Shaft-hub connection device for metal shafts and plastic hubs

Abstract

The present invention relates to a shaft-hub connection device for transmitting torque between a metal shaft (1) and a plastic hub (2) connected to said shaft in a positive-locking manner, wherein the shaft (1) is provided, at least in the connection region, with at least one longitudinal groove (3) having a concave cross section, and the hub (2) is provided with corresponding folding lever means extending inward from the inner wall (6) and resting in a positive-locking manner on both groove side regions (5a, 5b) of the longitudinal groove (3).

Description

[Technical Field]

[0001] The present invention relates to a shaft-hub connection device for transmitting torque between a metal shaft and a plastic hub connected to the shaft in a positive-locking manner, and also to an electric hand tool having a drive unit connected, in particular to a gear unit, via such a shaft-hub connection device.

[0002] The field of application of the invention mainly covers electric motor-driven machine tools, in particular hand tools such as drills, hammer drills or chisel hammers, whose rotary drive components, in particular electric motor drive units, are connected by a shaft-hub connection to downstream components, for example gear units, for the transmission and / or conversion of rotary drive energy. In the context of this application, the hub may be designed as a gear wheel, a plug-in sleeve or other part of a structural element arranged in the drive train.

[0003] As technology moves toward increasingly lightweight construction, hubs are often made of plastic materials, while shafts are typically made of metal. This combination of materials must be avoided, as wear at the connection points due to the increased torque transmitted through the shaft-hub connection must be avoided. For this reason, positive-locking connections, as of this writing, are typically selected for these special combinations of materials.

[0004] The commonly known prior art includes, for example, positive-locking shaft-hub connections that use spline connections, also known as keyway connections. This is a multi-drive connection in which torque is transmitted by toothed flanks. For this purpose, the shaft is provided with external teeth and the hub that interacts with the shaft is provided with internal teeth. This type of spline connection requires a high degree of manufacturing precision so that all toothed flanks are involved in the transmission in relation to slight elastic deformations.

[0005] Also commonly known are shaft-hub connections in which a shaft having a circular cross section interacts with a corresponding hole in a portion of the hub, and a positive locking fit is created via at least one connecting means, such as a set screw or bolt, which at least partially penetrates the two components transversely to the axial direction.Furthermore, feather keys and the like are also used as connecting means for such single drive connections, but feather keys are only suitable to a limited extent for use with plastic hubs due to the local concentration of torque transmission points.

[0006] German Utility Model No. 7740014 (U1) shows a typical shaft-hub connection device between a metal shaft and a plastic hub connected to the shaft in a positive-locking manner. The disclosure includes a plastic hub that can be inserted onto a shaft, particularly the hub of a plastic fan wheel that can be inserted onto the motor shaft of an axial fan. The hub has a metal portion that is assembled near the shaft hole before insertion and can be drivingly connected to the shaft via a fastening element. At least one U-shaped sheet metal tab with a leg opening oriented radially toward the shaft is inserted into the plastic hub, and when the plastic hub is inserted, a corresponding drive pin connected to the shaft engages with the sheet metal tab for a positive-locking connection. However, this technical solution requires several auxiliary components to provide the connection.

[0007] SUMMARY OF THE INVENTION It is an object of the present invention to further improve a shaft-hub connection device of the general type so that it is capable of producing a reliable positive-locking rotary connection without separate components.

[0008] Summary of the Invention This object is achieved on the basis of a shaft hub connection device according to the generic term of claim 1 together with the characteristic features of claim 1. With regard to an electric hand tool having a shaft hub connection device according to the invention, reference is made to claim 11. The remaining dependent claims describe advantageous developments of the invention.

[0009] The present invention includes the technical teaching that the shaft has at least one longitudinal groove having a concave cross section, at least in the connection region, and the hub has a corresponding folding lever means extending inward from the inner wall, preferably mainly radially inward, which folding lever means, in the assembled state, rests in a positive-locking manner on the groove side regions on both sides of the longitudinal groove.

