Method and apparatus for determining relative contributions of
Contents
1. OTHER PUBLICATIONS Snap on Tools Corporation manual for MT3000 En gine Analyzer No date Snap on Tools Corporation manual for MT3000 420 Power Balance Probe No date Primary Examiner Kevin J Teska Assistant Examiner Collin W Park Attorney Agent or Firm Emrich amp Dithmar 57 ABSTRACT A linearly moving external part of a multi cylinder internal combustion engine is contacted with a hand held contact tachometer for producing a waveform signal which along with a signal responsive to the igni tion of each cylinder are applied to an engine analyzer processor for display of a single engine cycle of the waveform signal on the CRT oscilloscope of the engine analyzer The variations and amplitude of the wave form signal correspond to speed variations of the mov ing part over an engine cycle to give an indication of the relative power contributions of the individual cylinders Cylinder ignition markers and cylinder zone markers are respectively displayed at the top and bottom of the screen respectively corresponding to the cylinders in their ignition order Each cylinder zone marker is de layed a predetermined time from its corresponding cylinder ignition marker and indicates the time period during which the engine responds to the ignition event of the corresponding cylinder 12 Claims 3 Drawing Sheets U S Patent Mar 7 1995 Sheet 1 of 3 5 396 427 VACUUM WAVEFORM 10 AVG VACUUM 0 0 ing Z UGN Fi2. processed by the microprocessor 31 which in turn actu ates the video drive circuit 32 to cause the CRT 33 to 5 10 30 35 40 45 50 55 60 65 4 display a generally sinusoidal waveform which is indic ative of the fluctuations in speed of the engine 20 as will be explained more fully below Referring in particular to FIG 2 the engine analyzer 30 has a set of six soft keys F1 through F6 arrayed along the bottom edge of the CRT screen 33 the func tions of which are software controlled and vary with the mode of operation of the engine analyzer 30 in a known manner More specifically the software for controlling the operation of the engine analyzer 30 causes an indication of each soft key function to be displayed on the screen immediately adjacent to the key The engine analyzer 30 also has a main keyboard 41 which includes a numerical keypad 42 including ten keys for digits O through 9 respectively four direction keys 43 for the directions up down right and left four function keys 44 six menu keys 45 a reset key 46 and a HELP key 47 The functions of these various keys in controlling the operation of the engine analyzer 30 are described in greater detail in the aforementioned co pending U S application Ser No 587 357 to produce a number of different types of screen displays including that illustrated in FIG 3 The present invention func tions similarly to that disclosed in co pending applic
3. 10 CYL 4 m HORIZONTAL CURSOR ADJUST WAVEFORM POSITION ADJUST CYLINDER SELECT 210 CYL 18 5 396 427 1 METHOD AND APPARATUS FOR DETERMINING RELATIVE CONTRIBUTIONS OF INDIVIDUAL CYLINDERS OF INTERNAL COMBUSTION ENGINE BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates to analysis of the rela tive power contributions of individual cylinders of an internal combustion engine and in particular relates to techniques for determining such power contributions from variations in the engine speed 2 Description of the Prior Art The present invention is an improvement of the in vention disclosed in copending U S application Ser No 604 191 filed Oct 20 1990 now U S Pat No 5 182 512 That application discloses a technique for determining cylinder power balance in an internal com bustion engine That technique involves utilizing a contact tachometer to detect the speed variations of an accessible external moving part of an engine such as a fan belt or the like the tachometer outputting a signal to an associated engine analyzer which may be of the type sold by Snap on Tools Corporation under the designa tion MT3000 and disclosed in copending U S applica tion Ser No 587 357 filed Sep 24 1990 now U S Pat No 5 250 935 Such an engine analyzer includes a num ber of probes adapted for connection to an associated engine which can detect among other things the i
