Abstract:
A device for the actuation of a gas shuttle valve in an internal combustion engine that allows an optimization of both engine performance and fuel consumption by providing a variable valve lift. The lift of the gas shuttle valve can be varied by adjusting the effective axial distance of the actuators. As needed, the valve lift is increased or decreased in order to either improve engine performance or fuel consumption.

Description:
FIELD OF INVENTION 
     The present invention relates to a device to actuate a gas shuttle valve in an internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     In internal combustion engines that use a valve drive without a camshaft of the type described, for example, in DE 199 35 871 A1, each valve is actuated by two actuators that act in an axial direction (the direction of the valve stem) and in directions opposite each other. Return springs that engage the valve shaft and that likewise act in directions opposite each other bias the valve to a neutral idle position between a valve open position and a valve closed position. Electromagnetic actuators have a magnet yoke and an anchor plate coupled to the valve stem. The valve lift is determined by the sum of the strokes of the two actuators. The stroke of each actuator is, in turn, determined by abutment of the anchor plate on the respective magnet yoke. In conventional valve drives, the valve lift is a compromise between the engine performance and the fuel consumption. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides a device for the actuation of a gas shuttle valve in an internal combustion engine that allows an optimization of both engine performance and fuel consumption by providing a variable valve lift. According to the invention, the lift of the gas shuttle valve can be varied by adjusting the effective axial distance of the actuators. As needed, the valve lift is increased or decreased in order to either improve engine performance or fuel consumption. Preferably, the valve lift is changed continuously so that a very precise adaptation to the operating conditions of the engine is ensured. 
     The axial distance between the actuators can be varied very simply with a slide or wedge that can be moved perpendicularly to the axial direction of the valve stem. The slide or wedge has a ramp surface on which one of the actuators bears axially. When electromagnetic actuators are used, the axial distance between the pole surface on the yoke of the one actuator and the pole surface of the other actuator is varied. The slide or wedge can be actuated by a simple hydraulic, mechanical or electromagnetic actuating drive. 
     In preferred embodiments of the invention, the spring force of the return spring is adapted to the variable valve lift. For this purpose, the axial position of the return spring support is adjusted. Such adjustment is preferably carried out synchronously with adjustment of the valve lift, especially by means of the same actuating drive. In order for the return force in the closed position of the valve to be independent of the magnitude of the valve lift, the bias of the return spring is reduced when the valve lift is increased and the bias of the return spring is increased when the valve lift is decreased. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional features and advantages of the invention ensue from the following description of several embodiments with reference to the accompanying drawings. The following is shown in the drawings: 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     FIG. 1 a schematic sectional view of a device for actuating a gas shuttle valve; 
     FIG. 2 a schematic diagram of the device in a first adjustment state; 
     FIG. 3 a schematic diagram of the device in a second adjustment state; 
     FIG. 4 a schematic diagram of a modified embodiment of the device in a first adjustment state; 
     FIG. 5 a view analogous to FIG. 4 in a second adjustment state; 
     FIG. 6 a schematic diagram of another embodiment of the device; 
     FIG. 7 a schematic side view of an adjustment slide, shown in a sectional view; 
     FIG. 8 the adjustment slide of FIG. 7 in a top view; 
     FIG. 9 a schematic diagram of another embodiment; and 
     FIG. 10 a schematic diagram of an embodiment of an actuating drive for the device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a valve stem X of a gas shuttle valve for an internal combustion engine in a cut-away view. In the position shown in FIG. 1, an actuating rod  10  has an end in abutment with the upper said face of the valve stem X. A drive element, i.e. an anchor plate  12 , is rigidly attached to the actuating rod  10 . The anchor plate  12  extends perpendicularly to the axis of the valve stem X and to the axis of rod  10  that is coaxial thereto. Electromagnetic actuators  14  and  16 , respectively, are located on each of the two opposite sides of the anchor plate  12 . The actuators  14 ,  16  are at a distance from each other in the axial direction of the valve stem. Each actuator  14 ,  16  has a winding  18 ,  18   a  and a magnet yoke  20 ,  20   a  surrounding the winding. The generally pot-shaped magnet yoke  20 ,  20   a  is surrounded by a housing  22 ,  22   a . The anchor plate  12  is situated between the pole surfaces of the magnet yokes  20 ,  20   a . One end of rod  10  is provided with a spring plate  11  on which a helical return spring  24  is supported. The actuators  14 ,  16  are arranged coaxially to rod  10 , which passes axially through actuators  14 ,  16 . 
     One of the two actuators, in FIG. 1 the lower actuator  16 , can be arranged so as to move axially with respect to the other actuator,  14  in FIG.  1 . For purposes of continuous adjustment of the stroke of anchor plate  12 , there is a slide  30  that can be moved perpendicularly to the axis of rod  10  and that has two ramp surfaces  30   a ,  30   b . Corresponding skewed surfaces on the yoke halves  20  and  20   a  of the actuator  16  are supported on the ramp surfaces  30   a ,  30   b.    
     As an alternative, actuator  16  is stationary and actuator  14  is axially movable. 
     The end of the return spring  24  facing the actuators is supported on a buttress that is formed by a support wedge  32  whose ramp surface facing away from the return spring  24  is supported on a wedge-shaped slide  34 . The slide  34  can also be moved perpendicularly to the axis of rod  10 . Due to the movement of the slide  34 , the support wedge  32  is raised or lowered in order to change the bias of the return spring  24 . 
