Patent Publication Number: US-6698406-B1

Title: Pressure sensor for an internal combustion engine

Description:
The invention relates to a mechanism for monitoring the operating efficiency of an exhaust recalculation valve for an internal combustion engine, with a pressure sensor that determines the pressure in a suction valve of the internal combustion engine. 
     The pollutant emission of internal combustion engines can be improved by a process termed exhaust recalculation. For this purpose there is provided on the exhaust side of the internal combustion engine an exhaust recalculation valve which controls an exhaust recalculation line ending on the intake side of the internal combustion engine in the intake pipe downstream from the throttle valve. Exhaust is added to the air intake and as a result chiefly the No. Exhaust of the internal combustion engine is reduced. 
     Since the exhaust recalculation valve represents an exhaust relevant component, its operating efficiency in motor vehicles must be monitored partly on the basis of already existing legal regulations (ODD II). Malfunctions which occur must be stored in a malfunction storage unit for the purpose of display in customer service inspections. The pressure in the intake pipe downstream from the throttle valve increases as a result of opening of the exhaust recalculation valve, that is, addition of exhaust to the air intake. 
     A simple method of monitoring the exhaust recalculation valve consists of mounting a suitable pressure sensor directly in the suction pipe or at the end of a negative pressure line (U.S. Pat. No. 5,337,725) branching off from the suction pipe, in order to register change in pressure when the exhaust recalculation valve is actuated. Mounting of a pressure sensor such as this on the intake pipe however is very costly from the viewpoint of installation and/or is not always possible because of considerations of space. 
     Another possibility for monitoring the exhaust recalculation valve is that of mounting the pressure sensor in a connecting line branching from the intake pipe, a line which leads to a compressed-air actuating element such as a vacuum-operated servo brake or vacuum dashpot switching intake pipe. However, this arrangement entails the disadvantage that uncontrollable pressure changes occur in the connecting line involved when such an operating element is actuated. If however an accidental simultaneous actuation of an operating element such as this occurs during testing of operation of the exhaust recalculation valve, the pressure sensor mounted in this connecting line erroneously registers changes in pressure which are not to be attributed to operation of the exhaust recalculation valve. On occasion this can result in generation of an erroneous operational verification result. 
     It is claimed for the invention that a mechanism with pressure sensor is provided for an internal combustion engine, a sensor in which the disadvantages indicated are avoided, assembly of which is simple and cost-effective, and which simultaneously permits reliable operational testing. 
     This result is obtained by means of the mechanism with the features described in the patent claim. The essential concept of the invention is represented by mounting the pressure sensor in a line leading to a fuel pressure regulator. A fuel pressure regulator such as this is not in the form of a pneumatic consuming device, that is, no sudden accidental pressure changes which would result in falsification of the measured value in operational testing can occur in the connecting line leading to this fuel pressure regulator. Hence reliable operational testing of the exhaust recalculation valve is made possible by this mounting of the pressure sensor. 
    
    
     The invention is described in detail in what follows on the basis of an exemplary embodiment illustrated in the drawing. 
     The sole FIGURE presented is a diagram of an internal combustion engine with exhaust recalculation. 
    
    
     On the intake side the internal combustion engine  1  has an intake pipe  5  in which a throttle valve  10  is installed. On the exhaust side the internal combustion engine  1  has an exhaust pipe  15  leading, by means not shown, to an exhaust system of the internal combustion engine  1 . There is mounted on the exhaust pipe  15  an exhaust recalculation valve  20  which controls an exhaust recalculation line  25  ending in the suction pipe  5  downstream from the throttle valve  10 . A connecting line  30  leads from the suction pipe  5  to a fuel pressure regulator  35 , also downstream from the throttle valve  10 . The fuel pressure regulator  35  is connected to a fuel tank  39  by way of a fuel return  37 . It regulates the fuel pressure in a distributor strip  32  which is also connected to the fuel tank by way of a fuel pump  34 . The distributor strip  32  also serves to supply fuel to an injection valve  33 . 
     It is claimed for the invention that a pressure sensor  40  is mounted in the connecting line  30  between suction pipe  5  and fuel pressure regulator  35 . A signal line  42  leads from the pressure sensor  40  to a control unit  50 . 
     The control unit  50  controls the exhaust recalculation valve  20  by way of a control line  22 . 
     The operation of the invention is described in detail in what follows. Pressure PO prevails in the suction pipe  5  upstream from the throttle valve  10 , while negative pressure P varying with the position of the throttle valve  10  prevails downstream from the throttle valve  10 . When the exhaust recalculation valve  20  is actuated by means of the control unit  50 , the valve  20  is opened and exhaust reaches the suction pipe  5  by way of the exhaust recalculation valve  25 . 
     As a result the pressure P in the suction pipe  5  increases by δP. This pressure change has an effect immediately in the connecting line  30 . This pressure change δP is registered by the pressure sensor  40 . Since the connecting line  30  and the fuel pressure regulator  35  in particular have only a very small volume, no significant air flow occurs to equalize the pressure. Hence the change in pressure exerts its effect immediately on the pressure sensor  40  and so is registered without delay. 
     The pressure sensor  40  generates an undistorted measuring signal of the pressure P in the suction pipe. 
     Uncontrolled effects resulting from accidental actuation of a pneumatic actuating element affect the measuring signal only to an insignificant extent. Accidental pressure changes in the suction pipe  5  due to changes in the throttle valve angle are detected by the control unit  50 , which is part of the engine control unit, and so allowance may be made for them in evaluation of the measurement signal. In order to keep evaluation of the measurement signal as simple as possible, provision is made such that operational testing of the exhaust recalculation valve  20  may be carried out only if there is no change in the angle of the throttle valve  10 . 
     If the torque required is made by the driver through change in the throttle valve angle during a test of operation of the exhaust recalculation valve  20 , the operational testing is interrupted and is repeated at a later time. 
     The essential features of the invention are that the pressure sensor  40  is mounted in a connecting line  30  leading from the suction pipe  5  to the fuel regulator  35 . Such a layout is simple from the viewpoint of assembly and at the same time permits reliable operational checking of the exhaust recalculation valve  20 .