中文譯文
車身結構和自動變速器
1 車身結構
車是一個人可以擁有的最迷人的設備，汽車也是一最普遍的設備，一輛車包含了許多不同的技術。每一個零部件都有自己專門的設計和工程技術領域。但是，任何汽車是由四個基本部分：發(fā)動機，底盤，車身和電氣系統(tǒng)。
作為動力源，發(fā)動機要求一個燃油系統(tǒng)提供燃料或混合空氣。它在動力生產過程中起著非常重要的作用。假設該發(fā)動機是一個汽油發(fā)動機，燃油泵系統(tǒng)的液體汽油從油箱到化油器位置使汽油與空氣可以混合?；旌衔锉粋鬟f到發(fā)動機燃燒。如果發(fā)動機電噴發(fā)動機，燃料從油箱被傳遞給噴油器通過一個電動燃油泵。燃料噴油器，直接控制進氣歧管中的燃油計量，由電控燃油噴射系統(tǒng)發(fā)出脈沖。電控燃油噴射系統(tǒng)根據發(fā)動機狀態(tài)確定的空氣燃料比。
一個是作為一個支持車身框架的底盤用來組裝所有的汽車零部件上。事實上，當從發(fā)動機的動力傳送到底盤，動力系統(tǒng)開始，接著轉向，車輪懸架，制動系統(tǒng)和輪胎。這些組件彼此聯系密切。實際上，驅動系統(tǒng)將發(fā)動機的動力傳輸到驅動輪。該驅動系統(tǒng)由離合器，變速箱，萬向節(jié)，驅動橋等組成。
汽車車身框架在底盤上，其功能是為用戶提供舒適，保護和空間。車身一般分為四個部分：前，上部或頂部，后部和底部。這些部分是進一步分成小單位，如發(fā)動機罩，擋泥板，頂板，車門，儀表盤，保險杠和行李艙。電氣系統(tǒng)被認為是汽車的電源為汽車供應照明用電。電氣系統(tǒng)包含電池的電氣系統(tǒng)，燈光，發(fā)電機，發(fā)動機點火，照明電路，以及控制其使用的各種開關。
隨著汽車工業(yè)的迅猛發(fā)展，新式的車正在設計和性能方面變得更好。當汽車非常受人們歡迎時，許多關于相應事實的負面問題應當由科學家考慮，如能源危機，空氣污染和交通堵塞。因此，科學家和汽車制造商致力于改善燃油經濟性，控制廢氣排放；同時政府正積極采取措施來解決交通問題。
2自動變速器
什么是變速器？
變速器是一個連接到發(fā)動機的背后和發(fā)送來自發(fā)動機的功率以驅動車輪的裝置。汽車發(fā)動機在一定轉速（旋轉/分鐘）處于最佳運行的范圍時，它的職責是傳輸以確保動力被傳遞到車輪使保持在該范圍內的發(fā)動機通過不同的齒輪聯合工作。在低速檔，發(fā)動機會使驅動輪轉得更快而在高速運轉時的發(fā)動機則是在偷懶----即汽車可能會在70邁的速度持續(xù)。除了各前進檔，傳輸也有個空擋即車輪斷開驅動和倒檔----驅動輪向相反的方向運動。最后，還有抱死的位置，在這個位置上，一種閉鎖裝置（不同于那些房門上呆板的自動鎖）是在輸出軸槽中插入鎖定驅動器以防止車輪轉動從而防止車輛滑動。
現代的自動變速箱是迄今為止，在今天的汽車中最復雜的機械部件。自動變速器包含機械系統(tǒng)，液壓系統(tǒng)，電氣系統(tǒng)和計算機控制，所有的工作中去幾乎沒有注意的完美和諧在一起，直到有一個問題。對于現代的汽車，自動變速器是一個復雜的組件，這種傳遞動力的方式，是液力變矩期充當離合器來連接發(fā)動機和變速器。
兩個基本類型的自動變速器基于該車輛是否是前驅動或后驅動。對發(fā)動機前置后驅動的汽車，變速器通常安裝在發(fā)動機后底盤中心與油門配合。變速器輸出軸連接到后橋，把發(fā)動機的動力傳遞到后輪，動力傳輸系統(tǒng)是直線的，從發(fā)動機通過液力變矩器、變速器、傳動軸、最后直接到到達車輪。
對于發(fā)動機前置前輪驅動的汽車，變速器通常和差速器裝在一起。對于前驅動的汽車，變速器安裝在發(fā)動機一側，前車軸直接連接到差速器上，把動力傳遞給前輪。在這個布置中，動力來自于發(fā)動機，通過液力變矩器、變速器輸出的動力通過了一個180度大轉彎，經過變速器沿發(fā)動機側邊通過傳動軸輸出到前輪。
還有其它的一些布置，發(fā)動機前置前驅動，發(fā)動機橫向布置，裝設一個分動器可以實現四輪驅動。但這種形式目前是最常用的：發(fā)動機中置后驅動，可以使重量均勻的分布在前、后輪之間，改善了操作性能；發(fā)動機后置后驅動，發(fā)動機、變速器、驅動輪都在后方，這種后置式的發(fā)動機的安排，是最滿意的。
