Patent Publication Number: US-8117904-B2

Title: System and method for evaluating an integrated coil on plug ignition system

Description:
BACKGROUND 
     1. Technical Field 
     One or more embodiments of the present invention generally relate to a system and method for evaluating an integrated coil on plug ignition system for an internal combustion engine. 
     2. Background Art 
     An ignition system for an internal combustion engine is an electrical system that provides a spark for igniting fuel within the engine to initiate combustion. The ignition system typically comprises an ignition coil coupled to both a electrical switch and a spark plug. The spark is triggered by an interruption of current flow within the ignition system which creates a high voltage signal that arcs across a spark plug to create a spark. There is a trend within automotive industry to mount the ignition coil directly to the corresponding spark plug. Such a system may be referred to as a coil-on-plug (CoP) ignition system. Additional trends within the automotive industry include integrating each electrical switch into a housing of the corresponding CoP assembly. Such a system may be referred to as an integrated CoP ignition system. 
     The ignition system is typically assembled to the engine at an engine assembly plant. An End of Line (EOL) tester may be used to evaluate the performance of the engine and its associated systems. Conventional EOL testers evaluate the ignition system by measuring an electrical signal present on an ignition circuit between the ignition coil and the electrical switch. A flyback voltage signature is present on the electrical signal when the ignition coil is fired. The flyback voltage is measured and compared to pre-existing data to evaluate the ignition system. Such an ignition system generally provides an external point that is accessible to a user to monitor the electrical signal. 
     However, by integrating the switch within the housing of the ignition coil, it may not be possible to gain access to any point between the ignition coil and the electrical switch. As such, the flyback voltage is not capable of being ascertained. 
     One conventional strategy for evaluating the performance of an integrated CoP ignition system includes obtaining the flyback voltage via an RF based system for example. An RF based antenna may detect an electrically radiated inductive noise spike that is generated when the ignition coil is fired. Such an approach requires an array of antennas and additional sensors that are sensitive to the placement and pickup of other uncontrolled stray electrical noise. 
     SUMMARY 
     In at least one embodiment, an apparatus for evaluating performance of an integrated coil on plug (CoP) assembly is provided. The apparatus comprises a controller. The controller is configured to transmit a control signal to activate the CoP assembly. The controller is further configured to receive an indirect signal including a low frequency (LF) component from the CoP assembly responsive to the control signal. The controller is further configured to compare the LF component to predetermined data to evaluate the performance of the CoP assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an apparatus for indirect measurement of an integrated coil on plug ignition system; 
         FIG. 2  is an equivalent ignition circuit diagram of the integrated coil on plug ignition system of  FIG. 1 , illustrating a transmission line effect; 
         FIG. 3  illustrates signals measured at a point (A) of  FIG. 1 ; 
         FIG. 4A  illustrates signals measured at points (A) and (B) of  FIG. 1 , illustrated when a cylinder is not under compression; 
         FIG. 4B  illustrates the signals measured at points (A) and (B) of  FIG. 1 , illustrated when the cylinder is under compression; 
         FIG. 5A  illustrates the signals measured at point (A) of  FIG. 1  for integrated coil on plug ignition systems having varying spark plug gap spacing; 
         FIG. 5B  is a plot illustrating a time delay between the firing of an ignition coil and the presence of a high frequency resonance feature of each signal of  FIG. 5A ; 
         FIG. 5C  is a plot illustrating an amplitude of the high frequency resonance feature of each signal of  FIG. 5A ; and 
         FIG. 6  is a flow chart illustrating a method for indirect measurement of the integrated coil on plug ignition system. 
     
    
    
     DETAILED DESCRIPTION 
     In general, with an engine EOL test apparatus for evaluating an ignition system, a test stand is electrically coupled to an ignition system of an engine. The test stand controls the firing of the ignition system while evaluating the performance of the ignition system. If an integrated CoP ignition system is tested, then a flyback voltage measurement location disclosed in the prior art is no longer externally accessible. An apparatus and method is provided for evaluating an integrated CoP ignition system. 
