GB2304067A

GB2304067A - Electric hammer drill

Info

Publication number: GB2304067A
Application number: GB9616338A
Authority: GB
Inventors: Hermann Schaible; Robert Simm
Original assignee: Scintilla AG
Current assignee: Scintilla AG
Priority date: 1995-08-05
Filing date: 1996-08-02
Publication date: 1997-03-12
Anticipated expiration: 2016-08-02
Also published as: ITMI961678A1; IT1290416B1; DE19528924A1; CN1069249C; DE19528924B4; JPH09117837A; GB9616338D0; ITMI961678A0; CN1154887A; GB2304067B

Description

1 Electric hammer drill

Background art

2304067 The invention proceeds from an electric hammer drill of the type defined in the preamble of claim 1.

In a known hammer drill of said type (EP 0 463 416 Bi) having a pneumatic impact mechanism driven by a wobble gear, the changeover lever has a third position, in which rotary drilling at higher speeds is possible. In a fourth position, the changeover lever decouples the workspindle from the drive train and, as a result of manually pressing in an additional locking pin, the workspindle is locked against rotation on the housing, thereby enabling purely impact drilling with the spindle arrested. Said locking pin engages into arresting teeth of a coupling ring which is seated in a non-rotatable and axially displaceable manner on the workspindle. The coupling ring is axially displaced via a control cam by the changeover lever and coupled selectively, for different rotational speeds of the workspindle, to two gearwheels of the drive train. Special measures for tool changing are not provided.

In an electric hand machine tool, in particular a circular hand saw, (DE 41 00 412 A1) it is known, for tool-free locking of the workspindle for the purpose of changing the rotary tool which is held by a tightening nut screwed on a threaded portion of the workspindle, to provide an arresting device for the workspindle comprising a slotted disk, which is seated nonrotatably on the workspindle and has two diametrical detent slots, and a detent pin which may be inserted counter to a restoring spring into the detent slots. Upon a tool change, the detent pin which is axially displaceable relative 2 to the workspindle is to be pressed in until it drops into one of the two detent slots and via the slotted disk locks the workspindle.

Advantages of the invention The electric hammer drill according to the invention having the characterizing features of claim 1 has the advantage that, by allocating a further function to the changeover lever, a significant ease of handling during tool changing is achieved in a simple manner without requiring the provision of an additional operating knob. During opening and closing of the chuck, the workspindle no longer has to be secured by hand, which if clumsily handled additionally impedes opening of the chuck, rather the changeover lever, which is provided anyway, now has to be rotated into a further operating position. As a result, the locking pin is displaced and latches - optionally after brief manual turning of the workspindle - into the receiver and locks the workspindle against further rotation. Said arresting of the workspindle for tool changing purposes is constructionally very simple and calls for only a slight additional manufacturing outlay to achieve a considerable handling advantage.

By virtue of the measures outlined in the further claims, advantageous developments and improvements of the electric hammer drill indicated in claim 1 are possible.

An, in terms of production engineering, very inexpensive construction is achieved when, according to a preferred embodiment of the invention, the changeover lever comprises a control cam, the locking pin is formed on a scanning head, which is axially displaceable in the housing and is pressed against the control cam by a contact pressure spring supported on the housing, and the control cam is constructed in such a way that, upon transfer of the changeover lever into its third 3 position, the scanning head with locking pin is axially displaced.

According to an advantageous embodiment of the invention, the first, second and third positions of the changeover lever are disposed in said order successively within the same direction of rotation of the changeover lever and, upon operation of the changeover lever, are run though successively and in inverse swivel directions of the changeover lever. In said case, the changeover lever comprises detents which are effective in the first and second position respectively, and its switchover into the third position is effected counter to the action of a restoring spring so that the changeover lever after release is automatically reset into the second position. Said construction ensures that the arrested position of the workspindle is automatically cancelled when the changeover lever is no longer actively held fast in its third "spindle arresting" position. Thus, the workspindle may not be accidentally arrested when the hammer drill is switched on, thereby ruling out damage to the drill. In the other two positions, the changeover lever is latched, i.e. may only be consciously released. This too helps to prevent damage to the drill as a result of careless handling. The restoring spring effective at least in the third position of the changeover level may take the form of a leaf spring or a helical pressure spring.

