GB2380442A

GB2380442A - A hand-held machine tool with pressure compensating device

Info

Publication number: GB2380442A
Application number: GB0220983A
Authority: GB
Inventors: Otto Baumann; Siegfried Fehrle; Andre Ullrich; Michael Weiss
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-09-14
Filing date: 2002-09-10
Publication date: 2003-04-09
Anticipated expiration: 2022-09-10
Also published as: DE10145296A1; GB2380442B; CH695672A5; GB0220983D0

Abstract

A hand-held machine tool comprises a pressure compensating device between a motor compartment 3 and a lubricant containing gear compartment 1. A drive shaft 9, which is driven by a motor 7 situated in the motor compartment, extends into the gear compartment, where it is in engagement with a gear shaft 23. The gear shaft terminates in the vicinity of a partition wall 5 which separates the motor compartment from the gear compartment, and is provided with at least one through opening 57. The pressure relief device comprises at least one channel 51, 53 which extends in the interior of the gear shaft and opens out on the one hand into the gear compartment and on the other hand in the vicinity of the at least on through opening of the partition wall. The hand-held machine tool may be a hammer drill including a wobble mechanism.

Description

Hand tool machine with a pressure relief device Prior art

The present invention relates to a hand tool machine with a pressure relief device between a motor compartment and a lubricant-containing gear compartment' wherein a drive shaft, which is driven by a motor situated in the motor compartment, extends into the gear compartment and, there, is in engagement with a gear shaft, which terminates in the vicinity of. a partition wall, which separates the motor compartment from the gear compartment and is provided with at least one through-opening In hand tool machines, e.g. hammer drills, particularly when they are equipped with a percussion mechanism, a very high pressure arises during operation because of extreme heat generation in the gear compartment. Sealing means are often incapable of withstanding said high pressure, with the result that lubricant escapes from the gear compartment and may penetrate into other appliance parts, e.g. the motor compartment. For combating said problem it is known, e.g. from DE 42 31 987 A1' to provide a pressure relief devices which allows air from the gear compartment to escape into the motor compartment or into the outer compartment of the hand tool machine. According to DE 42 31 987 Al, the pressure relief device comprises a through-opening, which is let into the partition wall between the gear compartment and the motor compartrnent7 wherein the partition wall has a projection, which projects into the gear compartment and through which the through-opening extends and opens out, on the one hand, into the gear compartment and, on the other hand, into the motor compartment. On the gear compartment side, a rotary element in the form of a cap is mounted over the projection provided with the through-opening and is set in rotation by Me gear shaft in the gear compartment so that by means of the rotating cap lubricant

situated in the gear compartment is slung radially outwards as a result of centrifugal force. Said rotary element prevents lubricant from passing from the gear compartment side into the through-opening in the partition wall. Said pressure relief device is of a relatively complex design and takes up a relatively large amount of space.

The object of the invention is therefore to indicate a hand tool machine with a pressure relief device of the type described initially, which may be realized with as simple means as possible and is as space-saving as possible.

Advantages of the invention Said object is achieved with the features of claim i in that in the interior OI the gear shaft, which terminates in the vicinity of a partition wall, which separates the motor compar nent from the gear compartment and is provided with at least one t}u-ough- opening, at least one channel extends, which opens out on the one hand into the gear compartment and on the other hand in the vicinity of the at least one through-opening of the partition wall. By virtue of the fact that the gear shaft rotates, lubricant situated in the region of the gear shaft is slung radially outwards as a result of centrifugal force and so lubricant is prevented from passing into the at least one channel, which extends through the gear shaft, and being carried further into the motor compartment. Said pressure relief device according to the invention, which merely entails at least one channel extending through the gear shaft' is not complicated to manufacture and is very space-saving.

Advantageous developments of the invention are indicated in the subclaims.

An advantageous construction is such that at least one first channel extending in longitudinal direction of the gear shaft and at least one second channel extending in transverse direction and opening into the first channel are let into the gear shaft, wherein the at least one first channel has an opening in an end of the gear shaft

facing the at least one through-opening of the partition wall and the at least one second channel has an opening in the lateral surface of the gear shaft facing the gear compartment. In said case, it is expedient when the at least one channel has an opening below a wobble mechanism hub supported on the gear shaft.

In a bearing provided between the wobble mechanism hub and the gear shaft a recess may be provided, through which air may pass into the at least one channel.

In said recess grease may be deposited for lubricating the bearing.

In case, despite the measures outlined above, small quantities of lubricant at the gear compartment side do pass into the at least one channel of the gear shaft, the lubricant may be kept away from the motor compartment by disposing one or more iubricant-absorDing Biter elements preferably made of felt - ilont of die at least one through-opening in the machine compartment.

