Abstract:
In a method for opening a valve, which valve separates a flow channel from a working chamber or connects it therewith and which is embodied as a plate valve that projects upon opening into the working chamber, energy is withdrawn from a flow from the working chamber into the flow channel, resulting form the excess pressure within the working chamber upon opening movement of the valve. The withdrawn energy is used for aiding in further opening of the valve.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method and device for opening a valve, especially a load changing valve of an internal combustion engine. 
     From German patent 30 24 109 C2 a device, operating without camshaft, for actuating a load changing of an internal combustion engine is known. To the stem of the load changing valve an armature plate is fastened which in the fully open position of the valve contacts the solenoid and in the closed position of the valve contacts another solenoid. The armature plate forms together with the valve and two oppositely acting springs an oscillation system which upon activation of one solenoid is secured in one end position, whereby, upon switching off the solenoid, the armature plate moves toward the other end position and is secured thereat by activation of the other solenoid. 
     Such electromagnetic actuating devices, operating without camshaft, for the load changing valves of an internal combustion engine have the advantage that the control time can be selected substantially freely so that fuel consumption advantages can be achieved and the exhaust gas quality can be improved. A problem of such actuating devices is that the opening of the valve by pressure within the working chamber or combustion chamber is greatly impaired. For example, an exhaust valve must be opened already in certain operational phases when within the combustion chamber there is still a high working pressure. This high working pressure must be overcome by a spring which crowds the valve in the opening direction so that energy is removed from the oscillating system defined by the springs which energy must be then supplied by the solenoid. The solenoid which secures the valve in the fully open position must therefore be designed relatively large so that catching of the valve is possible. In the alternative, the springs must be so strong that high securing forces and thus large solenoids are required. 
     It is an object of the invention to provide a method and a device for opening a valve, especially a load changing valve of an internal combustion engine, with which a load changing valve can be opened safely and with minimal energy expenditure even when it must be opened counter to the excess pressure within the working chamber. 
     SUMMARY OF THE INVENTION 
     The inventive method is deigned for opening a valve, especially a load changing valve of an internal combustion engine, that separates a flow channel from a working chamber or connects it therewith and is embodied as a plate valve. Upon opening, the valve projects into the working chamber, According to the inventive method, energy is withdrawn from a flow out of the working chamber into a flow channel, resulting from excess pressure within the working chamber upon beginning of the opening stroke of the valve, and this energy is used for supporting the further opening movement of the valve. 
     The inventive device is designed for opening a valve, especially a load change valve of an internal combustion engine, that separates a flow channel from a working chamber or connects it therewith and is embodied as a plate valve. Upon opening, the valve projects into the working chamber. The inventive device comprises a flow guide element connected to the valve and surrounding the valve at a spacing. The flow guide element projects from the backside of the valve seat ring through the flow channel into a blind bore extending away from the flow channel, whereby the circumferential edge at the valve side of the flow guide element for a small valve opening receives a portion of the initial flow from the working chamber into the flow channel and guides it into the space between the valve and the flow guide element. The circumferential edge of the flow guide element at the blind bore side and the circumferential wall of the blind bore are designed such that at least during a portion of the valve stroke a reduced a flow cross-section is provided between them. 
     In another embodiment of the inventive device, an auxiliary piston component having a tubular shaft, which surrounds the valve stem and is moveably guided coaxially to the valve stem in the cylinder head, is provided. This auxiliary component comprises an auxiliary piston, which cooperates with its circumferential edge with a cylindrical area of the opening of the flow channel into the working chamber, whereby the inner diameter of the cylindrical area corresponds substantially to the outer diameter of the auxiliary piston. An actuating device moves the auxiliary piston substantially in counter phase to the valve so that the auxiliary piston opens the flow channel for a small opening movement of the valve only partially and only opens it completely upon greater valve opening movement. 
     Inventively, the flow out of the working chamber into the flow channel, resulting from excess pressure present within the working chamber during the initial opening phase of the valve, is used to extract energy therefrom which energy is used for supporting (enhancing or aiding in) the opening action of the valve. In this manner, the energy required for opening the valve against the excess pressure in the working chamber is reduced. 
