輕型貨車變速器設計-三軸式四檔【三維UG模型】
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廣西科技大學（籌）2012屆畢業(yè)設計說明書
第1章 外文翻譯
1中文翻譯：
變速器
所有變速箱技術中，手動變速器的效益最高，輸出功率可達到輸入功率的96%，但并不是所有的人都能駕馭手動變速箱，也不是所有人愿意用它。因為用手動變速器需要踩離合器，這是在交通繁忙的時候很不舒服，駕駛員容易疲勞，而由扭矩中斷導致的“點頭”效應也會使乘客很難受。
由駕駛員操縱離合器而產生的扭矩中斷是手動變速器主要的缺點。在換檔加速時，駕駛員都必須通過松開油門并踩下離合器來使扭矩中斷，完成整個過程大概需要一秒，但在這段時間里車輛會暫時停止加速，速度也會降低。
與此截然不同的是自動變速箱，到目前為止現代汽車自動變速器是汽車上最復雜的元件。它是一種可以自己換擋的變速器。力矩轉換器或流體聯合器被用來代替手動離合器連接發(fā)動機。
汽車上變后輪驅動或前輪驅動是車輛自動變速器的兩種基本類型。在一個后輪驅動的速器通常放在發(fā)動機后面凸起后長板旁邊氣體踏板下方的位置。駕駛桿連接變速器后端，最終駕駛的準確位置在后軸，用操縱力控制后輪。發(fā)動機的動力簡單連續(xù)的在這個系統(tǒng)中循環(huán)，在通過變速器時改變力矩，通過傳動軸后在主減速器分流到兩后輪。
在前輪驅動汽車中，變速器常常兼有最終驅動叫做變速驅動橋。前輪驅動汽車通常在發(fā)動機的后下方安裝有橫向變速驅動橋。前橋直接連接在發(fā)動機的變速驅動橋上為前輪提供動力，動力從發(fā)動機出發(fā)轉過一個大鏈條后經180°轉變傳給變速器。從而，將主動力通過變速器后分流傳到驅動軸再送到兩前輪。
也有一些其他方式的前輪驅動車輛，車架前方代替另一邊的其他系統(tǒng)驅動四輪，但在這兒僅對其中的兩個系統(tǒng)進行說明。相對于前輪驅動來說最流行的是后輪驅動，在發(fā)動機上連接一個輸出軸，將改變后的力矩傳給后驅動輪。這個系統(tǒng)是探尋前后軸實施改進的新的節(jié)能動力平衡裝置。另一個驅動系統(tǒng)是把所有的驅動零件都按在后輪上。這種排列方式發(fā)動機通常后置。
現代自動變速器由許多的部件和系統(tǒng)組成，它們有行星齒輪組、液壓系統(tǒng)、密封圈和密封襯墊、變矩器、油壓調節(jié)器、調制器、節(jié)氣門拉線、電子控制裝置等，經精心設計運轉協(xié)調，其中的電子控制裝置經歷了多年的發(fā)展，已經以巧妙的形式溶入了許多人性化的設計。
汽車上的行星齒輪主要用在兩個地方，一是驅動橋減速器、二是自動變速器。很多網友都想知道，行星齒輪有什么功能，為什么汽車少不了它。
我們熟知的齒輪絕大部分都是轉動軸線固定的齒輪。例如機械式鐘表，上面所有的齒輪盡管都在做轉動，但是它們的轉動中心（與圓心位置重合）往往通過軸承安裝在機殼上，因此，它們的轉動軸都是相對機殼固定的，因而也被稱為"定軸齒輪"。 軸線固定的齒輪傳動原理很簡單，在一對互相嚙合的齒輪中，有一個齒輪作為主動輪，動力從它那里傳入，另一個齒輪作為從動輪，動力從它往外輸出。也有的齒輪僅作為中轉站，一邊與主動輪嚙合，另一邊與從動輪嚙合，動力從它那里通過。
