汽车手动五档变速器外文翻译

MANUAL GEARBOXES 9.1 MANUAL GEARBOX CLASSIFICATION Gearboxes are normally classied according to the number of toothed wheel couples (stages) involved in the transmission of motion at a given speed； in the case of manual vehicle transmissions, the number to be taken into account is that of the forward speeds only, without consideration of the nal gear, even if included in the gearbox. Therefore there are: Single stage gearboxes Dual stage or countershaft gearboxes Multi stage gearboxes Figure 9.1 shows the three congurations for a four speed gearbox. It is useful to comment on the generally adopted rules of these schemes. Each wheel is represented by a segment whose length is proportional to the pitch diameter of the gear； the segment is ended by horizontal strokes, representing the tooth width. If the segment is interrupted where crossing the shaft, the gear wheel is idle； the opposite occurs if the segment crosses the line of the shaft without interruption. Then the wheel rotates with the shaft. Hubs are represented according to the same rules, while sleeves are represented with a pair of horizontal strokes. Arrows show the input and output shafts. Single stage gearboxes are primarily applied to front wheel driven vehicles, because in these it is useful that the input and the output shaft are oset； in G. Genta and L. Morello, The Automotive Chassis, Volume 1: Components Design, 425 Mechanical Engineering Series, c Springer Science+Business Media B.V. 2009426 9. MANUAL GEARBOXES FIGURE 9.1. Schemes for a four speed gearbox shown in three dierent congurations: a: single stage, b: double stage and c: triple stage. conventional vehicles, on the other hand, it is better that input and output shafts are aligned. This is why rear wheel driven vehicles usually adopt a double stage gearbox. The multi-stage conguration is sometime adopted on front wheel driven vehicles with transversal engine, because the transversal length of the gearbox can be shortened； it is used when the number of speeds or the width of the gears do not allow a single stage transmission to be used. It should be noted that on a front wheel driven vehicle with transversal engine, having decided on the value of the front track and the size of the tire, the length of the gearbox has a direct impact on the maximum steering angle of the wheel and therefore on the minimum turning radius. The positive result on the transversal dimension of multi-stage gearboxes is oset by higher mechanical losses, due to the increased number of engaged gear wheels. It should be noted that in triple stage gearboxes, shown in the picture, the axes of the three shafts do not lie in the same plane, as the scheme seems to show. In a lateral view, the outline of the three shafts should be represented as the vertices of a triangle； this lay-out reduces the transversal dimension of the gearbox. In this case and others, as we will show later, the drawing is represented by turning the plane of the input shaft and of the counter shaft on the plane of the counter shaft and of the output shaft. Gear trains used in reverse speed are classied separately. The inversion of speed is achieved by using an additional gear. As a matter of fact, in a train of three gears, the output speed has the same direction as the input speed, while the other trains of two gears only have an output speed in the opposite direction； the added gear is usually called idler. The main congurations are reported in Fig. 9.2. In scheme a, an added countershaft shows a sliding idler, which can match two close gears that are not in contact, as, for example, the input gear of the rst speed and the output gear of the second speed. It should be noted that, in this scheme, the drawing does not preserve the actual dimension of the parts.9.1 Manual gearbox classication 427 FIGURE 9.2. Schemes used for reverse speed； such schemes t every type of gearbox lay-out. Scheme b shows instead two sliding idlers, rotating together； this arrange- ment oers additional freedom in obtaining a given transmission ratio. The coun- tershaft is oset from the drawing plane； arrows show the gear wheels that match when the reverse speed is engaged. Scheme c is similar to a in relation to the idler； it pairs an added specic wheel on the output shaft with a gear wheel cut on the shifting sleeve of the rst and second speed, when it is in idle position. Conguration d shows a dedicated pair of gears, with a xed idler and a shifting sleeve. The following are the advantages and disadvantages of the congurations shown in the gure. Schemes a, b and c are simpler, but preclude the application of synchro- nizers (because couples are not always engaged), nor do they allow the use of helical gears (because wheels must be