Machine tool with a chamber for lubricanting agent and a pressure equalisation device for said chamber

[0001] The present invention is directed to a machine tool having a compartment containing lubricant and a device for compensation of the pressure in the compartment according to the definition of the species in claim 1.

[0002] A machine tool forming the species, in particular a hand-operated hammer drill, is known from German patent 42 31 987.0 A1. The hammer drill has a driver motor, arranged within a motor compartment of a housing, having a motor shaft that extends through a housing section into a gear compartment, where it engages, via an integral pinion, with a gear unit for driving a tool-holding fixture. The gear compartment is provided with a pressure-compensation device that reduces a pressure, resulting during operation within the gear compartment, down to that of the atmosphere or of the motor compartment. The pressure-compensation device has a bore hole leading from the gear compartment to the outside or to the motor compartment and a rotary element, driven so that it is constantly rotating, in the form of a cover into which a passage is introduced.

[0003] The invention is directed to a machine tool, in particular to a hand-operated hammer drill, having a compartment containing lubricant and a pressure-compensation device of the compartment in the area of a bearing of a component able to be driven so as to allow rotation.

[0004] It is proposed that the bearing form at least a part of a lubricant seal of the pressure-compensation device via which a pressure in the compartment may be compensated. Additional components, space, weight, assembly effort and costs can be saved. This can be achieved in a particularly inexpensive and uncomplicated manner in terms of design by using a lubricant seal implemented as a groove seal, which is arranged between the bearing and a bearing seat, it being possible to arrange the groove seal between an outer ring and/or an inner ring of the bearing and a bearing seat. Furthermore, it is conceivable that the lubricant seal, which is simultaneously usable for pressure compensation, is formed by a channel through the bearing, for example, a channel through a cage of a roller bearing and/or through bearing sealing washers fastened appropriately to the bearing.

[0005] In another embodiment of the invention, it is proposed that the bearing and the bearing seat be formed of different materials having different coefficients of thermal expansion and that these be used to create the lubricant seal; specifically, it is beneficial that the bearing seat is formed of aluminum or an aluminum alloy and the bearing is formed of steel. If an outer bearing seat is formed of a material having a greater coefficient of thermal expansion than the bearing, as is beneficially the case for an aluminum bearing seat and a steel bearing, the bearing seat expands more when heated up and a gap between the bearing and bearing seat is created that may beneficially be used as a groove seal. Other material combinations that appear suitable to one skilled in the art are also conceivable in place of an aluminum-steel combination.

[0006] In this context, to prevent an undesired rotary movement of the bearing within the bearing seat, it is beneficially fixed in position in the circumferential direction within the bearing seat. This may be accomplished using various non-positive fit, positive fit and/or integral connections, for example, via a pin connection, a spring/groove connection and/or a positive-fit connection, in that an outer ring of the bearing has an outer contour that deviates from a round outer contour, etc. If the bearing is implemented as a locating bearing, and a component fixing the bearing in position in an axial direction is used to fix the bearing in position in the circumferential direction, additional components, space and assembly effort may advantageously be saved. For example, this can be achieved using a clasping component that holds the bearing in position in an axial direction, is torsionally fixed and has a projection that engages in a recess of an outer ring of the bearing.

[0007] In another embodiment of the invention, it is proposed that a pressure-compensation channel be introduced into a bearing surface of the bearing and/or into a bearing surface of the bearing seat. A beneficial cross-section for the pressure compensation may be achieved with simplicity of design, and simultaneously a groove seal and/or labyrinth seal may be realized.

[0008] The pressure-compensation channel in this case may be implemented, for example, in the form of an axial groove in a shaft, in an inner ring of a roller bearing, in an outer ring of a roller bearing and/or in a component forming an outer bearing seat, etc.

[0009] If the pressure-compensation channel is at least partially formed by a threaded-type recess, a beneficial labyrinth effect or labyrinth seal and, in addition, a recirculating effect may be achieved, which is done by coordinating the direction of threading and direction of rotation with each other. The threaded-type recess may in turn be introduced into the bearing and/or into a bearing seat. If the pressure-compensation channel opens through into at least one annular groove, it may be produced especially simply and economically, for example in one lathe operation, starting from a first annular groove and opening through into a second annular groove.

