Background
The past several years have been graced with an increase in the production and use of hybrid cars. Numerous automobile companies are exploring and introducing hybrid electric vehicles to the market, with several other companies to follows soon given the demand. It is imperative to outline that the introduction and the fast embrace and use of hybrid electric cars over the past few decades have been stimulated by several factors. Apart from the increasing demand for hybrid cars based on their advantages, the increase in production of these vehicles has been stimulated by the declining fuel reserves and concerns over environmental degradation.
The early designs of HEV varied in several ways; the size of the engine, vehicle platform, operational control algorithms, electric motors and batteries. The manner in which the various constituents of the vehicles are packaged, sized and controlled will significantly affect the system of the vehicle and is probably to present environmental impacts, fuel saving, customer acceptance and performance (Demirdöven and John 974). Original HEV design utilized fossil fuel for their operation, however, development of new designs have incorporated the use of grid-supplied electricity for vehicles which accommodate increased onboard energy storage.
It is imperative to note that hybrid car technology allows the use of more than one energy source in powering the vehicle engine. As a consequence, hybrid cars demonstrate numerous advantages associated with the use of both energy sources. An electric powered vehicle is incapable of going more than 161 km between recharging (Høyer 68). Additionally, it is daunting to recharge, and it does not go past 60 mpg. However, the vehicle produces little pollution as compared to the other cars. Consequently, hybrid vehicle design was proposed to mitigate the pitfalls of electric vehicles while improving its benefits. Hybrid vehicles demonstrate increased drive train efficiency of between 30 to 40 percent, increased fuel economy and reduced emission.
History
The history of hybrid cars dates back to 1800 and 1900s. The first patent was filed by Mr. Piper in 1905 for a gasoline engine-electric motor power train. According to Mr. Piper, the application and use of electric motor would be a perfect augment for a gasoline engine. The combination allowed a car to accelerate from zero to 25 miles per hour within ten seconds (Hawkins, Ola and Anders 998). This acceleration rate was much faster than the acceleration of gasoline engines at that time. However, by the time the patent was granted, the developments in gasoline engine propelled it to be able to attain the same acceleration rate as the one proposed by Mr. Piper. The popularity of hybrid cars gradually lessened as further developments and advancements were witnessed in the gasoline engine (Chan 250).
The technology emerged again in the mid-1970s during the oil crisis and faded again once oil became available. The availability of Toyota Prius and Honda Insight in the 1990s marked the first commercial success of hybrid cars. The two cars demonstrated a direct linkage from the internal combustion engine to the wheels for the engine to produce acceleration power. After the first commercial success of hybrid cars, the automobile industry ventured into mass production of these cars. The early productions were characterized by superior battery packs which could be recharged from the power grid.
Introduction
In this context, hybrid refers to the amalgamation of two or more source of power that is used to operate a vehicle. A car that operates on two or more energy sources is known as a hybrid vehicle. In most cases, it is referred to as hybrid-electric vehicle (HEV). It is imperative to point out that the two major source of power employed by hybrid cars on most occasions is internal-combustion engine and an electric motor. In this type of design, the internal-combustion engine is used as the final power source for the vehicle, though electric motors are employed as an alternative assistant when the vehicle demands power using stored energy. It should be noted that hybrid cars are totally different from all-electric cars (Demirdöven and John 975). An electric powered vehicle is incompetent of going more than 161 km between recharging. Furthermore, it is overwhelming to recharge, and it does not go past 60 mpg. However, the vehicle generates little pollution as compared to the other cars. As a result, hybrid vehicle design was proposed to alleviate the drawbacks of electric vehicles while enhancing its benefits. Hybrid vehicles exhibit increased drive train effectiveness of between 30 to 40 percent, increased fuel economy and reduced emission (Hawkins, Ola and Anders 998).
Hybrid cars employ the use gasoline as well as at least one alternate source of power in its operation. In most cases, hybrid cars employ the use of electricity through rechargeable batteries in addition to the internal combustion engine. They demonstrate attractive characteristics such as efficiency, innovative, low fuel emissions and affordability.
Operation of Hybrid cars
Hybrid cars operate by integrating the power of normal internal combustion engine (gasoline) with that of electric motor power by rechargeable batteries. Energy is provided to the electric motor by a high powered battery pack which gets recharged whenever the vehicle is decelerating through a process called regenerative braking. Apart from the automatic regard of the batteries, some of the hybrid cars employ the use of power-grid electricity in recharging the batteries.