shifted by sliding). Scheme d is more complex but can include a synchronizer and can adopt helical gears. Schemes a, b and c do not increase gearbox length.428 9. MANUAL GEARBOXES 9.2 MECHANICAL EFFICIENCY The mechanical eciency of an automotive gear wheel transmission is high com- pared to other mechanisms performing the same function； indeed, the value of this eciency should not be neglected when calculating dynamic performance and fuel consumption. The continuous eort of to limit fuel consumption justi- es the care of transmission designers in reducing mechanical losses. Total transmission losses are conveyed up by terms that are both dependent and independent of the processed power； the primary terms are: Gearing losses； these are generated by friction between engaging teeth (power dependent) and by the friction of wheels rotating in air and oil (power independent). Bearing losses； these are generated by the extension of the contact area of rolling bodies and by their deformation (partly dependent on and partly independent of power) and by their rotation in the air and oil (power independent). Sealing losses； they are generated by friction between seals and rotating shafts and are power independent. Lubrication losses； these are generated by the lubrication pump, if present, and are power independent. All these losses depend on the rotational speed of parts in contact and, therefore, on engine speed and selected transmission ratio. Table 9.1 reports the values of mechanical eciency to be adopted in calcu- lations considering wide open throttle conditions； these values consider a pair of gearing wheels or a complete transmission with splash lubrication； in the same table we can see also the eciency of a complete powershift epicycloidal auto- matic transmission and a steel belt continuously variable transmission. For the two last transmissions, the torque converter must be considered as locked-up. TABLE 9.1. Mechanical eciency of dierent transmission mechanisms. Mechanism type Eciency (%) Complete manual gearbox with splash lubrication 9297 Complete automatic transmission (ep. gears) 9095 Complete automatic gearbox (steel belt； without press. contr.) 7080 Complete automatic gearbox (steel belt； with press. contr.) 8086 Pair of cyl. gears 99.099.5 Pair of bevel gears 90939.2 Mechanical eciency 429 FIGURE 9.3. Contributions to total friction loss of a single stage gearbox designed for 300 Nm as function of input speed. It is more correct to reference power loss measurement as a function of rotational input speed rather than eciency. Figure 9.3 shows the example of a double stage transmission, in fourth speed, at maximum power； the dierent contributions to the total are shown. This kind of measurement is made by disassembling the gearbox step by step, thus eliminating the related loss. In the rst step all synchronizer rings are removed, leaving the synchronizer hubs only； mechanical losses of non-engaged synchronizers are, therefore, mea- surable. The loss is due to the relative speed of non-engaged lubricated conical surfaces； the value of this loss depends, obviously, on speed and the selected transmission ratio. In the second step all rotating seals are removed. In the third step the lubrication oil is removed, and therefore, the bulk of the lubrication losses is eliminated； some oil must remain in order to leave the contact between teeth unaected. By removing those gear wheels not involved in power transmission, their mechanical losses are now measurable. The rest of the loss is due to bearings； the previous removal of parts can aect this value. A more exhaustive approach consists in measuring the complete eciency map； the eciency can be represented as the third coordinate of a surface, where the other two coordinates are input speed and engine torque. Eciency calcu- lations can be made by comparing input and output torque of a working trans- mission. Such map can show how eciency reaches an almost constant value at a modest value of the input torque； it must not be forgotten that standard fuel consumption evaluation cycles involve quite modest values of torque and there- fore imply values of transmission eciency that are changing with torque. Figure 9.4 shows a qualitative cross section of the aforesaid map, cut at constant engine speed. It should be noted that eciency is also zero at input430 9. MANUAL GEARBOXES FIGURE 9.4. Mechanical eciency map, as a function of input torque at constant engine speed； the dotted line represents a reasonable approximation of this curve, to be used on mathematical models for the prediction of performance and fuel consumption. torque values slightly greater than zero； as a matter of fact, friction implies a certain minimum value of input torque, below which motion is impossible. A good approximation to represent mechanical eciency can be made using the dotted broken line as an interpolation of the real curve. 