[0010] A filter element is beneficially connected in series with the lubricant seal formed at least partially by the bearing. While simultaneously ensuring the pressure compensation function, the sealing effect can be improved. A felt gasket, which can be manufactured especially economically and has proven beneficial characteristics, is especially suitable as a filter element. The felt element may be formed by various fibrous materials deemed appropriate by one skilled in the art, in particular such as animal hairs, plant fibers and/or synthetic fibers, etc. In order to save on additional holding components, the filter element is beneficially held in position by a component that holds a bearing in place.

[0011] Furthermore, in a space-conserving design, a beneficially large filter volume can be achieved, in that at least two radial pressure-compensation channels branch off from the bearing, and in particular in that the bearing is surrounded by an annular filter element, and the pressure-compensation channels open out from the bearing radially outwardly at the filter element.

[0012] The design approach of the present invention may be used in all machine tools deemed suitable by one skilled in the art, in particular in hand-operated machine tools, for example, grinders, saws, milling cutters, planers, drills, chisel hammers, etc.

[0013] Further advantages result from the following description of the drawings. The drawings show exemplary embodiments of the present invention. The drawing, the specification and the claims contain numerous features in combination. One skilled in the art will also expediently examine the features individually, and combine them to form further useful combinations.

[0014] Shown are:

[0015] FIG. 1 a schematically illustrated hammer drill from the side,

[0016] FIG. 2 section of FIG. 1 marked II,

[0017] FIG. 3 a variant of FIG. 2 having pressure compensation channels running radially outwardly and

[0018] FIG. 4 a variation of FIG. 2 having a threaded-type pressure-compensation channel.

[0019] FIG. 1 shows a schematically illustrated hammer drill having a housing 104 in which a drive motor 58 is supported within a motor compartment 56. A tool holder 60 and a drill bit 62 secured in tool holder 62 are able to be driven by drive motor 58, via a gear unit (not shown) arranged within a gear compartment 10, in a manner allowing rotation and striking. The hammer drill may be guided using two hand grips 64, 66 that extend essentially perpendicular to an operating direction, one handgrip 64 on a side facing away from bit 62 being integrally molded onto housing 104, and one handgrip 66 on a side facing drill bit 62 being fastened to housing 104.

[0020] Drive motor 58 has a drive shaft 68 on which a fan impeller 80 is arranged in a torsionally fixed manner within motor compartment 56 (FIG. 2). Drive shaft 68 projects from motor compartment 56 through a partition wall 70 made of aluminum into gear compartment 10 and is mounted in partition wall 70 so that it is able to rotate within a ball bearing 48.

[0021] An outer ring 72 of ball bearing 48 is connected by a press-fit to partition wall 70, and its inner ring 74 is connected in a rotatably-fixed manner to drive shaft 68 by a press-fit. Ball bearing 48 is implemented as a locating bearing, and specifically it is supported axially in the direction of gear compartment 10 against a shoulder 78 in partition wall 70, and is axially supported in the direction of motor compartment 56 against a retaining ring 32 affixed in partition wall 70. Gear compartment 10, filled with lubricant, is sealed airtight and lubricant-tight at ball bearing 48 via a sealing washer 76 in the direction of motor compartment 56.

[0022] Integrally molded on one end of drive shaft 68 projecting into gear compartment 10 is a pinion 82 via which drive shaft 68 meshes with a gear wheel (not shown) arranged in a rotationally fixed manner on an intermediate shaft 20 of the gear unit. Intermediate shaft 20 is rotationally mounted via a ball bearing 16 in partition wall 70. Ball bearing 16 is implemented as a locating bearing, and specifically is axially supported in the direction of motor compartment 56 against a shoulder 88 in partition wall 70, and is axially supported in the direction of gear compartment 10 by a retaining element (not shown) that is fastened in partition wall 70.

[0023] According to the present invention, ball bearing 16 forms a part of a lubricant seal 24 of a pressure-compensation device 12 via which the pressure in gear compartment 10 is able to be equalized, that is, a buildup of pressure in gear compartment 10 due to heating during operation of the hammer drill may reliably be prevented. Ball bearing 16, with its inner ring 84, is connected in a rotatably-fixed manner to intermediate shaft 20 by a press-fit.