[0010] The advantages of the solution according to the invention lie in the fact that it allows a direct, positive-locking connection for assembling a metal shaft on a plastic hub, without the need for additional metal components to provide a rotational connection. The connection according to the invention also makes it possible to compensate for any movement play between the plastic hub and the metal shaft that would normally occur as a result of loading, since the elastic properties of the plastic material, together with the geometric design of the longitudinal groove in the form of a concave curvature, provide a play-compensating effect for the folding lever means formed on the plastic shaft. The functional integration of the folding lever means according to the invention as a positive-locking fixing component on the plastic hub means that no additional individual parts are required.

[0011] According to a preferred embodiment of the present invention, the folding lever means includes at least two lever legs extending from the same starting point on the inner wall and extending inward from said starting point in a V-shape. Distal ends of the lever legs rest in side regions of the recessed longitudinal groove to form a stable, positive-locking shaft-hub connection in both rotational directions. In another embodiment, the folding lever means can have lever legs extending from different starting points on the inner wall.

[0012] According to a further improvement of the invention, opposing locking tongues are pivotally formed in the distal end regions of the lever legs. Such locking tongues can also be pivotally connected to one another at adjacent distal ends by film hinges to ensure the desired connection security. Apart from this, in the locked position, the locking tongues also rest or rest against the groove base region of the concave longitudinal groove to fix the locked position of the lever legs in this position. Thus, the lever legs with the locking tongues interact with each other and with the concave longitudinal groove of the shaft to form a kind of bistable toggle lever mechanism.

[0013] In another design, a bistable element can be provided that is connected to the two lever legs. This is particularly used in place of the two locking tongues. The bistable element can be moved from an outwardly curved base position to an inwardly curved extended position. In the extended position, the bistable element assumes a self-locking position.

[0014] Preferably, the shaft should be provided with several concave longitudinal grooves distributed over its entire circumference, thereby obtaining a star-shaped cross section. Correspondingly, one or more folding lever means can be provided on the inner wall of the hub, each of which interacts with one of the concave longitudinal grooves.

[0015] For additional or alternative locking of the lever leg, according to a further optional measure, an insert element can be provided in the intermediate space formed by the lever leg to hold the lever leg in the locked target position. A pin having a circular or triangular shape is, for example, suitable as an insert element.

[0016] In the shaft-hub connection device according to the invention, the envelope diameter of the shaft is matched to the diameter of the hub so that there is at least a partial clearance fit along the axial connection portion of both components, which allows for a small amount of radial movement play in the component connection without affecting torque transmission, since torque transmission is via a folding lever means. [Brief explanation of the drawings]

[0017] Further ways of improving the invention will be explained in more detail below in conjunction with the description of preferred exemplary embodiments of the invention with reference to the drawings, in which: [Figure 1] 1 is a schematic cross-sectional view through the shaft-hub connection device at the attachment position of the shaft and hub. [Figure 2] 2 is a schematic cross-sectional view of the shaft hub connecting device according to FIG. 1 in a locked position after assembly.

[0018] According to FIG. 1, a shaft-hub connection device for transmitting torque is shown diagrammatically, consisting of a metal shaft 1 on the one hand and a plastic hub 2 on the other hand, which is only partially shown here.

[0019] The shaft 1 includes several concave longitudinal grooves 3 arranged adjacent to one another along its circumference. The longitudinal grooves 3 describe a pitch circle in cross section. Around its deepest point, each longitudinal groove 3 includes a groove base region 4 and groove side regions 5a and 5b adjacent to it on either side. In this exemplary embodiment, all three regions 4, 5a, and 5b occupy approximately the same curved portion of the groove cross section.

[0020] Corresponding to the longitudinal groove 3, a folding lever means is formed in the inner wall 6 of the hub 2. In this exemplary embodiment, the folding lever means, also made of the plastic material of the hub 2, is formed from two inwardly extending lever legs 7a and 7b, which extend in a V-shape from the same starting point on the inner wall 6. Opposing locking tongues 8a and 8b are formed in the distal end region of each of the lever legs 7a and 7b, which are moved in the direction indicated by the arrows to lock the positive-locking connection after assembly.

