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無錫太湖學院
信機 系 機械制造及自動化 專業(yè)
一、題目及專題
1、 題目 紡織機傳動系統(tǒng)設計
2、 專題 基于蝸輪蝸桿傳動
二、課題來源及選題依據
課題來源為沈陽紡織機械廠實際產品。通過畢業(yè)設計是為了培養(yǎng)學生開發(fā)和創(chuàng)新機械產品的能力，要求學生能夠結合原GD76X1型織機的傳動系統(tǒng)，針對實際使用過程中存在的問題，綜合所學的機械理論設計與方法，對GD76X1型織機變速箱的傳動系統(tǒng)進行改進，從而達到解決問題。
在設計傳動件時，在滿足產品工作要求的情況下，應盡可能多的采用標準件，提高其互換性要求，以減少產品的設計生產成本。
三、本設計（論文或其他）應達到的要求
1、該部件工作時，能運轉正常；
2、擬定工作機構和傳動系統(tǒng)的運動方案，并進行多方案對比分析；
3、當電動機輸入功率時，對主要工作機構進行運動和動力分析；
4、設計GD76X1型織機傳動件系統(tǒng)總裝圖1張（A0）；
5 、設計繪制寸行傳動件蝸輪箱的零件圖1張（A0）；
6、設計繪制零件工作圖12張（二張A0，一張A1，七張A1，
三張A4）；
7、編制設計計算說明書1份（2萬字以上）。
四、接受任務學生：
班 姓名
五、開始及完成日期：
自2012年11月7日 至2013年5月25日
六、設計（論文）指導（或顧問）：
指導教師 簽名
簽名
簽名
教研室主任
〔學科組組長研究所所長〕 簽名
系主任 簽名
年 月 日
I
無錫太湖學院
畢業(yè)設計（論文）
開題報告
題目： 紡織機傳動系統(tǒng)設計
基于渦輪蝸桿傳動
系 機械工程及自動化 專業(yè)
學 號：
學生姓名：
指導教師： （職稱：高工）
（職稱： ）
2012年11月14日
課題來源
沈陽紡織機械廠
科學依據（包括課題的科學意義；國內外研究概況、水平和發(fā)展趨勢；應用前景等）
（1）課題科學意義
在國外編機搶占中國市場的同時，我國的編織企業(yè)也在呼喚國產優(yōu)質編機，對國內編織機械企業(yè)提出新的要求。 在機理構造上，一些國產編機也與進口編機無太大差別。但國產編機在有關在線檢測方面與進口編機的功能差距較大，尚不能很好地滿足有些高檔產品的生產需要；另外，國產編機在生產中的通用性較強，而針對性不高，不易生產出特色產品，這些方面國產編機在今后的生產中有待加強。
國外企業(yè)的競爭，國內用戶要求的不斷提升，編機企業(yè)走創(chuàng)新路子，形成核心競爭力的呼聲更高。國產編織機械與國外同類產品的差距，除了研發(fā)能力．技術創(chuàng)新不足之外，還主要表現在加工精度和運行可靠性兩個方面。因此，必須下大力氣研究從生產過程、管理過程．流通過程與創(chuàng)新的系統(tǒng)優(yōu)化問題，借助系統(tǒng)論控制論的理論，努力消除現存的問題，縮短差距。應加強產學研結合，開創(chuàng)教育與企業(yè)新局面。通過企業(yè)和科研院所的人才與設施、科研與生產互動，加快人才培養(yǎng)和技術提升。
研究編織機的傳動系統(tǒng)，對于提高生產效率降低生產成本具有重要意義。此項研究也是對大學四年所學課程的一次總復習，它將機械制圖、機械設計和機電傳動控制等機械設計制造及其自動化主要專業(yè)課程緊密聯系在一起，利用所學的機械與控制相關知識來解決實際的生產問題，將理論設計與實際運用聯系起來，需要考慮多方面的問題，如成本、系統(tǒng)可靠性和機械設備使用壽命等等。
（2）發(fā)展趨勢
1、高速，高效 2、高靈活性 3、高品質 4、高環(huán)保性
5、紡織數字化
研究內容
通過調研應明白要對一個產品進行改進或創(chuàng)新以滿足用戶的需求，信息的獲取是非常重要的，分析GD76X1型織機傳動件的功能要求，完成GD76X1型織機傳動件的設計研究的結構分析、建模、工藝分析等，在滿足產品工作要求的情況下，應盡可能多的采用標準件，提高其互換性要求，以減少產品的設計生產成本。
擬采取的研究方法、技術路線、實驗方案及可行性分析
通過現場調研與相關資料查閱，對GD76X1型織機傳動進行數學建模，并通過模擬實驗分析建立GD76X1型織機傳動件的實體模型，設計GD76X1型織機傳動件，進行現場實驗，來進行傳動件的最優(yōu)化設計。
研究計劃及預期成果
研究計劃：
2012年10月12日-2012年12月25日：按照任務書要求查閱論文相關參考資料，填寫畢業(yè)設計開題報告書。
2013年1月11日-2013年3月5日：填寫畢業(yè)實習報告。
2013年3月8日-2013年3月14日：按照要求修改畢業(yè)設計開題報告。
2013年3月15日-2013年3月21日：學習并翻譯一篇與畢業(yè)設計相關的英文材料。
2013年3月22日-2013年4月11日：撰寫設計說明書。
2013年4月12日-2013年4月25日： 零件圖、工程圖的繪制。
2013年4月26日-2013年5月20日：畢業(yè)論文撰寫和修改工作。
特色或創(chuàng)新之處
適用于本廠的某生產線的設計，可降低工人的勞動強度和生產成本。
已具備的條件和尚需解決的問題
