Abstract:
A system for testing an insulative material for a spark plug comprises a test spark plug having at least a center electrode and an insulator comprised of an insulative material surrounding at least a portion of the center electrode, wherein the insulator has an end that is closed, whereby the closed end of the insulator encloses an end of the center electrode. The system further includes a test engine that simulates engine conditions, wherein a conventional spark plug is installed in a first ignition port of the test engine and the test spark plug is installed in a second ignition portion of the test engine and a control system for controlling ignition signals to the test spark plug and the conventional spark plug.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 62/030,974, filed Jul. 30, 2014, the content of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to systems and methods for testing spark plug insulators and, more particularly, to systems and methods for testing breakdown voltage/dielectric strength of spark plug insulators. 
     2. Description of the Background 
     Because of the trend of engine downsizing, longer and thinner spark plugs are needed to work with newer engines. These next generation spark plugs require high dielectric strength insulators, which offer reduced dimensions but better or at least equivalent performance when compared to a traditional sparkplug. Typically, ASTM D-149 is used to measure the dielectric strength of insulative materials, which tests the breakdown voltage the insulative material can resist at a certain thickness with a set of parallel electrodes. However, because of the complex geometry of spark plug insulators, as well as the aggressive manufacturing process, there is not always a direct correlation between the performance of the insulator and ASTM D-149 measurements. 
     In the spark plug industry, there are two most commonly used methods for testing the breakdown voltage/dielectric strength of an insulator, as shown in  FIGS. 1, 2A, and 2B . In a first method, as shown in  FIG. 1 , a system is created with a spark plug assembly including a spark plug insulator  20  surrounding a spark plug center electrode  22 . A first end  24  of a first wire contact  26  is wound around an end  28  of the center electrode  22  and a second end  30  of the first wire contact  26  is connected to a high voltage source (not shown), for example, a high voltage system as sold by Hipotronics of Brewster, N.Y. A first end  32  of a second wire contact  34  is wound around an end  36  of the insulator  20  opposite the end  28  of the center electrode  22  and a second end  38  of the second wire contact  34  is connected to a ground contact  40 . The entire system is placed in dielectric fluid  42  during testing of a spark plug insulator  20 , as shown in  FIG. 2 . 
     In a second method, as seen in  FIGS. 2A and 2B , a system is created with a spark plug assembly including a spark plug insulator  50  surrounding a spark plug center electrode  52 . A tip  54  at a first end of the spark plug center electrode  52  is sealed with epoxy and a ground contact  56  is connected to a portion of a metal shell  57  surrounding the insulator  50  adjacent the tip  54 . A second end  58  of the center electrode  52  is connected to a high voltage source  59 , for example, a system as sold by Hipotronics of Brewester, N.Y. As with the first test method, the entire system of the second test method is placed in dielectric fluid  42  during testing of a spark plug insulator  50 . 
     The methods of  FIGS. 1, 2A, and 2B  both involve using dielectric fluid to prevent spark and flashover during testing. Unfortunately, the use of dielectric fluid has limited the temperature capabilities of the tests and imposes confounding effects on dielectric breakdown of the insulator. Furthermore, the design of the electrodes (wire, as seen in  FIG. 1 , and shell, as seen in  FIGS. 2A and 2B ) leads to a concentrated electric field in a localized area of the insulator, and hence, the results are not representative of the performance of the insulator as a whole. 
     Accordingly, there is a need for a system and method for testing insulative materials for use in spark plugs to more accurately determine breakdown voltage/dielectric strength. 
     SUMMARY 
     In illustrative embodiments, a system for testing an insulative material for a spark plug comprises a test spark plug having at least a center electrode and an insulator comprised of an insulative material surrounding at least a portion of the center electrode, wherein the insulator has an end that is closed, whereby the closed end of the insulator encloses an end of the center electrode. The system further includes a test engine that simulates engine conditions, wherein a conventional spark plug is installed in a first ignition port of the test engine and the test spark plug is installed in a second ignition portion of the test engine, and a control system for controlling ignition signals to the test spark plug and the conventional spark plug. 