4. Size Select function actuated by soft key F3 the 25 40 45 50 60 65 6 changes in engine speed and therefore the overall am plitude of the waveform 80 will be less for an engine with more cylinders This is because the time interval between cylinder firings is smaller leaving less time for the engine to slow down between engine firings It is a significant aspect of the present invention that the points on the waveform 80 corresponding to cylin der ignitions are relatively easy to identify because of the cylinder zone indicia 75 More specifically the first low point in the waveform 80 within a given cylinder zone corresponds to the ignition of that cylinder Thus for example if the operator starts at the left end of the line 77 which is the beginning of the cylinder 1 zone and progresses along that zone the first low point in the waveform 80 is at 82 and therefore this corresponds to the ignition of cylinder No 1 and marks the beginning of its power stroke While the ignition points of the cylinders along the waveform 80 are not too difficult to identify in a nor mal operating engine this is usually not the case for an abnormally operating engine The waveform 90 for such an abnormally operating engine is illustrated in FIG 6 and as can be seen is much more irregular than the waveform 80 In order to identify the cylinder igni tions the operator looks for valleys of the waveform within each of the cy
5. be seen fluctuates in a generally sinusoidal manner The reason that the waveform 80 and accordingly the speed of the moving engine part being monitored fluctuate is the intermittent nature of the power source i e the discrete ignition events of individual cylinders spaced apart in time This results in a cyclical acceleration and deceleration of the engine crankshaft 24 Each time a cylinder ignition event oc curs the engine 20 first accelerates and then decelerates until the ignition event for the next cylinder The waveform 80 represents a four cylinder engine 20 which is operating normally The ignition of the No 1 cylinder occurs at 81 as indicated by the correspond ing ignition event marker 70 This ignition event is re flected in the movement of the engine at 82 in the wave form 80 which marks the initiation of the power stroke for the No 1 cylinder The engine responds by acceler ating during the power stroke as at 83 to a peak speed and then begins to slow down or coast as at 84 until the ignition for the next cylinder in the firing order which is the No 3 cylinder As can be seen the amplitudes of the peaks of the waveform 80 are generally the same indicating that each of the cylinders is contributing approximately the same power to the overall engine output which is the desired performance It will be appreciated that if the amplitudes of the waveforms are at the same setting as determined by the Waveform
6. detecting speed variations of an accessible external moving part of the engine 3 The apparatus of claim 2 wherein said speed sens ing means includes means for detecting linear speed of the moving part 4 The apparatus of claim 3 wherein said speed sens ing means includes a contact tachometer 5 The apparatus of claim 1 wherein said processing means includes means for causing said display means to display cylinder zone markers comprising a plurality of substantially equidistantly spaced apart indicators re spectively positioned at the beginnings of the cylinder 5 396 427 9 zones and corresponding cylinder numbers displayed respectively substantially in the middles of the cylinder zones 6 The apparatus of claim 5 wherein said display means includes a CRT screen said processing means including said means for causing zone markers to be displayed adjacent to the bottom of the screen 7 The apparatus of claim 5 wherein said processing means includes means for causing ignition event mark ers to be displayed at locations respectively correspond ing to the times of the ignition events of the cylinders 8 The apparatus of claim 7 wherein said ignition event markers include cylinder numbers displayed in the ignition order 9 The apparatus of claim 7 wherein said processing means includes means causing said cylinder zone mark ers to be respectively offset in time from the corre sponding cylinder ignition event markers b
7. United States Patent i5 Piehl et al 54 75 73 21 22 51 52 58 56 METHOD AND APPARATUS FOR DETERMINING RELATIVE CONTRIBUTIONS OF INDIVIDUAL CYLINDERS OF INTERNAL COMBUSTION ENGINE Inventors James R Piehl Robert D Braun Gary S Wollert all of Kenosha Wis Craig F Govekar Gurnee Ill Assignee Snap on Incorporated Kenosha Wis Appl No 848 274 Filed Mar 9 1992 FO RENE G01M 15 00 U S Cl Lu 364 431 04 364 431 07 364 551 01 364 565 73 116 73 518 73 529 324 161 324 163 324 379 Field of Search 364 431 03 431 04 364 431 07 551 01 565 73 116 488 489 518 527 529 117 2 117 3 324 378 379 160 163 178 161 References Cited U S PATENT DOCUMENTS 4 301 678 11 1981 Full et al 73 116 4 348 893 9 1982 Hendrix et al 73 116 4 525 781 6 1985 Konomi et al 364 431 01 4 539 841 9 1985 Schroeder et al 73 116 4 562 728 1 1986 Timmerman 73 116 4 625 546 12 1986 Sugo et al 73 116 4 800 378 1 1989 Putrow et al wes 340 722 4 843 870 7 1989 Citron et al nn 73 116 5 056 360 10 1991 Dosdall et al 73 116 5 182 512 1 1993 Braun et al 324 378 X US005396427A 11 Patent Number 5 396 427 45 Date of Patent Mar 7 1995 5 250 935 10 1993 Jonker et al 364 431 04 X