9.3 MANUAL AUTOMOBILE GEARBOXES 9.3.1 Adopted schemes In manual gearboxes, changing speed and engaging and disengaging the clutch are performed by driver force only. This kind of gearbox is made with helical gears and each speed has a syn- chronizer； some gearboxes do not use show the synchronizer for reverse speed, particularly those in economy minicars. We previously discussed a rst classication； additional information is the speed number, usually between four and six. Single stage gearboxes are used in trans-axles； they are applied, with some exceptions, to front wheel driven cars with front engine and rear driven cars with rear engine； this is true with longitudinal and transversal engines. In all these situations the nal drive is included in the gearbox, which is therefore also called transmission. Countershaft double stage gearboxes are used in conventionally driven cars, where the engine is mounted longitudinally in the front and the driving axle is the rear axle. If the gearbox is mounted on the rear axle, in order to improve the weight distribution, the nal drive could be included in the gearbox.9.3 Manual automobile gearboxes 431 By multi-stage transmissions, some gear wheels could be used for dierent speeds. The number of gearing wheels could increase at some speeds； this nor- mally occurs at low speeds, because the less frequent use of these speeds reduces the penalty of lower mechanical eciency on fuel consumption. Cost and weight increases are justied by transmission length reduction, sometimes necessary on transversal engines with large displacement and more than four cylinders. In all these gearboxes synchronizers are coupled to adjacent speeds (e.g.: rst with second, third with fourth, etc.) in order to reduce overall length and to shift the two gears with the same selector rod. We dene as the selection plane of a shift stick (almost parallel to the xz coordinate body reference system plane for shift lever on vehicle oor) the plane on which the lever knob must move in order to select two close speed pairs. For instance, for a manual gearbox following many existing schemes, rst, second, third, fourth and fth speed are organized on three dierent selection planes； the reverse speed can have a dedicated plane or share its plane with the fth speed. Figure 9.5 shows a typical example of a ve speed single stage gearbox. The rst speed wheels are close to a bearing, in order to limit shaft deection. In this gearbox the total number of tooth wheels pairs is the same as for the double stage transmission shown in Fig. 9.6. While in the rst gearbox there are only two gearing wheels for each speed, in the second there are three gearing wheels for the rst four speeds and none FIGURE 9.5. Scheme for a ve speed single stage transmission, suitable for front wheel drive with transversal engine.432 9. MANUAL GEARBOXES FIGURE 9.6. Scheme of an on-line double stage gearbox for a conventional lay-out. for the fth. This property is produced by the presence of the so called constant gear wheels (the rst gear pair at the left) that move the input wheels of the rst four speeds； the fth speed is a direct drive because the two parts of the upper shaft are joined together. The single stage gearbox in Fig. 9.5 shows the fth speed wheel pair posi- tioned beyond the bearing, witness to the upgrading of an existing four speed transmission； in this case the fth speed has a dedicated selection plane. The double stage gearbox in Fig. 9.7 is organized in a completely dierent way but also shows the rst speed pair of wheels close to the bearing. The direct drive is dedicated to the highest speed； the fth speed shows a dedicated selection plane. Six speed double stage gearboxes do not show conceptual changes in com- parison with the previous examples； synchronizers are organized to leave rst and second, third and fourth, fth and sixth speeds on the same selection plane. As already seen, the multistage conguration shown in Fig. 9.7 allows a reasonable reduction of the length of the gearbox. In this scheme, only rst and second speeds benet from the second countershaft； power enters the counter- shaft through a constant gear pair of wheels and ows to the output shaft at a reduced speed. Third, fourth and fth speed have a single stage arrangement. Reverse speed is obtained with a conventional idling wheel. 