       FIG. 1  is an EOL test apparatus  10  in accordance with one embodiment of the present invention. The apparatus  10  includes a test stand  28  and an engine  11  coupled to each other. The engine  11  includes an integrated CoP assembly  12 . The test stand  28  is configured to evaluate the performance of the CoP assembly  12 . 
     A spark plug  24  is operatively coupled to the engine  11  and electrically coupled to the integrated CoP assembly  12 . It is generally recognized that the engine  11  may include a plurality of integrated CoP assemblies, each being parallely coupled to one another and each being coupled to a corresponding spark plug  24 . For brevity, a single integrated CoP assembly  12  is shown that is coupled to a single spark plug  24 . 
     The integrated CoP assembly  12  includes an ignition coil  13  and an integrated switch  18  that are operably coupled to one another. The ignition coil  13  includes a primary coil  14  and a secondary coil  16  electromagnetically coupled to one another. A DC power supply  20 , positioned within the test stand  28  delivers electrical power to the ignition coil  13 . 
     The ignition coil  13  acts as a step up transformer to convert a low voltage signal on the primary coil  14  to a high voltage signal on the secondary coil  16  for firing the spark plug  24 . The primary coil  14  and secondary coil  16  are both wrapped around a common iron core. A controller  34 , positioned in the test stand  28  is configured to control the switch  18  to open or close. When the switch  18  is closed, current flows through the primary coil  14  to establish a magnetic field within the ignition coil  13 . When the controller  34  opens the switch  18 , the current flow in the primary coil  14  is interrupted which induces a high voltage in the secondary coil  16 . The high voltage arcs across a gap on the spark plug  24  which generates a spark. The induced voltage on the secondary coil  16  is proportional to the rate of change of the magnetic field, therefore an electrical switch  18  that switches quickly may be used. In one example, the switch  18  may be implemented as an insulated-gate bipolar transistor (IGBT). It is generally recognized that other suitable switching devices/mechanisms may be used. The particular type of switching device that is implemented may vary based on the desired criteria of a particular implementation. 
     The controller  34  may include signal conditioning equipment (not shown). The signal conditioning equipment may include a demodulator (not shown) that comprises filters for rejecting any undesired portions of a received signal. The signal conditioning equipment may also include a transformer (not shown) to scale the amplitude of the received signals to conform to an optimum dynamic range. The controller  34  may also include high speed data acquisition equipment “DAQ” (not shown) for digitizing the conditioned signals. The controller  34  accesses and analyzes the digitized signals (data) using signal analysis software. 
     A wire harness  23  is coupled between the power supply  20  and the CoP assembly  12 . An ignition circuit  22  is generally defined as the circuit formed by the power supply  20 , the integrated CoP  12  (including the ignition coil  13 , the switch  18 ) and the spark plug  24 . The ignition circuit  22  includes a primary circuit and a secondary circuit. The primary circuit is generally defined as a circuit formed by the power supply  20 , the primary coil  14  (of the integrated CoP  12 ), the switch  18  and the electrical connections between these components. The secondary circuit is generally defined as a circuit formed by the secondary coil  16  (of the integrated CoP  12 ) the spark plug  24  and the electrical connection between these components. The secondary circuit receives electrical power from the primary circuit, when the ignition coil  13  is fired, by the coupling between the primary coil  14  and the secondary coil  16 . 
     The EOL test apparatus  10 , may be used to test an engine  11  that is driven by combustion. Alternatively the apparatus  10  may be used for “cold motor” testing, where the engine  11  is driven by an alternate power supply. A servomotor  29  provides mechanical power to drive the engine  11  for performing “cold motor” testing on various aspects of the engine  11 . An adapter  30  couples the servomotor  29  to a crankshaft (not shown) of the engine  11 . 
