Signaling device for non-optimal engine operation. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

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The device described in the article is designed to control the parameters of the breaker-distributor of the ignition system and the speed of the crankshaft of an automobile engine. When they deviate from the norm, light and sound signals are given, reminding the driver of the need to make appropriate adjustments to the breaker assembly or switch to another gear to reduce fuel consumption.

Most domestic passenger cars VAZ, AZLK, GAZ and ZAZ are equipped with a classic ignition system, the central unit of which is a breaker-distributor [1]. The traction characteristics of the engine and, consequently, fuel consumption depend heavily on its technical condition and adjustments. The main parameters of this node are the angle of the closed state of the contacts (UZSK) of the interrupter and their electrical resistance. The deviation of these parameters from the norm leads to a drop in the power of the spark, causing incomplete combustion of the fuel. The control of these parameters is rather complicated, so many car owners simply neglect it, preferring to pay for excessive fuel consumption and experiencing certain difficulties in starting the engine at low ambient temperatures.

Meanwhile, during the operation of the engine, the electrical signal from the interrupter (Fig. 1) contains all the information necessary not only to measure the above parameters, but also to measure the ultrasonic testing of all four cylinders. This makes it possible to calculate the deviations of the angles from the average value and, thus, to indirectly assess the condition of the interrupter cam and the degree of wear of its roller. (It should be noted that a malfunction can occur not only due to wear, for example, due to insufficient lubrication of the distributor parts, but also when the fastenings of the adjusting elements are loosened due to vibration). In addition, the signal from the chopper allows you to determine the speed of the engine crankshaft. If it is excessively small when driving with a gear engaged, or, conversely, excessively large, then the engine also does not work optimally and consumes excess fuel. This situation indicates the need to switch to a lower gear in the first case or to a higher gear in the second.

As can be seen from fig. 1, the contact resistance is characterized by voltage U0 (it is directly proportional to the resistance). UZSK a for each of the cylinders can be calculated (in degrees) by the formula α = 90ti1/(ti1+ti2); and the engine crankshaft speed F (in revolutions per minute) - according to the formula

where i is the cylinder number.

The circuit diagram of the signaling device is shown in fig. 2. Its basis is MK Z86E0208PEC (DD1), the clock frequency is set by the ZQ1 quartz resonator at a frequency of 8 MHz. The device is powered by a 12-volt car battery through a parametric voltage regulator R1VD1. To attenuate interference in the power circuit, an oxide capacitor C1 and a ceramic capacitor C2 are provided.

The input signal is fed through the amplitude limiter R2VD3VD5 to the output P32 of the port P3, which is the non-inverting input of one of the two built-in comparators MK [2] The signal from the integrating circuit R3C6, which provides the function of analog-to-digital conversion [ 2].

The result of the software processing of the received signals is displayed on the LEDs HL1, HL2 and the sound piezo emitter BQ1, connected directly to the pins P26 and P27 of port P2.

Based on the measurement results, the device generates the following signals:

- green light signal (HL2) when the resistance of the breaker contacts is sufficiently low and when the values ​​of the average value of the UZSK of the breaker and its spread for different cylinders are within the normal range;

- a red light signal (HL1) in case of deviation of the indicated values ​​from the norm, indicating the need for preventive maintenance or repair of the breaker-distributor;

- a sound signal when the engine speed is too low or too high, warning the driver to change gear (at low frequency - low tone, at high frequency - high).

Since the MC operates in conditions of strong interference, to prevent its accidental transition to the PROM programming mode, protective diodes VD2-VD4 and capacitor C5 are introduced into the device (in accordance with the manufacturer's recommendations).

Setting the device to work in a particular class of vehicles is carried out by switches SA1 and SA2 in accordance with Table. 1.

The operation of the device is illustrated by the transition graph shown in Fig. 3.

The graph includes four state vertices corresponding to the modes:

• T_MEAS - (MEASURE TIME) - time measurement;
• U_MEAS - (MEASURE U) - voltage measurement;
• CALCUL - calculation mode in which the measurement results are processed;
• DISPLAY - display mode of calculation results.

