Patent Publication Number: US-7212005-B2

Title: Ignition coil tester

Description:
FIELD OF THE INVENTION 
   The present invention relates to an ignition coil tester for testing the functioning of rod-type ignition coils, which is connectible to a diagnostic tester, the rod-type ignition coil having a primary winding and a secondary winding for generating the ignition voltage as well as a field guide plate, a plug connector and a secondary output. 
   BACKGROUND INFORMATION 
   To measure the high voltage transmitted from an ignition coil to the spark plug via a cable for the purpose of testing the functioning of single-spark ignition coils, a tong-test instrument is already known, which can be clamped onto the outer shell of the line carrying the high voltage. For this purpose, two conductor surfaces of the tong-test instrument surround the high-voltage cable. In this manner, the ignition coil can be tested in the installed state. Ignition devices having multiple rod-type ignition coils for an internal combustion engine are known from German Published Patent Application No. 298 18 882. In this instance, the rod-type ignition coils are located within a so-called spark plug dome of the cylinder head of the internal combustion engine. 
   A high-voltage connector attached to the respective rod-type ignition coil, which establishes the connection between a high-voltage output of the rod-type ignition coil and a terminal stud of the spark plug that is mounted in a stationary manner in the spark plug dome, is inserted into the spark plug dome. 
   In internal combustion engines having rod-type ignition coils, in which the latter are directly connected to the spark plugs without the interconnection of a cable, an ignition coil test cannot be performed in the installed state of the rod-type ignition coils by using the known tong-test instrument since the secondary winding and the secondary circuit of the rod-type ignition coils for the ignition voltage diagnosis are partly inaccessibly located inside the spark plug domes. 
   For this reason, rod-type ignition coils today are tested in the uninstalled state. Requiring numerous auxiliary devices, the loose measuring structures used for this purpose, however, for safety-related reasons do not allow for the measurement to be carried out directly on the internal combustion engine. Moreover, the testing conditions of an uninstalled rod-type ignition coil are different that those of one that is installed. Consequently, the testing results do not completely match the actual values in the operating state or it is not possible to perform all tests under actual conditions. 
   The objective of the present invention is to provide an ignition coil tester in connection with a diagnostic tester for the component testing of a rod-type ignition coil uninstalled from an internal combustion engine. 
   SUMMARY OF THE INVENTION 
   The objective of the present invention is achieved in that an ignition coil tester has a housing and a spark plug dome for receiving the rod-type ignition coil, the dimensions and shape of which essentially correspond to those of a spark plug dome in an internal combustion engine and/or are adjustable to the dimensions of the latter. The ignition coil uninstalled from the internal combustion engine is installed into the ignition coil tester, where it is tested. Adjusting the shape of the ignition coil dome of the ignition coil tester to the shape of the ignition coil dome in the internal combustion engine allows the test to be performed under nearly actual ambient conditions. The compact construction of the ignition coil tester, into which the required auxiliary devices for spark plug testing are integrated, allows for ignition coils to be tested while respecting the safety-related requirements without having loose measuring structures outside of the internal combustion engine. 
   In a preferred specific embodiment, the diameter of the spark plug dome is adjustable to the diameter of the rod-type ignition coil and of the spark plug dome of the internal combustion engine by way of an interchangeable insulator and/or an interchangeable metal sleeve. This variable construction allows for the ignition coil tester to be optimally adapted to the geometry of the spark plug dome of the internal combustion engine. Through coupling capacitances to the electrical ground of the metal sleeve or of the housing of the ignition coil tester, the distance between the metal sleeve and the rod-type ignition coil determines the damping ratio, which in this manner can be adjusted to the actual conditions. 
   If the height of the spark plug dome can be adjusted to the length of the rod-type ignition coil and of the spark plug dome of the internal combustion engine using an interchangeable or adjustable distance adjustment piece, then the ignition coil tester can be used for different rod-type ignition coils of different lengths as well as for different internal combustion engines having spark plug domes of different lengths. Due to the fact that a spark plug or a gas spark gap can be inserted into the ignition circuit, the necessary tests can be carried out at the rod-like ignition coil. Thus, the spark plug may be switched into the ignition circuit for measuring ignition voltage and for testing diodes. For diagnosing the ignition signal and for testing the ignition reserve, on the other hand, a suitable gas spark gap may be used. 