針對實際使用過程中GD76X1型織機的傳動系統(tǒng)存在的問題，綜合所學的機械理論設計與方法，如何對GD76X1型織機變速箱的傳動系統(tǒng)進行改進，進而提高學生開發(fā)和創(chuàng)新機械產品的能力。
指導教師意見
指導教師簽名：
年 月 日
教研室（學科組、研究所）意見
教研室主任簽名：
年 月 日
系意見
主管領導簽名：
年 月 日
編號
無錫太湖學院
畢業(yè)設計（論文）
題目： 紡織機傳動系統(tǒng)設計
基于渦輪蝸桿傳動
信機 系 機械工程及自動化 專業(yè)
學 號：
學生姓名：
指導教師： （職稱：高工 ）
（職稱： ）
2013 年 5 月 25 日
III
無錫太湖學院本科畢業(yè)設計（論文）
誠 信 承 諾 書
本人鄭重聲明：所呈交的畢業(yè)設計（論文） 紡織機傳動系統(tǒng)基于渦輪蝸桿傳動 是本人在導師的指導下獨立進行研究所取得的成果，其內容除了在畢業(yè)設計（論文）中特別加以標注引用，表示致謝的內容外，本畢業(yè)設計（論文）不包含任何其他個人、集體已發(fā)表或撰寫的成果作品。
班 級：
學 號：
作者姓名：
年 月 日
編號
無錫太湖學院
畢業(yè)設計（論文）
題目： 紡織機傳動系統(tǒng)的設計
---基于蝸輪蝸桿傳動
機電 系 機械制造及自動化 專業(yè)
學 號：
學生姓名：
指導教師： （職稱：高工）
（職稱： ）
2013年 5 月 25 日
無無錫錫太太湖湖學學院院 屆屆畢畢業(yè)業(yè)作作業(yè)業(yè)周周次次進進度度計計劃劃、檢檢查查落落實實表表系別：信機系班級：機械97 學生姓名：儲傳民課題（設計）名稱：紡織機傳動系統(tǒng)設計周次起止日期工作計劃、進度每周主要完成內容存在問題、改進方法12013.3.4下達畢業(yè)設計任務實習實訓，參與工作存在問題：對于實際操作不是很了解。改進方法：參與工作，逐漸了解，參與其中。22013.3.8填寫畢業(yè)設計開題報告填寫畢業(yè)設計開題報告存在問題：對課題難易程度理解不夠，難點分析不足，分析能力欠缺，許多問題不是很明白。改進方法：在指導老師的幫助下，進一步消化本課題。32013.3.11檢查畢業(yè)設計準備情況 修改完善畢業(yè)設計開題報告存在問題：對課題難點分析不足，分析能力欠缺，對課題理解不深，頭腦里沒設計的東西的概念改進方法：在指導老師的幫助下，整改開題報告。42013.3.16查閱參考資料查閱與設計有關的參考資料不少于10本，其中外文不少于2本存在問題：由于工作原因，空閑時間很少，查閱資料太少。改進方法：利用一切時間，去圖書館和網上查找相關資料52013.3.23GD76X1型織機傳動工藝方案分析產品圖、分析沖壓工序，分析沖壓工藝，優(yōu)選確定模具沖壓工藝方案存在問題：缺乏實際操作經驗，制定的工藝方案不合理。改進方法：多去咨詢師傅了解實際生產過程，重新確立合理的工藝方案。62013.4.1GD76X1型織機結構分析與計算確定模具結構，計算所需各種尺寸存在問題：模具結構設計不合理，尺寸計算有誤差公式運用錯誤。對模具設計數據不了解改進方法：查閱多種參考資料，改進模具結構，提高計算正確率。72013.4.15GD76X1型織機工藝方案確定分析產品圖、分析沖壓工序，分析沖壓工藝，優(yōu)選確定模具沖壓工藝方案存在問題：缺乏生產經驗，對沖壓順序不了解，沖壓工序安排不合理改進方法：多了解實際生產過程，重新確立合理的工藝方案。82013.4.20裝配圖初步繪制減速器裝配圖存在問題：對CAD運用不熟悉，畫圖速度較慢改進方法：重新確定合理的表達視圖，多加運用繪圖軟件，提高畫圖速度92013.4.25裝配圖修改減速器裝配圖存在問題：2D裝配圖中部分標準件畫法不正確，尺寸不精確。改進方法：按機械制圖要求改正不正確的畫法，修改尺寸。102013.4.28完成零件圖修改減速器裝配圖存在問題：2D裝配圖中技術要求填寫不合理，明細欄填寫不正確。改進方法：按機械制圖要求改正不當之處。112013.5.5說明書、摘要、小結繪制減速器零件圖，不少于5個存在問題：零件圖的表達方案不合理，尺寸不符合實際需要，技術要求不規(guī)范。改進方法：修改零件圖的表達方案，完善尺寸標注和技術要求。122013.5.13檢查、指導設計說明書、摘要和小結編寫完成設計說明書、摘要和小結存在問題：說明書的格式不規(guī)范，摘要不合理，關鍵詞不恰當。改進方法：根據說明書規(guī)范要求更改，重新按要求編寫摘要。132013.5.15上交資料、答辯整理所有資料上交指導教師，答辯資料整理欠合理，按學院要求整理并裝訂，進行答辯 說明：1、“工作計劃、進度”、“指導教師意見并簽字”由指導教師填寫，“每周主要完成內容”，“存在問題、改進方法”由學生填寫。2、本表由各系妥善歸檔，保存?zhèn)洳?。系別：信機系班級：機械97 學生姓名：儲傳民課題（設計）名稱：紡織機傳動系統(tǒng)設計 存檔編碼：開始日期:指導教師意見并簽字備 注 說明：1、“工作計劃、進度”、“指導教師意見并簽字”由指導教師填寫，“每周主要完成內容”，“存在問題、改進方法”由學生填寫。開始日期:
無錫太湖學院
畢業(yè)設計（論文）
相關資料
題目： 紡織機傳動系統(tǒng)的設計
-----基于蝸輪蝸桿傳動
機電系 機械工程及自動化專業(yè)
學 號：
學生姓名：