8. a tion Ser No 587 357 with the following exceptions which now will be explained in connection with FIGS 4 6 After the engine analyzer bas been coupled to an idling engine in the manner illustrated in FIG 1 the operator by actuating the appropriate one of the menu keys 45 calls up the Cylinder Test Menu illustrated in FIG 4 This display includes a title at 51 and an instruc tional message at 52 This particular menu includes six options selected by soft keys F1 F6 which are respec tively labeled at 53a 53f as Cranking Amps Bar Graph Cylinder Shorting Bar Graph Cylinder Time Balance Bar Graph Vacuum Waveform Power Balance Waveform and Return to Start The Power Balance Waveform option selected by key F5 is the only one which is pertinent to the present invention When it is actuated it calls up the Power Balance Waveform screen display 60 illustrated in FIG 5 The Power Balance Waveform screen display 60 includes a title at 61 and an engine RPM display at 62 It also includes date and time displays at 63 and 64 respectively The main portion of the display is a graph 65 which essentially plots engine speed along the verti cal axis against time along the horizontal axis The soft keys F1 F4 are respectively labeled at 66a 66d as Grid On Off Cursors On Off Waveform Size Select and Vertical Position The soft keys F1 and F2 both toggle between ON and OFF conditions with th
9. cated at 113 The screen display 60 at FIG 5 is provided with a pair of vertical cursors and a pair of horizontal cursors not shown with one cursor of each pair being active at a time the active ones being selectable by toggling the SELECT key which is one of the function keys 44 this function being indicated at 114 If one of the menu keys 45 is pressed the program will move to 115 and call up the corresponding menu screen If the FREEZE key which is one of the func tion keys 44 is pressed the program will move to 116 and toggle i e either enter or exit the FREEZE mode If the engine to which the engine analyzer 30 is con nected has more than ten cylinders as indicated by the engine identification information entered by the user during setup the F5 and F6 soft keys will respectively have labels Select Cylinder and Short Cylinder displayed on the Power Balance Waveform screen 60 In this case if the F5 soft key is pressed its label will be highlighted and the directional keys 43 will be operative to select a cylinder The number of the selected cylin ders in the ignition event markers 70 will be high lighted Thus a higher or lower numbered cylinder can be selected by using the up or down arrows as at 117 or by using the right and left arrows as at 118 Any cylinder up to ten can also be selected by using the numerical keypad 42 as indicated at 119 Once a cylin der has been selected the program will default to s
10. e signed for the purpose of displaying instantaneous en gine speed information Accordingly that screen dis plays a number of features and functions relating to vacuum waveforms which the operator has to disregard in viewing a power balance waveform In particular the vacuum event markers 13 introduce considerable confusion since they are out of phase with the ignition event markers 12 by one half an engine cycle Accord ingly it is very difficult for an operator to determine the portion of the power balance waveform 11 which cor responded to the response of the engine to any particu 10 15 25 30 35 40 45 60 65 2 lar cylinder ignition event and careful attention to the user s manual for the contact tachometer is absolutely required in order to understand its use in connection with the Vacuum Waveform display screen SUMMARY OF THE INVENTION It is a general object of the present invention to pro vide an improved method and apparatus for determin ing cylinder power balance in an internal combustion engine which avoids the disadvantages of prior tech niques while affording additional structural and operat ing advantages An important feature of the invention is the provision of a method of determining cylinder power balance from engine speed variations during a single engine cycle which is relatively simple and easy to perform In connection with the foregoing feature another feature of the i