     The engine  11  includes a series of cylinders (not shown) and corresponding internal pistons (not shown). The pistons are typically driven by combustion to actuate within the cylinders as the engine operates. A crankshaft (not shown) is coupled to the pistons, such that the crankshaft rotates as the pistons actuate. The engine is vacuum sealed to allow pressure to build within the cylinders during engine operation. Each cylinder is operatively coupled to one of the spark plugs  24 . A crankshaft sensor  31  measures the position of the crankshaft of the engine  11 . The crankshaft sensor  31  transmits a position signal  33  that corresponds to the present position of the crankshaft, to the controller  34 . The controller  34  analyzes the crankshaft position to determine the timing of the actuation of the pistons, such that the controller can fire a spark plug  24 , via the ignition coil  13 , when the corresponding cylinder is under compression. 
     The controller  34  analyzes the position signal  33  so that the controller  34  may control the timing of the integrated CoP assembly  12 . The controller  34  transmits a control signal  36  to the switch  18  in response to the position signal  33 . The control signal  36  corresponds to the desired state of the switch  18  (e.g. “open” or “closed”). As noted above, while  FIG. 1  only illustrates a single integrated CoP assembly  12 , it is recognized that the engine  11  may contain a plurality of integrated CoP assemblies being connected to one another. As such, the controller  34  coordinates the time in which each integrated CoP assembly  12  fires a corresponding cylinder under compression. The controller  34  receives a trigger signal  38  to begin recording data. 
       FIG. 1  includes point (A) and point (B) on the wire harness  23  and within the integrated CoP assembly  12 , respectively, which indicates two different locations where conducted voltage measurements may be taken by the controller  34 . For example, a hardwired connection may be established between the controller  34  and point (A), so that the controller  34  is capable of taking a voltage measurement at such a point. The controller  34  receives an indirect signal  40  on a node where point (A) is located (e.g. between the ignition coil  13  and the power supply  20 ). The controller  34  is also capable of receiving a flyback signal  42  on a node where point (B) is located (e.g. between the ignition coil  13  and the switch  18 ). With the integrated CoP assembly  12 , it is not possible for the controller  34  to receive a signal from point B as point B is located within the housing of the integrated CoP assembly  12 . However, point B is introduced to illustrate the manner in which data received on the indirect signal  40  is compared to data collected at point (B). The relevance of point B is used for illustrative purposes and will be described in more detail in connection with  FIGS. 4A-4B . 
     The indirect signal  40  provides ignition signature information that can be used by the controller  34  to evaluate the performance of the integrated CoP  12 . Such information will be discussed in more detail in connection with FIGS.  3  and  4 A- 4 B. 
     The apparatus may be utilized for vehicle level diagnostic testing. For example, a service garage may implement a test apparatus for evaluating vehicle ignition systems. 
       FIG. 2  illustrates a circuit  122  that is generally equivalent to the circuit formed by the integrated CoP assembly  12 , the power supply  20  and the spark plug  24  (e.g. the ignition circuit  22 ) of  FIG. 1 . Generally, electrical systems, especially those having long wire harnesses may have inherent impedance characteristics. The parasitic elements of the long wire harnesses may behave as a second order RLC Circuit. Thus, although the circuit  122  may not necessarily contain discrete components, it may function as an RLC circuit. 
     The transmission of signals along the circuit  122  is also generally governed by transmission line behavior. Generally, transmission line theory, as symbolized by a transmission effect  32 , applies when the wavelength of the signal is on the order of the length of the physical wire harness  23 . 
     The circuit  122  generally includes a parasitic impedance, which is attributed to external cabling and the type and quantity of inactive integrated CoP assemblies (not shown). The wire harnesses  23  as depicted  FIG. 1  is generally defined as an external cable that may cause the presence of parasitic impedance. The type of integrated CoP assembly  12  generally refers to the design parameters and manufacturer of the specific integrated CoP assembly  12 . The quantity of integrated CoP assemblies corresponds to the number of cylinders on the engine  11 . 
     A series RLC resonant circuit  52  represents the parasitic impedance that may be present on the circuit  122 . The RLC circuit  52  includes a parasitic inductance component that is represented by an inductor  54 , a parasitic capacitive component that is represented by a capacitor  56  and a line resistance that is represented by a resistor  58 . 
