Digital self-test.

Every year the number of cars equipped with electronic engine management system and transmission. To diagnose these systems developed and widely used various scanners and personal computers. However, at present in Russia remains in operation about 12 million so-called classic cars with carburetor fuel system and electronic or mechanical ignition switch. For such vehicles do not diagnostic systems. The system adjusts the ignition electrician «by eye» of the engine knocking. The best characteristics of centrifugal and vacuum regulators ignition timing can be checked on the scan stand. But for that distributor should be removed from the vehicle, which creates some inconvenience, and increases the time required for diagnosis.

It is possible to measure the rotational speed of an object through the use of stroboscopic effect. The device can be used stationary or while driving.

Specifications of the instrument: -Designed to work with the 4-cylinder petrol engine; A range of measurement of rotational speeds of the crankshaft of the engine from 240 to 6500 m; is the greatest relative velocity measurement error of 3%; -razgonnaya engine performance is determined in a range of speeds from 1,200 to 5,000 m; ignition timing angle is measured from 0 to 64 in increments of 1; -instrument supply voltage of 12 … 14V on-board vehicle network.

The device operates as follows. Electro inductive sensors cerebral palsy and WPS are connected to the high-voltage wire of the ignition coil and the first (fourth) cylinder engine, respectively. When the switch S1 in N mode is realized tachometer, while in LSB LED indicator lights vanish, and the remaining three digits — a three-digit number, which together with zero gives the value of the rotational speed of the engine crankshaft, rounded to 10 and expressed in minutes.

The basis of the tachometer is a 10-bit counter and a read only memory ROM, which serves as a code converter. Pulses ICP enter the trigger circuit, where a period of time accounts. During this interval, the counter counts the number of pulses required. The count is input to a code converter which converts a number in a binary code rate, reduced by 10 times. The higher the rotational speed of the crankshaft of the engine, the lower the number of pulses applied to the input of filling the code converter. The objective of the converter is to establish a one-to-one correspondence between the number of pulses and speed.

The speed is displayed after the end of counting time during each revolution of the crankshaft of the engine. This causes instability of the readings (bounce LSB). To eliminate it in the scheme introduced by the regulator avtotestera time display, which can delay the change of testimony at the time from 0 to 10.

One time programmable ROM available to the developer, have a 10-bit address bus and an 8-bit data bus. Therefore, to increase the data bus width of up to 10 to use two ROM chips, are connected in parallel address lines. In this case, two junior level will be two senior bits (8 and 9), a ten-digit number reflecting the number of revolutions of the crankshaft, divided by 10. In this connection it is necessary to program each ROM separately. For example, the decimal number 857 corresponds to the binary number 1101011001. considering separately the two MSBs and eight junior, you can see that 11 corresponds to the decimal number 3, and 01011001 — decimal number 89.

By brute force alone, and the two most significant bits of the eight junior 10-bit numbers in the range of 650 to 24, were found patterns that allow the ROM program to convert numbers counting pulses in the number of revolutions of the crankshaft. The results are summarized in the table.

From the table of numerical data, you can get information about the errors of the code converter. Sources of error are discrete pulses by filling ± 1 pulse of relevant data and rounding to the nearest whole number. The average relative error tachometer from a loss or excess of one count pulse depends on the number n of pulses counted during the counting. At speeds of 240 to 2550 m the error is 1%, at speeds from 240 to 2550 min — 2% at higher speed error increases to 2.7%. It follows that the tachometer can be used as an exemplary device for calibration of motor tachometers.

Catch the acceleration time to evaluate the dynamic qualities of the engine by sharp pressing a pedal throttle. The lower the acceleration time to the set speed, the better the ignition system and customized nutrition and the greater the power developed by the engine. For evaluation of this parameter in the unit interval allocated four rates: 1 — from 1200 to 2000 m; 2 — from 2000 to 3000 m; 3 — from 3000 to 4000 min, 4 — from 4000 to 5000 m. Locking ramp time can be measured, and stored in registers by the operator to transmit the SI time intervals for which the subject has developed the engine speed from the lower to the upper limit of the range.

The multiplexer connects the 4-times-row indicator SI to the output latch. MSB indicator allocated places, and on the lower one digit is displayed the symbol C (second). The unit of the acceleration time is 1/100 of a second. The maximum time that can lock the meter, 9.99 seconds. These values ​​occur during acceleration of a vehicle on the road or cross the stand. During acceleration the engine without a load value of the measured time menshe.Takzhe order as in the tachometer base latch circuit constitute a pulse-frequency converters, counts the number of pulses with a period of 0.01 seconds, part of the time interval between two successive pulses of cerebral palsy. The results of measurements of the acceleration in each of the four intervals are displayed on the digital indicator SI by successive pressing S2 (point number) located on the front panel.

Ignition timing is measured in degrees of crankshaft and measured from the true ground. Angle has a special name «ignition timing» (POPs). The angle is positive if the ignition of the working mixture occurs before the TDC and a negative — after TDC. Application stroboscopic method allows visualization of this angle by means of two tags, one of which is on the crankshaft pulley, and the second — on the engine block. These labels at the same time highlights the flash strobe light. The flash occurs at the time of the spark in the first (fourth) cylinder engine, which is fixed by the sensor of the first cylinder (WPS). Image 1 mark on a rotating pulley can be visually move to the label 2 by delay strobe lamps in relation to the time of formation of a spark in the first (fourth) cylinder. If this delay expressed as angular degrees, it is possible to quantify the CPP. The unit of CPP proposed to use the 1 degree. Degrees corresponds to 1/180 of the cycle time of cerebral palsy. In order to measure POPs at any speed of rotation of the crankshaft, it is necessary as part of the control unit have strobe divider cycle time by a factor of division ICP 180. Then at any engine speed between two adjacent pulses cerebral palsy will be placed 180 counting pulses that form a variable frequency generator .

When you turn on the device SCH1 and SCH2 counters are reset. Code values ​​A and B at the inputs of the comparator code KK zero. Encoder pulses of the first cylinder (WPS) switch logic and output of the counter is set zero SCH2 code A is also zero. At this point the output QC the impulse equality A = B, which initiates a stroboscopic flash lamp. The next pulse of the first cylinder gives a second flash, and so on. Eye operator sees the starting position marks 1 and 2. The operator, press «Account», located on the handle of a stroboscope. Each press of a single pulse generator (IEF) is input to a pulse counter SCH1. A code value increases by one. The total number of clicks is induced on two-digit digital display cm2. On the counter input SCH2 pulses of divider slot. Their number is displayed code B. when A = B, code comparator will enable impulse stroboscopic lamp. But now the lamp turns on with a delay of the number of pulses IEF and as each pulse corresponds to 1 °, the one label image is approximated to the label 2 and corresponding number of aligned taps with it. Digital display shows Cu2 POPs in whole units of degrees. The measurement error is 1 degree POPs.

The measuring function of the angular velocity of any rotating object is carried out by incorporating the S5 and the direction of the beam strobe light on the object. The frequency of the internal oscillator is measured by a tachometer, and served on the strobe. At the time of stop motion picture visual indicator SI1 shows the angular velocity of the object. This feature of the device may be useful in the diagnosis of diesel engines.

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