汽車手動變速箱外文翻譯

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1、　　MANUAL GEARBOXES　　9.1 MANUAL GEARBOX CLASSIFICATION　　Gearboxes are normally classi?ed according to the number of toothed wheel　　couples (stages) i

2、nvolved 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, wit

3、hout consideration of the ?nal gear, even if　　included in the gearbox.　　Therefore there are:　　? Single stage gearboxes　　? Dual stage or

4、countershaft gearboxes　　? Multi stage gearboxes　　Figure 9.1 shows the three con?gurations for a four speed gearbox.　　It is useful to comment on the generally

5、 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 strok

6、es, 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<

7、/p>　　shaft without interruption. Then the wheel rotates with the shaft. Hubs are　　represented according to the same rules, while sleeves are represented with a　　pai

8、r 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 tha

9、t the input and the output shaft are o?set; in　　G. Genta and L. Morello, The Automotive Chassis, Volume 1: Components Design, 425　　Mechanical Engineering Series,<p

10、>　　c Springer Science+Business Media B.V. 2009426 9. MANUAL GEARBOXES　　FIGURE 9.1. Schemes for a four speed gearbox shown in three di?erent con?gurations:　　a: single stage, b

11、: 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 whee

12、l driven vehicles usually adopt a double stage gearbox.　　The multi-stage con?guration is sometime adopted on front wheel driven　　vehicles with transversal engine, because the tra

13、nsversal 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.

14、　　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

15、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 m

16、ulti-stage gearboxes is　　o?set by higher mechanical losses, due to the increased number of engaged gear　　wheels.　　It should be noted that

17、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 t

18、hree 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,

19、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.　　Gea

20、r trains used in reverse speed are classi?ed separately. The inversion of　　speed is achieved by using an additional gear. As a matter of fact, in a train of　　three gears, the out

21、put 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 i

22、dler.　　The main con?gurations are reported in Fig. 9.2.　　In scheme a, an added countershaft shows a sliding idler, which can match　　two close gears that are

23、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 preserv

24、e the actual dimension of the parts.9.1 Manual gearbox classi?cation 427　　FIGURE 9.2. Schemes used for reverse speed; such schemes ?t every type of gearbox　　lay-out.<

25、/b>　　Scheme b shows instead two sliding idlers, rotating together; this arrange-　　ment o?ers additional freedom in obtaining a given transmission ratio. The coun-&

26、lt;p>　　tershaft is o?set 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;

27、 it pairs an added speci?c　　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.

28、;　　Con?guration d shows a dedicated pair of gears, with a ?xed idler and a　　shifting sleeve.　　The following are the advantages and disadvantages of the con?gurations&

29、lt;p>　　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

30、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.&l

31、t;/p>　　? Schemes a, b and c do not increase gearbox length.428 9. MANUAL GEARBOXES　　9.2 MECHANICAL EFFICIENCY　　The mechanical e?ciency of an automotive gear wheel t

32、ransmission is high com-　　pared to other mechanisms performing the same function; indeed, the value of　　this e?ciency should not be neglected when calculating dynamic performance

33、　　and fuel consumption. The continuous e?ort of to limit fuel consumption justi-　　?es the care of transmission designers in reducing mechanical losses.　　Tota

34、l 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 f

35、riction between engaging teeth　　(power dependent) and by the friction of wheels rotating in air and oil　　(power independent).　　? Bearing losses; these are ge

36、nerated 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 a

37、nd oil (power　　independent).　　? Sealing losses; they are generated by friction between seals and rotating　　shafts and are power independent.<p

38、>　　? 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 cont

39、act and,　　therefore, on engine speed and selected transmission ratio.　　Table 9.1 reports the values of mechanical e?ciency to be adopted in calcu-　　lations c

40、onsidering 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 t

41、he e?ciency of a complete powershift epicycloidal auto-　　matic transmission and a steel belt continuously variable transmission. For the　　two last transmissions, the torque conve

42、rter must be considered as locked-up.　　TABLE 9.1. Mechanical e?ciency of di?erent transmission mechanisms.　　Mechanism type E?ciency (%)　　Complete manual gear

43、box　　with splash lubrication 92–97　　Complete automatic transmission　　(ep. gears) 90–95　　Complete automatic gearbox

44、　(steel belt; without press. contr.) 70–80　　Complete automatic gearbox　　(steel belt; with press. contr.) 80–86　　Pair of cyl. gears 99.0–99.5<p

45、>　　Pair of bevel gears 90–939.2 Mechanical e?ciency 429　　FIGURE 9.3. Contributions to total friction loss of a single stage gearbox designed for　　300 Nm as function of input s

46、peed.　　It is more correct to reference power loss measurement as a function of　　rotational input speed rather than e?ciency. Figure 9.3 shows the example of

47、　a double stage transmission, in fourth speed, at maximum power; the di?erent　　contributions to the total are shown.　　This kind of measurement is made by disassembling the gearbo

48、x step by　　step, thus eliminating the related loss.　　In the ?rst step all synchronizer rings are removed, leaving the synchronizer　　hubs only; mechanical los

