汽油機活塞的熱力耦合應力分析
汽油機活塞的熱力耦合應力分析,汽油機,活塞,熱力,耦合,應力,分析
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譯文題目： Hybrid Electric Vehicles
混合動力汽車
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Hybrid Electric Vehicles
Abstract
Conventional vehicles with IC engines provide good performance and long operating range by utilizing the high-energy-density advantages of petroleum fuels. However, conventional IC engine vehicles have the dis- advantages of poor fuel economy and environmental pollution. The main reasons for their poor fuel economy are (1) mismatch of engine fuel efficiency characteristics with the real operation requirement (refer to Figures 2.34 and 2.35); (2) dissipation of vehicle kinetic energy during braking, especially while operating in urban areas; and (3) low efficiency of hydraulic transmission in current automobiles in stop-and-go driving patterns (refer to Figure 2.21). Battery-powered EVs, on the other hand, possess some advantages over conventional IC engine vehicles, such as high-energy efficiency and zero environmental pollution. However, the performance, especially the operation range per battery charge, is far less competitive than IC engine vehicles, due to the much lower energy density of the batteries than that of gasoline. HEVs, which use two power sources(a primary power source and a secondary power source), have the advantages of both IC engine vehicles and EVs and over- come their disadvantages.1,2 In this chapter, the basic concept and operation principles of HEV power trains are discussed.
5.1 Concept of Hybrid Electric Drive Trains
Basically, any vehicle power train is required to (1) develop sufficient power to meet the demands of vehicle performance, (2) carry sufficient energy on- board to support the vehicle driving a sufficient range, (3) demonstrate high efficiency, and (4) emit few environmental pollutants. Broadly, a vehicle may have more than one power train. Here, the power train is defined as the combination of the energy source and the energy converter or power source, such as the gasoline (or diesel)–heat engine system, the hydrogen–fuel cell– electric motor system, the chemical battery–electric motor system, and so on. A vehicle that has two or more power trains is called a hybrid vehicle. A hybrid vehicle with an electrical power train is called an HEV. The drive train of a vehicle is defined as the aggregation of all the power trains.
A hybrid vehicle drive train usually consists of no more than two power trains. More than two power trains will make the drive train very complicated. For the purpose of recapturing braking energy that is dissipated in the form of heat in conventional IC engine vehicles, a hybrid drive train usually has a power train that allows energy to flow bidirectionally. The other one is either bidirectional or unidirectional. Figure 5.1 shows the concept of a hybrid drive train and the possible different power flow routes.
A hybrid drive train can supply its power to the load by a selective power train. There are many available patterns of operating two power trains to meet the load requirement:
1. Power train 1 alone delivers its power to the load.
2. Power train 2 alone delivers its power to the load.
3. Both power train 1 and power train 2 deliver their power to the load simultaneously.
4. Power train 2 obtains power from the load (regenerative braking).
5. Power train 2 obtains power from power train 1.
6. Power train 2 obtains power from power train 1 and the load simultaneously.
7. Power train 1 delivers power to the load and to power train 2 simultaneously.
8. Power train 1 delivers its power to power train 2, and power train 2 delivers its power to the load.
9. Power train 1 delivers its power to the load, and the load delivers the power to power train 2.
FIGURE 5.1 Conceptual illustration of a hybrid electric drive train.
In the case of hybridization with a gasoline (diesel)–IC engine (power train
1) and a battery–electric machine (power train 2), pattern (1) is the engine- alone propelling mode. This may be used when the batteries are almost completely depleted and the engine has no remaining power to charge the batteries, or when the batteries have been fully charged and the engine is able to supply sufficient power to meet the power demands of the vehicle. Pattern (2) is the pure electric propelling mode, in which the engine is shut off. This pattern may be used for situations where the engine cannot operate effectively, such as very low speed, or in areas where emissions are strictly prohibited. Pattern (3) is the hybrid traction mode and may be used when large power is needed, such as during sharp accelerating or steep hill climbing. Pattern (4) is the regenerative braking mode, by which the kinetic or potential energy of the vehicle is recovered through the electric motor functioning as a generator. The recovered energy is then stored in the batteries and reused later on. Pattern (5) is the mode in which the engine charges the batteries while the vehicle is at a standstill, coasting, or descending a slight grade, in which no power goes into or comes from the load. Pattern (6) is the mode in which both regenerating braking and the IC engine charge the batteries simultaneously. Pattern (7) is the mode in which the engine propels the vehicle and charges the batteries simultaneously. Pattern (8) is the mode in which the engine charges the batteries, and the batteries supply power to the load. Pattern (9) is the mode in which the power flows into the batteries from the heat engine through the vehicle mass. The typical configuration of this mode is that the two power trains are separately mounted on the front and rear axles of the vehicle, which will be discussed in the following sections.