現代的自動變速器包括了許多組件和系統(tǒng)的協(xié)同工作，有行星齒輪組、液壓系統(tǒng)、密封件和墊圈、變矩器、調節(jié)器、節(jié)氣門拉線、計算機控制這些都是多年來由機械式演變過來的。這用簡單、通用的解釋，描述一下這些系統(tǒng)。
2.1行星齒輪組
? ? 自動變速器箱體內有很多齒輪，有各種不同的組合，在一個變速箱內，齒輪的滑動沿軸線從一個位置到另一個位置，對各種大小齒輪的要求，有正確的傳動比。在一個自動變速箱，至始至終，不是齒輪的機械移動來達到這一點的，通過行星齒輪組來完成。
基本的行星齒輪組成由一個太陽輪、一個齒圈、并且有兩個或兩個以上的行星齒輪，全部齒輪都是常嚙合。行星齒輪的相互聯系通過一個共同的載體，使齒輪相互嚙合在一起。一個傳遞方式，這個系統(tǒng)可以從發(fā)動機的輸出連接到齒圈作為主動件，連接行星輪作為從動件，并鎖定太陽輪，使起不能轉動。在這情況下，當我們把齒圈、行星齒輪，沿太陽輪轉動，主動件與從動件就同向轉動，從動件的轉速慢，齒輪減速就類似汽車的一擋。
如果解開太陽輪和鎖定其它兩個元素，這就會使這三個要素以同樣的速度轉動，齒輪的傳動就類似于汽車是第三或高擋位。另一個方式是，把行星架鎖定，使太陽輪作為主動輪，齒圈作為從動件，這時它們的轉動方向就相反，就類似以汽車的到擋。
上面所說的，在實際的傳動過程是如何控制。齒圈為輸入軸，行星架為輸出軸，都是通過盤式離合器控制。太陽輪一個單向離合器，一個制動器，當制動器作用時，太陽輪只能從一個方向轉動。
在這情況下，離合器的使用，鎖定行星架與太陽輪迫使它們以相同的轉速轉動。如果它們的離合器和制動器都被釋放，該系統(tǒng)在自由狀態(tài)。變速器的行星齒輪組太陽輪是自由的，比輸出動力。在一擋位，制動器制動太陽輪跟隨轉動，從第一擋到高擋制動器釋放和離合器使用到輸入軸，它們以同一個速度轉動。
使用兩個或兩個以上的行星齒輪組以各種方式連接，可提供不同的前進速度和扭矩，普遍的使用以現代的自動變速器。
2.2 片式離合器
片式離合器主要由若干交替排列的離合器盤和離合器片組成。每片離合器盤上有伸出的突線，勾住離合器鼓，以輸入軸連接。離合器片內的鍵槽與離合器殼互相嚙合，離合器殼與中間軸鍵槽連接，中間軸又與后行星排內齒圈用鍵槽連接。因此，離合器盤和離合器片分別與輸入軸和湖行星排內齒圈連接。操作離合器的活塞安裝以離合器鼓上，離合器鼓亦稱做為活塞缸。
2.3 單向離合器
單向離合器是一種只可以使元件在一個方向轉動，如把齒圈自由在一貫方向，而不能反向轉動，這種作用就象是，自行車踏板轉動時，可以帶動車輪轉動，當車輪轉動或向另一個方向轉動是自由的
一個單向離合器用于一擋時，在驅動方向是，當從停止開始加速，在第一個齒輪輸出動力，如果繼續(xù)加速，不在一擋位？汽車繼續(xù)加速，他就是一個方向自由的。此時，單向離合器不在輸出動力，當車速慢下來時，轉速慢，它就可以起作用。這一個現象由于，在提供力的時候它才起作用，在高速時，是自由的。
2.4 液力變矩器
對于自動變速器，液力變矩器取代離合器裝于車上。它的作用是：當車停下來，發(fā)動機還可以繼續(xù)運轉。傳遞扭矩的原理，比如，把一個風扇吹向另一個，另一個不用插電也能跟它一起轉動，如果你壓住扇片，它就不會轉動，但你一放手，它就開始加速，直到速度接近動力風扇。它們兩者的差異就是：變矩器不是利用空氣，而是利用油液，以使他的傳遞更加準確。
液力變矩器是一個較大的盆壯裝置，安裝在發(fā)動機與變速器之間。它包含三個部件，協(xié)同工作，為變速器提供動力，液力變矩器的三要素是：泵論、渦輪、導輪，泵論是通過螺栓直接安裝在發(fā)動機的曲軸上，轉速與發(fā)動機的相同，渦輪連接到變速器的輸入軸上，為汽車提供動力，導輪上裝有一個單向離合器，使他只可以在一個方向轉動，而在另一方被固定，每一個要素之間通過液流傳遞扭矩。
發(fā)動機啟動后，輸入軸開始旋轉，帶動泵輪旋轉，因旋轉產生的離心力使泵輪葉片間的液流沿葉片從外緣向外甩出；接著又由于泵輪和渦輪轉速差引起泵輪葉片外緣與渦輪葉片外緣產生了壓力差，液流從液壓高的泵輪葉片外緣流進渦輪葉片外緣，同時，泵輪的旋轉也使得其葉片帶動液流隨工作輪旋轉，這一旋轉就使液流流進渦輪時方向改變，從而沖擊渦輪葉片推動渦輪繞泵輪同一方向旋轉。從渦輪流出的液流進入固定不動的導輪，經導輪葉片改變方向后回流至泵輪。如果渦輪的速度大大低于泵輪轉素時，導輪仍鎖住不動。導輪停止，液流通過導輪時重新進入泵輪，促使泵輪旋轉起到扭矩增大的作用。由于泵輪和導輪的轉速增加，液流開始改變方向流向泵輪葉片背面，也可以產生增矩的作用。由于車速的提高，這三要素句以相同的轉速旋轉，為了提高燃油經濟性，在液力變矩器上裝了一個鎖止離合器，車速達到40—50英里的時候，鎖止離合器就把三要素連為一體，這種控制是計算機控制。