指導教師： 鮑（職稱：高工 ）
（職稱： ）
2013年 5 月 25日
目錄
（1） 封面；
（2） 目錄；
（3） 畢業(yè)設計（論文）開題報告；
（4） 畢業(yè)設計（論文）外文資料翻譯及原文；
（5） 學生“畢業(yè)設計（論文）計劃、進度、檢查及落實表”；
（6） 實習鑒定表。
無錫太湖學院
Designing and Modeling a Torque and Speed Control
Transmission (TSCT)
1 Background
The Partnership for a New Generation of Vehicles (PNGV) was formed between the Federal Government, Ford Motor Company, General Motors Corporation, and Chrysler Corporation. The goal of this partnership was to allow the major U.S. automotive manufactures to collaborate with each other and produce high fuel efficiency, low emissions vehicles for sale to the general public. The performance objective for these manufacturers was to create mid-sized passenger cars capable of attaining an 80 mpg (gasoline) composite fuel economy rating on the Environmental Protection Agency (EPA) city and highway cycles.
Hybrid vehicle technology has shown great promise in attaining the goals set forth by the PNGV. Hybrid electric vehicles (HEV ) employ technology that helps bridge the gap between the future hope of an electric vehicle (EV) and today’s current vehicles. Within the past year hybrid electric vehicles have gained an important place in the vehicle market. American Honda Motor Company, Inc. is currently releasing their first generation HEV, the Insight. The Insight is a compact, two pass engey, parallel HEV which achieves more than 65 mpg (composite) on the EPA test cycles: the highest of any production vehicle ever tested. Toyota Motor Corporation has also released a hybrid vehicle for sale to the general public. The Toyota Prius is currently for sale in Japan and will come the United States in the beginning of the year 2000. The Prius is a four passenger combination hybrid employing an a gasoline engine, high power electric motor, and an electromechanical continuously variable transmission (CVT) comprised of a planetary gear train and a high power alternator/motor. It is through technology incorporated in vehicles such as the Prius that automotive transmission design and operation will make significant new advances.
1.1 Current Automotive Transmission Technologies
