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Spark start delay assembly. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Ignition

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Light domestic motorcycles with a single-cylinder engine ("Minsk", "Voskhod", "Owl", "Courier") are equipped with an alternator and a contactless electronic ignition system. To simplify the design, the ignition timing is set constant, optimized for average crankshaft speed (rotational speed - 2000 ... 2500 min "1). This leads to a number of negative consequences, of which, perhaps the most unpleasant and even dangerous is strong recoil ( Kickback) of the starter lever into your leg when starting. Kickback can be very painful and can result in serious injury.

The reason for the described phenomenon is the occurrence of an ignition spark too early for the starting mode of the engine (500 ... 600 min "1). Setting a smaller ignition timing would eliminate the kickback of the start lever and make it easier to start the engine, but then it will not pick up speed well, lose power will smoke and overheat.

It is possible to get rid of kickback when starting the engine, without impairing its operation at high speeds, by introducing a spark delay only for the time of starting. For this purpose, I propose to use a simple device, the circuit of which is shown in the figure. It does not require any alterations of the generator and the ignition unit, but effectively solves the problem.

Spark Start Delay Assembly

The ignition unit is connected to the generator with three wires using a detachable knife-type connection. The letter "0" indicates the wire from the generator winding, "D" - from the induction ignition pulse sensor, "M" - common. The shape of the sensor pulses is close to rectangular. By the positive difference of these pulses, the switching trinistor of the ignition unit opens, which together with the ignition coil forms high-voltage ignition pulses.

The duration of the sensor pulses is such that if the trinistor is opened by the negative drop of the same pulses, this will ultimately provide the necessary spark delay. In other words, there will be a decrease in the ignition timing. The resulting ignition delay is sufficient for easy starting and idling of the engine.

The principle of operation of the described node consists in the appropriate conversion of pulses from the ignition sensor. The amplitude of the sensor pulses is approximately proportional to the crankshaft speed, and the pulse frequency is equal to the speed, so the R1C2 integrating circuit provides effective normalization of the signal amplitude supplied to the converter assembled on the DD1 chip. In addition, the R1C2 circuit suppresses parasitic pulses of smaller amplitude that occur at the output of the sensor in pauses between workers due to the design features of the generator. It also creates an additional small time delay (about 1,7 ms).

The Schmitt trigger DD1.1 generates rectangular pulses at the output with a steep rise and fall. Resistor R3 protects the trigger from voltage surges from the ignition pulse sensor. According to the positive differences in the Schmitt trigger pulses (i.e., according to the decays of the ignition sensor pulses), the differentiating circuit C3R4 and the trigger-inverter DD1.2 form short (about 25 μs) negative pulses. Such a short pulse duration was chosen in order to reduce the average current consumed by the node.

These pulses, after being inverted and boosted by four inverters DD1.3-DD1.6, connected in parallel, are fed to the ignition unit through the current-limiting resistor R5 and the contacts of the pressed button SB1. When the button is released, the signal from the sensor comes to the ignition unit bypassing the delay unit.

The node is powered from the on-board network through a half-wave diode rectifier VD1 and a parametric stabilizer VD2R2. Capacitors C1 and C4 are smoothing.

Immediately before starting the engine, the SB1 button is pressed, and after the engine starts, the button is released.

Given the lack of free space on a motorcycle, when choosing parts for the manufacture of the device, preference should be given to the smallest. Capacitors C2, C3 must have a temperature stability no worse than NZO. If it is supposed to use imported capacitors C2 and C3, then they must be with a dielectric no worse than X7R. There are no other detail requirements. Zener diode 1N4734A can be replaced with KS156G. Button SB1 -KM1-1.

The MC14584 chip can be replaced with its analog CD4584; MC14106 and CD4106 microcircuits are also suitable - six Schmitt triggers. The use of domestic microcircuits KR1564TL2 and K561TL1 is not excluded, but in this case, before applying pulses to the SB1 switch, they must be amplified in current. To do this, you will have to assemble an output emitter follower on a KT315E (or KT3102B) transistor.

I assembled the assembly in a miniature telephone jack housing (with one connector). Installation - hinged, on the conclusions of the microcircuit. I removed the wires and contacts from the socket, and used the screws to fix the input and output harnesses. After checking for operability, the installation was filled with epoxy compound. The finished assembly was placed near the connector of the ignition unit.

The button is most conveniently placed on the left handlebar, under the light switch, on the L-shaped bracket.

If, when the button is pressed, the running engine runs only at idle and stops when trying to add speed, it is necessary to replace the resistor R1 with another, less resistance.

The operating experience of the spark delay assembly has shown its good reliability and effective elimination of backstrokes. Despite the fact that these shocks have not completely disappeared (obviously, there are other circumstances that contribute to their occurrence, for example, a lean combustible mixture), the process of starting the engine has become much more comfortable - instead of frequent and strong shocks, there are occasionally rather soft shocks. This, by the way, made it possible to set the ignition timing earlier than recommended by the manufacturer of the car, and get a noticeable increase in its speed and acceleration dynamics.

Author: F. Kasatkin, St. Petersburg; Publication: radioradar.net

See other articles Section Automobile. Ignition.

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