Abstract:
A system for measuring an injection process in a combustion engine includes a tank configured to hold a fuel. A storage container is configured to hold a compressed fuel. At least one injection valve is arranged at the storage container. A fuel line in which a fuel conveying pump and a high-pressure fuel pump are arranged. The fuel conveying pump and the high-pressure fuel pump are configured to convey the fuel into the storage container. A first pressure sensor is configured to measure a pressure in the storage container. A detection device is configured to detect control data of the at least one injection valve. A measuring device is arranged in the fuel line. The measuring device is configured to measure a temporally resolved volumetric or gravimetric flow process. A processor is connected to the measuring device and to the first pressure sensor via a data transmission line.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     This application is a U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/EP2010/064626, filed on Oct. 1, 2010 and which claims benefit to German Patent Application No. 10 2009 043 718.5, filed on Oct. 1, 2009. The International Application was published in German on Apr. 7, 2011 as WO 2011/039343 A1 under PCT Article 21(2). 
     FIELD 
     The present invention refers to a system for measuring injection processes in a combustion engine comprising a tank which holds fuel, a storage container storing compressed fuel, at least one injection valve arranged at the storage container, a fuel line in which a fuel pump and a high-pressure fuel pump are arranged to convey the fuel into the storage container, a pressure sensor through which the pressure in the storage container can be determined, and means for detecting the control data of the injection valves. The present invention also provides a method for measuring injection processes using such a system. 
     BACKGROUND 
     Such systems are substantially known per se and form the structure of the common-rail system of modern combustion engines. The pressure sensors arranged in the storage containers serve in particular for the failure analysis of such systems. 
     DE 199 46 506 C1 describes a method for detecting a malfunction in the pressure system of an engine wherein a pressure signal of a pressure sensor is registered in a temporally resolved manner so that periodic pressure variations caused by the operation of the injectors and the piston strokes of the piston pump can be monitored. The development of the pressure signal is measured and compared to a stored pattern so that a malfunction is deduced from a deviation of the pattern with respect to amplitude or periodicity. The difference between the largest and the smallest pressure measurement signal within a period is also determined. A malfunction in the system is again deduced should this difference differ from the stored pattern. The determination of a rate-of-discharge curve is not disclosed. 
     A method for monitoring the functionality of an injection system is described in DE 10 2005 004 423 B3 wherein a malfunction is deduced from a deviation from a set pressure curve using the measured pressure curve of a sensor arranged at the storage container. Both the time characteristic of the pressure and the absolute pressure are here considered. This method also does not allow the determination of an actual rate-of-discharge curve for individual valves. 
     A similar structure is described in DE 197 40 608 A1. In this case, however, a pressure curve in the storage container is detected with high resolution by the pressure sensor and a pattern is obtained from the pressure curve through which a fuel injection-related parameter, such as the injection volume of the injection time, is determined individually for each combustion chamber and each injection process. This is done via a neural network. However, this network first has to be trained at a test bench in order to obtain plausible results. The absolute values of the injection volumes are in particular impossible to determine without a previous learning process of the network. A separate learning process must thus be carried out for each engine so that an application in serial production is not feasible. 
     SUMMARY 
     An aspect of the present invention was to provide a system and a method for measuring injection processes in a combustion engine which not only allow for failure detection, but which also allow for an exact determination of rate-of-discharge curves. A further, alternative, aspect of the present invention is to allow the determination of absolute values and to differentiate between the pilot injection and the main injection for each single cylinder. 
     In an embodiment, the present invention provides a system for measuring an injection process in a combustion engine which includes a tank configured to hold a fuel. A storage container is configured to hold a compressed fuel. At least one injection valve is arranged at the storage container. A fuel line in which a fuel conveying pump and a high-pressure fuel pump are arranged. The fuel conveying pump and the high-pressure fuel pump are configured to convey the fuel into the storage container. A first pressure sensor is configured to measure a pressure in the storage container. A detection device is configured to detect control data of the at least one injection valve. A measuring device is arranged in the fuel line. The measuring device is configured to measure a temporally resolved volumetric or gravimetric flow process. A processor is connected to the measuring device and to the first pressure sensor via a data transmission line. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in greater detail below on the basis of embodiments and of the drawings in which: 
         FIG. 1  shows a system for measuring an injection processes in a combustion engine. 
