Shaper of the optimal ignition timing. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Shaper of the optimal ignition timing. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Ignition

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The problem of obtaining maximum power from an internal combustion engine is of interest to many motorists. To increase engine power, you can bore and polish fuel lines, adjust their joints with the combustion chamber, boost, etc. But, besides this, there is another way to increase engine power - minimizing losses due to maintaining the optimal ignition timing (UOZ) over the entire range of crankshaft rotation speed (KB).

Most of the "western" firms solved this issue long ago - the on-board computer controls and controls all processes in the operation of the engine. In the domestic automotive industry, this issue was not given due attention and, as a result, the characteristic of the UOS, formed by a centrifugal regulator installed on almost all domestic cars, coincides with the optimal characteristic at best in 2-3 points (Fig. 1) In some areas, it may differ from the optimal by more than 30%, and with long-term operation of the car, this value increases.

Shaper of the optimal ignition timing
Ris.1

The amateurs were the first to react to this. Thanks to them, quite simple schemes of ignition advance correctors appeared. Their work is based on the principle of forming an adjustable time interval for which sparking is delayed. so much so that it does more harm than good. Therefore, some authors turn off the correction at KB speeds above 2000-2500 rpm.

The next step was the creation of correctors, the principle of operation of which was based on the formation of a directly regulated SPD. formed by a centrifugal controller. Therefore, the next step is to abandon the use of a centrifugal controller and create optimal SPD generators based on a ROM containing codes for the optimal SPD distribution depending on the rotational speed CV. One of these devices is described below.

The operation of the device is based on the principle according to which the optimal characteristic of the UOS in the entire range of engine operation (from 600 to 6000 rpm) is divided into 256 sections. On each section, the value of the UOZ is encoded in the range from 0 to 256 and recorded in a ROM with a capacity of 256 bytes. operational displacement of the specified characteristic along the vertical (smooth) and horizontal (stepped) axes, which makes it possible to adapt it to different types of engines and different brands of gasoline.

(click to enlarge)

Circuit operation

The shaper circuit is shown in Fig. 2.

His work can be divided into three stages.

- the stage of measuring the angular frequency of rotation KB - the stage of the formation of an adjustable UOS (vertical adjustment)

- the stage of formation of the optimal SPD.

The first stage begins when a high logic level is received from the magnetic sensor at the input of the device. In this case, the integrating circuit C4 R6 generates a pulse along the leading edge of which the generator (G1) assembled on DD1 3 starts to work

Pulses with a frequency f1 through D3 3 are fed to the input of cascade-connected counters DD4, DD5, working to increase the count and accumulate information about the duration of the input pulse. Upon completion of the input pulse, information about its duration (that is, about the value of revolutions KB) from the outputs DD4 DD5 in binary code enters the address inputs of the ROM In the ROM, in accordance with the received address, a time delay code is generated corresponding to the optimal UOS (for the measured value of revolutions KB) This code is written in binary form in parallel to the registers of the counters DD7, DD8 by a pulse generated by the C7 R9 chain At the same time, the generator G1 is blocked by the generator G2 assembled on DD1 4 begins to generate pulses with a frequency f2 and the counters DD4 DD5 start to work to reduce the count, i.e. it begins the second stage.

It should be noted that at the first stage in the engine start mode (at KB revolutions below 600 rpm), the counters DD4 DD5 overflow. in turn, blocks the operation of the counters DD7, DD5 with the maximum information recorded in them (code 2) In this state, the circuit is until the end of the input pulse on the decline of which a negative pulse is formed through the integrating chain C3 R3, which writes the code 2 to DD1 DD4 Simultaneously through the chain C5 R255 is reverse switching trigger T7 and allowed to work on the subtraction of counters DD9 DD255.

When the counters D4, D5 "count down to zero, a short negative pulse is generated at pin 7 of the counter DD5, switching trigger T1, which in turn blocks the operation of the counters DD4, DD5 and enables the operation of DD7, DD8. At this, the second stage ends and the third begins .

