6 傳動系統(tǒng)的近期發(fā)展

6.1 電動轉(zhuǎn)向器

近年來，電動轉(zhuǎn)向器取代了中小型汽車常用的液力轉(zhuǎn)向器。這里采用了不同的設(shè)計，即所謂的“雙主動齒輪”轉(zhuǎn)向器或管柱型轉(zhuǎn)向器。在設(shè)計中，伺服作用通過第二主動齒輪與齒條嚙合。其結(jié)構(gòu)詳見圖18。轉(zhuǎn)向力由駕駛員經(jīng)轉(zhuǎn)向盤傳遞給齒輪和齒條。

電動機(jī)由傳感器裝置激活，而后者利用一個交叉軸螺旋齒輪對主動齒輪提供支撐。與液力轉(zhuǎn)向器相比，電動轉(zhuǎn)向器無需使用常設(shè)能源，相反能源僅在轉(zhuǎn)向時提供。這將明顯降低油耗。圖1 9是電動轉(zhuǎn)pressure angle was increased additionally at some side steps.Increasing the number of teeth is most effective.Reduced addendum and increased operating pressure angle have less influence.Traces of noise excitation level versus load range of 10to 100%of nominal load are plotted in Fig.15for some examples from Fig.14.Differences are clearly visible and they have to be considered in optimizing gears for low power loss.Improvements can be achieved with adjusted tooth modifications in doing so.Maximum stresses in case of nominal load are shown in Fig.16.Hertzian pressure is nearly constant for all variants.A distinctive increase of root stresses appears over decreasing loss factor from variant A to H.So an inadequate load－carrying capacity can be a result of minimizing power losses by changing tooth geometry.Finally the load distribution along the line of action is also influencing the level of power losses.Tooth loads at begin and end of contact can be reduced by increased tip relief，which decreases their large proportion to overall power loss as shown in Fig.17.Means of relieving start and end of contact for increased load－carrying capacity are also helpful for minimizing power losses of meshing gears.

圖17 齒端修緣對功率損失的影響Fig.17 Influence of tip relief on gearing power loss

6 Recent transmission developments

6.1 Electromechanical power steering

圖18 一個高度復(fù)雜的機(jī)電一體化的電動轉(zhuǎn)向器結(jié)構(gòu)圖［4］Fig.18 Electromechanical power steering assemblies as a highly complex mechatronic system［4］

In recent years，hydraulic power steering for向系統(tǒng)在NEDC循環(huán)試驗中的測量結(jié)果。采用電動轉(zhuǎn)向器后可節(jié)約6%的油耗。采用一千萬套電動轉(zhuǎn)向器共可減少CO2排放930萬噸［4］。

6.2 自動變速器

為滿足不斷增加的降低油耗和CO2排放的要求，ZF公司開發(fā)了用于標(biāo)準(zhǔn)傳動的8檔自動變速器［5］。新一代變速器的目標(biāo)是為用戶帶來效益。圖20所示的8檔變速器具有5套換檔機(jī)構(gòu)和4個行星排。傳動比范圍是7.05。理想的速比范圍、高效的齒輪傳動效率、平衡的旋轉(zhuǎn)速度以及轉(zhuǎn)矩分流等特點造就了一個高效和緊湊的設(shè)計。small and mid－sized vehicles was replaced by electromechanical power steering.There are different designs，so－called“dual pinion”steering system or a column type steering.In this design the servo effect is brought to the rack via a second pinion.Another configuration is presented in Fig.18.The steering impulse is carried from the driver via the steering wheel to a steering pinion and the steering rack.

The electric motor is activated via a sensor unit，which gives the steering support to a steering pinion via a crossed helical gear transmission.In contrast to all hydraulic steering systems，the electric power steering system does not use permanent energy；rather，energy is only used when it is steered.This leads to significant fuel consumption economization.Fig.19shows measurement results with an electrical steering system for a NEDC driving cycle.This subsequently leads to fuel consumption economization of approx.6%through use of the EPS（electric power steering）in comparison to a hydraulic steering system.The use of 10million such steering systems would lead to reductions of approx.9.3million tons of

圖19 電動轉(zhuǎn)向系統(tǒng)的節(jié)能潛力（NEDC、1 400kg轎車、2l發(fā)動機(jī)）Fig.19 Conservation potential with electro－mechanical steering systems（New European Driving Cycle，car 1 400 kg，2lengine）

圖20 8HP70自動變速器剖視圖［5］Fig.20 Transmission section 8HP70［5］

6.2 Automatic transmissions

In order to meet the continually rising requirements in fuel consumption economization and CO2reduction，ZF decided to develop a new 8－speed automatic transmission model range for standard drives［5］.Each new generation of transmissions has come with new goals，which bring an improved benefit to the customer compared with the previous generation.The 8－speed transmission，F(xiàn)ig.20，is based on a gear set system with 5shifting elements and 4planetary gear sets.The overall gear spread is 7.05.The harmonic transmission ratio series，the good gear set efficiency as well as balanced ro－tational speed and torque splitting within the transmission provides the conditions for a compact construction as well as good internal efficiency.

