城市公交車節(jié)能減排能力分析設(shè)計(jì)--制動(dòng)能量回收系統(tǒng)

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集成式發(fā)動(dòng)機(jī)輔助混合動(dòng)力系統(tǒng) 摘要 本論文介紹了用于設(shè)計(jì)和開發(fā)Honda Insight發(fā)動(dòng)機(jī)的技術(shù)方法，一種新的發(fā)動(dòng)機(jī)輔助混合動(dòng)力汽車，其總開發(fā)目標(biāo)是在廣泛的行駛條件下達(dá)到當(dāng)今Civic消耗量的一半，實(shí)現(xiàn)35km/L（日本10-15模式），3.4L/km（98/69/EC）的消耗量。為了達(dá)到這個(gè)目標(biāo)，加入了許多用于包裝和集成發(fā)動(dòng)機(jī)輔助系統(tǒng)以及改善發(fā)動(dòng)機(jī)效率的新技術(shù)，開發(fā)了一種新的集成式發(fā)動(dòng)機(jī)輔助混合動(dòng)力發(fā)動(dòng)機(jī)系統(tǒng)。這是結(jié)合了一種低空氣阻力的新型輕稆車身開發(fā)的。環(huán)境性能目標(biāo)也包括了低排放（日本2000年標(biāo)準(zhǔn)的一半，EU2000標(biāo)準(zhǔn)的一半），高效率和楊回收性。對消費(fèi)的關(guān)鍵特性全面考慮，包括碰撞安全性能，操縱性和運(yùn)行特性。 1． 緒論 為減小汽車對社會和環(huán)境的沖擊要求其更干凈并且能量效率更高更節(jié)能，空氣質(zhì)量更好。降低CO2排放問題作為全球環(huán)境焦點(diǎn)提出，解決這些問題的方法之一就是混合動(dòng)力汽車。Honda已開發(fā)并向遍及全球的幾大市場輸入Insight，新一代車輛設(shè)計(jì)。?Insight將混合動(dòng)力系與先進(jìn)的車身技術(shù)特性相結(jié)合以符合取得實(shí)際的最高燃油經(jīng)濟(jì)性的總目標(biāo)。 混合動(dòng)力系是發(fā)動(dòng)機(jī)的輔助并聯(lián)平行結(jié)構(gòu)，把IMA叫做集成式發(fā)動(dòng)機(jī)輔助。此動(dòng)力系將把一個(gè)高效電動(dòng)機(jī)與一個(gè)新型小排量VTEC發(fā)動(dòng)機(jī)結(jié)合起來，很輕的鋁車身，改良的空氣動(dòng)力學(xué)以實(shí)現(xiàn)3.4L/100km(CO2：80g/km)98/69/EC燃油經(jīng)濟(jì)性。低排放性能也已達(dá)到EU排放水平為目標(biāo)。 除減速能的重用之外，集成式發(fā)動(dòng)機(jī)在典型的市區(qū)行駛加速時(shí)提供大助力扭矩，顯著地減小了發(fā)動(dòng)機(jī)拜師，提高了發(fā)動(dòng)機(jī)效率。接近56kW每噸的功率/質(zhì)量比保證了穩(wěn)定的爬坡能力和高速的常速行駛能力。新發(fā)動(dòng)機(jī)技術(shù)包括促進(jìn)高效快速的催化劑活性化的一種新VTEC（電子控制可變配氣相位和氣門升程）缸蓋設(shè)計(jì)，促進(jìn)稀薄燃燒能降低排放的新型稀NOx催化轉(zhuǎn)化器，廣泛的減摩及減重特色也用于其中。 2． 開發(fā)目標(biāo)及開發(fā)理念 開發(fā)目的在于達(dá)到極低燃油消耗量。我們定下的目標(biāo)是當(dāng)今產(chǎn)品Civic燃油經(jīng)濟(jì)性的兩倍，Honda的典型高燃油經(jīng)濟(jì)性轎車——7.0L/100km(93/116/EC)，因而Insight在世界汽油機(jī)轎車中擁有最低的燃油消耗量。排放性能由于低燃油消耗量的緣故而趨于犧牲，但是，我們?nèi)詻Q定配備其它大多數(shù)批量生產(chǎn)的汽車所具備的低排放性能，在回收性（另一重要環(huán)境問題），碰撞安全性能以及操縱性和造型等汽車的基本性能方面也有考慮。綜上所述，我們的開發(fā)目標(biāo)如下： 世界最好燃油消耗性能 超低排放 超回收性 全世界最高碰撞安全性能水平 先進(jìn)造型 實(shí)用特色和操縱靈敏性 舒適的帶有個(gè)性使用空間的二座結(jié)構(gòu) 3． 降低燃油消耗量的策略 為了建立起取得低燃油消耗目標(biāo)的技術(shù)途徑，我們對一輛裝配1.5L發(fā)動(dòng)機(jī)聽Civic基型車輛能量消耗進(jìn)行細(xì)節(jié)分析。為取得低燃油消耗和其它上述目的，我們發(fā)現(xiàn)將目標(biāo)效率如圖形1所示粗略地分為三部分是十分有用的。劃分如下： 發(fā)動(dòng)機(jī)自身熱效率的改善 混合動(dòng)力裝置制動(dòng)能量再生和怠速止擋應(yīng)用 降低重復(fù)和減小空氣阻力和滾動(dòng)阻力的車身技術(shù) 圖1. 兩倍于CIVIC燃油經(jīng)濟(jì)性的目標(biāo) 我們開發(fā)這種新集成式發(fā)動(dòng)機(jī)輔助動(dòng)力系瞄準(zhǔn)為21世紀(jì)汽車動(dòng)力系建立一個(gè)基準(zhǔn)。這種動(dòng)力系適合于下一代汽車，同時(shí)達(dá)到了極低3.4L/100km極低的燃油消耗量和低廢氣排放性能。本篇論文對新開發(fā)的IMA系統(tǒng)作了報(bào)告，包括用于Honda Insight的稀燃發(fā)動(dòng)機(jī)，電動(dòng)機(jī)功率控制單元，蓄電池技術(shù)和廢氣排放控制技術(shù)。 4． IMA系統(tǒng)的目的 為達(dá)到目的世界最低燃油消耗量，在開發(fā)下一代IMA 混合動(dòng)力系統(tǒng)時(shí)我們盡可能多地結(jié)合已取得的技術(shù)方法。為達(dá)到這個(gè)目標(biāo)，建立了以下四個(gè)系統(tǒng)開發(fā)主題： 減速能量的再生 發(fā)動(dòng)機(jī)效率的改善 怠速止擋系統(tǒng)運(yùn)用 動(dòng)力系尺寸、重量的減小 5． 1系統(tǒng)結(jié)構(gòu) 圖2. IMA 系統(tǒng) 圖 3IMA系統(tǒng)的發(fā)動(dòng)機(jī)速度 (rpm)/輸出特性曲線 如圖2所示，IMA系統(tǒng)以發(fā)動(dòng)機(jī)作為主動(dòng)力源，加速時(shí)用電動(dòng)機(jī)作為輔助動(dòng)力源。