49、ses 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,

50、 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 remo

51、ved, and therefore, the bulk of　　the lubrication losses is eliminated; some oil must remain in order to leave the　　contact between teeth una?ected.　　By remov

52、ing 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

53、　　a?ect this value.　　A more exhaustive approach consists in measuring the complete e?ciency　　map; the e?ciency can be represented as the third coordinate of

54、a surface, where　　the other two coordinates are input speed and engine torque. E?ciency calcu-　　lations can be made by comparing input and output torque of a working trans-</p

55、>　　mission.　　Such map can show how e?ciency reaches an almost constant value at a　　modest value of the input torque; it must not be forgotten tha

56、t standard fuel　　consumption evaluation cycles involve quite modest values of torque and there-　　fore imply values of transmission e?ciency that are changing with torque.</p&g

57、t;　　Figure 9.4 shows a qualitative cross section of the aforesaid map, cut at　　constant engine speed. It should be noted that e?ciency is also zero at input430 9. MANUAL GEARBOXES

58、;　　FIGURE 9.4. Mechanical e?ciency map, as a function of input torque at constant　　engine speed; the dotted line represents a reasonable approximation of this curve, to be<p

59、>　　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　　cert

60、ain minimum value of input torque, below which motion is impossible.　　A good approximation to represent mechanical e?ciency can be made using　　the dotted broken line as an interp

61、olation of the real curve.　　9.3 MANUAL AUTOMOBILE GEARBOXES　　9.3.1 Adopted schemes　　In manual gearboxes, changing speed and engaging and disengaging the clut

62、ch　　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

63、 the synchronizer for reverse speed,　　particularly those in economy minicars.　　We previously discussed a ?rst classi?cation; additional information is the　　s

64、peed 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

65、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</p

66、>　　therefore also called transmission.　　Countershaft double stage gearboxes are used in conventionally driven cars,　　where the engine is mounted longitudinally in t

67、he 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

68、 gearbox.9.3 Manual automobile gearboxes 431　　By multi-stage transmissions, some gear wheels could be used for di?erent　　speeds. The number of gearing wheels could increase at so

69、me speeds; this nor-　　mally occurs at low speeds, because the less frequent use of these speeds reduces　　the penalty of lower mechanical e?ciency on fuel consumption.

70、　　Cost and weight increases are justi?ed by transmission length reduction,　　sometimes necessary on transversal engines with large displacement and more　　than four cylind

71、ers.　　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<

72、p>　　to shift the two gears with the same selector rod.　　We de?ne as the selection plane of a shift stick (almost parallel to the xz　　coordinate body reference system plane for

73、 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 s

74、chemes, ?rst, second,　　third, fourth and ?fth speed are organized on three di?erent selection planes; the　　reverse speed can have a dedicated plane or share its plane with the ?f

75、th 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 de?ection.&l

76、t;p>　　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

77、 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, sui

78、table 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.<p&g

79、t;　　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 s

80、peeds; 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-

81、　　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.

82、The double stage gearbox in Fig. 9.7 is organized in a completely di?erent　　way but also shows the ?rst speed pair of wheels close to the bearing. The direct　　drive is dedicated

83、to the highest speed; the ?fth speed shows a dedicated selection　　plane.　　Six speed double stage gearboxes do not show conceptual changes in com-&l

84、t;p>　　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 alrea

85、dy seen, the multistage con?guration shown in Fig. 9.7 allows a　　reasonable reduction of the length of the gearbox. In this scheme, only ?rst and　　second speeds bene?t from the s

86、econd 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

87、single stage arrangement.　　Reverse speed is obtained with a conventional idling wheel.　　9.3.2 Practical examples　　Four speed gearboxes represented the most w

88、idely 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 ?

89、ve speed gearbox, suitable for front wheel driven　　car with transversal engine.　　With the increase in installed power, the improvement in aerodynamic per-　　f

90、ormance 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;

91、 as a matter of fact car weight continued to increase and engine　　minimum speed did not change signi?cantly.　　To achieve satisfactory performance all manufacturers developed ?ve

92、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

93、 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.</b&g

94、t;　　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

95、　　other hand, having the most frequently used pairs of wheels close to the bearing　　reduces the noise due to shaft de?ection.　　Synchronizers of fourth and third speed are mounted

96、 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. Synchr

97、onizers　　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).

98、　　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 countersh

99、aft o?er 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

100、 introduces the example of a single stage gearbox for a front　　longitudinal engine. The input upper shaft must jump over the di?erential, which　　is set between the engine and the

101、 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 secti

102、ons of the box additional　　bearings are provided to reduce the shaft de?ection.　　The input shaft features a ball bearing close to the engine and three other

103、　needle bearings that manage solely the radial loads. The output shaft has two　　tapered roller bearings on the di?erential side and a roller bearing on the opposite　　side. This c

104、hoice is justi?ed by the relevant axial thrust emerging from the bevel　　gears.　　The ?rst and second speed synchronizers are on the output shaft and feature<

105、/p>　　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 synchr

106、onizers 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 n

107、oted 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

108、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 th

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