GB2465978A

GB2465978A - Gearbox with synchronizers on input shaft to reduce inertia

Info

Publication number: GB2465978A
Application number: GB0822033A
Authority: GB
Inventors: Joerg Boenning; Jan Sporleder
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2008-12-03
Filing date: 2008-12-03
Publication date: 2010-06-09
Also published as: GB201107496D0; GB2478869A; WO2010063336A1; GB0822033D0

Abstract

A gearbox for a motor vehicle comprises an input shaft 3 and an output shaft 11 and at least first and second gear trains for selectively transmitting torque from the input shaft 3 to the output shaft 11. The gear trains comprise a first idle gearwheel 5 on the input shaft 3 and a second idle gearwheel 6 on the input shaft 3. The output shaft 11 and a countershaft 14 also have idle gearwheels 16, 17, 8 and 20 which together with fixed gears 4, 15, 19, 9 and 10 form of part of a third gear train and a fourth gear train. All of the idle gearwheels 4, 5, 6, 9, 10, 15 and 19 are fixed to their respective shafts 3, 11, 14 with synchronizers 7, 12, 18 so that the gearbox provides gear ratios form first to sixth. In another embodiment additional gearwheels (9' and 10', fig 3) which are integral with the gearwheels 9 and 10 are provided. This measure reduces gearwheel width and load.

Description

Gearbox for a motor vehicle

Description

The present invention relates to a gearbox for a motor vehicle comprising an input shaft and an output shaft and at least first and second gear trains for selectively transmitting torque from the input shaft to the output shaft at respective first and second transmission ratios.

Conventionally, gearboxes of this type have used idle gearwheels on the output shaft meshing with fixed gearwheels on the input shaft, so that the gearwheels follow each change of the speed of rotation of the input shaft. For overcoming the inertia of the gearwheels, energy must be invested. This expense of energy is noticeable whenever the gearbox is switched: in order to achieve synchronization between input and output shafts, the speed of rotation of the input shaft and the gearwheels has to be changed by a factor equal to the quotient of the transmission ratios of the involved gears. Moreover, synchronization not only costs fuel, but a high inertia of the gearwheels imposes a high load on synchronizers of the gearbox, causing wear and slowing down the shifting process.

The object of the invention is therefore to provide a gearbox for a motor vehicle which supports fast and energy-efficient shifting.

This object is achieved by a gearbox for a motor vehicle comprising an input shaft and an output shaft and at least first and second gear trains for selectively transmitting torque from the input shaft to the output shaft at respective first and second transmission ratios, in which the first gear train comprises a first idle gearwheel on the input shaft, the second gear train comprises a second idle gearwheel on the input shaft, and the input shaft carries locking means for selectively locking one of said first and second idle gearwheels to the input shaft. In this design, since the idle gearwheels are in meshing engagement with the output side of the gearbox, essentially only the input shaft has to be synchronized when the gearbox is shifted from said first to the second transmission ratio or vice versa. The speed of rotation of the gearwheels is unaffected. Therefore the inertia of the input side of the gearbox is extremely small, and the input shaft can be synchronized with little expense of energy and in an extremely short time.

In order to accommodate a high number of gears in a compact gearbox, it is preferred that a third gear train comprises a third idle gearwheel on a driven counter shaft, the third idle gearwheel engaging a gearwheel of said first gear train mounted on said output shaft. In this way, said gearwheel on the output shaft is used in two different gears, allowing to reduce the total number of gearwheels in the gearbox and, hence, its total moment of inertia.

Similarly, it is preferred that a fourth gear train comprises a fourth idle gearwheel on the countershaft, the fourth idle gearwheel engaging a gearwheel of said second gear train mounted on said output shaft.

Again, in order to minimize the number of moving parts and the inertia, the third and fourth gear trains preferably share coupled gearwheels on the input shaft and the output shaft by which the output shaft is driven.

In order to minimize the contribution of the shared gearwheel to the moment of inertia of the input side of the gearbox, it is preferred that the shared gearwheel should be smaller than the first and second idle gearwheels.

For similar reasons, said shared gearwheel on the countershaft preferably is smaller than the third and fourth idle gearwheels.

The required coupling between the shared gearwheels can be by means of a fifth idle gearwheel mounted on the output shaft.

The output shaft preferably carries locking means for selectively locking said fifth idle gearwheel to the output shaft. In this way, the fifth idle gearwheel can contribute to three different gears.

A fifth gear train may be provided which comprises a sixth idle gearwheel mounted on the output shaft.

Weight and space may be saved if the locking means of the output shaft is for selectively locking one of said fifth and sixth idle gearwheels to the output shaft.

Since, as explained above, the shared gearwheel on the input shaft preferably is among the smallest gearwheels of the gearbox, it is a geometrical necessity that the fifth idle gearwheel be among its largest. In order to reduce its moment of inertia, it is preferred that the fifth gearwheel should have a cavity. If the cavity is a hollow side of the fifth idle gearwheel facing the locking means, space may be saved if the locking means is allowed to engage the hollow side when it locks the fifth idle gearwheel to the output shaft.

Similarly, the sixth idle gearwheel may have a hollow side facing the locking means.

Further features and advantages of the invention will become apparent from the subsequent description of embodiments thereof referring to the appended drawings.