Currently, there are two general categories of hybrid cars. The first type of hybrid cars is one where the electric motor is used as an alternative to the gas combustion engine. These types of hybrid cars are known as Mild hybrid. It offers assistance whenever surplus energy is required. It is imperative to note that in this type of hybrid cars, the electric motor alone is unable to operate the vehicle (Chan 256). The car cannot be operated entirely by the electric motor. It is used as an alternative to the internal combustion engine only when surplus power is required. An example of mild hybrid cars includes Civic and Insight, which employs Honda's Power Assist technology. Gasoline internal combustion engine is employed as the main source of power while the electric motor provides surplus power whenever required in mild hybrids.
The second type of hybrid cars is known as a Full hybrid. In this type of hybrid cars, both the gasoline internal combustion engine and the electric motor can operate the hybrid car independently. It should be noted that the electric motor operates the car at lower speeds. The gasoline engine is initiated when more speed is required. Some of the vehicles that employ the full hybrid technology include the Ford Escape and the Toyota Prius. It is imperative to point out that whether mild or full hybrid cars exhibit some common benefits like better fuel economy and lower emissions. The size of the internal combustion engines (diesel and gasoline alike) implemented in hybrid cars is usually smaller as compared to conventional cars given that they employ the use of the electric motor for supplement energy.
The electric motor is employed in city travel with go and stop conditions in addition to the power consuming features like power steering and power windows. The gasoline internal combustion engine supplies power at high speeds. A computer control is used in switching between the different sources of power so as to eliminate the manual control. There are several reasons as to why hybrid cars have thrived since their inception. They are environment-friendly given that they have extremely low emissions. Hybrid cars have the potential to reduce pollution by 90 percent. As compared to normal gasoline cars, hybrid cars are economical in a long and medium run given their excellent fuel economy (Chan 263). Additionally, hybrid cars are more reliable as a compared to electric cars given that they possess gasoline internal combustion engine as an alternative source of energy. They reduce the dependency on fossil fuel given the alternative electric energy source. Additionally, they are more efficient owing to their small engines, improve mileage and aid in the reduction of the greenhouse effect.
Components of Hybrid electric cars
Hybrid cars are made up of several components which work together to present the performance characteristics described in the start of this document. While the other components of hybrid cars are similar to the normal gasoline cars, the power source varies greatly. As a consequence, this section will cover the components of the power source and transmission of hybrid cars. The main components of hybrid cars which differ from the normal cars include; hybrid battery, hybrid engine, electric motor, transmission and generator.
Hybrid Engine
Hybrid vehicle posses a gasoline internal combustion engine similar to that found in regular cars. However, the hybrid engine found in hybrid cars is small as compared to those found in regular cars. Additionally, the engine employs advanced technology to increase efficiency and reduce emissions (Demirdöven and John 974). There are different types of engines which can be employed in hybrid cars depending on specific weight (Kg/KW), minimum bsfc (kg/KWh) and specific volume (liters/KW). Based on their small weight and relatively small weight, there is three basic type of engines used in hybrid cars. The three types of engines employed in hybrid cars include; the direct injected 2-stroke engine, the rotary engine, and the gas turbine engine.
Hybrid battery
Rechargeable batteries are used in hybrid cars to store electric power which is used to drive the electric motor. As opposed to gasoline present in the fuel tank which can only energize the gasoline engine, the electric motor is capable of recharging the batteries as well as drawing energy from them (Hawkins, Ola and Anders 999). Hybrid batteries are used to perform two main functions in hybrid cars; to supply electric energy to the electric motor and to store electric energy during recharging from the electric motor. In most cases, the specific energy is employed as the core parameter in assessing the suitability of a battery for use in hybrid cars for the required driving range.
Similarly, specific energy power is employed as a significant parameter in assessing the suitability of battery required acceleration and gradability. The State of Charge is the battery's outstanding charge capability on a scale between Zero to one. It is not measured directly on real battery. However, for most battery technologies like Lithium Ion and Lead Acid, there is a correlation between battery voltage and SOC of the battery. The battery state of charge is depleted when the battery is discharged. On the other hand, the state of charge of the battery increases when the battery is charged (Demirdöven and John 975).
Electric motor
It is imperative to note the sophistication of the electric motor employed in hybrid cars. It acts both as a motor and a generator through the aid of advanced electronics. For instance, the electric motor is capable of drawing energy from the rechargeable batteries in a time of need to accelerate the car. Similarly, it is capable of recharging the battery while acting as a generator and slowing the car down (Hawkins, Ola and Anders 998).The mechanical construction of electric motors used in hybrid cars is less complex as compared to other electric motors. They are capable of attaining 90 percent energy transformation efficiency over a full assortment of speeds as well as power output (Høyer 67). Additionally, the energy conversion process can be precisely regulated. In most cases, the electric motor is amalgamated with regenerative braking systems with the ability to transform movement energy into stored electricity within the rechargeable battery. The process is employed to minimize the wear and tear on the brake friction materials d the entire braking system. It is imperative to highlight that regenerative braking is more specifically effective for city use which is characterized with numerous starts and stops.
