Abstract
A hybrid car is a car used to drive the drive wheels more than one energy source.
Hybrid car called the vehicle driven by using the hybrid power plant. A distinctive feature of the hybrid power plant is to use two or more sources of energy and their corresponding engines that convert energy into mechanical work. Some sources of information used, the term "hybrid engine", which from a technical point of view is incorrect.
Despite the diversity of sources of energy (thermal energy of gasoline or diesel fuel, electricity, compressed air energy, the energy of the compressed liquefied gas, solar energy, wind energy, etc.) on an industrial scale for hybrid cars use a combination of internal combustion engine and electric motor.
General Description
The main advantage of a hybrid car is a substantial reduction in fuel consumption and emissions of harmful substances into the atmosphere, which is achieved by:
- coordinated work of the engine and the electric motor;
- using a large capacity battery;
- using braking energy, the so-called regenerative braking that converts kinetic energy of motion into electrical power.
However, in hybrid cars used many other innovations that will help conserve fuel and protect the environment, including variable valve timing system; stop-start system; EGR; heating system coolant exhaust gases; improved aerodynamics; electric accessories (water pump, aircon, power steering, etc.); Tyres with reduced rolling resistance.
It should be noted that the larger the effect of hybrid cars is observed when driving in town cycle, which is characterized by frequent stops work at idle. When driving at a constant high speed (extra urban) hybrids are not as effective.
Depending on the nature of the interaction of the combustion engine and the electric motor distinguish the following scheme hybrid propulsion systems: serial, parallel, series-parallel.
Sequential scheme of a hybrid vehicle
In series connection car driven by an electric motor. The internal combustion engine is connected only to the generator which in turn feeds the electric motor, and charges the battery.
In the hybrid vehicle with the serial circuit power plant typically provides the ability to connect to the mains at the end of the trip. These vehicles are called Plug-in Hybrid (literally - connected hybrid). Implementation of this function is to use higher capacity batteries (lithium-ion batteries), leads to a reduction in the use of the internal combustion engine and thus reduce emissions.
Representatives of Plug-in Hybrid cars are Chevrolet Volt, Opel Ampera. They are also called electric vehicles with extended-range (Extended Range Electric Vehicle, EREV). These vehicles have the possibility of up to 60 kilometers and up battery power 500 km power generator driven by the engine.
The parallel scheme of a hybrid car
In a parallel circuit the motor and the internal combustion engine are installed so that they can work both independently and jointly. This is achieved by combining the combustion engine, electric motor and gearbox with an automatically controlled clutches.
Hybrid cars that use parallel circuit are called Mild Hybrid (literally - moderate hybrid). They use a small electric power (about 20 kW), which provides, as a rule, the extra power for accelerating the vehicle. In most designs, the motor disposed between the engine and the gearbox, carries out also the function of a starter and a generator.
Known hybrid vehicles with parallel scheme are Honda Insight, Honda Civic Hybrid, BMW Active Hybrid 7, Volkswagen Touareg Hybrid, Hyundai Elantra Hybrid. A pioneer in this field is Honda and its system Integrated Motor Assist, IMA (literally - an integrated motor assistant).
When the system IMA can select the following characteristic modes:
- Work from the motor.
- Teamwork engine and an electric motor.
- Work from the ICE and charging the battery from the electric motor as a generator.
- Charging the battery in the regenerative braking mode.
Series-parallel circuit of a hybrid car
With a series-parallel circuit of the internal combustion engine and an electric motor connected through a planetary gear. The power of each of the motors may be transmitted to the driving wheels simultaneously in a ratio of from 0 to 100% of nominal power. Unlike the parallel circuit in series-parallel circuit added generator providing energy operation of the motor.
Hybrid cars that use serial-to-parallel circuit are called Full Hybrid (literally - full hybrid). Known full hybrid cars are the Toyota Prius, Lexus RX 450h, Ford Escape Hybrid. In this market segment dominated by hybrid cars, Toyota and its system Hybrid Synergy Drive, HSD.
Propulsion system HSD is an internal combustion engine (coupled to carrier planetary gear unit), motor (connected to the ring gear of the planetary gear), generator (connected to the sun gear of the planetary gear unit).
The internal combustion engine runs on the Atkinson cycle, which can be realized with cardinality mediocre performance at low engine speeds, respectively, achieved great fuel economy and lower emissions.
In this paper, Hybrid Synergy Drive system are the following modes:
- Electric mode, in which the engine is switched off and feeds the electric battery.
- Mode motion with constant (cruising) the rate at which the power of the internal combustion engine is distributed between the drive wheels and the generator. The generator in turn supplies a motor whose power is added to the power of the engine. If necessary, a battery charging.
- Forced mode in which the motor is attached to the internal combustion engine, powered by a battery, providing power pulse.