11. e selected condition being highlighted in the corre sponding label display 66a or 66b When the grid is ON vertical and horizontal grid lines 67 appear on the graph 65 to facilitate reading the graph The screen 60 also includes ignition event markers 70 which comprise highlightable numbers at equidistantly spaced apart points along the top of the graph 65 re spectively corresponding to the engine cylinders in their firing order For purposes of illustration the dis play for a four cylinder engine is illustrated in FIG 5 The ignition event markers 70 respectively appear at the times along the graph 65 at which the ignition events for the corresponding cylinders occur i e when the ignition pulse is applied to the cylinder In horizon 5 396 427 5 tal alignment with the ignition event markers 70 at the right end of the graph 65 is the highlighted designation IGN indicated at 71 which designates the function of the ignition event markers 70 It is a significant aspect of the invention that the screen 60 also includes cylinder zone indicia 75 along the bottom of the graph 65 These indicia comprise a plurality of equidistantly spaced apart markers 76 in the form of short vertical lines respectively marking the beginnings of each of the cylinder zones these markers 76 being interconnected by a horizontal line 77 The numbers of the cylinders in their firing order are indi cated at 78 respectively in the centers of the cy
12. elec 5 10 15 20 25 35 45 55 60 65 8 tion of the No 1 cylinder upon actuation of the F5 soft key subsequent actuation of the F6 soft key will cause the selected cylinder to be shorted at 120 If the engine does not have more than ten cylinders then the direction keys 43 have other functions con trolled by the F2 and F4 soft keys If the cursors are toggled ON by the F2 soft key then the program will move the horizontal cursor at 121 in response to actua tion of the up and down arrow keys and will move the vertical cursor at 122 in response to actuation of the left and right arrow keys If the F4 soft key is actuated the program will adjust the vertical position of the wave form at 123 in response to the actuation of the up and down arrow keys In this regard it will be appreciated that the F2 and F4 soft keys are mutually exclusive i e only one can be active at a time Thus for example if the F4 soft key label is illuminated and the F2 key is depressed to toggle the cursors ON the F2 soft key label will be illuminated and that for the F4 soft key will be extinguished so that the up down arrow key can have only one function at a time If any other key is pressed the program recognizes it at 124 as an invalid key and gives a suitable indication From the foregoing it can be seen that there has been provided an improved apparatus and method for deter mining the relative power contributions of ind
13. event of the cylinder corresponding to that zone marker The invention consists of certain novel features and a combination of parts hereinafter fully described illus trated in the accompanying drawings and particularly pointed out in the appended claims it being understood that various changes in the details may be made without departing from the spirit or sacrificing any of the ad vantages of the present invention BRIEF DESCRIPTION OF THE DRAWINGS For the purpose of facilitating an understanding of the invention there is illustrated in the accompanying drawings a preferred embodiment thereof from an in spection of which when considered in connection with the following description the invention its construc tion and operation and many of its advantages should be readily understood and appreciated FIG 1 is a block diagrammatic illustration of the apparatus of the present invention coupled to an inter nal combustion engine shown in front perspective view with portions broken away for clarity of illustration 5 396 427 3 FIG 2 is a front elevational view of the engine analy zer of the present invention which is diagrammatically illustrated in FIG 1 FIG 3 is an elevational view of a screen display of a prior art engine analyzer FIG 4 is a elevational view of the screen display of the engine analyzer of FIG 2 FIG 5 is an elevational view of another screen dis play of the engine analyzer of FIG 2 illus
14. g 3 PRIOR ART 3 H fi i i i i MB o ad GRID CURSORS vacuum VERTICAL Ac DC NEXT Em s t o n t U S Patent Mar 7 1995 Sheet 2 of 3 5 396 427 CYLINDER TEST MENU TO PROCEED PRESS A FUNCTION KEY BELOW OR CHOOSE ANOTHER MENU FROM THE KEYBOARD 53b 53c 53d 53e CRANKING CYLINDER CYLINDER VACUUM POWER RETURN AMPS SHORTING TIME BALANCE WAVEFORM BALANCE TO BAR GRAPH BAR GRAPH BAR GRAPH WAVEFORM START ON P je Y MMDDY POWER BALANCE WAVEFORM DAY MWDDY POWER BALANCE WAVEFORM 59 AM RPM 719 U S Patent Fig 7 POWER BALANCE Mar 7 1995 Sheet 3 of 3 5 396 427 KEYBOARD WAVEFORM CHECK 102 INITIALIZATION F1G 8 105 MEMORY OR CHECK PROBE FREEZE ID FOR PWR CHECK BAL CONNECTION 106 RPM UPDATE 104 Oe eee SG T ER A E PRIMARY OR DISIRIBU TORTES RPM UPDATE SECONDARY IGNITION WITH ENGINE SYNC CHARACTERIZATION ENGINE SYNC 1 SYNC SELECTION ROUTINE m LUO 103 112 Fi F2 F3 FA Mrk GRID CURSORS WAVEFORM VERTICAL ED ON OFF ON OFF SIZE SELECT POSITION 114 co 60 TOCYE TEST SELECT UP DOWN SELECT MENU HIDDEN T RSOR ARROW CYLINDER gt 10 NEXT PAGE OGGLE CU ROWS 120 SHORT CYLINDER 710 CYL VERTICAL CURSOR ADJUST GO TO CYLINDER TEST MENU 115 KEYS 0 9 FREEZE KEY To CD en SHORT MENU KEYS ENTER EXIT ARROWS GS 119 16 124 122 E CYLINDER SELECT