9.3.2 Practical examples Four speed gearboxes represented the most widely distributed solution in Europe until the 1970s, with some economy cars having only three speeds.9.3 Manual automobile gearboxes 433 FIGURE 9.7. Scheme of a triple stage ve speed gearbox, suitable for front wheel driven car with transversal engine. With the increase in installed power, the improvement in aerodynamic per- formance and increasing attention to fuel consumption, it became necessary to increase the transmission ratio of the last speed, having the rst speed remain at the same values； as a matter of fact car weight continued to increase and engine minimum speed did not change signicantly. To achieve satisfactory performance all manufacturers developed ve speed gearboxes； this solution is now standard, but many examples of six speed gear- boxes are available on the market, not limited to sports cars. Figure 9.8 shows an example of a six speed double stage transmission with the fth in direct drive； here the rst and second pair of wheels are close to the bearing. This rule is not generally accepted； on one hand having the most stressed pairs of wheels close to the bearing allows a shaft weight containment. On the other hand, having the most frequently used pairs of wheels close to the bearing reduces the noise due to shaft deection. Synchronizers of fourth and third speed are mounted on the countershaft； this lay-out reduces the work of synchronization, improving shifting quality by an amount proportional to the dimension of the synchronizing rings. Synchronizers of rst and second gear on the output shaft are, because of their diameter, larger434 9. MANUAL GEARBOXES FIGURE 9.8. Double stage six speed gearbox (GETRAG). than those of the corresponding gear； the penalty of the synchronization work is paid by the adoption of a double ring synchronizer. Synchronizers on the countershaft oer a further advantage: In idle position the gears are stopped and produce no rattle； this subject will be studied later on.9.3 Manual automobile gearboxes 435 Figure 9.9 introduces the example of a single stage gearbox for a front longitudinal engine. The input upper shaft must jump over the dierential, which is set between the engine and the wheels. The increased length of the shafts suggested adopting a hollow section. Because of this length the box is divided into two sections； on the joint between the two sections of the box additional bearings are provided to reduce the shaft deection. The input shaft features a ball bearing close to the engine and three other needle bearings that manage solely the radial loads. The output shaft has two tapered roller bearings on the dierential side and a roller bearing on the opposite side. This choice is justied by the relevant axial thrust emerging from the bevel gears. The rst and second speed synchronizers are on the output shaft and feature a double ring. The reverse speed gears are placed immediately after the joint (the idler gear is not visible) and have a synchronized shift. Remaining synchronizers are set in the second section of the box on the input shaft. The output shaft ends with the bevel pinion, a part of the nal ratio. It should be noted that the gears of the rst, second and reverse speeds are directly cut on the input shaft, in order to reduce overall dimensions. Most contemporary cars use a front wheel drive with transversal engine； the number of gearboxes with integral helical nal ratio is, therefore, dominant. In these gearboxes geared pairs are mounted from the rst to the last speed, starting from the engine side. An example of this architecture is given in Fig. 9.10. Like many other transmissions created with only four speeds, it shows the fth speed segregated outside of the aluminium box and enclosed by a thin steel sheet cover； this placement is to limit the transverse dimension of the power train, in the area where there is potential interference with the left wheel in the completely steered position. This solution is questionable as far as the total length is concerned but shows some advantage in the reduction of the span between the bearings. Each bearing is of the ball type； on the side opposite to the engine the external ring of the bearing can move axially, to compensate for thermal dierential displacements. One of the toothed wheels of the reverse speed is cut on the rst and second shifting sleeve. The casing is open on both sides； one of these is the rest of one of the bearings of the nal drive. A large cover closes the casing on the engine side and, in the meantime, provides installation for the second bearing of the nal drive and the space for the clutch mechanism； it is also used to join the gearbox to the engine. In this gearbox synchronizers are placed partly on the input shaft and partly on the output shaft. Figure 9.11 shows a drawing of a more modern six speed gearbox, in which it was possible to install all the gears in a conventional single stage arrangement, thanks to the moderate value of the rated torque.436 9. MANUAL GEARBOXES FIGURE 9.9. Single stage six speed gearbox for longitudinal front engine (Audi).9.4 Manual gearboxes for industrial vehicles 437 FIGURE 9.10. Five speed transmission for a transversal front engine (FIAT). Gears are arranged from the rst to the sixth, starting from the engine side； as we have already said this arrangement is demanded by the objective of minimizing shaft deection. Only the synchronizers of rst and second speed found no place on the input shaft； they are of the double ring type, as for the rst speed. The reverse speed is synchronized and benets of a countershaft not shown in this drawing. 