外文翻译混合动力电动汽车机械和再生制动的整合mechanical-and-regenerative-braking-integration-for-a-hy.doc

Xx00学院毕业设计（论文）——外文文献原稿和译文

外文文献原稿和译文

原 稿

Mechanical and Regenerative Braking Integration for a Hybrid Electric Vehicle

Abstract

Hybrid electric vehicle technology has become a preferred method for the automotive industry to reduce environmental impact and fuel consumption of their vehicles. Hybrid electric vehicles accomplish these reductions through the use of multiple propulsion systems, namely an electric motor and internal combustion engine, which allow the elimination of idling, operation of the internal combustion engine in a more efficient manner and the use of regenerative braking. However, the added cost of the hybrid electric system has hindered the sales of these vehicles.
A more cost effective design of an electro-hydraulic braking system is presented. The system electro-mechanically controlled the boost force created by the brake booster independently of the driver braking force and with adequate time response. The system allowed for the blending of the mechanical and regenerative braking torques in a manner transparent to the driver and allowed for regenerative braking to be conducted efficiently.
A systematic design process was followed, with emphasis placed on demonstrating conceptual design feasibility and preliminary design functionality using virtual and physical prototyping. The virtual and physical prototypes were then used in combination as a powerful tool to validate and develop the system. The role of prototyping in the design process is presented and discussed.
Through the experiences gained by the author during the design process, it is recommended that students create physical prototypes to enhance their educational experience. These experiences are evident throughout the thesis presented.
1.1 Modern Hybrid Electric Vehicles
With rising gas prices and the overwhelming concern for the environment, consumers and the government have forced the automotive industry to start producing more fuel efficient vehicles with less environmental impact. One promising method that is currently being implemented is the hybrid electric vehicle.
Hybrid vehicles are defined as vehicles that have two or more power sources [25]. There are a large number of possible variations, but the most common layout of hybrid vehicles today combines the power of an internal combustion engine (ICE) with the power of an electric motor and energy storage system (ESS). These vehicles are often referred to as hybrid electric vehicles (HEV’s) [25]. These two power sources are used in conjunction to optimize the efficiency and performance of the vehicle, which in turn will increase fuel economy and reduce vehicle emissions, all while delivering the performance the consumer requires. In 1997, the Toyota Prius became the first hybrid vehicle introduced into mass production in Japan. It took another three years for the first mass produced hybrid vehicle, the Honda Insight, to be introduced into the North American market. The release of the Honda Insight was closely followed by the release of the Toyota Prius in North America a couple of months later [35].
Hybrid electric vehicles have the distinct advantage of regenerative braking. The electric motor, normally used for propulsion, can be used as a generator to convert kinetic energy of the vehicle back into electrical energy during braking, rather than wasting energy as heat. This electrical energy can then be stored in an ESS (e.g. batteries or ultracapacitors) and later released to propel the vehicle using the electric motor.
This process becomes even more important when considering the energy density of batteries compared to gasoline or diesel fuel. Energy density is defined as the amount of energy stored in a system per unit volume or mass [44]. To illustrate this point, 4 kilograms (4.5 litres) of gasoline will typically give a motor vehicle a range of 50 kilometres. To store the same amount of useful electric energy it requires a lead acid battery with a mass of about 270 kilograms [25]. This demonstrates the need for efficient regenerative braking to store electrical energy during driving, which in turn will keep the mass of the energy storage system down and improve the performance and efficiency of the HEV.
1.2 Research Scope - Regenerative Braking Systems
The scope of the research presented is to create a low cost regenerative braking system to be used on future economical hybrid vehicles to study the interaction between regenerative and mechanical braking of the system. This system should be able to control the combination of both regenerative and mechanical braking torque depending on driver demand and should be able to do so smoothly and safely. Controlling the regenerative braking torque can be done using control algorithms and vector control for induction motors. However, controlling the mechanical braking torque independently of the driver pedal force, while maintaining proper safety back-ups, proved to be more of a challenge. To overcome this problem, a system was developed that would attenuate the pressure in the brake booster in order to control the amount of mechanical torque developed by the braking system．