[0021] 2, the locking tongues 8a and 8b of the lever legs 7a and 7b lie against the groove base region 4 of the longitudinal groove 3 in the locked position, thereby expanding the lever legs 7a and 7b in the direction indicated by the arrows. This forces the lever legs 7a and 7b apart like a toggle lever clamping mechanism, so that the lever legs 7a and 7b are pressed against the longitudinal groove 3 at their distal end region. Such a locked position can be further secured by an insert element (not shown) in the intermediate space formed by the lever legs 7a and 7b.

[0022] It can be seen that there is a gap between the inner wall 6 of the hub 2 and the envelope diameter of the shaft 1, which gap results in a loose fit between the two components along the axial connection, but which is converted into an interference fit by the locked folding lever means. In this exemplary embodiment, only a folding lever means assigned to a single longitudinal groove 3 is shown. However, such folding lever means are provided for several longitudinal grooves 3 distributed over the entire circumference.

[0023] The invention is not limited to the preferred exemplary embodiment described above. Modifications are also conceivable, which are covered by the scope of protection of the following claims. For example, it is possible to provide only some of the longitudinal grooves arranged along the periphery with folding lever means assigned for the positive locking connection. It is therefore not necessary to provide recessed longitudinal grooves around the entire periphery of the shaft, so that a star-shaped configuration is formed. The number of recessed longitudinal grooves of the shaft interacting with positive locking connection means and having folding lever means on the hub side is primarily determined by the maximum torque to be transmitted. [Explanation of symbols]

[0024] 1 shaft 2 Hub 3 longitudinal grooves 4 Groove base area 5 Groove side area 6 Inner wall 7 Lever leg 8 Locking Tongue

Claims

1. A shaft-hub connection device for transmitting torque between a metal shaft (1) and a plastic hub (2) connected to the metal shaft in a positive locking manner, comprising: A shaft-hub connection device, characterized in that the shaft (1) has at least one longitudinal groove (3) with a concave cross section at least in the connection region, and the hub (2) has corresponding folding lever means extending inward from the inner wall (6) and resting in a positive-locking manner on groove side regions (5a, 5b) on both sides of the longitudinal groove (3).

2. characterised in that the folding lever means comprises at least two lever legs (7a, 7b) extending from the same starting point on the inner wall (6) and extending inwards in a V-shape from said starting point.

2. The shaft hub connection device of claim 1.

3. Opposing locking tongues (8a, 8b) are pivotally formed in the distal end regions of the lever legs (7a, 7b), 3. The shaft hub connecting device according to claim 1 or 2.

4. characterised in that the locking tongues (8a, 8b) lie against the groove base region (4) of the longitudinal groove (3) in the locked position.

4. A shaft-hub connecting device according to any one of claims 1 to 3.

5. characterised in that several concave longitudinal grooves (3) are arranged adjacent to one another around the circumference of said shaft (1), thereby creating a star-shaped configuration; 5. A shaft hub connecting device according to any one of claims 1 to 4.

6. characterised in that in order to lock the lever legs (7a, 7b) an insert element arranged in an intermediate space formed by the lever legs is held in a target position.

6. A shaft hub connecting device according to any one of claims 2 to 5.

7. characterised in that there is at least a partial clearance fit between the inner wall (6) of the hub (2) and the envelope circle diameter of the shaft (1) along the axial connection portion.

7. A shaft-hub connection device according to any one of claims 1 to 6.

8. characterised in that the shaft (1) is designed as a gear shaft, 8. A shaft hub connection device according to any one of claims 1 to 7.

9. The hub (1) is a component of a gear.

9. A shaft hub connection device according to any one of claims 1 to 8.

10. characterised in that the gear is designed as a toothed wheel, a friction wheel or a belt pulley, 10. The shaft hub connection device of claim 9.

11. 11. A power hand tool having a drive unit connected to a gear unit via a shaft hub connection device according to any one of claims 1 to 10.

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