A DRIVING WHEEL WITH A BELT PULLEY

Abstract: The invention refers to a driving wheel for car engines or the like, incorporating a gear wheel, which is intended to cooperate with a cogged belt, and a pulley (9) attached to one side of the gear wheel and arrested to this. The invention is characterized therein that the gear wheel is moulded from a plastic or similar material having a high coefficient of thermal expansion and that a helix (3) of steel or another material with desired coefficient of thermal expansion is embedded in the gear rim (1) of the wheel radially inside the cogs (2), whereby the helix (3) has such a strength and dimension that it determines the thermal expansion properties of the gear rim (1).

Description: The present invention refers to driving wheels with belt pulley, particularly such as used in connection with car engines. A large number of different driving wheels with pulley are earlier known. They are usually mounted at the front of an engine upon a protruding drive shaft. The driving wheels commonly cooperate with driving belts for driving further devices such as a dynamo. The driving wheels are subjected to high requirements. They shall be reliable under different temperature conditions and the requirements are high for accuracy, as transferred motions shall be synchronized with each other. The driving wheels generally consist of a gear wheel with ledge-shaped, axially directed cogs and a sheet metal pulley screwed thereto. It is essential that no rotation of the pulley in relation to the gear wheel may occur, and it is as important that the gear wheel fitted to a shaft may not move in relation to the shaft. It therefore has earlier been provided a central screw, which connects the driving wheel to the shaft and a plurality of more periferially situated screws, which connect the pulley to the gear wheel. The driving wheels are commonly manufactured by means of powder metallurgy, and the material is a steel alloy. The wheels may also be forged. It has been a desire since long to be able to produce driving wheels of the above mentioned type, which are simple in design and have low weight. It is particularly important that the driving wheels can be assembled in a simple manner by robots. It is then not possible to have too many components, such as screws, if such an assembly shall be appropriate and rapid. At the known devices a big number of screws is thus a drawback. The problems at the known driving wheels have been solved in accordance with the present invention and it has been provided a light driving wheel with a pulley for car engines or the like, which incorporates a gear wheel with axial, ledge-shaped teeth, intended to cooperate with the cogs of a cogged belt and a pulley attached to one side of the gear wheel and arrested to this, and which is characterized therein that the gear wheel is moulded from a plastic or similar material having a high coefficient of thermal expansion, and that a helix of steel or another material with desired coefficient of thermal expansion is embedded in the gear rim of the wheel radially inside the teeth, whereby the helix has such a strength and dimension that it determines the thermal expansion properties of the gear rim. The driving wheel according to the invention shall be designed thus that the gear wheel at its side facing the pulley is equipped with lugs intended to cooperate with recesses in the cogged belt for locking this against rotation relative to the gear wheel. The hub of the gear wheel according to the invention may also be provided with a helix of steel or another material with desired coefficient of thermal expansion and of such a strength, that it can determine the thermal expansion properties of the entire hub. As plastic material has a high coefficient of thermal expansion is it appropriate for avoiding material stresses, that the intermediate part in the gear wheel interconnecting the hub and the gear rim is provided with knees having the ability of absorbing dimensional deformations in the wheel. The invention hereinafter will be further described with reference to the accompanying drawing, which shows a section throug a driving wheel having a sheet metal pulley in accordance with the invention. In the figure is shown a gear wheel having a gear rim 1 with axially extending, ledge shaped teeth 2. Inside these there is inserted a steel helix 3. This has been embedded in that it prior to the moulding of the moulding mass, which in this case is plastic material, has been inserted into a mould with somewhat smaller diameter than the helix 3, whereupon the moulding mass has been injected. The helix then will get a slight pre-tension. In order to ascertain that the teeth bottoms to the major part shall be filled with plastic material some of the teeth of the mould, e.g. each fifth tooth has been equipped with a rule, which retains the helix 3 at some distance from the teeth. The figure further shows a hub 4 on the gear wheel, which hub 4 is also reinforced with a steel helix 5 of desired strength. Between the hub 4 and the gear rim 1 extends an intermediate portion 6. This is provided with appropriate knees 7 for compensating dimensional deformations caused by temperature changes. A characteristic detail at the gear rim 1 is that it is provided with projecting bosses 8 of appropriate number, e.g. 4. These bosses 8 are intended to prevent rotation of the sheet metal pulley 9 in relation to the gear wheel. As can be seen from the figure the driving wheel with sheet metal pulley has been mounted on the shaft 10 by means of one single screw or bolt 11. The sheet metal pulley can be smooth and only clamped between the shaft 10 and the bolt 11, such as shown at the upper side of the bolt, but it may also be equipped with lugs 12 entering in recesses in the shaft 10, as an additional safety device against unintentional rotation. The hub 4 of the gear wheel may also be secured against rotation in relation to the shaft 10 in that e.g. two plane surfaces have been provided in the internal surface of the hub, which plane surfaces cooperate with corresponding surfaces on the shaft 10. By the present invention is obtained the advantage, that it is possible to use only one screw or bolt 11 for mounting the driving wheel with pulley upon the shaft 10, at the same time as it is ascertained that there will occur no rotation of the components in relation to each other and that the thermal expansion of the gear wheel follows that of the steel, although it is primarily made of plastic or similar material having a high coefficient of thermal expansion. If it e.g. is desired to exchange the cogged belt pulley this is also possible in that the pulley 9 is removed, whereby it is necessary to loosen only one screw 11. The invention is not limited to the embodiment shown but can be modified in different manners within the scope of the claims.

Claims: 1. A driving wheel with a belt pulley (9) for car engines or the like, incorporating a gear wheel with axial, ledge-shaped teeth (2), intended to cooperate with the cogs of a cogged belt and a pulley (9) attached to one side of the gear wheel and arrested to this, characterized thereby that the gear wheel is moulded from a plastic or similar material having a high coeffecient of thermal expansion and that a helix (3) of steel or another material with desired coefficient of thermal expansion is embedded in the gear rim (1) of the wheel radially inside the teeth (2), whereby the helix (3) has such a strength and dimension that it determines the thermal expansion properties of the gear rim (1). 2. The driving wheel as claimed in claim 1, characterized thereby that the gear wheel at its side facing the pulley (9) is equipped with lugs (8) intended to cooperate with recesses in the cogged belt for locking this against rotation relative to the gear wheel. 3. The driving wheel as claimed in claim 1 or 2, characterized thereby that also the hub (4) of the gear wheel is provided with a helix (5) of steel or another material with desired coefficient of thermal expansion and of such a strength, that it can determine the thermal expansion properties of the entire hub (4). 4. The driving wheel as claimed in claims 1 - 3, characterized thereby that the intermediate part (6) in the gear wheel, inter­ connecting the hub (4) and the gear rim (1), is provided with knees (7) having the ability of absorbing dimensional deformations in the wheel.

Inventors: HALLERBACK, STIG, Hallerbäck, Stig
Applicants: SKF NOVA AB
Application year: 1987
Main classification: F16H55
IPC codes: F16H55