Abstract:
A method for ascertaining the leakage from injection systems is proposed which is fully automatable and which furnishes unambiguous measurement results, which make a simple decision possible about the tightness of an injection system, in particular of an injector or of an injection valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 03/03322 filed on Oct. 7, 2003. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is directed to an improved method of measuring the leakage fuel from fuel injection systems, and to apparatus and a computer program for use in the method. 
     2. Prior Art 
     Fuel injection systems for internal combustion engines and their components, such as common rail injectors, must be leakproof in operation. Moreover, they must be leakproof even when the engine is shut off, to prevent fuel from emerging from the injection systems or the injectors and possibly being a threat to persons, to the engine, or to the environment. The tightness testing required for this before the injection systems are shipped to the customer has been done until now by visual testing, once the injection system has been subjected to a test pressure for a certain length of time. This visual testing is a subjective measurement method that cannot be quantified and that sometimes leads to results that depend on the person performing the test. Moreover, the result of the tightness testing cannot be quantified. 
     OBJECTS AND ADVANTAGES OF THE INVENTION 
     The object of the invention is to furnish an automatable method, which produces objective measurement results and which on the basis of predeterminable limit values leads to an unambiguous result as to whether a tested injector or an injection valve is leakproof, or not. 
     According to the invention, this object is attained by a method for measuring the leakage from injection systems, in particular for internal combustion engines of motor vehicles and in particular in production testing, in which the injection system, in particular injectors or injection nozzles, is connected to a measurement chamber; a test fluid is introduced into the measurement chamber; the pressure in the injection system or in the measurement chamber is varied; subsequently or simultaneously, the motion of a piston that at least in some regions defines the measurement chamber is detected by a detection device; and the measurement signals furnished by the detection device are evaluated. 
     According to the invention, this object is also attained by a method for measuring the leakage from injection systems, in particular for internal combustion engines of motor vehicles and in particular in production testing, in which the injection system, in particular injectors or injection nozzles, is connected to a measurement chamber; a test fluid is introduced into the measurement chamber; subsequently or simultaneously, the motion of a piston that at least in some regions defines the measurement chamber is detected by a detection device; and subsequently at least one measurement signal furnished by the detection device is evaluated by comparison with at least one reference value. 
     These methods are relatively simple in terms of their sequence and are therefore readily automatable. Moreover, by a comparison of the measurement signals at various pressures, or by comparison of them with a reference value, any leakage that might occur is quantifiable, and in conjunction with a predeterminable limit value, the decision can automatically be made whether the tested injection system can be considered tight, or not. Automating the tightness testing economizes on cost, and the quality of the products shipped increases, since mistakes in the tightness testing can be precluded. 
     The method according to the invention can be further simplified if the test fluid is introduced into the measurement chamber from the injection system or the injector or the injection nozzle, since these injection systems and injection components are intended anyway for injecting metered quantities of fuel into the combustion chamber of an internal combustion engine. The functionalities required for introducing a test fluid into the measurement chamber are therefore already present anyway. 
     The evaluation of the automated tightness testing can be improved still further if a chronological series of the measurement signals furnished by the detection device is evaluated by comparison with a chronological series of reference values. 
     The conclusiveness of the tightness testing performed by the method of the invention can moreover be further enhanced by varying the test pressure p test  prevailing in the injection system and evaluating at least one measurement signal, furnished by the detection device, for each pressure. It is understood that this feature of the method may also be employed in conjunction with the detection of a chronological series of measured values. 
     From the evaluation of various chronological series of measured values that have been picked up at various test pressures, the cause of any leak in the injection system that might occur can possibly already be detected, making the ensuing correction of the defect easier. 
     The object of the invention is also attained by an apparatus for measuring the leakage from injection systems, in particular injectors and injection nozzles, for internal combustion engines, particularly in production testing, having a measurement chamber into which a test fluid can be injected from the injection system, having a piston that at least in some regions defines the measurement chamber, the piston being prestressed counter to the test fluid, and having a detection device which detects a motion of the piston and furnishes a corresponding measurement signal, or a chronological series of measurement signals, in that it is employed for performing one of the methods of the invention. 