2.5 液壓系統(tǒng)
液壓系統(tǒng)是一個復雜的迷宮壯通道，液流壓力控制變速器扭矩的輸出。液流有若干用途，包括：換擋控制、潤滑、冷卻。不象發(fā)動機，它只用來潤滑，每一個流動，是依賴于不斷提供的液體壓力。為了使油液在一個正常的溫度工作，部分液流從散熱器中流過以便散熱。液體通過此通道被冷卻，然后返回到傳輸通道。液里變矩器和散熱器，是用來給液流散熱的。事實上大部分的摩擦表面都淹沒在油液中，比如：離合器盤、離合器片，也能正常的工作。
2.6 油泵
油泵主要是負責提供油液傳輸過程中的壓力，油泵安裝在前面的泵輪上，并且以發(fā)動機的曲軸相連，當發(fā)動機轉動時，帶動油泵運轉，產生壓力，提供足夠的油。油進入油泵時通過一個空氣濾清器，安裝在油底殼的底部。壓力調節(jié)器、調壓閥、壓力修正閥調節(jié)后送到各個管路。
2.7 閥體
閥體是自動變速器的控制中心。它包含一個迷宮壯的通道輸送液壓油，在每一個工況下控制離合器和其它伺服機構，順利的控制齒輪傳動情況。
最重要的閥門一個直接控制的手動閥。手動閥是直接連接到齒輪變速箱里面的，根據它所在位置打開或關閉各種通道，控制換擋節(jié)奏。用齒輪變速傳動來舉例說明，監(jiān)控車輛的速度和油門的位置，以便它能確定最佳的換擋時間，。計算機的控制，通過電磁閥控制油壓壓力，控制離合器或制動器，以更精確的控制換擋點。
2.8 密封墊和墊圈
一個自動變速器有許多的密封件和墊圈，以控制流動的液壓油，使它不外泄。主要有兩個外部密封墊：前油封和后油封。前油封安裝到變速器的變矩器，這使得油底殼到變矩器的油液能自由流動，而不外泄。后密封墊使游液不泄漏到輸出軸。
密封墊通常用橡膠（類似汽車擋風玻璃雨刮器葉片），它是用來保持不泄漏到其它部分，如旋轉軸。在有的情況下，用一個彈簧和橡膠在一起，如用在花鍵軸。
墊圈是一種用來密封兩個固定部分，使其連接在一起。一些常見的襯墊材料是：硬紙、軟木、橡膠、有機硅和軟金屬。
除了主要的密封墊，也有一些其它的密封墊和墊片，因使用條件而定，有的從軸到軸的連接。一個常見的例子是橡膠O型密封圈用來密封換的擋軸。就是說，你所操作的邊速杠在轉動時，另一個例子是大部分常見的油底殼墊片，事實上，密封墊是隨時進行更換，防止油不泄漏。
2.9計算機控制
計算機控制是利用傳感器對發(fā)動機和變速器提取數據，因為節(jié)氣門位置、汽車行駛速度、發(fā)動機轉速、發(fā)動機負荷等是變數。利用這些數據可以精確控制換擋點，以便換擋平順。一些電腦數據，能了解行駛條件，并不斷的適應行駛條件的變化，使汽車穩(wěn)定的行駛。
由于計算機的控制，通過一個特殊的元素代替了手動控制，在每一個工況都是安全的。計算機的控制，確保發(fā)動機轉速不至于過高而使發(fā)動機損壞。
另一個好處是，這些精確的數據輸入系統(tǒng)，有一個自診斷系統(tǒng)，以便能使我們及時的發(fā)現問題，當有問題時，故障指示燈就閃爍。維修人員就可以根據檢測設備檢測出的故障碼，很快的找到問題所在部位。
參考文獻
[1]岡村和柏原，傳輸的發(fā)展3KType無級變速（第一次報告，傳動設計）。 JSME，C系列57-538，（1991），288-293。
[2]弗蘭克·NAJLEPSZY，機械設計，57-25（1985），68-75
The ZF AS Tronic Family Automotive Transmissions for
All Commercial Vehicle Classes
1 Requirements for Commercial Vehicle Transmissions
Customers demand high efficiency along with increasing vehicle comfort and safety. As an independent transmission manufacturer, ZF customer needs include the needs of drivers, forwarding companies, and vehicle manufacturers.