2.1 Hybrid Electric Vehicle Overview
Hybrid vehicles have emerged as one of the short term solutions for reducing vehicle　emissions and improving fuel economy. Over the past 10 years almost all of the major　automotive　companies have developed and released for sale their own hybrid electric　vehicles to the public. The popularity of hybrid electric vehicles has grown considerably since the turn of　the century. With enormous pressure to become more environmentally friendly and with　unpredictable gas prices, the sales of hybrid electric vehicles have increased dramatically　in recent years.
2.1.1 Hybrid Configurations
For the past 100 years the objective of the hybrid has been to extend the range of electric　vehicles and to overcome the problem of long recharging times [35]. There are three　predominant hybrid electric vehicle configurations currently on the market today. These configurations are known as series hybrids, parallel hybrids and series/parallel hybrids.
Each configuration has its advantages and disadvantages which will be discussed in the following sections.
Series Hybrids
In series hybrids the mechanical output from the internal combustion engine is used to　drive a generator which produces electrical power that can be stored in the batteries or　used to power an electric motor and drive the wheels. There is no direct mechanical　connection between the engine and the driven wheels. Series hybrids tend to be used in　high power systems such as large trucks or locomotives but can also be used for lower power passenger vehicles [18]. The mechanically generated electrical power is combined with the power from the battery in an electronic controller. This controller then compares the driver demand with the vehicle speed and available torque from the electric motor to determine the amount of power required from each source to drive the vehicle. During braking, the controller also switches the power electronics to regenerative mode, and directs the power being regenerated to the batteries [55].
There are many advantages made possible by the arrangement described above. It is possible to run the ICE constantly at its most efficient operating point and share its electrical output between charging the battery and driving the electric motor. By operating the engine at its most efficient operating point, emissions can be greatly reduced and the most electrical power can be generated per volume of fuel. This configuration is also easierto implement into a vehicle because it is less complex which makes this method more cost effective.
Parallel Hybrids
In parallel hybrid configurations the mechanical energy output from the ICE is transmitted to a gearbox. In this gearbox the energy from the ICE can be mechanically combined with a second drive from an electric motor. The combined mechanical output is then used to drive the wheels [35]. In this configuration there is a direct connection between the engine and the driven wheels. As in series hybrids the controller compares the driver demand with the vehicle speed and output torque and determines the amount of power to be used from each source to meet the demand, while obtaining the best possible efficiency. A parallel hybrid also controls regenerative braking similarly to a series hybrid. Parallel hybrids are usually used in lower power electric vehicles in which both drives can be operated in parallel to provide higher performance [18].
There are a number of advantages of a parallel hybrid over a series hybrid. The most important advantage is that since only one conversion between electrical and mechanical power is made, efficiency will be much better than the series hybrid in which two conversions are required. Since the parallel hybrid has the ability to combine both the engine and electric motor powers simultaneously, smaller electric motors can be used without sacrificing performance, while getting the fuel consumption and emission reduction benefits. Lastly, parallel hybrids only need to operate the engine when the vehicle is moving and do not need a second generator to charge the batteries.
Series/Parallel Hybrids
Combined hybrids have the features of both series and parallel configurations. They use a power split device to drive the wheels using dual sources of power (e.g. electric motor only, ICE only or a combination of both). While the added benefits of both series hybrids and parallel hybrids are achieved for this configuration, control algorithms become very complex because of the large number of driving possibilities available.
2.1.2 Degree of Hybridization
Since most HEV’s on the road today are either parallel or series/parallel, it is useful to define a variable called the ‘degree of hybridization’ to quantify the electrical power potential of these vehicles.

