CA2018334C - A tachometer system for an internal combustion engine which senses an electromagnetic signal produced by a firing of the engine - Google Patents

Abstract

A tachometer system for an internal combustion engine.
The tachometer system uses one of two electromagnetic pulse sensing means to detect an electromagnetic signal produced by a firing of the engine. The sensing device may be an antenna or an inductive pickup. One of the signals is chosen and processed. A parameter indicative of pulse timing in the output signal is determined. This parameter is most advantageously a time between different ones of the output signals. The parameter is then converted into a value indicative of revolutions per unit time of the engine. The converting structure is advantageously formed by a personal computer.

Description

TACHOMETER SYSTEM FO~ AN 1~1~K~A~ COMBUSTION ENGINE WHICH
SENSES AN ~CTR0MAGNETIC SI~NA~ PRODUCED BY A FIRING OF THE
~GI~
FIE~D OF In~ lNv~llON

The present invention relates to a t~cht ~er which ~enses an electromagnetic signal pro~uce~ by a firing of 6aid engine.
More specifically, the present invention relates to a tach~ ?ter system which can operate with either of an ~ntenna type non-contact sensor, or an $nduction type pickup which senses a sparX plug firing, to determine revolutions per unit time of an engine.

BACKGROUND OF THE lNV~;NllON
It is often necess~ry to determine revoluti~ns per unit time of an internal co~bustion engine. Such a measurement typically uses A de~ice known as a t~h~ ?ter. Tar~ ?ters are most often used in automotive applications. For instance, applications for repet~tive automotive testing may reguire an accurate RPM
reading. This is reguired ~n ~uch fields as automotive emission testing or safety inspectlons. Such testing operations not only reguire an accurate measurement of RPM, but also reguire that the device be easily and temporarily attached to the ~utomobile operative portions. Much time can be saved if the user does not have to physically connect the device to the internal combustion englne.
Devices in the prior art have typically either physically ro~nected a device to a moving part of the internal ~ombustion engine, or bav~ used an opt~cal ~e~eor to detect the movement of the lnternal __ stion engine. The use of an optical ~en or is disadvantageous since a white line or marker of that type must be attached to the internAl c~mbust~on engine before the detection can be made. ~oreover, this wbite line can be~ e obscured by natural grea~e that forms within the engine compartment of the engines.

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Physical contact with the internal c hu~tion engine can also be dangerous ~or the people operating the device.
Furthermore, many new ~n~in~s being manufactured today use a so-called distributorless system. These engines will not Arc~ te a conventional tachometer ~ystem. For instance, the GM Quad 4 has no Acce~sible spark plug wires or eY~ose~ ignition cords. qhe inventors of the present invention have found that a non-contact antenna ~ystem which ~en6es ele~L,. -gnetic signals produced by firing of the eng~ne, would lend itsel~ very well to this application. Such a sy6tem could be u~ed with no ~pecialized testing equ~pment being required, nor would any complicated hook-up bs neoessAry.
It would alco be advantageous ~f this tachometer cystem could intPrface with ~ personal computer. This would enable RPM
readings to be stored in the c. ~er's memory and to per~orm comparative analysis of RPM versus hydrocarb~n, carbon monoxide or carbon dioxide emissions.
, . .
~mar~ of the Invention In recognition of all these problems, ~he present invention provides a non-contact tachomet~r which can be used in two d~fferent modes. A ~irst mode uses an ~ntenna ystem ~hich ce~ses an electromagnetic pul~e pro~ e~ by an ignition coil of the engine. A Fecond mode uses an inductive pickup coupled to a Epark plug wire of the eng~ne. Both of these modes are no~, oontact modes in the sense that no p~ysical connection to a lead, or to a portion of the engine is neces~ry.
Either of the~e ~ystems c~n be used for acguiring an tn~i~Ation of _n electro~agnetic signal pro~e~ by ~ ~iring Or the engine. An o~L~ut ~gn~l ~n~iç~t$ve thereof i~ pro~n~e~.
Timing $ndicative of the p~ e~ in the o~y~L ~ignal ~s determined, ~nd ~onverted i~to a value ~nA~tive of revolutions o~ the intern~l combustlon engine per unit time.
In ~ particularly preferred ~ ~odiment of the invention, the tachometer circuit board ~s in the form of an expansion ~ard ~or ;~ 3g~

a known personal computer. The RR~ value di~played is the actual RPM, plus or minus 50, o~ the car's engine.
This tachometer circu~t board also itself includes other novel features. One ¢uch feature is a pulse stretching circuit which stretches the pul~e width of the signals from the non-contact 6ensor while ~a~nt~1n1~g a voltage (or proportional voltage) thereof. ~he pul~e ~tretching circuit receives the input signals and applies the input signalc to one input of each of a plurality of c- ~rators. A voltage dividing structure is provided for pr~a7uc~n~ a plurality of voltages which differ from one another by a ~ubstantially constant amount. These volta~es are connected to the other ~nput of each of the ~- ~rators. The output of the comparators ~Ai~tes which of the inputs is the larger signal. Each o~y~t of each coDparator is coupled to one of a plurality of ~eans for pro~-~c~n~ a pulse. This pulse can typically ~e pro~ucer1 by a monostable multivibrator. Therefore, a different J~ r of these pulse pro~au~1~g structures are triggered, based on how nany o~ the comparators are in a predetermined state. O~L~uLs of all of the pulse width producing means are summed 50 that the ~mplitude of the ~um~7ed ou~put ic proport~onA1 to the voltage of the ~hort pulse input.
Another preferred ~ ~a; ~qt of the invention counts ~ime between the pulses in a new and novel way.