用電動(dòng)機(jī)作為輔助動(dòng)力源簡化了整個(gè)系統(tǒng)并可采用輕型緊湊的發(fā)動(dòng)機(jī)，蓄電池和功率控制單元（PCU）。 在發(fā)動(dòng)機(jī)與變速器間布置了一個(gè)永磁直流無電刷電動(dòng)機(jī)，減速時(shí)為每個(gè)傳動(dòng)裝置計(jì)算出減速比，PCU控制發(fā)電機(jī)發(fā)電（再生能量）對鎳金屬氫蓄電池充電，加速時(shí)由油門開度，發(fā)動(dòng)機(jī)參數(shù)，蓄電池充電狀態(tài)計(jì)算出輔助動(dòng)力提供量（此后稱輔助），PCU控制蓄電池流向驅(qū)動(dòng)馬達(dá)的電流量。 5. 2再生減速能量 通過回收再生減速能量可在加速時(shí)補(bǔ)充發(fā)動(dòng)機(jī)輸出并減小油耗量。減小包括發(fā)動(dòng)機(jī)摩擦損失在內(nèi)的工作能量損失引起的阻力可增加可用的再生能，尤其是使發(fā)動(dòng)機(jī)拜師減少到最小是減小摩擦的有效措施。降低發(fā)動(dòng)機(jī)排量還有其它好處，例如減輕重量增加熱效率。IMA系統(tǒng)通過優(yōu)化發(fā)動(dòng)機(jī)和變速箱參數(shù)有效地增加了減速時(shí)的再生能量。 5．3減小發(fā)動(dòng)機(jī)排量 改善混合動(dòng)力系燃油經(jīng)濟(jì)性中減小發(fā)動(dòng)機(jī)排量是一個(gè)十分重要的因素。但是現(xiàn)代汽車須在廣泛的動(dòng)態(tài)范圍內(nèi)運(yùn)行，減小排量就等于降低汽車的基本性能特征。如圖3所示的輸出特性曲線，利用電動(dòng)機(jī)的大轉(zhuǎn)矩性能特征IMA系統(tǒng)在低速范圍內(nèi)輔助發(fā)動(dòng)機(jī)。電動(dòng)機(jī)在低轉(zhuǎn)速時(shí)能將總轉(zhuǎn)矩提高50%，IMA系統(tǒng)取得了快速重啟和不可思議的平滑啟動(dòng)成果。高轉(zhuǎn)速范圍時(shí)用電子控制可變配氣相位和氣門升程發(fā)動(dòng)機(jī)提高輸出。因此保證了足夠的峰值功率，便可用一個(gè)新的1.0L小排量發(fā)動(dòng)機(jī)。 5．4稀燃發(fā)動(dòng)機(jī)運(yùn)行 基于節(jié)氣門開度，以電動(dòng)機(jī)輔助，創(chuàng)造出十分線性的轉(zhuǎn)矩特性，由此改善了操縱靈活性。除此之外，電動(dòng)機(jī)輔助在中載條件下可擴(kuò)大稀燃運(yùn)行范圍，顯出了新開發(fā)稀烯發(fā)動(dòng)機(jī)的潛力。 5．5怠速止推系統(tǒng) 制動(dòng)時(shí)停止發(fā)動(dòng)機(jī)而不是怠速空轉(zhuǎn)也是減小消耗量的有效措施。如圖4所示，為了以最小消耗量重啟發(fā)動(dòng)機(jī)，發(fā)動(dòng)機(jī)須在打火前通過集成式發(fā)動(dòng)機(jī)快速轉(zhuǎn)到600rpm或更高的的轉(zhuǎn)速。加上發(fā)動(dòng)機(jī)停止運(yùn)行空轉(zhuǎn)省油，可以使消耗量最小。在執(zhí)行怠速止擋時(shí)須注意許多問題，包括判斷駕駛者停車趨向，重啟準(zhǔn)備，提供減速平滑感，發(fā)動(dòng)機(jī)停止時(shí)最小化車身振動(dòng)。 Figure 4.Time (sec) The number of cranking in the engine start 圖4 起動(dòng)電機(jī)的轉(zhuǎn)矩 5． 電動(dòng)機(jī)輔助機(jī)構(gòu) 6． 1開發(fā)目標(biāo) 通過限速IMA電動(dòng)機(jī)功能在阻力和再生兩方面，確立的開發(fā)主題以取得以下兩點(diǎn)： 簡單緊湊結(jié)構(gòu) 系統(tǒng)重量不大于整車質(zhì)量的10% 6．2直流無電刷電動(dòng)機(jī) 薄且緊湊的直流無電刷電動(dòng)機(jī)具有發(fā)動(dòng)機(jī)輔助和能源再生功能安裝在曲軸上（圖5），加速時(shí)輔助電動(dòng)機(jī)是減小消耗量的十分有效的措施。這是一種高效、緊湊、輕型、永磁型三相同步電動(dòng)機(jī)，最大輸出功率為10kW。除了開發(fā)技術(shù)以減輕重量、提高效率之外，我們也盡可能把電動(dòng)機(jī)做得最薄以獲得緊湊的動(dòng)力系。熔模鑄造法用于轉(zhuǎn)子，靠安裝在曲軸上的彎曲而旋轉(zhuǎn)。與正常鑄造產(chǎn)品相比取得了高強(qiáng)度更輕的重量。轉(zhuǎn)子磁鐵方面，對HONDA EV PLUS的燒結(jié)釹磁鐵作了進(jìn)一步的改良，扭轉(zhuǎn)強(qiáng)度提高了近90%，熱阻也得到改良。這種設(shè)計(jì)也使電動(dòng)機(jī)無需冷卻系統(tǒng)。發(fā)明了一種有凸極集中繞組的可拆式定子結(jié)構(gòu)并用于減小電動(dòng)機(jī)的軸向?qū)挾?。比傳統(tǒng)波形繞法，如圖6所示。除此之外，從銅極引出的集中配電母線卡環(huán)可用于向定子兩端線圈供電的線束固定，這使結(jié)構(gòu)變得極簡單緊湊。這些改良得到了一個(gè)厚度僅60mm的極薄電動(dòng)機(jī)，與傳統(tǒng)技術(shù)相比在厚度減小了40%。 圖5 電機(jī)剖面圖 Wave winding Salient pole winding 圖6 繞阻比較 圖7 電機(jī)的剖視圖 6．3鎳金屬氫蓄電池 鎳金屬氫蓄電池用于存儲和為電動(dòng)機(jī)輔助提供電力。這是一種先進(jìn)的蓄電池，它安裝于HONDA EV PLUS電動(dòng)汽車上，已經(jīng)在高能蓄電池中取得了成就。這種混合動(dòng)力汽車蓄電池以穩(wěn)定輸出為特色，而不管蓄電池充電狀態(tài)如何，且在應(yīng)用中十分耐用。蓄電池是20個(gè)模塊的集成結(jié)構(gòu)，每個(gè)模塊包括以網(wǎng)格狀串聯(lián)的6個(gè)D型單電池，這120個(gè)1.2V的單電池全部以串聯(lián)方式聯(lián)結(jié)形成了總電池容量為144V的容量。 6．4功率控制單元（PCU） PCU精確控制電動(dòng)機(jī)輔助/再生并向12V動(dòng)力源提供動(dòng)力，它具備內(nèi)置冷卻功能。這就使其有一輕型，有效緊湊的結(jié)構(gòu)。使用高效率冷卻肋片和鎂冷卻套集成的購銷風(fēng)冷系統(tǒng)使重量顯著減輕。