GB2360010A

GB2360010A - Power tool bearing

Info

Publication number: GB2360010A
Application number: GB0100527A
Authority: GB
Inventors: Karl Frauhammer; Manfred Hellbach; Frank Mueller; Karl Treyz; Heinz Schnerring; Joerg Friedrich; Andreas Strasser
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-01-14
Filing date: 2001-01-09
Publication date: 2001-09-12
Anticipated expiration: 2021-01-09
Also published as: GB0100527D0; GB2360010B; CH694959A5; JP2001239472A; DE10001192A1

Abstract

A power tool has at least one rotary, in particular highly loaded component (16, 34), which is mounted in at least one bearing (10, 12) having at least one rotatably mounted bearing component (14). The rotary component (16, 34) is supported in at least one direction (18, 20) by means of the rotatably mounted bearing component (14) of the bearing (10, 12) via at least two successively arranged sliding surface pairs (22, 24, 26, 50, 52). The arrangement is described in relation to an eccentric drive in an impact tool and also applicable to an overload clutch.

Description

2360010 1 13.01.00 ROBERT BOSCH GMBH; D-70442 Stuttgart Power tool

Background art

The invention proceeds from a power tool according to the preamble of claim 1.

In power tools, highly loaded rotary components, e.g. in a drilling hammer or chisel hammer a journal for supporting an eccentric of a striking mechanism or a journal for supporting a clutch part of an overload clutch etc., are generally mounted in rolling-contact bearings. Rollingcontact bearings as a rule comprise a first ring rotating with the component and a second ring non-rotatably connected to a housing, wherein rolling elements are disposed between said rings. To avoid mutual contact of the rolling elements, maintain a uniform distance between the rolling elements and hold the rolling elements together when the bearing is disassembled, the rolling elements are mostly held in a cage.

Less highly loaded rotary components in power tools are, on the other hand, frequently mounted in plain bearings. The rotary component is in said case supported against a fixed bearing shell or bearing bush in the housing in radial direction and/or via a bearing race, which is non-rotatably connected to the component, on a fixed bearing ring in axial direction.

2 - Advantages of the invention The invention proceeds from a power tool having at least one rotary, in particular highly loaded component, which is mounted in at least one bearing having at least one rotatably mounted bearing component.

It is proposed that the rotary component is supported in at least one direction by means of the rotatably mounted bearing component of the bearing via at least two successively arranged sliding surface pairs. Given a high permissible rotational speed of the rotary component it is possible to achieve low relative velocities between the sliding surface pairs, long stability times of a lubricant, and in the case of highly loaded, in particular impactloaded bearing points a long service life, and indeed with a space-saving and lightweight construction which is particularly suitable for hand-held power tools.

The solution according to the invention may be used with thrust and/or radial bearings for shafts or axles. In a refinement of the invention it is proposed that the rotary component is formed by a journal, which is supported radially by means of at least one first bearing ring and by means of a second bearing ring and at least one bearing ring is rotatably mounted. The bearing rings may be disposed radially outside of the journal or radially inside a journal, e.g. in a coaxial recess of the journal. The rotary component or the journal may alternatively be supported by means of only one rotatably mounted bearing ring. With at least two bearing rings, however, a sliding surface pair may be defined solely by bearing materials, independently of a material of the journal and a housing part. The bearing materials may be purposefully adapted to their bearing function substantially independently of other marginal conditions. If the journal is supported radially 1 by means of three bearing rings and the radially middle bearing ring is rotatably mounted, all of the sliding surface pairs may advantageously be defined by bearing materials, e.g. in that a first bearing ring is disposed on the journal, a second bearing ring is disposed nonrotatably in a housing part and a third bearing ring is disposed rotatably between the first and the second bearing ring.

An angular velocity arising in the case of the rotatably mounted bearing ring may be influenced by means of a clearance of the rotatably mounted bearing ring relative to its adjacent components. The angular velocity of the bearing ring may, depending on clearance, assume between one and two thirds of an angular velocity of the journal. The clearance is advantageously so selected that between a sliding surface pair defined solely by bearing materials a greater relative velocity arises than, for example, between the rotatably mounted bearing ring and the journal.

To save components, installation space, weight and expenditure for an axial bearing arrangement, the journal or a component connected to the journal is advantageously supported additionally in axial direction against the rotatably mounted bearing ring. The advantageous effect according to the invention of the rotatably mounted bearing component and of the plurality of sliding surface pairs may be utilized simultaneously for an axial and a radial bearing arrangement.

Furthermore, additional components, installation space and weight may be saved and, in particular, ease of assembly may be achieved in that the rotatably mounted bearing ring is advantageously supported in axial direction by means of a component, which is fixed by the second bearing ring.