Drawings There follows a detailed description of the invention with reference to an embodiment which is illustrated in the drawings. The drawings show:

Fig. 1 in a cutout manner, a longitudinal section of a hammer drill, 4 Fig.2 in a cutout manner, a section along the line II-II in Fig.1, Figs.3 to 5 in each case a plan view in the direction of arrow III in Fig.1 of a cutout of changeover lever and locking pin in the hammer drill in three different positions of the changeover lever.

Description of the embodiment

The electric hammer drill illustrated in a cutout manner in longitudinal section in Fig.1 comprises a housing 10, in which a workspindle 11 is supported so as to be rotatable and axially displaceable to a limited extent. The workspindle 11 is driven by an electric motor, of which only the output shaft 12 is shown in Fig.i. The output shaft 12 is provided at its end with a driving pinion 13, which meshes with the gear rim of a spur gear 14 seated firmly on the workspindle 11. Output shaft 12 and workspindle 11 are rotatably supported in a housing-fixed bearing bracket 15. The two bearings 16 and 17 take the form of radial bearings, preferably rolling-contact or needle roller bearings.

The workspindle 11 as it rotates may, by means of a selectively engageable impact mechanism 18, be additionally displaced periodically in an impact-like manner in an axial direction so as to enable so-called impact drilling. The impact mechanism 18 in the form of a so-called detent impact mechanism acts upon the workspindle 11 by way of two rings having detent cams or detent bevels 19, 20 uniformly distributed over the periphery, of which the detent bevels 19 are formed on a detent disk 21 pressed into the bearing bracket 15 and the detent bevels 20 are formed on the end face of the spur gear 14 directed towards the bearing bracket 15. During impact drilling, the two detent bevel rings are held in a meshed state by the tool contact pressure of the operator counter to the action of a helical pressure spring 42, which is supported on the one hand on the workspindle 11 and on the other hand on a housing- fixed sleeve 22 coaxially surrounding the workspindle 11. The detent bevels 19, 20, which slide along on one another as the workspindle 11 rotates, generate the axial displacement impacts of the workspindle 11.

In the top half of Fig.1, the hammer drill is shown in its "impact drilling" operating position, in which the described impact mechanism 18 is effective. The bottom half of Fig.1 shows the "rotary drilling" operating position of the hammer drill, in which the impact mechanism 18 is decoupled. For adjusting the various operating modes of the hammer drill, a changeover lever 23 is provided, which has a first "impact drilling" position and a second "rotary drilling" position as well as a third "spindle arresting" position. The changeover lever 23 comprises an operating disk 24, which is rotatable in the housing 10 about an axis of rotation 25 parallel to the housing axis, and a handle piece 26 which is integrally formed on the periphery of the operating disk 24, projects at right angles from the operating disk 24 and extends in the direction of the housing axis. Formed on the operating disk 24 is a sliding face 27 which ascends over the angle-of-rotation range of the operating disk 24 in the direction of the latter's axis of rotation 25 from the first position to the third position, as is evident from the views of Figs.3 to 5. The direction of displacement of the sliding face 27 upon swivelling of the operating disk 24 through the swivel angle a in Fig.2 is indicated in Figs.3 to 5 by the double arrow 28a.