15. gni tion events spark plug firings in the case of gasoline engines or combustion signals fuel pulses in the case of diesel engines of each cylinder The microprocessor of the engine analyzer utilizes the output of the contact tachometer to generate a waveform signal indicative of engine speed variations and displays a single engine cycle of that waveform signal so that speed variations from one cylinder cycle to the next can be analyzed In this regard an engine cycle is the time period between consecutive ignition events of the same cylinder and a cylinder cycle is the time period from the ignition event of one cylinder to the ignition event of the next cylinder in the ignition firing order However that prior system operates to display the waveform signal on a Vacuum Waveform display screen of the engine analyzer which screen in addition to the waveform displays at the top of the screen indi cations of the cylinder ignition events in the ignition order and at the bottom of the screen indicates cylin der vacuum events in the vacuum order Such a screen designated by the numeral 10 is illustrated for example in FIG 3 wherein the waveform signal is indicated at 11 the ignition event markers are indicated at 12 and the vacuum event markers are indicated at 13 The Vacuum Waveform screen is utilized for the wave form display since it is the only suitable display screen available with that engine analyzer but it is not d
16. hereby the in formation to be displayed is passed to the display board in the engine analyzer 30 for driving the CRT screen 33 In this routine the program also checks the probe ID to see that the contact tachometer 38 is properly con nected Referring to FIG 8 the RPM update routine 104 is entered at 106 and proceeds to 107 to determine if the engine to which the engine analyzer 30 is connected is a distributorless ignition engine in which case different probe inputs will have to be read as is explained in greater detail in the co pending aforementioned appli cation Ser No 587 357 The program also does an RPM update utilizing the Engine Sync signal at 108 or the 1 sync signal at 109 depending upon whether a primary or secondary sync signal is being used as se lected by the routine at 110 Referring to FIG 9 the keyboard check routine 103 is described in greater detail This routine is entered at 111 and proceeds to scan the soft key set 40 in the main keyboard 41 to determine which if any keys have been actuated If none have been actuated the program sim ply proceeds to 112 and will continue in the main loop of the program as is described more fully in the copend ing application Ser No 587 357 Although the F6 soft key has no label on the Power Balance Waveform screen 60 illustrated in FIG 5 it has a hidden or non displayed function which will return the screen to the Cylinder Test Menu display 50 of FIG 4 as indi
17. herein the detecting step includes detecting linear speed of the moving part
18. ividual cylinders of a multi cylinder internal combustion engine which is much easier to use than prior techniques We claim 1 Apparatus for determining relative power contri butions of individual cylinders of a multi cylinder inter nal combustion engine wherein an engine cycle is a time period between consecutive ignition events of the same cylinder said apparatus comprising a speed sensing means for detecting speed variations of the engine during an engine cycle and generat ing an electrical output signal indicative thereof b ignition sensing means for detecting the ignition events of each cylinder c processing means coupled to said speed sensing means and to said ignition sensing means and re sponsive to said output signal for generating a waveform signal representative of the speed varia tions of the engine over time and d display means coupled to said processing means for displaying a single engine cycle of the wave form signal from which said relative power contri butions are determined said processing means including means for causing said display means to display cylinder zone mark ers equal in number to and respectively corre sponding to the cylinders in their ignition order each zone marker indicating a time period during which the engine responds to the ignition event of the cylinder corresponding to that zone marker 2 The apparatus of claim 1 wherein said speed sens ing means includes means for