     In other illustrative embodiments, a method of testing an insulative material for a spark plug may comprise the step of providing a test spark plug having at least a center electrode and an insulator comprised of an insulative material surrounding at least a portion of the center electrode, wherein the insulator has an end that is closed, whereby the closed end of the insulator encloses an end of the center electrode. The method may further comprise the steps of installing the test spark plug and a conventional spark plug in first and second ignition portions, respectively, of a test engine and controlling ignition signals to the test spark plug and the conventional spark plug. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features, and advantages of the disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a side elevational view depicting a set-up of a first system and method for testing breakdown voltage/dielectric strength of an insulator of a spark plug assembly; 
         FIG. 2A  is an isometric view of a set-up of a second system and method for testing breakdown voltage/dielectric strength of an insulator of a spark plug assembly; 
         FIG. 2B  is an enlarged view of a portion of the spark plug assembly of  FIG. 2A ; 
         FIG. 3A  is a side elevational view of a spark plug assembly for use with the systems and methods of the present disclosure and generally including a center electrode, an insulator, and a metal shell, wherein an end of the insulator is closed; 
         FIG. 3B  is a side elevational of the insulator of  FIG. 3A  having a closed end; 
         FIG. 4  is a phantom view of portions of the spark plug assembly of  FIG. 3A  depicting the closed end of the insulator; 
         FIG. 5  depicts an internal view of a combustion chamber of a cylinder head of a test engine for use in the systems and methods of testing breakdown voltage/dielectric strength of an insulator of a spark plug assembly as disclosed herein; 
         FIG. 6  depicts a correlation between output voltage of an ignition coil to a charging time; and 
         FIG. 7  is a perspective view of a diagram of the dielectric testing apparatus used to test dielectric strength of the insulating material. 
     
    
    
     The subject matter is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. 
     Other aspects and advantages of the present invention will become apparent upon consideration of the following detailed description, wherein similar structures have like or similar reference numerals. 
     DETAILED DESCRIPTION 
     The present application is directed to systems and methods for testing a breakdown voltage/dielectric strength of insulators for spark plugs. While the systems and methods of the present application may be embodied in many different forms, several specific embodiments are discussed herein with the understanding that the present application is to be considered only as an exemplification of the principles of the application, and it is not intended to limit the application to the embodiments illustrated. 
     In order to better evaluate the dielectric performance of spark plug insulators with new ceramic materials, a system and method for testing spark plug insulators involving a test engine and a specially designed insulator has been developed. The test system and method utilizes a test engine to generate a testing environment similar to that of a real world application within a production engine (i.e., temperature, combustion gas product, etc.). Also, because of the low ionization voltage of combustion gases (i.e., similar to air), the electric field concentration due to complex electrode geometry (i.e., spark plug shell) is also minimized to allow the evaluation of an entire tip of the insulator. 
     The test systems and methods disclosed herein include three components: (1) a spark plug assembly with a specially designed insulator for testing purposes, (2) a test engine with dual spark plugs, and/or (3) an electric/ignition control unit. 
       FIGS. 3A, 3B, and 4  depict a spark plug assembly  100  with a specially designed insulator  104  for use with the systems and methods of the present disclosure. The spark plug assembly  100  is similar to a traditional spark plug assembly in that it includes a center electrode or centerwire  102 , an insulator  104  surrounding the center electrode  102 , and a metal shell  106  at least partially surrounding the insulator  104 . The spark plug assembly  100  is different than traditional spark plug assemblies in that an end  108  of the insulator  104  is spaced from a tip  110  of the center electrode  102  and is closed. In an illustrative embodiment, the closed end  108  of the insulator  104  may be made of the same or a different material than a remainder of the insulator  104 . In an illustrative embodiment in which the closed end  108  is made of a different material than the remainder of the insulator  104 , the closed end  108  may be made of, for example, glass and/or potting materials. 
     The closed end  108  of the insulator  104  will confine the electric field between the center electrode  102  and the metal shell  106  so that arcing or flashing does not occur between the center electrode  102  and a ground electrode (not shown). This will ensure a location of puncture that signifies failure of the insulator  104  is through a side wall  112  of a nose  114  of the insulator  104  and hence, testing the actual performance of the insulator  104 . The thickness of the ceramic at the closed end  108  of the insulator  104  may be varied from about 0.02 inch to about 0.2 inch. If the ceramic at the closed end  108  is too thin, it runs into the risk of puncturing at the closed end  108  instead of through the side wall  112  of the nose  114 . If the ceramic at the closed end  108  is too thick, the closed end  108  of the insulator  104  may protrude into the engine too deep and interfere with the movement of the engine components (i.e., the piston and/or the intake/exhaust valves). The closed end  108  of the insulator  104  is pressure sealed with a resistor/contact glass and then is assembled with the metal shell  106  to form the spark plug assembly to form test samples for the systems and methods described herein. 
