GB2237766A

GB2237766A - Electrically driven power hand tool

Info

Publication number: GB2237766A
Application number: GB9022015A
Authority: GB
Inventors: Karl Frauhammer; Heinz Schnerring; Frank Mueller
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1989-11-06
Filing date: 1990-10-10
Publication date: 1991-05-15
Anticipated expiration: 2010-10-10
Also published as: DE3936849A1; CH682312A5; GB9022015D0; GB2237766B

Abstract

Until now, the axial mounting of the crank gear on electrically driven power hand tools with crank gears, in particular percussion hammers, has not been satisfactorily solved. This may result in premature wear in the crank gear. A simple, inexpensive measure is proposed which ensures both the axial mounting of crank disc (12) and connecting rod (9) and also the lubrication of the crank boil (11). This is achieved by a cover (25), which is fitted into an opening (23) of the gear housing (16). On the cover (25) there is formed a flat annular surface (26) covering the path of bolt (11), which surface only leaves a narrow gap (27) free with respect to rod (9) to prevent offsetting or dropping-out of rod 9 from bolt 11. In the cover (25) there is formed a hollow space (28) filled with lubricant, from which space a high viscosity grease gradually passes into the sliding bearing between bolt (11) and rod (9). The invention can be applied to all power hand tools with crank gears. The cover may have two adjoining metal parts 32, 33 with an opening 36 in one part to allow egress of lubricant. <IMAGE>

Description

1 is

Electricallv driven power hand tool Prior art

The invention is based on a power hand tool designed as a hammer, of the generic type of Claim 1. German Offenlegungsschrift 3,731,244 already discloses a hammer of which the crank disc and connecting rod on the side remote from the motor are not secured in the axial direction. In particular operating states this may result in the connecting rod deflecting away from the crank disc transversely with respect to the fixing bolt in the piston and causing increased friction on the crank bolt. There is thus the risk of damage occurring to the crank gear.

Advantages of the invention The hammer according to the invention, having the characterizing features of Claim 1, has in comparison the advantage that a low-wear operation of the crank gear is ensured in every operating position of the hammer. This is achieved by crank disc and connecting rod being secured against lateral deflections in both directions. This is performed by a cover fixed to the housing of the crank gear, which cover is arranged in the region of the crank bolt. It is particularly advantageous if the cover has a hollow space which is filled with a lubricant. As a result, the friction between the crank bolt and the connecting rod as well as in the toothings of crank disc and motor pinion are considerably reduced for the serviceable lifetime.

Advantageous further developments and improvements of the hammer specified in Claim 1 are possible by the measures listed in the further claims.

Drawing Two exemplary embodiments of the invention are represented in the drawing and explained in more detail in the description which follows. Figure 1 shows an is overall view of a percussion hammer. Figure 2 shows a longitudinal section through the crank gear and Figure 3 likewise shows a section through a crank gear, in a second exemplary embodiment.

Description of the exemplary embodiment

An electrically operated percussion hammer 1 has a housing 2 and a tool holder 3, in which a cutter tool 4 is arranged. Within the housing 2 there is a pneumatic percussion mechanism 5, known per se, with a piston 7 guided in a guide tube 6 (see Figure 2). The piston 7 is connected via a bolt 8 to one end of a connecting rod 9 of plastic or aluminium, the other end of which has a bore 10 for a crank bolt 11 mounted rotatably in it. The crank bolt 11 is pressed with its other end into a crank disc 12, which for this purpose has an eccentrical ly arranged bore 13. The crank disc 12 bears a journal 14, which is mounted in needle bearings 15, which are held in a gear housing 16. The crank disc 12 is axially supported on the gear housing 16, with a disc 17 interposed. The crank disc 12 has on its periphery a toothing 18, which meshes with a pinion 20 of an electric drive motor 21. The shaft of the drive motor is likewise mounted in the gear housing 16, which additionally holds the guide tube 6 of the percussion mechanism 5. The gear housing 16 encloses, furthermore, the crank gear 22, consisting of crank disc 12 and connecting rod 9, from the lower side facing the motor 21 as well as laterally in the region of the toothing 18. On the opposite. upper side, the gear housing 16 has an opening 23. which is necessary for the assembly of the crank gear. A cover 25. formed from sheet metal. in fitted into the opening 23, with a sealing ring 24 interposed. and is screwed to the gear housing 16. The cover 25 is arched inwards towards the connecting rod 9 and forms a flat annular surface 26. which leaves only a narrow gap 27 free between cover 25 and the connecting rod 9. The flat annular surface 26 covers the path which zhe crank bolt 11 describes during one crank revolution. In its central middle region, the cover 25 is arched outwards away from the connecting rod 9 and forms a 1 1 1 1 i 1 'i is hollow space 28 in a dome 29. The hollow space 28 is filled with a high viscosity lubricant, which gradually passes via the gap 27 into the sliding bearing between connecting rod 9 and crank bolt 11. This has the simultaneous effect of lubricating the connecting rod 9 with respect to the cover 25. The cover 25 is advantageously designed as a deep-drawn sheet steel part. To facilitate the entry of the lubricant, the connecting rod 9 protrudes by a small amount beyond the crank bolt 11 on its side facing the cover 25, so that a flat depression is produced.

