SE1100492A1 - Vehicle transmission - Google Patents

Abstract

Vehicle transmission (20, 60, 70) comprising a pair of meshing gearwheels (61,68; 71,78) that rotate about parallel axes;. of said gearwheels one gearwheel (21, 61, 71) is rotatably arranged on a shaft (22, 62, 72);said rotatably arranged gearwheel is axially supported (22s, 62s, 72g) relative said shaft in one direction, only, and the flanks of the gear teeth of said pair of gearwheels have opposite hands of helix.Figure 1 for publication

Description

15 20 25 30 35 _ 2 _ arranging a pair of opposed tapered roller bearings between the gearwheel and the shaft. An example can be seen as gearwheel 8 in DE19901067A1. Another way is to use two cylindrical roller bearings and a shoulder in- between that is integrated with the gearwheel, as in figure 2 in WOO3/010445Al. These designs can be regarded as expensive, but are used for rotatably arranged gearwheels that transfer power while having a relative rotation to the shaft. In vehicle transmissions, however, most rotatably arranged gearwheels are rotationally locked to the shaft when transferring power. Then, e.g., shoulders on the shaft, can be sufficient as axial guiding of the gearwheel. Examples thereof are gearwheels 7, 9, 10, ll and 12 in DE1990lO67A1 as well as figure l in W003/0lO445Al. simple abutments, One axial abutment can in some cases be embodied as a shoulder on the shaft, in DE1990l067Al. embodied by another part. Often, as between gearwheels 9 and 10 The opposite abutment must normally be that part has another use, (gearwheels 7 and 12 in DEl990l067A1 and figure 1 in W003/010445A1), a hub for a mechanical tooth clutch (gearwheels 9, 10, 11 and 12 in DE19901067A1) gearwheel that is fixed to the shaft. for instance an inner ring of a bearing Ora Sometimes it would be undesirable to have two axial abutments for a rotatably arranged gearwheel. Possible Then, guiding of the gearwheel must be accomplished in reasons for this can be space or cost. axial another way. One possibility would be to use herringbone or double helical gearing. Another way would be to use thrust washers at the side of the gear teeth, as in W02005/045281A1. both of those designs are expensive, require axial space, Unfortunately, and may make the assembly more difficult. No simple, less expensive systems for axially guiding a rotatably 10 15 20 25 30 35 _3_ arranged gearwheel with less than two axial abutments are known, Thus, there is a need for a simple and cost-effective design in a stepped non-planetary vehicle transmission to axially guide a rotatably arranged gearwheel using only one axial abutment.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a longitudinal section of a prior art rotatably arranged gearwheel that is axially guided by abutments on both sides.

Figure 2 shows a similar longitudinal section of a rotatably arranged gearwheel that is axially guided by an abutment on one side, only.

Figures 3a, 3b and 3c show gear mesh forces in views radially inwards of gearwheels.

Figures 4a, 4b and 4c show longitudinal and cylindrical sections of gear teeth according to the invention assuming a two-step way of machining.

Figures 5a and 5b show longitudinal and cylindrical sections of gear teeth according to the invention assuming a preferred one-step way of machining.

Figures 6a and 6b show a meshing gearwheel pair according to the invention.

Figure 7 shows a longitudinal section of a central synchronizing unit with a rotatably arranged gearwheel that is axially guided by an abutment on one side, only, according to the invention.

DESCRIPTION OF THE INVENTION In figure 1 a gearwheel 11, being part of a partly shown stepped transmission 10, is rotatably arranged on a shaft 12. The gearwheel 11 is radially carried by the shaft 12 with a needle bearing 13. A shoulder 12s on the shaft provides an axial abutment on one side for On the other side, axial abutment is provided by the hub 14 of a tooth clutch 15. This tooth clutch 15 further comprises an engaging sleeve 16 and gearwheel 11. 10 15 20 25 30 35 _4_ external clutch teeth 11 e on the gearwheel 11. A retaining ring 17 prevents axial motion of the hub 14.

Internal clutch teeth 16i on the engaging sleeve 16 engage with external clutch teeth 14e on the hub 14.

