The simplest ZSK angle meter. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Automobile. Ignition

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It is known that the optimal power characteristics of a car engine with a traditional contact ignition system can be achieved (ceteris paribus) only in the case of a correctly selected time of the closed, and hence the open state of the contacts of the ignition system interrupter. This is important because the closed time actually determines the amount of energy stored by the ignition coil in each sparking cycle, and the open time determines the burning time of the fuel mixture. With an electronic ignition unit, an incorrectly set status time can lead to malfunctions in the start of the ignition system.

Unfortunately, most motorists underestimate the factor noted above. Usually, the gap between the contacts of the breaker (namely, the time of the closed state of the contacts depends on the size of the gap) is set "by eye", without using any devices. It is clear that such an approach can lead to a drop in power and loss of engine efficiency. The magazine reported more than once about the options for solving this important problem. The author of the article offers another solution to it.

The time of the closed state of the contacts (ZSK) of the breaker is usually judged by the angle by which the shaft of the breaker-distributor of the engine rotates during this time. The angle of rotation is conveniently determined through the average value of the voltage Ucp, measured, for example, at the contacts of the chopper [1]. This voltage decreases linearly with increasing angle, so the reading on the voltmeter scale must be carried out in the opposite direction, in accordance with the formula (valid in this case for a four-cylinder engine):

αzsk (deg.) = 90 (Uct-Ucp) / Uct (1).

A simplified electrical measurement circuit (it is used in an industrial autotester) is shown in the figure.

The method described in [1] for measuring the SC angle does not require preliminary calibration of the device when servicing any vehicles, but has a significant drawback - the need for a "reverse" scale of the device and its preliminary digitization. In fact, the device measures the angle of the open state of the contacts.

You can measure the angle of the ZSC and a conventional DC voltmeter, as described in [2]. In this case, the average voltage is measured at the low voltage terminals of the ignition coil. The process is carried out in two steps - first, with the engine running, the voltage Ub.s of the on-board network is measured, and then the average voltage Ucp is measured at the ignition coil terminals. Then the angle of the ZSK (in degrees) for a four-cylinder engine will be equal to: αzsk=90Usr/Ub.s (2). The scale of this device is straight, and it measures the angle of the ZSK.

The advantages of this method are obvious, but it is associated with the need for calculations, which, of course, is inconvenient in most cases. In the case under consideration, it is impossible to do without calculations, because the voltage of the on-board network, even on one car, can change for many reasons, but on different cars it is always different. And this means that there can be no constant graduation of the αzsk scale in principle.

Nevertheless, there is a way to directly measure the angle of the ZSK with a conventional, widespread DC voltmeter (avometer) that performs the function of an integrator.

Let us return to formula (2) and rewrite it in a slightly different form:

αzsk=90nср/n6.с (3),

where n6.s is the number of divisions of the voltmeter scale by which the arrow deviated when measuring U6.s and nav is the same when measuring (on the same scale). We take n6. with a constant value. In this case αзк=К.nср (4), where К=90/n6.с=const.

Thus, we obtain a linear equation with a constant coefficient showing how many degrees of the angle of the ZSC fall on one division of the scale. It is easy to see that if K = 1, i.e. nb.s is taken equal to 90 divisions of the scale, then nav will directly reflect the angle of the ZSC in degrees:

αesc=1ncp(5).

In practice, it is usually not required to measure the angle of the WSC in the range from zero to the maximum pointer deflection. It is quite enough to select on the scale a section of permissible (recommended) angle values, and this section can be calculated and plotted on it in advance, provided that the number nb.s will then be unchanged for all measurements. The absolute value of pb.s can be taken by anyone, but to reduce the measurement error, it should be chosen at the end of the scale and preferably such that K is an integer. Therefore, the voltmeter scale, which has 90 or 100 divisions, is very convenient, which allows direct reading of the ZSC angle in accordance with (5), although (4) shows that a wide variety of scale options are possible.

As a device for measuring, any ready-made DC voltmeter or avometer is suitable, having, among others, subranges of 0 ... 1 or 0 ... 10 V. Connect the device to the circuit under study through a series variable resistor (rheostat); it is built into the body of the voltmeter, bringing the handle to one of the side walls, or made out as a separate attachment.

The resistance of a variable resistor (in kiloohms) can be approximately calculated using the formula:

R \u1,5d 103- 6 (UXNUMX C-Unp) / Ip.o,

where Unp is the limit of the voltmeter scale used, V; Ip.o - current of the total deflection of the arrow, μA.

The process of measuring the WSC angle does not fundamentally differ from that described in [2], but contains one new operation. When measuring the voltage Ubs with an additional variable resistor, set the voltmeter needle to a pre-selected value nbs (and this is done for each measurement of the ZSK angle), after which the angle itself is measured by directly reading its value on the scale.

In the most general case, the scale of the instrument, after selecting the value, is calibrated or marked within the required limits according to formula (4). To increase the objectivity of measurements, the installation of nbs and the reading of ncp should be carried out at stable low engine speeds.

The error in measuring the angle of the WSC depends mainly on the accuracy class of the pointer device used and is usually within 3 ... 5% (the accuracy of 2% indicated in [0,3] is erroneous). This is quite enough, since the technical conditions allow for a rather significant spread in the values ​​of this angle (for a Zhiguli engine, for example, 52 ... 58 degrees). It is practically impossible to set the angle of the ZSK with an error of less than 2 ... 3 degrees due to the backlash of the engine mechanism.

For those who have already repeated the device described in [2], I advise you to re-enter the sub-range 0 ... 1 V into it and build in a variable resistor that ensures that nbs is set near the end or at the end of the scale. When making a voltmeter on your own, you can use microammeters with a full deflection current of the needle from 50 to 500 μA and a resistance of 200 to 2000 ohms. With a scale that is inconvenient in terms of graduation, I recommend highlighting on it only the sector of the required (permissible) values ​​of the ZSK angle, and designate the extreme sections as "More" or "Less". The sector boundaries are determined by formula (4), and nbs is chosen at the end of the scale. In the simplest case, the calculated angle values ​​are simply recorded on the front panel of the instrument.

For a voltmeter, two sub-ranges are quite enough: 0 ... 1 and 0 ... 15 V (or 0 ... 20 V), and the first of them can generally be assigned only for measuring the angle of the ZSK.

The described device provides the setting of the angle of the ZSK of the breaker of the battery ignition system with the required accuracy, which was verified by the author in practice. If the car is equipped with an electronic ignition unit, it is necessary to temporarily return to the battery system to set the angle.

Literature

1. Zatulovsky M The device of a motorist. - Radio, 1981, No. 2, p. 21, 22.
2. Khukhtikov N. A simple device for a car enthusiast. - Radio, 1994, No. 2, p. 34, 35.

Author: G. Karasev, St. Petersburg

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