Therefore, ZF considers the many requirements that a new transmission concept must fulfill when developing a transmission, Figure 1 .
圖1商用車輛的需求
Fig. 1 Requirements for commercial vehicles
Keeping costs low is a considerable challenge, initially in terms of acquisition and later during operation. That is why fuel consumption is increasingly one of the decisive vehicle features that separate the competition. A modern transmission can make an important contribution here: On the one hand by improving efficiency and on the other hand in automatic transmissions by the optimal selection of the gear ratio dependent on the driving situation. Reducing the transmission, s weight also leads to re duced costs: Using less material reduces acquisition costs and enabling a higher payload reduces operating costs. On the one hand, decreased oil consumption contributes to environmental protection; additionally, it has an immediate influence on the costs, however, that accrue throughout the vehicle ’ s service life.
The demand for system comfort increasingly approaches the standard set by car technology, whereas in this case limits are set by mass ratios and cost constraints. Low noise emissions are a re sult of legal regulations on the one hand but also contribute to more comfortable driver workplaces when met. Furthermore, electronic systems increasingly support the driver and relieve him/her from routine tasks. This benefits safety in traffic.
2 Advances with Automatic Transmissions
Automatic transmissions can satisfy many of the demands that customers make on commercial vehicles considerably better than manual transmissions. Despite the fact that automatic transmissions are generally more expensive, if one takes the complete installed manual transmission system including the gearshift system into account, the difference in acquisition costs is no longer as great. Moreover, the goal of future developments is to further reduce the costs for automatic transmissions.
Even today the higher acquisition costs are already paying for themselves relatively quickly due to lower operating costs so that automatic transmissions are economically advantageous in the long run. The efficiency of the AS Tronic family of transmissions is comparable to a manual transition; however, as a rule, the shifting point selection is better due to the application of an automatic driving strategy, which positively affects fuel consumption. A long term study conducted by ZF and DEKRA found that the automatic shifting point se lection represents the consumption performance of a very good, concentrated driver. Thus, averaging all drivers and driving situations in a commercial fleet, consumption is reduced on the order of 3 percent since the engine operates reliably in the optimum speed range with regard to fuel consumption; a process that is controlled independently of the driver, s qualification.
An additional advantage in terms of operating costs is reduced clutch wear. Reduced differential speeds during starting and shifting operations lengthen the service life of the clutch, which has al so been proven in long term tests. Many vehicle manufacturers take this into account and offer a significantly longer warranty cover on the clutch in AS Tronic transmissions.
By automating the clutch, the clutch pedal is no longer needed, which clearly simplifies operation for the driver, particularly in stop and go traffic or when maneuvering. The automatic gear selection relieves the driver from shifting as well, whereby he/she can concentrate better on road traffic. How ever, at the same time, the driver can engage manually at any time, for instance in driving situations where the driver's forward field of vision is in question. This takes place according to Shift by Wire via an electromechanical control switch so that only very little actuating forces are applied when manually selecting gears. The rapid automatic shifting and the protection against operating error also contribute to the increase in driver comfort while at the same time protecting the transmission and driveline. In addition, the absence of a mechanical link between shift lever and transmission reduces cabin noise.
Using an automatic transmission also has advantages for vehicle manufacturers. Like the clutch control, the complete shift linkage is no longer needed, which makes both left and right hand steering vehicles easy to manufacture. When designing the driver workplace, anything is possible in terms of operating the transmission.
3 The ZF AS Tronic Family
ZF began developing automated manual trans missions for commercial vehicles early. The first product was a partially automated transmission with automatic pre selection, which was introduced into the market in 1984. Ten years later, an automated transmission followed with the introduction of the first AS Tronic; however, the driver still had to select gears. Its successor model was first equipped with an intelligent shift program, which has been in production since 1998. Thus, a fully automatic solution was offered in a heavy commercial vehicle for the first time.
