GB2399784A

GB2399784A - Electric tool with air discharge bore in gear unit housing

Info

Publication number: GB2399784A
Application number: GB0406502A
Authority: GB
Inventors: Winfried Habel; Otto Baumann; Siegfried Fehrle; Andre Ullrich; Michael Weiss
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-03-25
Filing date: 2004-03-23
Publication date: 2004-09-29
Also published as: GB0406502D0; CN1532015A

Abstract

An electric tool comprises an electric drive motor (22, Fig 1) for driving a rotating tool holder (20, Fig 1), and a gear unit (24, Fig 1) disposed between the drive motor and the tool holder, which comprises a substantially closed gear unit housing 25 and grease lubrication. An air discharge bore 40 is provided in the gear unit housing for overpressure compensation, which has a labyrinthine shape. The air discharge bore may be at least partially sealable by means of a felt insert 44, and may comprise an axial portion 42 and a radial portion 48. The electric tool may be a hand drill or a hammer drill.

Description

Electric tool The invention relates to an electric tool according to the

preamble of claim 1.

Background art

Electric tools such as hand drills and hammer drills have an electric drive motor, by means of which a rotating chuck with a tool clamped therein is driven directly or via an intermediate gear unit. The gear unit usually has a closed housing and a grease filling for lubricating the gear unit.

Operation over an extended period leads to a temperature rise within the gear unit, this possibly occurring e.g. in the case of through-bores or the like. This in turn may lead to increased internal pressure in the machine and consequently to an unwanted and uncontrolled escape of grease. Given a hermetically sealed gear unit housing there is the danger, in the event of too great an overpressure, that the grease will escape in an uncontrolled manner at connecting, sealing or screw- fastening points. In order to avoid this, air discharge bores may be provided. Through these, however, the grease filling may possibly pass outwards even during normal operation.

Advantages of the invention In an electric tool having an electric drive motor for driving a rotating tool holder and having a gear unit, which is disposed between drive motor and tool holder and has a substantially closed gear unit housing and grease lubrication, it is provided according to the present invention that an air discharge bore is provided as overpressure compensation in the gear unit housing and has a labyrinthine shape. By said means, it may be substantially ensured that during normal operation no grease of the gear unit lubricant escapes outwards.

An embodiment of the invention provides that the air discharge bore is at least partially sealed by means of a felt insert, thereby guaranteeing that any minimal escape of grease from the gear unit housing is caught.

The air discharge bore preferably comprises an axial portion, the longitudinal extension direction of which is parallel to a motor axis of rotation, and an adjoining radial portion. The radial portion of the electric tool opens into the gear unit housing and the axial portion into a ventilation chamber between drive motor and gear unit.

Preferably, the air discharge bore is introduced in an adapter flange of the gear unit housing and designed in such a way that it connects the gear unit interior to the environment. By selecting the bore position it is possible, in the typical operating and handling situations of the tool, to prevent an increased escape of grease.

Preferably, the felt insert is inserted into the axial portion. and secured against sliding out by means of an end shield. The end shield may be connected to the adapter flange and typically effects axial fixing of an armature bearing arrangement of the drive motor.

With the air discharge bore according to the invention a passive, integrated system is provided, which manages without additional structural parts such as rotating parts, springs or the like. Thus, in terms of manufacture and cost, an optimum solution is provided.

Further advantageous developments of the invention arise from the remaining features described in the dependent claims.

Drawings There now follows a detailed description of preferred embodiments of the invention with reference to the accompanying drawings. These drawings show: Figure 1 a diagrammatic side view of an electric tool, Figure 2 a detail section II according to Figure 1, Figure 3 a plan view of part of a gear unit housing and Figure 4 a further detail section of an air discharge bore according to the invention.

Description of the embodiments

Figure 1 shows a diagrammatic side view of an electric tool exemplified by a hand drill and/or a so-called hammer drill 10. This comprises an oblong housing 12 having at a rear end a pistol- like handle portion 16 with a switch 14 disposed therein. Projecting from the front end of the housing is a rotating chuck 20. The housing 12 is preferably divisible in axial direction, wherein in the assembled state the two housing halves are sealingly connected to one another.