With the advent of the automobile also came the creation of the automotive transmission. Early vehicles were simple with manual controls for all functions including the transmission. As advances have been made in vehicles over the past several decades, transmission technology has also advanced. The automatic transmission has nearly replaced the manual transmission in all but economy and performance cars. This trend can be attributed to ease of use, higher power engines becoming available, and congestion in urban areas. Another new transmission technology beginning to see application particularly in foreign markets is the continuously variable transmission that offers continuous operation without shifting between a high and low gear ratio.
These three types of transmissions are all similar in function though their objectives are accomplished in different ways. The capabilities of these transmissions are limited to decoupling the engine speed from the speed of wheels and thereby providing one of several forward or reverse gear ratios. Each transmission is also a single input (engine) and single output (drive device). There are typically no provisions for attaching multiple power sources or for extracting power from more than one point.
The exception to this is heavy-duty transmissions equipped with provisions for a power take off for driving auxiliary mechanical equipment. Single input, single output operation limits drive train flexibility for newer systems employing multiple power sources such as those used in the next generation of hybrid vehicles.
1.1.1 Manual Transmission Operation
Manual transmissions are the least complex and oldest design of power transmission available. In simplest form, a manual transmission is a linear combination of a clutch and a directly geared connection. More sophisticated examples rely on this design but add the ability to select other gear ratios to allow different output speeds for the same input speed. Of these types of transmissions, there are two variations: synchronized and unsynchronized. Synchronized manual transmissions are typically used for light duty applications. Coupled to each gear is a synchronizer that allows the operator to disengage the clutch and select whatever gear necessary. The selection of a different gear engages the synchronizer, which then matches engine input speed and transmission output speed before the gears are engaged.