Cooperating with the sliding face 27 is a scanning head 28, which is pressed by a pressure spring 29 against the sliding face 27. At its rear, the scanning head 28 carries a locking element in the form of a locking pin 30 with a reduced diameter. Scanning head 28 and locking pin 30 are an integral unit and form a sliding journal 31. The sliding journal 31 is guided in an axially displaceable manner in a stepped bore 32 6 in the bearing bracket 15, the scanning head 28 lying in the larger- diameter bore portion of the stepped bore 32 and the locking pin 30 lying in the smaller-diameter bore portion of the stepped bore 32. The larger- diameter bore portion of the stepped bore 32 extends over part of the locking pin 30 and accommodates the pressure spring 29, which surrounds the locking pin 30 and is supported at its ends, on the one hand, on the radial transition shoulder of locking pin 30 and scanning head 28 and, on the other hand, on the radial shoulder at the transition from the largerdiameter bore portion to the smaller-diameter bore portion of the stepped bore 32. The smaller-diameter bore portion of the stepped bore 32 may also be provided in the detent disk 21, thereby achieving an increased bearing stability for the locking pin 30.

Fig.3 shows operating disk 24 and sliding Journal 31 in the position they assume in the first "impact drilling" position, designated 1 in Fig.2, of the changeover lever 23. Fig.4 shows operating disk 24 and sliding journal 31 in the position they assume in the second "rotary drilling" position, designated 2 in Fig.2, of the changeover lever 23. Fig.5 shows operating disk 24 and sliding journal 31 in the position they assume in the third "spindle arresting" position, designated 3 in Fig.2, of the changeover lever 23. As virtue of the ascending sliding face 27, the sliding journal 31 is increasingly inserted into the stepped bore 32 in the bearing bracket 15 until finally, in the third position (Fig.5), the free end of the locking pin 30 engages into a locking pin receiver 33, which is introduced as axial bore 41 in the spur gear 14. In said position of the changeover lever 23, the spur gear 14 is fixed by the locking pin 30 in a non-rotatable manner on the bearing bracket 15 and, since the spur gear 14 is non-rotatably connected to the workspindle 11, the latter is also incapable of being rotated. From Figs.3 to 5 it is clearly evident that provided in the sliding face 27 on the operating disk 24 are two depressions or detent holes 34, 35, 7 which are disposed in such a way that the spherically shaped end of the scanning head 28 drops, in position 1 of the changeover lever 23, into the detent hole 34 (Fig.3) and, in position 2 of the changeover lever 23, into the detent hole 35 (Fig.4). Said two positions of the changeover lever 23 are therefore latched, and the changeover lever 23 may be rotated back out of said positions 1 and 2 only by applying a specific torque.

As Fig.2 shows, upon transfer of the changeover lever 23 from its second position 2 into its third position 3 a restoring spring is effective between housing 10 and operating disk 24, said spring resetting the changeover lever 23 after the latter's release back into its position 2. In Fig.2, said restoring spring takes the form of a leaf spring 36 which is fastened to the operating disk 24 and, in position 2 of the changeover lever 23, comes to rest against a housing projection 37. Upon transfer of the changeover lever 23 from position 2 into position 3, said leaf spring 36 is bent in the manner indicated in Fig.2. Instead of the leaf spring 36 it is possible to provide a helical pressure spring, which is held in a guide along a peripheral arc of the operating disk 24 and is supported by its ends on the operating disk 24 and on a housing projection.

As already mentioned, in position 2 ("rotary drilling" position) of the changeover lever 23 shown in Fig.4, the impact mechanism 18 is decoupled from the workspindle 11. To achieve this, a blind hole with a ball 38 inserted therein is provided at the end of the workspindle 11 in the manner shown in Fig.l. Upon switching of the changeover lever 23 from position 1 into position 2, an operating plate 39 passes between operating disk 24 and ball 38 and in the process displaces the workspindle 11 with the spur gear 14 firmly seated thereon axially by such a displacement distance that the detent bevels 19, 20 of the impact mechanism 18 disengage. This is shown in the bottom part of Fig.l.