9.4 MANUAL GEARBOXES FOR INDUSTRIAL VEHICLES 9.4.1 Lay-out schemes The gearboxes we are going to examine in this section are suitable for vehicles of more than about 4 t of total weight； lighter vehicles, usually called commercial vehicles, adopt gearboxes that are derived from automobile production, as noted in the previous section.438 9. MANUAL GEARBOXES FIGURE 9.11. Six speed transmission for a transversal front engine (FIAT). Gearboxes used in industrial vehicles also feature synchronizers； they can be shifted directly, as in a conventional manual transmission, or indirectly with the assistance of servomechanisms. Non-synchronized gearboxes are sometimes used on long haul trucks, because of their robustness. Assisted shifting mechanisms are widespread because of the easy availability of power media. Automatic or semi-automatic transmissions are also used, the rst type especially in buses. For gearboxes with four up to six speeds, the double stage countershaft architecture represents a standard； the scheme is the same as seen before. The constant gear couple is used for all speeds but the highest. Also notable is that the lowest speed wheels are close to the bearings. As shown in the drawings of Fig. 9.12, the highest speed can be obtained either in direct drive (scheme b) or with a pair of gears (scheme a)； in this last case the direct drive is used for the speed before the last: these architectures are called direct drive and overdrive. In the gure, only the last and the rst before the last speed are represented. The choice between the two alternatives can be justied by the dierent vehicle mission； virtually the same gearbox can be used on dierent vehicles with dierent frequently used speeds (a truck and a bus for example).9.4 Manual gearboxes for industrial vehicles 439 FIGURE 9.12. Alternative constant gear schemes with last or rst before the last speed in direct drive. Sometime the constant gear is set on the output shaft, after the dierent speed gears； this conguration oers the following advantages: Reduction of the work of synchronization, because of the smaller gear di- mension at the same torque and total transmission ratio Less stress on the input shaft and countershaft On the other hand, the following disadvantages emerge: Bearings rotate faster. Constant gear wheels are more highly stressed. This applies for single range transmissions. Multiple range transmissions feature, in addition to the main gearbox, other gearboxes that multiply the number of speeds of the main gearbox by the number of their speeds. With this architecture the total number of gear pairs might be reduced, for a given number of speeds, and, sometime the use of the gearshift lever can be simpler. This arrangement is used when more than six speeds are necessary. A multi- ple range transmission is therefore made out of a combination of dierent coun- tershaft gearboxes, single range gearboxes or epicycloidal gearboxes. Each added element is called a range changer if it is conceived as being capable of using the main gearbox speeds in sequence, in two completely non- overlapping series of vehicle speeds； for example, if the main gearbox has four speeds, the rst speed in the high range is faster than the fourth speed in the low range. The element is called a splitter if it is intended to create speeds that are intermediate to those of the main gearbox； in this case, for example the third440 9. MANUAL GEARBOXES FIGURE 9.13. Scheme of a 16 speed gearbox for industrial vehicles； it is made with a four gear main gearbox, a double speed splitter and a double speed range changer with direct drive. speed in the high range is faster than the third speed in the low range, but slower than the fourth speed in the low range. We call the gearbox with the highest number of speeds the main gearbox； the splitter and the range changer will be set in series before and after the main gearbox. Figure 9.13 shows the scheme of a gearbox featuring a splitter and a range changer. The splitter is made out of a pair of wheels that work as two dierent constant gears for the main gearbox. The countershaft can therefore