   The electrical connection between the rod-type ignition coil and the chosen spark gap may be established by an adjustment sleeve as a connecting piece from the secondary output of the rod-type ignition coil to the gas spark gap or the spark plug. The adjustment sleeve may be adjusted in its dimensions as well as in the design of its end contacts to the rod-type ignition coil to be tested in the respective installation configuration and to the contacts of the spark gaps, which allows for a correspondingly versatile use of the ignition coil tester. 
   For capacitive ignition signal uncoupling for diagnosing the ignition voltage, a capacitive sensor may be attached to the adjustment sleeve. In this region it is possible to provide sufficient space for accessing the secondary electric circuit. Furthermore, the construction of the adjustment sleeve may be optimally adjusted to the measuring task of determining the precise ignition voltage by choosing suitable dimensions and materials. 
   Due to the fact that the housing in the region of the capacitive sensor has an aperture for a measuring line of the capacitive sensor and/or in the region of the field guide plate has an aperture for contacting the field guide plate, the corresponding measuring signals may be transmitted via measuring and/or signal lines from the housing of the ignition coil tester to the output electronics and the diagnostic system. 
   The aperture for contacting the field guide plate and the metal sleeve is preferably insulated with respect to a signal line by a high-voltage insulation. This prevents the measuring signal from being diverted to the housing of the ignition coil tester when an insulation test is performed at this location regarding high-voltage flashovers in the rod-type ignition coil to the field guide plate or to the surroundings. 
   For reasons of a simple manufacture of the ignition coil tester, the housing may be provided as a one-part or multi-part design. Particularly a multi-part construction may avoid difficult undercutting processes. 
   A particularly compact and user-friendly design of the entire assemblage is achieved when the control module is connected with the housing as one unit. 
   The ignition coil tester may also be designed in such a way that it can be used for testing single-spark ignition coils having secondary windings situated outside of the spark plug dome. Here too it is an advantage that the single-spark ignition coil can be tested in the spark plug dome of the ignition coil tester under almost actual conditions. The ignition coil tester may thus be used in a very versatile manner. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     The FIGURE shows a sectional view in the longitudinal direction of an ignition coil tester with an inserted rod-type ignition coil. 
   

   DETAILED DESCRIPTION 
   The FIGURE shows an ignition coil tester  1  with an inserted rod-type ignition coil  20 . Ignition coil tester  1  is made of a housing  30 , which is made up of an upper housing part  40  and a lower housing part  50 . 
   Upper housing part  40  surrounds a recess  41 , the dimensions of which essentially correspond to the dimensions of a spark plug dome of common internal combustion engines. An interchangeable insulator  11  and within it an interchangeable metal sleeve  12  are inserted in recess  41 . 
   Recess  41 , insulator  11  and metal sleeve  12  have a cylindrical shape in the design shown. However, depending on the shape of rod-type ignition coil  20  and of the spark plug dome of the internal combustion engine to be adjusted, other geometries are possible as well. 
   On the side facing lower housing part  50 , the cylindrically shaped region  11   a  of insulator  11  is bounded by a peripheral frontal termination  11   b , which has metal sleeve  12  abutting against it. Metal sleeve  12  is thus completely insulated with respect to housing  30 . If no insulation test is conducted, then metal sleeve  12  may be connected to ground (B−) via a switch  75 . 
   Rod-type ignition coil  20  having primary winding  21  and secondary winding  22 , field guide plate  24  and secondary output  25  is located within metal sleeve  12 , which bounds spark plug dome  10  of ignition coil tester  1 . Only plug connecter  23  of rod-type ignition coil  20  having built-in switch-on diode  26  and integrated output stage is located outside of spark plug dome  10 . 