~RIEF DES~K~ ON OF THE DRAWINGS
A presently preferred e~bodiment of the lnvention will be described in det~il with reference to the ~r~ nying drawings, wherein:
FIGU~E 1 shows a block diagram of the t~rh~ ?ter syste~ of the present invention;
FIGURE 2 6hows an example o~ the antenna used ~n the antenna mode;
FIGURE 3 shows ~n example of the induction pickup used in the induction pickup aode;

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FIGURE 4 6hows, in block diaqram ~orm, a detailed layout of the ~mtenna processing circuitry of FIGURE l;
FIGURE 5 shows a detailed layout of the automatic gain control circuit 408 of ~IGURE 4;
FIGURE 6 ~how~ the comparator integrator circuit 414 of FIGURE 4 in detail:
FIGURE 7 ~hows the pulse ~tretching network in detail;
FIGURE 8 shows a detailed layout of the processing for the inductive pickup along with ~he dividing network for the antenna, along with the ~electing network;
FIGURE 9 ~hows a detailed layout of the pulse counting circuitry;
FIGURE 10 ~hows a ti~ing diagram for thi~ pul~e counting circuitry, with reference to which the pulse counting circuitry is explained: and FIGURE 11 ~hows a flow chart used by proce~sor 116.

DFTATT~n DESCRIPTION OF T~ ~K~ I) EMBO~
FIGURE 1 show~ a bloc~ diagram of the tachometer system used according to the present invention. This basic embodi~ent includes two different electromagnetic pulse ~ensing ~eans. Both of the ~eans ~re coupled in a n~l- cGr,~act manner to ~n operative area o~ the internal co~bustion engine. The first possible pulse 6ensing ~eans is a ~ensing antenna 100 which Fence~ an electromagnetic pul~e pro~ce~ by an ignition ooil of the engi~e.
Sensing antenna 100 i8 ronnected to antenna ~ ocessing circuitry 102. This include~ circuitry to remove noise ~rom the signal and to lncrease the level thereof, to ensure that tha ou~yuL ~ignal thereof accurately ~ey eocnt~ the ele~ gnetic p~ F ~o.~ e~
~y the engine o~ the vehicle. Since ~ensing antenna 100 will deteot every firing of the engine, the ou~u~ thereof ~ust ~e divided by ~ divider 104 for re~sonC clari~ied later. Divider 104 ~ncludes a programma~le dlvider circuit. ~eco~er 106 is provided which receives input signals from the processing means which is a personal computer in this embs~ t, and which ;~ 333~

programs the divider to divide by N, where N ratio is dependent on the number of cylinders of the ~ehicle. In order to ~aximize the flexibility of the ~t ~o~ule, the divider ratio is programmable, ~o that it may be used with 811 different number cylinder engines. The output of divider ~04 is coupled to selector 108 which will be described later.
The alternative pickup configuration includes inductive pickup 110. Inductive pickup 110 is sdapted to be located near a spark plug wire of the engine ~o as to acquire an indication of the electromagnetic signal produced by the firing of one cylinder of the engine, as indicated by a signal through the spar~ plug wire. Accordingly, ~ince inductive pickup 110 is located on only one of the park plug wires, the number of pulses received thereby will be l/N of the number of pulses received b~ the sensing antenna 100. The o~ L of inductive pickup 110 is coupled through isolation/processing circuitry 112 to selector 108, Since inductive pickup 110 receives only l/N the number o~
sign~ that are received by ~ensing antenna 100, if divider 104 is set to l/N, both inputs to selector 108 ~ho~ be the same.
This is the object of divider 104, ~o that ~elector 108 receives two input signals, each indicating one single pul~e for each N
firings (where N is the number of cylinders) of the engine.
Counter circuitry 114 detects a parameter in the timing in the ~LpUt fiignal, while conversion to RPM is performed by processor 11~. The final converted value i8 displ~yed on display 118.
Sensing antenna 100 is ~hown in more detail in FIGURE 2.
Antenna 100, in this preferred r ~odi - t, is formed of a number 61 material ferrite rod with .~20/.780 O.D, by 2.2/2.3 long, and three coil wi~ s of egual ~ize wound around the rod.
Each coil is wound 1,000 turns using 30 AWG wire. All three coils are wound in-phase, ~nd are wired in parallel. A passive filter 11 is wired to the output of the ~ignal ~ lead. Passive filter 11 includes a lKn resi~tor 130 in parallel with a 6200 pF
capacitor 132.