驅(qū)動(dòng)馬達(dá)的變壓器是PCU內(nèi)部最重要的元件，將開關(guān)元件集成為鄭重三相交流的單獨(dú)模塊，而在EV PLUS上都是分立的。驅(qū)動(dòng)電路最小分并以高密度集成為IC。這些改良不僅使重量顯著減輕，也改變了功率轉(zhuǎn)化效率，更好的是，采用高效相控驅(qū)動(dòng)電動(dòng)機(jī)降低了發(fā)熱量，使其可以用輕型簡單的風(fēng)冷系統(tǒng)。 Figure 8.Inverter Cut view of PCU Heat Sink case 圖8 7發(fā)動(dòng)機(jī) 7．1開發(fā)目標(biāo) 為了在廣泛的工況下獲得低油耗以下四點(diǎn)作為開發(fā)主題： 熱效率改善 減小機(jī)械損失（與傳統(tǒng)設(shè)計(jì)相比小10%） 減小尺寸和降低重量（同類產(chǎn)品中最輕） EU2000標(biāo)準(zhǔn)的一半 7．2發(fā)動(dòng)機(jī)總觀及其規(guī)格 發(fā)動(dòng)機(jī)規(guī)格如表格1所示，其主要新特色和他們的目的如表格2所示。首先，配備IMA系統(tǒng)的汽車以接近1000cm3的排量為最佳，因此選擇了3缸發(fā)動(dòng)機(jī)以使燃燒室的面容比最小，并減小機(jī)械損失。 7．3油耗 由于在低轉(zhuǎn)速時(shí)電動(dòng)機(jī)輔助加強(qiáng)和VTEC發(fā)動(dòng)機(jī)充足的峰值輸出功率使得在電動(dòng)機(jī)輔助動(dòng)力系中可以大大地減小發(fā)動(dòng)機(jī)排量。這款發(fā)動(dòng)機(jī)的一個(gè)重要特色是通過稀燃技術(shù)而有顯著的改善的燃燒率。采用了包括進(jìn)氣渦流口新氣缸內(nèi)強(qiáng)化渦流技術(shù)以達(dá)到這點(diǎn)，通過改良指示效率而獲得的緊湊燃燒室和高壓縮比對其也有幫助。這導(dǎo)致了與傳統(tǒng)稀燃發(fā)動(dòng)機(jī)相比更短的燃燒時(shí)間，在更高的空燃比下使其在更稀的范圍內(nèi)燃燒，顯著地降低了油耗。這種強(qiáng)渦進(jìn)氣口和緊湊的燃燒室結(jié)果是在傳統(tǒng)VTEC稀燃技術(shù)上的革新。傳統(tǒng)VTEC發(fā)動(dòng)機(jī)中，渦流是靠在低速工況下關(guān)閉一個(gè)進(jìn)氣閥門產(chǎn)生的，然而在新發(fā)動(dòng)機(jī)中進(jìn)氣閥和進(jìn)氣口被排式豎直結(jié)構(gòu)以在可燃物流向氣缸時(shí)產(chǎn)生強(qiáng)渦流。 傳統(tǒng)VTEC結(jié)構(gòu)中進(jìn)排氣搖臂各由獨(dú)立的搖臂軸支撐，如圖10所示，新VTEC機(jī)構(gòu)將其合成一根單獨(dú)的搖臂軸，顯著地減小了尺寸，還將氣門角從460減小為300，容許強(qiáng)旋渦形氣門及更緊湊的燃燒室。 圖9 發(fā)動(dòng)機(jī)的側(cè)視圖 圖10 氣缸的剖面圖 7．4減小機(jī)械損失 除了改良指示熱效率，減小機(jī)械損失對改善燃油經(jīng)濟(jì)性也很重要，為了達(dá)到這個(gè)目標(biāo)，采用了以下低磨擦技術(shù)： 同軸滾子VTEC機(jī)構(gòu) 活塞微波紋處理 偏置氣缸結(jié)構(gòu) 低張力活塞環(huán) 連桿滲碳 同軸滾子VTEC結(jié)構(gòu)Honda S2000（大功率跑車發(fā)動(dòng)機(jī)）技術(shù)向單凸輪軸VTEC機(jī)構(gòu)的改進(jìn)。通過凸輪軸上的搖臂滑動(dòng)區(qū)域使用滾針軸承可將凸輪軸驅(qū)動(dòng)機(jī)構(gòu)損失減小70%。另外，將VTEC開關(guān)活塞加入滾針軸承內(nèi)軸同時(shí)減小了尺寸與重量。 圖11 VTEC滾子剖面圖 活塞微波紋處理由創(chuàng)造微波表面的活塞裙部處理組成，它提高了油膜抑制性能，使用低摩擦損失機(jī)油時(shí)將減小近30%的摩擦，這些功效開發(fā)了 標(biāo)準(zhǔn)相符的0W-20級低粘度油，其摩擦減小效用是發(fā)動(dòng)機(jī)馬達(dá)試驗(yàn)測量的，測試結(jié)果如圖12所示。現(xiàn)今發(fā)動(dòng)機(jī)技術(shù)中，HTTS處于極限摩擦值進(jìn)精度為7.5Mpa，同先進(jìn)低摩擦發(fā)動(dòng)機(jī)結(jié)合應(yīng)用，極限值比當(dāng)今的發(fā)動(dòng)機(jī)低得多。如圖13所示，低摩擦技術(shù)大大地減小了發(fā)動(dòng)機(jī)的總摩擦力。總的來說，與傳統(tǒng)1.0L發(fā)動(dòng)機(jī)相比降低了10%以上。 圖12 摩擦減小中的極限 圖13 發(fā)動(dòng)機(jī)摩擦 7．5減小重量 總觀了發(fā)動(dòng)機(jī)中幾乎所有零件結(jié)構(gòu)和材料，帶著創(chuàng)造世界1.0L產(chǎn)品中最輕的發(fā)動(dòng)機(jī)目的，減輕重量甚至延伸到了骨架式結(jié)構(gòu)技術(shù)和材料技術(shù)領(lǐng)域，如用于S2000的連桿滲碳。表面強(qiáng)化處理大大加快了發(fā)動(dòng)機(jī)的營運(yùn)速度，我們以此為IMA發(fā)動(dòng)機(jī)制造出更細(xì)的連桿，與傳統(tǒng)連桿相比重量減輕了近30%。 圖14 磁性油底殼 大多數(shù)油底殼是用鋼板或鋁合金制造，傳統(tǒng)的鎂材料已經(jīng)有高溫機(jī)油承受能力的問題，與傳統(tǒng)材料相比，能在1200C以上溫度承受顯著落差的蠕變強(qiáng)度，我們開發(fā)的新型鋁制的底殼（圖14）能承受高達(dá)1500C的蠕變強(qiáng)度。油底殼用有鋁制墊片的鋼制螺栓固定以防止電蝕。此油底殼經(jīng)鋁制的輕35%，在重量的減輕是與兩金屬比質(zhì)量相比的 為進(jìn)一步擴(kuò)大塑制零件的應(yīng)用，塑制材料在進(jìn)氣歧管、缸罩、水泵、皮帶輪等進(jìn)氣系統(tǒng)零件中得到采用，這些變化使發(fā)動(dòng)機(jī)自重小于60kg是世界1.0L產(chǎn)品中最小的。 7．6廢氣排放性能 本發(fā)動(dòng)機(jī)采用能同時(shí)達(dá)到稀燃和低排放的技術(shù)，顯著地降低了NOx排量，排氣系統(tǒng)發(fā)動(dòng)機(jī)后置改善服燃燒（圖15）。除此之外，將排氣歧管集成在缸蓋上，新開發(fā)了一種能在稀燃工況時(shí)吸收NOx的催化劑，能降低NOx排放。 