   At the upper opening of recess  41 , a receptacle  42  in the form of a peripheral, stepped milled-out recess is provided for receiving an interchangeable distance adjustment piece  13 . Using this distance adjustment piece  13 , it is possible to adjust the height of spark plug dome  10  to the length and to the diameter of rod-type ignition coil  20 . Rod-type ignition coil  20  rests with its plug connector  23  against distance adjustment piece  13 . 
   On the opposite side, recess  41  passes over into a cylindrical duct  45  having a smaller diameter than recess  41  of upper housing part  40 . 
   In the region of field guide plate  24  of rod-type ignition coil  20 , upper housing part  40  has a radially positioned aperture  43  in the form of a bore hole, the surface of which is lined with a high-voltage insulation  44 . Aperture  43  receives a signal line  71 . 
   Lower housing part  50  is flanged to upper housing part  40  on the side of duct  45 . Together with the bottom side of upper housing part  40 , it forms a recess  51 , which, separated by a moveable mounting plate  53 , is closed off by a spark chamber  52 . On or at grounded mounting plate  53  in the design shown, a gas spark gap  15  is mounted as well as, in a specifically provided tape hole, a spark plug  16 , the electrodes of which project into spark chamber  52 . However, additional spark gaps, for example various gas spark gaps, may also be provided. 
   An adjustment sleeve  14  is provided between secondary output  25  of rod-type ignition coil  20  and spark plug  16  switched into the ignition circuit as a spark gap in the example shown. This is made up of a conductive core  14   a , which is embedded in an insulating sleeve  14   b . Insulating sleeve  14   b  itself is fitted into duct  45  of upper housing part  40  and projects with its one side into recess  41  of upper housing part  40  and with its other side into recess  51  of lower housing part  50 . On the side of upper housing part  40 , an input contact  14   c  connected to conductive core  14   a  provides a conductive connection to secondary output  25  of rod-type ignition coil  20 , and an output contact  14   d , likewise connected to conductive core  14   a , provides a conductive connection to the chosen spark gap, in the case shown to spark plug  16 . 
   On the side of lower housing part  50 , a capacitive sensor  17  is situated on the outer surface of adjustment sleeve  14  in the region of conductive core  14   a . This is connected to a measuring line  72 , which is guided to the outside via an aperture  54  radially positioned in lower housing part  50 . The sensor is used for uncoupling the ignition signal for the diagnosis of the ignition voltage. 
   Measuring line  72  and signal line  71  are guided into a schematically represented output electronics  70 , which in turn has two measuring outputs  73 ,  74  for connecting a diagnostic system (not shown). 
   Plug connector  23  of rod-type ignition coil  20  is connected to a control module  60  via an adapter line  61 . Ignition coil tester  1  is supplied with voltage via a voltage input  63  on control module  60 . Control module  60  has a shunt  64  for measuring the secondary ignition current (measuring point ( 69 )) and, in the variant of the embodiment shown, an output stage  62 . In the case of rod-type ignition coils  20  that have an integrated output stage, this output stage  62  may be omitted, although the fundamental construction of ignition coil tester  1  and its mode of operation remain the same. Supply voltage B+ (input ( 65 )) of rod-type ignition coil ( 20 ) may be set in a variable manner, whereby the secondary voltage can be adjusted to the specification of the ignition coil. This makes it possible to test the ignition reserve and the voltage endurance of the insulation of rod-type ignition coil ( 20 ). Within control module ( 60 ), primary control signal ( 66 ) adjustable in terms of pulse duration, primary voltage (measuring point ( 67 )), primary current (measuring point ( 68 )), adjustable supply voltage (input ( 65 )) and secondary ignition current (measuring point ( 69 )) are available for evaluation. By disconnecting the supply voltage, the spark gaps can be safely changed. 
   An extension of the described ignition coil tester ( 1 ) makes it possible also to adjust parameters such as the operating temperature of the rod-type ignition coil ( 20 ) and the compression pressure in spark chamber ( 52 ) to the actual conditions existing in the internal combustion engine. It is then possible to test rod-type ignition coils ( 20 ) under the same conditions as in the internal combustion engine.