Patent GB-1286110-A (GB)
Title: Analyser for internal combustion engine
IPC: G01R13/20
Filed: 1969-10-13
Abstract: 1286110 Cathode-ray tube displays; transistor staircase generators MARQUETTE CORP 13 Oct 1969 [15 Oct 1968] 50147/69 Headings H3T and H4T Signals derived from the electrical ignition system associated with an internal-combustion engine are displayed on a cathode-ray tube against a time-base which is initiated by closure of the breaker points of the system. This arrangement ensures that the display (Fig. 2) of the first part of the ignition voltage is not lost since the latter is initiated after the start of the time base on the subsequent opening of the breaker points. However a switching arrangement allows the time-base to be initiated when the breaker points open if such operation is required (Fig. 3). As shown in Figs. 1A and 1B a generator 65 produces a square wave output voltage which is positive when the breaker points 16, 17 open and goes to negative when the points close and this square wave is supplied (with the switches 115 in the position shown, which is for initiation of the time-base by the opening of the breaker points) via conductors 134 and 118 to an invertor circuit 124. This square wave is differentiated by capacitor 133 and the positive peaks, which coincide with the opening of the breaker points, trigger transistor 129 and produce a negatively going pulse at its collector and this pulse is supplied over conductor 136 and switches 115 to conductor 140 (via switch blade 110 and contact 138) and an amplifier 125 which responds only to a negatively going input to trigger the horizontal time base generator 126. When operation according to the invention is required switch blade 116 is moved to its upper contact and the square wave on conductor 118 is then supplied directly to conductor 140 without inversion and the negative portion of the pulse (contacts 16, 17 closed) operates via amplifier 125 to trigger the time-base 126. The length of the horizontal trace produced by the latter is a function of the rate of operation of the contacts 16, 17 (i.e. a function of engine speed) and to produce a trace of a required length the rate of charging of the time-base capacitor 143 may be controlled either manually by adjustment of potentiometer or automatically by setting switch blade 147 on contact 149 to switch in an automatic control circuit 128. A maximum of six horizontal traces, cyclically repeated, may be produced (i.e. one trace for each cylinder of a six cylinder engine) and any one trace may be selected for display. This is achieved by means of a six stage ring counter 45 which counts the pulses from generator 65 and is re-set by a pulse input at terminal 49 from a generator 66 controlled by a selected one of the spark-plugs or, with linked switches 69, 94, 99 set against their contacts, by a pulse from a generator 98 triggered by a secondary output 60, or 61 from the fourth and sixth stages of the counter 45 when switches 79 or 80 are actuated depending on whether a four or six cylinder engine is under test. To produce the actual display the output of the time-base generator 126 is supplied via the horizontal amplifier 120 to the horizontal deflection plates 37 of the display CRT 35 the vertical plates 38 of which are supplied from the vertical amplifier 160. The latter has two inputs 161, 162, input 161 being connected, with blade 113 (of switch 105) on contact 168, to the primary 11 of the ignition coil 10 via conductor 167 and potential divider 166, whilst input 162 is connected via potentiometer 182 to an amplifier 175 which, when energized over conductor 177 from a + 10V supply on switch blade 111 supplies a step waveform successive steps of which occur synchronously with successive horizontal time-base traces so that successive waveforms from the primary winding 11 and which are indicative of the firing condition of each cylinder are spaced vertically as shown in Fig. 4. The amplifier 175 forms part of a raster generator 170 which operates by repeatedly discharging a capacitor 173 (charged from the +20V source) through transistor 171 by the negative portion of each pulse from generator 65. The discharge path including a further capacitor 174 which receives an increment of charge for each discharge of capacitor 173 and these charge increments provide the step voltage input to amplifier 175. At the end of each cycle a pulse from generator 66 switches " on " transistor 172 which discharges capacitor 174 and a new cycle then commences. The vertical position of the trace may be adjusted by means of potentiometer 182 and by setting the slides 183 at the " earthy " end (zero vertical shift voltage) all of the traces may be displayed on the same horizontal trace. With switch 105 in the position shown (selector arm 106 on " Primary Pattern ") the display is produced, as described, by the waveform of the primary 11 of the ignition coil. By setting arm 106 on " Secondary Pattern " the waveform at the secondary 12 is supplied via a releasable contact 226, and conductor 233 and the various capacitors shown (which act as voltage dividers) to an amplifier 236 and thence to the input 161 of vertical amplifier 160 to provide a trace such as shown in Fig. 5, when only one cylinder is selected. In both the " Primary " and " Secondary " modes of operation the beam of the tube is normally blanked and unblanking of one or more of the traces is produced when one or more of the cylinders is selected for test by operation of the appropriate one(s) of switches 69-74. The blanking is effected by means of the output from a free-running multivibrator 212 the output of which is supplied over conductor 214 and the network including capacitors 216, 219, resistor 218 and diode 216 as a negative blanking pulse to the control grid 40 of the CRT over conductor 217. When a particular cylinder is selected by operation of switches 69-74 the pulse(s) from the appropriate stage(s) of counter 45 is/are supplied over conductor 68 and switch blade 109 to switch-" on " a transistor 213 which causes a negative voltage to be supplied to the base of transistor 270 in the multivibrator which is thereby prevented from oscillating and the blanking voltage is therefore no longer generated. In a third position of switch arm 106, termed " Parade ", the ignition waveforms (from the secondary coil 12) of all the cylinders of the engine are displayed on a single trace as shown in Fig. 7. This is achieved by interrupting the unblanking operation by means of switch blade 109, connecting the input to time-base amplifier 125 over conductor 140 to a pulse generator 243 over switch blade 110 and contact 246 and removing the operation potential from amplifier 175 by means of switch blade 11. Pulse generator 243 produces an output pulse on conductor 245 on the occurrence of an output from the stage of the counter 45 appropriate to four or six cylinder engines (i.e. outputs 60 or 61) depending on which of the switches 79, 80 is operated. The pulse from generator 243 thus triggers the time-base once for cycle of the engine and to increase the time constant of the charging circuit of the time-base generator switch blade 114 connects a further capacitor 248 in parallel with the time-base capacitor 143. In a fourth position of switch arm 106, termed " Power Check " tests are made with one or more of the sparking plugs short circuited. This is effected by connecting the breaker points 16, 17 across an SCR 257 via switch blade 108 contact 258 and a comparatively low valued resistor 260, the SCR being triggerd by the output of a Schmidt trigger 256 which is itself triggered via contact 261, switch blade 109 and conductor 68 by a pulse from the stage(s) of the counter 45 appropriate to the plug(s) to be short-circuited and selected by switches 69-74.