     From German Patent DE 100 64 511 C2, a so-called IQI (injection quantity indicator) is known. This IQI comprises a housing in which a piston is guided. The interiors of the housing and of the piston define a measurement chamber. The measurement chamber has an opening, at which an injection system, such as an injector with an injection nozzle, can be inserted in pressure-tight fashion. If the injection system injects fuel into the measurement chamber, a fluid located in the measurement chamber is positively displaced. As a result, the piston moves, which is detected by a travel sensor. From the travel of the piston, a conclusion can be made about the change in volume of the measurement chamber or in the volume of the fluid contained there, and as a result about the quantity of fuel injected. 
     For measuring the motion of the piston, in the known injection quantity indicator, measurement is done with an arrangement comprising a measuring tappet and an inductive travel measuring system. The measuring tappet is embodied as a feeler or is solidly connected to the piston. Upon a motion of the piston, the measuring tappet is thus also put into motion, and finally the motion of the measuring tappet is detected, and a corresponding signal is forwarded to an evaluation unit. 
     These injection quantity indicators are used for high-precision measurement of the quantity of fuel injected under certain conditions by an injection system, in particular an injector or an injection nozzle. Since the injection quantity indicators have all the requisite characteristics for testing the method of the invention for testing the tightness of injection systems, in particular injectors or injection nozzles, it is recommended that these injection quantity indicators also be used for performing the method of the invention. This has additional major commercial advantages: First, a new apparatus does not have to be manufactured for performing the method of the invention, and furthermore, the injection quantity testing and the tightness testing of an injection system can be done in a vise and in succession in the same apparatus, namely the injection quantity indicator. As a result, outfitting and shipping times are eliminated, and manipulating the course of testing an injection system is simplified considerably. All in all, this leads to considerable commercial advantages because of the transition from visual testing to the method that according to the invention can be automated for testing the tightness of injection systems. 
     The injection quantity indicator used for performing the method of the invention may include a damping device which at least intermittently damps the motion of the piston. It is advantageous if the degree of damping of the damping device is chronologically adjustable, and particularly if the degree of damping is triggerable by a open- and closed-loop control device, so that even the control of the degree of damping can be done in fully automated fashion and thus without additional costs. 
     To attain comparable test results, it is recommended that the piston be prestressed counter to the test fluid by means of a helical spring. Alternatively or in addition, the piston can also be subjected to a gas pressure. Given a known spring rate and a known gas pressure, the pressure in the measurement chamber can readily be calculated, and from the measured quantity of leakage, a conclusion can be made about the tightness or lack of tightness of the injection system tested. 
     The invention finally also relates to a computer program, which is suitable for performing the above method when it is performed on a computer. It is especially preferred if the computer program is stored in a memory, in particular a flash memory. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One exemplary embodiment of the invention is described in detail below, in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a section through an apparatus for measuring the injection quantity of injection systems for internal combustion engines, with a damping device; 
         FIG. 2  is a graphical representation of the measurement signal obtained by the method of the invention and a reference value are plotted over time. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In  FIG. 1 , an apparatus for measuring the injection quantity in injection systems is identified overall by reference numeral  10 . It includes a centrally located body  12  that is seated on a damping device  14  which in turn is retained on a sleeve  16 . This sleeve stands on a bottom plate  18 , which is anchored to a base. A substantially central bore  20  is made in the central body  12 . A cylindrical insert  22  is inserted into the upper portion of this bore and is sealed off from the central body  12  by way of  0 -ring seals (not identified by reference numerals). A head  24  is placed in pressure-tight fashion on the insert  22 , and a stepped bore  26  is made in the head and, in the assembled state shown in  FIG. 1 , extends coaxially to the bore  20  in the central body  12 . 
     An adapter  28  is inserted into the stepped bore  26  and sealed off from the stepped bore  26 . An injection system, in the present case an injector  30  with its injection nozzle (not identified by reference numeral), is inserted into the adapter  28 . The injector  30  communicates in turn with a variable high-pressure test fluid supply  31 . The injector  30  is shown only schematically, in dashed lines, in  FIG. 1 . An injection damper (not shown) may be inserted into the lower region of the stepped bore  26  in the head  24 . 