The degree of hybridization ranges from (DOH = 0) for a conventional vehicle to (DOH = 1) for an all electric vehicle [25]. As the degree of hybridization increases, a smaller ICE can be used and operated closer to its optimum efficiency for a greater proportion of the time, which will decrease fuel consumption and emissions. The electric motor power is denoted by Pem and the internal combustion engine power is denoted by Pice.
Micro Hybrid
Micro hybrids have the smallest degree of hybridization and usually consist of an integrated starter generator (ISG) connected to the engine crankshaft. The ISG allows the engine to be shut off during braking and idling to conserve fuel and then spins the crankshaft up to speed before fuel is injected during acceleration. The ISG also provides small amounts of assist to the ICE during acceleration and acts as a generator to charge the batteries during braking. Micro hybrids usually improve fuel economy by about 10 percent compared with non hybrids [53].
Mild Hybrid
Mild hybrids have a similar architecture to the micro hybrid except that the ISG is uprated in power to typically greater than 20 kW. However, the energy storage system is limited to less than 1 kWh [35]. Mild hybrids usually have a very short electric-only range capability but can provide a greater assist to the ICE during accelerations. The electrical components in a mild hybrid are more complex than a micro hybrid and play a greater role in the vehicle operation. Fuel economy can be improved by 20 to 25 percent with a mild hybrid over non hybrid vehicles [53].
Full Hybrid
Full hybrids do away with the ISG and replace it with a separate electric motor and alternator/starter that perform the same function. The electric motor has the ability to propel the vehicle alone, particularly in city (stop and go) driving. The energy storage system is upgraded to improve electric-only range capability and the engine is usually downsized to improve fuel economy and emissions. Full hybrids can achieve 40 to 45 percent fuel consumption reductions over non hybrids [53].
Plug-in Hybrid
Plug-in hybrids are very similar to full hybrids except that they have a much larger ESS that can be connected to an outside electrical utility source for charging. These vehicles use only the electric motor to propel the vehicle within the range of the batteries and then operate like full hybrids once the batteries have discharged to a predefined level.
2.1.3 Fundamentals of Regenerative Braking
One of the most important features of HEV’s is their ability to recover significant amounts of braking energy. The electric motors can be controlled to operate as generators during braking to convert the kinetic energy of the vehicle into electrical energy that can be stored in the energy storage system and reused. However, the braking performance of a vehicle also greatly affects vehicle safety. In an emergency braking situation the vehicle must be stopped in the shortest possible distance and must be able to maintain control over the vehicle’s direction. The latter requires control of brake force distribution to the wheels [12].
Generally, the braking torque required is much larger than the torque that an electric motor can produce [12]. Therefore, a mechanical friction braking system must coexist with the electrical regenerative braking. This coexistence demands proper design and control of both mechanical and electrical braking systems to ensure smooth, stable braking operations that will not adversely affect vehicle safety.
Energy Consumption in Braking
Braking a 1500 kg vehicle from 100 km/h to 0 km/h consumes about 0.16 kWh of energy based on Equation 2.2.

If 25 percent of this energy could be recovered through regenerative braking techniques, then Equation 2.2 can be used to estimate that this energy could be used to accelerate the vehicle from 0 km/h to about 50 km/h, neglecting aerodynamic drag, mechanical friction and rolling resistance during both braking and accelerating. This also assumes that the generating and driving modes of the electric motor are 100% efficient. This suggests that the fuel economy of HEV’s can be greatly increased when driving in urban centres where the driver is constantly braking and accelerating. Note that the amount of energy recovered is limited by the size of the electric motor and the rate of which energy can be transferred to the ESS.
2.1.4 Methods of Regenerative Braking
There are two basic regenerative braking methods used today. These methods are often referred to as parallel regenerative braking and series regenerative braking. Each of these braking strategies have advantages and disadvantages that will be discussed in this section.
Parallel Regenerative Braking
During parallel regenerative braking, both the electric motor and mechanical braking system always work in parallel (together) to slow the vehicle down [48]. Since mechanical braking cannot be controlled independently of the