Unsynchronized manual transmissions are more robust by nature. The operator must double-clutch between shifts to match engine and transmission speed manually. However, this allows a transmission of a given size to handle greater load as space previously occupied by the synchronizers can now be dedicated to the use of wider gears. Applications of these types of manual transmissions are for over-the-road trucks and up to larger equipment with total vehicle weights over 100 tons. [1]
1.1.2 Automatic Transmission Operation
Automatic transmissions are a complex assembly of many components that allow for seamless power transmission. Those currently available in production vehicles use torque converters, clutches, and planetary gear sets for the selection of different output ratios. The engine is connected to the torque converter that acts very much like a clutch under some conditions while more like a direct connection in others. The torque converter is a hydraulic coupling that will slip under light load (idle), but engage progressively under higher load. While the torque converter transmits power to the transmission there is a speed reduction across the unit during low speed operation. This reduction is typically between 2.5:1 to 3.5:1 .Once higher vehicle speeds are attained, the torque converter input and output may be locked together to achieve a direct drive though the unit. The output of the torque converter is typically connected to a hydraulic pump that provides the necessary pressure to engage different clutches within the transmission and the planetary drive. Different gear ratios are created through the use of two or more planetary gear sets. These gear sets are combined with clutches on different elements. By clutching and declutching different elements, multiple gear ratios are possible.
Basic automatic transmissions are equipped with a single control input that is throttle position. The combination of this with the hydraulic pressure created within the transmission allows for mechanical open loop control of all gear selections. Newer variations of the automatic transmission are equipped with electronic feedback controls. Shift logic is dependent on many more variables such as engine speed, temperature, current driving trend, throttle position, vehicle accelerations, etc. This allows the transmission controller to monitor vehicle operation and using a rule-based control strategy decide , which gear is best suited to the current driving conditions. Newer systems are also integrated with the engine controller such that a vehicle control computer has authority over engine and transmission operation simultaneously. This allows for such features as increasing engine speed during high-speed downshifts to match engine and transmission speed for smoother shifting and retarding fueling and ignition timing during high power up shifts to reduce ‘jerk’. Previously, transmission control was much simpler because overrunning clutches were employed in higher gears that only allowed for coasting to conserve fuel. [1]
1.1.3 Continuously Variable Transmission Operation
Continuously variable transmissions are one of the emerging transmission technologies of the last twenty years. This type of transmission allows power transmission over a given range of operation with infinitely variable gear ratios between a high and low extreme. These transmissions are constructed using two variable diameter pulleys with a belt connecting the two. As one pulley increases in size, the other decreases. This is accomplished by locating on one shaft a stationary sheave and a movable sheave. For automotive applications, a hydraulic actuator controls movement of the sheave. However, centrifugal systems along with high power electronic solenoids may be used. A second shaft in the CVT contains the other stationary sheave and movable sheave also controlled hydraulically. A flexible metal belt is fitted around these two pulleys and the movable sheaves are located on opposite sides of the belt.
There are two variations of this type of transmission: push belt and pull belt Pull belt CVT were the first type to be manufactured due to simplicity. A clutch is attached between the first pulley and the engine while the output of the second pulley was connected to a differential and thus the wheels. A hydraulic pump is used to control the diameter of the two different pulleys. As power is applied the first pulley creates a torque that is transmitted through the belt (under tension) to the second pulley. Control of the transmission ratio is usually a direct relationship dependent upon throttle position.
Push belt CVT, similar in design to the Van , are much the same as pull belt CVT , except that power is transmitted through the belt while under compression. This provides a higher overall efficiency due to the belt being pushed out of the second pulley and lowering frictional losses. Current work with these transmissions is being focused on creating larger units capable of handling more torque.