Thus, the engaging sleeve 16 is rotationally fixed but axially slidably arranged on the hub 14 and can be _- brought in and out of engagement with the external clutch teeth 11 e on the gearwheel 11. The hub 14 is rotationally fixed to the shaft 12 by internal spline teeth l4i that engage with external spline teeth 12e. the gearwheel 11 can be rotationally locked to the shaft 12. ' Hence, by axial motion of the engaging sleeve 16, Figure 2 shows an alternative design for the same function as in figure 1. Corresponding parts are referred by the same numbers except for the first digit (2 instead of 1). teeth 26i that are in engagement with external teeth 22e on the shaft. required. The gearwheel 21 has internal clutch teeth The engaging sleeve 26 has internal Thereby, no intermediate hub is 21i that can be brought in and out of engagement with external clutch teeth 26e on the engaging sleeve 26. A retaining ring 27 guides the needle bearing 23 axially and can also serve as an axial stop for the engaging sleeve 26.

In the design in figure 2, the rotatably arranged gearwheel 21 is guided in axial direction by the shoulder 22s, made sure that the gearwheel will be pushed towards only. For proper function, it must be this shoulder. The most dominant forces on a rotatably arranged gearwheel are those that act on the gear and clutch teeth. The forces in clutch teeth, in general, have very low axial components. Gear mesh forces, however, may have very large axial components. Figures 3a, 3b and 3c show schematically a cylindrical section vehicle transmissions are along in figure 2. Mostly, used for both engine driving and engine braking, giving lO 15 20 25 30 35 _5_ opposite directions of power flow. In the figures, this is distinguished by reference "d" for engine driving and "b" for engine braking for the gear mesh forces shown.

In figure 3a, helical gear teeth with helix angle ß are shown. There, large axial components Fad and Fab, having opposite directions, will result. That cannot be combined with a one-sided axial guiding of the gearwheel. Thus, the design in figure 2 is not compatible with helical gear teeth. Furthermore, spur gear teeth are shown in figure 3b. With such teeth, there is no nominal axial mesh force component.

However, due to misalignment and deformation of components, there will, in practice, be a small axial force component, whose direction may vary or be difficult to predict. So, suited to spur gear teeth, the design in figure 2 is not either.

Figure 3c shows gear teeth where the axial gear mesh force component has the same direction independent of the direction of the power flow. In principle, the two flanks of each gear teeth have opposite hands of helix.

This can be referred to as opposed helical gearing. In practice, it has shown to be sufficient with helix angles ßb, ßd less than five degrees for safely pushing a rotatably arranged gearwheel towards an axial. abutment. Thereby, opposed helical gear teeth according to figure 3c can be used in the design of figure 2.

Figures 4a, 4b and 4c show how opposed helical gear teeth can be made using production methods and equipment for conventional helical gearing. In the first step, figure 4b, ordinary helical gear teeth with helix angle ßd are formed. That will give one of the flanks of the opposed helical gear teeth. A subsequent second step will form the other flank, in this example with helix angle ßb. The result will be opposed helical gear teeth. 10 15 20 25 30 35 _6_ Two operational steps are required in the method of producing the opposed helical gear teeth in figures 4a, 4b and 4c. must be taken at the second step in order to achieve That increases the cost, and special care correct tooth thicknesses. An alternative preferred way of producing the opposed helical gear teeth is shown in figures 5a and 5b. There, the feeding motion of the tooth-forming tool is not parallel to the centre axis of the gearwheel 51. Instead, the tool is moved along a feeding path 5lf that is at an angle 6 to the centre Then, same angle to the centre axis and not have a constant axis. the root 5lr of the gearing will have the diameter. The result will be opposed helical gear teeth that are formed in one operational step.

The method of producing opposed helical gearing in figures 5a and 5b is identical or at least very similar to the one used for so called beveloid gear teeth. An application thereof is shown in DElO200603l267Al.

Beveloid gearing can be regarded as being in-between and bevel cylindrical gearing, having parallel shafts, gearing, for shafts with intersecting axes. Beveloid gearing is used for relatively small angles of intersection, and can in general be produced using equipment for cylindrical gearing.

Figures 6a and 6b show a part of a transmission 60 comprising a shaft 62 on which a gearwheel 61 is rotatably arranged and in mesh with an integrated shaft and gearwheel 68. Both gearwheels have opposed helical gearing. Thereby, independent of the direction of power transfer, pushed towards the shoulder 62s of the shaft 62. no other axial abutment is required. the rotatably arranged gearwheel 61 will be Hence, Figure 7 shows a further preferred application and embodiment of the invention. It concerns central synchronizing units that can be used in dual clutch e.g., in US5l50628 transmissions, (referred to as 30). 10 15 20 25 30 35 _ 7 _ In a central synchronizing unit, a friction clutch equalizes the speeds of a shaft and a rotatably arranged gearwheel. This will facilitate the engagement of a tooth clutch somewhere in the transmission. The gearwheel may not be used for transfer of driving there will be constraints on the power. In such a case, axial space required by the gearwheel.