Generator
The generator used in hybrid cars is same as the electric motor. However, it operates only to generate electric power used to recharge the rechargeable batteries when the car is decelerating. It is highly employed in series hybrid cars. It employs the technology of an alternator which is an electromechanical device which is used to transform mechanical energy into electrical power in the form of electric current. The same principle employed in DC generators is used in alternators in the production of electricity which is used to recharge the batteries. It takes advantage of the fact that current is induced whenever there is an alteration in the magnetic field around a conductor. It is fitted with a rotating magnet known as the rotor. It turns within a stationary collection of conductors (rotor), thus producing an induced electromagnetic field. Current is generated in the conductor when it cuts across the field.
Transmission and Gearing
Only a few states of the electric art drive-lines employ the use of speed transmission. In most cases, gearing is employed only in to slow down the speed of the motor. As a consequence, a series hybrid does not require a multi-speed transmission. On the other hand, a parallel hybrid requires a multi-speed transmission between the main differential, the engine, and the clutches so as to decouple the electric motor as well as the internal combustion engine from the driveshaft whenever their torque is not required to drive the vehicle (Zheng et al. 1790).The technology that allows the capability extends the abilities of both mechanical and electrical paths of power is known as two-mode hybrid transmission. It employs two modes of operation; input split mode and compound split mode.
In input split mode, the car can move with either the internal combustion engine, electric motor or both at low speed. Input split mode allows the car to enjoy the benefits associated with a full hybrid. In this mode, all the electrical accessories still retain functioning on electric energy while the engine can restart immediately if required. The input split mode allows one of the motor/generator to act as the generator whiles the other to function as the motor.
Conversely, the compound split mode operates at heavier loads or higher speeds. In this mode, the gasoline internal combustion engine always functions while the system employs the use of sophisticated technologies such as Late Intake Valve Closing and Active Fuel Management to maximize fuel and engine efficiency.
Types of hybrid cars
Hybrid vehicles are widely categorized into four types; Parallel hybrid cars, Power split (Series-parallel hybrid), Series hybrid cars and Plug-in hybrid electrical cars.
Parallel hybrid cars
This type of hybrid cars employs the use of parallel hybrid systems. The parallel hybrid systems exhibit both electric motor and internal combustion engine linked to a mechanical transmission. In most cases, the design of parallel hybrid cars amalgamates the huge electrical generator and a motor in a single unit which is positioned between the transmission and the combustion engine (Hawkins, Ola and Anders 999). It uses a large set of rechargeable batteries with high voltages to store power. Electrical accessories like air conditioning, power windows, and power steering are energized by an electrical motor instead of being linked to the combustion engine. This combination enables efficiency gains given that the accessories can operate at a constant speed regardless of how slow or fast the combustion engine is operating.
Series hybrid cars
As opposed to parallel hybrid cars, series hybrid vehicles are operated through electric traction only. Electric motors are regarded to be competent as compared to internal combustion engines with the extremely high power to weight ratio. It is significant to note that electric motors matched to the vehicle do not need a transmission between the wheels and engine shifting torque ratio as opposed to internal combustion engine (Hawkins, Ola and Anders 998).Transmission augments sap power, weight, and bulk from the engine. On the other hand, automatic mechanical shifting can be very advanced. The internal combustion engine operates the electric generator as opposed to directly driving the wheels. It provides energy for operating the electric motor.
Power-split hybrid cars
These types of hybrid cars are parallel hybrids. They amalgamate split power devices which enable for power paths from the engine to the driving wheel that can be either electrical or mechanical. It employs the decoupling of the energy supplied by the engine and other sources of the energy required by the driver.
Conclusion
Hybrid cars present several advantages over normal cars especially in fuel economy, low fuel emissions, and high efficiency. The fuel saving features of hybrid cars are extremely wonderful. The regenerative braking feature allows for extreme fuel economy in hybrid cars. Additionally, the use of electric motor enables for more competent engine design. It is imperative to note that the embrace and use of hybrid cars have the potential to extremely reduce the emission of greenhouse gasses. Reduced emission of greenhouse gasses has a significant environmental impact. The low emission is one of the reasons hybrid vehicle are popular. On the other hand, the cars are extremely expensive and possess complex systems which require the attention of specialized mechanics only. However, improvements in the current design are imperative so as to exploit fully the benefits this technology has to offer.
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