Abstract:
A test apparatus serves to test cam-driven fuel injection systems. The apparatus includes a camshaft which can act on a piston of the fuel injection system at least indirectly via a lever. It is proposed that the lever have a multiplicity of fastening positions for an actuating element which can act on the piston and that the fastening positions be disposed at different distances from a pivot axis of the lever.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a 35 USC 371 application of PCT/EP 2006/068022 filed on Nov. 2, 2006. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a testing device for a cam-driven fuel injection system, in particular a unit injector injection system or unit pump injection system. 
   2. Description of the Prior Art 
   In modern diesel engines, a fuel injection system injects the fuel at high pressure directly into the combustion chamber. There are various types of fuel injection systems used for this, for example unit injector injection systems or unit pump injection systems. Both fuel injection systems are actuated directly on the engine itself by means of a cam shaft. Via a lever, a cam on the cam shaft produces a stroke of a pump piston of the fuel injection system. This produces a very high pressure at a nozzle of the fuel injection system, which pushes a valve needle into an open position and as a result, fuel is injected into a combustion chamber of the engine. The injection quantity is adjusted by means of a solenoid valve, which controls the buildup of pressure in the fuel injection system. 
   The injection pressure and the injection quantity depend, among other things, on the shape of the cam and its stroke. Different fuel injection systems have different strokes and cam shapes. In some cases as well, identical fuel injection systems are actuated with an identical stroke in different types of engines with different cams. 
   Testing devices used for testing purposes and for the quality control of the above-described cam-driven fuel injection systems are known from the market. One such testing device has a cam-driven fuel injection system built into it. The piston of the fuel injection system is acted on by means of a cam shaft and a lever so as to simulate an operating situation. In the known testing device, the same cam is used for various types of fuel injection systems and all fuel injection systems are operated with the same stroke. In order to avoid damage, this stroke is relatively small. There is also a known testing device in which the cams of the cam shaft are replaceable. It is thus possible to associate each fuel injection system with a specific cam. 
   OBJECTS AND ADVANTAGES OF THE INVENTION 
   The object of the present invention is to disclose a testing device of the type mentioned at the beginning that is able to carry out testing on the various fuel injection systems in an inexpensive and technically meaningful fashion. 
   This object is attained by a testing device with the defining characteristics of the invention. Important defining characteristics of the invention are contained in the description and the drawings. It should be noted at this point that these defining characteristics can be essential to the invention in widely varying combinations, without having to be explicitly referred to herein. 
   With the testing device according to the invention, various strokes of the piston in a fuel injection system can be implemented with one and the same cam. As a result the fuel injection systems can be tested not only in the lower pressure range, but also in the upper pressure range, which improves the significance of the test carried out. A complicated changing of the cams is not required, resulting in low operating and manufacturing costs of the testing device according to the invention. 
   This is made possible by the fact that the lever is embodied so that it can be operated with various lever arms and therefore with various strokes. The various lever arms can be represented by discrete fastening positions or for example by means of a linear adjustability of the actuating element on the lever. In this case, the lever is preferably embodied in the form of a pivoting lever or rocking lever. 
   An advantageous modification of the testing device according to the invention is distinguished by the fact that the lever includes a replaceable intermediate element on which the different fastening positions for the actuating element are provided. In this way, the application range of the testing device can be expanded even further and the manufacturing and operating costs of the testing device are reduced since the lever can be standardized and instead the intermediate plate is provided with the corresponding fastening positions. For example, a model-specific intermediate plate with different fastening positions can be provided for each of the various models of fuel injection system. The intermediate element is significantly less expensive to manufacture than the lever. 
   A particularly preferable embodiment is distinguished by the fact that the fastening positions are composed of threaded bores into which the fastening element is screwed. This implementation is particularly inexpensive and simple to use. 