Drawings There now follows a detailed description of an exemplary embodiment of the

invention, which is illustrated in the drawings. The drawings show: Figure 1 a detail from the gear compartment and an adjacent motor compartment of a hand tool machine with a pressure relief device and Figure 2 a cross section A-A through the gear shaft with a pressure relief device.

Description of an exemplary embodiment

Figure 1 shows a detail from a hand tool machine e.g. a hammer drill. A hand tool machine usually has a lubricant-containing gear compartment 1 and a motor compartment 3. The motor compartment 3 is separated from the gear compartment 1 by a partition wall 5 so as to prevent lubricant passing from the gear compartment 1 into the motor compartment 3. Situated in the motor compartment 3 is a motor 7, which sets a drive shaft 9 in rotation. In the motor

compartment 3 a fan impeller 11 is disposed non-rotatably on the drive shaft 9 The drive shaft 9 projects from the motor compartment 3 through the partition wall 5 into the gear compartment 1 and is rotatably supported in a ball bearing 13 in the partition wall 5. Inserted between the ball bearing 13 and the partition wall 5 is an O-ring IS, which seals off the motor compartment 3 to prevent the penetration of lubricant from the gear compartment 1.

The drive shaft 9 on its end projecting into the gear compartment 1 has a pinion 17, which meshes with a gear rim 19 of a gear wheel 21. The gear wheel 21 is mounted non-rota/ably, e.g. with an interference fit, on a gear shaft 23 provided in the gear compartment 1. Thus, the gear shaft 23 is set in rotation by the drive shaft 9 of the motor 7. In a marmer generally known e.g. from hammer drills, a spindle of a tool holder for receiving a drill or chisel is set in rotation by means of said gear shaft 23, which is often also described as an intermediate shaft. The transfer of the rotary drive from the gear shaft 23 to a tool spindle is not illustrated in the drawings because it is not part of the invention and moreover belongs to prior art.

It is equally lmown that the rotation of the gear shaft 23 is converted into a percussive motion of the spindle of the tool holder. An, as such, known wobble mechanism, which is illustrated in Figure 1, is used for said purpose. Said wobble mechanism comprises a wobble mechanism hub 25, which is supported on the gear shaft 23 and has at its outside an annular track 27 for balls 29, which is inclined relative to the axis of the wobble mechanism hub 25. A track 33 for the balls 29, which is cut into the inside of a wobble plate 31 in the form of a ring, is associated with the track 27 in the wobble mechanism hub 25 so that the balls 29 are guided between the two tracks 27 and 33. Situated on the wobble plate 31 is a driver 35, which is rotatably connected to a piston 37. When the gear shaft 23 rotates, the piston 27 is set by the driver 35 of the wobble plate 31 into a reciprocating motion in the direction of the longitudinal axes 39 of the non-

illustrated spindle of the tool holder. The reciprocating motion of the piston 37

via an air cushion sets a non-illustrated percussion mechanism into a percussive motion in the direction of the longitudinal axis 39 of the spindle. Situated between the axially non-displaceable wobble plate 31 and the gear shaft 23 is a plain bearing 41 which, when the wobble mechanism is disconnected, enables a rotation of the gear shaft 23 relative to the wobble mechanism hub 25 without co-

rotation of the latter.

The wobble mechanism hub 25 at its inside facing the lateral surface of the gear shaft 23 has a tooth system 43. Adjoining the tooth system 43 of the wobble mechanism hub 25 is a cross-sectionally widened portion 47 of the gear shaft 23, which portion has a mating tooth system 45. When the portion 47 of the gear shaft 23 is moved by a non-illustrated displacement mechanism to the right in the direction of the wobble mechanism nub 25, me manug food system 45 OI one gear shaft 23 meshes in the tooth system 43 of the wobble mechanism hub 25, with the result that the wobble mechanism hub 25 co-rotates with the gear shaft 23 and the percussive mode is activated. When the portion 47 of the gear shaft 23 is displaced to the left, the mating tooth system 45 of the gear shaft 23 disengages from the tooth system 43 of the wobble mechanism hub 25, with the result that the wobble mechanism hub 25 is no longer driven by the gear shaft 23 and the percussive mode is therefore deactivated.

The gear shaft 23 terminates in the vicinity of the partition wall 5 and is rotatably supported there by means of a ball bearing 49.