The chosen transmission concept for AS Tronic resulted in the most efficient solution possible for larger volumes. Extensive integration and removal of unnecessary components opened up potential cost savings. As a group drive, AS Tronic is designed with an unsynchronized basic transmission and synchronized splitter and range change group, Figure 2.
圖2 ZF AS Tronic的3D剖示圖
Fig. 2 ZF AS Tronic: 3D section cut
In order to reduce the weight of the transmis sion, a design with two countershafts was chosen, which is optimal in this performance class in terms of weight. Due to a modular design and a basic transmission with 3 or 4 speeds, l6 peed, 12 speed, and 10 speed variants could be represented.
In the basic transmission, the synchronizations were replaced with shift dogs, because the synchronization can take place by controlling the internal combustion engine in modern EDC engines. An additional transmission brake is then required for up shifts, which is located on one of the two counter shafts. A standard dry clutch is used. It is fully automatic so that a clutch pedal is no longer necessary. All automated components are pneumatically operated and are combined within modules that are integrated into the transmission housing. The coordinated operation of transmission, clutch, and engine takes place by electronic control, which is located in the shift module. The interfaces to the out side were minimized.
AS Tronic was initially limited to torques of 2, 300 Nm (12 speed) and 2, 600 Nm (16 speed). Afterward, variants were introduced in a two step de velopment, which expand the torque ranges of 12 speed transmissions upwards. AS Tronic is offered in direct drive and overdrive designs and is generally available with an integrated secondary retarder “Intarder. ’’
Automatic transmissions have found increasing acceptance in heavy commercial vehicles in the past few years and enjoy enormous popularity among customers. However, the advantages of these transmissions are also demonstrated especially in light and medium duty commercial vehicles. Vehicles in these classes are primarily used in city and regional traffic. Relief from operating the transmis sion and the clutch is especially important in this case because the traffic environment requires the driver’s full attention. Furthermore, this sector is marked by a high number of untrained drivers and frequent driver turnover. Therefore, reducing the driver's influence on fuel consumption and clutch wear is an unmistakable advantage, not to mention safeguarding against transmission and clutch damage caused by the driver.
For these reasons ZF decided to expand the product portfolio for automatic transmissions sys tematically into the area of low torques, Figure 3.
圖3變速器型譜:ZF AS Tronic的轉矩范圍
Fig. 3 Transmission portfolio： the ZF AS Tronic products with torque ranges
Starting from the technical fundamental principle- two pedal solutions with automatic shifting and a customer benefit that is commensurate with the AS Tronic- smaller AS Tronic transmission will be developed as well. They receive additional coding to their genuine designation in order to mark their as sociation to the respective vehicle applications. AS Tronic mid will be used for applications from 800 Nm to 1, 600 Nm； AS Tronic lite will cover trucks in the lower torque range up to 1, 050 Nm with 6 speed transmissions.
4 ZF AS Tronic mid
The vehicle sector where the AS Tronic mid series will be used is very sensitive to price and highly differentiated in terms of application types. Thus, midrange vehicles will service both distributor and long distance transport as well as construction sites. Therefore, one of the focal points of development lies in a cost effective design that will fulfill the many and diverse customer requirements easily and also cover the wide torque range.
Consistent product planning led to the development of an uncompromising midrange transmission series designed for automation. It encompasses seven transmission types combined into one modular design. With 840 mm short and 900 mm long transmission variants, the modular design concept is primarily based on the variation of the wheel widths in order to cover the torque ranges up to 1, 200 Nm and 1，600 Nm respectively. Both transmission lengths will be offered in direct and overdrive de signs. Compared to the AS Tronic, the AS Tronic mid transmissions are approx. 50 to 65 kg lighter. In order to optimize costs, a consistent complexity management system was pursued. Approximately 40% of the components were taken from existing transmissions in production at ZF.
In order to offer uniform automation technology for all commercial vehicles in the midrange and heavy duty sectors, the proven AS Tronic components such as transmission/clutch actuators, electronics, and software were used. Due to the inter face equality this achieved, the vehicle manufacturer can offer both AS Tronic and AS Tronic mid series in almost identical vehicles with various drive line variants at minimal expense.
In a preliminary concept study, various gear set concepts were considered. Eight gear set formulas were compared using eleven selected evaluation criteria in terms of function, costs, and deadline. In order to provide this complex decision matrix with the necessary transparency, a decision making software tool was used. The choice was made for a 12 speed gear set (2x3x2), which is comparable to a conventional 9 speed gear set in terms of design space and weight and even has advantages compared to a 10 speed gear set, Figure 4.