Any other suitable sensing antenna which senses engine firing pulses could alternately ~e used.
FIGURE 3 shows the inductive pickup type antenna. This induction pickup 12 is ~ ~tandard part made by Sun Electric, part num~er 507-006. Pickup 12 is co~nected to cable 13 which is embodied by a Sun Electric part number 507-006 with ~lden 9259 coax.
FIGURE 4 hows a ~ore detailed layout of ~ignal processing circuitry 102 shown $n ~IGURE 1. FIG~RE 2 6hows the antenna lO0 as producing two 6ignals: a plus ~ignal ~nd a min~s signal.
These ~ignals are fed into a high impe~Ance 1DW drift instrumentation amplifier 400. In this ~ ~o~iment, instrumentation amplifier 400 is configuxed ~s a differential amplifier with a voltage gain o~ approximately lO0. Differential amplifier circuitry 400 has the purpose of removing ~ ~r mode noise from the antenna leads. The où~uL of differential nmplifier 400 is pACse~al through high pass ~ilter 402 which has a cut-off freguency of 360 ~z as a further noise-reducing te~hn~que. Therefore, 60 cycle noise along with common harmonics thereof are removed. The ~ of high pass filter 402 is ~onnected through capacitor 404 to full-wave rectirier 406. This full-wave rectifier 406 in this ~ ~oai~ent is for~ed by an opexat~o~l amplifier configured as a rectifier and need not be configured as ~ passive full-wave rectifier, ~l~ho-~qh such is possible. The ~S~S of full-wave rectifier 406 is fed directly to an ~utomatic ~in ~on~ol ~mpl$fier (AGC) 408. Automatic gain ~o~ ol ~mplifier 408 has the ~u~pose of ~aint~n~ng the ~i~n~l ~trength, in~ep~n~ent of the type of engine ~eing measured or the di~tance between the ignit~on coil and antenna lO0. It is very important that the o~u~ ~ignal fro~ ~ntenna procecs~n~
circuitry 102 ~e ~n~epDn~ent of the type o~ eng~ne being used, or the characterist~cs o~ the operator. AGC 408 ~erves to ~aintain constant ouL~u~.
The ~u~ of AGC 408 is connected back through ~ feedback loop to the ga~n control input 410 of AGC 408. The output of AGC

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408 is ~onneeted first to peak detector 412 which detects the peaks in this o~p~L gignal, per unit time. The ~L~u~ sf peak detector 414 is connected to ~ c ,-rator/ integrator circuit 414 where it is ~ red with a predeter ~ned refe~ence and ~lightly integrated. The resulting 6ignal is buffered in buffer ~16 and optically isolated by optoisolator 418.
A detailed circuit diagram of AGC 408 and opto 418 is Fhown in FIGURE 5. AGC408 is formed in t~is e ~o~; ~nt by a National Semiconductor part number LF356 amplifier, connected as an inverting amplifier. Capacitor 502 in this . ho~ t has a value o~ 32 p~ with resistor 504 having a value 200 kn. Opto 418 is a part n h~r CLM6000 which inclu~es a variable photo-resistor 506 and photo-diode 508.
A detailed layout of comparator/integrator circuit 414 i~
shown in FIGURE 6. Comparator/ integrator circuit 414 i8 formed of a type MC1458 operational amplifier 600 ~-on~cted ~s a comparator. A reference ~oltage i~ applied to the non-inverting ~nput and is adjustable using potentiometer 602. The integration uses potentiometer 604 as ~ re~istance in ser~es witb capacitor 606 which is a 22 pF capacitor.
The o~yu~ of AGC408 in FIGURE 4 is connected in a pulse stret~h~n~ network 450. This pulse stretchin~ network will he described in more detail with reference to FIGURE 7. Briefly ~tated, however, the pulse ~tretc~n~ networ~ lengthe~s the length o~ the pulse while pro~v~ a voltage o~yuL ~ignal which i8 proportional to the volt~ge input. The pulse-stretching network 450 takes the very short duration p~ e~ of typically 20 - micro~coon~s that co~e~onA to the 6park plug fir~n~g. The~e pul~es are wi~ene~ to 500 microse~QnA~, while ~t~ll maint~n~n~
an ou~ ignal proportional ~n peak voltaqe to the input ~ignaI. The wider time pulse is desirable to allow tbe peak detector 452 a suffioient amount o~ tlme to charqe up to its full peak voltags. The pulse si~nal output by pul6e-~tretching network 450 is also fed to a ~con~ A~C amp 45~ which has ~
digital dividing networX therein. The ouL~u~ of pul~c ~etching : .
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network goes into input Z of AGC 454 while the ~h~UI of peak detector 452 enters input X of peak detector 454. The ouL~1 y follows the relation (y=lOZ/X). This 454 AGC is typically ~ ho~ed by an analog divider.
The Ga~p~L of AGC amp 454 is co~nected to comparator 458 wh~ch compares the output thereof with a voltage reference --typically eight volts. Anyth~ng less than this voltage reference is rejected as noi~e. The o~u~ of comparator 458 is connected to a one-shot 460 which pro~1ces a pulse correspon~i"7 to each pulse that is detected as being a real firing of the engine.
One-~hot 460 pro~res a pulse of approximately 5 ~ill~ec-on~c limited to a +5 volt peak-to-peak output. The output of one-shot 460 is then conn~cted to divider 104 in FIGURE l.
PU1~e ~.etching network 450 will now be de~cribed with reference to FIGURE 7.
FIGURE 7 shows the preferred r ~o~ment of the pulse-6tretch~n~ network of the present,$nvention. This networ~
has an object o~ pro~llc~n7 p~-16~5 as ~ ts that have a predetermined width, but which have an 6UL~u~ voltage proportional to the input voltage. Accordingly, thi~ circuit amplifies the p1~l0eF ~o~ewhat, still keeping a p~G~o~-ional voltage to the ~nput voltage. P~_ve , the width of these p~lffes i8 widened.
The voltage pul~e is input from AGC 408 at receiving area 700. This input ~s coupled to the compare inputs of each of the comparators in comparator b~nk 702. Al~ho~1~h only ~even _~ ,Drators nre ~hown ln ~IGURE 7, lt is un~erstood that many ~ore co~parators 2re contemplated. In ~act, the preferred . ~o~i ?nt contemplates a ~ank of 12 comparatorfi being used, with a greater number o~ comparators increasing the accuracy. The reference input of each comparator i~ biased with ~ voltage ~rom vo~tage ladder 704. Voltage ladder 704 provides a pluxality o~
stepped voltages ~aving constant lnterval~ therebetween. These stepped voltages are co~ected to the referenc~ inputs of the respective comparat~r~. Therefore, each o. ~orator has the AGC

