Switchboard: what is it? Switch circuit, control and faults

In various technical texts, the term "commutator" can be found. What it is? In the most general sense, it is a device for switching electrical circuits (signals), which can be electronic, electron beam or electromechanical.

In a narrow sense, this is usually called the ignition switch, which is equipped with any vehicles with gasoline engines. This article is devoted to this variety of switches, mainly automotive ones.

Background of ignition systems

As is known, in each cycle of operation of a gasoline internal combustion engine, there is a stage of preparing a fuel-air fuel mixture and a stage of its combustion. But to burn the mixture, it needs to be set on fire.

The first solution used in the earliest automotive ICEs was ignition of the mixture from the calyx tube inserted into the cylinder and preheated before starting the engine. During its operation, the temperature of this tube was constantly maintained by the mixture burning in each cycle of operation.

It is interesting that the spark ignition system from magneto was used in parallel with the ignition of the car engines, but first only for industrial gas engines. This principle was quickly adopted and the automakers, and after the invention of R. Bosh in 1902 the usual spark plug spark system has become generally accepted.

Principle of spark ignition

Currently, the most common battery ignition system containing a current source in the form of a car battery at start-up and an automobile generator with the engine running, an ignition coil that is a transformer with a high-voltage secondary winding to which a spark-ignition spark plug is attached and an ignition distributor . The operation of the switch consists in the periodic interruption of the primary winding circuit of the ignition coil. With each such current interruption, its magnetic field, existing at the points of space occupied by the wires of the secondary winding of the ignition coil, decreases very rapidly. In this case, according to the law of electromagnetic induction, a very large vortex electric field appears at the same points in space , the intensity of which creates a high (up to 25 kV) EMF in the secondary winding of the ignition coil broken by the spark plug electrodes. The voltage between them quickly reaches a value sufficient for the breakdown of the air gap, and then an electric spark ignites the fuel-air mixture.

What is commutated in the ignition system?

So, the car switchboard. What is it and why is it needed? Briefly speaking, this device, whose task is to break the current circuit in the primary winding of the ignition coil at the most favorable moment for this.

In the four-stroke ICE, this moment occurs at the end of the compression stroke (the second stroke of the ICE), shortly before the piston reaches the so-called top dead center (TDC), in which the distance from any point of the piston to the axis of rotation of the engine is maximal. Since the crankshaft performs a circular rotary motion, the moment of the current interruption is tied to a certain position before reaching the TDC position with the piston. The angle between this position of the crankshaft and the vertical plane is called the ignition timing. It varies from 1 to 30 degrees.

Given the story, the question: "Car commutator: what is it?" - It should be answered that this is first mechanical, and later, as technology develops, an electronic current interrupter in the ignition coil.

Mechanical precursor of the ignition switch

Actually, this device began to be called a switch only in recent years, after it became fully electronic. And before, since 1910, when the auto-ignition system appeared on the Cadillac cars for the first time, its function, along with other tasks, was carried out by a distributor-distributor (trampler). This duality of the name arose because of its dual function in the ignition system. On the one hand, the current in the primary winding of the ignition coil must be interrupted - hence the "breaker". On the other hand, the voltage of the high-voltage coil of the ignition coil should be alternately distributed among the candles of all the cylinders, with the required advance angle. Hence the second half of the name - "distributor".

How did the tramblers work?

The interrupter-distributor has an internal shaft rotatable from the crankshaft, on which a dielectric rotor-slider with a rotating current-carrying plate at its end is fixed. A spring-loaded carbon brush slides over the plate, connected to a high-voltage central contact in the distributor cap, which in turn is connected to the secondary coil of the ignition coil. The current-carrying plate periodically approaches the contacts of the high-voltage wires located in the cap of the trambler, going to the candles of the cylinders. At this moment, a high voltage arises in the secondary winding of the coil , which breaks through two air spaces: between the current-difference plate and the wire contact to this candle and between the candle electrodes.

On the same shaft are installed cams, the number of which is equal to the number of cylinders, and the protrusions of each cam open simultaneously with the connection of a particular candle the contacts of the current interrupter included in the primary circuit of the ignition coil.

To prevent sparks from opening between the breaker contacts, a large capacitor is connected in parallel. When the contacts of the breaker are opened, the EMF induction in the primary winding causes the capacitor to charge current, but due to its high capacitance, the voltage on it, and therefore also between the open contacts, does not reach the value of air breakdown.

And what about the angle of advance?

As is known, when the crankshaft rotational speed is reduced, the mixture in the cylinders must be ignited in the compression stroke later, just before the TDC itself, i.е. The ignition timing must be reduced. On the contrary, when the speed of rotation is increased, the mixture in the compression stroke must be ignited earlier, i.e. Advance the angle of advance. In the tumblers, this function was performed by a centrifugal regulator mechanically connected to the cams of the current interrupter. He turned them on the distributor shaft in such a way that they opened the breaker's contacts early or later in the compression stroke of the mixture.

Changing the angle of advance is also necessary at a constant frequency, when the load on the engine changes. This work carried out a special device - a vacuum ignition controller.