The abundant operation modes in a hybrid vehicle create much more flexi- bility over a single power train vehicle. With proper configuration and control, applying a specific mode for a special operating condition can potentially optimize the overall performance, efficiency, and emissions. However, in a practical design, deciding which mode should be implemented depends on many factors, such as the physical configuration of the drive train, power train efficiency characteristics, load characteristics, and so on.
Operating each power train in its optimal efficiency region is essential for the overall efficiency of the vehicle. An IC engine generally has the best efficiency operating region with a wide throttle opening. Operating away from this region will cause low operating efficiency (refer to Figures 2.30, 2.32, 2.34, 2.35, and 3.6). On the other hand, efficiency suffering in an electric motor is not as detrimental when compared to an IC engine that operates away from its optimal region (refer to Figure 4.14).
FIGURE 5.2 A load power is decomposed into steady and dynamic components.
The load power of a vehicle varies randomly in real operation due to frequent acceleration, deceleration, and climbing up and down grades, as shown in Figure 5.2. Actually, the load power is composed of two components: one is steady (average) power, which has a constant value, and the other is dynamic power, which has a zero average. In designing the control strategy of a hybrid vehicle, one power train that favors steady-state operation, such as an IC engine and fuel cell, may be used to supply the average power. On the other hand, another power train, such as an electric motor, may be used to supply the dynamic power. The total energy output from the dynamic power train will be zero in a whole driving cycle. This implies that the energy source of the dynamic power train does not lose energy capacity at the end of the driving cycle. It functions only as a power damper.
In a hybrid vehicle, steady power may be provided by an IC engine, a Stirling engine, a fuel cell, and so on. The IC engine or the fuel cell can be much smaller than that in a single power train design because the dynamic power is taken by the dynamic power source, and then can operate steadily in its most efficient region. The dynamic power may be provided by an electric motor powered by batteries, ultracapacitors, flywheels (mechanical batteries), and their combinations.1,3
5.2 Architectures of Hybrid Electric Drive Trains
The architecture of a hybrid vehicle is loosely defined as the connection between the components that define the energy flow routes and control ports. Traditionally, HEVs were classified into two basic types: series and parallel. It is interesting to note that, in 2000, some newly introduced HEVs could not be classified into these kinds.4 Hence, HEVs are presently classified into four kinds—series hybrid, parallel hybrid, series–parallel hybrid, and complex hybrid—that are functionally shown in Figure 5.3.5 Scientifically, the classifications above are not very clear and may cause confusion. Actually, in an HEV, there are two kinds of energy flowing in the drive train: one is mechanical energy and the other is electrical energy. Adding two powers together or splitting one power into two at the power merging point always occurs with the same power type, that is, electrical or mechanical,
FIGURE 5.3 Classifications of hybrid EVs. (a) Series (electrically coupling), (b) parallel (mechanical coupling), (c) series–parallel (mechanical and electrical coupling), and (d) complex (mechanical and electrical coupling).
not electrical and mechanical. So perhaps a more accurate definition for HEV architecture may be to take the power coupling or decoupling features such as an electrical coupling drive train, a mechanical coupling drive train, and a mechanical–electrical coupling drive train.
Figure 5.3a functionally shows the architecture that is traditionally called a series hybrid drive train. The key feature of this configuration is that two electrical powers are added together in the power converter, which functions as an electric power coupler to control the power flows from the batteries and generator to the electric motor, or in the reverse direction, from the electric motor to the batteries. The fuel tank, the IC engine, and the generator constitute the primary energy supply and the batteries function as the energy bumper.
Figure 5.3b is the configuration that is traditionally called a parallel hybrid drive train. The key of this configuration is that two mechanical powers are added together in a mechanical coupler. The IC engine is the primary power plant, and the batteries and electric motor drive constitute the energy bumper. The power flows can be controlled only by the power plants—the engine and electric motor.