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volta~e coupled to one (c~mrAre) $nput thereof and a respective and different reference input couplad to the reference input thereof. The voltages lower down the ladder are therefore lower than those higher ln the ~ Pr. Moreover, the higher the voltage from AGC 408 become6, ~he more comparators within c_ ,srator bank 702 will trigger.
Each pulse from AGC 408 therefore triggers a 1 '~r of c- ,arators proportional to on its voltage. Each comparator that is triggered trig~ers one o~ the one-chots ~n one-shot bank 706.
Each one-shot produces a corresp~n~in~ pulse of approximately 500 microse~on~ he plurality of pulses are ~ together in analog summer 708.
The result is that the o~ L pulse will have a time width of 500 microseco~C. ~w.ver, ~he voltage of the pulse will depend on how ~any one-6hots have firedJ which itself is based on how many comparators have been triggered. Therefore, the volt~ge at input 700 will ~or,L~ol the voltage out of analog summer 708.
The ou~ of the antenna ~.ucessing 102 is cnnnected to a programmable divider 104. Div~der 104 is diagrammatically ~hown in ~IGURE 8.
Address signals A0-A15 are received from ~he personal computer (proces~or 114) to address the FIGURE 8 c6r.t,01 circuitry. Address ~j~nA?~ A0-A2 set the divide by ratio. The lowest order lines A0, Al and A2 ~et the divide by x ratio and are connected to the inputs of z three-to-eight ~ecQ~r 800.
Three-to-eight ~ero~r 800 pro~lces a plurality of o~tp~s ~ndicative of the number of cyl1n~rs which are ~elected. A
plurality of ouL~uLs labeled d~vide by 5, divide by 6, divide by 8, divide by 4, etc., ~re co~nected to cylinder networX 31.
Cylinder divider network 31 receives the inductive-pickup pulses from one-shot 460 of FIGURE 4. Cylinder d~vider network is a fitandard pro~r~ ~ble divide by N ~ivider, and divides the pulses ~y the ~elected ~mount.
The o~ L o~ cylinder divider network 802 is co~ected to Z~B33~