     In the cylindrical insert  22 , there is also a bore  32 , which in the installed position shown in  FIG. 1  is coaxial with the bore  20  in the central body  12  and with the stepped bore  26  in the head  24 . A piston  34  is guided slidingly in the bore  32 . The piston  34  is pressed upward by a helical spring  36 . This helical spring is braced at the bottom on a step (not identified by reference numeral) of a stepped bore  38  in an intermediate piece  40 . The intermediate piece  40  is received in the lower region of the bore  20  in the central body  12 , that is, below the cylindrical insert  22 . 
     Between the top of the piston  34  (in upper terminal position of the piston  34  as shown in  FIG. 1 ) and the head  24 , one portion of the stepped bore  26  in the head  24  and one portion of the bore  32  form a measurement chamber  42 . This measurement chamber is filled with a test fluid (not shown), typically a test oil, which comes as close as possible to the properties of the fuel to be injected in actual operation by the injector  30 . The temperature of the test oil that is located in the measurement chamber  42  is detected by a temperature sensor  44 , which is introduced through a bore from obliquely outward through the head  24  as far as the measurement chamber  42 . 
     The piston  34  is embodied as a circular-cylindrical hollow body. A tappet  46  of tubular construction is secured to the lower end wall of the piston  34  and extends downward through the bore  38  in the intermediate piece  40 , to beyond the intermediate piece  40 . The tappet  46  is sealed off from the lower region of the stepped bore  38  in the intermediate piece  40  via an O-ring seal (not identified by reference numeral). Mounted on the lower end of the tappet  46  is a rodlike extension  48 , which extends coaxially to the tappet  46  downward to an inductive travel pickup  50 . Instead of the inductive travel pickup mentioned, other kinds of travel pickup may also be employed. 
     The damping device  14  located below the central body  12  is constructed as follows: In a frame  52 , piezoelectric elements  54  are retained on both sides of the tappet  46  or its extension  48 , diametrically opposite one another. The piezoelectric elements  54  act with rounded-off final control elements  56  on actuation arms  58 . The two actuation arms  58  are each joined, via a thin bridge of material  60  on their lower end, in terms of  FIG. 1 , to a respective base part  62 , which in turn is firmly screwed to the frame  52 . The bridge of material  60  thus forms a hinge, which specifies a hinge axis, located perpendicular to the plane of the drawing in  FIG. 1 , for the corresponding actuation arm  58 . However, the bridge of material  60  is stiff enough that the respective actuation arm  58  is prestressed only very slightly counter to the final control element  56  of the respective piezoelectric element  54 . 
     On the upper ends, in terms of  FIG. 1 , the actuation arms  58  each have a portion aimed at the tappet  46 , whose end face  64  oriented toward the tappet  46  is located with a slight spacing from the surface of the tappet  46 , in the state of repose shown in  FIG. 1 . The end face  64  of each actuation arm  58  is embodied as a friction face. 
     Besides the damping device  14  that has just been described, the apparatus  10  also has an additional damping device  66 : It is a flow brake, which is constructed as follows: The space below the lower end face of the piston  34  in the bore  20  of the cylindrical insert  22 , the upper region of the stepped bore  38  in the intermediate piece  40 , and a tie line leading obliquely outward from this region are all filled with test oil and form a first flow chamber  68 . The tie line in the intermediate piece  40  leads to a throttle or baffle  70 , located in the central body  12 , which is adjustable via an adjusting screw  72 . From the baffle  70 , a conduit  74  leads upward to a second flow chamber  76 , which is bounded at the top by the end face of a piston  80  that is prestressed by a helical spring  78 . The flow chamber  76  can be evacuated via a valve  82 . 
     The apparatus  10  further includes a open- and closed-loop control device  84 , which may include a programmable computer, which is connected on the input side to the temperature sensor  44  and the inductive travel pickup  50  and on the output side to a magnet valve, not shown, and to the two piezoelectric elements  54 . 