在包含行星齒輪的齒輪系統(tǒng)中，情形就不同了。由于存在行星架，也就是說，可以有三條轉動軸允許動力輸入/輸出，還可以用離合器或制動器之類的手段，在需要的時候限制其中一條軸的轉動，剩下兩條軸進行傳動，這樣一來，互相嚙合的齒輪之間的關系就可以有多種組合：動力從其中一個太陽輪輸入，從另外一個太陽輪輸出，行星架通過剎車機構剎死；動力從其中一個太陽輪輸入，從行星架輸出，另外一個太陽輪剎死；動力從行星架輸入，從其中一個太陽輪輸出，另外一個太陽輪剎死；兩股動力分別從兩個太陽輪輸入，合成后從行星架輸出；兩股動力分別從行星架和其中一個太陽輪輸入，合成后從另外一個太陽輪輸出；動力從其中一個太陽輪輸入，從另外一個太陽輪和行星架分兩路輸出；動力從行星架輸入，分兩路從兩個太陽輪輸出。
由于采用了變矩器，這種變速器的換檔質量不錯但效率相對較差雖然目前有所改進。因此，目前進行了許多研究，試圖發(fā)現傳統(tǒng)變速器的有效的代替方案。
主要的技術還是無級變速器（CVT）、雙離合變速（DCT）和手自一體（AMT）變速器。它們在不同的方面優(yōu)于傳統(tǒng)的行星齒輪式自動變速器。
無級變速器采用帶、鏈或錐盤滾輪來產生無限多種速比，與傳統(tǒng)自動變速器相比其效率和成本都有所改善。之所以有這些優(yōu)點，是因為它結構簡單，這種變速器的零部件很少，通常只有一根橡膠或金屬傳動帶、一個液壓作用的驅動帶輪、一個機械扭矩感應式驅動帶輪、一些微處理器和傳感器等。
這種變速器的工作原理是改變兩個主帶輪表面之間的距離，帶輪上掛傳動帶的地方開了V形槽，一側的帶輪沿軸向固定，另一側的帶輪可在液壓的作用下移動。
在驅動輪后，液壓缸可增加或減少帶輪兩側之間的距離，這樣會使傳動帶在帶輪側壁上的位置上下變動，變動的方式取決于駕駛情況。這樣就會使變速比改變。錐盤滾輪型變速器的工作原理與此類似但用的是驅動盤和動力滾輪。
CVT（無極）變速器的特點對技術人員最具有吸引力。因為這樣沒有檔位，CVT可使發(fā)動機保持在最佳的功率范圍內。這樣可以使效率提高并在相同的油耗下增加行駛里程。CVT可將發(fā)動機工作曲線上的每一點轉變?yōu)槠浔旧砉ぷ髑€上相應的點。
這種變速器最受日本汽車制造商青睞，并且日本變速器生產商JACTO是主要生產者，但在歐美國家，情況就有所不同。盡管奧迪和其它一些制造商在一些車型上推出了CVT，但在這方面他們追趕的步伐仍然很緩慢。
DCT實際上是將兩臺手動變速器合在一起，換檔過程是通過兩臺變速器的離合器之間的相互切換來實現的。這種變速器的換檔質量和傳統(tǒng)的自動變速器相同，但由于系統(tǒng)會發(fā)生滑動、液體阻力和液壓損失，其效率和加速性只比傳統(tǒng)行星齒輪自動變速器稍有提高，開發(fā)控制系統(tǒng)的成本也很高。
“最近在傳統(tǒng)自動變速器技術上所取得的進展，使開發(fā)和生產CVT或DCT的呼聲有所降低。”變速器生產企業(yè)Zeroshift公司的執(zhí)行總裁比爾馬丁說，“由于成本過高，有些汽車廠已經取消了DCT項目?！?
