Abstract:
In a method for measuring the injection quantity of injection systems, in particular for motor vehicles and in particular in production testing, an injection system injects a testing fluid into a measuring chamber. A detection device detects a movement of a piston, which at least partially defines the measuring chamber. This detection device generates a corresponding measurement signal. In order to increase the precision of the calculation of the injected testing fluid mass, the invention proposes that the pressure of the testing fluid in the measuring chamber be detected and that the measurement signal be processed taking into account the detected pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 02/00376, filed on Feb. 1, 2002. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The current invention relates to a method for measuring the injection quantity of injection systems, in particular for motor vehicles and in particular in production testing, in which a testing fluid is injected into a measuring chamber by an injection system and the injection-induced movement of a piston, which at least partially defines the measuring chamber, is detected by a detection device, which transmits a measurement signal. 
   2. Description of the Prior Art 
   A method of the above kind is known from the market. The method is applied by using a device, which is referred to as an injected fuel quantity indicator. This component is comprised of a housing in which a piston is guided. The inner chamber of the housing and the piston define a measuring chamber. This measuring chamber has an opening against which an injection system, for example an injector with an injection nozzle, can be placed in a pressure-tight manner. When the injection system injects fuel into the measuring chamber, a fluid contained in the measuring chamber is displaced. This causes the piston to move, which is detected by a distance sensor. The volume change of the measuring chamber and of the fluid contained therein and therefore the quantity of fuel injected can be calculated from the distance traveled by the piston. 
   In the known injected fuel quantity indicator, a device comprised of a measuring plunger and an inductive distance measuring system is used to measure the movement of the piston. The measuring plunger is embodied as a probe or is connected to the piston. When the piston moves, this also causes the measuring plunger to move and finally, the movement of the measuring plunger is detected and a corresponding signal is sent to an evaluation unit. 
   The known method already operates with a very high degree of precision with regard to the detected movement of the measuring plunger. However, the mass of the injected testing fluid calculated from this movement and the volume of injected fuel likewise calculated from it fall somewhat below the path measurement in terms of the precision. This problem is more intense the smaller the movement of the piston is, i.e. the smaller the injected testing fluid quantity is. But it is precisely these small quantities of testing fluid that current and future injection nozzles must be able to reliably inject. 
   The object of the current invention, therefore, is to modify a method of the type mentioned at the beginning so that it permits a more precise determination of the mass of the injected testing fluid and of the volume of testing fluid injected. 
   This object is attained in that the pressure of the testing fluid is detected in the measuring chamber and the measurement signal is processed taking into account the pressure detected. 
   SUMMARY OF THE INVENTION 
   Detecting and measuring pressure changes results in the fact that with an injection of testing fluid, the actually injected fluid mass can be determined with greater precision. The invention is in fact based on the recognition that the mass of a particular volume depends on the density prevailing in this volume. However, the density inside a volume also depends on the pressure prevailing in the volume. 
   Because the pressure, which prevails in the testing fluid contained in the measuring chamber, is detected according to the invention, the properties of the testing fluid in the measuring chamber can be precisely determined and consequently, the corresponding injected mass can also be calculated precisely from the measured volume. By taking into account the pressure actually prevailing in the measuring chamber, it is also possible to convert the injected volume measured at a particular pressure into a particular comparison value (e.g. 1 bar). In this manner, it is very easily possible to compare different injections and different injection systems to one another since these measured injection quantities are based on the same ambient conditions. 
   The method according to the invention thus makes the determination of the mass of testing fluid injected into the measuring chamber more precise and also permits the calculation of a volume based on particular ambient conditions, which in turn permits a better comparison of different injection systems. 
   In a first modification, the invention proposes that the temperature of the testing fluid be detected in the measuring chamber and that the measurement signal be processed taking into account the temperature of the testing fluid. This modification assures that the properties of the testing fluid contained in the measuring chamber depend not only on the pressure but also on the temperature of the testing fluid in the measuring chamber. This further increases the precision and comparability of testing values. 
   Alternatively, the invention also proposes that taking into account the measured pressure and possibly the measured temperature, the density of the testing fluid in the measuring chamber is determined and based on this, a comparison volume at a particular comparison pressure and possibly at a particular comparison temperature is determined. This is a simple and very precise method for determining a parameter, which can be used to precisely compare the quality of different injection systems. 
   In another modification of the method according to the invention discloses that the progression of the pressure during an injection is detected and the measurement signal is processed taking into account the detected progression of the pressure. This allows the method to take into account the fact that the pressure in the measuring chamber can change during an injection. 
   The invention also proposes that when the pressure of the testing fluid in the measuring chamber exceeds a limit, an error message is generated. It is relatively important for the precision of the measurement that the pressure of the testing fluid in the measuring chamber lie with a particular range of values. An excessive pressure in the measuring chamber, like an insufficient pressure, can lead to a distortion of the measurement result. This fact is taken into account by this modification. 