19. linder zones ie substantially midway between adjacent markers 76 At the right hand end of the horizontal line 77 appears the highlighted designation CYL indi cated at 79 to designate the function of the cylinder zone indicia 75 Each cylinder zone on the graph 65 represents the time period during which the engine will respond to the ignition event for that cylinder Thus for example cylinder zone 1 is the time period during which the engine is responding to the ignition of cylinder 1 and that zone ends with the ignition of cylinder 3 which is next in the firing order whereupon the engine will respond to the cylinder 3 ignition It will be noted that the start of each cylinder zone as indicated by the cylin der zone indicia 75 is delayed or offset a slight distance in time from the ignition event for that cylinder as indicated by the ignition event markers 70 This is be cause there is a certain time delay from the time the ignition pulse is applied to a cylinder until ignition oc curs and the engine actually starts to respond by the corresponding piston starting its power stroke This offset is predetermined based on the particular type of engine being analyzed and will typically correspond to at least a 20 rotation of the engine crankshaft 24 The output of the contact tachometer 38 is displayed as a waveform 80 on the graph 65 More specifically one complete engine cycle of the waveform 80 is dis played and as can
20. linder zones Thus the valley at 91 marks the ignition of the No 1 cylinder The engine responds by accelerating and decelerating until the ignition of the No 3 cylinder at 92 The next valley occurs at 93 in the cylinder No 4 zone and marks the ignition of that cylinder It will be noted that this igni tion occurs somewhat later then the earlier ignitions and the engine responds by accelerating very little to a peak 94 then starts to decelerate to the ignition of the No 2 cylinder at 95 After the firing of the No 4 cylinder it accelerates further to 96 in response to the firing of the No 2 cylinder This waveform 90 indicates that the No 4 cylinder is malfunctioning and that that cylinder is not contribut ing the proper amount of power to the engine This power drop could result not only from a misfiring but also from mechanical or fuel system problems What ever the source the faulty cylinder can be identified It can be seen that there is a leveling off of the waveform 90 at 94a and in the prior art engine analyzer an opera tor might mistake this for the ignition event of a No 2 cylinder and conclude that there were problems with both the Nos 4 and 2 cylinders However with the present invention it is clear that this is not an ignition event for the No 2 cylinder since it does not occur in the No 2 cylinder zone As can be readily appreciated the advantages af forded by the cylinder zone indicia 75 of the present i
21. nvention are even more significant the greater the number of cylinders in the engine since the peaks and valleys of the waveform will be even closer together As can be seen from the waveform 90 although there is a problem in only one cylinder this affects the shape of the waveform in other cylinder zones It will be appre ciated that if more than one cylinder is faulty the wave form can become extremely erratic In such a case the proper analysis of the waveform can be extremely diffi cult with prior engine analyzers and therefore in such cases the present invention is even more advantageous to the operator Referring now to FIGS 7 9 the operation of the program 100 for the microprocessor 31 in response to selection of the Power Balance Waveform mode 5 396 427 7 from the Cylinder Test Menu of FIG 4 will be de scribed When the function key F5 is actuated the pro gram enters the Power Balance Waveform mode at 101 FIG 7 and first goes through an initialization se quence at 102 and then performs a memory or freeze check to determine if the screen is to display a live waveform which is the default condition or if this is to be a display of a previously frozen screen or if the waveform to be displayed is one previously saved in long term memory The program also performs a key board check at 103 an engine RPM update at 104 to ascertain and display the current engine RPM and a serial communications routine at 105 w
22. nvention is the provision of the method of the type set forth which utilizes a digital engine ana lyzer and affords a simple and easily understood display of the power balance information Another feature of the invention is the provision of an apparatus for performing the method of the type set forth These and other features of the invention are attained by providing apparatus for determining the relative power contributions of individual cylinders of a multi cylinder internal combustion engine wherein an engine cycle is the time between consecutive ignition events of the same cylinder the apparatus comprising speed sensing means for detecting speed variations of the engine during an engine cycle and generating an electri cal output signal indicative thereof ignition sensing means for detecting the ignition events of each cylinder processing means coupled to the speed sensing means and to the ignition sensing means and responsive to the output signal for generating a waveform signal repre sentative of the speed variations of the engine over time and display means coupled to the processing means for displaying a single engine cycle of the waveform signal the processing means including means causing the dis play means to display cylinder zone markers equal in number to and respectively corresponding to the cylin ders in their ignition order each zone marker indicating the time period during which the engine responds to the ignition