AMT是成本最低的自動變速器技術，AMT用執(zhí)行器來代替?zhèn)鹘y(tǒng)的離合器踏板和換檔桿，這種變速器保留了手動變速器的高效率和加速性能，但某些型號的變速器換檔質量不高，扭矩中斷和“點頭”效應仍是主要的缺點。
那么什么是最好的代替方案？變速器方面的新技術是層出不窮的，但Zeroshift公司聲稱其變速器的效率優(yōu)于手動變速器，提高失去駕駛的燃油經濟性，同時，其換檔效率可以和改進后的自動變速器相媲美。
Zeroshift公司采用的是一種改進版的AMT技術，這種技術用先進的犬牙嚙合系統(tǒng)代替同步器。
犬牙嚙合技術許多年前就已經在賽車運動中采用，目的是為了加快換檔速度。傳統(tǒng)的犬牙式變速器并不適合在公路上，因為驅動環(huán)或犬牙之間的空隙很大，會產生后坐——由扭矩突然轉向而產生的一種不舒適的竄動。
Zeroshift公司通過增加第二套驅動犬牙來解決這一問題，這種技術還使每組犬牙只能傳遞兩種相反方向扭矩中的一種?！巴ㄟ^對兩套犬牙的嚙合和分離，可在上一個檔位沒有分離的情況下換入新的檔位?！瘪R丁說，“換檔質量超過采用現代化的6檔變速器的豪華轎車?！?
換檔可在瞬間完成，而扭矩不發(fā)生中斷，而且這種方法既可用于升檔又可用于降檔。
“在使用傳統(tǒng)的AMT變速器時，由于需要關閉并重新打開油門，換檔過程中排放會達到高峰，而通過這種無過渡的換檔方式可以消除這種現象?！瘪R丁說，“這樣還能降低燃油消耗。”
“盡管在技術上變速器領域還比較新，但公司稱已經引起了歐美各大汽車制造商的注意，最大的吸引力在于其成本比DCT低”，馬丁說。
由于可以保留大部分手動變速器的結構，這種變速器的成本和復雜性都不會高于傳統(tǒng)的AMT變速箱?？刂葡到y(tǒng)的成本也會大大降低，這對試圖減少排放和削減成本的工程師來說是個好消息。
“大部分制造商都來參觀過，”馬丁說，“有些公司馬上就和我們簽合同，另一些未作決定，拒絕的一個都沒有?！边@再清楚不過的表明了汽車制造商現在正在將動力系統(tǒng)開發(fā)的重點轉移到變速箱上。
Zeroshift公司的變速系統(tǒng)是怎樣工作的呢？它的硬件部分包括兩套犬牙，安裝在兩個獨立的犬牙環(huán)上并受其驅動，兩套犬牙有一個共同的蓋，蓋和一個花鍵軸相連。
每個犬牙都有特殊的輪廓。在一側是用于嚙合的直角面。這些直角面是沿對角線相對的，這樣的犬牙在對某一個檔位具有驅動功能的同時，對另一個檔位具有超越傳動的功能。嚙合面有輕微的后向錐度，以保證犬牙能在加載時鎖定在嚙合齒輪上。
相對角上有一個斜坡，可在新檔位嚙合后將犬牙從前一個檔位推離。
在空檔時，兩個犬牙環(huán)處于變速比的中間位置。選一檔時，犬牙會發(fā)生移動并和犬牙嚙合面發(fā)生嚙合。犬牙通過與換檔執(zhí)行器相連的換檔撥叉驅動。
驅動犬牙將一檔齒輪與輸出軸鎖定在一起，將扭矩從齒輪傳遞到輸出軸。一檔的超越傳動犬牙也會移動并將齒輪以相反的方向和輸出軸鎖定。這樣可以在油門關閉且發(fā)動機倒拖時將扭矩從齒輪傳遞到輸出軸。這樣就消除了犬牙嚙合式變速器常見的后坐現象。
在加大油門換檔時，一檔齒輪的超越傳動犬牙卸載后和二檔齒輪嚙合。然后換入二檔時，前一個驅動環(huán)卸載。
如果犬牙之間不能完全嚙合，即實現兩個犬牙面之間的嚙合，由于相對速度差的存在，二檔齒輪會打開一個嚙合缺口。在犬牙抵住嚙合面后，在撥叉和執(zhí)行器的共同作用下，儲存的能量會將犬牙送入缺口內。
此時，一檔超越傳動犬牙成為二檔的驅動犬牙。在換入二檔后，一檔的驅動犬牙隨即卸載。這時候，這些犬牙不再受其固定面固定，可以被執(zhí)行器或犬牙上的斜面推離檔位。
2 外文原文：
TRANSMISSION
Of all transmission technologies, the manual gearbox is the most efficient; around 96 per cent of the energy that is put in comes out of the other end. But not everyone can drive one or wants to. Because you have to dip the clutch pedal, it is less comfortable to drive in heavy traffic. It makes the driver tired and the torque interruptions’ head-nod effect on passengers can be wearing.