   Another, particularly advantageous embodiment of the testing device according to the invention is distinguished by the fact that it includes a fastening device with a plurality of fastening positions for the fuel injection system; each fastening position corresponds to a particular spacing of a longitudinal axis of the piston of the fuel injection system from the pivoting axis of the lever. This reduces the transverse forces that the actuating element introduces into the piston of a fuel injection system and provides a good simulation of the actual operating conditions of the fuel injection system to be tested. Here, too, a plurality of discrete fastening positions can be provided or a device can be used that is linearly adjustable and consequently makes it possible to achieve a multitude of intermediate positions. 
   Here, too, adapter elements can be provided that permit various fuel injection apparatuses to be attached to the fastening positions of the fastening device. This extends the application range of the testing device according to the invention to very different types of fuel injection apparatuses while simultaneously keeping down costs since the actual fastening device can remain unchanged for all fuel injection apparatuses. 
   It is particularly advantageous if the fastening positions are individualized so that each type of vehicle system is unmistakably associated with a particular fastening position. This assures that the respective test specimen is associated with the correct stroke. This in turn simplifies the use of the testing device according to the invention and reduces the frequency of false test results. 
   Another particularly advantageous embodiment of the testing device according to the invention is distinguished by the fact that it includes a sensor that at least indirectly detects a reaction force that occurs during an actuation of the fuel injection system. This permits it to also detect defects or deficiencies, for example in the leak-tightness of the fuel injection system tested, which cannot be detected solely by measuring the injection quantity or by means of a visual inspection. 
   In this case, the sensor can be situated on the lever so that it detects the force there. But it is even more preferable if the fastening device is supported in pivoting fashion and is supported by means of a pendulum support and if the sensor detects a force acting on the pendulum support or on a bearing block of the pendulum support. The latter embodiment minimizes transverse force influences on the measurement result and thereby increases the significance of the reaction force measurement. 
   According to another embodiment, the cam shaft has a plurality of different cams situated next to one another and the lever, together with the fastening device for the fuel injection apparatus, can be moved into various operating positions in the axial direction of the cam shaft; in each operating position, the lever cooperates with a different cam. As a result, it is also possible to implement various pressure curves in the fuel injection systems tested without requiring the expense of a cam change. This reduces the changeover time when using the testing device according to the invention, thus also reducing operating costs. Naturally, in practice, the aim is to use the lowest possible number of cams. Since the cam shapes have only slight differences, an identical stroke achieves approximately the same levels of pressure. However, it is useful in each instance to first detect reference values by means of corresponding reference measurements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A particularly preferred exemplary embodiment of the present invention will be explained in greater detail below in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a schematic, partially sectional depiction of a testing device for a cam-driven fuel injection system; and 
       FIG. 2  is a perspective, likewise partially sectional, more detailed depiction of the testing device from  FIG. 1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIGS. 1 and 2 , a testing device is labeled as a whole with the reference numeral  10 . It is used to test a cam-driven fuel injection system, in the current example a unit injector injection system  12 , which is only shown in  FIG. 1 . First, a description will be given of its design and function. 
   The unit injector injection system  12  includes a housing  14  with a nozzle tip  16  that protrudes into an injection chamber  18  of the testing device  10 . The housing  14  contains a nozzle needle  20  that is accommodated in sliding fashion and acted on by a spring  22  that moves it into a closed position. 
   A pump of the unit injector injection system  12  is labeled  24  and includes a piston  26  that delimits a delivery chamber  28 . This delivery chamber communicates with a pressure chamber  30 , which is delimited by a pressure surface  32  that is embodied on the nozzle needle  20  and acts in its opening direction. The delivery chamber  28  can also be connected by means of a solenoid control valve  34  and a prefeed pump  36  to a fluid reservoir  38 , which in the present instance, stores a testing fluid. 
   During an intake stroke of the piston  26  when the control valve  34  is open, testing fluid is drawn from the fluid reservoir  38  into the delivery chamber  28 . When the control valve  34  is closed during a delivery stroke of the piston  26 , the testing fluid enclosed in the delivery chamber  28  is compressed, which results in a corresponding pressure increase in the pressure chamber  30 . When the hydraulic force acting on the pressure surface  32  exceeds the force of the spring  22 , the nozzle needle  20  opens and testing fluid is injected from the nozzle tip  16  into the injection chamber  18 , where it is collected and relayed elsewhere. 