Figure 15. Section view of emission system 圖15 排放系統(tǒng)的剖面圖 7．6．1集成排氣歧管和缸蓋 傳統(tǒng)缸蓋每個(gè)氣缸獨(dú)立的排氣門，在缸蓋上再安裝一排氣歧管將這些排氣門合起來。如圖16所示，Insight缸蓋有內(nèi)置的排氣門合并的結(jié)構(gòu)，大大地減輕了重量。小小的熱輻射表面減小了廢氣熱損失，使催化過程更早進(jìn)行。 圖16 氣缸蓋主視圖 7．6．2稀NOX催化劑 Insight催化系統(tǒng)包含了NOX吸附材料的三元催化轉(zhuǎn)化器，如圖17所示。 Figure 17. Exhaust gas purification mechanism 圖17 廢氣凈化裝置 在稀燃工況下，廢氣中的NOX被催化劑吸附。傳統(tǒng)三元催化在稀燃工況下，能小量降低NOX，把大部分HC、CO氧化成CO2和H2O。由于廢氣中有大量的氧，所以相對少地降低NOX，大部分NOX都存儲于吸附材料表面。在理論空燃比和更高時(shí)，廢氣被阻擋，利用HC和CO作為還原劑將吸附的NOX還原為氮，同時(shí)吸附過程也在進(jìn)行。因此，利用有NOX吸附作用的三元催化器可有效地降低NOX、HC和CO。此催化劑在稀燃和理論配比工期況下表現(xiàn)出良好的轉(zhuǎn)化性能，在NOX吸附量滿載前有必要再生大氣。稀燃時(shí)催化劑直接吸收NOX，在理論配比時(shí)將NOX還原為無害的氮排出，此催化劑以稀燃工況直接吸附NOX于表面為特征，而不是作為化合物吸附于表面內(nèi)，方便了減小轉(zhuǎn)化，提供了更高的高溫承受能力。此催化器將稀燃工況下的NOX排量降低了傳統(tǒng)的1/10。值得一提的是其吸附轉(zhuǎn)化性能對燃料中硫含量十分敏感，因?yàn)榱驎cNOX爭奪吸附空間。傳統(tǒng)催化器在稀燃運(yùn)行時(shí)基本沒有降低NOX排量，因此需減小稀燃范圍以降低NOX排量。此催化劑確保了稀燃工況下改善燃油經(jīng)濟(jì)性，達(dá)到了EU2000標(biāo)準(zhǔn)，是遵守世界排放標(biāo)準(zhǔn)的高效稀燃發(fā)動(dòng)機(jī)。 7． 結(jié)論 本論文總觀了新開發(fā)電動(dòng)機(jī)輔助混合動(dòng)力系，對其各元件及效率與排放性能作了描述。此動(dòng)力系同時(shí)滿足了極低油耗和低排放，達(dá)到了輕型緊湊的質(zhì)量，我們相信此系統(tǒng)能推動(dòng)21世紀(jì)的汽車技術(shù)。 Development of Integrated Motor Assist Hybrid System: Development of the ‘Insight’, a Personal Hybrid Coupe Kaoru Aoki, Shigetaka Kuroda, Shigemasa Kajiwara, Hiromitsu Sato and Yoshio Yamamoto Honda R&D Co.,Ltd. Copyright ?2000 Society of Automotive Engineers, Inc. ABSTRACT This paper presents the technical approach used to design and develop the powerplant for the Honda Insight, a new motor assist hybrid vehicle with an overall development objective of just half the fuel consumption of the current Civic over a wide range of driving conditions. Fuel consumption of 35km/L (Japanese 10-15 mode), and 3.4L/100km (98/69/EC) was realized. To achieve this, a new Integrated Motor Assist (IMA) hybrid power plant system was developed, incorporating many new technologies for packaging and integrating the motor assist system and for improving engine thermal efficiency. This was developed in combination with a new lightweight aluminum body with low aerodynamic resistance. Environmental performance goals also included the simultaneous achievement of low emissions (half the Japanese year 2000 standards, and half the EU2000 standards), high efficiency, and recyclability. Full consideration was also given to key consumer attributes, including crash safety performance, handling, and driving performance. 1. INTRODUCTION To reduce the automobile’s impact on society and the environment requires that it be increasingly cleaner and more energy efficient. The issues of energy conservation, ambient air quality, and reduction in CO2 emissions are increasing raised as global environmental concerns. One solution for dealing with these issues is the hybrid automobile. Honda has developed and introduced to several major markets worldwide the Insight, a new generation of vehicle design. The