     It is noteworthy that, because of the added ceramic thickness at the closed end  108  of the insulator  104 , the insulator  104  will protrude further into the combustion chamber of the engine when installed. Accordingly, test spark plug assembly  100  disclosed herein is likely to experience higher temperature in comparison to spark plug assemblies having an insulator with an open end (and not extending beyond a tip for the center electrode) during similar engine conditions. This is likely to cause the test spark plug assemblies  100  with insulators  104  having closed ends  108  to fail at lower breakdown voltages. 
     As noted above, a second aspect of the systems and methods disclosed herein is the use of a test engine  150  with dual ignition spark plugs, as seen in  FIG. 5 , to test the test spark plug assembly  100 . Test engine  150  provides conditions that mimic the conditions in a production engine. Test engine  150  is used to control different ignition conditions, thereby simulating the engine environment during different driving conditions, which generates different combustion atmospheres, temperatures, cylinder pressures, etc. More specifically, a load is placed on the test engine to mimic different real world conditions. These load conditions impact the effects on the insulator material under electric stress and lead to dielectric breakdown at different levels. Therefore, using a test engine  150  in combination with the test spark plug assembly  100  allows for testing of the dielectric performance of the spark plug at different driving conditions with repeatable results. As seen in  FIG. 5 , the test engine  150  includes two spark plugs per cylinder to determine a more accurate breakdown voltage/dielectric strength of the insulator in the test spark plug assembly  100 . 
     The test systems and methods presented herein more accurately determine breakdown voltage/dielectric strength because of the use of dual spark plugs, with a first spark plug  200  located close to an exhaust valve  152  of the test engine  150  and the test spark plug  100  located close to an intake valve  154  of the test engine. During the test methods described herein, a standard or conventional spark plug  200 , which can be acquired off-the-shelf, may be installed in a first ignition port  156  while a test spark plug assembly  100 , including the insulator  104  with the closed end  108 , may be installed in a second ignition port  158 . In an alternative illustrative embodiment, the conventional spark plug  200  may be installed in the second ignition port  158  and the test spark plug assembly  100  may be installed within the first ignition port  156 . During testing, voltage is supplied to the spark plugs  200  and  100 , via ignition coils, in order to simulate normal usage (i.e., voltage that is used to cause the center electrode within a spark plugs to fire), as discussed in more detail below. As testing occurs in the present test set-up, only the conventional spark plug  200  will spark to ignite fuel, thereby generating a combustion environment similar to a desired driving condition (i.e., based on various factors). While subjecting the engine to real-time combustion conditions, the test spark plug assembly  100  (which has the insulator  104  having a closed end  108 ) is thereby subjected to a controlled ramp of ignition voltage until the insulator  104  is electrically punctured. The voltage at which the insulator  104  breaks down, as well as other characteristics of the test (including temperature, time, size of spark plug, etc) will then be recorded to represent the dielectric performance of the test spark plug assembly  100 , and more specifically the performance of the insulator material and make-up of the insulator  104 . 
     The third and last component of the test systems and methods disclosed herein is an electric/ignition control system. As illustrated in  FIG. 7 , separate ignition coils  300  and  302  are used for each spark plug, in part because different ignition voltages may be applied to the conventional spark plug  200  (e.g. ignition voltage) and the test spark plug assembly  100  (e.g. elevated test voltage). Main ignition coil  300  provides a consistent voltage to conventional spark plug  200  in order to provide the necessary spark to ignite the air/fuel mixture in the combustion chamber. Variable ignition coil  302  is used to provide variable voltage to the test spark plug assembly  100 . Variable ignition coil  302  is controlled by the controller  304  to apply an increasing voltage to the test spark plug assembly  100  until a voltage leak occurs in the insulator  104 . 
     More particularly, controller  304  receives an ignition signal from a firing spark plug (the conventional spark plug  200  that fires from operation of the main ignition coil  300 ) and uses the signal to control the variable ignition coil  302  to apply increasing voltage to the test spark plug  100  at a programmable ramping schedule. In illustrative embodiments, the ignition signal may be transmitted to the controller  304  via an electronic signal path  310 , and the controller  304  controls the ignition coils  300  and  302  via electrical signal paths  312  and  314 , as illustrated in  FIG. 7 . A delay of “firing” of an applied voltage to the test spark plug  100  may be controlled with a program so that a combustion front on the conventional spark plug  200  will be at or past that of the test spark plug  100 , to cause the test spark plug  100  simulate an actual firing condition similar to the conventional spark plug  200 . It has been discovered that, a delayed ignition/prolonged coil charge time can be used to control a level of the ignition voltage. 