AND çlate 804. AND gate 804, along with latch 806, acts as the selector of the present invention.
In this embodiment, the ~election of whether 6ensing antenna 100 or inductive pickup 110 should be used is provided by the two lowest order bits of the three-to-eight ~eco~er. Once the antenna ~nduction 6election is made, it ~ n~ in force until a different elect~on is made. The ou~ s CT and NC, representing respectively ~ensing antenna 100 and ~nduc~ive pickup 110, are co~nected to SR latch 806. SR latch 806 latches an output corresponding to the sensing structure which ~hould be used. The ouL~uL, which is low for ~ctive ou~pu~, is indicative of the inductive pickup 110 havins been selected ~nd is connected to the enable input of AND ~ate 804. Therefore, when sensing ~ntenna 100 is selected, contact Q~6elect is high, and conditioned pllls~e 33 from cylinder divider network 802 ~re p~sse~ through AND gate 804. In cor.L,ast, when inductive pickup 110 is ch~sen, the Q~
ou-~u~ is low, disabling AND gate 804. However, AND gate 820 is enabled by a h~gh o~Lp~L on Q~of the latch 806.
Addresses A3-A15 represent the board address. These addresses are co~nected into ~ddress ~ecoders A28 ~nd A29, respectively. Each address Aeco~r pro~lces a signal when the proper address is received. These signals ~re used as enables to the three-to-ei~ht ~?coA~r 800.
Inductive pickup 110 is also shown in FIGURE 8. Inductive pickup 110 is co~ne~tcd to isolation processing 112 which ~ncludes an opto isolator 841 connected to a one-shot 842. Since the p~ses from the induction pickup will typically include muc~
~oise, opto isolator 841 isolates these ~ignals fro~ the remainder of the circuit to ~e~el.~ component damage. One-shot 42 is used to obtain a pulse width of 20 milli~econ~e to ~atch the pulse width o~ L of one-~hot 460 of FIGVRE 4. The o~
of one-shot 842 is c~nneçted to AND gate 820 which is enabled when inductive pickup i~ ~elected. Thererore, AND g~te 804 ls enabled when sensing pic~up is ~elected ~nd AND gate 112 is enabled when inductive pickup ~s selected. Whichever pulses are 2~

_elected by either AND gate 804 or 820 are coupled through OR
gate 822 to the pulse counting circuit 114. This is ~hown in more detail in FIGURE 9.
Pulses 900 sre ~nput from the ~tructure of FIGURE 8 into the S structure of FIGURE 9 which e~bodies the count pul5e structure 114 shown in FIGURE 1. Pulses 900 which are input into this ~tructure are from either on~ of the ~ources, sensing antenna 100 or inductive pickup 110. However, these pulses 900 ~re treated as indistin~ichAhle from thi~ point onward, ~nd are counted by .
the QtruCture of FIGURE 9. The counting of p~lses 900 will be explained with reference to the circuit of FIGURE 9 and the timing diagram of FIGURE 10.
Pulses 900 are first input to D-type flip flop 902 D-type flip flop 902 is configured w~th tbe D input and the preset co~nected to a "1~ ~o that clock p1~ses clock in a "1", and a reset causes the o~ of the system to return to a zero.
Therefore, when one of the p~ 900 goes high ~s shown in FIGURE lO~a), lt r~l~Q~ the Q~904 to go low. ~his removes.binary counter 906 from its previously held clear ~tate (high clear) and enables counting to begin. FIGVRE lO(B) shows Q~904 going low in response to a ri6~ng edge of ~ pulse 900.
Clock source 910 pro~l~ces a stream of p~lls~Q which are shown in FIGURE lO~c). In thi8 embodiment, the pulses are at a freguency of 74.53 kilohertz, divided fro~ a clock of 4.77 m~gahertz. Clock p~ $ 912 are coupled to the clock input of binary counter 906 80 that it will count whenever it ~s not held in clear.
The o~pu~ ~ignal~ from binary counter 906 are used to control tbe operation o~ the pulse counting circuit 114 during this crucial ti~e when a firing p~l~e has been received. Binary counter 906 counts for 5 count~ ch count is $nitiated by a falling edge of clock signal 912. Tbe states which binary counter 906 ~ssume are labeled ~s ~tate~ 1-5 in FIGURE 9 . State 1 produces a "1~ on line ~14 ~nd on no other lines. ~he operation of line 914 ~s ~hown diagrammatically in FIGURE lO~d), 3~

with line 916 being shown in FIGUhE 10(e) and line 918 ~eing shown in FIGURE 10(f). When line 914 i8 high and no other line is h.igh, the state is defined as count number 1 state. During count number 1 state, however, nothing occurs, except preparation for the remaining control functions.
State 2 is indicated by a binary count of ~10", that is a "1" on line 916 and a NO~ on line 914. The ~1" on line 916 is con~ected through inverter 922 to AND gate 924, to i~mediately cause a 6eco~ D-type flip flop 920 to be cleared. When line 916 is low~ both inputs to AND gate 924 are high, leaving a low input to D-type flip flop 920. However, when either input to AND gate 924 heco ~c a '0', D-type flip flop 920 is i~mediately clearedO
Therefore, state 2 of binary counter 906 clears D-type flip flop 920. Alternately, an external reset signal from reset line 926 clears D-type flip flop 920.
When D-type flip flop 920 is cleared, the Q ou~ 928 thereof assumes a low state. This ~orces the two main counters 955 and 956 to stop counting as will be ~;F~1~CSed here~n.
Specifically, AND gate 930 is interposed ~ een clock pulses 912 and the 16-bit counter assembly including counters 955 and 956.
Counters 955 and 956 are normally arranged to count ~nput cloc~
pulses thereto. However, when Q o~L~uL 928 o~ D-type flip flop 920 goes "low", AND gate 930 i~ disabled, thus preventing any further clock p-l~es from being propagated tberethrough.
Thsrefore, counters 955 and 956 stop receiving clock p~ es and top counting. ~:
Therefore, count 2 prevents further count~ng of the main counter~ 955 and 956.
Count 3 i~ indicated by both line~ 914 and 916 being high.
When this oo~u~, AND gate 932 propagates a ~1" therethrough to indicate state 3, count ~er 3. The signal pro~uce~ by count 3 is shown in FIGURE 10(~ his signal is input to one input of AND gate 934~ The ot~er input of AND gate 934 normally receives a "1". ~he output ~ignal of AND gSte 934 is labeled ~50 herewith. When this signal goes high, it enables four, four-bit 2~ 3~

