Shaft-hub connection assembly between a metal shaft and a plastic hub

Abstract

The invention relates to a shaft-hub connection assembly for transmitting torques between a metal shaft (1) and a plastic hub (2) which is interlockingly connected thereto, 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, in a manner corresponding thereto, with folding lever means which extend inwardly from the inner wall (6) and which come to bear in an interlocking manner in groove flank regions (5a, 5b) on both sides of the longitudinal groove (3).

Description

[0001] SHAFT-HUB CONNECTION ARRANGEMENT BETWEEN A METALLIC SHAFT AND A PLASTIC HUB

[0002] DESCRIPTION

[0003] The present invention relates to a shaft-hub connection arrangement for transmitting torque between a metallic shaft and a plastic hub that is positively connected thereto. Furthermore, the invention relates to an electric hand tool with a drive unit that is connected, in particular, to a gear unit via such a shaft-hub connection arrangement.

[0004] The field of application of the invention extends primarily to electric motor-driven machine tools, in particular hand tools such as drills, rotary hammers, or chisel hammers, whose rotationally driven components, in particular an electric motor drive unit, are to be connected via a shaft-hub connection to a downstream component, for example, a gear unit for translating and / or converting the rotational drive energy. Within the scope of the present application, hubs can be designed as gears, plug-in sleeves, or other parts of a component arranged in the drive train.

[0005] With the technological trend toward increasing lightweight construction, hubs made of plastic are increasingly being used. Shafts, in contrast, are usually made of metal. With this material pairing, it is important to prevent wear at the connection point as the torque to be transmitted increases via the shaft-hub connection. For this reason, a positive connection, which is of interest here, is usually chosen for this particular material pairing.

[0006] The generally known state of the art includes positive-locking shaft-hub connection arrangements that utilize, for example, spline engagement—also known as keyway engagement. This is a multiple-drive connection, with the torque being transmitted by the tooth flanks. For this purpose, the shaft has external teeth, and the hub interacting with it has internal teeth. Such spline engagement requires a high degree of manufacturing precision to ensure that as many tooth flanks as possible participate in the transmission within the scope of a slight elastic deformation.

[0007] Also well known are shaft-hub connection arrangements in which a shaft with a round cross-section interacts with a corresponding bore on the hub side. The positive connection is achieved via at least one connecting element, such as a set screw or bolt, that at least partially penetrates the two components transversely to the axial direction. Furthermore, parallel keys and the like are also used as connecting elements in such single-drive connections, although these are only of limited suitability for use with plastic hubs due to the locally concentrated torque transmission point.

[0008] DE 77 40 014 U1 discloses a generic shaft-hub connection arrangement between a metallic shaft and a plastic hub positively connected thereto. Disclosed is a plastic hub that can be slipped onto a shaft, in particular a hub of a plastic fan wheel that can be slipped onto a motor shaft of an axial fan, with a metal part machined near the shaft bore prior to insertion, which metal part can be brought into a driving connection with the shaft via a fastening element. At least one U-shaped sheet metal tab with a leg opening directed radially toward the shaft is incorporated into the plastic hub, into which a corresponding driving pin connected to the shaft engages when the plastic hub is slipped on, creating a positive connection. However, this technical solution requires several auxiliary components to facilitate the connection.

[0009] The object of the present invention is to further improve a shaft-hub connection assembly of the generic type so that a reliable, positive-locking rotary connection can be produced without separate components. Brief description of the invention

[0010] The object is achieved based on a shaft-hub connection arrangement according to the preamble of claim 1 in conjunction with its characterizing features. With regard to an electric hand tool comprising the shaft-hub connection arrangement according to the invention, reference is made to claim 11. The remaining dependent claims reflect advantageous developments of the invention.

[0011] The invention includes the technical teaching that the shaft is provided with at least one longitudinal groove which is concave in cross-section, at least in the connection region, and that the hub is provided with corresponding folding lever means extending from the inner wall inwards - preferably predominantly radially inwards - which, in the assembled state, come into positive contact in both sides of the groove flank regions of the longitudinal groove.