     Controller  304  can be used to start test engine  150  and controls main ignition coil  300  to apply a voltage to conventional spark plug  200 . Alternatively, a separate control system can be used to control test engine  150  and operating conditions. Controller is programmed to run the test engine  150  to a desired temperature and RPM, controller  304  can also place a load on test engine  150  to simulate a motor vehicle towing a load or going up a grade. Once test engine  150  is at the desired RPM and temperature, the controller  304  initiates variable ignition coil  302  at a starting voltage in kilovolts (Kv). Since the operator typically has a sense for the voltage range that a test insulator would puncture, the controller  304  is programmed to initiate a starting voltage of a desired voltage such as 38 kilovolts, for example. Lower or higher starting voltages can also be used as desired. Voltage from variable ignition coil  302  is measured by a high voltage probe  320  that measures the voltage between center electrode  102  and metal shell  106  of test spark plug assembly  100 . High voltage probe  320  measures approximately 50 voltage spikes at a first voltage before the controller  304  increases the output voltage of the variable ignition coil  302  by a set incremental amount. For example, high voltage probe  320  measures 50 voltage spikes per second at 38 Kv before the controller  304  increases the voltage to 39 Kv. High voltage probe  320  then measures 50 voltage spikes per second at 39 Kv before the controller  304  increases the output voltage to 40 Kv. Controller  304  continues to increase the output voltage of variable ignition coil  302  until there is a drop in voltage read by the high voltage probe  320  due to a puncture of the insulator  104 . For example, high voltage probe  320  may have a voltage reading of 42 Kv followed by a drop in voltage down to 15-20 Kv indicating that a puncture in the insulator  104  has occurred. The user evaluates the data from the high voltage probe  320  recorded by the controller  304  and determines the highest voltage before the voltage drop. The highest voltages recorded before puncture provides an indicator as to the strength of the insulator  104 . 
     The graph of  FIG. 6  depicts a correlation between output voltage of the variable ignition coil  302  to a charging time. As the charging time increases, the ignition voltage increases. This arrangement allows the system to better control applied ignition voltage on the test spark plug assembly  100  with a repeatable and consistent ignition voltage, which allows for repeatable results in breakdown voltage/dielectric strength. Ignition voltage is affected by many variables, such as spark plug electrode gap distance, cylinder pressure, cylinder temperature, combustion byproducts, etc. and, hence, ignition voltage is very difficult to control. Determining the correlation between output voltage of ignition control and charging time allows one to control ignition voltage of a test spark plug and, hence, allows for testing of the test spark plug repeatedly until breakdown. Without this method, there may be no means to control ignition voltage at a targeted level. 
     A method of using the system described above includes the steps of preparing the test spark plug assembly  100 . In particular, the test spark plug assembly  100  may be assembled in any suitable manner, for example, by inserting the center electrode  102  into the insulator  104  with the closed end  108  and, thereafter, attaching the metal shell  106  to the center electrode  102 /insulator  104  combination. The closed end  108  of the insulator  104  may be shaped during formation of the insulator  104  and may be pressure sealed with a resistor/contact glass prior to or after being assembled with the center electrode  102 . Further, the insulator  104  may be pressure sealed with a resistor/contact glass prior to or after being assembled with the metal shell  106 . Other methods of preparing the test spark plug assembly  100  as herein described are envisioned. 
     Once the test spark plug assembly  100  is fully assembled, the conventional spark plug  200  and the test spark plug  100  are installed within the appropriate ignition ports, as detailed above. Thereafter, the test engine is turned on to run at a selected set of conditions (which can be programmed via the control box) from about 15 to about 30 minutes to reach a steady condition. An illustrative test engine set of conditions may be: 2500 rotations per minute (RPM) and 30% open throttle, and an estimated insulator tip temperature is about 530 degrees Celsius. The RPM may be varied from about 800 RPM to about 4000 RPM and the open throttle may be varied from about 20% to about 100% open throttle. 
     While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the disclosure is not limited to such disclosed embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.