The driver's clutch control and corresponding torque interruptions are also the manuals weak point. When accelerating up through the gearbox, each up-shift requires the driver to cut the torque momentarily by lifting the gas pedal and dipping the clutch. It may just take a second to complete the operation, but during this time the vehicle is losing speed and acceleration.
At the opposite end of the spectrum is the traditional automatic. The modern transmission is by far, the most complicated mechanical component in today’s automobile. It is a type of transmission that shifts itself .A fluid coupling or torque converter is used instead of a manually operated clutch to connect the transmission to the engine.
There are two basic types of automatic transmissions based on whether
the vehicle is rear wheel drive . On a rear wheel drive car , the transmission is usually mounted to the back of the engine and is located under the hump in the center of the floorboard alongside the gas pedal position . A drive shaft connects the rear of the transmission to the final drive which is located in the rear axle and is used to send power to the rear wheel. Power flow on this system is simple and straight forward going from the engine, through the torque converter , then through the transmission and driver shaft until it reaches the final driver where it is split and sent to the two rear wheel .
On a front wheel drive car, the transmission is usually combined .With the final drive to from what is called a transaxle. The engine on a front wheel driver car is usually mounted sideways in the car with the transaxle tucked under it on the side of the engine facing the rear of the car. Front axles are connected directly to the transaxle and provide power to the front wheels. In this example, power flows from the engine through the torque converter to a large chain that sends the power through a 180 degree turn to the transmission that is along side the engine. From there，The power is routed through the transmission to the final drive where it is split and sent to the two front wheels through the drive axles.
There are a number of other arrangements including front drive vehicles where the engine is mounted front to back instead of sideways and there are other systems that drive all four wheels but the two systems described here are by far the most popular. A must less popular rear drive arrangement has the transmission mounted to the final drive at the rear and is connected by a drive shaft to the torque converter which is still mounted on the engine. This system is found on the new corvette and is used in order to balance the weight evenly between the front and rear wheels for improved performance and handling. Another rear drive system mounts everything, the engine, transmission and final drive in the rear. This rear engine arrangement is popular on the Porsche.
The modern automatic transmission consists of many components and systems that are designed to work together in a symphony of planetary gear sets, the hydraulic system, seals and gaskets, the torque converter, the governor and the modulator or throttle cable and computer consider being an art form.
On the automobile planet gear mainly uses in two places, one is the driving axle reduction gear, two is the automatic transmission. Very many net friends all want to know that, the planet gear has any function, why automobile must have it
. We knew very well the gear major part all rotates the spool thread fixed gear. For example mechanical type clock and watch, above all gears although all in make the rotation, but their rotation center (with center of a circle position superposition) often installs through the bearing on the cabinet, therefore, their rotating axis all is the relative cabinet fixed, thus also is called "dead axle gear"
. Has must have surely moves, the corresponding place, some kind of not that manner knows very well is called "planet gear" the gear, their rotation spool thread is not fixed, but is installs the support which may rotate in (blue color) on (in chart black part is shell, yellow expression bearing). The planet gear (green) besides can look like the dead axle gear such to revolve own rotating axis (B-B) to rotate, their rotating axis also (is called planet) along with the blue color support to circle other gears the spool thread (A-A) to rotate. Circles oneself spool thread the rotation to be called "rotation", circles other gear spool threads the rotation to be called "revolution", looks like in solar system planet such, therefore acquires fame.