The appearance of the first switches

By the end of the 70s of the last century it became clear that the weakest node of the trambler is the contacts of the breaker, through which the full current of the primary winding was flowing. They constantly burned and went out of order. Therefore, the first solution was a special electronic circuit of the switch for interrupting the current in the coil. In its input low-current circuit included wires from the terminals of the traditional contact breaker of the trambler. However, now his contacts were interrupted by not a full current of the ignition coil, but a small current in the input circuit of the commutator.

Actually, the electronic switch was structurally executed in a separate unit and was connected (at the request of the driver) to a classic tracer. Such an ignition system is called a contact electronic. It was very popular in the 80s of last century. And in our time you can still find cars equipped with it.

The circuit of the switch of the contact electronic system was assembled on transistors.

The next step is the rejection of the contact breaker

The contact current interrupter, even in the low-current version, used in the electronic ignition system, remained a very unreliable node. Therefore, the automakers made considerable efforts to exclude it. These efforts were crowned with success after the creation of a non-contact sensor-distributor based on the Hall sensor.

Now, instead of a few cams on the distributor shaft, a cylindrical hollow screen with slots and shutters between them is installed, the number of curtains and slots being equal to the number of cylinders of the engine. Curtains and screen slots move in a magnetic field created by a permanent magnet, past the miniature Hall sensor. While the screen curtain is moving past it, the output voltage of the Hall sensor is missing. When the curtain is replaced by a slit, the front of the voltage pulse is removed from the Hall sensor by an electronic circuit, indicating the need to interrupt the current in the primary winding of the ignition coil. This voltage pulse is transmitted via wires to the current switch unit in the ignition coil, where it is pre-amplified and then used to control the main power switching stage.

Another variant of the non-contact sensor-distributor is a unit with an optical sensor, in which a phototransistor is used instead of the Hall sensor, and instead of a permanent magnet, an LED. The optical sensor has the same rotating screen with slits and curtains.

The appearance of the switch as such

So, in a contactless ignition system, instead of one contact trambler, there are two separate nodes: a contactless (but only low voltage) distribution sensor and an electronic switch. The function of the distribution of the high voltage on the spark plugs in the sensor-distributor is still performed by a mechanical rotor-slider with a current-carrying plate.

And what about the adjustment of the angle of ignition? These tasks are still performed by the centrifugal and vacuum regulators in the sensor-distributor. The first of them now turns on the shaft is not cams, but shifts the screen curtains, thereby changing the angle of ignition. The vacuum controller has the ability to shift the Hall sensor with its support plate, also adjusting this angle.

Considering the above, to the question: "Modern car commutator: what is it?" - it should be answered that this is a structurally separate electronic unit of the contactless ignition system.

Failure to distribute high voltage

The longest time in the switchboard was a mechanical high-voltage voltage distributor on the candles of the cylinders. The most interesting thing is that this site was quite reliable and did not cause much criticism. However, time does not stand still, and at the beginning of this century, the switching circuit of the switch has undergone yet another major change.

In modern cars there is generally no distribution of high voltage from one coil to different candles. On the contrary, in them the coils themselves "multiplied" and became the accessory of the candles of each cylinder. Now instead of contact switching of candles at high voltage, contactless switching of their coils on low voltage is performed. Of course, this complicates the circuit of the switch, but the possibilities of modern circuit technology are much wider.

In modern cars with injector engines, the switch is controlled either by an autonomous engine control unit or by an on-board computer of the car. These control devices analyze not only the rotational speed of the crankshaft, but many other parameters that characterize the fuel and coolant, the temperature of the various components and the environment. Based on their analysis in real time, the timing of the ignition timing changes.

Switch Faults

The most common malfunction of the mechanical toggle is the ignition of its contacts: both moving and high-voltage contacts of the candles. To prevent this from happening (at least not too quickly), you should regularly inspect them, and if they have formed a deposit, it should be removed with a nail file or a fine sandpaper.

If the capacitor, which is connected in parallel to the contacts of the breaker, or the resistor in the circuit of the central high-voltage electrode fails, they can be replaced.

Malfunctions of the electronic switch, caused by the failure of the Hall sensor pulser or the coil current switch, are usually not eliminated, since such a switch is not collapsible. In this case, as a rule, the faulty unit is simply replaced with a new one.

How to test the switch?

If the engine's idling speed "floats", or it stalls on the fly, or does not start at all, you should check for a spark on the spark plugs connected to the ignition distributor with the Hall sensor. To do this, you need to unscrew them, put on the tips of the armored ones, put the candles on the "mass" and "spin" the crankshaft with the starter. If there is no spark or it is weak, you need to go to the switch.

But how to test the switch? It is necessary to turn on the ignition and evaluate how the arrow of the voltmeter deviates. If the switch is functional, then it should deviate in two steps. First, the arrow takes some intermediate position, in which there are 2-3 seconds, and then goes to the final (regular) position. If the arrow immediately occupies the end position, then you can try to replace the switch.

Switch connection

How to connect the switch to a non-contacting ignition system? It should be remembered that its terminal block is connected by two wires to terminals "B" and "K" of the ignition coil, a three-wire harness with a connector to the Hall sensor on the distributor and one wire to the "mass". With the "+" terminal of the battery, the switch circuit is connected to the "B" terminal of the coil.