Fig. 1 is a schematic diagram of a gearbox according to a first embodiment of the invention; Fig. 2 is a diagram of a gearbox according to a second embodiment; and Fig. 3 is a diagram of a gearbox according to a third embodiment of the invention.

In Fig. 1 reference numeral 1 denotes an internal combustion engine connected to an input shaft 3 of the gearbox by a friction clutch 2. The input shaft 3 carries a small, fixed gearwheel 4, two idle gearwheels 5, 6 and a synchronizer 7 for locking either gearwheel 5 or gearwheel 6 or none of both to input shaft 3.

Gearwheels 4, 5, 6 mesh with an idle gearwheel 8, a fixed gearwheel 9 and a fixed gearwheel 10 respectively, on an output shaft 11. A synchronizer 12 is provided for selectively locking idle gearwheel 8 to the output shaft 11. An output pinion 13 of output shaft 11 meshes with a differential drive, not shown.

A countershaft 14 carries a fixed gearwheel 15 and idle gearwheels 16, 17 which mesh with gearwheels 8, 9, 10, respectively, of output shaft 11.

The hatching pattern of each component of the gearbox indicates how it is connected: Components having a dense hatching patterns with lines rising from left to right are permanently coupled to the input shaft 3 and follow each change of its rotation speed; components having a loose hatching pattern with descending lines are connected to the output shaft 11.

Among all gearwheels of the Fig. 1 gearbox, gearwheel 4 is the smallest, and gearwheel 8 is the biggest. Therefore a first gear is formed when synchronizer 12 locks gearwheel 8 to the output shaft 11, and the other synchronizers 7, 18 are idle.

Depending on the ratio of sizes of gearwheels 4 and 15, the second gear may involve the use of countershaft 14 or not. In the embodiment shown in Fig. 1, gearwheel 15 is bigger than gearwheel 4, and gearwheels 5, 18 are still bigger than their respective neighbouring gearwheels 4, 15. Therefore, a second gear is formed by locking gearwheel 5 to input shaft 3, and a third is formed by locking gearwheel 16 to counter shaft 14. I.e. in the third gear torque is transmitted from input shaft 3 via gearwheels 4, 8, 15 to countershaft 14 and from there to output shaft 11 via gearwheels 16, 9.

Similarly, a fourth gear is formed by locking gearwheel 6 to input shaft 3 using synchronizer 7 and a fifth gear is formed by locking gearwheel 17 to countershaft 14 using synchronizer 18.

Of course, in an alternative embodiment, it might be contemplated to set the distances between input and output shafts 3, 13 and between the output shaft 11 and counter shaft 14 so that second and third gears are obtained using gearwheels 5 and 6, respectively, and fourth and fifth gears are formed using gearwheels 16 and 17, respectively.

The embodiment of Fig. 2 is distinguished from that of Fig. 1 by a further gear train comprising meshing gearwheels 19, 20 on input shaft 3 and output shaft 11, respectively. Gearwheel 19 on input shaft 3 is fixed, whereas gearwheel 20 on output shaft 11 is idle and can be locked to the output shaft 11 by synchronizer 12. In principle, the gear ratio of this gear train can be chosen arbitrarily. In the embodiment of Fig. 2, gearwheel 19 is still smaller than gearwheel 4, so that gearwheels 19, 20 form a first gear, whereas the other gearwheels form second to sixth gears.

The idle gearwheels 8, 20 on output shaft 11 have cavities 21, 22 facing synchronizer 12, and a gearing, not shown, for locking engagement with a displaceable sleeve of synchronizer 12 is provided in each cavity 21, 22. The existence of the cavities 21, 22 not only reduces the moment of inertia of the input-side members of the transmission, i.e. of those shafts and gearwheels which are permanently connected to input shaft 3 and follow any changes of its rotation speed which may be necessary to achieve synchronization, but they also reduce the dimension of the gearbox in the axial direction which is needed for accommodating gearwheels 4, 8, 16, 19, 20 and synchronizer 12.

If the distance between shafts 3 and 11 is the same as between shafts 11 and 14, gearwheels 16, 17 must be axially offset with respect to gearwheel pairs 5, 9 and 6, 10, respectively, and additional gearwheels 9', 10' must be provided to mesh with gearwheels 16 and 17, as shown in Fig. 3. In that case, a further fixed gearwheel 23 meshing with gearwheel 20 may be provided on counter shaft 14, and torque is transmitted to countershaft 14 by two parallel paths, namely via gearwheels 4, 8, 15, on the one hand, and gearwheels 19, 20, 23, on the other. Due to this measure, the load on gearwheels 4, 8, 5 and 19, 20 is less than in the embodiment of Fig. 2, and the width of these gearwheels can be reduced.

List of reference signs 1. internal combustion engine 2. clutch 3. input shaft 4. fixed gearwheel 5. idle gearwheel 6. idle gearwheel 7. synchronizer 8. idle gearwheel 9. fixed gearwheel 10. fixed gearwheel 11. output shaft 12. synchronizer 13. output pinion 14. countershaft 15. fixed gearwheel 16. idle gearwheel 17. idle gearwheel 18. synchronizer 19. gearwheel 20. gearwheel 21. cavity 22. cavity 23. gearwheel