   It is particularly preferable that when the pressure of the testing fluid in the measuring chamber exceeds a limit, a safety device is activated, which reduces the pressure of the testing fluid in the measuring chamber. For example, it is possible that the movement of the piston might become blocked. In this instance, the pressure in the measuring chamber during an injection could reach a level that is critical for the measuring device. This can be detected by the pressure measurement and appropriate countermeasures can be initiated. 
   The current invention also relates to a computer program, which is suitable for executing the above method, when it is run on a computer. It is particularly preferable if the computer program is stored in a memory, in particular a flash memory. 
   In addition, the invention relates to a device for measuring the injection quantity of injection systems, in particular for motor vehicles, and in particular in production testing, having a measuring chamber into which a testing fluid can be injected by an injection system, having a piston, which at least partially defines a measuring chamber, and having a detection device, which detects a movement of the piston and generates a corresponding measurement signal. 
   In order to increase precision in the detection of the injected fluid mass, and also to permit a better comparison of the injection quantities and injection volumes measured in different injections, the invention proposes that the device include a detection device for the pressure of the testing fluid in the measuring chamber as well as a processing unit in which the measurement signal is processed, taking into account the pressure detected. 
   It is particularly preferable if the processing unit of the device is provided with a computer program as described above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of the invention will be explained in detail below in conjunction with the accompanying drawings,in which: 
       FIG. 1  shows a section through an exemplary embodiment of a device for measuring the injection quantity of injection nozzles; and 
       FIG. 2  shows a flowchart of a method for operating the device from  FIG. 1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1 , a device for measuring the injection quantity of injection systems is labeled as a whole with the reference numeral  10 . It includes a centrally disposed body  12 , which is secured to a sleeve  14 . This sleeve is in turn supported on a base plate  16 . The device  10  is fixed by means of the base plate  16 . 
   An essentially central stepped bore  18  is let into the central body  12 . A cylindrical insert  20  is inserted into the upper section of the stepped bore  18  and is supported by means of a collar  22  against the top of the central body  12 . A head  24  is placed onto the insert  20  in a pressure-tight fashion, which likewise has a stepped bore  26  let into it, which in the assembled state shown in  FIG. 1 , extends coaxial to the stepped bore  18 . An adapter  28  is inserted from above into the stepped bore  26  and is sealed in relation to the stepped bore  26  by means of O-rings  30 . An injection system, in this instance an injector  32 , is inserted with its injection nozzle  33  into the adapter  28 . The injector  32  is in turn connected to a high pressure testing fluid supply (not shown). An injection damper  34  is inserted into the lower region of the stepped bore  26  in the head  24 . 
   The insert  20  also contains a bore  38 , which in the installation position shown in  FIG. 1 , extends coaxial to the stepped bore  18  and to the stepped bore  26 . A piston  40  is guided so that it can slide in the bore  38 . A helical spring  42 , which is supported against a transducer receptacle  44 , pushes the piston  40  upward. A measuring chamber  45  is defined by the top end of the piston  40 , the lower unthreaded region of the injection damper  34 , and the lower region of the stepped bore  26 . The piston  40  is embodied as a closed, hollow body. 
   The measuring chamber  45  formed between the piston  40  and the head  24  is filled with a testing fluid (unnumbered). The pressure of this testing fluid in the measuring chamber  45  is measured by a pressure sensor  50 , which is disposed outside the intersecting plane of  FIG. 1  and is therefore only depicted symbolically in the drawing. The pressure sensor  50  is inserted into the measuring chamber  45  through an oblique through bore (not shown). A temperature sensor  46  detects the temperature of the testing fluid in the measuring chamber  45 . The pressure sensor  50  and the temperature sensor  46  are connected to a control and processing unit  52 , whose output is connected to a magnetic drain valve  53 , through which the testing fluid can be drained from the measuring chamber  45 . To the left of the central body  12 , there is also a constant pressure valve  54 , which, even at very different gas pressures underneath the piston  40 , provides for a drainage rate from the measuring chamber  45  that is virtually independent of the gas pressure underneath the piston  40  when the electromagnetically actuated drain valve  53  is open. 
   The transducer receptacle  44  likewise contains a stepped bore  56 , which in the installation position shown in  FIG. 1 , is likewise coaxial to the other stepped bores  18 ,  26 , and  38 . A spring retainer  58  with a cylindrical shoulder  60  is mounted onto the underside of the transducer receptacle  44 . The shoulder  60  engages in the stepped bore  56 . The spring retainer  58  and its shoulder  60  also have a central stepped bore  62 , which is open toward the bottom. 