     The apparatus  10  shown in  FIG. 1  for measuring the injection quantity of an injection system  30  can also be used, according to the invention, for ascertaining the leakage of the injection system  30 , as follows: 
     At the instigation of the open- and closed-loop control device  84 , via the high-pressure test fluid supply, test fluid (not shown) is delivered to the injector  30  and its injection nozzle and is injected into the measurement chamber  42  that is likewise filled with test fluid. Injecting test fluid into the measurement chamber  42  increases the volume of test fluid in the measurement chamber  42 . The volume additionally reaching the measurement chamber  42  speeds up the piston  34  downward, counter to the force of the helical spring  36  and counter to the gas pressure below the piston  34 . 
     As a result, the tappet  46  and the extension  48  mounted on it also move, which leads to a measurement signal of the inductive travel pickup  50  that corresponds to the distance travelled by the extension  48 . From this measurement signal, in the open- and closed-loop control device  84 , in a processing unit not shown but present in the open- and closed-loop control device, the injected test fluid volume is calculated, taking the specific geometric conditions into account. 
     The quantity of fuel injected by the injection system  30  into the measurement chamber  42  is thus known, and the method according to the invention for testing the tightness of the injection system  30  begins. 
     For that purpose, the injection system  30  is closed, and a contrary pressure, hereinafter called the injection pressure p test , is maintained in the injection system. 
     If the injection system  30  closes 100% tightly, then no test fluid can get into the injection system  30  from the measurement chamber  42 . The same is true for the fluid in the injection system  30  at the test pressure p test  in the opposite direction. 
     Because of the internal leakage of the injection quantity indicator, and in particular the leakage between the piston  34  and the bore  32  in which the piston  34  is guided, as well as any possible leakage at the valve  82 , the piston, driven by the contact pressure of the helical spring acting on the piston  34  as well as any gas pressure that may be present and acts on the underside of the piston  34 , will move back into its outset position. The measurable distance-time law of the motion of the piston  34  is a measure of the internal leakage in the injection quantity indicator. 
     In  FIG. 2   a , the distance-time curve of an injection quantity indicator is shown in a graph on the left. It is assumed that the injection system  30  is tight. This distance-time curve, which is also designated s ref  in  FIG. 2   a , is a straight line with a negative slope. 
     If an injection system  30  is now connected to the injection quantity indicator  10  that does not close tightly, as is represented in the right-hand part of  FIG. 2   a , then because of the test pressure p test  prevailing in the injection system  30 , test fluid is forced out of the injection system  30  into the measurement chamber  42  through the leak. The reason for this is the fact that the test pressure p test  is greater than the pressure in the measurement chamber  42 . Because of the test fluid flowing into the measurement chamber  42 , the distance-time curve for the motion of the piston  34  changes. Based on the same starting value at time t=0, the piston  34  moves more slowly back to its outset position, which is expressed by the lesser negative slope of the measured values s m  compared to the reference values sref, which latter values of course stand for an injection quantity indicator with a tight injection system  30  connected to it. 
     In the right-hand part of  FIG. 2   a , the reference values s ref  are shown in dashed lines, for illustrating what has been said above. 
     In  FIG. 2   b , the chronological derivation of the variables shown in  FIG. 2   a  are presented in graph form. The chronological derivation of the distance-time law yields the leakage L in mm 3 /s. The leakage L has a value L 1 , in the case of an injection system  30  without leaks (left-hand part of  FIG. 2   b ). In the case of an injection system  30  that does not close tightly, the leakage L 2  is less than in the first case, because of the test fluid flowing in as replenishment. The leakage L 2  is smaller in amount than the leakage L 1 . The difference ΔL between the leakage L 1  and the leakage L 2  is a measure for the leakiness of the valve. It is understood that the leakiness ΔL is also dependent on the test pressure p test  that prevails in the injection system  30  in the closed state. By ascertaining the leakage L 2  at varying test pressures p test , further findings can be made about the extent of the leakiness of the injection system  30 . In some cases, further information about the type and source of the leakage can also be obtained from the change in the leakage ΔL as a function of a modified test pressure p test . 
     In a variant of the method described in conjunction with  FIG. 2 , the tightness of the injection system  30  can also be ascertained by varying the pressure in the injection system  30  or in the measurement chamber  42 . By evaluating the measurement signals s m, i  thus obtained, the tightness of the injection system  30  can also be ascertained by comparing the measurement signals s m, i  obtained at various pressures. 
     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.