基于c2b模式的二手车鉴定评估方法研究说明书论文
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毕 业 设 计（论 文）外 文 参 考 资 料 及 译 文译文题目：Electric Vehicles 电动汽车 学生姓名： 王思远 学 号： 1204202028 专 业： 车辆工程 所在学院： 机电工程学院 指导教师： 贾 永 刚 职 称： 讲 师 2016 年 2 月 4 日Electric VehiclesEVs use an electric motor for traction, and chemical batteries, fuel cells, ultracapacitors, and/or flywheels for their corresponding energy sources. The EV has many advantages over the conventional internal combustion engine vehicle (ICEV), such as absence of emissions, high efficiency, independence from petroleum, and quiet and smooth operation. The operational and fundamental principles in EVs and ICEVs are similar, as described in Chapter2. There are, however, some differences between ICEVs and EVs, such as the use of a gasoline tank versus batteries, ICE versus electric motor, and different transmission requirements. This chapter will focus on the methodology of power train design and will investigate the key components, including traction motor, energy storage, and so on.4.1 Configurations of EVsPreviously, the EV was mainly converted from the existing ICEV by replacing the IC engine and fuel tank with an electric motor drive and battery pack while retaining all the other components, as shown in Figure 4.1. Drawbacks such as its heavy weight, lower flexibility, and performance degradation have caused the use of this type of EV to fade out. In its place, the modern EV is purposely built, based on original body and frame designs. This satisfies the structure requirements unique to EVs and makes use of the greater flexibility of electric propulsion.1A modern electric drive train is conceptually illustrated in Figure 4.2.1 The drive train consists of three major subsystems: electric motor propulsion, energy source, and auxiliary. The electric propulsion subsystem is comprised of the vehicle controller, the power electronic converter, the electric motor, mechanical transmission, and driving wheels. The energy source subsystem involves the energy source, the energy management unit, and the energy refueling unit. The auxiliary subsystem consists of the power steering unit, the hotel climate control unit, and the auxiliary supply unit.Based on the control inputs from the accelerator and brake pedals, the vehicle controller provides proper control signals to the electronic powerconverter, which functions to regulate the power flow between the electric motor and energy source. The backward power flow is due to the regenera- tive braking of the EV and this regenerated energy can be restored into the energy source, provided the energy source is receptive. Most EV batteries as well as ultracapacitors and flywheels readily possess the ability to accept regenerative energy. The energy management unit cooperates with the vehicle controller to control the regenerative braking and its energy recovery. It also works with the energy refueling unit to control the refueling unit and to monitor the usability of the energy source. The auxiliary power supplyprovides the necessary power with different voltage levels for all the EV auxiliaries, especially the hotel climate control and power steering units.There are a variety of possible EV configurations due to the variations in electric propulsion characteristics and energy sources, as shown in Figure 4.3.1a. Figure 4.3a shows the configuration of the first alternative, in which an electric propulsion replaces the IC engine of a conventional vehicle drive train. It consists of an electric motor, a clutch, a gearbox, and a differential. The clutch and gearbox may be replaced by an automatic transmission. The clutch is used to connect or disconnect the power of the electric motor from the driven wheels. The gearbox provides a set of gear ratios to modify the speedpower (torque) profile to match the load requirement (refer to Chapter 2). The differential is a mechanical device (usually a set of planetary gears), which enables the wheels ofFIGURE 4.3 Possible EV configuration: (a) conventional driveline with multigear transmission and clutch, (b) single-gear transmission without need of a clutch, (c) integrated fixed gearing and differential, (d) two separate motors and fixed gearing with their driveshaft, (e) direct drive with two separate motors and fixed gearing, and (f) two separate in-wheel motor drives.1both sides to be driven at different speeds when the vehicle runs along a curved path.b. With an electric motor that has a constant power in a long speed range (refer to Chapter 2), a fixed gearing can replace the multispeed gearbox and reduce the need for a clutch. This configuration not only reduces the size and weight of the mechanical transmission, it also simplifies the drive train control because gear shifting is not needed.c. Similar to the drive train in (b), the electric motor, the fixed gearing, and the differential can be further integrated into a single assembly while both axles point at both driving wheels. The whole drive train is further simplified and compacted.d. In Figure 4.3d, the mechanical differential is replaced by using two traction motors. Each of them drives one side wheel and operates at a different speed when the vehicle is running along a curved path.e. In order to further simplify the drive train, the traction motor can be placed inside a wheel. This arrangement is the so-called in-wheel drive. A thin planetary gear set may be employed to reduce the motor speed and enhance the motor torque. The thin planetary gear set offers the advantage of a high-speed reduction