1. Field of the Invention
The invention relates to a common rail injector for injecting fuel in a common rail injection system of an internal combustion engine, having a nozzle body which is secured with the aid of a lock nut on a retaining body that has a fuel inlet in communication with a central high-pressure fuel reservoir outside the injector and with a pressure chamber inside the injector, from which chamber fuel subjected to high pressure is injected as a function of the position of a control valve that assures that a nozzle needle, which can reciprocate in a longitudinal bore of the injector axially counter to the prestressing force of a nozzle spring received in a nozzle spring chamber, lifts from a seat when the pressure in the pressure chamber is greater than the pressure in a control chamber that communicates with the fuel inlet via an inlet throttle.
In common rail injection systems, a high-pressure fuel pump feeds the fuel into the central high-pressure reservoir, which is called a common rail. From the common rail, high- pressure lines lead to the individual injectors, which are assigned one to each of the engine cylinders. The injectors are triggered individually by the engine electronics. The rail pressure prevails in the pressure chamber and at the control valve. When the control valve opens, fuel subjected to high pressure enters the combustion chamber, moving past the nozzle needle, which is lifted counter to the prestressing force of the nozzle spring.
In conventional injectors, of the kind known for instance from German Patent Disclosure DE 197 24 637 A1, relatively long nozzle needles with a so-called thrust rod are used. In operation, as a consequence of the high pressures and the rapid load changes, very strong forces are exerted on the nozzle needles. As a result of these forces, the nozzle needle is stretched and compressed in the longitudinal direction. This in turn means that the nozzle needle stroke varies as a function of the forces acting on the nozzle needle.
In German Patent Disclosure DE 199 36 668, not published by the priority date of the present application, injectors are described that work without a thrust rod. To define the control chamber, a sleeve is used that is displaceable, performing sealing, on the end of the nozzle needle remote from the combustion chamber and that is retained in contact with the injector housing with the aid of the nozzle spring. Sealing off of the control chamber is achieved by a bite edge embodied on the bearing face of the sleeve. If a leak occurs at the bite edge, this can cause failure of the affected injector.
The primary object of the invention is to furnish a common rail injector that while using conventional injection nozzles permits markedly higher nozzle needle speeds and that functions stably. Furthermore, the injector of the invention should be simple in design and capable of being economically produced.
In a common rail injector for injecting fuel in a common rail injection system of an internal combustion engine, having a nozzle body, which is secured with the aid of a lock nut on a retaining body that has a fuel inlet in communication with a central high-pressure fuel reservoir outside the injector and with a pressure chamber inside the injector, from which chamber fuel subjected to high pressure is injected as a function of the position of a control valve which assures that a nozzle needle, which can reciprocate in a longitudinal bore of the injector axially counter to the prestressing force of a nozzle spring that is received in a nozzle spring chamber, lifts from a seat when the pressure in the pressure chamber is greater than the pressure in a control chamber which communicates with the fuel inlet via an inlet throttle, this object is attained in that the control chamber is integrated with the nozzle body; that embodied on the end of the nozzle needle remote from the combustion chamber is a control peg which is guided in the control chamber, and that the nozzle spring chamber is disposed outside the control chamber. The invention offers the advantage that the control chamber and the nozzle spring chamber can be disposed on the end of the nozzle needle remote from the combustion chamber, yet the volume of the control chamber does not depend on the installation space for the nozzle spring. It is therefore possible to build in a large-volume nozzle spring with high spring rigidity, which assures good closure of the nozzle needle. As a result, the injection time and the instant of injection can be defined exactly.
A particular feature of the invention is characterized in that the fuel inlet discharges into the nozzle spring chamber, and that at least one flat face is embodied at the nozzle needle between the nozzle spring chamber and the pressure chamber. This creates a fluidic communication between the nozzle spring chamber and the pressure chamber, through which the fuel to be injected can travel from the fuel inlet into the pressure chamber. The bore to the pressure chamber that is present in conventional injectors can be omitted.
Another particular feature of the invention is characterized in that the nozzle body is embodied in two parts, and that the control chamber is embodied in the part of the nozzle body remote from the combustion chamber. In the production of the nozzle body, a lengthened nozzle body is required. Before the part remote from the combustion chamber is cut off, a central bore for the needle and two fixation bores for receiving a fixation pin in the assembled state are advantageously made in the nozzle body. As a result, a lateral offset of the needle bore and guide bore and thus an overdetermined needle guidance are avoided.
A further particular feature of the invention is characterized in that a valve piece, which has a central run-up bore with an outlet throttle and a valve seat, is disposed in the part of the nozzle body remote from the combustion chamber. The central run-up bore creates communication between the control chamber and a relief chamber. The valve seat cooperates with a control valve member that controls the injection course of the injector of the invention. Because the outlet throttle is integrated with the valve piece, easy replacement of the outlet throttle is assured.
A further particular feature of the invention is characterized in that the inlet throttle is provided in a bore is in the nozzle body, which bore connects the control chamber with the nozzle spring chamber. For production and/or cost reasons, the inlet throttle can also be provided in some other component, such as the nozzle needle.
A further particular feature of the invention is characterized in that a shoulder, which forms a stop for a shim that acts as an abutment for the nozzle spring, is embodied on the nozzle needle. By a suitable choice of the thickness of the shim, the initial tension and the stroke of the nozzle needle can be adjusted.