precision of the valve actuation system. For fast and accurate engine valve lift control, a simplified dynamic model of the system (average model) is derived based on the energy and mass conservation principles. A discrete time sliding mode controller is designed based on the system average model and it is implemented and tested on the experimental setup. To improve the energy efficiency and robustness of the proposed valve actuator, the system design parameters are subjected to an optimization using the genetic algorithm method. Finally, an energy recovery system is proposed, designed and tested to reduce the hydraulic valvetrain power consumption. The presented study is only a small portion of the growing research in this area, and it is hoped that the results obtained here will lead to the realization of a more reliable, repeatable, and flexible engine valve system.

Author: Ahmad M. Sabri
Publisher:
ISBN:
Category :
Languages : en
Pages : 486

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Author: John S. Ma
Publisher:
ISBN:
Category :
Languages : en
Pages : 416

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Author: Mitchell Terpstra
Publisher:
ISBN:
Category : Automobiles
Languages : en
Pages : 116

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Conventional engines with camshafts with fixed timings force a compromise between performance at high engine loads and fuel economy at low engine loads. Adjusting internal combustion engine valve timing and lift through a variable valve actuation (VVA) system is an established method of improving engine performance [1]. A fully flexible hydraulic variable valve actuation (HVVA) system in development at the University of Waterloo allows the valve timing to be optimized for any engine operating condition. This project is a further development of this HVVA system. First, the previous prototype was thoroughly tested and evaluated. Major design issues and challenges were addressed, and changes were incorporated into a new prototype design. This prototype was designed to be robust and more compact than the previous system. A completely new concept was developed for the phasing system used to adjust the valve timings. The new HVVA design was manufactured, assembled, and installed on a single cylinder test engine. Initial experiments of the new HVVA system validated its ability to change engine valve timing and match the profiles of different VVA strategies. The system was able to switch between different profiles in

Author: Geoffrey Leyland
Publisher:
ISBN:
Category : Actuators
Languages : en
Pages : 206

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Author: Matthew Chermesnok
Publisher:
ISBN:
Category :
Languages : en
Pages : 76

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This thesis documents the development of a fully continuous, hydraulics-based variable valve timing system. This hydraulics based variable valve timing system is capable of controlling an engine valves lift height and infinitely varying the engine valves lift profile. Along with full valve controllability during normal operation, the variable valve timing system is capable of providing the same operation as a classic cam shaft under engine power loss conditions. This is possible due to the rotating hydraulic spool valves coupled to the engines crank shaft, which are used to actuate the engine poppet valves. The main focus of this thesis is to investigate, alter and implement a new iteration of the hydraulic variable valve timing system on a standalone test bench to validate the systems operating principles. The test bench utilizes servo motors to act as an engines crank shaft which runs the rotating hydraulic spool valves and hydraulic pump. This serves as an intermediate step to full engine implementation of the variable valve timing system. The research begins by analyzing the current mechanical spool valve and hydraulic cylinder design for any potential problems that may occur either during assembly or full operation. The basic system equations are presented to give a glimpse into the working principles of the rotary valves. The mechanical, electrical, and hydraulic subsystems are discussed in terms of what was considered during the design and implementation process. Then design changes that were performed on the rotary valve system to overcome any failures. Lastly the resulting data is presented from the current variable valve timing design to verify proper system functionality.

Author: Mohammad Sharif Siddiqui
Publisher:
ISBN:
Category : Automobiles
Languages : en
Pages : 102

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The combustion characteristics in an engine cylinder can greatly change over a range of speeds and loads. However, conventional engines x the timing and amount of intake and exhaust, which can lead to higher emissions, wasted fuel, and lower power output. This thesis studies the application of a hydraulics based variable valve actuation system to change the valves' lift and timing on a single cylinder spark ignition engine. In addition to controlling the valve actuation, a hydraulics based design has the advantage of protecting against engine failure in cases of electrical power loss, reverting the system to behave as a conventional camshaft valve train. The research extends the previous iterations of the hydraulics design to prevent leakage, retain pressure, and reliably open and close the engine valves. A hydraulic cylinder is used to replace the conventional cam where pressurized fluid opens, and spring force closes, the engine valve. The pressurized fluid is supplied to, or removed from, the cylinder using rotary spool valves coupled to the engine crankshaft. Additionally, the system is modelled in Simulink to determine the effect of system pressure, flow area, and spring rate on the resulting valve pro file. After modelling the system's performance for achieving variable lift and timing, the system was designed, manufactured, and tested on a single cylinder engine with the aid of a dynamometer. Experimental results for valve lift showed good agreement with the simulation models. Majority of the tests were performed using manual control, followed by experiments with active control of the system pressure to reach a desired valve lift. The lift controller is able to achieve the desired valve actuation in under 2 seconds with active pressure feedback. Lastly, the ability of the hydraulic variable valve system as a viable alternative is shown by achieving combustion at 1500 RPM engine idle speed.

Author: Gilbert Ray Hardesty
Publisher:
ISBN:
Category :
Languages : en
Pages : 86

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Author: Steven Paul Kagoda
Publisher:
ISBN:
Category :
Languages : en
Pages : 220

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