- 4 In a further refinement of the invention it is proposed that at least one sliding surface pair is lubricated by means of a lubricant. An advantageous liquid friction with low coefficients of friction and a long service life may be 5 achieved.

To avoid additional components and installation space taken up by them, the sliding surface pair is advantageously lubricated hydrostatically via an already provided pressure source and/or hydrodynamically. If at least in a basic operating position the sliding surface pair is disposed in an oil sump, in a constructionally simple manner at least a basic supply of lubricant to the sliding surface pair may be ensured.

The rotary component is in a particularly advantageous manner formed by a journal, which is used to mount an eccentric of a striking mechanism or a clutch part of an overload clutch. Bearing points of said journals are highly loaded, in particular impact-loaded. With the solution according to the invention it is possible to achieve large supporting and lubricating surfaces which are advantageously capable of absorbing impact loads. In principle, however, the solution according to the invention may be used with various rotary components of a power tool and, in particular, of a hand-held power tool, which appear meaningful to the person skilled in the art.

It is moreover possible to use various bearing materials which appear meaningful to the person skilled in the art, such as e.g. cast iron, sintered materials, alloys, plastics materials etc. A hardened ball bearing steel may advantageously also be used. With a ball bearing steel a high hardness may constantly be achieved at.low cost.

Drawings Further advantages arise from the following description of the drawings. In the drawings embodiments of the invention are illustrated. The drawings, the description and the claims contain numerous features in combination. The person skilled in the art will advantageously consider the features also individually and combine them into meaningful further combinations.

The drawings show:

Fig. 1 a cutout of a striking mechanism of a handcontrolled percussion hammer and Fig. 2 a variant according to Fig. 1 with three bearing rings.

Description of the embodiments

Fig. 1 shows a cutout of a striking mechanism of a handcontrolled percussion hammer. The striking mechanism comprises an eccentric 42 with an eccentric wheel 34, which is mounted by means of a journal 16 in a bearing 10. The eccentric wheel 34 is driven by a rotor shaft 44 of an electric motor (not shown in detail) and via a pin 46 and via a rod 48 drives a piston (not shown in detail), which is guided in a hammer tube.

According to the invention, the journal 16 is supported in radial direction 18 by means of a first, rotatably mounted bearing ring 14 and by means of a second bearing ring 30, which is pressed into a housing 28. The bearing rings 14, 30 are made of a hardened ball bearing steel. The journal 16 is supported radially via a sliding surface pair 22 between the journal 16 and the bearing ring 14 and via a sliding surface pair 24 between the bearing ring 14 and the 6 bearing ring 30. When the journal 16 is driven by the rotor shaft 44 via the eccentric wheel 34, the bearing ring 14 rotates at approximately half the angular velocity of the journal 16. Between the sliding surface pairs 22, 24 low relative movements arise compared to a conventional plain bearing having only one sliding surface pair in one direction.

The bearing ring 14 has a radial clearance relative to the journal 16 and relative to the bearing ring 30 of altogether a few hundredths of a millimetre, by means of which a ratio between the angular velocity of the journal 16 and the angular velocity of the bearing ring 14 may be adjusted.

is The eccentric wheel 34 is supported in axial direction 20 by means of the rotatably mounted bearing ring 14 and by means of a ring 36 against the housing 28. The relative velocity of the journal 16 and/or of the eccentric wheel 34 is distributed to a sliding surface pair 50 between the eccentric wheel 34 and the bearing ring 14 and to a sliding surface pair 52 between the bearing ring 14 and the ring 36. The ring 36 is fixed by means of the bearing ring 30 in the housing 28.

The sliding surface pairs 22, 24, 50, 52 are lubricated hydrodynamically by a lubricant 38. In a basic operating position, namely in a substantially horizontal operating position of the percussion hammer, the sliding surface pairs 22, 24, 50, 52 are disposed in an oil sump 40. The electric motor is sealed off from the oil sump 40 by a seal 54, which is disposed at a side of a ball bearing 56 of the rotor shaft 44 directed towards the oil sump 40.

Introduced in the bearing ring 14 are lubricant pockets 58, 60 which serve as lubricant reservoirs for the sliding - 7 surface pairs 22, 24, 50, 52. Instead of the lubricant pockets 58, 60, other forms of construction which appear meaningful to the person skilled in the art and which assist the hydrodynamic lubrication are conceivable, e.g. bearing rings with grooves, which give rise to a purposeful feed direction of the lubricant 38, etc. Furthermore, a space 62 enclosed between a bottom end of the journal 16 and the housing 28 serves as a lubricant reservoir.

