GEARWHEEL INTENDED TO BE PRESS-FITTED ONTO A SHAFT AND A SHAFT CARRYING A PRESS-FITTED GEARWHEEL

Abstract: Gearwheel, intended to be connected through press fitting to a shaft, the gearwheel exhibiting a hub and a cog path connected to the hub, the hub exhibiting at least one flank extending axially outside the cog path and a through-hole with a first area situated axially outside the cog path and a second area situated radially inside the cog path, and a shaft supporting a press fitted gearwheel that exhibits a hub and a cog path connected to the hub, the hub exhibiting at least one flank extending axially outside the cog path whereby the hub exhibits a through-hole with a first area situated axially outside the cog path and a second area situated radially inside the cog path.

Description: Gearwheel intended to be press-fitted onto a shaft and a shaft carrying a press-fitted gearwheel Technical field The invention relates to a gearwheel, intended for connection to a shaft through press fitting according to the preamble of claim 1, and a shaft supporting a press fitted gearwheel according to the preamble of claim 7. In particular the invention relates to a gearwheel and a shaft supporting a gearwheel in which the press fitting is designed so that the average contact pressure in the press joint in a first area, situated radially within a cog path positioned on the gearwheel, is below the average contact pressure in an area situated outside said first area. Background of the Invention It is previously known, during manufacture of vehicle gearboxes, to utilize gearwheels, which are connected to a shaft through press fitting. In this case, press fitting implies that a gearwheel, equipped with a central through hole having a diameter below that of the shaft to which the gearwheel is to be joined. In one assembly method the gearwheel is forced into place, whereupon it is retained by the forces that arise due to the elastic deformation of the shaft and the gearwheel. For example, the functional description of the Saab-Scania gearbox GRS900, Saab- Scania Division service (110) 1991, discloses a gearwheel equipped with a flange, which gearwheel is joined to a shaft in the gearbox through press fitting. Press fitted gearwheels are used mainly when machining, construction, or economy does not allow the use of shafts with integrated gearwheels. Technical problem When a gearwheel is pressed onto a shaft in order to achieve a press joint, very large tensions arise in the gearwheel as well as in the shaft. These tensions are a necessity to create a strong joint. In vehicle gearboxes, in particular in gearboxes for heavy vehicles, very large torqueses are transferred through the gearwheels included in the gearbox. In turn, this transferred torque gives rise to tensions, which are superimposed on the tensional field from the press fitting. The increased level of tension entails a risk for crack formation, in particular at the cog root, which leads to the possibility of a break due to fatigue. Summary of the invention The object of the invention is to provide a gearwheel, intended to be connected through press fitting to a shaft, and a shaft supporting a press fitted gearwheel where the risk of crack formation at the cog root, and thus fatigue breakdown, is reduced. This object is achieved by designing the gearwheel in accordance with the characterising part of claim 1, and the shaft in accordance with the characterising part of claim 2. By designing the gearwheel with at least one hub that exhibits a flank extending axially outside the cog path, and a through hole with a first area situated axially outside the cog path and a second area situated radially inside the cog path, and by arranging the gearwheel and the shaft in such a way that, during press fitting of the gearwheel on the intended shaft, the average contact pressure within the first area exceeds substantially the mean contact pressure within the second area, the tension in the area situated radially inside the cog path is reduced. This entails that the tensional field that arises through the press fitting is reduced within the area surrounding the cog path, with the consequence that the risk of fatigue failure in the cog roots is diminished. During operation, the main part of the torque is transferred from the gearwheel to the shaft through the joint within the first area, which means that the cog path is relieved from the load caused by the press fitting. In a preferred embodiment, a relief zone is arranged between the first and second areas. In a preferred embodiment this relief zone has the form of a concentric groove in the mantle surface of a cylindrical through-hole in the hub. Brief description of the drawings The invention will be described in detail below, in connection with the enclosed drawings, in which: Fig. 1 shows a cross section of a side view of a gearwheel equipped with a flank, and a view from one end of the gearwheel, Fig. 2 shows a cross section of one symmetry half of the gearwheel according to a first embodiment of the invention, Fig. 3 shows an enlargement of the indicated area in Fig. 2, Fig. 4 shows a cross section of a symmetry half of the gearwheel according to a second embodiment of the invention, Fig. 5 shows an enlargement of the indicated area in Fig. 4, Fig. 6 shows a cross section of a symmetry half of a shaft, upon which the gearwheel is intended to be press fitted, and Fig. 7 shows an enlargement of the indicated area in Fig. 6. Preferred embodiment In Fig. 1, a gearwheel is shown which is generally designated as 1. The gearwheel supports a cog path 2, which is directed radially outwards. The cog path is connected to a hub 3. The hub 3 exhibits a flank 4, which extends axially outside the cog path. The gearwheel. The gearwheel is intended to be pressed onto a shaft (not shown), which exhibits a diameter slightly exceeding the diameter of the through-hole 5, whereby a so- called press joint between the gearwheel and the shaft is accomplished. The through- hole 5 exhibits a mantle surface with a second area 6, situated radially inside said cog path, and a first area 7, situated outside said second area. Fig. 2 shows a cross section of a symmetry half of the gearwheel according to a first embodiment of the invention. In this embodiment the first and the second areas 6, 7 are separated by a relief zone 8. The relief zone is constituted by a groove in the mantle surface. The function of the relief zone is to ensure that the tension that arises upon press fitting within the first area spreads to a lesser degree to the cog path via the second area. According to the enlarged view shown in Fig. 3, it is clear that the through-hole exhibits a larger diameter d2 within the second area 6 than the corresponding diameter dl within the first area 7. In this case, the gearwheel is intended to be mounted onto a shaft with a cross section of constant diameter. In Figs. 4 and 5 a second embodiment of the invention is shown in which the diameters dl and d2 of the through-hole at the first and second areas 6, 7 are of the same size. This gearwheel is intended to be mounted onto a shaft as shown in Figs. 6 and 7 which exhibits a mantle surface 9 with a first area 10 of a diameter d3, exceeding the diameter d4 of a second area 11 of the mantle surface. When mounting the gearwheel onto this shaft in such a way that the second area 6 of the gearwheel, i.e. the area lying radially inside the cog path, is positioned radially outside the second area 11 of the shaft, and the first area 7 of the gearwheel, i.e. the one lying axially outside the cog path, is placed radially outside the first area 10 of the shaft, the tension within the first area 7, 10 will exceed the tension within the second area 6, 11. The invention is not limited to the embodiment described above and shown in the drawings, but can be varied within the scope of the appended claims. For example, the first area 7, 10, i.e. the one situated axially inside the cog path, may be made from a material that exhibits greater resistance towards deformation than the material from which the second area 6, 11, situated radially inside the cog path, is made. In a further embodiment, the gearwheel can be manufactured with greater material thickness within the first area 7, i.e. the one situated axially inside the cog path, than within the second area 6. The radius within the first area 7 thereby becomes greater than the radius within the second area 6. In this manner, a greater contact pressure will arise within the first area during press fitting onto a shaft with constant cross section. Combinations of the four mentioned methods to achieve the advantages of the invention may also be contemplated.