     If the valve is to assume a neutral position between an open valve position and a closed valve position while the actuators are at idle, a further return spring Y is provided in an opposite arrangement with respect to the return spring  24  on the valve shaft X to urge the valve stem X against rod  10 . 
     The slides  30 ,  34  are rigidly coupled to each other by a bridge element  36  and they are synchronously moved by an actuating drive (not shown). The slide  34  has a ramp surface  34   a  that is slanted like the ramp surfaces  30   a ,  30   b  of the slide  30 . 
     An adjustment screw Z serves to adjust the neutral position of the anchor plate  12 . 
     Operation of the device is now explained with reference to FIGS. 2 and 3. 
     In the embodiment schematically shown in FIGS. 2 and 3, slide  30  complements magnet yoke  20   a  and is made of a ferromagnetic material. On the side of the slide  30  facing the anchor plate  12 , slide  30  forms a pole surface; on its opposite side, it is provided with the ramp surfaces  30   a ,  30   b . The magnet yoke  20   a  has correspondingly slanted support surfaces on which the ramp surfaces  30   a ,  30   b  bear slidingly. By moving the slide  30  perpendicularly to the axis of the valve shaft  10 , the axial distance between the pole surfaces of the magnet yokes  20 ,  20   a  is changed. 
     In FIG.  2  and FIG. 3, anchor plate  12  abuts the pole surface of magnet yoke  20 , corresponding to the open position of the gas shuttle valve. The lift of the gas shuttle valve according to FIG. 2 is set at the maximum value H 1 , corresponding to the maximum distance between the anchor plate  12  and the pole surface of magnet yoke  20   a . At the same time, return spring  24  is additionally stressed by the slide  34  and has an axial length S 1 , corresponding to the distance between a spring plate  10   a  on the free end of the valve stem and the opposite buttress of return spring  24 . 
     In FIG. 3, by adjustment of the slide  30 , the pole surface of magnet yoke  20   a  is moved close to anchor plate  12  by the maximum possible value. The lift of the gas shuttle valve is reduced to the value H 2 . In the extreme case, H 2 =0 and the gas shuttle valve X remains closed. At the same time, due to the relief of the return spring  24  by synchronous adjustment movement of the slide  34 , the axial length of the return spring  24  is increased to the value S 2 . Consequently, in the opposite closed position of the gas shuttle valve, a constant return force of the return spring  24  is ensured, independent of the valve lift that has been set. 
     In the embodiment schematically shown in FIGS. 4 and 5, the slides  30  and  34  are each replaced by two slide or wedge members  30   1 ,  30   2  and  34   1 ,  34   2  respectively, which can be moved in the opposite directions. The slide members are moved towards each other or away from each other perpendicularly to the axis of the valve stem by means of an actuating drive. When the ramp surfaces of the slide members  30   1 ,  30   2  are slanted opposite to the slant of the corresponding ramp surfaces of the slide members  34   1 ,  34   2 , as shown in FIGS. 4 and 5, movement of the slide members  30   1 ,  30   2  has to be opposite from movement of the slide members  34   1 ,  34   2 . FIG. 4, analogously to FIG. 2, shows the setting to the maximum lift H 1 , and FIG. 5, analogously to FIG. 3, shows the setting to the minimum lift H 2 . 
     Even if the same actuating drive is used to change the lift of the gas shuttle valve and to adjust the bias of the return spring, lift and bias can be varied relative to each other. In the embodiment shown in FIG. 6, reference numeral  40  designates an actuating drive that performs a pivotal movement of a two-armed adjusting lever  42 . The slide  30  is attached to one end of the lever  42  and the slide  34  is attached to the other end. In this embodiment, the slides  30 ,  34  move in opposite directions. The ratio of the movement strokes of the slides  30 ,  34  is determined by the position of the actuating drive  40  between the ends of the two-armed lever  42 . A double arrow between the two-armed lever  42  and the slide  34  indicates that, in the actuating path to the slide  34 , there can be another actuating means  44  that can be used to change the position of slide  34 . 
     FIG. 7 shows the slide  30  in a cross-sectional side view; FIG. 8 shows a corresponding top view. Between the two slide members on which the ramp parts  30   a ,  30   b  are formed, there is a recess  30   c  through which rod  10  passes. 
     As an alternative to FIG. 6, FIG. 9 shows an embodiment analogous to FIGS. 2 and 3, in which the slides  30 ,  34  are moved in the same direction. Like in FIG. 1, they are coupled to each other by a bridge member  36  and, via the latter, to a shared actuating drive. In the actuating path between the bridge member  36  and the slide  34 , there is an actuating member  44  with which the bias force of the return spring  24  can additionally be changed. 
     FIG. 10 shows an embodiment of an actuating drive with an adjusting rod  46  that can be reciprocated parallel to the axis of rod  10  and of valve shaft X. The adjustment rod  46  is coupled via articulated links  48 ,  50  to slide members  30   1 ,  30   2 , which can be moved in opposite directions, and via further articulated links  52 ,  54  to the slide members  34   1 ,  34   2 , which can likewise be moved in the opposite directions.