data latches 951, 952, 953 ~nd 954 ln parallel. These data latches 951-954 receive the Ou~UI S Of counters 955 and 956 to at their respective Dl-D4 input_, ~s input data. Count 3 c~- ~n~c ~he latches to p~ss the information at its Dl-~4 inputs to the microprocessor data bus. At this time, an interrupt is also produced by line 950, co~manding the fflain processor to read the data which is now available on the data bus.
Therefore, the ~i~.u~oceqsor is commanded to read information indicative of a count of the previous ti~e period during state number ~.
~ tate number 4 is indicated by a ~1" being present on line 918, witb "l"s not being pre6ent on any other line. A "1"
appearing on line 918 iR ~hown ~n FIGURE 10(g), ~nd is input to OR gate 960. When either input of OR gate 960 goes high, the o~uL thereof goes high. The ou~u~ 962 o~ OR gate 960 is connected to the clear inputs of both 16-bit counters 955 and 956. This is hec~ e the contents of these counters have been read by the mic~u~ocDssor durin~ the previous state, ~tate 3.
Since the contents of 16-bit counters 955 and 956 have been read, they are cleared to "0" during ~tate number 4.
Therefore, state 4 clears the two 16-bit counters.
State number S i8 defined when a "1" simult~neoucly appears on lines 918 and 914. This i_ detected by AND gate 964, which produces a "1" o~ t only when it receives two ~lN inputs.
Count nu~ber 5 therefore produces a ~1" on line 966. This is connected through inverter 968 to AND gate 9~0, where it overrides AND gate 970 to PL~Ce one ou~ut on line~972. This clears counter 902, c~t~R~n~ the Q-output thereof to go high, thereby holding binary counter 906 in a clear state. This prevents bin~ry counter 906 from performi~g any ~urther counting until the next t~Chr ~ter pulse arrives on line 900.
Line 966 pro~lce~ by count r.- '~r S also triggers D-type flip flop 920, toggling its Q ~L~ 928 to n high state. When Q
output 928 is high, AND ~ate 930 is once again enabled, enabling clock pulses fro~ 912 fro~ clock ~ource 910 to be passed through 3~

AND gate 930 and to counter~ 955 and 956. This causes the next counting sequence to begin, ~nd to continue until 6tate 2 a~ter the mext tachometer pulse.
Therefore, state S disables counter 906 until the next tachometer pulse is received, ~nd al~o ~egins counters 955 and 956 counting once again.
The entire sy6tem is c~n~olled by the processinq means. In this preferred embodi~ent, the processing ~eans is an IBM compatible PC XT ~ er. The y.~cessi~g means operates accor~ing to a predetermined flowchart, which will now be descxibed with reference to FIGURE 11.
~ he flowchart begins at step 1100 and is followed by a short self test at step 112. The first ~tep the ~UgL - must perform is to determine whether the ~tructure will operate in sensing lS antenna mode or in inductive pickup ~ode. T~is determination is made nt step 1104. If the operation will be in 6ensing ~ntenna mode, the variable W (de~cribed later) is ~et to 1. If the operation is detected to be ~nductive pickup mode, the number of cylinders must be determined at step llOS. '~his can be received from the keyboard or by 2ny other ~eans. Step 1108 determines if the ~ er o~ cylinders are valid, and if not requests the number of cylinders to be entered once again. A map o~ the valid cylinder - ~rs are 6tored in a memory location, ~hown in the flowchart as step 1110.
If the number of cylinders ~s determined to be valid ~t ~tep 1108, a test is made at 6tep 1111 to determine if the ~-r of cylinder~ is 10 or 12. This t~st ~ ~ade fox the ~ 05C of 8etting the variable W . W i8 a ~ariable which is used to co~pensate ~or engines with more than 8 cylinders ~nd less ~han 4 cylinders by an appropriate weighting. Ba~ed on the number of cylinders which the engine has, the pro~essor must determine how to configure the cylinder dividing network 104.
If the ~ r of cylinders ~s 10 or 12, ~tep 1112 ~ets the number of cylinder variable CYL% equal to the number of cylinders entered, divided by 2. At this ti~e, the variable W is ~et to 2 3~