Counters DD7, DD8 with the information recorded at the end of the first stage work for subtraction. According to the T1 trigger enable signal coming through the DD2.1 element, they begin to perceive the pulses generated by the GZ generator assembled on DD1.1, and when it reaches zero, they generate a negative pulse (at pin 7 of DD8), switching the trigger to DD3.1, DD3.4 (T2), which in turn through DD2.1 blocks the counters DD7, DD8, and through VT1 generates a delayed output signal.

Timing diagrams of the circuit operation are shown in Fig.3.

Shaper of the optimal ignition timing
Ris.3

Characteristic points of diagrams:

O - the beginning of a positive input pulse, allowing the counters DD4, DD5 to increment until the end of the input pulse or until they overflow;

1 (only for the engine start mode) - the contents of the counters DD4, DD5 have reached the maximum (255); blocking DD4, DD5 until the end of the input pulse;

2 - recording the contents of DD4, DD6 through the code converter DD6 to DD7, DD8; end of work G1; reset blocking DD4, DD5 and the beginning of their work from G2 to subtract;

3 - the content of DD4, DD5 has reached zero, and their work is blocked; work permit DD7, DD8;

4 - the content of DD7, DD8 has reached zero, and their work is blocked; a signal is formed on the VT1 collector, on the leading edge of which ignition occurs;

5 - top dead center of the corresponding piston;

6 - reset blocking DD4, DD5; start of the next cycle.

To set up the device, it is necessary to know two parameters: - the length of the pulse emitted by the magnetic sensor, expressed in angular values (degrees) relative to the rotation period KB; - the optimal characteristic of the UOS (dependence on the speed of the KB). Since this characteristic is specific to different cars, there are two ways to do it.

The first method.

Using the free address bits of the used ROM (A8, A9, A10), switched by switches S1 ... S3 (Fig. 2), we write into it 8 options for characteristics obtained by shifting along the horizontal axis every 50 ... 100 rpm of the original characteristic 2 (Fig. 1), which is typical for many cars. After that, operating the switches S1 ... S3 and the regulator R2, in the course of numerous tests, according to subjective characteristics, we determine the most suitable one. It should be noted that when switching to gasoline with a lower octane number, it is necessary to switch to a characteristic that is located to the left of the original one, and vice versa. Having found the most suitable characteristic, it is advisable to rewrite the ROM, again shifting the obtained characteristic, but with a smaller step, for example, after 20 ... 30 rpm, while the choice of the required brand of gasoline is made by switches S1 ... S3.

The disadvantages of this scheme include the low stability of the generators. To increase it, generators need to use resistors with a minimum TCR and capacitors with zero TKE (MPO groups). For the same reason, it is better to place the device in the passenger compartment, where temperature differences are less than under the hood.

To reduce interference on the power outputs of each microcircuit, it is advisable to install ceramic capacitors with a capacity of 0,1 μF, and with long switching connections at the input of the DD1.2 microcircuit, the simplest low-pass filter with a time constant of about 0,01 ms (for example, R = 30 kOhm, C = 300 pF). In addition, in some instances of the counters, when the fronts of the counting and control signals coincide, as well as when the count passes from one stage to another, malfunctions occur. To eliminate this phenomenon, it is necessary to install capacitors with a capacity of 100 ... 200 pF between terminals 6 DD2, 7 DD8 and a common power wire.

The shaper is installed in the gap between the magnetic camshaft speed sensor and the electronic ignition system. When installing the shaper, the shutter of the standard centrifugal regulator must be locked in the position corresponding to the maximum rotation speed of the CV.

Additionally, to organize an anti-theft function, it is convenient to use a resistor R2 with a switch that is connected in series with the regulator. When the contacts of the switch are opened in the extreme position R2, the engine will not start. For these purposes, you can also use a code lock, the output of which must be connected to the outputs of 9 counters DD4, DD5. When typing the correct code, the specified outputs should receive a low logic level.

Authors: V. Petik, V. Chemeris; Publication: N. Bolshakov, rf.atnn.ru

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