8 The ("spindle arresting") position 3 of the changeover lever 23 is used during a change of the drilling tool, i.e. of the impact or rotary drilling bit, to enable operation of the quick-action chuck 40 which is disposed on the workspindle 11 and by means of which the drilling tool is held non-rotatably in the workspindle 11. By means of the changeover lever 23, the workspindle 11 is arrested in a tool-free manner and need not be specially secured during operation of the quick-action chuck 40. Said third position of the changeover lever 23 makes it much easier to operate the quick-action chuck 40 during a tool change.

9

Claims

1. Electric hammer drill having a workspindle (11) which carries a chuck, in particular a quick-action chuck (40), for tool- holding purposes, is rotatably supported in a housing (10) and is set in rotation by an electric motor, having an engageable impact mechanism (18) which additionally displaces the workspindle (11) periodically in an impact-like manner in an axial direction, and having a manually operable changeover lever (23) which is fixed on the housing (10), in a first "impact drilling" position (1) releases the workspindle (11) for coupling to the impact mechanism (18) and in a second "rotary drilling" position (2) keeps the workspindle (11) decoupled from the impact mechanism (18), characterized in that, to operate the chuck for tool-changing purposes, the changeover lever (24) has a third "spindle arresting" position (3), in which at least one housing-fixed locking element (30) coupled to the changeover lever (24) engages positively into a locking element receiver (33) which is non-rotatably connected to the workspindle (11).

Drill according to claim 1, characterized in that the changeover lever (23) comprises a control cam (27), that the locking element (30) is formed on a scanning head (28), which is axially displaceable in the housing (10) and is pressed against the control cam (27) by a contact pressure spring (29) supported on the housing, and that the control cam (27) is constructed in such a way that at least upon transfer of the changeover lever (23) into its third position (3) the scanning head (28) with locking pin (30) is axially displaced.

Drill according to claim 1 or 2, characterized in that the first, second and third positions (1, 2, 3) of the changeover lever (23) are disposed in said order successively within the same direction of rotation of the changeover lever (23).

Drill according to one of claims 1 to 3, characterized in that the changeover lever (23) comprises detents (34, 35) which are effective in the first position (1) and in the second position (2) respectively and that a restoring spring (36) is provided which, upon transfer of the changeover lever (23) into the third position (3), is bent and resets the changeover lever (23) after its release.

5. Drill according to claim 4, characterized in that the restoring spring takes the form of a leaf spring (30) or a helical pressure spring.

6. Drill according to one of claims 1 to 5, characterized in that the locking element receiver (33) takes the form of an axial bore (41) introduced into a gearwheel (14), which is non-rotatably connected to the workspindle (11), of a gearing inserted between electric motor and workspindle (11).

Drill according to one of claims 1 to 6, characterized in that the locking element is a locking pin (30) integrally formed on the scanning head (28) and having a reduced outside diameter compared to said scanning head, that the scanning head (28) is guided in an axially displaceable manner in the larger-diameter bore portion and the locking pin (30) is guided in an axially displaceable manner in the smaller-diameter bore portion of a stepped bore (32) which is introduced in a housing-fixed bearing bracket (15), and that the contact pressure spring (29) takes the form of a helical pressure spring, which is 11 seated on the locking pin (30) and supported on the one hand on the scanning head (28) and on the other hand on the radial transition shoulder formed between the bore portions in the stepped bore (32).

8. Drill according to one of claims 1 to 7, characterized in that the changeover lever (23) comprises an operating disk (24), which is supported in the housing (10) so as to be rotatable about an axis of rotation (25) parallel to the housing axis, and that the control cam takes the form of a sliding face (27) ascending in an axial direction on the disk surface.

9. Drill according to one of claims 4 to 8, characterized in that the detents in the first and second positions (1, 2) of the changeover lever (23) are realized by depressions (34, 35) in the sliding face (27), into which depressions the spherically shaped end of the scanning head (28) drops under the action of the contact pressure spring (29).

10. A hammer drill substantially as herein described with reference to the accompanying drawings.