indicating a weighting factor of 2. This allows the halved number of cylinders to be used, ~nd ~-nc~tes using ~he varialble W. If the ~- ~Dr of cylinders is 2 or 3, the cylinder ~l her is multiplied ~y 2 ~nd W i8 set to ~ at step 1114. If the number of cylinders is 4, 5, 6 or 8, the ~ er of cylinders remain ~chAnged and W is ~et to 1. It is ~een that 10 or ~2 are ~ultiples of S and 6 and 2 and 3 ~re ~ultiples of 4 and 6.
Therefore, by use of the variable W , only the div$ding ratios 4, 5, 6 and 8 need be used. This ~implifies both t~e hardw~re and software that is necessAry.
Based on this detection, the cylinder number ~eco~r 800 is set at ~tep 1118. A test for in~tialization ~s made at step 1120, and if not the Rystem enters an infinite loop until ~uch initialization oc~u~. If initialization has oc~ ed, control p~ses to step 1122 which obtains the count from the count buffers 941-945. The actual count is stored in a variable called "count" at step 1124 ~nd is egual to the count received from the count buffer times the variable W . The RPM is then calculated at step 1126 according to the relation:
RPM ~ t74531.25~ * (120/count).
Control then pAC6es to step 1120 entering ~n infinite loop which continl~lly calculates the RPM of the ~ystem.
As described above, the preferred ~ hoAiment of this invention uses an IBN PC XT with two floppy disc drives, a monitor and a ke~board as the processi~g me~ns, and the tachometer circuit is configured as an expansion card for the PC.
~n induction pick~p and the antenna are att~he~ to thi~
expansion card to receive data from the spark plug wlres.
To begin the operation of the system, application ~ortware is loaded into the PC by a floppy disc. Once the ~o~tware is booted up, the operator ls prompted to select either sensing antenna or inductive sensing mode. This corresponds to the decision block in step 1104. If induction mode is selected, the operator must install the induction pickup around the ~park plug wire. Pulses recei~ed ~y the induction picXup ~re then sent to , .. ' '' ' .

3 ~

the t~rht ~ter ~Yp~neion card where the ~pacings between the pulses are converted to digital information. The c uter analyzes this in~ormation and displays an RPM reading on the screen based thereon.
If antenna mode is t2elected, the operator must enter the number of cylinders into the computer, or receive this number of cylinders via some other means, to ini~ialize the cylinder divider network on the tachometer circuit board. Once this is accomplished, the antenna may be placed on the automobile hood in a location close in proximity to the ignition coil. Signals are once again sent to the tacho~eter expansion card to be transformed into digital information ~or analysis by the processor.
Although only a few e~bodi~ents have been described ~bove, those of ordinary skill ~n the art would readily realize that ~any modifications are possible 'n the preferred ~ ho~ ~ts without materially departing from the teachings thereof. For instance, although the calculation has been set forth as being performed by software, it could ~150 easily be performed by a hard-wire dedicated hardware ~ystem. Also, any other computer besides the IBM could alternately be used as the processing ~eans.
Accordingly, ~11 6uch ~odifications ~re inte~ to be ~ncc -sse~ within the following clai~s.

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Claims (7)

1. A tachometer system for an internal combustion engine, comprising:
electromagnetic pulse sensing means, coupled in a non-contact manner to an operative area of said internal combustion engine. for sensing an electromagnetic signal produced by a firing of said engine, and producing an output signal indicative thereof;
means for sensing a parameter indicative of pulse timing in said output signal;
means for converting said parameter into a value indicative of revolutions of said internal combustion engine per unit time; and said sensing means comprising:
means for receiving said output signal from said electromagnetic pulse sensing means;
means for detecting a pulse in said output signal;
means for counting an elapsed time;
means for selectively enabling and disabling said counting means;
means for selectively providing an accumulated count of said counting means to an external port; and control means, connected to said receiving means, said detecting means said counting means, said providing means and said selecting means, for initiating a sequence upon detecting a pulse by said detecting means, by, in order: 1) disabling said counting of said counting means, 2) commanding said providing means to provide said accumulated amount, 3) resetting said counting means, and finally 4) enabling said counting means.