     Referring to  FIG. 3 , a plot depicting various characteristics of the indirect signal  40  is shown. The indirect signal  40  includes a low frequency damped oscillation component (or “LF component”)  60  and a high frequency impulse resonance component (or “HF component”)  62  . 
     The LF component  60  directly correlates to the start of an ignition coil firing event. Energy is stored in the RLC circuit  52  during the coil dwell interval when the switch  18  is closed. Once the switch  18  is opened (e.g. in response to the control signal  36 ), the energy resonates/dissipates in the form of the LF component  60  on the indirect signal  40 . The controller  34  is generally configured to measure the LF component  60  on the indirect signal  40 . The LF component  60  generally includes a frequency in the range of 50 KHz to 250 KHz. 
     In contrast, the HF component  62  corresponds to the arcing event. The HF component  62  is generally present on the ignition circuit  22  and is an input to the controller  34  on the indirect signal  40 . In general, the HF component  62  is generated by an arc that forms across a gap of the spark plug  24 . 
     The HF component  62  may occur due to a quarter wavelength transmission line effect  32 . Such an effect  32 , is present at the indirect measurement (A) and allows the HF component  62  to be observed on the indirect signal  40  for analysis by the controller  34 . It is generally recognized that the wavelength of the HF component  62  is on the order of or shorter than the length of the wire harness  23  to enable the transmission line effect  32  to occur. The HF component  62  includes a frequency of between 2 MHz and 30 MHZ. 
     It is generally contemplated that a tuned regulator  150  comprising discrete components may be added to the circuit  122  (or to any node between the power supply  20 , the CoP assembly  12 , and the spark plug  24  as shown in connection in  FIG. 2 ) to further tune the LF component  60  that is transmitted on the indirect signal  40 . The tuned regulator  150  includes a discrete inductor  154  and/or a discrete capacitor  156 . The tuned regulator  150  tunes the LF component  60  on the indirect signal  40  by adjusting the resonant frequency, the amplitude and/or the damping characteristics of the LF component  60 . 
       FIG. 4A  is a plot depicting a waveform for the indirect signal  40  and the flyback signal  42  as measured by the controller  34  when the ignition coil  13  is fired, and the cylinder is not under pressure. As noted above in connection with  FIG. 1 , the flyback signal  42  represents a measurement taken at point (B) of  FIG. 1 . As further noted above, data on the flyback signal  42  is not a signal that is capable of being ascertained because the housing within the CoP assembly  12  generally prevents access to point (B). The flyback signal  42  is described herein for illustrative purposes. Indirect signal  40  illustrates a simultaneously measured signal at point (A) of  FIG. 1 . By comparing the signals (e.g., the indirect and flyback) it is observed that different characteristics are present on both the indirect signal  40  and the flyback signal  42 . For example, a rapid voltage decrease  64  is present on the flyback signal  42  when the magnetic field created by the primary coil  14  collapses. A HF burst is induced on the indirect signal  40  when the magnetic field created by the primary coil  14  collapses. 
       FIG. 4B  is a plot depicting a waveform for the indirect signal  40  and the flyback signal  42  as measured by the controller  34  when the ignition coil  13  is fired, and the cylinder is under pressure. As mentioned above, the proper firing of the ignition coil  13  should correspond to when the cylinder is under compression. Secondary arc events  68  are induced on the flyback signal  42 . The HF component  62  that is present on the indirect signal  40  is created by arc events  68 . 
     Referring to  FIGS. 4A-5C , the controller  34  is configured to detect defects in the integrated CoP assembly  12  by analyzing an energy of the LF component and the amplitude and time delay of the HF component  62  on the indirect signal  40  within their corresponding frequency bands. As mentioned above in connection with  FIG. 3 , the LF component  60  is included in a frequency that is between 50 to 250 KHz, and the HF component  62  is included in a frequency that is between 2 to 30 MHZ. Typically, defects associated with the primary coil  14  are detected by analyzing the LF component  60  and defects associated with the secondary coil  16  are detected by analyzing the HF component  62 . Such detectable defects may include, but are not limited to, primary circuit continuity issues, secondary circuit continuity issues, improper wiring connections, and improper gap spacing of the spark plug  24 . 
