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Teknikimobil.com-Friends of technicianmobil, this article will discuss Internal Combustion Engine and Hybrid Vehicles which is the second part of the entire article regarding the architecture (design) of electric vehicles. In the first article we discussed vehicles that use battery electricity . Let’s look at the second part of this article together.
Hybrid vehicles have two or more power sources to power the entire vehicle body, which provides a very large variance. The most common type of hybrid vehicle combines an IC engine (internal combustion such as gasoline and diesel engines) with a battery and electric motor and generator.
There are two basic settings for a hybrid vehicle: series hybrid and parallel hybrid, as shown in the following figure respectively.
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In a series of hybrid car designs, the vehicle is driven by one or more electric motors supplied directly from the battery or from an IC-engine based generator unit or from both. In this type of parallel hybrid circuit the vehicle can be driven either by an engine working directly through the transmission system, or by one or more electric motors working through the transmission or coupled directly to the wheels – or both by the electric motor and IC engine at once. There are different settings for parallel hybrid systems. The image below shows a type of parallel hybrid where the engine can drive the front wheels via the front axle, while the electric motor drives the rear wheels.
Parallel hybrid system with an IC engine driving the front axle, and electric power driving the rear wheels (Source: Electic vehicle technology).
From the entire picture above, it shows the design that this electric car’s battery cannot be recharged, the car can continue to move using a full internal combustion (IC) engine.
Another alternative is to use a rechargeable hybrid which usually has a much larger battery to give the vehicle effective range when running from the battery alone. Both series and parallel hybrid designs allow for regenerative braking – so that the drive motor functions as a generator while simultaneously slowing the vehicle and charging the battery.
Traditional series hybrids are only used in special applications. For example, diesel-powered train engines are almost always series hybrids, as are some ships. Some specialty all-terrain vehicles are series hybrids, with separately controlled electric motors at each wheel. The main disadvantage of a series hybrid is that power from the engine cannot be transmitted mechanically to the wheels but must pass through a generator and motor.
On the other hand, parallel hybrid has a very wide scope for use. Electric machines can be much smaller and cheaper, because they don’t have to convert all the energy. There are various ways in which parallel hybrid vehicles can be used. The simplest can be run on electricity from a battery, for example in a city where exhaust emissions are undesirable, or can be powered only by an IC engine, for example when traveling out of town. Alternatively, and more usefully, parallel hybrid vehicles can use the IC engine and battery simultaneously, continuously optimizing the efficiency of the IC engine. A popular arrangement is to get basic power to run the vehicle, usually around 50% of peak power requirements, from the IC engine, and to take additional power from the electric motor and battery, recharging the battery from the engine generator when the battery is not needed Using modern control techniques, Engine speed and torque can be controlled to minimize exhaust emissions and maximize fuel savings.
In parallel hybrid systems, it is useful to define a variable called ‘degree of hybridization’ as follows
$$
DOH=frac{electric motor power}{electric motor power+IC engine power}.
$$
The greater the degree of hybridization, the greater the scope of using the smaller IC engine, and making it operate at optimum efficiency for a larger proportion of the time.
Hybrid vehicles are more expensive than conventional vehicles; However, there are several benefits to be gained. In a series arrangement there is no need for a gearbox, the transmission can be simplified and the differential can be eliminated by using a pair of motors attached to opposite wheels. In series and parallel setup the usual battery starter setup can be eliminated.
There are several hybrid vehicles currently on the market and this is a sector that will grow rapidly in the coming years. The Toyota Prius is a non-rechargeable hybrid car. Nickel metal hydride batteries are used in this car. At startup or at low speed the Prius is only powered by an electric motor, avoiding the use of an IC engine when it is most likely to pollute the environment and is least efficient. This car uses regenerative braking and has a high overall fuel economy of around 56.5 mpg (US) or 68 mpg (UK). The Prius has a top speed of 160 kph (100 mph) and accelerates to 100 kph (62 mph) in 13.4 seconds. The Prius battery is only charged from the engine and does not use an external socket. Therefore, it only needs to be filled with gasoline, using the conventional method. Plus, the car has four comfortable seats, and boot space is barely affected by the somewhat larger-than-usual battery. The fully automatic transmission system is a further attraction of this car which has brought electric cars well within the reach of the common man making the various journeys they expect their car to handle.
The Prius mainly has parallel hybrid characteristics, that the IC engine can directly power the vehicle. However, it has a separate motor and generator, can operate in series mode rather than a ‘pure’ parallel hybrid. The car has a fairly complex ‘power splitter’ gearbox, based on epicyclic gears, which allows power from the electric motor and IC engine, in almost any proportion, to be sent to the wheels or gearbox. Power can also be sent from the wheels to the generator for regenerative braking.
Many car manufacturers are now bringing out the vehicles they produce as hybrids. Honda Insight is an example that deserves to be appreciated. Some notable examples do not use a gearbox, to combine the motor power of an engine and an electric motor, but instead use another set of wheels. Meanwhile, the following image shows the principle of the Daimler Chrysler hybrid SUV. The electric motor is adjacent to the gearbox behind the engine and drives a shaft that points forward to the front axle. This can be used in ‘motor mode’ to increase the vehicle’s traction. It can also be used in ‘generator mode’, for example when braking.
The parallel hybrid setup is similar to the one used on DaimlerChrysler’s hybrid SUV (Source : Electric vehicle technology).
In vehicles such as the Chevrolet Volt, the vehicle battery can be charged from a separate electrical supply, such as a wall outlet, when the vehicle is not in use. This vehicle carries a larger battery than a non-rechargeable hybrid and can travel up to 40 miles (64 km) on the battery alone. When the pure initial EV battery capacity drops below a preset threshold of full charge and while the Volt is operating as a series hybrid, the Volt control system will optimally select the most efficient drive mode to improve performance and increase high-speed efficiency. At certain loads and speeds, namely 30-70 mph (48-112 kph), the IC engine can sometimes be engaged mechanically via a clutch to a separate output gear and assist the traction motor to propel the Volt. Therefore, the Volt can operate as a pure EV, series hybrid or parallel hybrid depending on the battery condition (SOC) and operating conditions.[]