The spool thread fixed gear drive principle is very simple, meshes mutually in a pair in the gear, some gear takes the driving pulley, the power spreads from its there, another gear takes the driven wheel, the power outputs from it toward outside. Also some gears only take the stopover station, at the same time meshes with the driving pulley, one side meshes in addition with the driven wheel, the power passes from its there.
In contains the planet gear in the gear system, the situation was different. Because has the planet frame, in other words, may have three rotating axes permissions power input/Output, but also may use the coupling or the brake and so on method. in needs time limits axis the rotation, is left over two axes to carry on the transmission, as the matter stands, meshes mutually between the gear relations may have the many kinds of combinations: The power from sun gear input, outputs from other sun gear, the planet put through brake mechanism has checked dies; Power from sun gear input, from planet output, moreover a sun gear ecks dies; The power from a planet input, outputs from sun gear, moreover a sun gear checks dies; Two powers separately from two sun gears inputs, after synthesis from planet output; Two powers separately from the planet and sun gear input, after the synthesis output from other sun gear; The power from sun gear input, divides two groups outputs from other sun gear and the planet frame; The power from a planet input, divides two groups to output from two sun gears;
Its shift quality is good thanks to its torque converter, but efficiency is relatively poor despite recent advances. Because of this, a lot of the current research is trying to find an efficient alternative to the conventional automatic.
The main technologies are continuously variable transmissions (CVTs); dual clutch transmissions (DCTs) and automated manual transmission (AMTs).They all offer different benefits over the conventional planetary automatic.
The CVT uses a belt chain or torodial shaped dish drive to vary an infinite number of gear ratios. It has improved efficiency and cost when compared to conventional automatics. Its advantage comes from its simplicity. It consists of very few components；usually a rubber or metal-link belt；a hydraulically operated driving pulley, a mechanical torque-sensing driving pulley, microprocessors and some sensors.
The transmission works by varying the distance between the face of the two main pulleys. The pulleys have V－shaped grooves in which the connecting the belt rides. One side of the pulley is fixed axially; the other side moves, actuated by hydraulics.
When actuated, the cylinder can increase or reduce the amount of space between the two sides of the pulley. This allows the belt to ride lower or higher along the walls of the pulley, depending on driving conditions. This changes the gear ratio. A torodial-type design works in a similar way but runs an discs and power- rollers
The "step less" nature of its design is CVT's biggest draw for automotive engineers .Because of this, a CVT can work to keep the engine in its optimum power range, thereby increasing efficiency and mileage. A CVT can convert every point on the equine’s operating curve to a corresponding point on its own operating curve.
The transmission is most popular with Japanese carmakers and Japanese supplier JATCO is a major producer. But in the US and Europe driving styles are different. Uptake has been slow despite Audi and other manufacturers having Offered CVT operations on their ranges.
The DCT is, in effect, two manual gearboxes coupled together. Gear shifts are made by switching from one clutch on one gearbox to another clutch on the other. The shift quality is equal to a conventional automatic, but slip, fluid drag and hydraulic losses in the system result in only slightly improved efficiency and acceleration over the conventional planetary automatic. Developing the control strategy is costly too.
"Resent advances in conventional automatic technology have weakened the argument to develop and set up production for CVT or DCT," says Bill Martin, managing director of transmission firm Zeroshift "Some carmakers have cancelled DCT projects because of the cost."
The cheapest way to build an automatic is with an AMT. AMTs use actuators to replace the clutch pedal and gear stick of a conventional manual. They keep the high efficiency and acceleration of a manual gearbox, but the shift quality on some models is lacking. Torque interruptions and the head-nod effect are the most common complaint.
SO what is the alternative? There are always new ideas in transmissions, but Zeroshift says that its technology has efficiency benefits over a manual, delivering fuel economy improvements to city driving. Shift quality can also be equal to that of a refined automatic.
Zeroshift's approach is an upgrade to the AMT. The synchromesh is replaced with an advanced dog engagement system.