Figure 5.3c shows the configuration that is traditionally called a series– parallel hybrid drive train. The distinguished feature of this configuration is the employment of two power couplers—mechanical and electrical. Actually, this configuration is the combination of series and parallel structures,possessing the major features of both and more plentiful operation modes than those of the series or parallel structure alone. On the other hand, it is relatively more complicated and may be of higher cost.
Figure 5.3d shows a configuration of the so-called complex hybrid, which has a similar structure to the series–parallel one. The only difference is that the electric coupling function is moved from the power converter to the batteries and one more power converter is added between the motor/generator and the batteries.
We will concentrate more on the first three configurations—series, parallel, and series–parallel.
5.2.1Series Hybrid Electric Drive Trains (Electrical Coupling)
A series hybrid drive train is a drive train in which two electrical power sources feed a single electrical power plant (electric motor) that propels the vehicle. The configuration that is most often used is the one shown in Figure 5.4. The unidirectional energy source is a fuel tank and the unidirectional energy converter (power plant) is an IC engine coupled to an electric generator. The output of the electric generator is connected to a power DC bus through a controllable electronic converter (rectifier). The bidirectional energy source is a battery pack connected to the power DC bus by means of a controllable, bidirectional power electronic converter (DC/DC converter). The power bus is also connected to the controller of the electric motor. The traction motor can be controlled as either a motor or a generator, and in forward or reverse motion. This drive train may need a battery charger to charge the batteries by wall plug-in from a power grid. The series hybrid drive trainoriginally came from an EV on which an additional engine–generator is added to extend the operating range that is limited by the poor energy density of the batteries.
FIGURE 5.4 Configuration of a series hybrid electric drive train.