be moved at two dierent speeds, according to the position of the splitter unit. Because the main gearbox has four speeds, this splitter unit can create a total of eight speeds, one of them being in direct drive. At the output shaft of this assembly, there is a range changer unit made as a two speed double stage gearbox with direct drive； this unit multiplies by two the total number of obtainable speeds. The range changer is qualied by the signicant dierence between the two obtainable speeds. The range changer can be made with a countershaft gearbox or an epicy- cloidal gearbox with direct drive； the advantage in the latter case is the possi- bility of an easier automatic actuation, by braking some of the elements of the epicycloidal gear.9.4 Manual gearboxes for industrial vehicles 441 FIGURE 9.14. Transmission ratios obtained with the scheme of transmission shown in Fig. 9.15； speed identication shows the main gearbox speed with the number, the splitter position with the rst letter, the range changer position with the second； L stands for low, H stands for high. It is also possible to place the range changer before the main gearbox and the splitter unit after the main gearbox. A dierent way of dening the functions of range change units is to say that the splitter is a gearbox that compresses the gear sequence, because it reduces the gap between speeds, while the range changer is a gearbox that expands the gear sequence, because it increases the total range of the transmission. Figure 9.14 explains the concept of compression； the bars represent the ratios obtained in all shifting lever positions. Ratios obtained with the splitter unit in the L position (the rst letter in the speed identication, L stands for lower ratio) are interspersed with the ratios obtained with the splitter unit in the H position (H stands for higher ratio, in this case 1:1) and reduce the amplitude of the gear steps of the main gearbox. The same gure also explains the concept of expansion, showing on the same graph the ratio obtained with the range changer in the H position (second identication letter) and the L position； the gear step between the rst in low gear and the rst in high gear is as big as the range of the main gearbox, and the total transmission range is widened. The range changer is therefore seldom used, when driving conditions change suddenly, as, for example, when leaving a normal road for a country road that must be driven more slowly, or when encountering a strong slope with a fully loaded vehicle. The splitter allows the dynamic performance of the vehicle to be improved, making the optimum transmission ratio available to obtain the desired power. The splitter is therefore used frequently. In a fully loaded vehicle, for example, all split ratios can be used in sequence during full throttle acceleration from a standstill.442 9. MANUAL GEARBOXES The range changer and splitter are usually made as modular units that can be mounted at both ends of the main gearbox, or changed with simple covers, in order to satisfy all application needs with limited total production costs. Generalizing these concepts could suggest building transmissions using ad- ditional range changing units arranged in series. These could be conceived as being made only of splitter units with direct drive. In such a case, with n pairs of tooth wheels it is possible to obtain a total of z transmission ratios, given by the formula: z =2n1 . (9.1) The formula expresses the number of possible states that can be obtained from n 1 pairs of gears； one unit is subtracted because one pair must be a constant gear to move the countershaft. With four pairs of gears, for example, four speeds can be obtained in a double stage gearbox； while using a cascade of splitters eight dierent speeds could be obtained. The goal of good shift manoeuvrability and the implications for mechanical losses must not be forgotten, while dening the best architecture. Figure 9.15 shows the scheme of the 16 speed transmission with splitter and range changer we already described. In this picture are represented the spans of shafts under torque； the dotted line shows where upper input and output shafts are loaded, while the solid line shows when the lower countershaft is loaded. The two lines are joined where a pair of wheels is gearing. A totally dierent approach is shown by the double countershaft transmis- sion in Fig. 9.16 (Fuller scheme)； the power ow is divided between two coun- tershafts by two constant gears and exits through a single output shaft. This conguration has been conceived with the objective of shortening the gearbox, because it is possible, in this way, to divide the torque on two gear wheels work- ing in parallel. The teeth width can be reduced by about 40% at the same level of rated torque. On the other hand the transmission is much wider； this choice can represent a favorable compromise for certain vehicles such as road saddle tractors. In this scheme, after the main gearbox, there is a three speed splitter； one splitter speed is direct drive, one is over-drive, the last is under-drive； the total number of speeds is therefore 12. It can be noticed that the reverse speed is obtained with the same wheels used for the rst speed and with two small idlers. With this arrangement it is also possible to use the splitter in reverse speed. 