     
    
    
     DETAILED DESCRIPTION 
     In an embodiment of the present invention, a processor is used which is connected to a device for measuring temporally resolved volumetric or gravimetric flow processes and to the pressure sensor via data transmission lines, the device being arranged in the fuel line. Control times determined by the means for detecting the control data, measured values of the pressure sensor at the storage container and measured values of the device for measuring temporally resolved volumetric or gravimetric flow processes in the fuel line can thus be transmitted to processor and, from these measured values, the injection rate shapes of the injection valves can be computed in the processor by superposition of the storage container flows calculated from the measured pressure curves of the pressure sensor at the storage container with the measured values of the device for measuring temporally resolved volumetric flow processes in the fuel line. By using the additional device for measuring temporally resolved volumetric or gravimetric flow processes, the value obtained from the pressure curve can be computed back to a calibrated volumetric or gravimetric flow value so that statements on the absolute values of the injected volumes are possible. Differences between two injectors and, as a consequence, malfunctions in the system can also be identified and attributed. 
     In an embodiment of the present invention, a temperature sensor can, for example, be arranged at the storage container which is connected to the processor. The temperature in the storage container is accordingly measured by the temperature sensor at the storage container, the temperature curve is transmitted to the processor, the compressibility module of the fuel is calculated in the processor and the calculated compressibility module is thereafter used in the determination of the injection rate shape. A very precise determination of the absolute values of the injection volumes is thus achieved. 
     In an embodiment of the present invention, a pressure sensor can, for example, be arranged at the inlet of the high-pressure pump which is connected to the processor. The measured values of this pressure sensor are transmitted to the processor, a high-pressure pump flow is calculated in the processor based on the measured values, and subsequently, the calculated flow is superposed with the measured values of the device for measuring temporally resolved volumetric flow processes in the fuel line and with the calculated storage container flows. A corrected rate-of-discharge curve is calculated therefrom which also considers the apparent flow through the high-pressure pump caused by the changing set pressure in the rail and the resulting changing masses to be conveyed. 
     In an embodiment of the present invention, a temperature sensor can, for example, be provided at the inlet of the high-pressure vacuum pump which is connected to the processor so that the temperature at the inlet of the high-pressure pump is measured using the temperature sensor at the inlet of the high-pressure pump, the temperature curve is transmitted to the processor, the compressibility module of the fuel at the high-pressure pump is calculated in the processor and the calculated compressibility module is used in determining the high-pressure pump flow. A still improved result of the computation of the rate-of-discharge curve is thereby achieved since the measured apparent flow can also be determined in an accurate manner. 
     In an embodiment of the present invention, a fuel return line can lead from the high-pressure pump or from the storage container to the tank via a pressure regulation valve, whereby an additional possibility for a pressure regulation is provided. 
     In an embodiment of the present invention, the fuel line can form the fuel return line in the section where the device for measuring temporally resolved volumetric flow processes is arranged. This allows omitting additional sensors and further devices for measuring flow processes in the return lines that would additionally have to be provided. 
     In an embodiment of the present invention, a system and an associated method are accordingly provided with which injection volumes can be determined exactly in a common rail system. A resolution is here possible for each individual injector, even allowing the differentiation between the pilot injection and the main injection. The calculation of the rate-of-discharge curves is thus accurate to the cycle and cylinder-selective. A use in diagnosing the injection system is also possible. 
     An embodiment of a system according to the present invention is schematically illustrated in  FIG. 1 . The present invention will be described hereunder with reference to  FIG. 1 . 
     The system illustrated essentially comprises the components of a known common rail fuel system. A tank  2  is in communication with a fuel pump  6  via a fuel line  4 . The pump conveys fuel to a high-pressure fuel pump  8  which most often is a piston pump. A high-pressure line  10  provides for fluid communication between the piston pump and a storage container  12  in which a pressure sensor  14  and a temperature sensor  16  are arranged. Further, in the present embodiment, four fuel injection valves  18  are arranged at the storage container  12 , through which fuel can be injected into associated cylinders of a combustion engine. 
