CC BY
5
УДК 05.22.10
Pirmatov N.B. professor
Tashkent State Technical University Mahamadjonov S. Yu.
assistant Arzikulov H.M. master
Andijan Institute of Mechanical Engineering CAR GENERATORS
Annotation: This article discusses the basic requirements for automotive alternators and the principles of generator operation.
Key words: generator, car, load, frequency, battery, voltage.
The electrical equipment of any car includes a generator - the main source of electricity. Together with a voltage regulator, it is called a generator set. On modern cars, alternators are installed. They most meet the requirements.
Basic requirements for car alternators
1. The generator must provide uninterrupted current supply and have sufficient power to:
- simultaneously supply electricity to working consumers and charge the battery;
- when all regular power consumers were turned on at low engine speeds, there was no strong discharge of the battery;
- the voltage in the on-board network was within the specified limits in the entire range of electrical loads and rotor speeds.
2. The generator must have sufficient strength, a large resource, small weight and dimensions, low noise and radio noise.
Basic concepts
Domestic developers and manufacturers of electrical equipment use the following concepts.
Car power supply system - designed for uninterrupted power supply of electrical appliances included in the vehicle electrical system. It consists of a generator set, a battery and devices that provide performance monitoring and protect the system from overloads.
A generator is a device that converts mechanical energy received from an engine into electrical energy.
Voltage regulator - a device that maintains the voltage of the vehicle's onboard network within the specified limits when the electric load, the rotation frequency of the generator rotor and the ambient temperature change.
Rechargeable starter battery (accumulator) - accumulates and stores electricity to start the engine and power electrical appliances for a short time (when the engine is idle or there is insufficient power developed by the generator).
The principle of operation of the generator
The generator is based on the effect of electromagnetic induction. If the coil, for example, from a copper wire, penetrates the magnetic flux, then when it is changed, an alternating voltage appears on the terminals of the coil. Conversely, for the formation of a magnetic flux, it is sufficient to pass an electric current through the coil. Thus, to obtain an alternating electric current, a coil is required through which a constant electric current flows, forming a magnetic flux, called an excitation winding, and a steel pole system, the purpose of which is to bring a magnetic flux to coils called a stator winding, in which an alternating voltage is induced. These coils are placed in the grooves of the steel structure, the magnetic circuit (iron package) of the stator. The stator winding with its magnetic circuit forms the generator stator itself, its most important fixed part, in which electric current is generated, and the field winding with the pole system and some other details (shaft, contact rings) - the rotor, its most important rotating part. The excitation winding can be powered by the generator itself. In this case, the generator operates on self-excitation. In this case, the residual magnetic flux in the generator, i.e., the flux that forms the steel parts of the magnetic circuit in the absence of current in the field winding, is small and provides self-excitation of the generator only at too high rotational speeds. Therefore, in the circuit of the generator set, where the field windings are not connected to the battery, such an external connection is introduced, usually through a lamp for monitoring the operational state of the generator set. The current flowing through this lamp into the field winding after turning on the ignition switch and provides the initial excitation of the generator. The strength of this current should not be too large so as not to discharge the battery, but not too small, because in this case the generator is excited at too high rotational speeds, so manufacturers specify the required power of the control lamp - usually 2 ...3 watts
When the rotor rotates opposite the coils of the stator winding, the "north" and "south" poles of the rotor appear alternately, that is, the direction of the magnetic flux penetrating the coil changes, which causes the appearance of an alternating voltage in it. The frequency of this voltage f depends on the frequency of rotation of the rotor of the generator N and the number of its pairs of poles p:
f=p*N/60
With rare exceptions, generators of foreign firms, as well as domestic ones, have six "south" and six "north" poles in the rotor magnetic system. In this case, the frequency f is 10 times less than the rotational speed i of the generator rotor. Since the rotor of the generator receives its rotation from the crankshaft of the engine, the frequency of rotation of the crankshaft of the engine can be measured by the frequency of the alternating voltage of the generator. To do this, the stator winding is output from the generator, to which the tachometer is connected. In this case, the voltage at the input of the tachometer has a pulsating character, since it turns out to be connected in parallel with the diode of the power rectifier of the generator. Taking into account the gear ratio i of the belt drive from the engine to the generator, the frequency of the signal at the input of the tachometer ft is related to the engine speed Ndv by the ratio:
f=p*Ndv(i)/60
Of course, in case of slipping of the drive belt, this ratio is slightly violated and therefore it should be ensured that the belt is always sufficiently tensioned. For p = 6, (in most cases) the above ratio is simplified ft = Ndv (i) / 10. The onboard network requires a constant voltage to it. Therefore, the stator winding feeds the vehicle electrical system through a rectifier built into the generator.
The stator windings of generators of foreign companies, as well as domestic ones, are three-phase. It consists of three parts, called phase windings or simply phases, in which the voltage and currents are offset from each other by a third of the period, i.e. 120 electrical degrees, as shown in Fig. I. Phases can be connected in a "star" or "triangle". In this case, phase and linear voltages and currents are distinguished. Phase voltages Uf act between the ends of the phase windings. I currents If flow in these windings, but the linear voltages Ul act between the wires connecting the stator winding to the rectifier. In these wires, linear currents Jl flow. Naturally, the rectifier rectifies those quantities that are supplied to it, i.e., linear.
Fig. 1. Schematic diagram of the
Ufl - Uf3 - voltage in the phase windings: Ud - rectified voltage; 1, 2, 3 -windings of the three phases of the stator: 4 -diodes of the power rectifier; 5 - rechargeable battery; 6 - load; 7 - diodes of the rectifier of the field winding; 8 - field winding; 9 - voltage
When connected to a "triangle", the phase currents to the root of 3 times less than linear, while the "star" linear and phase currents are equal. This means that with the same current given by the generator, the current in the phase windings, when connected to a "triangle", is much less than that of a "star". Therefore, in high-power generators, a
"triangle" connection is often used, since at lower currents the windings can be wound with a thicker wire, which is more technologically advanced. However, the linear voltage of the "star" in the root of 3 is greater than the phase, while the "triangle" has the same voltage to obtain the same output voltage, at the same rotational speeds the "triangle" requires a corresponding increase in the number of turns of its phases compared to "star".
Sources used:
1. Latest design and development aspects of engines for light commercial vehicles to meet future emission limits / M. Egert, W. Cartellieri, U.Veit, R. Walter. // F1SITA World Automotive Congress, Sept. 27-Oct. 1. 1998
2. Akimov S.V., Akimov A.V. Automotive gensets. M .: Transport, 1995
3. Akimov A.V., Akimov S.V., Leikin L.P. Generators of foreign cars.- M.: Publishing. "At the wheel", 1997