Dog engagement has been used for many years in motor sport to allow fast shifts. Conventional dog Boxes are unsuitable for road use as the large spaces between the drive lugs or 'dogs" create backlash, an uncomfortable shunt caused by the sudden change in torque direction.
Zeroshift's technology solves this problem by adding a second set of drive dogs. It has also made each of The two sets of dogs only capable of transmitting torque in one or other opposing directions By controlling the engagement and disengagement of the two sets you can shift into the new gear before disengaging the previous gear," says Martin "The shift quality is smoother than a typical modern six-speed automatic luxury car"
The shift is instant and the torque is not interrupted. This philosophy is used for both up and down shifts.
"In conventional AMT there is an emissions spike during a shift due to the need to back off and reintroduce throttle, this is eliminated by going seamless," says Martin.” This also reduces fuel consumption. “
It is a relative newcomer to the transmission sector, but the firm says that it is already attracting the attention of major European and US carmakers. The big draw is as a low-cost alternative to DCT, says Martin.
Because the manual gearbox architecture is largely maintained, production costs and complexity are not greater than for a conventional AMT. Development of tile controls side is also considerably cheaper. Music to the ears of engineers trying to cut emissions and costs.
"Most of the carmakers have seen the system at least once," says Martin "Some signed us up immediately some have said not yet. None have said no." That may be the clearest sign yet that when it comes to power train developments, carmaker are starting to focus on the transmission.
How zeroshift works? The hardware consists of two sets of bullets mounted and actuate on two independent bullet rings. Both set of bullets run on the common hub, which is attached to the shaft with splints.