圖4 ZF AS Tronic mid變速器剖示圖 Fig. 4 ZF AS Tronic mid in complete view
It consists of engaging and disengaging input constants ( splitter group), 3 speed main transmission, and an output end planetary drive stage (range change group). Synchronizations are used in the splitter and range change group; the main transmission shifting ele ments are designed as dogs. The gear steps has a slightly progressive gear interval due to a small increase in the gear ratio. Thus, at a total gear spread of approx. 12. 8, the gear ratio of 23. 8 % from 11th to 12th speed is on par with a comparable 16 speed transmission. For the first time, the gear ratio of the reverse gear was designed 13. 1, i. e. slower than 1st gear on a range change group transmission by an offset engagement over the reverse idler gear. In close cooperation with the customers, high drivability was already emphasized in the specification phase. Upon completion of the rough design, the drivability release criteria of one customer were already proven in simulations.
A detailed cost analysis of the gear units in ZF transmissions led to the design of the planetary rear mounted range change group in the AS Tronic mid，in which the most cost effective solutions were adopted in each case. Thus, the design of the new gear unit is marked by the synchronization of the AS Tronic and the gear set design of the Ecosplit Figure 5.
圖5 ZF AS Tronic mid:行星齒輪傳動
Fig. 5 ZF AS Tronic mid： planetary drive detail
The bearings of the swing fork in the range change group are realized between the two housing parts, which minimizes seal points to the outside and possible corrosion weak points. The clutch actuating cylinder was turned in driving direction from the 6 o’ clock position for AS Tronic to the 8 o'clock position for AS Tronic mid. This not only increases vehicle road clearance and brings the actuating cylinder out of the danger zone, it al so offers the flexibility to react to potential requirements pushed clutch release under compression.
Different from the AS Tronic, the AS Tronic mid gear set will only be designed with one counter shaft. The solution was the best in a parameter study for the torque range considered, which takes into account both the modular design aspects as regards optimal gear set length variation as well as the legally permitted noise requirements. As a result, the developer faced an additional challenge. If the oil pump and transmission brake are each driven by one countershaft in the AS Tronic, then both components now must be combined in a joint, cost effective brake pump module.
