Patent Publication Number: US-6340018-B1

Title: Control valve for a fuel injection valve

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a control valve for a fuel injection valve, having a valve needle that is displaceable in a control chamber that is provided with an inlet, an outlet, and a valve seat. 
     One such control valve is known from German Patent Disclosure DE 197 27 896 A1, for instance, and serves to bring about the opening of a nozzle needle of the injection valve in order to inject fuel into a cylinder of an internal combustion engine. 
     The nozzle needle is acted upon continuously with an opening pressure that seeks to lift the nozzle needle away from the associated valve seat. This opening force counteracts a closing force that is generated in a control pressure chamber. As long as the pressure in the control pressure chamber is kept at a high level, the closing force generated there is higher than the opening force acting on the nozzle needle, and thus the nozzle needle remains closed. Conversely, if the pressure in the control pressure chamber and consequently the closing force generated there drop, then the opening force succeeds in lifting the nozzle needle away from the valve seat. Fuel can now be injected. 
     The pressure in the control pressure chamber is controlled by the control valve, by opening or closing an outlet. If the medium, typically fuel, delivered to the control pressure chamber is dammed up by closure of the outlet, then a high pressure is generated in the control pressure chamber and keeps the nozzle needle in a closed state. If conversely the control valve opens the outlet, the pressure in the control pressure chamber drops, so that the nozzle needle can open. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The control valve according to the invention has an advantage that at little expense, two different open states of the control valve can be attained, namely a partly open state, in which the fluid can escape from the control pressure chamber through the throttle bores, and a fully open state, in which both the throttle bores and the outlet conduit are open. The switchover between these two open states is effected solely by controlling the stroke of the valve needle. In this way, different types of injection can be attained. 
     In a preferred embodiment of the invention, the valve needle is provided with a needle head, which is larger than the inside diameter of the throttle ring, and the throttle ring is disposed between the needle head and the valve seat. Is this version, the valve needle serves not only for switching but also simultaneously as a guide for the throttle ring. The throttle ring is retained firmly in the axial direction between the needle head and the valve seat. 
     It is preferably also provided that a spring that urges the throttle ring away from the valve seat toward the needle head is disposed in the control chamber, and that a stop for the throttle ring is provided in the control chamber and limits the stroke of the throttle ring away from the valve seat. By means of the spring, the throttle ring can be displaced in an especially simple way in the interior of the control chamber, without requiring a separate actuating element controlled from outside. Also with this version, a partly open state of the control valve can be attained that is maximally independent of positional tolerances of the valve needle. Specifically, a tolerance range can be established within which the throttle ring is already lifted from the valve seat but has not yet struck the stop. Within the entire tolerance range, an outflow cross section through the throttle bores is obtained that is virtually independent of the position of the valve needle in this partly switched state. 
     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of a preferred embodiment taken in conjunction with the drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a fuel injection valve; 
     FIG. 2, in an enlarged view which shows a control valve according to the prior art, which can be used in the fuel injection valve of FIG. 1; and 
     FIG. 3 is a cross-sectional view of a control valve of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1, a conventional fuel injection valve with a control valve (see FIG. 2) is shown. The fuel injection valve has a valve body  10 , in which a nozzle needle  12  is mounted displaceably. The nozzle needle  12  controls the injection of fuel into a cylinder of an internal combustion engine (not shown). The delivered fuel exerts an opening force on the nozzle needle  12  that seeks to displace both the nozzle needle and an actuating part  14 , on which the nozzle needle  12  is braced, toward a control pressure chamber  16 . 
     Fuel is also delivered to the control pressure chamber  16 , and because of the pressure prevailing in the control pressure chamber  16 , this fuel exerts a closing force on the actuating part  14 . The fuel is furnished via an inlet  18 , and an outlet  20  extends away from the control pressure chamber  16  and leads to a control chamber  22  of a control valve  24 . For the control valve  24 , the outlet  20  acts as an inlet, and an outlet  26  is provided through which the fuel can flow out of the control pressure chamber  16  and the control chamber  22 . 