[0012] The advantage of the solution according to the invention lies in the fact that it enables a direct, positive-locking connection for mounting a metal shaft in a plastic hub without the need for additional metal components to provide a rotary joint. Furthermore, the connection according to the invention enables compensation for the play that normally occurs between the plastic hub and the metal shaft as a result of load. This is because the resilient properties of the plastic material ensure that the folding lever means formed on the side of the plastic shaft, in conjunction with the geometric design of the longitudinal groove as a concave curvature, compensate for play. The functional integration of the folding lever means according to the invention as a positive-locking fastening component on the plastic hub eliminates the need for additional individual parts.

[0013] According to a preferred embodiment of the invention, the folding lever means comprise at least two lever arms extending from the same starting point on the inner wall and inwardly extending therefrom in a V-shape. The distal ends of the lever arms rest in the flank area of ​​the concave longitudinal groove, thus creating a stable, positive-locking shaft-hub connection in both directions of rotation. In an alternative embodiment, the folding lever means can also have lever arms extending from different starting points on the inner wall.

[0014] According to a measure further improving the invention, mutually facing locking tongues are pivotably formed in the distal end region of the lever legs. These locking tongues can also be pivotally connected to one another with a film hinge at the abutting distal ends to ensure the desired connection security. Furthermore, in the locked position, the locking tongues also nestle against the groove base area of ​​the concave longitudinal groove or are supported against the groove base area of ​​the concave longitudinal groove to secure the locked position of the lever legs in this position. The lever legs equipped with the locking tongues thus form a type of bistable toggle lever mechanism in interaction with one another and with the concave longitudinal groove of the shaft.

[0015] In an alternative design, a bistable element can be provided that is connected to the two lever arms. This bistable element is used, in particular, instead of the two locking tongues. The bistable element can be moved from an outwardly curved basic position toward an inwardly curved, spread position. In the spread position, the bistable element assumes a self-locking position.

[0016] Preferably, the shaft should be provided with several concave longitudinal grooves distributed over the entire circumference, resulting in a star-shaped cross-section. Correspondingly, one or more folding levers can be provided on the inner wall of the hub, each of which interacts with one of the concave longitudinal grooves.

[0017] For additional or alternative locking of the lever arms, according to a further optional measure, the space created thereby can be provided with an insert element to hold the lever arms in the locked desired position. Suitable insert elements include, for example, pins with a round or triangular profile. In the shaft-hub connection arrangement according to the invention, the outer diameter of the shaft is matched to the hub diameter in such a way that a clearance fit exists at least partially along the axial connecting section between the two components. This allows for a slight radial play of the component connection without impairing torque transmission, since torque is transmitted via the folding lever means.

[0018] Detailed description based on drawing

[0019] Further measures improving the invention are described in more detail below, together with the description of a preferred embodiment of the invention, with reference to the figures. It shows:

[0020] Fig. 1 is a schematic cross-section through the shaft-hub connection arrangement in the assembled position of the shaft with the hub, and

[0021] Fig. 2 shows a schematic cross-section through the shaft-hub connection arrangement in locked position after assembly according to Fig. 1.

[0022] According to Fig. 1, the schematically illustrated shaft-hub connection arrangement for transmitting torque consists of a metallic shaft 1 on the one hand and a hub 2 made of plastic on the other hand - which is only partially shown here.

[0023] The shaft 1 is provided along its circumference with several concave longitudinal grooves 3 arranged adjacent to one another. The longitudinal grooves 3 describe a partial circle in cross-section. Each longitudinal groove 3 comprises a groove base region 4 around the deepest point and groove flank regions 5a and 5b bordering it on both sides. In this embodiment, all three regions 4, 5a, and 5b occupy approximately the same arcuate section of the groove cross-section.

