2.2.1　Parallel Hybrid

In a parallel HEV，an electric motor and an ICE are connected to the transmission through a mechanical coupling device，such as separate clutches，so that the vehicle can either be driven by the ICE，or by the electric motor，or by both.The power requirements of the motor in a parallel HEV are lower than that of an EV with similar size.The configuration of the parallel HEV is shown in Figure 2.6.

Figure 2.6　Configuration of a parallel HEV

The parallel HEV has the following advantages.First，a parallel HEV needs only two propulsion components，ICE and an electric motor.The motor can be operated as a generator and vice versa.Second，the engine and the motor can be rated at reduced power levels for shortdistance trips.For long-distance trips，the engine may be designed for maximum power，while the motor/generator may still be rated to half the maximum power.However，the mechanical structure and power-train control is complex due to the necessity of power coupling for the ICE and the motor.It is also this complexity that gives more freedom for the power-train control to optimize fuel economy and vehicle performance.

The mechanical coupling is realized through the use of pulleys，gears，clutches，or a common shaft for the engine and motor.Mechanical coupling between motor and ICE can be configured to share a common transmission，or use separate transmissions or even separate axles.The mechanical transmission is also no longer restrained by the traditional automatic transmissions.For example，planetary gear sets have been introduced in parallel hybrids in place of the traditional CVT.The flexibility of configurations in parallel HEV offers the maximum advantage for fuel economy optimization in hybrid electric vehicles.

New words and expressions（单词和短语）

1.New words（单词）

2.Expressions（短语）

Notes to the text（难点解析）

★1.Hybrid electric vehicles can be classified into four different types according to how the power-train components are arranged:series，parallel，series-parallel and complex hybrid.根据动力总成系统组件的配置情况，混合动力电动汽车可以分为四种不同的类型:串联式、并联式、混联式以及复联式混合动力电动汽车。

★2.However，the mechanical structure and power-train control is complex due to the necessity of power coupling for the ICE and the motor.It is also this complexity that gives more freedom for the power-train control to optimize fuel economy and vehicle performance.然而，电动机与发动机功率耦合会导致机械结构与动力总成控制较为复杂。但同时正是这种复杂性，使动力总成控制更加灵活，以优化燃油经济性与车辆动力性能。

Exercises（练习）

◆1.Translate the following passages（expressions）into Chinese（英译汉）

（1）For long-distance trips，the engine may be designed for maximum power，while the motor/generator may still be rated to half the maximum power.

（2）The flexibility of configurations in parallel HEV offers the maximum advantage for fuel economy optimization in hybrid electric vehicles.

（3）parallel hybrid

（4）planetary gear sets

◆2.Translate the following passages（expressions）into English（汉译英）

（1）并联式混合动力电动汽车的电动机功率需求低于同样大小的纯电动汽车。

（2）电动机

（3）发电机

（4）图a

图a　并联式混合动力电动汽车的结构

Reading material（阅读材料）

The parallel hybrid needs only two propulsion devices，the ICE and the electric motor，which can be used in the following modes:

1）Motor-alone mode:When the battery has sufficient energy，and the vehicle power demand is low，the engine is turned off.And the vehicle is powered by the motor and battery only.

2）Combined power mode:At high power demand，the engine is turned on and the motor also supplies power to the wheels.

3）Engine-alone mode:During highway cruising and at moderately high power demands，the engine provides all the power needed to drive the vehicle.The motor remains idle.This is mostly due to the fact that the battery SOC is already at a high level but the power demand of the vehicle prevents the engine from turning off，or it may not be efficient to turn the engine off.

4）Power split mode:When the engine is on，but the vehicle power demand is low and the battery SOC is also low，a portion of the engine power is converted to electricity by the motor to charge the battery.

5）Stationary charging mode:The battery is charged by running the motor as a generator and driven by the engine，without the vehicle being driven.

6）Regenerative braking mode:The electric motor is operated as a generator to convert the vehicle's kinetic energy into electric energy and store it in the battery.Note that，in regenerative mode，it is in principle possible to run the engine as well，and provide additional current to charge the battery more quickly（while the propulsion motor is in generator mode）and command its torque accordingly，that is，to match the total battery power input.In this case，the engine and motor controllers have to be properly coordinated.