The assembly of the gear parts of the hammer according to the invention is very simple. owing to the sliding seating of the bearings 15, the crank disc 12, with already fitted crank bolt 11, can be fitted simply into the gear housing 16. This at the same time ensures an axial securing from below. Subsequently, the connecting rod 9 is pushed with-its bore 10 over the crank bolt 11, so that it rests on the crank disc 12. Consequently, the connecting rod 9 is fixed from below in the axial direction of the crank bolt 11. In conclusion, the cover 25 is fitted into the opening 23 and screwed to the gear housing 16. Consequently, an axial securing of crank disc 12 and connecting rod 9 from above is then also ensured. The play of the connecting rod 9 possible in the axial direction of the crank bolt 11 is closely restricted by the width of the gap 27, so that an offsetting or even dropping-out of the connecting rod 9 from the crank bolt mounting is no longer possible. Even when working with the percussion hammer in an inclined position or with the top side down, the crank gear is f ixed in the axial direction securely and in a simple way. The cover 25 performs both the function of an axial securing means and the function of a grease depot for the crank gear 22 and the reduction gear with motor pinion 20 and crank disc 12. Due to the centrifugal force during operation, lubricant, which gets onto the crank disc 12. is conveyed to the toothing 18 of the latter and consequently also lubricates the fast-running pinion 20.

- 4 is The second exemplary embodiment according to Figure 3 differs from the first exemplary embodiment only by the different design of the cover. Therefore, the same reference numerals have been used for the same parts. The cover 31 screwed to the gear housing 16 consists of two adjoining sheet metal parts 32 and 33, which between them form a hollow space 34. The lower sheet metal part 32 is arched inwards towards the connecting rod 9 and forms a flat circular surface 35 at a small distance from the said connecting rod. In the region of the crank bolt 110 the sheet metal part 32 has one or more openings 36, through which a low viscosity lubricant in the hollow space 34 can pass into the sliding bearing between connecting rod 9 and crank bolt 11. In this exemplary embodiment as well, there is between the cover 31 and the connecting rod 9 a narrow gap 37, which prevents a constant friction occurring between the cover and the connecting rod. The upper part 33 of the cover 31 is designed substantially in the form of a disc. The two parts 32 and 33 are sealed by a sealing ring 38, in order to avoid an escape of lubricant. The function and assembly of the hammer according to the second exemplary embodiment correspond to those of the first described exemplary embodiment.

The invention is not restricted to percussion hammers. It can be applied equally well in the case of drilling hammers and other power hand tools with crank gears.

1 1 1 1 j i 1 - 5

Claims

Claims

Electrically driven power hand tool, in particular percussion hammer, with a crank gear having a crank disc and a connecting rod, the connecting rod resting on the crank disc and being connected to the latter by means of a crank bolt fitted in assigned bores# and the crank disc being held, on its side remote from the connecting rod, in the axial direction in the gear casing of the power hand tool, characterized in that the connecting rod (9) is secured against dropping out on its side remote from the crank disc (12) by a cover (25. 31) fixed to the gear housing (16), which cover has a flat surface (26, 35) covering the region of the crank bolt (11) during a crank revolution.
2. Power hand tool according to Claim 1, characterized in that the cover (25, 31) has a hollow space (28, 34), which is filled with a lubricant.
3. Power hand tool according to Claim 1 or 2 characterized in that the hollow space (28, 34) of the cover (25, 31) has openings (36) facing the crank bolt (11).
4. Power hand tool according to one of the preceding claims, characterized in that the cover (25, 31) is made as a drawn part of sheet steel.
5. Power hand tool according to one of the preceding claims, characterized in that the cover (31) consists of two adjoining and mutually sealed parts (32, 33).
6. Power hand tool according to one of the preceding claims, characterized in that a narrow gap (27. 37) is provided between the connecting rod (9) and the cover (25, 31).
7. Power hand tool according to one of the preceding claims,, characterized in that the connecting rod (9) protrudes by a small amount beyond the crank bolt (11) on Its side facing the cover (25, 31).
8. Either of the electrically driven power hand tools substantially as herein described with reference to the accompanying drawing.

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