Maximizing transmission efficiency in order to reduce fuel consumption attracted much interest during development. By consistently changing splash lubrication to injection lubrication, quasi dry sump lubrication was achieved so that diving losses do not occur. In order to optimize the lubrication system, oil flow calculations were conducted. The oil itself was handled like a structural/ design element. ZF has worked intensively for years with lubricant manufacturers in order to develop synthetic oils such as the ZF Ecofluid M, which is used in these transmissions. This oil has low viscosity and therefore contributes low internal losses; however, at the same time it offers sufficient lubricating film to guarantee the service life of gears, bearings, and synchronizations. An additional advantage of Ecofluid M is high stability, which makes clearly longer oil change intervals possible and greatly reduces oil consumption.
Shift dogs in the main transmission and a com pact transmission design with small center distance also contribute to loss reduction. All these meas ures together increased the efficiency in the direct gear from 99. 2 to 99. 6% under comparable operating conditions. Active heat management enabled additional fuel savings. If the transmission runs at approx. 60℃ oil sump temperature on road, the oil viscosity can be further reduced by additionally heating to 80℃. In this case, AS Tronic mid is optionally available for the addition of a highly integrated heat exchanger. Short payback periods of approx, one year are ensured by cost effectively integrating the heat exchanger cartridge with the integrated bypass valve in the oil circulation on the intake side.
ZF AS Tronic系列-適用于各種商用車輛的自動變速器
1 商用車輛變速器的需求
客戶的要求是在提高車輛舒適性和安全性的同 時也提高效率。作為一個獨立的變速器制造商，ZF 公司的客戶還包括駕駛人員、運輸公司和車輛制造商。
因此，ZF認為在開發(fā)變速器時就必須考慮到應 滿足各種需求，（圖1)。
圖1商用車輛的需求
Fig. 1 Requirements for commercial vehicles
繼續(xù)降低制造和使用成本是一個很大的挑戰(zhàn)。這就是燃油經濟性為什么正成為車輛競爭的決定性因素之一的緣故。一個現代化的變速器具有以下貢獻：一方面通過優(yōu)化速比改進效率、實現自動化、降低變速器重量以減少成本、減少金屬材料用量降低制造成本、提供更大的有效載 荷降低使用成本等。另一方面，減少燃油消耗還有助于環(huán)境保護，它直接影響到使用成本，因而可提高 車輛的服務壽命。
對系統(tǒng)舒適性需求的增加已成為車輛技術的標準配置，盡管這受制于檔位數量和成本限制。低噪聲一方面是由于法規(guī)要求，同時也提高了駕駛員工作環(huán)境的舒適程度。進一步而言，為駕駛員提供支持的電子系統(tǒng)減輕了他們的工作任務。這有益于交通安全。
2 自動變速器的優(yōu)點
自動變速器比手動變速器更能滿足客戶對商用車輛的需求。除了自動變速器成本較高的事實外，但如果考慮到手動變速器及相應的換檔操縱系統(tǒng)的話，兩者成本的差距并不太大。因此進一步發(fā)展的目標是降低自動變速器的成本。
在今天，較高的制造成本由于更低的使用成本而迅速補償，因此自動變速器最終具有經濟性方面的優(yōu)勢。將ZF AS Tronic系列變速器與手動變速器相比，由于采用了自動駕駛模式其換檔點的選擇更具優(yōu)勢，這有助于燃油經濟性。一項由ZF和 DEKRA公司的長期研究發(fā)現換檔點的自動確定相當于一個具有高超技術駕駛員集中精力的駕駛。因而一個具有平均駕駛水平的車隊燃油消耗可降低 3%，因為發(fā)動機能可靠地工作在最佳速度區(qū)域，而整個過程與駕駛員的素質無關。
另一個優(yōu)點是可降低離合器的磨損。在起步和換檔過程中減少滑差可增加離合器的使用壽命，這己被長期試驗所證明。許多車輛制造商為配置AS Tronic變速器的車輛提供更長的離合器保修期限。
采用自動離合器后，離合器踏板己不再需要，簡化了駕駛員的工作，特別是在頻繁起步、停車工況下。檔位自動選擇解放了駕駛員的換檔動作，駕駛員的注意力可集中在道路交通上。同時,駕駛員仍可在任何時候切換為手動模式，例如當駕駛員視野出現問題時。這些都根據線控換檔系統(tǒng)和機電一體化的控制開關完成，因此在手動換檔時僅需很小的操縱力。迅速地自動換檔和防止操縱失誤增加了駕駛舒適性，同時也保護了變速器和傳動系。另外變速器和換檔操縱桿之間無機械聯接可降低駕駛室的噪聲。
使用自動變速器對車輛制造商也有好處。像離合器控制和換檔操縱裝置己不再需要，方便制造轉向盤左置和右置的車輛。在設計駕駛員工作區(qū)域時更能隨心所欲。
3 ZF-AS Tronic 系列
ZF早就開始開發(fā)適用于商用車輛的機械自動變速器。第一個產品是帶自動預選檔位的半自動變速器，在1984年投入市場。十年后，推出的是AS Tronic的第一代產品，但是駕駛員仍需要選擇換檔。在1998年，其后續(xù)產品采用了智能化的換檔程序，而全自動化的產品則首先用于重型商用車輛。
圖2 ZF AS Tronic的3D剖示圖
