Patent Publication Number: US-6215310-B1

Title: Glow plug circuit tester

Description:
GOVERNMENT USE 
     The invention described here may be made, used and licensed by the or for the U.S. Government for governmental purposes without paying me any royalty. 
    
    
     BACKGROUND 
     The US Army, like many other military organizations, is interested in lengthening the life of its vehicles and vehicle components. Doing so not only reduces the need to purchase new equipment but also reduces the logistical effort needed to sustain vehicles in the field or in forward combat areas. A case in point is the ignition system for the Army&#39;s High Mobility Multipurpose Wheeled Vehicle, or HMMWV. Recently, the Army developed a control circuit that increases the life of glow plugs in the HMMWV&#39;s diesel engine. Very basically, the circuit operates by imposing a duty cycle on the glow plugs. The cycle controls the level and duration of electrical power sent to the glow plugs to effect engine ignition and provides for controlled delays between applications of electrical power to the plugs. In order to test glow plug life through repetitions of the duty cycle, it was necessary to develop a test mechanism that emulated the environment of the glow plugs, that allowed sensors to be easily mounted on the test apparatus, and that provided a quick, simple way to immediately detect a plug&#39;s failure to glow at the appropriate point in the duty cycle. That testing mechanism was developed and is the subject of this patent application. 
     The mechanism is also useful for testing diesel ignition systems on fielded vehicles generally to determine whether the system is functioning properly. The mechanism is easily built from commonly available materials and requires very little in terms of instrumentation. Also, the source of electrical power and pressurized water needed by the mechanism can be provided by the battery and water pump of an automotive vehicle. Consequently, the mechanism can be used in the field, and particularly can be used under conditions typical of those behind the lines in a combat zone. 
     SUMMARY 
     The mechanism comprises an electrical power source and a source of fluid under pressure, the fluid normally being water. The mechanism includes glow plugs receiving power from the electrical power source and a control circuit connected to the electrical power source and the plugs. As mentioned above, the control circuit governs the duty cycle during which the plugs are heated by electricity and allowed cool. The mechanism includes an elongate jacket constructed of thin walls of material conductive of heat and electricity, the jacket having a fluid inlet port at one end and having a fluid outlet port at the other end. The jacket is provided with receptacles which accept the glow plugs, the receptacles being passages that extend all the way through the jacket and seal the plugs from the fluid. The receptacles conduct heat and electricity and provide a link in the electrical path by which the glow plugs are grounded. The tips of the plugs extend out of the receptacle and beyond the jacket and these tips glow when the plugs are energized, whereby the success or failure of the plug to function during energization is immediately apparent to a human viewer. The glowing tips show that there is no break in the electrical path from the power source to the control circuit, or through lines from this circuit to the plugs or in the plugs themselves. Thus, the entire circuit of which the glow plugs are part is visually tested for electrical continuity. The testing mechanism also includes means to control the rate of flow of the fluid through the jacket, and the flow control means can be governed as a function of the jacket&#39;s temperature by means of a flow control circuit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top elevational view of a jacket that is an element of the glow plug circuit tester. 
     FIG. 2 is a side elevational view of the jacket. 
     FIG. 3 is a partly sectioned detail view of a receptacle that is a feature of the jacket. 
     FIG. 4 is the top elevational view of an alternate embodiment of the jacket shown in FIGS. 1 and 2. 
     FIG. 5 is a semi-schematic representation of the glow plug circuit testing mechanism of which the jacket is part. 
    