     Referring to  FIG. 5A , the controller  34  may detect continuity defects along the primary circuit, by analyzing the energy of the LF component  60 . The energy of the LF component  60  is measured by calculating the area under the waveform, and generally referenced as numeral  80 . As noted above, the primary circuit is formed by the power supply  20 , the primary coil  14 , the switch  18 , and the electrical connections between these components. Primary circuit continuity defects may include, but are not limited to, an open circuit in the primary coil  14 , an open circuit in the switch  18  and an open circuit along the wire harness  23 . By comparing the energy of the LF component  60  on the indirect signal  40  to predetermined data (e.g., a predetermined energy value), the controller  34  may detect a primary circuit continuity defect. For example, an open circuit in the primary circuit (e.g. within the primary coil  14 , switch  18  or harness  23 ) may result in a generally flatline signal, represented by numeral  140 , having a minimal energy measurement. Whereas a properly functioning (baseline) primary circuit may have an energy component as shown via numeral  80 . 
     The controller  34  may also detect continuity defects along the secondary circuit, by analyzing the amplitude, and time delay of the HF component  62 . As noted above, the secondary circuit is formed by the secondary coil  16 , the spark plug  24  and the electrical connection between the components. Secondary circuit defects may include, but are not limited to, an open circuit in the secondary coil  16  and an open circuit in the electrical connection between the secondary coil  16  and the spark plug  24 . By comparing the amplitude and the time delay of the HF component  62  on the indirect signal  40  to predetermined data (e.g., a predetermined amplitude and time delay), the controller  34  may detect a secondary circuit continuity defect. For example, an open circuit in the secondary circuit (e.g. within the secondary coil  16 ) may result in an indirect signal  40 , absent a noticeable HF component  62  (not shown). 
     The apparatus  10  may also detect short circuit continuity defects in the event such defects were desired for detection. 
     With reference to  FIGS. 4A-4B , the controller  34  may detect defective wiring connections along the ignition circuit  22 . Such defective wiring connections may include, but are not limited to, improper connections to the switch  18  or improper connections to the ignition coil  13 . A defective wiring connection may also be present in the event that the controller  34  fires an ignition coil  13  that is coupled to a cylinder that is not currently under compression. Defective wiring connections may be detected by analyzing the amplitude, frequency and time delay of the HF component  62  on the indirect signal  40 . 
     The HF component  62  as shown in connection with  FIG. 4A  is generally indicative of a defective wiring connection. The HF component  62  as shown in connection with  FIG. 4B  is generally indicative of proper wiring connection. By comparing the high frequency components of  FIGS. 4A and 4B , it is observed that the HF component  62  on the indirect signal  40  has a larger amplitude and greater time delay than the HF burst on the indirect signal  40  of  FIG. 4A . In general, the controller  34  may determine the presence of a defective wiring connection by measuring the amplitude and the time delay of the HF component  62  on the indirect signal  40 . The controller  34  may determine that a defective wiring connection is present if the measured amplitude and time delay on the HF component  62  of the indirect signal  40  is less than a predetermined amplitude and/or a predetermined time delay. For example, with reference to  FIGS. 4A-4B , the threshold values for determining whether or not there is a defective wiring connection may be 10 Vpp and 0.7 s. It is generally recognized that the threshold values may vary based on the desired criteria of a particular implementation. 