Each bullet has a special profile. On one side they have an angled face for engagement. These are diagonally opposed, allowing the bullet to have a drive function for one gear and an overrun function for the other gear. The engagement faces taper backwards slightly to ensure the bullet latches onto the engaged under load.
The opposite corners have a ramp, which pushes the bullet out of the previous gear once the new gear has been engaged.
In neutral both bullet rings are positioned midway between the ratios. To select first gear, the bullets are moved into mesh with the engagement dogs. The bullets are actuated via shift forks connected to the shift actuators.
第2章 變速器的方案論證
2.1 變速器類型選擇及傳動方案設計
變速器的種類很多，按其傳動比變化方式不同可以分為有級式、無級式和綜合式三種。有級式變速器根據前進擋數的不同，可以分為三、四、五擋和多擋變速器；而按其軸中心線的位置又分為固定軸線式、螺旋軸線（行星齒輪）式和綜合式。其中，固定式變速器應用較廣泛，又可分為兩軸式，三軸式和多軸式變速器。
現代汽車大多都采用三軸式變速器。對發(fā)動機前置前輪驅動的轎車，如變速器傳動比小，則常采用兩軸式變速器。以下是兩軸式和三軸式變速器的傳動方案。要采用哪一種方案，除了汽車總布置的要求外，主要考慮以下四個方面：
2.1.1 結構工藝性
兩軸式變速器輸出軸與主減速器主動齒輪做成一體，當發(fā)動機縱置時，主減速器可用螺旋圓錐齒輪或雙曲面齒輪，而發(fā)動機橫置時用圓柱齒輪，因而簡化了制造工藝。
2.1.2 變速器的徑向尺寸
兩軸式變速器的前進擋均為一對齒輪副，而三軸式變速器則有兩對齒輪副。因此，對于相同的傳動比要求，三軸式變速器的徑向尺寸可以比兩軸式變速器小得多。
2.1.3 變速器齒輪的壽命
兩軸式變速器的低擋齒輪副大小相差懸殊，小齒輪工作循環(huán)次數比大齒輪要高得多，因此，小齒輪工作壽命比大齒輪要短。三軸式變速器的各前進擋均為常嚙合齒輪傳動，大小齒輪的徑向尺寸相差較小，因此壽命比較接近。在直接擋時，齒輪只是空轉，不影響齒輪壽命。
2.1.4 變速器的傳動效率
兩軸式變速器，雖然可以有等于1的傳動比，但是仍要有一對齒輪傳動，因而有功率損失。而三軸式變速器，可以將輸入軸和輸出軸直接相連，得到直接擋，因而傳動效率高，磨損小，噪聲也較小。
載貨汽車則多采用三軸式變速器。
這次設計的變速器是輕型貨車使用，采用三軸式變速器。
2.2變速器傳動機構的分析
根據第一節(jié)所述，采用中間軸式變速器，在各擋數相同的條件下，各變速器的差別主要在常嚙合齒輪對數，換擋方案和倒擋傳動方案。
2.2.1 換擋結構形式的選擇
目前，汽車上的機械式變速器的換擋結構形式有直齒滑動齒輪、嚙合套和同步器換擋三種。
1）滑動齒輪換擋
通常是采用滑動直齒輪換擋，但也有采用滑動斜齒輪換擋的。滑動直齒輪換擋的優(yōu)點是結構簡單、緊湊、容易制造。缺點是換擋時齒端面承受很大的沖擊會導致齒輪過早損壞，并且直齒輪工作噪聲大，所以這種換擋方式一般僅用在一擋和倒擋上。
2）嚙合套換擋
用嚙合套換擋，可以將結構為某傳動比的一對齒輪，制造成常嚙合的斜齒輪。用嚙合套換擋，因同時承受換擋沖擊載荷的接合齒齒數多，而輪齒又不參與換擋，因此它們都不會過早損壞，但是不能消除換擋沖擊，所以仍要求駕駛員有熟練的操作技術。此外，因增設了嚙合套和常嚙合齒輪，使變速器的軸向尺寸和旋轉部分的總慣量增大。因此，這種換擋方法目前只在某些要求不高的擋位及重型貨車變速器上使用。這是因為重型貨車擋位間的公比較小，要求換擋手感強，而且在這種車型上又不宜使用同步器（壽命太短，維修不便）。
3）同步器換擋
現在大多數汽車的變速器都采用同步器換擋。使用同步器能保證迅速、無沖擊、無噪聲換擋，與操作技術熟練程度無關，從而提高了汽車的加速性、經濟性和行駛安全性。同上述兩種換擋方法相比，雖然它有結構復雜、制造精度要求高、軸向尺寸大、同步環(huán)使用壽命短等缺點，但仍然得到廣泛應用。近年來，由于同步器廣泛使用，壽命問題已得到基本解決。