[0024] Corresponding to the longitudinal groove 3, folding lever means are formed on the inner wall 6 of the hub 2. In this embodiment, the folding lever means, which are also made of the plastic material of the hub 2, are formed from two lever legs 7a and 7b that emerge in a V-shape from the same starting point on the inner wall 6 and extend inwards. In the distal end region of the respective lever legs 7a and 7b, mutually facing locking tongues 8a and 8b are formed. These are moved in the direction indicated by the arrow after assembly to lock the positive connection. According to Fig. 2, the locking tongues 8a and 8b of the lever legs 7a and 7b, respectively, nestle against the groove base region 4 of the longitudinal groove 3 in the locked position and thereby spread the lever legs 7a and 7b in the respective direction indicated by the arrow.This causes the lever arms 7a and 7b to be pushed apart in the manner of a toggle lever tensioning mechanism, so that their distal end region is pressed against the longitudinal groove 3. This locked position can be additionally secured by an insert element (not shown) in the space formed by the lever arms 7a and 7b.

[0025] It is evident that there is a gap between the inner wall 6 of the hub 2 and the enveloping diameter of the shaft 1, which creates a clearance fit between the two components along the axial connecting section. However, this gap is converted into a press fit by the locked folding lever means. Although the folding lever means associated with a single longitudinal groove 3 are illustrated in this exemplary embodiment, such folding lever means are provided for several of the longitudinal grooves 3, distributed over the entire circumference.

[0026] The invention is not limited to the preferred embodiment described above. Rather, modifications thereof are also conceivable, which are also encompassed by the scope of the following claims. For example, it is also possible to provide only a portion of the longitudinal grooves arranged along the circumference with associated folding lever means for positive connection. Accordingly, it is also not necessary to equip the entire circumference of the shaft with the concave longitudinal grooves, thus forming a star profile. The number of concave longitudinal grooves of the shaft with hub-side folding lever means that interact with positive connection means depends primarily on the maximum torque to be transmitted. List of reference symbols

[0027] 1 wave

[0028] 2 Hub 3 Longitudinal groove

[0029] 4 Groove base area

[0030] 5 Groove flank area

[0031] 6 inner wall

[0032] 7 Lever leg 8 Locking tongue

Claims

CLAIMS 1. Shaft-hub connection arrangement for transmitting torques between a metallic shaft (1) and a plastic hub (2) which is positively connected thereto, characterized in that the shaft (1) is provided with at least one longitudinal groove (3) which is concave in cross-section, at least in the connection region, and in that the hub (2) is provided with corresponding folding lever means which extend inwards from the inner wall (6) and which come into positive contact in groove flank regions (5a, 5b) of the longitudinal groove (3) on both sides.

2. Shaft-hub connection arrangement according to claim 1, characterized in that the folding lever means comprise at least two lever legs (7a, 7b) starting from the same starting point on the inner wall (6) and extending inwards in a V-shape.

3. Shaft-hub connection arrangement according to claim 1 or 2, characterized in that in the distal end region of the lever legs (7a, 7b) mutually facing locking tongues (8a, 8b) are pivotably formed.

4. Shaft-hub connection arrangement according to one of the preceding claims, characterized in that the locking tongues (8a, 8b) nestle against the groove base region (4) of the longitudinal groove (3) in the locked position.

5. Shaft-hub connection arrangement according to one of the preceding claims, characterized in that several concave longitudinal grooves (3) are arranged adjacent to one another over the circumference of the shaft (1), so that a star profile is obtained.

6. Shaft-hub connection arrangement according to one of claims 2 to 5, characterized in that, for locking the lever legs (7a, 7b), an insert element arranged in the space formed thereby is held in the desired position.

7. Shaft-hub connection arrangement according to one of the preceding claims, characterized in that there is at least partially a clearance fit between the inner wall (6) of the hub (2) and the enveloping circle diameter of the shaft (1) along the axial connection section.

8. Shaft-hub connection arrangement according to one of the preceding claims, characterized in that the shaft (1) is designed as a gear shaft.

9. Shaft-hub connection arrangement according to one of the preceding claims, characterized in that the hub (1) is a component of a gear wheel.

10. Shaft-hub connection arrangement according to claim 9, characterized in that the gear wheel is designed as a gear wheel, friction wheel or a pulley.

11. An electric hand tool comprising a drive unit connected to a gear unit via a shaft-hub connection arrangement according to any one of the preceding claims.

Images