Control apparatus for internal combustion engines, in particular a correction device dependent on charge pressure for super-charged diesel vehicle engines

#The invention relates to a control apparatus for internal combustion engines.

#Known control apparatuses of this kind (German laid-open applications Nos. 24 48 656 and 24 32 830) function in accordance with the absolute pressure of the aspirated air in the suction tube of the engine; in aspirating engines, that is, they function in accordance with atmospheric pressure, and in supercharged engines they function in accordance with the charge air pressure. Because of the limited work capacity of the diaphragm pressure boxes which process the absolute pressure of the aspirated air, the adjusting member of this apparatus, having a movable wall, is preceded by a control device, in which the position of a valve member for controlling a servo pressure medium is determined by an evacuated diaphragm pressure box exposed to the aspirated air pressure. This control device functions as a hydraulic follower-piston unit, and the diaphragm pressure box must generate either a control path corresponding to the required adjusting-member path for twisting an adjuster eccentric or, in the case of the German laid-open application No. 25 32 830, a control path such as is required for displacing a three-dimensional cam. This sometimes requires relatively long adjustment paths, which involve friction, and thus also necessitates correspondingly large diaphragm box sets. Furthermore, the supply and sealing of the structural elements exposed to the hydraulic medium represents a relatively great expense.

#Other known control apparatuses, which functions without a servo medium and include adjustment members directly exposed to the diaphragm pressure boxes, likewise have much too little work capacity, and the necessary adjustment paths are difficult to attain. Control apparatuses are also known whose diaphragm adjustment members, exposed directly to the charge air pressure, by contrast do have a larger work capacity; however, they work only with the differential pressure between the charge air pressure and atmospheric pressure and cannot furnish any absolute pressure signal such as is required in order to prevent impermissible smoke generation, especially when the engine is operated in areas of extreme variations in altitude.

#In simplified form, the drawings show:

#FIG. 1, a first exemplary embodiment serving to explain the basic function of the apparatus;

#FIG. 2, a second example containing the essential characteristics of a practially realized control apparatus;

#The exemplary embodiment shown in FIG. 1 serves the purpose of explaining the basic function of the control apparatus according to the invention. This apparatus serves in particular as a charge-pressure-dependent correction apparatus for supercharged Diesel vehicle engines. Adjoining a charge air line 10 communicating with the suction tube of the engine (not shown) is a first pressure chamber 11 of a pneumatic pressure converter 12 functioning in the manner of a pneumatic pressure scale and acting as the control apparatus. A servo air line 14 is connected to the second pressure chamber 13 thereof, which is made up of two partial chambers 13a and 13b which communicate with one another. By way of the servo air line 14, compressed air acting as the servo pressure medium and preferably derived from an air brake system is delivered into partial chamber 13a by means of an inlet opening 16 controlled by a valve member 15; a portion of this compressed air continuously flows out of this partial chamber via a discharge opening 17 embodied as an outflow throttle.

#An evacuated diaphragm pressure box 18 is disposed in the first pressure chamber 11 and, exposed to the charge air pressure p.sub.L delivered via the charge air line 19, is secured on one side to a housing 19 of the pressure converter 12 and on the other side to an actuation member 21 provided with the valve member 15. The actuation member 21 is furthermore connected with a control diaphragm 22 defining the partial chamber 13b of the second pressure chamber 13. The control diaphragm 22 is exposed by way of a third pressure chamber 23, disposed between the two partial chambers 13a and 13b, to the atmospheric air pressure p.sub.A which reaches this pressure chamber 23 via an aperture 24. The second pressure chamber 13 communicates by way of the partial chamber 13b and a line 25 with a work chamber 27 of an adjustment member 28. The work chamber 27 is defined by a rolled diaphragm 26. The rolled diaphragm 26, which as a movable wall is exposed to the control air pressure p.sub.St delivered to the work chamber, actuates an adjusting rod 31 counter to the force of a restoring spring 29. The adjusting rod 31 engages the governor linkage of an rpm governor, not shown in detail, in a known manner via an articulation point 31a, or it actuates a pivotable or displaceable full-load stop for limiting the position of a supply quantity adjustment member of the fuel metering apparatus.

#The evacuated diaphragm pressure box 18 exposed to the aspirated air pressure p.sub.L acts counter to the control diaphragm 22 exposed to the control air pressure p.sub.St, and both diaphragm elements 18 and 22 determine the position of the actuation member 21 which governs the control air pressure p.sub.St, and thus the position of the valve member 15. If the compressed air continuously flows out of the second pressure chamber 13 via the fixedly set discharge throttle 17, then, when there is a state of balance between the actuation forces exerted upon the actuation member 21 by the diaphragm pressure box 18 and the control diaphragm 22, the control air pressure p.sub.St prevailing in the pressure chamber 13 is controlled in proportion to the absolute pressure of the aspirated air delivered via the charge air line 10 into the first pressure chamber 11, because the inlet cross section of the inlet opening 16 is set by the valve member 15 in accordance with the control air pressure p.sub.St to be controlled. When there is a pressure increase in the first pressure chamber 11, this inlet cross section is enlarged; when there is a pressure drop, the inlet cross section is reduced in size. Because the control air pressure p.sub.St is directly proportional to the absolute pressure of the aspirated air and is always an overpressure at a level above the minimum atmospheric pressure, a conventionally available diaphragm adjustment member 28 functioning counter to atmospheric pressure can be used as the adjustment member, as shown here.