ratio as well as an inline arrangement of the input and output shaft.f. By fully abandoning any mechanical gearing between the electric motor and the driving wheel, the out-rotor of a low-speed electric motor in the in-wheel drive can be directly connected to the driving wheel. The speed control of the electric motor is equivalent to the con- trol of the wheel speed and hence the vehicle speed. However, this arrangement requires the electric motor to have a higher torque to start and accelerate the vehicle.4.2 Performance of EVsA vehicles driving performance is usually evaluated by its acceleration time, maximum speed, and gradeability. In EV drive train design, proper motor power rating and transmission parameters are the primary considerations to meet the performance specification. The design of all these parameters depends mostly on the speedpower (torque) characteristics of the traction motor, as mention in Chapter 2, and will be discussed in this chapter.4.2.1 Traction Motor CharacteristicsVariable-speed electric motor drives usually have the characteristics shown in Figure 4.4. At the low-speed region (less than the base speed as marked in Figure 4.4), the motor has a constant torque. In the high-speed region (higher than the base speed), the motor has a constant power. This characteristic is usually represented by a speed ratio x, defined as the ratio of its maximum speed to its base speed. In low-speed operation, voltage supply to the motor increases with the increase of speed through the electronic converter while the flux is kept constant. At the point of base speed, the voltage of the motor reaches the source voltage. After the base speed, the motor voltage is kept constant and the flux is weakened, dropping hyperbolically with increasing speed. Hence, its torque also drops hyperbolically with increasing speed.24 Figure 4.5 shows the torquespeed profiles of a 60 kW motor with different speed ratios x (x = 2, 4, and 6). It is clear that with a long constant power region, the maximum torque of the motor can be significantly increased, and hence vehicle acceleration and gradeability performance can be improved and the transmission can be simplified. However, each type of motor inherently has its limited maximum speed ratio. For example, a permanent magnet motor has a small x ( 6 and induction motors about x = 4.2,54.2.2 Tractive Effort and Transmission RequirementThe tractive effort developed by a traction motor on driven wheels and the vehicle speed are expressed as（4.1）=0and(4.2)=300where Tm and Nm are the motor torque output in N m and speed in rpm, respectively, ig is the gear ratio of transmission, i0 is the gear ratio of final drive, t is the efficiency of the whole driveline from the motor to the driven wheels, and rd is the radius of the driven wheels.The use of a multigear or single-gear transmission depends mostly on the motor speedtorque characteristic. That is, at a given rated motor power, if the motor has a long constant power region, a single-gear transmission would be sufficient for a high tractive effort at low speeds. Otherwise, a multigear (more than two gears) transmission has to be used. Figure 4.6 shows the tractive effort of an EV, along with the vehicle speed with a traction motor of x = 2 and a three-gear transmission. The first gear covers the speed region of abc, the second gear covers def, and the third gear covers gfh. Figure 4.7 shows the tractive effort with a traction motor of x = 4 and a two-gear transmission. The first gear covers the speed region of abc and the second gear def. Figure 4.8 shows the tractive effort with a traction motor of x = 6 and a single-gear transmission. These three designs have the same tractive effort versus vehicle speed profiles. Therefore, the vehicles will have the same acceleration and gradeability performance.4.2.3 Vehicle PerformanceBasic vehicle performance includes maximum cruising speed, gradeability, and acceleration. The maximum speed of a vehicle can be easily found by the intersection point of the tractive effort curve with the resistance curve (rolling resistance plus aerodynamic drag), in the tractive effort versus vehicle speed diagram shown in Figures 4.6 through 4.8. It should be noted that such an intersection point does not exist in some designs, which usually use a larger traction motor or a large gear ratio. In this case, the maximum vehicle speed is determined by the maximum speed of the traction motor as(4.3)= 30 0()where Nm max is the allowed maximum rpm of the traction motor and ig minis the minimum gear ratio of the transmission (highest gear).Gradeability is determined by the net tractive effort of the vehicle, Ftnet (Ftnet = Ft Fr Fw), as shown in Figures 4.6 through 4.8. The gradeability at mid- and high speeds is smaller than that at low speeds. The maximum grade that the vehicle can overcome at the given speed can be calculated by(4.4)=(+)where Ft is the tractive effort on the driven wheels, Fr is the tire rolling resistance, and Fw is the aerodynamic drag. However, at low speeds, the gradeability is much larger. Calculations based on Equation 4.4 will cause significant error; instead, Equation 4.5 should be used:(4.5)sin=12+21+2d = Ft Fw/Mg is called the vehicle performance factor (refer to Chapter 2) and fr is the tire rolling resistance coefficient.Acceleration performance of a vehicle is evaluated by the time used to accelerate the vehicle from a low speed V1 (usually zero) to a higher speed (10
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