23. trating a normal power balance waveform FIG 6 is a view similar to FIG 5 illustrating an abnormal power balance waveform and FIGS 7 9 are flow charts of the computer program for the microprocessor of the engine analyzer of FIG 1 DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG 1 there is illustrated a multi cylin der internal combustion engine generally designated by the numeral 20 of a type with which the present inven tion is useful The engine 20 is shown as a V 6 gasoline engine but it will be appreciated that the present inven tion may be used with any other configuration of multi cylinder internal combustion engine The engine 20 has a distributor 21 which is coupled by wires 22 to spark plugs 23 respectively positioned for igniting the fuel mixture in each of the several cylinders in standard fashion The engine has an output crankshaft 24 A fan belt 25 is coupled to a pulley 26 at the front end of the crank shaft 24 for driving a cooling fan or other associ ated equipment Similarly a generator belt 27 is coupled to the pulley 26 for driving a generator or alternator 28 The crankshaft 24 is also coupled to a flywheel or ring gear 29 for coupling to an associated transmission not shown in a known manner The present invention includes an engine analyzer 30 which may be of the type sold by Snap on Tools Corpo ration under its designation MT 3000 and includes a microprocessor 31 coupled to a video dri
24. ve circuit 32 which is in turn connected to a CRT oscilloscope 33 The engine analyzer 30 may include a plurality of input leads one of which is a conductor 36 coupled to a pickup 37 which may be an inductive or capacitive pickup and is adapted to be coupled to the wire 22 for the No 1 spark plug 23 i e the spark plug for the cylinder which has been designated by the manufac turer as the first cylinder in the firing order In the case of a diesel engine a piezoelectric pickup to sense fuel pulses or known pickups for sensing combustion may be used in a similar manner Engine speed is detected by a contact tachometer 38 which may be of the type disclosed in the aforemen tioned copending application Ser No 604 191 and the output of which is connected by a cable 39 to the micro processor 31 of the engine analyzer 30 In operation the encoder wheel of the contact tachometer 38 is held against one of the readily accessible external linearly moving parts of the engine 20 such as the fan belt 25 The encoder wheel rotates at a speed proportional to the linear speed of the moving engine part with which it is engaged which latter speed is in turn proportional to the speed of the engine 20 The contact tachometer 38 responds to the rotation of its encoder wheel to gen erate an output signal which is in the nature of a fluctu ating voltage the amplitude of which is directly pro portional to the speed of the engine 20 The signal is
25. y a predeter mined time period 10 A method for determining relative power contri butions of individual cylinders of a multi cylinder inter nal combustion engine wherein an engine cycle is a time period between consecutive ignition events of the same cylinder and wherein a cylinder cycle is the time period from the ignition event of one cylinder to the 15 20 10 ignition event of the next cylinder in the ignition order said method comprising the steps of a detecting speed variations of the engine during an engine cycle and generating an electrical output signal indicative thereof b detecting the ignition events of each cylinder c processing the output signal to generate a wave form signal representative of the speed variations of the engine over time d displaying the waveform signal as a graph in which speed and time are respectively measured along orthogonal axes such that the cylinder cycles occupy substantially equal distances along the time axis e displaying adjacent to the graph cylinder zone markers respectively corresponding to the cylinder cycles and f determining said relative power contributions by comparing the cylinder cycles of the waveform during a single engine cycle 11 The method of claim 10 wherein the detecting step includes detecting speed of an accessible external 25 30 35 40 45 50 55 60 65 moving part of the engine 12 The method of claim 11 w
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