每個行星排具有兩個軸類零件。設(shè)計空間與上一代6HP28相仿；采用輕量化結(jié)構(gòu)后重量甚至有所降低。變速器采用了一個三相變矩器，其鎖止離合器獨立調(diào)節(jié)。根據(jù)文獻(xiàn)［5］，多工況扭轉(zhuǎn)減振器安裝在殼體內(nèi)，對傳動系統(tǒng)實施最優(yōu)調(diào)整。為降低油耗，鎖止離合器在齒輪起步后能夠立即鎖止。供油的葉片泵采用平行軸設(shè)計，緊靠控制單元，并通過滾子鏈傳動。制動器與離合器的空間和重量最輕，并能以多種方式根據(jù)發(fā)動機(jī)轉(zhuǎn)矩加以調(diào)整。變速器殼體只是耐久性的一個方面，壁厚被減少了3 mm。塑料油底殼采用的是上一代變速器的產(chǎn)品。停車鎖采用久經(jīng)考驗的錐／爪系統(tǒng)；可采用增強(qiáng)型滿足重型車輛或牽引需求。隨著能源成本的增加和降低CO2排放，減少油耗自然成為最主要的開發(fā)目標(biāo)。與第二代變速器相比，新變速器能夠節(jié)省6%的油耗。6%的油耗主要依靠更大的速比范圍、更多的行星排、內(nèi)部牽引轉(zhuǎn)矩減少、高效油泵和離合器切換轉(zhuǎn)速低等因素，詳見圖21.由于傳動系統(tǒng)采用平行開發(fā)模式，許多產(chǎn)品可采用相同或相似的部件。變速器可配備不同的起步系統(tǒng)和四輪驅(qū)動技術(shù)。不考慮尺寸的話，還可集成各種混合動力裝置；變速器因而可作為今后的傳動系統(tǒng)。這里，車輛起停系統(tǒng)還能節(jié)約5%的油耗。當(dāng)發(fā)動機(jī)停車時液壓蓄能器可通過液壓泵驅(qū)動變速器。

圖21 ZF8檔自動變速器的節(jié)油途徑Fig.21 Measures by ZF to reduce fuel consumption in 8－speed automatic transmissions［2］

This is additionally supported by just two open shift elements per gear.The design space is comparable to the 6HP28forerunner transmission；the weight was reduced even further with a lightweight construction.A new triple－line converter is used in the transmission，with the lock－up clutch regulated by a separate line.According to［5］，various torsion damper systems are available in the building set，in order to enable an optimal adjustment to the particular driveline.For consumption reasons，the luck up clutch can be closed immediately after the start－up operation.For the oil supply，a vane cell pump was developed parallel to the axle，lying close to the control unit and powered via a roller chain.Wheel sets and clutches are constructed with optimized design space and weight，and can be adjusted to the engine torque in various configurations.The transmission housing is one－sided because of rigidity，and the wall thickness was reduced locally to 3mm.The plastic oil pan was largely carried over from the forerunner transmission.The parking lock is based on the proven cone／catch system；a strengthened version is available for heavy vehicles or trailing loads.In these times of increasing energy costs and requirements for lower vehicle CO2emissions，the reduction of fuel consumption was naturally one of the primary development goals.A significant value was achieved，with a contribution of 6%as compared with the 2nd generation 6－speed transmissions Approx.6%better fuel consumption results from the larger transmission－ratio spread and greater number of gears，the reduced internal drag torque，the efficiency－optimized pump and the low converter clutch rpm connections Fig.21.Because of the parallel development of transmissions within the model range，many synergies can be exploited by using similar or identical parts.The transmissions can be equipped with different starting systems and 4WD technologies.Regardless of the dimensions，micro hybrid，mild hybrid and hybrid systems can be integrated；the transmission is therefore well equipped even for future drivelines.Meanwhile，there is also a start／stop function that leads to a fuel consumption reduction of approx.5%.A hydraulic impulse accumulator provides the transmission with hydraulic oil while the engine is still at a standstill.