     In the control chamber  22 , the control valve  24  has a valve needle  28 , which cooperates with a valve seat  30 . When the valve needle  28  is resting on the valve seat  30 , the control valve  24  is closed, so that the fuel delivered to the control pressure chamber  16  via the inlet  18  is dammed up in the control pressure chamber. The high pressure generated in this way exerts a closing force on the actuating part  14  that is greater than the opening force acting on the nozzle needle  12 . The fuel injection valve is consequently closed. Conversely, if the valve needle  28  is lifted from the valve seat  30 , the fuel can flow out of the control pressure chamber  16  via the control chamber  22  and the outlet  26 , so that the pressure in the control pressure chamber drops. The then-reduced closing force enables the opening of the nozzle needle, so that fuel is injected. 
     The control valve of the invention will now be described, in conjunction with FIG.  3 . The valve needle  28  is provided with a needle head  32 . A throttle ring  34  is disposed displaceably on the valve needle  28  and is provided with a plurality of throttle bores  36 . These throttle bores extend parallel to a longitudinal axis of the valve needle  28  and are disposed on a radius such that the bores can be closed by contact with a throttle seat  30 ′. 
     The throttle seat  30 ′ is embodied on a cylindrical protrusion  37 , around which a compression spring  38  is disposed. The compression spring  38  urges the throttle ring  34  away from the throttle seat  30 ′, toward the needle head  32 . 
     The control chamber  22  is provided with a shoulder  40 , which, as a stop, is opposite an end of the throttle ring  34 , on a side of the throttle ring remote from the compression spring  38 , and limits the maximum stroke of the throttle ring. 
     The outer diameter of the valve needle  28  and the inner diameter of the throttle ring  34  are adapted to one another in such a way that between the valve needle  28  and the throttle ring  34 , an outlet conduit  42  is formed through which the fuel can flow out of the control chamber  22  to the outlet  26 . A bottom surface of the throttle ring between the bores  36  and the inner diameter of the throttle ring forms a valve seat  30  upon which the needle head  32  seats. 
     The control valve described has three different switching states. In a first state, the valve needle  28  is in its upper position, in which the valve needle head  32  presses the throttle ring  34  against the throttle seat  30 ′, counter to the action of the spring  38 . In this state, the control valve is closed, since the outlet conduit  42  is closed by contact of the needle head  32  with the throttle ring  34  and the throttle bores  40  are closed by contact with the throttle seat  30 ′. 
     The control valve has a partly open switching state, in which the valve needle  28 , beginning at the closed state, is displaced by a stroke in the direction of the control pressure chamber  16  that is shorter than Δh. In this state, the throttle ring  34  continues to rest on the needle head  32  by the action of the spring  38 , but is at a distance from the throttle seat  30 ′. Thus the fuel can escape from the control chamber  22  through the throttle bores  36  to the outlet  26 . 
     Since only a comparatively small outlet cross section is available by way of the outlet bores  36 , the pressure in the control pressure chamber  16  drops correspondingly slowly, and the nozzle needle  12  also begins to move slowly. This accordingly produces a slow increase in the nozzle needle stroke. 
     A third switching state is attained when the valve needle  28  executes a stroke in the direction of the control pressure chamber  16  that is greater than Δh. This long stroke cannot be executed by the throttle ring  34 , since before that the throttle ring is resting on the stop  40 . The outlet conduit  42  is thus opened. This outlet cross section is added to the outlet cross section furnished by the throttle bores  36 , so that now a large outlet cross section is available, which assures a rapid pressure relief in the control pressure chamber  16 . 
     The control valve described can be switched in such a way that the valve needle  28  executes a stroke greater than Δh for a brief period of time. The large outlet cross section that is then available assures a rapid relief of the control pressure chamber  16 , so that the nozzle needle quickly lifts from the nozzle needle valve seat. In order to keep the nozzle needle suspended afterward, the outflow from the control pressure chamber  16  must be reduced, while the inflow via the inlet  18  is constant. To that end, the stroke of the valve needle  28  is adjusted to a value less than Δh, so that now only the outlet cross section determined by the throttle bores  36  is available. In this way, a boot injection can be attained. 
     The foregoing relates to a preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.