       FIG. 5A  generally is disclosed to describe the manner in which the controller  34  is capable of determining whether the gap of the spark plug  24  is properly spaced. For example, assume that the HF component  62  generally corresponds to a HF component  62  that may be exhibited if the gap of the spark plug  24  is properly spaced. In one example, the HF component  62  as shown in  FIG. 5A  may correspond to a spark plug  24  that includes a gap spacing of 0.038 in. The controller  34  may measure various HF components for a number of spark plugs and compare such measurements to the amplitude and time delay of the HF component  62  as depicted in  FIG. 5A . Generally speaking, in the event the controller  34  determines that the HF component for a particular spark plug (e.g., under test) exhibits a smaller amplitude and a smaller time delay (e.g., see waveforms  76  and  78 ) than that exhibited by the HF component  62  in  FIG. 5A . Then the controller  34  may determine that the particular spark plug that is being tested includes a gap that is smaller than desired gap (e.g., smaller than 0.038 in.), or shorted altogether. Waveform  76  depicts the amplitude and time delay for a particular spark plug that exhibits the condition in which a corresponding gap of the spark plug is 0.018 in. which is less than the desired gap of 0.038 in. Waveform  78  depicts the amplitude and time delay for a particular spark plug that exhibits the condition in which the gap of a particular spark plug is shorted together. 
     Likewise, in the event the controller  34  determines that the HF component for a particular spark plug (under test) exhibits a greater amplitude and a greater time delay (e.g., see waveform  74  in  FIG. 5A ) than that exhibited by the HF component  62  in  FIG. 5A , then the controller  34  may determine that the particular spark plug being tested includes a gap that is greater than the desired gap. Waveform  74  of  FIG. 5A  depicts the amplitude and time delay for a particular spark plug that exhibits the condition in which a corresponding gap is greater than the desired gap spacing. 
       FIGS. 5B-5C  are provided to illustrate that the gap size for a spark plug can be ascertained as a function of the amplitude and time delay as measured on the indirect signal  40 . 
       FIG. 6  illustrates a method  100  for evaluating the performance of the integrated CoP assembly  12 . The controller  34  generally includes any number of microprocessors, ASICs, ICs, memory (e.g., FLASH, ROM, RAM, EPROM and/or EEPROM) which co-act with software code to perform the operations of the method  100 . 
     In operation  102 , the controller  34  receives the position signal  33  to determine the position of the crankshaft. 
     In operation  104 , the controller  34  analyzes the data on the position signal  33  to determine the timing for the integrated CoP assembly  12  in order to make sure the spark plug is fired, via the ignition coil  13 , when the corresponding cylinder is under compression. 
     In operation  106 , the controller  34  transmits the control signal  36  to the switch  18  to command the switch  18  to close for a fixed “dwell” period of time, followed by a command for the switch  18  to open. 
     In operation  108 , the controller  34  monitors the moment in which the control signal  36  is received at the switch  18  (e.g. to close the switch  18 ), which also serves as the trigger signal  38  for the DAQ. 
     In operation  110 , the controller  34  initiates the process of collecting data. For example, an input of the controller  34  is hardwired into the ignition circuit  22  (e.g., at point (A)) to receive the indirect signal  40 . 
     In operation  112 , the controller  34  conditions data on the indirect signal  40  into a desired format for analysis. 
     In operation  114 , the controller  34  compares the energy of the LF component  60  and the amplitude and the time delay that is present on the HF component  62  of the indirect signal  40  to predetermined data. For example, the controller  34  compares the energy of the LF component  60  to predetermined energy data. The controller  34  may compare the measured energy of the LF component  60  to the predetermined energy data to determine if the primary circuit has a continuity defect. The controller  34  also compares the amplitude and the time delay that is present on the HF component  62  of the indirect signal  40  to predetermined amplitude and time delay data to determine if the gap size for the spark plug  24  that is currently under test is correct. 
     In operation  116 , the controller  34  may determine a continuity defect if the measured energy, is smaller than the predetermined energy. Such a condition may correspond to a continuity defect along the primary circuit (e.g. open circuit in the primary coil  14  or open circuit in the switch  18 ). Additionally the controller  34  may determine a gap size fault if the measured amplitude and the measured time delay is greater or smaller than the predetermined amplitude and the predetermined time delay, respectively. Such a condition may correspond to the gap size of the spark plug  24  being greater than or smaller than (or even shorted together) than the desired gap size of the spark plug  24 . 
     In operation  118 , the controller  34  sets a fault if one or more conditions of operation  116  are met. 
     While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.