Fig. 2 ZF AS Tronic： 3D section cut
選擇ZF AS Tronic變速器將具有更好大批量裝車的可能性。高度集成和省略不必要的元件使得在降低成本方面仍具潛力。作為一組合式變速器，AS Tronic被設計成由不帶同步器的主變速器、前置同步分流的副變速器和擴展速比的后置副變速器組成，圖2。
為減輕主變速器的重量，采用了雙副軸結構。由于主變速器是3或4檔，因此可構成16、12和10檔的變速器。在主變速器，同步器被換檔檔塊所替換，因為同步過程可由現代化的EDC發(fā)動機完成。一個附加的變速器制動裝置用于升檔，它位于兩副軸之一上。采用標準的干式離合器。由于是全自動變速器故無需離合器踏板。所有的換檔元件由氣壓操縱并被以模塊形式集成在變速器殼體上。利用電控系統(tǒng)控制變速器、離合器及發(fā)動機，該裝置安裝在換檔模塊上。外部界面做成最小。
AS Tronic的輸入轉矩為2300Nm(12速）和 2600Nm(16速）。副變速器具有2檔速比，它能擴大12速變速器的轉矩。AS Tronic提供直接傳動和超速，通常集成一個第二緩速器“Intarder”。
在過去幾年里，自動變速器在商用車輛上的應用正在增加并贏得了消費者的巨大信任。然而，變速器的優(yōu)點主要體現在輕型和中型商用車輛上。這些車輛主要行駛在城市和近郊交通繁忙的區(qū)域。這時減輕變速器和離合器的操作特別重要，因為交通情況需要駕駛員集中全部精力。另外，車輛是由大量非專業(yè)人員駕駛而且頻繁更換駕駛員。因此減少駕駛員對燃油消耗和離合器磨損的影響是一個顯著的優(yōu)點，同時也減少了駕駛員對變速器和離合器的傷害。
為此ZF決定系統(tǒng)地擴展自動變速器的產品型譜，如圖3。
圖3變速器型譜:ZF AS Tronic的轉矩范圍
Fig. 3 Transmission portfolio： the ZF AS Tronic products with torque ranges
從技術基本原則開始，即采用兩個踏板的AS Tronic是解決自動換檔和方便駕駛的方法，因此也將開發(fā)較小的AS Tronic變速器。對應于實際產品它們都有附加的代碼以表示其各種的車輛應用場合。AS Tronic mid適用于800Nm到 1600Nm; AS Troniclite是適用于卡車的6檔變速器,從低轉矩直到1050Nm。
4 ZF AS Tronic mid
適用于AS Tronic mid系列的車輛對價格很敏感，具有廣泛的應用場合。中型車輛適用于經銷商、長距離運輸和建筑等場合。因此，設計開發(fā)的關注點之一是效費比，它將容易地滿足消費者的各種需求和覆蓋廣的轉矩范圍。
ZF公司一貫的產品規(guī)劃產生了一個執(zhí)著的中型變速器系列產品的開發(fā)。在一個模塊化設計中它包含7種變速器。從840mm的短變速器到900mm 的長變速器，模塊化設計觀念基于不同的車輛寬度以覆蓋1200Nm到1600Nm的轉矩范圍。兩種長度的變速器都提供直接和超速設計。和AS Tronic相比AS Tronic mid輕50 - 65kg。為降低成本，采用了相同的操縱系統(tǒng)。約40%的部件源自ZF現有變速器。
為在中型和重型商用車輛方面提供相同的自動操作技術，應用了經檢驗的AS Tronic部件如變速 器/離合器執(zhí)行機構、電子元件和軟件等。由于界面相同，車輛制造商可以最低的代價將AS Tronich和 ASTronic mid系列的各種傳動系統(tǒng)提供給幾乎相同的車輛。
在初步概念階段，考慮了各種齒輪結構。8檔變速是比較了11種評價指標，如功能、成本和壽命等。為對該復雜的決策矩陣提供必要的透明度而采用了決策軟件。12檔變速器則設計成2X3X2形 式，它與常規(guī)的9檔變速器具有相同的設計空間和重量，比10檔變速器更先進，圖4。
圖4 ZF AS Tronic mid變速器剖示圖 Fig. 4 ZF AS Tronic mid in complete view
它由前置副變速器(分流）、3檔主變速器和后置行星齒輪變速器 (擴大速比)組成。同步器用在兩副變速器上，主變速器換檔機構被設計成擋塊。檔位間隔稍有變化使得速比有所增加。其總速比約為12. 8,和16擋變 速器相比在11和12檔之間速比增加了23. 8%。通過一個附加的倒檔惰輪首次將倒檔速比設計成低于 1檔速比的13. 1。設計時與用戶緊密協(xié)作，在規(guī)格中強調高的傳動性能。完成初步設計后，對每個用戶的傳動性能都進行了相應的仿真。
圖5 ZF AS Tronic mid:行星齒輪傳動
Fig. 5 ZF AS Tronic mid： planetary drive detail
對ZF變速器齒輪裝置仔細地成本分析導致了在AS Tronic mid上采用行星齒輪機構的后置副變速器，這是具有最佳效費比的解決方案。因而設計的新變速裝置用于AS Tronic而常規(guī)變速裝置則是 Ecosplit，圖5。
換檔擺動叉軸承安裝在兩殼體零件上，這使得外部密封點和可能的腐蝕點最少。AS Tronic的離合器執(zhí)行機構活塞沿傳動方向旋轉6 點鐘，而AS Tronic mid則旋轉8點鐘。這不僅增加了車輛的離地間隙而且使得執(zhí)行機構活塞處于非 危險區(qū)域，同時也提供了將推式離合器改成拉式離合器的靈活性。
與AS Tronic不同，AS Tronic mid的齒輪機構僅有一根副軸。這是在該轉矩范圍內的最佳解決方案，該方案考慮了模塊化設計中優(yōu)化齒輪機構長度和噪聲法規(guī)兩方面的問題。其結果是開發(fā)者面臨著額外的挑戰(zhàn)。例如燃油泵和變速器制動由AS Tronic的同一副軸驅動，兩部件必須合成為一個制動油泵模塊。
在開發(fā)過程中非常誘人的是將變速器效率最大化以減少油耗。將飛濺潤滑改成噴射潤滑和半干油池潤滑后甩油損失不復存在。潤滑油被處理成象一個結構/設計元件。ZF通過多年來和潤滑劑生產商的共同研宄，開發(fā)出適用于這些變速器的合成潤滑油，如ZF Ecofluid M。該潤滑油粘度低，因此內部損失低;但是它能提供足夠的潤滑油膜以確保齒輪、軸承和同步器的壽命。另外Ecofluid M的附加優(yōu)點是高穩(wěn)定性，這意味著更長的換油間隔和大大減少潤滑油消耗。
緊湊設計的主變速器上的換檔擋塊徑向尺寸小，也可減少損失。所有這些努力將直接檔的效率從99. 2%增加至99. 6%。主動溫度管理能節(jié)省燃油。如果變速器工作時油底殼溫度在60 °C左右的話，通過加熱油溫至80 °C潤滑油粘度能進一步減少。這時AS Tronic mid可選擇附加的高度集成的熱交換器。約一年左右可確保收回成本，因為在潤滑油回路進口處帶旁路閥的集成熱交換器具有高的效費比。