Insight combines a hybrid power train with advanced body technology features to meet an overall goal of achieving the highest fuel economy practical. The hybrid power train is a motor assist parallel configuration, termed IMA for ‘Integrated Motor Assist’. This power train combines a highly efficient electric motor with a new small displacement VTEC engine, a lightweight aluminum body, and improved aerodynamics to realize 3.4L/100km (CO2:80g/km) on 98/69/EC fuel economy. Low emissions performance was also targeted with emission levels achieving the EU2000. In addition to recapturing deceleration energy, the integrated motor provides high torque assist during typical urban driving accelerations. This allows a significant reduction in engine displacement and higher engine efficiency. Sustained hill climbing performance and high speed cruising capability are assured by a power-toweight ratio of approximately 56kW per metric ton. New engine technology includes the application of a new VTEC (Variable valve Timing and valve lift, Electronic Control) cylinder head design promoting high efficiency and fast catalyst activation, and a new lean NOx catalyst system which promotes lean burn combustion and a reduction in emissions. Extensive friction and weight reducing features are also applied. 2. DEVELOPMENT TARGETS AND CONCEPT Development was aimed at the achievement of extremely low fuel consumption. We set a target of twice the fuel economy of the current production Civic, Honda’s representative high fuel economy car at 7.0 L/100km (93/116/ EC). As a result, the Insight has the lowest fuel consumption in the world, among gasoline passenger cars. Exhaust emission performance often tends to be sacrificed for the sake of low fuel consumption. However, we also decided to match the low emissions performance achieved by other mass production cars. Consideration was also given to recyclability (another important environmental issue), crash safety performance, and the basic car characteristics including handling and styling. Summarizing the above, our development targets were as follows: · The best fuel consumption performance in the world · Ultra-low exhaust emissions · Superior recyclability · The world's highest level of crash safety performance · Advanced styling · Practical features and responsive handling · Comfortable two-seat configuration with personal utility space 3. POLICIES FOR FUEL CONSUMPTION REDUCTION In order to establish the technical approach for achieving the fuel consumption target, we conducted a detailed analysis of the energy consumption of the base car, a Civic equipped with a 1.5 liter engine. We found that it was useful to divide the targeted efficiency gains roughly into thirds, as shown in Fig. 1, in order to achieve the low fuel consumption and numerous other above-mentioned goals. These divisions are as follows. · Improvement of the heat efficiency of the engine itself · Recovery of braking energy and employment of idle stop using a hybrid power plant · Car body technologies including reduction of weight and reduced aerodynamic and rolling resistance. Figure 1. Target of double the fuel economy of CIVIC Aiming to establish a benchmark for 21st century automobile power trains, we developed this new Integrated Motor Assist power train. This power train simultaneously achieves both extremely low fuel consumption of 3.4L/100km, and low exhaust gas emission performance, befitting a next-generation car. This paper reports on the newly developed IMA system, including the lean burn engine, electric motor, power control unit, battery technology, and exhaust emission control technology used in the "Honda Insight". 4. AIM OF THE IMA SYSTEM While developing this next-generation IMA hybrid system, we incorporated as many currently achievable technologies and techniques as possible, in order to achieve the "world's lowest fuel consumption". The following four system development themes were established in order to meet this target. 1. Recovery of deceleration energy 2. Improvement of the efficiency of the engine 3. Use of idle stop system 4. Reduction of power train size and weight 5. OVERVIEW OF THE IMA SYSTEM 5.1. SYSTEM CONFIGURATION – As shown in Fig. 2, the IMA system uses the engine as the main power source and an electric motor as an auxiliary power source when accelerating. Using a motor as an auxiliary power source simplifies the overall system and makes it possible to use a compact and lightweight motor, battery, and power control unit (PCU). Figure 2. IMA System A permanent magnet DC brushless motor is located between the engine and the transmission. When decelerating, the rate of deceleration is calculated for each gear and the PCU controls the motor to generate electricity (recover energy), which charges a nickel-metal hydride battery. When accelerating, the amount of auxiliary power provided (hereafter called "assist") is calculated from the throttle opening, engine parameters, and battery state of charge. The PCU controls the amount of current flowing from the battery to the drive motor 5.2. RECOVERY OF DECELERATION ENERGY – Recovering deceleration energy through regeneration makes it possible to supplement the engine’s output during acceleration and reduce the amount of fuel consumed. Reducing resistance due to running losses, including engine frictional losses, increases the available energy for regeneration. In particular, minimizing the engine displacement is an effective means of reducing friction. Engine displacement reduction also has several other benefits, such as weight reduction and increased thermal efficiency. The IMA system effectively increases the amount of regeneration during deceleration by optimizing the engine and transmission specifications. 