     The invention is not only useful for electromagnetically operated load changing valves of internal combustion engines. They are also useful for conventionally actuated load changing valves because the invention lowers the actuating energy. The invention is also suitable for use with valves of pumps or other control members which must open against an excess pressure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The object and advantages of the present invention will appear more clearly from the following specification in conjunction with accompanying drawings, in which: 
     FIG. 1 shows a cross-section of a portion of a valve mounted within the cylinder head of an internal combustion engine and having a flow guide element; and 
     FIG. 2 shows a basic schematic of a further embodiment of the inventive device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in detail with the aid of several specific embodiments utilizing FIGS. 1-4. 
     FIG. 1 shows a cross-section of a portion of a cylinder head  6  which has an outlet channel or flow channel  8  which extends away from the combustion chamber or the working chamber  10 . 
     At the opening of the outlet channel  8  into the working chamber  10  a valve seat ring  12  is arranged which cooperates with the valve plate  14  of a valve  16 . The valve stem  18  penetrates the outlet channel  8  and is guided in a guide bushing  20  within the cylinder head  6 . Between the cylinder head  6  and the stem  18  a non-represented valve closing spring is arranged. 
     The aforementioned arrangement with regard to the design and function is known to a person skilled in the art and is therefore not disclosed in further detail. The actuating device for the valve  16  can be embodied conventionally by a camshaft, push rods, rocker arms etc. or performed hydraulically electromagnetically, or pneumatically. 
     Inventively, a flow guide element  24  is provided that surrounds the valve  16  such that a flow space is created. The flow guide element  24 , adjacent to the valve seat ring  12  or the backside  14   a  of the valve plate  14 , ends in a circumferential edge  26  and, adjacent to the cylinder head  6 , ends in a circumferential edge  28 . 
     The cylinder head  6  is embodied with a blind bore  30  which extends concentrically to the valve shaft  18 . The circumferential edge  28  of the flow guide element  24  projects into the blind bore  30 . 
     The depth of the blind bore  30  is such that the circumferential edge  28  of the flow guide element  24  in the closed state of the valve  16  is positioned in the vicinity of the bottom  32  of the blind bore  30 . The outer diameter of the circumferential edge  28  corresponds essentially to the inner diameter of the blind bore  30  or is somewhat smaller so that the circumferential edge  28  cooperates with the inner side of the blind bore in the manner of a gap seal. 
     The circumferential edge  26  at the valve plate side of the flow guide element  24  is embodied such that it forms with the backside of the valve plate  14  an annular gap  35  which receives, upon opening of the valve  16 , the flow exiting from the working chamber in the manner of an opening of a Pitot tube for measuring the flow pressure. In the represented embodiment the circumferential edge  26  in the closed state of the valve  16  projects into a cylindrical portion  34  of the valve seat ring  12  or the opening of the outlet channel  8 , whereby the inner diameter of the cylindrical area  34  corresponds to the outer diameter of the circumferential edge  26 . 
     The flow guide element  24  is embodied such that between it and the outer circumference of the valve  16  a flow passage  36  is provided whereby the spacing between the flow guide element  24  and the valve  16  in the most narrow portion of the flow passage is, for example, within a magnitude of 0.5 mm. 
     The flow guide element  24  can be a shaped sheet metal piece comprised of a highly temperature-resistant sheet metal and can be welded to the valve  16 , for example, by individual spot welds  38 . 
     The function of the flow guide element  24  is as follows: 
     It is assumed that the valve  16  is in its closed position and that in the working chamber a pressure P zyl  is present which is greater than the pressure in the outlet channel  8 . When the valve  16  is only slightly open, a large portion of the flow-cross section, formed between a conical surface of the valve plate  14  and the conical surface of the valve seat ring  12 , is filled by the annular gap  35  between the circumferential edge  26  and the backside of the valve plate  14  so that the flow resulting from the excess pressure within the working chamber  10  is received by the annular gap  35  and is guided into the flow passage  36  between the flow guide element  24  and the valve  16 . This has the effect that in the blind bore  30  within a short amount of time substantially the same pressure P zyl  is present. With a corresponding embodiment of the annular gap  35  in the manner of an inlet opening of a Pitot tube, the annular gap  35 , for further opening of the valve, will receive the entire pressure of the flow and will guide it into the blind bore. A reduced outflow cross-section from the blind bore  30 , when the circumferential edge  28  cooperates advantageously with the inner side of the blind bore  30  in the manner of a gap seal (frictional freedom), is without substantial impact on the pressure conditions within the blind bore  30 . 
