VALVETRONIC

VALVETRONIC

Abstract

The most important breakthrough in the hunt for a more efficient valve-train design will prove to be the elimination of the camshaft by actuating the valves with an electrically operated and computer controlled system. The camshaft, among other valve-train components of the Internal Combustion Engine could soon become obsolete. In mechanical and automotive engineering fields today, a great deal of time and research is being directed towards developing a better valve-train. For years there have been several characteristics which have defined an engine. One of the major ones is the presence of a cam or cams, spun by the crankshaft, which actuate the valves and allow the ICE to intake air and expel exhaust gasses. The ICE relies on petroleum to function. Consequently, automobiles manufacturers are trying everything they can to increase gas-mileage while maintaining horsepower and controlling emissions. Several technologies are currently being researched and/or employed in the valve-trains of engines that may be mass produced in years to come. There are also new materials and designs being used to create the valves of the future. The main goal of these technologies is to reduce mechanical losses within the engine, and in effect make the ICE more efficient.

Introduction

As long as there have been internal combustion engines in automobiles, the common goal of engineers has been to maximize their power while maximizing their efficiency as well. In the past this has taken place through innovations in engine design, head modifications, and the largest leap in recent history is fuel injection. However, with the eminent approach of the end petroleum resources, more and more people are criticizing combustion engines for their reliance on a finite resource as well as their harmful emissions.

Since the birth of the combustion engine, there have been many parts that are considered integral components of the design and have remained constant. The valve-train is one of them. The valve-train is the assembly which opens and closes valves in a cylinder’s combustion chamber to allow air in and exhaust gasses out. The valve-train relies on a camshaft which actuates the valves and is driven by the crankshaft, and in effect uses approximately 10 % of the engine’s total power output. (This can vary depending on the size of the engine, number of camshafts, or number of valves.) This means that the camshaft is one of the main influences of the overall performance of the vehicle.

Lately engineers have been making innovations to make the valve-train more efficient. Some of these innovations include modifying the materials used in making the valves and looking for ways to eliminate the camshaft altogether.

(The rotary engine does not apply to these statements because it does not operate with cam-shafts or valves.)

Due to the fact that the timing of the engine depends both on the rotational velocity of the camshaft and the shape of its lobes, engineers make decisions that affect an engine’s performance early in the design process. “The resulting design represents a compromise between fuel efficiency and engine power. Since maximum efficiency and maximum power require unique timing characteristics, the cam design must comprise between the two extremes.”[2]

Camshafts in automobiles differ by their profiles. A camshaft’s profile depends on three main variables: timing, lift, and duration. Timing defines exactly when in the cycle the cam will actuate the valve. Timing is measured in degrees. Lift is the variable that dictates how far the valve will extend into the combustion chamber and is typically measured in thousandths of an inch. A typical street engine’s valves have a lift of approximately .375 inches while racing engines have a lift of approximately .5 inches. Duration is the measurement of how long the valve is held open, and is also expressed in degrees.

Some engines today (Such as Honda’s VTECH) utilize Variable Valve Timing to optimize engine torque in low RPM’s and horsepower in high RPM’s. These designs remain mostly mechanical in nature, consequently limiting the range of timing changes. Although there may be some differences between automotive manufacturer’s designs, they all still rely on the camshaft; therefore there are still limitations since the timing depends on the speed of the engine. The main goal in developing new valve-trains is to allow them to be infinitely variable. The best way to accomplish this remains undecided, but there are working and tested concepts in the world today; all of which are based on a cam-less design.

Download full seminar papers At
http://www.enjineer.com/forum