Solenoid Valve For Controlling A Fuel Injector
Solenoid valve part for controlling a fuel injector in a fuel injection system has a valve needle
, the open and closed positions of which may be controlled by the solenoid valve valve part. The solenoid valve valve part has a valve ball which rests on a valve seat and which lifts up from the valve seat when current flows through the solenoid valve valve part.
The valve seat is in hydraulic connection with the fuel injector via a borehole. When the valve ball lifts up from the valve seat, a pressure medium such as high-pressure fuel flows through the borehole into a pressure relief chamber in the solenoid valve valve part. In the further progression this causes the fuel injector to open. To prevent the formation of cavitation bubbles and the damage thus caused, the borehole includes, at least in part, one or more sections having a cross section which continuously expands in the direction of the valve seat. A separation in flow brought about by sharp transition edges, which may cause cavitation bubbles, is thus counteracted.
Solenoid valves are used to control fuel injectors in a fuel injection system having a valve needle, the open and closed positions of which may be controlled by the solenoid valve.
The solenoid valve has a valve ball, which lifts up and opens a valve seat when current flows through the magnet assembly of the solenoid valve. This valve seat is in hydraulic connection with the control pressure chamber of the fuel injector via a borehole. When the valve seat opens, the pressure in the pressure chamber of the fuel injector drops, and the fluid (pressure medium) flows through the borehole in the direction of the valve seat and further into a pressure relief chamber. This causes the valve needle or the fuel injector to open.
It is believed that the common rail injector (CRI) operates according to this conventional operating principle, which permits a main injection and a pilot injection having very brief injection times. Such a solenoid valve is referred to, for example, in German Published Patent Application No. 196 50 865.
Cavitation may cause severe damage to the valve seat of the valve part. The borehole extending through the valve part includes a cylindrical A-throttle adjoining a pilot borehole in the control pressure chamber of the fuel injector, and a subsequent cylindrical diffuser bore leading to the valve seat. The cavitation damage may, for example, occur in the region of an abrupt transition from the diffuser bore to the valve seat. This damage may cause "washout" of the seat edge. As the damage increases, this edge may break off, resulting in total failure of the injector and operational failure of the vehicle. To solve this problem, the formation of cavitation bubbles should be reduced, and the site of implosion of any remaining bubbles should be shifted to a location, such that this effect no longer influences the correct functioning of the injector.
An exemplary solenoid valve according to the present invention includes a borehole which has, at least in part, one or more sections having a cross section that continuously expands in the direction of the valve seat. Sharp-edged transitions within the borehole, for example, in the transition region from the A-throttle to the diffuser bore, may thus be avoided. It is believed that a conical geometry of the expanding section is advantageous.
A severe separation in flow may occur when the fluid (pressure medium) flows through the A-throttle to the outlet edge downstream, which is sharp-edged due to the manufacturing process, toward the diffuser bore. Dead water and recirculation areas may form at those locations. These effects may result in fluctuations in the reproducibility of the amount of fluid flowing through, as well as in the formation of zones at partial vacuum and cavitation bubbles.
Further within the borehole, the flow again contacts the bore walls. Shortly before reaching the throttle point at the valve seat situated further downstream, the pressure in the medium rises again and the cavitation bubbles floating in the liquid stream implode, thereby causing the described cavitation damage at the wall of the flow channel.
As a result of the borehole of an exemplary solenoid valve according to the present invention, the flow geometry in the valve part is altered, so that a generally turbulence-free transition of the medium from the A-throttle to the valve seat may be achieved without the described negative effects.
by: Bowman
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