混 合 動 力 汽 車
摘要
傳統(tǒng)內(nèi)燃機汽車通過利用石油燃料高熱值高密度的優(yōu)點，提供給其良好的性能和較好的續(xù)航能力。但同時又不可避免的有燃油經(jīng)濟性差和環(huán)境污染的缺點。下面是其燃油經(jīng)濟性差的主要原因：（1）發(fā)動機燃油效率特性與實際運行工況不匹配（如圖2.34和圖2.35）；（2）制動過程中的動能損失，尤其是在城市運行的時候；（3）當前汽車在走走停停的駕駛模式下液力傳動裝置的效率低下（如圖2.21）。純電動汽車，在一方面，相比傳統(tǒng)內(nèi)燃機汽車有一些優(yōu)勢，如高效能和零污染。然而，在性能方面，特別是每次充電所能行駛的里程要遠少于內(nèi)燃機汽車，原因在于電池的能量密度遠低于汽油。混合動力汽車有兩個動力源（一個主要的和一個輔助的），它擁有內(nèi)燃機汽車和純電動汽車的各自優(yōu)點并且同時避免了它們的不足。在這一章里，我們將就混合動力汽車動力驅動裝置的基本概念和操作準則進行討論。
5.1混合動力驅動系統(tǒng)的概念
基本上，任何汽車動力驅動系統(tǒng)都需要（1）提供充足動力來滿足汽車性能需求；（2）攜帶足夠的能量以支持行駛足夠的里程；（3）具有高效能；（4）排放較少的環(huán)境污染物。一般來說，一輛汽車可能擁有不止一個動力驅動系統(tǒng)。在這里,這個動力系統(tǒng)被定義成能量源和能量轉換裝置的結合或者動力源,比如汽油(或柴油)--熱機系統(tǒng), 氫燃料電池電動系統(tǒng),化學電池--電機系統(tǒng)等等。一個擁有兩個或兩個以上動力系統(tǒng)的汽車稱為混合動力車。一個具有電動動力系統(tǒng)的混合動力車稱為電動混合動力車。車輛的驅動系統(tǒng)將所有的動力系統(tǒng)聚集起來。通常混合動力車的驅動系不會多于兩個動力系統(tǒng)。多于兩個動力的驅動系非常的復雜。為了回收傳統(tǒng)內(nèi)燃機車輛制動過程中變成熱消耗掉的能量,混合動力驅動系通常有一個動力系統(tǒng)允許能量雙向流動。另外一個可能是雙向的也可能不是。圖5.1表示的是混合動力驅動系的概念和可能的能量流動路線?；旌蟿恿︱寗酉悼梢詫恿νㄟ^可選擇的路線傳遞給負載。兩個動力系統(tǒng)滿足負載的有效方式有很多種:
1、 動力系統(tǒng)1單獨傳遞動力到負載。
2、 動力系統(tǒng)2單獨傳遞動力到負載。
3、 動力系統(tǒng)1和2同時傳遞動力到負載。
4、 動力系統(tǒng)2從負載獲得能量(再生制動)。
5、 動力系統(tǒng)2從動力系統(tǒng)1獲得能量。
6、 動力系統(tǒng)2同時從動力系統(tǒng)1和負載獲得能量。
7、 動力系統(tǒng)1同時將動力傳遞給動力系統(tǒng)2和負載。
圖5.1 混合汽車驅動系統(tǒng)的概念說明
8、動力系統(tǒng)1將能量傳遞給動力系統(tǒng)2,動力系統(tǒng)2將能量傳遞給負載。
9、動力系統(tǒng)1將動力傳遞給負載,負載將動力傳遞給動力系統(tǒng)2。
汽油機(柴油機)--內(nèi)燃機(動力系統(tǒng)1)和電動動力系統(tǒng)(動力系統(tǒng)2)組合的情況下,方式(1)是發(fā)動機單獨驅動模式。通常是電池幾乎完全用盡并且發(fā)動機沒有剩余動力給電池充電,或者是電池已經(jīng)完全充滿而發(fā)動機能夠提供足夠的動力來滿足車輛的負載需求。方式(2) 是純電動模式,發(fā)動機關閉。這種方式是在發(fā)動機不能有效地運行的場合,比如速度非常低,或者某些嚴禁排放的區(qū)域。方式(3)是混合驅動模式,可能在需要大功率的情況下運用,比如急加速或者爬陡坡。方式(4)是再生制動模式, 通過電動機作為發(fā)電機運行來回收動能或潛在的能量。再生的能量儲存到電池里,以后再利用。方式(5) 是充電模式,當車輛停止,滑行或者下小斜坡的時候,沒有動力傳遞到負載，也沒有動力傳回來。方式（6）再生制動和內(nèi)燃機同時給電池充電模式。方式（7）是發(fā)動機驅動車輛行駛同時給電池和負載充電。方式（8）發(fā)動機給電池充電，電池提供動力給負載。方式（9）是發(fā)動機將動力通過車身傳遞給電池。典型的這種模式是，兩個動力系統(tǒng)分別裝在前后軸上，在接下來的部分里將進行論述。
混合動力車豐富的操作模式相比于單一動力系統(tǒng)的汽車提供了更多的靈活性。用正確的結構和控制，針對特殊的工況運用相應的模式可以潛在的優(yōu)化整體性能，效率和排放。然而在一個特定的設計中，決定執(zhí)行哪一種模式取決于很多因素，比如驅動系統(tǒng)的結構，動力系統(tǒng)的效率特性，負載特性等等。在各自的優(yōu)化效率區(qū)域運行每個動力系統(tǒng)對一輛汽車總體性能至關重要。內(nèi)燃機一般在較大節(jié)氣門開度下具有最優(yōu)的效率運行區(qū)。離開這個區(qū)域將導致效率下降。另一方面，電動機不在最優(yōu)區(qū)域工作的效率則不像內(nèi)燃機那樣糟糕。
圖5.2 平均負載功率和動態(tài)負載功率