2. A tachometer system for an internal combustion engine, comprising:
electromagnetic pulse sensing means, coupled in a non-contact manner to an operative area of said internal combustion engine, for sensing an electromagnetic signal produced by a firing of said engine, and producing an output signal indicative thereof;
means for sensing a parameter indicative of pulse timing in said output signal;
means for converting said parameter into a value indicative of revolutions of said internal combustion engine per unit time;
filtering means, coupled between said electromagnetic pulse sensing means and said parameter sensing means, for filtering characteristics of pulses from said electromagnetic pulse means, said filter means comprising a circuit for extending pulse widths of input pulses while maintaining a voltage proportional to said input pulse, comprising:
means for receiving said input pulses;
means for producing a plurality of voltages which differ from one another by a substantially constant amount;
a plurality of comparators, each connected to receive said input pulses at one compare input, and each connected to receive one of said voltages from said voltage producing means at another compare input, for producing an output signal, indicative of which of said compare inputs has a larger signal;
a plurality of means for producing a pulse having an extended width, one being connected to each of said output of each said comparator to produce said extended width pulse based on a state of said comparator to which it is connected;
and means for summing outputs of all of said pulse width producing means, so that an amplitude of an output thereof corresponds to a number of said pulse width producing means which are producing said extending width pulse.

3. A tachometer system for an internal combustion engine, comprising:
means for receiving a signal of an antenna which senses an electromagnetic pulse produced by an ignition coil of the engine;
means for receiving a signal from an inductive pickup coupled to a spark plug wire of the engine to sense an electromagnetic pulse produced thereby;
means for selecting one of said signals;
means for sensing a parameter indicative of pulse timing in said selected signal, wherein said sensing means comprises:
means for receiving an output signal from said selecting means;
means for detecting a pulse in said output signal;
means for counting an elapsed time;
means for selectively enabling and disabling said counting means;
means for selectively providing an accumulated count of said counting means to an external port; and control means, connected to said receiving means, said detecting means, said counting means, said providing means and said selecting means, for initiating a sequence upon detecting a determination of a pulse by said detecting means, by, in order: 1) disabling said counting of said counting means, 2) commanding said providing means to provide said accumulated count, 3) resetting said counting means, and finally 4) enabling said counting means; and a personal computer for converting said parameter into a value indicative of revolutions of said internal combustion engine per unit time having a display for visually displaying said value.

4. A tachometer system for an internal combustion engine, comprising:
means for receiving a signal of an antenna which senses an electromagnetic pulse produced by an ignition coil of the engine;

means for receiving a signal from an inductive pickup coupled to a spark plug wire of the engine to sense an electromagnetic pulse produced thereby;
means for selecting one of said signals;
means for sensing a parameter indicative of pulse timing in said selected signal; and means for converting said parameter into a value indicative of revolutions of said internal combustion engine per unit time wherein said converting means is formed by a personal computer having a display for visually displaying said value;
filtering means between said selecting means and said sensing means, for filtering characteristics of pulses from said selecting means, wherein said filtering means comprises a circuit for extending pulse widths of input pulses while maintaining a voltage proportional to said input pulse, comprising:
means for receiving said input pulses;
means for producing a plurality of voltages which differ from one another by a substantially constant amount;
a plurality of comparators, each connected to receive said input pulses at one compare input, and each connected to receive one of said voltages from said voltage producing means at another compare input, for producing an output signal indicative of which of said compare inputs has a larger signal;
a plurality of means for producing a pulse having an extended width, one being connected to each said output of each said comparator to produce said extended width pulse based on a state of said comparator to which it is connected;
and means for summing outputs of all of said pulse width producing means, so that an amplitude of an output thereof corresponds to a number of said pulse width producing means which are producing said extended width pulse.

5. A circuit for extending pulse widths of input pules while maintaining a voltage relation between said pulses, comprising:
means for receiving said input pulses;
means for producing a plurality of voltages which differ from one another by a substantially constant amount;
a plurality of comparators, each connected to receive said input pulses at one compare input, and each connected to receive one of said voltages from said voltage producing means at another compare input, for producing an output signal indicative of which of said compare inputs has a larger signal;
a plurality of means for producing a pulse having an extended width, one being connected to each said output of each said comparator to produce said extended pulse width based on a state of an associated comparator; and means for summing outputs of all of said pulse width producing means, so that an amplitude of an output thereof corresponds to a number of said pulse width producing means which are producing said extended pulse width.

6. A circuit as in claim 5, wherein said circuit is used in a tachometer system for an internal combustion engine, said tachometer system comprising:
means for receiving a signal of an antenna which senses an electromagnetic pulse produced by an ignition coil of the engine;
means for receiving a signal from an inductive pickup coupled to a spark plug wire of the engine;
means for selecting one of said signals;
means for sensing a parameter indicative of pulse timing in said selected signal; and means for converting said parameter into a value indicative of revolutions of said internal combustion engine per unit time.

7. A system as in claim 6, wherein said sensing means comprises:

means for receiving an output signal from said selecting means;
means for detecting a pulse in said output signal;
means for counting an elapsed time;
means for selectively enabling and disabling said counting means;
means for selectively providing an accumulated count of said counting means to an external port; and control means, connected to said receiving means, said detecting means, said counting means, said providing means and said selecting means, for initiating a sequence upon detecting a determination of a pulse by said detecting means, by, in order: 1) disabling said counting of said counting means, 2) commanding said providing means to provide said accumulated count, 3) resetting said counting means, and finally 4) enabling said counting means.