Claims: Claims 1) A gearwheel, intended to be connected through press fitting to a shaft, said gearwheel exhibiting a hub (3) and a cog path (2) connected to the hub, said hub exhibiting at least one flank (4) extending axially outside the cog path (2) and a through-hole (5) with a first area (7) situated axially outside the cog path and a second area (6) situated radially inside the cog path (2), characterised in that during press fitting of the gearwheel onto a shaft intended therefor, the mean contact pressure within the first area (7) substantially exceeds the mean contact pressure within the second area (6). 2) A gearwheel according to claim 1, characterised in that the gearwheel exhibits a cylindrical recess (5) with a diameter smaller than the diameter of the shaft and that the difference in diameter within the first area (7) is smaller than the difference in diameter within the second area (6). 3) A gearwheel according to claim 3, characterised in that the cylindrical recess exhibits a smaller diameter within the first area (7) than within the second area (6). 4) A gearwheel according to any of the preceding claims, characterised in that a relief zone is situated between the first area (6) and the second area (7). 5) A gearwheel according to claim 4, characterised in that said relief zone is constituted by a groove in the mantle surface of the cylindrical recess. 6) A gearwheel according to any of the preceding claims, characterised in that the material in the flank (4) is designed with a radius greater than that of the cog path (2). 7) A shaft supporting a press fitted gearwheel that exhibits a hub (3) and a cog path (2) connected to the hub, the hub exhibiting at least one flank (4) that extends axially outside the cog path (2) whereby the hub (3) exhibits a through-hole with a first area (7) situated axially outside the cog path (2) and a second area (6) situated radially inside the cog path (2), characterised in that during press fitting of the gearwheel onto said shaft, the mean contact pressure within the first area (7) substantially exceeds the mean contact pressure within the second area (6). 8) Shaft according to claim 7, characterised in that the gearwheel exhibits a cylindrical recess (5) with a diameter smaller than the diameter of the shaft and that the difference in diameter within the first area (7) exceeds the difference in diameter within the first area (6). 9) A shaft according to claim 8, characterised in that the cylindrical recess (5) exhibits a smaller diameter within the first area (7) than within the second area (6). 10) A shaft according to any one of the claims 7 - 9, characterised in that a relief zone is situated between the first area (7) and the second area (6). 11) Shaft according to claim 10, characterised in that said relief zone is constituted by a groove in the mantle surface of the cylindrical recess. 12) A shaft according to any of the claims 7 - 11, characterised in that the material of the flank (4) is designed with a greater radius than that of the cog path (2).

Inventors: HEDMAN ANDERS, HEDMAN, ANDERS
Applicants: HEDMAN ANDERS, VOLVO LASTVAGNAR AB, HEDMAN, ANDERS
Application year: 2000
Main classification: F16H55
IPC codes: F16D1, F16H55, F16H57