5.3. REDUCTION OF ENGINE DISPLACEMENT – Reducing engine displacement is a very important factor in improving fuel economy of a hybrid drive train. However, modern automobiles have to perform over a wide dynamic range. Reducing the displacement is equivalent to lowering the basic performance characteristics of the car. As shown in the output characteristics graph in Fig. 3, the IMA system assists the engine in the low rpm range by utilizing the hightorque performance characteristic of electric motors. The motor can increase overall toruque by over 50% in the lower rpm range used in normal driving. Output in the high rpm range is increased by using a Variable valve Timing and valve lift Electronic Control (VTEC) engine. Thus sufficient peak power is assured and makes it possible to use a new, small displacement 1.0 liter engine. Figure 3.Engine speed (rpm) Output performance of IMA SYSTEM Assist from the electric motor while accelerating is a very efficient means of reducing the amount of fuel consumed. 5.4. ACHIEVING LEAN BURN ENGINE OPERATION – Assist from the electric motor, based upon the throttle opening, creates quite linear torque characteristics. This, in turn, improves driveability. In addition, motor assist is also provided under moderate load conditions to broaden the lean-burn operating range, bringing out the full potential of the newly developed lean burn engine. 5.5. IDLE STOP SYSTEM – Stopping the engine rather than idling at stops is also an effective means for reducing fuel consumption. In order to restart the engine with the minimum amount of fuel consumption, the engine is quickly cranked to 600 rpm or more by the hightorque integrated motor before ignition occurs, as shown in Fig. 4. This makes it possible to minimize the amount of fuel consumed, in addition to the fuel saved by not running the engine at idle. There are many issues to be considered when performing idle stop. These include judging the driver's intent to stop, preparing for the restart, providing a smooth feeling of deceleration, and minimizing vibration of the car body when the engine stops. Figure 4.Time (sec) The number of cranking in the engine start This IMA system results in the achievement of both very quick restarts and exceptionally smooth starts. 6. MOTOR ASSIST MECHANISM 6.1. DEVELOPMENT OBJECTIVES – By limiting the IMA motor functions to assistance and regeneration, development themes were established to achieve the following two points. 1. A simple and compact structure 2. A system weight of 10% (80 kg) or less of the completed car weight 6.2. THIN PROFILE DC BRUSHLESS MOTOR – A thin and compact DC brushless motor with engine assist and energy regeneration functions was coupled to the engine crank-shaft (Fig. 5). Figure 5. Section view of Motor This is a high efficiency, compact, and lightweight permanent magnet-type three-phase synchronous electric motor with a maximum output of 10 kW. In addition to developing technologies to reduce the weight and increase efficiency, we also aimed to make