    
     DETAILED DESCRIPTION 
     Shown in FIGS. 1 and 2 is a simplified jacket  2  having a plurality of partly threaded receptacles  4  passing therethrough, there being a sectioned detail view of a receptacle shown in FIG.  3 . Jacket  2  is hollow and elongate, and preferably has a square or rectangular cross-section. Sides  6  and  8  of jacket  2  are thin metal walls normally fabricated from aluminum sheet or tube stock, but these walls can be fabricated from steel or other metals. Likewise, ends  10  and  12  of the jacket are thin walls made from aluminum or steel, the aforementioned sides and ends forming a sealed rectangular chamber. On end  10  is a fluid inlet nipple  14  and on end  12  is a fluid outlet nipple  16 . It is contemplated that hoses will be suitably attached to the nipple so that water, air or other fluid will be introduced and exhausted from the jacket. Also attached to the ends of jacket  2  are brackets  18  by which the jacket can be affixed to a test stand or other suitable structure. A final pair of elements on the exterior of jacket  2  is mount elements  20  and  22 , which typically serve as attachment points for temperature sensors or ground wires or like elements. 
     Receptacle  4  is a sealed circular passage extending all the way through jacket  2 . As best seen in FIG. 3, the receptacle may include a well  24  at side  6 . From this well leads a narrower, duct-like segment  26  that has an opening at side  28  on the opposite side of jacket  2  from side  6 . Intermediate the ends of segment  26  is an internally threaded section  29  that mates with complementary on the body of conventional glow plug  30 , which screws into receptacle  4 . Glow plug  30  has a connector post  32 , a plug body  34 , an insulator  36  separating post  32  from body  34 , and a glow tip  38  that receives power from post  32 . Tip  38  extends beyond side  28  and is exposed to the view of a person observing jacket  2 . Plug  30  is grounded in that electricity flows from body  34  to receptacle  4  into jacket  2 , which itself is grounded in conventional manner. 
     FIG. 4 shows a second embodiment  40  of jacket  2 . Jacket  40  includes the same receptacles  4  and plugs  30  as jacket  2 , except that the receptacles and plugs in jacket  40  have a different juxtaposition relative to the body of the jacket. In FIG. 4, one set of four receptacles and plugs is oriented perpendicularly to a second set of receptacles and plugs. Within each set, the receptacles and plugs are in a staggered relation, not in a straight line. The perpendicularity of the sets and the staggering within sets is believed to increase the receptacles&#39; exposure to fluid flowing through jacket  40  and to thereby increase its cooling efficiency. 
     FIG. 5 shows an overall system  42  in which jacket  2  is incorporated. There, electrical power is provided from a source  44 , which can be an automotive vehicle battery. Power from source  44  passes to plugs in jacket  2  over lines  46   a  through  46   h,  and the cyclic timing and intensity of power pulses to the plugs is governed by a control circuit  48 . As noted earlier, plugs  30  are grounded through jacket  2 , which itself is grounded by a suitable means  50 , which can be a vehicle body or a test stand. 
     Typically for each glow plug, full electrical power is sent to the plug for 6 to 15 seconds, whereupon the plug tip heats to a specified temperature of, say, 1900° F. Thereafter, a partial current is sent to the plug so that it maintains the specified temperature for a predetermined time, which we refer to as the afterglow. Afterglow normally occurs for approximately one minute and then, for another predetermined amount of time, no current is allowed to flow to the plug. The second predetermined time is typically in the neighborhood of two minutes. After the second predetermined amount of time, the cycle can begin again with the 6 to 15 seconds of full power the plug. The particulars of the cycle are described in a prior patent application entitled, “Improved Diesel Engine Starting Controller and Method,” Ser. No. 09/030,519 filed Feb. 23, 1998 and having Attorney Docket No. TA-2989. 
     Tips  38  of plugs  30  glow visibly after being subjected to full electrical power for 6 to 15 seconds and during the afterglow portion of the cycle. This allows the personnel conducting the test to determine whether the plug, the appropriate one of lines  46   a  through  46   h,  control circuit  48  and power source  44  are all operating. Experience has shown that the power source and the plugs are much less likely to fail than the control circuit or the lines on any given occasion when a plug does not glow when it should. Consequently, the test apparatus can be regarded as a mechanism to test the control circuit and the lines. It is contemplated that those ordinarily skilled in the relevant arts could appropriately select from among standard electrical power sources, electrical grounding devices, valves, pumps, reservoirs, cooling mechanisms, valve control circuits, glow plug control circuits and temperature sensors in making an operational replication of applicants&#39; system shown in FIG.  5 . 
     Referring again to FIG. 5, jacket  2  receives fluid through inlet conduit  52 , the fluid normally being ordinary tap water or water from the cooling system of a vehicle engine, although air or another gas can be used. Fluid exits jacket  2  via exit conduit  54 . The rate of flow of the fluid through jacket  2  is controlled so that that plugs  30  are cooled at the same rate as if they were in an engine, where the engine temperature in the vicinity of the plugs is typically approximately 180° F. We have found that ordinary tap water having a temperature between 50° F. and 60° F. flowing through the jacket at a rate of at least 0.5 gallons/min creates a sufficient cooling effect. A temperature sensor  56  can be used to monitor the jacket&#39;s temperature, and the sensor can input to a valve control mechanism  58  governing valve  60 . Valve  60  allows more fluid to flow into jacket  2  if the jacket&#39;s temperature exceeds a given limit and restricts flow more greatly if the jacket&#39;s temperature falls below a given threshold. 
     Fluid flowing from jacket  2  in line  54  will enter a cooling mechanism  62 , which can be a vehicle radiator. From mechanism  62 , the fluid is transported via conduit  64  to a reservoir  66 . Pump  68 , which can be a vehicle water pump, takes fluid from reservoir  66  and provides the pressure in line  52  to initiate fluid flow through jacket  2 . An alternative to having cooling mechanism  62  and reservoir  66  is simply to have a source of pressurized water flow into conduit  52  from a faucet and let the water drain from jacket  2  through conduit  54 . It will be noted that the system shown in FIG. 5 can be part of a dressed diesel engine assembly, where power source  44  is the vehicle battery, circuit  48  is the vehicle glow plug control circuit, mechanism  62  is the vehicle radiator, and pump  68  is the vehicle&#39;s water pump. 
     We wish it to be understood that we do not desire to be limited to the exact details of construction or method shown herein since obvious modifications will occur to those skilled in the relevant arts without departing from the spirit and scope of the following claims.