The transitions between states, shown by graph edges, are triggered by the following events:

• TI - (TIMER INTERRUPT) - interrupt from the MK timer;
• Fl - (FALLING INTERRUPT) - interrupt on the fall of the input signal;
• CI - (COMPARE INTERRUPT) - interruption from the comparator built into the MK;
• TE, UE, CE, DE - the end of the processes of measuring time, voltage, calculation and display, respectively.

After turning on the power, the MK auto-resets and the TMEAS state is initialized. Initially, interruption is allowed only on the input signal decay (see Fig. 1), and if there is a recession, the MC “captures” it and starts measuring time intervals. The timer interrupts are then enabled. By counting their number, the duration of the first time interval is calculated. When a signal front arrives at the input of the MK, the count value is stored and the measurement of the next interval begins. Similarly, the duration of all eight intervals is measured, after which the MC enters the voltage measurement state U0 (U_MEAS).

In this state, the MK generates a log potential at the output of P00. 1, due to which the formation of a quasi-linear rising voltage at the RZZ input begins using the R3C6 circuit. At the same time, the MK timer is started for a time corresponding to the level U0 \u0,2d XNUMX V. Interrupts from the timer and comparator are allowed. If the first interrupt comes from the comparator, then the fact of the normal state of the contacts is fixed, and if from the timer, then the state of the contacts is unsatisfactory.

Further, the device switches to the CALCUL mode, when the crankshaft speed, the average value of the UZSK and the amount of its deviation from this value are calculated. Moreover, the last two parameters are calculated only if the calculated frequency does not exceed 1000 min-1 (the nominal value of UZSK is measured only at idle). Upon completion of calculations, the program switches to the DISPLAY mode.

In this mode, the vehicle type code set by the SA1, SA2 switches is read, the calculated values ​​of the UZSK and UZSK unevenness are compared with the corresponding constants "hardwired" in the PROM, and based on the results of the comparison, an ignition signal of one or another LED is generated. Then, the “hit” of the current crankshaft speed within the selected boundaries is checked and, if it is outside the set values, the sound of the corresponding tone is turned on. Then the whole working cycle is repeated.

A printout of the program's boot module is shown in Table. 2. The amount of program code - 504 bytes.

(click to enlarge)

The details of the device are placed on a printed circuit board made according to the drawing shown in Fig. 4. The board is designed for the installation of MLT resistors, capacitors K50-35 (C1) and KM (others), switches PD9-2 (SA1, SA2), three-slot block KSK1.5-3. An 18-slot panel was used to connect the microcontroller.

Setting up the device begins with checking the supply voltage. To do this, without reinstalling the microcontroller, turn on the power and measure the voltage on pin 5 of its panel. It must be at least 4,5 V, otherwise the VD1 zener diode must be replaced with another one with the desired stabilization voltage. Then they check the serviceability of the LEDs (for this, contact 5 of the MK panel is connected in turn with its contacts 12 and 13 with a piece of wire).

Further, with the power off, the programmed MK is installed in the panel and the device is connected to the breaker terminal. If the device does not work when the power is turned on, an oscilloscope (with an input resistance of at least 6 MΩ) is connected to pin 1 of the DD10 microcircuit and check whether the MK clock generator is excited. The absence of oscillations of a sinusoidal waveform with a frequency of 8 MHz indicates that the generator is not working. In this case, you need to check the quartz resonator ZQ1 and capacitors C3 and C4.

In the car, the device is placed on the front panel in the driver's field of vision.

The functions of the device can be significantly expanded by using modifications of the MK with indexes 86, 0208 instead of the Z04E08PEC, which are compatible in terms of outputs and have large program and data memory resources.

Literature

1. Reznik A. M. Orlov V. P. Electrical equipment of cars. - M.: Transport, 1981.
2. Gladshtein M.A. Microcontrollers of the Z86 family from Ztlog. Programmer's guide. - M.: DODEKA, 1999.

Authors: M.Gladstein, M.Pudov, Rybinsk

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