Efficiency of the CVT is directly related to how much tension is in the belt between the two pulleys. CVT torque handling capacity increases as tension in the belt increases. However, this increased tension lowers power transmission efficiency. The belt must slide across the faces of each pulley as it enters and exits upon each half rotation. This sliding of the belt creates frictional losses within the system. In addition, there may be significant parasitic losses associated with raising the hydraulic pressure required to move or maintain the position of the sheaves in each pulley. [2]
1.1.4 Automatically Shifted Manual Transmission Operation
Automatically shifted manual transmissions are a fairly recent innovation. The benefit of the manual transmission is that (due to the direct mechanical connection through fixed gears) efficiency is very high. The drawback is that there must be some interaction with the user in the selection and changing of gears. Automatically shifted manuals were created to address this issue. These types of transmissions are traditionally synchronized manual transmissions with the addition of automation of the gear selection and control of the clutch. A logic controller is also employed to decide when and how to shift. Automatic shifting is usually accomplished through the use of electro-hydraulics. A high-pressure electric pump supplies pressure to hydraulic solenoids that are used to shift the transmission. A hydraulic ram is also used to engage and disengage the clutch. Current versions of these transmissions also employ unsynchronized gears. This allows for overall smaller packaging to accomplish the same task. Input speed of the engine is monitored along with lays haft speed. When a gear change is initiated, the controller opens the clutch, shifts to the desired gear while matching engine and lay shaft speed, and then closes the clutch again. This shifting operation can all be achieved in less than one third of a second. Automatically shifted manual transmissions shift gears faster than humanly possible. [3]
1.1.5 Manually Shifted Automatic Transmission Operation
Manually shifted automatic transmissions are a variation on control of the transmission. The user is allowed to select either automatic or manual shifting modes.
During automatic mode, the transmission functions identically to an automatic transmission. While in manual shift mode however, the transmission controller allows the user full authority over gear changes as long as the gear change will not over speed the engine. This mode of operation traditionally offers the user tighter, more positive shift feel. The only requirement of an automatic transmission for manual shifting is that shifts must be accomplished rapidly enough to allow the user a feeling of fluidity. The act of shifting must provide the immediate desired response. [3]
1.1.6 Planetary Gear Drive Transmission Operation
Planetary gear sets are unique in that the combination of gears creates a two degree-of-freedom system. The gear sets are comprised of a ring gear, a sun gear in the center, and planetary gears that contact both the ring and the sun gears. Motion of the planetary gears is controlled by the carrier on which each of the planetary gears rotate.
The carrier maintains the position of the planets in relation to each other but allows rotation of all planets freely. Inputs (or outputs) to the gear train are the ring gear, sun gear, and planetary carrier. By prescribing the motion of any two of these parameters, the third is fixed in relation to the other two. By employing one planetary gear train, a fixed ratio between input and output is created. Increasing or decreasing the number of teeth on the sun and ring gears can change this ratio. This in turn changes the number of teeth on the planetary gears, which has no other effect as these gears act as idlers.
When combining more than one planetary gear train at one time, braking or allowing the movement of different elements can create a wide range of effective operation in terms of relative speeds, torque transfer, and direction of rotation. This is the type of system that is used in automatic transmissions described above. These systems are also employed in large stationary power transmission applications. [1]
1.2 Current Hybrid Electric Vehicle Transmission Design
Hybrid vehicles are vehicles that utilize more than one power source. Current propulsion technologies being favored are compression ignition (CI) engines, spark ignition(SI) engines, hydrogen-fueled engines, fuel cells, gas turbines, and high power electric drives. Energy storage devices include batteries, ultra-capacitors, and flywheels.
Hybrid power trains can be any combinations of these technologies. The aim of these vehicles is to use cutting edge technology combined with current mass-produced components to achieve much higher fuel economy combined with lower emissions without raising consumer costs appreciably. These vehicles are targeted to bridge the gap between current technology and the future hope of a Zero Emission Vehicle (ZEV), presumably a hydrogen-fueled fuel cell vehicle. The operation of these systems must also be transparent to the user to enhance consumer acceptability and the vehicle must still maintain all required safety features with comparable dynamic performance all at an acceptable cost.