     The pressure increase Δp effects at the valve  16  an additional opening force Δp×F, whereby F is the effective surface, i.e., the surface limited by the circumferential edge  28  minus the cross-sectional surface of the stem  18 . Depending on the diameter of the circumferential edge  28 , an additional force of greater or smaller magnitude can be produced which compensates the excess pressure in the working chamber or maybe even overcompensate this pressure. This additional force becomes active and is maintained as long as in the working chamber a pressure P zyl  is present which is greater than the pressure in the outlet channel  8 . In this manner, the flow energy from the working chamber is used for improving the opening action of the valves  16 . 
     The embodiment can be such that upon further opening of the valve  16  the circumferential edge  26  will increasingly free the outlet cross-section into the outlet channel  8  whereby the circumferential edge  28  first keeps the blind bore  30  closed and, only upon further valve stroke, will exit from the blind bore  30 . 
     As can be taken from the above, the flow guide element  24  provides a device which reduces the energy required for opening the valve  16  counter to an excess pressure within the working chamber  10  by guiding the excess pressure to the backside of the valve  16  in order to create a force in the opening direction. The flow guide element  24  not only employs static pressure but also employs the flow energy. 
     FIG. 2 shows schematically a changed embodiment of a device for enhancing the opening movement of the valve which functions primarily by employing static pressure. 
     The valve  60  operates in the outlet opening of an outlet channel  62  of a combustion chamber or working chamber  64 . 
     The stem  66  of the valve  60  is guided in a guide bushing  68  which is received in a tubular shaft  70  of an auxiliary piston component  72 . The tubular shaft  70  is guided by a further guide bushing  74  in the cylinder head  76 . 
     The opening of the outlet channel  62  into the working chamber  64  is embodied with a cylindrical area  78  having an inner diameter which matches substantially the outer diameter of the auxiliary piston  79  which is a part of the auxiliary piston component  72 . 
     In the shown embodiment, for actuating the valve  60  a crank mechanism with a reciprocating actuating lever  80  is provided that is driven by a non-represented device. The actuating lever  80  engages a crank  82  of a shaft  84  connected to the engine. The shaft  84  has connected thereto a two-arm lever  86 . One arm  88  is connected by lever  90  to the tubular shaft  70  of the auxiliary piston component  72 , and the other arm  92  is connected by a lever  94  to the valve stem  66 . 
     The arrangement is such that, in the closed state of the valve  60  (lever  86  according to FIG. 2 rotated in the clockwise direction to a substantially horizontal position), the auxiliary piston  79  with its circumferential edge  79   a  is moved into this cylindrical area  78  and is positioned in the vicinity of the end of the cylindrical area  78  that is close to the working chamber directly behind the valve  60 . 
     When the valve  60  is now opened by pivoting of the lever  86  in a counter clockwise direction, the auxiliary piston component  72  is moved counter to the movement of the valve  60  whereby the auxiliary piston  79  remains initially within the cylindrical area  78  and closes the inlet into the outlet channel  62  substantially completely so that the auxiliary piston is loaded with the excess pressure present within the working chamber  64  and is thus forced upwardly and supports the opening movement of the valve  60  via the levers  90 ,  86 , and  94 . Only upon further opening of the valve  60 , respectively, pivoting of the lever  86 , the circumferential edge  79   a  of the auxiliary piston  79  is released from the cylindrical area  78  so that the flow into the outlet channel  62  is possible. 
     It is understood that the cylindrical area  78  with respect to its depth and with respect to its design details (transition into a substantially partially conical area) are designed according to desired specifications. 
     In the device according to FIG. 2, the excess pressure in the working chamber, respectively, its release to the backside of the valve plate at the beginning of the opening stroke of the valve, is used in order to reduce the energy for opening the valve. 
     The specification incorporates by reference the disclosure of German priority document 198 35 403.7 of Aug. 5, 1998. 
     The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.