6.3 商用車自動變速器

商用車發(fā)動機(jī)的平均驅(qū)動轉(zhuǎn)矩增長相當(dāng)迅速。其主要原因是發(fā)動機(jī)技術(shù)的提高。汽缸容積相同時輸出轉(zhuǎn)矩／功率均增加。由于運輸量和運輸效益的提升，也要求提高車速。這些都要求增加輸出轉(zhuǎn)矩。隨地區(qū)和應(yīng)用場合不同，平均轉(zhuǎn)矩每年增加20至30Nm［6］。隨著EURO6標(biāo)準(zhǔn)發(fā)動機(jī)在2014年的啟用，轉(zhuǎn)矩大于3 000Nm將變得可能。是否所有種類的變速器都需要滿足頂層要求。顯然手動變速器除去，主要依靠AS Tronic自動變速器。在歐洲自動變速器的份額約為50%，詳見圖22。自動變速器的應(yīng)用場合是多樣化的。

雖然在德國轎車CO2排放應(yīng)下降11%而商用車僅需下降5%，ZF公司仍然發(fā)現(xiàn)了為此作出貢獻(xiàn)的需求和機(jī)會。相關(guān)的措施有減輕變速器重量、優(yōu)化車輛和變速器相互影響、智能化行駛策略以及進(jìn)一步優(yōu)化已相當(dāng)高的變速器效率（約99%，MT／AT直接檔）等。根據(jù)文獻(xiàn)［6］，緊湊和高效的AS Tronic系列自動變速器具有轉(zhuǎn)矩／重量高、智能化行駛功能以及與車輛、發(fā)動機(jī)最優(yōu)共同工作等特性，相比手動變速器能夠節(jié)省3－5%的油耗。通常一個優(yōu)秀的駕駛員即便使用手動變速器也有很好的效果。但是作為一個車隊的平均值，從星期一工作到星期五，自動變速器在任何情況下都有一個滿意的結(jié)果，見圖23。駕駛員能夠不受繁忙的交通所累。變速器可提供如同轎車那樣的舒適性。同時還能改善道路安全性。還可利用擴(kuò)大傳動比實現(xiàn)油耗和CO2排放的進(jìn)一步改善（40噸貨車的變速器傳動比可達(dá)17：1或更高）。相對于所謂的超速檔變速器（OD），ZF通常采用直接檔（DD）傳動。在長距離行駛時，90%采用最高檔傳動。直接檔作為最高檔傳動時可節(jié)省額外的0.4－0.5l／100km油耗。重要的是具有足夠的檔位數(shù)以降低油耗，這樣發(fā)動機(jī)能夠總是工作在最佳油耗點。這里貨車是先驅(qū)者，通常有12檔或16檔。

圖22 AS Tronic在歐洲重型商用車自動變速器的市場占有率Fig.22 Market development for automatic transmissions for heavy commercial vehicles in Europe with the example of AS Tronic

圖23 自動變速器降低車隊的油耗［3］Fig.23 Reduced fleet consumption with automatic transmissions［3］

6.3 Automated commercial vehicle transmissions

The median driving torque of commercial vehicle engines is growing steadily.The reasons for this are advances made in engine technology.More torque／power is achievable from the same piston displacement.Because of the rising transport volume and the pressure on the transport efficiency，possible speeds are also rising，where permitted.This pushes drive torque up.The median torques have risen up to now，according to region and application，between 20and 30Nm per year［6］.With EURO 6engines starting in 2014，torque of significantly more than 3 000Nm will be possible.It remains to be seen whether all transmission types will be desired for the top transmission segments.It is conceivable to do without manual transmissions in these segments and to rely on automatic AS Tronic transmissions.The market share in Europe for automatic transmissions is almost 50%，F(xiàn)ig.22.The applications of automatic transmissions are extremely versatile.

Although 11%of CO2emissions in Germany come from passenger cars and only 5%from commercial vehicles，ZF sees the need and the opportunity to make an appropriate contribution.These relate，among others，to the reduction of the transmission weight，the optimal interplay of vehicle and transmission，an intelligent driving strategy，as

圖24 驅(qū)動橋降低CO2排放的潛力［2］Fig.24 Possibilities for CO2reduction with rear axle transmissions［2］