By combining multiple power sources, overall vehicle efficiency can be improved by the ability to choose the most efficient power source during the given operating conditions. This is key in improving vehicle efficiency because current battery technology dictates that nearly all total energy used by the vehicle across a reasonable range of driving comes from the on-board fuel. Highly adaptive control strategies that may be employed in the next generation of HEV may monitor vehicle speed, desired torque, energy available, and recent operating history to choose which mode of operation is most beneficial. These advanced control schemes will maximize the usage of the fuel energy available by choosing the most efficient means of power delivery at any instant. The reduced usage of energy for a given amount of work may also result in lower exhaust emissions due to a reduction in fuel energy used.
1.2.1 The Advantages and Disadvantages of Series Hybrid Vehicles
Series hybrid vehicles typically have an internal combustion engine (ICE) that is coupled directly to an electric alternator. The vehicle final drive is supplied entirely by an electric traction motor that is supplied energy by the battery pack or combination of engine and alternator. The benefit of this type of operation is the engine speed and torque are decoupled from the instantaneous vehicle load and the engine needs only to run when battery state of charge (SOC) has dropped below some lower level. This allows engine operation to be optimized for both fueling and ignition timing in the case of a spark ignited engine, or fueling and injection timing for a compression ignition engine. The engine is also operated in the most efficient speed and torque without encountering transient operation regardless of load. The result is excellent fuel economy and low emissions. Series HEV operation is exceptionally well suited to highly transient vehicle operation which is prevalent in highly urban areas and city driving. The disadvantage to series hybrid operation is the efficiency losses associated with converting mechanical to electrical and then electrical to mechanical energy. Further losses in system efficiency are realized when the energy is stored in the battery pack for later use. Only a fraction of the energy put into the batteries can be returned due to the internal resistance of the batteries. The mechanical energy of the engine is directly converted to electricity by an alternator that has losses both in internal resistance and eddy currents present. Further losses are incurred when this electrical energy is converted back to mechanical energy by the traction motor and controller. Dynamic performance is also limited, as the engine cannot supplement the traction motor in powering the vehicle.
1.2.2 The Advantages and Disadvantages of Parallel Hybrid Vehicles
Parallel systems also employ two power sources, typically an engine and a traction motor with both directly coupled to the wheels typically through a multi-speed transmission. This requires that the engine see substantial transient operation. However, the motor can act as a load-leveling device allowing the engine to operate in a more efficient operating region. When the vehicle is operating in a low load state the engine can be decoupled from the drive train and shut off, or the motor can be used to charge while driving creating a greater power demand for the engine and storing energy in the battery pack. The disadvantage of parallel hybrids is that direct connection of the engine to the wheels requires transient engine operation. This operation lowers fuel economy and increases exhaust emissions especially when employing SI engines. Ignition timing and fueling cannot be optimized for a single region of operation either. However, dynamic performance of parallel hybrids is much better than that of series hybrids using the same components. Much more power is available as both the engine and motor can provide power to the wheels simultaneously. These characteristics lend parallel HEV to excel in higher load, less transient situations and when using high efficiency engines such as CI engines.
1.2.3 The Advantages and Disadvantages of Combination Hybrid Vehicles
The third variation of hybrid vehicle drive trains is the combination, which is a system that can function both as a series and parallel hybrid. Complex combinations of engines, alternators, and motors can accomplish this with geared connections and multiple clutches. By clutching and declutching different elements, a combination can be designed to function as a series hybrid under low speed transient conditions and then as a parallel hybrid under higher speed and load. This allows for increased efficiency as each mode of operation is employed under the ideal operating conditions. Drawbacks to these systems are increased mechanical and drive train control complexity along with higher weight associated with more components. Controlling these types of systems is much more difficult than either a series or parallel HEV. The system must first be capable of operating as a