- Eco mode, in which the battery powers the generator. The generator converts electrical energy into mechanical energy, slowing rotation engine. At the same time the engine torque is not reduced, and fuel economy is achieved.
- Braking mode, in which the electric motor acts as a generator, and electricity is used to rotate the sun gear in the opposite direction, slowing down the speed of the vehicle.
- Mode battery charging are controlled via the engine and generator.
Thermodynamic Engines Cycles
Currently sources of mechanical energy in cars are mainly internal combustion engines. Conversion of fuel energy into mechanical energy in them is associated with significant losses, so it is necessary first of all to find ways to reduce these losses and to achieve maximum impact of the energy contained in the fuel. For this purpose, first of all, necessary to select the optimum thermodynamic cycle.
In the internal combustion engine is used two different thermodynamic cycles. The gasoline engine is operated in such a manner that the cylinder intake stroke is absorbed by the air-fuel mixture which is then compressed on the compression stroke, and then when the piston is at top dead center (TDC), an electrical spark ignites and burns. Caused by combustion gases expand at the expense of the heat released their pressure increases, and the action of this pressure, the piston stroke. The subsequent movement of the piston from the cylinder to TDC Exhaust gases. Such idealized cycle (Otto cycle) involves filling and cleaning of the cylinder when the piston is in the blind spots and flow of combustion when the piston is at TDC.
Other thermodynamic cycle (cycle Diesel) proceeds in a similar manner with the only difference that no combustion occurs when the piston is stationary, and during its movement from TDC, so that the gas pressure during combustion remains constant, and only after the complete combustion of the fuel begins its expansion . In reality, both of the combustion cycle occurs when moving the piston and changing pressure, ie the actual internal combustion engine cycles are cycles of mixed supply of heat. More consideration of both cycles and their differences can be found in the literature.
Engine efficiency is important, showing how much energy fuel is converted into mechanical work. Indicated efficiency does not account for mechanical losses and losses in gas exchange, so that the effective efficiency of the engine is the product of the indicator on the mechanical efficiency. Thus, more complete utilization of the energy consumption can be achieved by not only improving the tracer, but also mechanical performance.
When the internal combustion engine 1/3 of the fuel energy is transformed into mechanical, 1/3 is passed through a cooling environment and the third is given in the form of heat contained in the exhaust gases. Any use of the heat losses of the last two species means saving energy, more efficient use of engine power and thermal improvement, the balance of the car.
Thus, the use of heat absorbed by the coolant, which is necessary in principle to withdraw from the engine to heat the cab or the body, is a typical example of economy of fuel needed for independent heating. The same examples are heating exhaust gases body trucks that carry loads regedit (ore, coal, liquid), the use of exhaust gas energy to drive the turbocharger turbine or auxiliary heater exhaust gases hydride battery to extract hydrogen from it.
As a criterion for evaluation of thermodynamic cycles is often used Carnot cycle.
Requirements of an ideal Carnot cycle does not execute any of the known cycles (Otto, Diesel, Rankine, Stirling). From the analysis of the Carnot cycle that depends on the efficiency of the thermodynamic cycle of the difference between the maximum temperature and the minimum temperature T1 T2. Since the temperature T2 can be in the worst case ambient temperature, the efficiency of the thermodynamic cycle will never reach 100%.
Combustion of fuel directly into the cylinder and permits maximum difference between the temperatures T1 and T2. A steam engine or turbine can never reach the efficiency of internal combustion engine as shown in the specific consumption of fuel.
When comparing thermal cycle engine uses three types of them, characterized by the process pressure and temperature changes of gas in the cylinder:
- cycle with a supply of heat at a constant volume, and the piston is at top dead center (TDC);
- cycle with supply of heat at constant pressure and changing volume;
- cycle with a mixed supply of heat, ie, the first inlet at a constant volume, but then at constant pressure.
In cylinders heat engines is changing state of the gas, including for comparison the most important are the following:
- adiabatic expansion and contraction, at which the heat through the wall of the cylinder is not supplied to the gas and is removed from it;
- Isothermal compression and expansion, the temperature at which the gas is constant;
- polytropic compression and expansion, which is characterized as a heat supply to the gas, and gas heat transfer during the process.
An example of a polytropic process, the compression stroke of the internal combustion engine. At the beginning of the stroke to the heat reaching the cold gas at the inlet is fed from the hot cylinder walls, and at the end of cycle gas heated by compression to a temperature above the temperature of the cylinder wall, has the warmth gives the cylinder walls.
In the case of ideal thermodynamic cycle is assumed that the heat transfer from the cylinder walls have, i.e. processes are adiabatic.
Sources
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Thomas, Justin (2007-03-27). "Hybrid Truck Unveiled by Kenworth". TreeHugger.
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