上述三種換擋方案，可同時用在同一變速器中的不同擋位上，一般倒擋和一擋采用結構較簡單的滑動直齒輪或嚙合套的形式，對于常用的高擋位則采用同步器或嚙合套。
本次設計方案五個前進擋和倒擋均采用同步器換擋。
2.2.2倒擋的形式及布置方案
倒擋使用率不高，常采用直齒滑動齒輪方案換入倒擋。為實現傳動有些利用在前進擋的傳動路線中，加入一個中間傳動齒輪的方案，也有利用兩個聯體齒輪的方案。
圖2-1倒擋結構方案
常見的倒擋結構方案有以下幾種：
方案1.（如圖2-1a）所示）
在前進擋的傳動路線中，加入一個傳動，使結構簡單，但齒輪處于正負交替對稱變化的彎曲應力狀態(tài)下工作。此方案廣泛用于轎車和輕型貨車的四擋全同步器式變速器中。
方案2.（如圖2-1b）所示）
此方案的優(yōu)點是可以利用中間軸上一擋齒輪，因而縮短了中間軸的長度，但換擋時兩對齒輪必須同時嚙合，致使換擋困難。某些輕型貨車四擋變速器采用此方案。
方案3.（如圖2-1c）所示）
此方案能獲得較大的倒擋傳動比，突出的缺點是換擋程序不合理。
方案4.（如圖2-1d）所示）
此方案針對前者的缺點作了修改，因而經常在貨車變速器中使用。
方案5.（如圖2-1e）所示）
此方案中，將中間軸上一擋和倒擋齒輪做成一體其齒體、寬加大，因而縮短了一些長度。
方案6.（如圖2-1f）所示）
此方案中，采用了全部齒輪副均為常嚙合齒輪，換擋方便。
方案7.（如圖2-1g）所示）
為了充分利用空間，縮短變速器軸向長度，有些貨車采用此方案，其缺點是一擋和倒擋得各用一根變速器撥叉軸，使變速器上蓋中的操縱機構復雜一些，一般3、4、5、6、7這五種方案用于五擋變速器。
綜合考慮，本次設計采用一擋和倒擋共用一個同步器換擋。
2.3 變速器操縱機構方案分析
2.3.1變速器操縱機構的功用
變速器操縱機構的功用是保證各擋齒輪、嚙合套或同步器移動規(guī)定的距離，以獲得要求的擋位，而且又不允許同時掛入兩個擋位。
2.3.2 設計變速器操縱機構時，應該滿足的基本要求：
1、要有鎖止裝置，包括自鎖、互鎖和倒擋鎖；
2、要使換擋動作輕便、省力，以減輕駕駛員的疲勞強度；
3、應使駕駛員得到必要的手感。
2.3.3換擋位置
設計操縱機構首先要確定換擋位置。換擋位置的確定主要從換擋方便考慮。為此應該注意以下三點：
1、按換擋次序來排列 ；
2、將常用擋位放在中間位置，其它擋位放在兩邊；
3、為了避免誤掛倒擋，往往將倒擋安排在最靠邊的位置，有時于1擋組成一排。
2.4 齒輪形式的分析確定
斜齒圓柱齒輪雖然工作時有軸向力且加工復雜些，但仍以其運轉平穩(wěn)噪聲低壽命長的突出優(yōu)點得到變速器的普遍采用。本次設計一檔和倒擋采用直齒輪，其它各擋均采用斜齒輪。
2.5 齒輪副安排的分析確定
各齒輪副的相對安排位置，對于整個變速器的結構布置有很大的影響。各擋位置的安排，應考慮以下四個方面的要求：
2.5.1 整車總布置
根據整車的總布置，對變速器輸入軸與輸出軸的相對位置和變速器的輪廓形狀以及換擋機構提出要求。比如說是該車是采用發(fā)動機前置前驅動還是發(fā)動機前置后驅動等等，這些問題都牽連著變速器的設計方案。
2.5.2 駕駛員的使用習慣
人們習慣于按擋的高低順序，由左到右或由右到左排列來換擋，如下圖b和c。值得注意的是倒擋，雖然它是平常換擋序列之外的一個特殊擋位，然而卻是決定序列組合方案的重要環(huán)節(jié)。例如在四擋變速器中采用的基本序列組合方案有三種，見圖2.2。其中b和c是倒擋與序列不結合的方案，即掛擋時，需先換位再掛倒擋。倒擋與序列結合與不結合兩者比較，前者在結構上可省去一個撥叉和一根變速滑桿，后者如布置適當，則可使變速器的軸向長度縮短。
按習慣，倒擋最好與序列不結合。否則，從安全考慮，將倒擋與一擋放在一起較好。
根據以上的要求，本次設計的擋位布置方案如圖2.2所示：
圖 2-2 擋位布置方案
2.5.3 提高平均傳動效率
為提高平均傳動效率，在三軸式變速器中，普遍采用具有直接擋的傳動方案，并盡可能地將使用時間最多的擋位實際成直接擋。
2.5.4改善齒輪受載狀況
各擋齒輪在變速器中的位置安排，應考慮齒輪的受載狀況。承受載荷大的低擋齒輪，一般安置在離軸承較近的地方，以減小軸的變形，使齒輪的重疊系數不致下降過多。變速器齒輪主要是因接觸應力過高而造成表面點蝕損壞，因此將高擋齒輪安排在離兩支承較遠處較好。該處因軸的變形而引起齒輪的偏轉角較小，故齒輪的偏載也小。
本次設計傳動方案如圖2.4所示
傳動路線：
Ⅰ擋：一軸→1→2→中間軸→5→6→6和9間的同步器→二軸→輸出
Ⅱ
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