Disposed in the rear housing half is an electric drive motor 22, which is activated by means of the switch 14 and the speed of which is optionally variable. Disposed between drive motor 22 and rotating chuck 20 is a gear unit 24, which is used for torque and/or speed adaptation purposes. Furthermore, in a front region of the front housing half an auxiliary handle 18 is provided, with the aid of which during a percussion drilling operation a support against torque may be effected and additional pressure may be exerted on the drilling tool clamped in the chuck 20.

Figure 2 shows a detail section II according to Figure 1 with an armature bearing arrangement of the drive motor 22.

An armature shaft 28 of the drive motor 22 is supported and rotatably mounted by means of a rolling-contact bearing 30 in an adapter flange 32. A tooth system on the free end of the armature shaft 28 is in mesh with a gear wheel of the gear unit 24 (not shown), which in turn drives the chuck 20 directly or via further transmission steps.

The adapter flange 32 simultaneously forms part of a gear unit housing 25. The gear unit 24 is provided with a grease filling for lubrication purposes. An air discharge bore 40 is used for overpressure compensation, especially in the event of a steep temperature rise of the gear unit as a result of loading over an extended period. The air discharge bore 40 connects the interior of the gear unit housing 25 to an expansion chamber 46, in which a fan impeller 36 rotates, which is connected in a rotationally fixed manner to the armature shaft 28. Venting channels (not shown) lead outwards from the expansion chamber 46.

The fan impeller 36 ensures adequate cooling of the electric drive motor 22 while it is in operation.

The air discharge bore 40 is sealed by means of a felt insert 44, which is held in position by means of an end shield 34. The end shield is fixed by means of at least two screw connections 38 to the adapter flange and simultaneously effects axial fixing of the rolling-contact bearing 30.

Figure 3 shows a plan view of the adapter flange 32 with a supporting surface for the end shield, which is to be mounted thereon and which is held at its narrow sides by means of two oppositely arranged screw connections 38. In the mounted state of the end shield the air discharge bore is partially sealed, wherein the felt insert 44 is held in axial direction in an axial portion 42 of the air discharge bore 40 and prevented from falling out.

Figure 4 shows a further detail section of the air discharge bore 40, the axial portion 42 of which opens into the expansion chamber 46. In the direction of the gear unit housing 25 the axial portion 42 verges into a radial portion 48 situated at right angles thereto and opening into the gear unit housing 25.

By selecting the bore position it is possible, in typical operating situations of the drill, to prevent an increased escape of grease. The air discharge bore 40, which is preferably integrally cast in the adapter flange 32, is situated in the appliance at a point where, in the typical operating situations when the tool is in a horizontal or vertical position, no grease may pass outwards. In order to absorb the minimal escape of grease that occurs, the air discharge bore 40 is sealed by means of the felt insert 44.

Claims

Claims 1. Electric tool having an electric drive motor for driving a

rotating tool holder and having a gear unit, which is disposed between drive motor and tool holder and comprises a substantially closed gear unit housing and grease lubrication, characterized by an air discharge bore (40) in the gear unit housing (25) as overpressure compensation, which has a labyrinthine shape.
2. Electric tool according to claim 1, characterized in that the air discharge bore (40) is at least partially sealable by means of a felt insert (44).
3. Electric tool according to claim 1 or claim 2, characterized in that the air discharge bore (40) comprises an axial portion (42), the longitudinal extension direction of which is parallel to a motor axis of rotation, and an adjoining radial portion (48).
4. Electric tool according to claim 3, characterized in that the radial portion (48) opens into the gear unit housing (25).
5. Electric tool according to claim 3 or claim 4, characterized in that the axial portion (42) opens into a ventilation and/or expansion chamber (46) between drive motor (22) and gear unit (24).
6. Electric tool according to one of claims 2 to 5, characterized in that the felt insert (44) is inserted into the axial portion (42).
7. Electric tool according to claim 6, characterized in that the felt insert (44) is prevented from sliding out by means of an end shield (34).
8. Electric tool substantially as herein described with reference to the accompanying drawings.