     A pressure regulation valve  19  is further arranged at the storage container  12 , which, like the inlet of the high-pressure pump  8 , is connected with a fuel return line  20  via which excess fuel can be returned to the tank  2 . This fuel return line  20  first opens into the fuel line  4  in which a differential flow or a resultant fuel flow is thus created in this portion of the fuel line. 
     According to the present invention, this resultant fuel volume conveyed into the storage container  12  is measured by means of a device  22  for measuring volumetric flow processes, which device is arranged in the fuel line  4  between the tank  2  and the branch to the fuel return line  20 . 
     Such a device  22  is described in DE 103 31 228 B3 and comprises a rotary displacement device and a translational volume difference sensor arranged in a bypass channel to the displacement device, the sensor being in the form of a piston arranged in a measuring chamber. The course of the piston is continuously detected, the pump being operated substantially at a constant speed during one cycle. The conveying and the return of the fuel cause an overlapping movement of the piston which is a measure of the volume actually conveyed into the storage container. In addition, a pressure sensor and a temperature sensor are provided in the measuring chamber, whose measured values are supplied to an evaluation unit so that apparent flows caused by pressure and temperature variations can be eliminated. The processes occurring between the high-pressure pump  8  and the injectors  18  cannot, however, be measured by this device  22 . 
     For this reason, the pressure sensor  14 , the temperature sensor  16  and the device  22  for measuring volumetric flow processes are connected to a processor  26  via data transmission lines  24 . The processor  26  stores a rail model for calculating temporally resolved volumetric flow processes. In addition, models for various lines and volumes can be stored which have a certain size and may thus cause apparent flows due to pressure and temperature variations. For example, the pump model illustrated can be used which provides further improvement to the results of the rail model. However, this requires the arrangement of further sensors, such as pressure sensors and temperature sensors, in the vicinity of the high-pressure pump  8 . 
     When calculating the instantaneous fuel consumption, it has to be taken into consideration that in particular in the storage container  12 , due to the given volumes, slight pressure variations will result in significantly different measured volumes because of the compressibility of the fuel. 
     According to the present invention, first the control data and the control times, respectively, of the injection valves  18  are transmitted to the processor  26 . This may be done by a direct transmission of the data from the engine control unit to the processor. It is also conceivable to measure the opening times through corresponding current and position sensors. 
     At the same time, the measured values of the pressure sensor  14  at the storage container  12  and the measured values of the device  22  for measuring temporally resolved volumetric flow processes in the fuel line  4  are transmitted to the processor  26 . The pressure variations measured by means of the pressure sensor  14  are first weighted using an optional proportionality factor and are added over a sufficient period of time. The sum of these weighted pressure variations is then compared with the flow measured by the device  22  for measuring temporally resolved volumetric flow processes, from which comparison the proportionality factor can be calculated by superposition. Given a constant proportionality factor, a concrete volume flow and thus a rate-of-discharge curve for that period of time can then be calculated for each individual subset thereof, i.e., for any optional phase thereof. 
     It has been found that even very short phases around the injection can be used herein. 
     A further improvement of the results can be achieved by measuring the temperature in the storage container in addition to the pressure. Variations of the temperature in the storage container cause apparent flows that can, however, be calculated with the formula ΔV T =V 0 ·α·ΔT. Using the corresponding results, the determined flow volumes can thereafter be calculated. 
     A continuous measuring of the pressure at the high-pressure pump inlet allows the additional calculation of a high-pressure pump flow whereby the pressure development caused by an injection can be separated from a pressure variation caused by the conveying action of the high-pressure pump. For this purpose, the calculated rate-of-discharge curve is corrected by superposing the pump flow resulting from the measured pressure and the measured temperature with the measured values of the device for measuring temporally resolved volumetric flow processes in the fuel line. Injection volumes can thereby be separated exactly from the conveyed volumes. Of course, also in this case, the compressibility module can be corrected accordingly by measuring the temperature, so as to achieve further improved results. 
     With these methods and the structure described, injection processes in a high-pressure fuel system of a combustion engine can be quantified with high accuracy. It is also possible to differentiate between pilot and main injections and to determine the injection volumes. It is also of course possible to identify defective injection valves. Problems with injection valves that cause changed injection volumes can first be identified and then be compensated for by corresponding regulations and adjusted opening times. 
     The present invention is not limited to embodiments described herein; reference should be had to the appended claims.