Here, the, particularly in percussive mode, exbeme heat generation in the gear compartment 1 leads to a very high pressure, which is diverted into the motor compartment 3 by means of the measures described below. For said purpose, there is introduced into the gear shaft 23 a first channel 51, which extends in longitudinal direction and opens out at the end of the gear shaft 23 facing the partition wall 5. A second channel 53 in the interior of the gear shaft 23 extends in transverse direction relative to the longitudinal axis of the gear shaft 23 and

opens out into the first channel 51. The second, transversely extending channel 53 has an opening or, if it extends over the entire diameter of the gear shaft 23 (as illustrated in Figure 1), two openings in the lateral surface of the gear shaft 23. A cross section A-A shown in Figure 2 clarifies the position of the two channels 51 and 53.

In the exemplary embodiment illustrated in Figure l, the transversely extending second channel 53 opens out in the lateral surface of the gear shaft 23 below the plain bearing 41 of the wobble mechanism hub 25. Through the gap between the plain bearing 41 and the gear shaft 23 air may pass into the second channel 53 and, via the latter, into the longitudinally extending first channel 51. At the underside of the plain bearing 41 a recess 55 may be provided in the region of the opening OI the second channel 53. Said recess 55 pre-f:eraloly has a width extending beyond the opening of the second channel 53. Grease may namely then be deposited in the recess 55 outside of the opening of the second channel 53.

The grease deposited in the recess 55 lubricates the plain bearing 41.

In a departure from the exemplary embodiment illustrated in the drawings, a plurality of longitudinally extending channels and a plurality of transversely extending channels may be provided, wherein the transverse channel or channels need not necessarily extend below the wobble mechanism hub 25 but may also be disposed in a region of the gear shaft 23 not overlapped by the wobble mechanism hub 25. Furthermore, the channels 51, 53 of the pressure relief device are not tied to the provision of a wobble mechanism and/or to a wobble mechanism of the type described above.

In order to enable the air conveyed through the channels 51 and 53 to be transferred into the motor compartment 3, at least one through-opening 57 is situated in the partition wall 5, namely in the vicinity of the opening of the longitudinally extending first channel 51.

Where possible, however, no lubricant situated in the gear compel trident 1 should pass with the air through the channels 51, 53 and the throughopening 57 into the motor compartment 3. This is prevented very effectively in that the rotation of the gear shaft 23 causes the lubricant to be slung radially outwards, thereby keeping the lubricant away from the region of the opening(s) of the second channel 53. In case small quantities of lubricant do nevertheless pass through the channels 51, 53 and the through-opening 57 into the motor compartment 3, one or more lubricant-

absorbing filter elements 59 - preferably made of felt - may be disposed in front of the at least one through-opening 57 in the machine compartment 3. The filter element(s) 59 may be covered by an end shield 61 of the ball bearing 13 of the motor drive shaft 9. The end shield 61 is fastened e.g. by one or more screws 63 to the partition wall 5.

The ball bearings 13 and 49 for the drive shaft 9 and the gear shaft 23 may additionally be provided with sealing means (not shown in the drawings) in order to prevent the lubricant from escaping through the bearings into the motor compartment 3.

Claims

Claums 1. Hand tool machines with a pressure relief device between a motor

compartment (3) and a lubricant-containing gear compartment (1), wherein a drive shaft (9), which is driven by a motor (7) situated in the motor compartment (3), extends into the gear compartment (1) and, there, is in engagement with a gear shaft (23), which terminates in the vicinity of a partition wall (5), which separates the motor compartment (3) from the gear compartment (l) and is provided with at least one through- opening (57), characterized in that the pressure relief device comprises at least one channel (51, 53), which extends in the interior of the gear shaft (23) and opens out on the one hand into the gear compartment (1) and on the other hand in the vicinity of ibe at least one lid ough- opening (57) of ibe partition wall (5).
2. Hand tool machines according to claim 1 characterized in that at least one first channel (51) extending in longitudinal direction of the gear shaft (23) and at least one second channel (53) extending in transverse direction and opening into the first channel (51) are let into the gear shaft (23), wherein the at least one first channel (51) has an opening in an end of the gear shaft (23) facing the at least one through-opening (57) of the partition wall and the at least one second channel (53) has an opening in the lateral surface of the gear shaft (23) facing the gear compartment ( 1).
3. Hand tool machines according to one of claims 1 or 2 characterized in that the at least one channel (S 1, 53) has an opening below a wobble mechanism hub (25) supported on the gear shaft (23) and that in a bearing (41) provided between the wobble mechanism hub (25) and the geaI shaft (23) a recess (55) is provided, through which air may pass into the at least one channel (51, 53)
4. Hand tool machines according to one of claims 1 or 2, characterized in that one or more lubricant-absorbing filter elements (593 - preferably made of felt - are disposed in front of the at least one through-opening (57) in the machine compartment (3).
5. A hand tool machine substantially as herein described with reference to the accompanying drawings.