Internal-combustion engines – Charge forming device – With fuel pump
Patent
1995-02-16
1996-07-30
Moulis, Thomas N.
Internal-combustion engines
Charge forming device
With fuel pump
F01L 112, F01L 118
Patent
active
055402070
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a camshaft drive over a camshaft for the exhaust valve and the inlet valve and for actuating the injection pump of a diesel engine, only one cam being provided for actuating the three functions of each cylinder. Shortening the camshaft, particularly of small diesel engines, is an objective aimed for by the designer. He will therefore attempt to reduce the number of cams for the drives that are to be actuated over the camshaft. In this connection, the different requirements of the courses of motion, on the one hand, for the two valves and, on the other, for the injection pump, are a problem. The valve timing aims at keeping the inlet valve, when it reaches the top dead center, and the outlet valve, when it reaches the bottom dead center, open for a sufficiently long time, so that good filling and emptying of the cylinder can be achieved. Accordingly, the designer aims for a more elongated, ideally rectangular course for the curve between the top dead center and the bottom dead center. The mass accelerations of the valve drive and the Hertz forces can be limited by a curve approximating such a rectangular profile.
On the other hand, the requirements for the driving mechanism of the injection pump are such as to make the actual injection time as short as possible. The ideal curve for the plunger velocity, related to the cam angle, is a curve for the velocity of the plunger of the injection pump that rises particularly steeply up to the top dead center; in this connection, the three phases of the pump control, namely the preliminary stroke, during which the intake port is closed, an intermediate stroke, during which the retraction volume in the injection pump is filled and, finally, the injection stroke, which is terminated shortly before the top dead center of the pump plunger is reached, are connected timewise within this rising branch of the velocity curve. On the other hand, if anything, the decreasing branch of the velocity profile must be described as noncritical.
Starting out from these different requirements for the timing of the two valves on the one hand and of the injection pump on the other, the designer previously has been forced to provide separate camshaft drives, for example, in the form of a camshaft with two cams, namely one for actuating the drag lever for the inlet valve and the exhaust valve and a further one for actuating the injection pump, in order to realize the two functions.
Moreover, a cam drive for the three functions, but with only one cam is known (DE-A1-3325510), this function meaning the actuation of the injection pump as well as of the inlet valve and the exhaust valve. However, the requirements, which are explained above and must be met by the different courses of motion, cannot be fulfilled with the known cam drive.
With the above as a background, it is an object of the present invention to provide a simple, multifunctional camshaft drive, which requires reduced constructive effort and enables a compact construction, so that it does justice to the requirements of very small diesel units in a special manner.
Pursuant to the invention, this objective is accomplished owing to the fact that the actuation through the cam takes place in each case directly over a rocker arm and that, for controlling the plunger velocity of the injection pump, the mechanical advantage with respect to the swiveling axis of the rocker arm and its distance from the connecting line between the rolling-off point of the rocker arm with the cam and the rolling-off point of the rocker arm with the plunger is selected so that, for a pump stroke of at most 10 mm, the velocity profile for the plunger velocity, based on the cam angle, increases more steeply than that for the two valves. By these means, not only is an extremely small structural volume achieved for the whole of the camshaft drive, including disposing the injection pump, but also, aside from the three functions mentioned, further engine functions, such as a lubricating oil pump and/or a fuel supply pump can be actuated ove
REFERENCES:
patent: 3814067 (1974-06-01), De La Fuente
patent: 3908613 (1975-09-01), Loby
patent: 4412513 (1983-11-01), Obermayer et al.
patent: 4602604 (1986-07-01), Kauer
patent: 5390642 (1995-02-01), Thoma
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