The design of the camshaft and drive

There are three important characteristics of the construction of a camshaft, and they control the engine power curve: gas distribution phase of the camshaft, valve opening duration and magnitude of valve lift. Later in this article we will describe what constitutes a design camshafts and their drive. Valve lift is usually calculated in millimeters and represents the distance at which the maximum valve moves away from the saddle. The duration of valve opening - this time, which is measured in degrees of crankshaft rotation. Length can be measured in different ways, but because the maximum flow with a small valve lift, duration measures the usually after the valve is already rising from the seat by a certain amount, often it is 0,6 or 1,3 mm. For example, a specific camshaft may be the duration of the opening in 2000 turns when climbing in the 1.33 mm. As a result, if we use the rise of the pusher in the 1.33 mm as a stopping point and started lifting the valve, the camshaft will hold the valve in the open state during the 2000 rotation of the crankshaft. If the duration of valve opening will be measured at zero lift (when he was just moving away from the seat or in it), the length of the crankshaft will be 3100 or even more. Moment when a certain valve closes or opens, often called phase camshaft timing. For example, the camshaft can perform the action of opening the intake valve at 350 before top dead center and close it at 750 after the bottom dead center. Increase the separation valve lift can be a useful effect in increasing engine power, since power can be added without significant interference with the engine performance, especially at low revs. If you delve into the theory, the answer to this question is quite simple: design a camshaft with a short opening time of valves needed to increase the maximum engine power. Work it will theoretically. However, drive mechanisms in valves and not as simple. In this case, the high speed valves, which are caused by these profiles will greatly reduce the reliability of the engine. When the valve opening speed increases, then the movement of the valve from the closed position to complete his recovery and return to your starting point is less time. In case the movement will become even shorter, you will need valve springs with great effort. Often it becomes mechanically impossible, not to mention the fact that in motion valves pretty low revs. As a result, what is reliable and practical value of the maximum valve lift? Camshafts with the magnitude of recovery, more than 12.8 mm (at least for the motor in which the drive is carried out with hoses), are impractical for conventional motor area. Camshafts with the duration of the intake stroke at least 2900, which combined with the magnitude of valve lift more than 12.8 mm, provide very high speed opening and closing valves. This certainly will create additional pressure on the valve train, which significantly reduces the reliability: the camshaft lobes, valve guides, rods, valves, valve springs. However, the shaft with a high speed valve lift can be operated in a pretty good start, but the service life of valve guides and sleeves, most likely will not exceed 22000 km. Well, most manufacturers camshaft design your details so that they achieved a compromise between the duration of valve opening and lift values, for reliability and long life. Duration of stroke and discussed valve lift are not only among structural elements of a camshaft that affect the engine performance. Moments, opening and closing valves on the situation of the camshaft are also equally important parameters for optimizing the characteristics of the motor. These phase camshaft timing can be found in the data table, which is attached to any quality camshaft. Such a data table and graphically illustrates the numbers of the angular position of a camshaft, when final and intake valves are closed and opened. They will be precisely defined in degrees of crankshaft rotation before the top or bottom dead center. The angle between the centers of the cams - this is the angle of displacement between the center line of an outlet valve cam (which is called the exhaust cam) and the center line inlet valve cam (which is called the intake cam). The angle of the cylinder is frequently measured in the angles of rotation cam "because we discuss the shift cams relative to one another, this is one of the few moments when the characteristic of the camshaft is specified in degrees of rotation of the shaft, but not in degrees of crankshaft rotation. The exceptions are those where the engines, incorporates two camshafts in the cylinder head (cylinder head). The angle chosen in the design of the camshaft and drive directly affect the valve overlap, ie the period when the exhaust and intake valves are open simultaneously. Valve overlap is often measured SB angles of rotation of crankshaft. In times of decreasing the angle between the centers of the cams, the intake valve is opening and closing the outlet valve. You always have to remember that the valve overlap and affect change in opening hours: in case of increasing the duration of the opening, overlapping valves will also be large, while ensuring that no change of the angle to compensate for these increases.