9.4.2 Practical examples A practical example of a gearbox for a medium duty truck is shown in Fig. 9.17； in this example a double stage four speed main gearbox is joined to a two speed splitter, oering a total of eight speeds. The splitter unit with its direct drive9.4 Manual gearboxes for industrial vehicles 443 FIGURE 9.15. Power ow scheme in the 16 speeds of a gearbox； lines are dotted when the torque ows through the countershaft. They are solid when the torque ows through the upper shafts (input and output shafts). FIGURE 9.16. Scheme of a Fuller gearbox featuring 12 speeds, created from a main four speed double countershaft gearbox and a splitter gearbox with three speeds； one of these last is direct drive. The two countershafts in the main gearbox and in the splitter allow the gear wheel width and therefore the total length of the gearbox to be reduced.444 9. MANUAL GEARBOXES FIGURE 9.17. Truck gearbox with eight speeds； on the lower side there is the reverse idler (IVECO).9.4 Manual gearboxes for industrial vehicles 445 FIGURE 9.18. Truck gearbox with 16 speeds including splitter and range changer (IVECO).446 9. MANUAL GEARBOXES FIGURE 9.19. Fuller gearbox (IVECO). can obtain the same transmission ratios as the main gearbox, while a reduced speed can obtain transmission ratios that are set between the ratios of the main gearbox. Section A-A on the lower right side shows a detail of the idler of the reverse speed； the reverse speed is doubled by the splitter.9.4 Manual gearboxes for industrial vehicles 447 In the main gearbox the wheels of the rst and reverse speeds are close to the rear bearing； the wheels of the following speeds are set in increasing order from the left to the right. The eighth speed is direct drive. The synchronizers of the rst and second speed show a double ring, while the reverse speed has no synchronization. This gearbox can receive a conventional manual shifting mechanism or a power assisted mechanism that can be fully automatic. A three element gearbox with a total of 16 speeds is shown in Fig. 9.18. A four speed main gearbox (the same as in the previous example) is joined with a two speed splitter and a two speed range changer. The wheels in the main gearbox are ordered in increasing speed from the rear bearing. The 16th gear is a direct drive. The range changer is made with epicycloidal gears； when the rear shifting sleeve is moved to the left, the epicycloidal gear is blocked and acts like a locked joint. When the rear shifting sleeve is moved to the right the annulus wheel is blocked with the casing and the carrier speed will be reduced, with the same direction of the input speed. The reduced speeds stay in a range that is fully separated from the normal speed range； they will be used when a very high torque or a very low speed are needed. The main gearbox shows ball bearings and tapered roller bearings, while the epicycloidal gear train, where the radial thrusts are self-equilibrated, shows only needle bearings and a ball bearing. The main gearbox countershaft rotates also in idle speed； it shows a spline end that can be used to move auxiliary equipments such as a hydraulic pump useful to operate a tilting loading plane. A practical example of the Fuller scheme is shown in Fig. 9.19； in this ex- ample the gearbox has a total of 16 speeds and is made of a four speed main gearbox, a two speed splitter and a two speed range epicycloidal gear changer. Notice the two reverse speed idlers. The splitter shift is synchronized, while the main gearbox features dog clutches. Gear shifts are semi-automatic, manually pre-selected； in this case the gear shift lever does not move the shifting sleeves mechanically, but launches an auto- matic sequence, where electric valves operate pneumatic actuators. The selection and shift motions do not occur when the lever is moved but when the power is cut o because the accelerator pedal is released or the clutch pedal is depressed 手动变速箱 1.手动变速箱分类 变速箱的 分类 通常 根据 参与传输运动齿轮的数目。 在 手动汽车变速箱的情况下， 只考虑前进的速度，不考最终的传动齿轮，即使它被包含在变速箱内。因此有 单级齿轮箱 、双级或副轴齿轮箱 、 多级齿轮箱。 图 1.1显示了 三种 配置的四速变速箱。 对 这些 采用 普遍规则的评论是很有用的，每个齿轮被分割很多段，其螺距与齿轮的直径成正比。 该段 最后 的 水平 行程， 代表牙宽度 。 如果 该 段 被 交叉轴 中断，则该