the motor as thin as possible in order to achieve a compact power train. Lost wax precision casting process was used for the rotor, rotating by bending coupled to the crankshaft. This achieves high strength and lighter weight (approximately -20%) compared with normal cast products. For the rotor magnets, further improvements were made to the neodymium-sintered magnets used in the HONDA EV PLUS, realizing approximately 8% greater torque density and improved heat resistance. This design also results in a motor structure that does not require a cooling system. A split stator structure with salient pole centralized windings was developed and used to reduce the motor axial width. A split stator was adopted to drive the rotor. This makes it possible to use the salient pole centralized windings, which are both more compact and efficient than the conventional coil wave winding method, as shown in Fig. 6. In addition, centralized distribution bus rings (Fig. 7) formed from copper sheets were used for the harness that supplies electricity to the coils on both sides of the stator. This results in an extremely compact and simple structure. These improvements achieve an extremely thin motor with a width of only 60 mm. This represents a 40% reduction in width compared to conventional technology. Wave winding Salient pole winding Figure 6. Compare of winding Figure 7. Cut view of Motor 6.3. NICKEL-METAL HYDRIDE (NI-MH) BATTERY – A nickel-metal hydride battery is used to store and provide electrical energy for the motor assist. This is an advanced battery which has already achieved proven results in the high specific energy version used for the HONDA EV PLUS electric vehicle. The hybrid vehicle battery features stable output characteristics, regardless of the state-of-charge status. It is also extremely durable in this application. The battery pack has an integrated structure consisting of 20 modules, each having six D-size cells connected in series, arranged in a lattice formation. These 120 1.2 V cells are all connected in series for a total battery pack voltage of 144 V. 6.4. POWER CONTROL UNIT (PCU) – The PCU performs precise control of motor assist/regeneration and supplies power to the 12 V power source. It has built-in cooling functions, which give it a lightweight, efficient and compact structure. Significant weight reduction was achieved by integrating an air cooling system using highly efficient cooling fins and a magnesium heat sink case. The inverter for the drive motor, which is the most important component within the PCU, has switching elements integrated into a single module for generating the three-phase AC current. These were separate components on the EV PLUS. The drive circuit has been miniaturized and converted to an IC using high density integration. These improvements have resulted not only in significant weight reduction, but have also improved the power conversion efficiency. Further,