   For the testing of the unit injector injection system  12 , the testing device  10  has two essential subordinate devices: an actuating device  40  and a fastening device  42 . First, with regard to the latter: 
   The fastening device  42  has a guide plate  44  equipped with a number of parallel guide grooves  46 , only one of which, for the sake of clarity, is provided with a reference numeral. These guide grooves  46  define different fastening positions for an adapter element embodied in the form of an adapter plate  48 . This adapter plate  48  in turn is fastened in a way that is not shown in detail here to the housing  14  of the unit injector injection system  12 . 
   The guide plate  44  is attached at  50  in an hinging fashion to a stationary base  52  of the testing device  10 . In order to prevent the guide plate  44  from tilting during operation, at its end oriented away from the hinge  50 , it is supported by a pendulum support  54  on a bearing block  56  that is likewise attached to the stationary base  52 . Mounted on the bearing block  56  is a sensor embodied in the form of a strain gauge  58 , which detects a transverse force acting on the bearing block  56  by means of the pendulum support  54 . 
   The actuating device  40  is constructed as follows. A cam follower  60  is also supported in pivoting fashion at  62  on the stationary base  52 . The hinge joint  62  here is spaced laterally apart from a longitudinal axis  64  of the piston  26  of the unit injector injection system  12 . One arm  66  of the cam follower  60  extends toward the piston  26 . It has an intermediate plate  68  fastened to it that constitutes an intermediate element and contains a plurality of threaded bores  70  (once again for the sake of clarity only one of these is provided with a reference numeral). These threaded bores constitute fastening positions for an actuating element  72  provided with a ball-shaped head. As is clear from  FIG. 1 , the threaded bores  70  are spaced different distances apart from the pivot axis of the cam follower  60  defined by the hinge  62 . The ball-shaped head of the actuating element  22  cooperates with a complementary recess (unnumbered) in the piston  26  of the unit injector injection system  12 . 
   On its side oriented away from the piston  26 , the arm  66  is provided with a roller support  74  equipped with a roller  76 . This in turn cooperates with a cam  78  of a cam shaft  80 . The camshaft is driven by a drive motor not shown here, for example an electric motor. A second arm  82  of the cam follower  60  is acted on by a compression spring  84 , which is clamped between the arm  82  and the stationary base  52 . In this way, the roller  76  is continuously pressed against the cam  78 . 
   The testing device  10  functions as follows: when the cam shaft  80  rotates, the cam follower  60  is pivoted around its pivot axis  62 . Because of the lever arm between the actuating element  72  and the pivot axis defined by the hinge  62  (this lever arm is labeled  86  in  FIG. 1 ), a particular stroke results for each threaded bore  70 . This stroke is at a minimum when the actuating element  72  is screwed into the threaded bore  70  in which it is situated in  FIG. 1 . This produces a corresponding, comparatively small stroke of the piston  26 . The reaction force that is introduced into the guide plate  44  via the housing  14  and the adapter plate  48  by means of the pressure increase in the delivery chamber  28  is transmitted via the pendulum support  54  into the bearing block  56  and is detected there by the strain gauge  58 . 
   If the same unit injector injection system  12  is to be tested with a larger stroke, the adapter plate  48  is simply fastened into other guide grooves  46  of the guide plate  44  and the actuating element  72  is screwed into another one of the threaded bores  70 . If another unit injector injection system  12  is tested, then another adapter plate  48  is used. It is possible, but not shown, for the guide grooves to be individualized so that each type of fuel injection system is unmistakably associated with a particular fastening position and therefore a particular stroke. In an exemplary embodiment that is likewise not shown, it is also possible for the fastening device, together with the actuating device (without a cam shaft), to be shifted in the longitudinal direction of the cam shaft. The corresponding cam shaft then has a plurality of different cams situated next to one another so that the roller cooperates with a different cam depending on the position of the actuating device. 
   The foregoing relates to the preferred exemplary embodiment 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.