   A shoulder of the stepped bore  62  in the spring retainer  58  supports a helical spring  64 , which pushes a sensor retainer  66  upward against a collar of the transducer receptacle  44  that protrudes radially inward. The sensor retainer  66  is tubular or sleeve-shaped and its upper region has an eddy current sensor  68  screwed into it so that the top end of this sensor is a short distance under the bottom end of the piston  40 . A connecting line  70  of the eddy current sensor  68  is routed outward through the tubular sensor retainer  66  and the spring retainer  58  and is connected to the control and processing unit  52 . 
   In the event of a malfunction, for example due to an insufficient emptying of the measuring chamber  45  between two injections or two injection cycles, if the piston  40  moves too far downward, then it comes to rest with its bottom end in contact with the top end of the eddy current sensor  68 . Because the sensor retainer  66  is supported by the helical spring  64 , the piston  40 , together with the eddy current sensor  68  and the sensor retainer  66 , can move further downward—in this instance counter to the initial spring stress of the helical spring  64 . A downward motion of the piston  40  is possible provided that the testing fluid can flow out of the measuring chamber  45  through a circumferential groove (unnumbered) in the stepped bore  38  of the insert  20 . This prevents damage to the device  10  in the event of a malfunction. 
   The device  10 , which is depicted in  FIG. 1  and is for measuring the injection quantity of an injection nozzle  28 , operates according to the following method (see  FIG. 2 ): 
   Testing fluid (not shown) is supplied by means of the high pressure testing fluid supply to the injection system  32  and its injection nozzle  33  and, by means of the injection damper  34 , is injected into the measuring chamber  45  that is likewise filled with testing fluid. The injection damper  34  prevents the injection jets from directly striking the top end of the piston  40 . A direct impact of the injection jets against the piston  40  could set the piston into oscillations, which do not correspond to the actual course of the injection. The injection of testing fluid into the measuring chamber  45  increases the testing fluid volume in the measuring chamber  45 . The additional volume traveling into the measuring chamber  45  moves the piston  40  downward, counter to the force of the helical spring  42  and the gas pressure underneath the piston  40 . This changes the distance between the bottom end of the piston  40  and the eddy current sensor  68 . 
   This change in the distance between the eddy current sensor  68  and the bottom end of the piston  40  results in a change in the complex input impedance on the input side of the winding of the eddy current sensor  68 . This change is metrologically evaluated in the control and processing unit  52  and is used to determine a distance sm (block  72  in  FIG. 2 ) that the piston  40  has traveled. 
   Based on the measured distance sm—after the start of the calculation in block  71 , a volume Vm is determined in block  74 . This corresponds to the volume by which the measuring chamber  45  has increased due to the movement of the piston  40 . This volume is calculated from the measured distance sm and the cross sectional area of the piston  40 , which is waiting in block  76  and has been called up from a memory  78 . 
   In block  80 , this volume Vm, which is also referred to as the “displacement volume”, is used to calculate the injected mass mi of testing fluid. This is done by multiplying the displacement volume Vm by the density of the testing fluid. However, the density of the testing fluid in the measuring chamber  45  on the one hand, depends on the temperature T (block  82 ) and on the other hand, depends on the pressure p (block  84 ), which prevail in the testing fluid in the measuring chamber  45 . These are detected by the pressure sensor  50  and the temperature sensor  46  and, based on the detected values, in block  80 , first the density prevailing in the testing fluid in the measuring chamber  45  is determined at the detected pressure p and the detected temperature T, and based on this density, the injected mass mi is determined. 
   Based on the actually injected mass mi of testing fluid, which has been injected into the measuring chamber  45 , in block  86 , a comparison or norm volume Vnorm is calculated based on a determined pressure pnorm and a determined temperature tnorm (block  88 ). This comparison or norm volume Vnorm is particularly well-suited for comparing different injections and for comparing different injection systems  32 . The method depicted in  FIG. 2  ends at block  92 . 
   The device shown in  FIG. 1  and the method shown in  FIG. 2  can considerably improve the precision in the calculation of a volume injected into the measuring chamber  45  under defined norm conditions (norm temperature and norm pressure) and in the calculation of the actually injected testing fluid mass. This increase in precision has an especially significant effect, particularly on the measurement of small injection quantities. 
   In an exemplary embodiment that is not shown, the pressure which prevails in the testing fluid in the measuring chamber and is detected by the pressure sensor is also used for malfunction and safety monitoring of the device. If the pressure of the testing fluid in the measuring chamber lies beyond a defined limit, then it can be assumed that there is a malfunction in the system so that an error message is generated. For example with a jam med piston, a very rapid increase in the pressure in the measuring chamber can occur, which can cause damage to the device. In this instance, when the pressure of the testing fluid in the measuring chamber exceeds a limit, the magnetic drain valve  53  is triggered by the control and processing unit so that the valve opens and testing fluid is drained from the measuring chamber and the pressure in the measuring chamber is reduced. This reliably prevents damage to the device for example due to a jamming of the piston. 
   The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.