For an improved supply/removal of lubricant to/f rom the oil sump 40 and to/from the sliding surface pairs 22, 24, 50, 52 during operation, a plurality of continuous channels 64 extending in axial direction of the journal 16 are introduced in the eccentric wheel 34. It is however alternatively possible to introduce only one channel in the eccentric wheel. Furthermore, for the supply of lubricant there is disposed in the journal 16 and in the eccentric wheel 34 a concentric, continuous channel 66. By means of the channels 64. 66, moreover, an advantageous cooling action of the bearing 10 may be achieved.

Fig. 2 shows a variant of the embodiment in Fig. 1, which comprises a bearing 12 with three bearing rings 14, 30, 32. Components remaining substantially identical are basically denoted by the same reference characters. Furthermore, with regard to features and functions, which remain identical, reference may be made to the description pertaining to the embodiment in Fig. 1.

The journal 16 is supported in radial direction 18 by means of the bearing ring 32, which is pressed onto the journal 16, by means of the rotatably mounted bearing ring 14 and by means of the bearing ring 30, which is pressed in the housing 28. The journal 16 is in said case supported radially via a sliding surface pair 26 between the bearing ring 32 and the bearing ring 14 and via a sliding surface - 8 pair 24 between the bearing ring 14 and the bearing ring 30. When the journal 16 is driven by the rotor shaft 44 via the eccentric wheel 34, the bearing ring 14 rotates at approximately half the angular velocity of the journal 16.

The bearing ring 14 has a radial clearance relative to the bearing ring 32 and relative to the bearing ring 30 of altogether a few hundredths of a millimetre, by means of which a ratio between the angular velocity of the journal 16 and the angular velocity of the bearing ring 14 may be 10 adjusted.

The eccentric wheel 34 is supported in axial direction 20 by means of the rotatably mounted bearing ring 14 and by means of the ring 36 against the housing 28.

- 9 13.01.00 ROBERT BOSCH GMBH; D-70442 Stuttgart Reference characters bearing 40 oil sump 12 bearing 42 eccentric 14 bearing component 44 rotor shaft 16 component 46 pin 18 direction 48 rod direction so sliding surface pair 22 sliding surface pair 52 sliding surface pair 24 sliding surface pair 54 seal 26 sliding surface pair 56 ball bearing 28 component 58 lubricant pocket bearing ring 60 lubricant pocket 32 bearing ring 62 space 34 component 64 channel 36 component 66 channel 38 lubricant - 10 13.01.00 ROBERT BOSCH GMBH; D-70442 Stuttgart

Claims

Claims

Power tool having at least one rotary, in particular highly loaded component (16, 34), which is mounted in at least one bearing (10, 12) having at least one rotatably mounted bearing component (14), characterized in that the rotary component (16, 34) is supported in at least one direction (18, 20) by means of the rotatably mounted bearing component (14) of the bearing (10, 12) via at least two successively arranged sliding surface pairs (22, 24, 26, 50, 52) 2. Power tool according to claim 1, characterized in that the rotary component (16) is formed by a journal, which is supported radially by means of at least a first and a second bearing ring (14, 30, 32) of the plain bearing (10, 12) and at least one bearing ring (14) is rotatably mounted.

3. Power tool according to claim 2, characterized in that the rotary component (16) is supported radially by means of three bearing rings (14, 30, 32) and the radially middle bearing ring (14) is rotatably mounted.

Power tool according to claim 2 or 3, characterized in that the rotary component (16, 34) is supported in axial direction (20) against the rotatably mounted bearing ring (14).

11 5. Power tool according to claim 4, characterized in that the rotatably mounted bearing ring (14) is supporte in axial direction (20) by means of a component (36), which is fixed by the second bearing ring (30).

Power tool according to one of the preceding claims, characterized in that at least one sliding surface pair (22, 24, 26, 50, 52) is lubricated by a lubricant (38).

Power tool according to claim 6, characterized in that the sliding surface pair (22, 24, 26, 50, 52) is lubricated hydrodynamically.

8. Power tool according to claim 6 or 7, characterized in that the sliding surface pair is lubricated hydrostatically via an already provided pressure source.

9. Power tool according to one of claims 6 to 8, characterized in that at least in a basic operating position the sliding surface pair (22, 24, 26, 50, 52) is disposed in an oil sump (40).

10. Power tool according to one of the preceding claims, characterized in that the rotary component (16) is formed by a journal, which is used to mount an eccentric (42) of a striking mechanism.

11. Power tool according to one of claims 1 to 9, characterized in that the rotary component is formed by a journal, which is used to mount a clutch part of an overload clutch.

12. A Power tool substantially as herein described with respect to the accompanying drawings.