Schematically in figure 7, a partially shown dual clutch transmission 70 comprises a central synchronizer gearwheel 71 that is rotatably arranged on a shaft 72.

A bearing 73 guides the gearwheel 71 in radial direction. A power-transferring gearwheel 72g is fixed to the shaft gearwheel 71. 72 and provides an axial abutment to the A second shaft 78 and a coaxial third shaft 79 are arranged parallel to shaft 72; On the second shaft 78, in mesh with the central synchronizer gearwheel 71. a second synchronizer gearwheel 78g is Similarly, a power-transferring mating gearwheel 79g on the third shaft 79 is in mesh with the power- transferring gearwheel 72g, Further, a synchronizer cone 76 is arranged axially moveable but rotationally fixed on the shaft 72. the synchronizer cone 76 can be brought in contact with An external cone surface 76c on a mating internal cone surface 71 c on the central synchronizer gearwheel 71. Then, a friction torque will arise that will reduce a relative rotational speed between the shaft 72 and the central synchronizer gearwheel 71. When that has been accomplished, the third shaft 79 will rotate faster than the second shaft 78, determined by the radial sizes of the gearwheels 78g, 71, rotational speeds in not shown mechanical tooth clutches. Then, facilitated. 72g and 79g. This will reduce the relative the engagement thereof can be The central synchronizer gearwheel 71 and second synchronizer gearwheel 78g have opposed helical gear teeth. Then, it is sufficient to have the central lO l5 20 25 _8_ synchronizer gearwheel 7l axially guided by the power- transferring gearwheel 72g. Thus, no axial space is required for an axial stop on the right side in figure 7 of the central synchronizer gearwheel 71. So, the transmission 70 can be made shorter, or with wider power-transferring gearwheels.

Opposed helical gear teeth are suited to production e.g., ßd provide draft that facilitates ejection from the dies. methods that involve plastic deformation, forging. The helix angles ßb, The invention is particularly suited to transmissions with twin countershafts as in US5385066. For the rotatably arranged gearwheel, that would simplify the arrangement of axial guiding, which can be quite complex, as shown in DEl9633282Al.

The invention has been described with a certain degree of particularity. However, several Variations are possible within the scope of the invention, as is obvious to a person skilled in the art. For instance, an axial stop can be provided by some types of ball and e.g., contact ball bearings. Moreover, roller bearings, tapered roller or angular the rotatably arranged it does not gearwheel can be an idler gearwheel, i.e., need to be connectable to the shaft.

Claims (7)

10 15 20 25 30 35 234s5sE, 2011-06-21 AH PATENT CLAIMS

1. Vehicle transmission (20, 60, 70) <61,68; 71,78) comprising a pair of meshing gearwheels that rotate about parallel axes; of said gearwheels one gearwheel (21, 61, 71) is (22, 62, 72); characterized in that said rotatably arranged gearwheel (22s, 62s, 72g) relative said shaft in one direction, and the flanks of the gear teeth of said pair of gearwheels have opposite rotatably arranged on a shaft is axially supported only, hands of helix.

2. Vehicle transmission as in the preceding claim, characterized in that said rotatably arranged gearwheel can be locked to said shaft by a tooth clutch (25).

3. Vehicle transmission as in the preceding claim, characterized in that said gear teeth produced by a tool feeding path (51 f) (51 a).

4. Vehicle transmission as in the preceding claim, at an angle to the gearwheel axis characterized in that said gear teeth are produced, at least partly, by forging.

5. Vehicle transmission as in the preceding claim, characterized in that said gear teeth have helix angles (at pitch circle diameters) between one and five degrees.

6. Vehicle transmission as in the preceding claim, characterized in that said pair of gearwheels is a part (71,76,78g).

7. Vehicle transmission as in the preceding claim, of a central synchronizing unit characterized in that said vehicle transmission has twin countershafts, and said rotatably arranged gearwheel is arranged on a shaft between these countershafts.