在實際操作中，因為頻繁加減速，上下坡，如圖5.2所示，車輛的負載功率是隨機變化的。實際上，負載功率由兩部分組成：一是穩(wěn)定（平均）功率，有一個固定不變的數(shù)值。另一個是動態(tài)功率，平均值為零。在混合動力車控制策略的設計中，一個動力系統(tǒng)支持穩(wěn)定的狀態(tài)的運行，如內(nèi)燃機和燃料電池，提供平均功率。另一方面，另一個動力系統(tǒng)，如電動機，可能用來提供動態(tài)功率。動態(tài)動力系統(tǒng)總的能量輸出為零，在一個完整的行駛循環(huán)里。這就意味著動態(tài)動力系統(tǒng)在一個行駛循環(huán)的最后并沒有損失能量。它的功能僅相當于一個能量緩沖器。在混和動力車里，穩(wěn)定的動力可能由內(nèi)燃機，轉子發(fā)動機，或者燃料電池等提供。內(nèi)燃機或燃料電池比單一動力系統(tǒng)的設計要小很多，因為動態(tài)功率可以用動態(tài)動力系統(tǒng)來彌補，并且可以在最有效率的區(qū)域穩(wěn)定的工作。電動機動態(tài)動力系統(tǒng)，可以由電池，超級電容器，飛輪（機械電池）和其他組合提供。
5.2混合動力驅動系統(tǒng)
混合動力汽車的架構一般定義為在能量流路線上的組件和控制端口之間的連接。傳統(tǒng)上，混合動力汽車可以分別為兩種類型，一種是串聯(lián)式混合動力，一種是并聯(lián)式混合動力。有趣的是，在2000年，一些新引入的混合動力汽車不能被分為這兩種之一。因此，混合動力汽車被分為四種類型：串聯(lián)式混合動力、并聯(lián)式混合動力、串并聯(lián)式混合動力和復雜混合動力，其各功能如圖5.3所示?？茖W的來講，上面的分類不是很清楚，可能會導致混亂。實際上，混合動力汽車中有兩種驅動系統(tǒng)中的能量的流動，分別是機械能和電能。把兩種能量添加在一起或者在功率合并點上把能量一分為二時，總伴有相同的能量類型，也就是說，是電能和機械能，不是電氣和機械。所以對混合動力汽車結構更準確的定義或許是把功率耦合或者是解耦的一個特性，比如電子耦合驅動系統(tǒng),機械耦合驅動系統(tǒng)和機電耦合驅動系統(tǒng)。
圖 5.3 混合動力汽車的分類 (a) 串聯(lián)式 (電耦合), (b) 并聯(lián)式 (機械 耦合), (c) 串并聯(lián)式 (機電耦合),和 (d) 復雜式(機電耦合) .
圖5.3a是傳統(tǒng)上被稱為串聯(lián)式混合動力驅動系統(tǒng)的配置。這種配置的主要特點是兩種電能加在一起的電力耦合，電源轉換器的功能是控制電流的流向，使電流從電動機到發(fā)電機，或者在相反的方向上，從電動機到電池。電源轉化器為燃油箱，內(nèi)燃機和發(fā)電機提供主要能量并且具有作為能量保險杠的電池的功能。
圖5.3b是傳統(tǒng)上稱為并聯(lián)式混合動力驅動系統(tǒng)的配置。這種配置的主要特性是兩種機械能加在一起在的機械耦合。內(nèi)燃機是主要的動力源，電池和電動馬達驅動器構成能量保險杠。能量流只可以被能量源（發(fā)動機和電動馬達）控制。
圖5.3c是傳統(tǒng)上被稱為串并聯(lián)式混合動力驅動系統(tǒng)的配置。這種配置的主要特性是機械能和電能的動力耦合。實際上,這個配置是串聯(lián)和并聯(lián)的組合結構,它具有串聯(lián)式混合動力和并聯(lián)式混合動力配置所有的特性甚至更多。另一方面,它相對更復雜,可能成本更高。
圖5.3是被稱為復雜混合動力驅動系統(tǒng)的配置，它和串并聯(lián)式混合動力有類似的結構。唯一的區(qū)別是,電動耦合功能從電源轉換器移到了電池組上，同時增加了一個電源轉換器用來連接電動機/發(fā)電機和電池。
我們將注重研究前三種動力驅動系統(tǒng)——串聯(lián)式、并聯(lián)式和串并聯(lián)式。
5.2.1串聯(lián)式混合動力驅動系統(tǒng)（電耦合）
串聯(lián)式混合動力驅動系統(tǒng)是兩種電能共同給一個單獨動力裝置（電動機）提供動能來推進汽車的系統(tǒng)。最常用的配置如圖5.4所示：單向的能量來源是燃油箱，單向換能器(動力裝置)則是一個內(nèi)燃發(fā)動機和發(fā)電機的耦合。發(fā)電機的輸出通過一個可控的電子轉換器(整流器)連接到電源直流總線。雙向能量的來源是通過可控的、雙向的電力電子轉換器(直流/直流轉換器)連接到電源直流總線的電池組。電源總線也連接到電動馬達的控制器上。牽引電機通過不同控制，既可作為電動機正向運動也可作為發(fā)電機反向運動。這種驅動系統(tǒng)可能需要利用充電器通過墻上通電的插頭給電池充電。串聯(lián)式混合動力驅動系統(tǒng)通常會像電動汽車一樣，添加一個額外的內(nèi)燃發(fā)電機來彌補因電池能量密度低導致的續(xù)航能力不足。
圖5.4 混合動力汽車動力驅動系統(tǒng)配置.
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