[0024] Moreover, ball bearing 16 is mounted, with its steel outer ring 86, via a sliding fit in a bearing seat 28 formed by partition wall 70. Then the hammer drill is operated, ball bearing 16 and partition wall 70 heat up. Because of their differing coefficients of thermal expansion, partition wall 70 made of aluminum expands to a greater extent than ball bearing 16 made of steel. Between outer ring 86 of ball bearing 16 and partition wall 70 there arises a gap that functions as lubricant seal 24 or as a groove seal of pressure-compensation device 12, via which a pressure is able to be equalized. A bearing gap between inner ring 84 and outer ring 86 of ball bearing 16 is sealed airtight and lubricant-tight by a sealing ring 90.

[0025] To prevent an undesired rotary movement of outer ring 86 of ball bearing 16 within partition wall 70, the outer ring is connected in the circumferential direction in a rotatably-fixed manner by a positive-fit connection to partition wall 70 via the retaining element axially holding ball bearing 16 in position in the direction of gear compartment 10.

[0026] A filter element 46 formed by a felt ring is connected in series with the groove seal created between outer ring 86 and partition wall 70. Filter element 46 is placed in a recess 94 in partition wall 70, the recess surrounding ball bearing 48 in a ring shape, and is held in its place by retaining ring 32. Introduced into partition wall 70, coaxially with respect to intermediate shaft 20, is a bore hole 92 that is covered in the direction of motor compartment 56 by filter element 46 and via which a pressure difference between gear compartment 10 and motor compartment 56 may be equalized.

[0027] FIG. 3 shows one variant of FIG. 2 having a pressure-compensation device 14. Components that essentially remain the same are always numbered using the same reference numbers in the illustrated exemplary embodiments. Moreover, concerning features and functions that remain the same, refer to the description for the exemplary embodiment in FIGS. 1 and 2. The following description is essentially limited to the differences from the exemplary embodiment in FIGS. 1 and 2.

[0028] A drive shaft 22 of a drive motor 58 is supported via a ball bearing 18 in a partition wall 106. Ball bearing 18, according to the present invention, forms a part of a lubricant seal 26 of pressure-compensation device 14 via which the pressure in a gear compartment 10 is able to be compensated. Ball bearing 18, with its inner ring 96, is connected in a rotatably-fixed manner by a press fit to drive shaft 22. Moreover, ball bearing 18, with its steel outer ring 98, is mounted via a sliding fit in a bearing seat 30 formed by partition wall 106. When the hammer drill is operated, ball bearing 18 and partition wall 106 heat up. Because of their differing coefficients of thermal expansion, partition wall 106 made of aluminum expands to a greater extent than ball bearing 18 made of steel. Between outer ring 98 of ball bearing 18 and partition wall 106 there arises a gap that functions as a lubricant seal 26 or as a groove seal of pressure-compensation device 14 via which a pressure is able to be compensated. A bearing gap between inner ring 96 and outer ring 98 of ball bearing 18 is sealed airtight and lubricant-tight via a sealing ring 90.

[0029] To prevent an undesired rotary movement of outer ring 98 of ball bearing 18 within partition wall 106, the outer ring is connected in the circumferential direction in a rotatably-fixed manner by a form-fitting connection to partition wall 106 via a retaining ring 32 which axially holds ball bearing 18 in position in the direction of gear compartment 10.

[0030] A filter element 46 formed by a felt ring is connected in series with the groove seal created between outer ring 98 and partition wall 106. Filter element 46 is placed in a recess 94 in partition wall 106, the recess surrounding ball bearing 18 in a ring shape, and is held in its place by retaining ring 32. Extending from outer ring 98 of ball bearing 18 are four radial pressure-compensation channels 50, 52 which are distributed evenly over the periphery, are introduced into partition wall 106 and open out radially outwardly at filter element 46.

[0031] An intermediate shaft 20 of a gear unit (not shown) in gear compartment 10 is supported via a ball bearing 100 in intermediate wall 106. Partition wall 106 is sealed off, in the area of ball bearing 100, from gear compartment 10 in the direction of motor compartment 56.

[0032] In an exemplary embodiment in FIG. 4, an intermediate shaft 54 is rotationally mounted via a ball bearing 36 in a partition wall 70. Ball bearing 36, according to the present invention, forms a part of a lubricant seal 38 of a pressure-compensation device 34 via which the pressure in a gear compartment 10 is able to be compensated. Ball bearing 36, with its inner ring 84, is arranged in a rotatably-fixed manner on a bearing seat 40 of intermediate shaft 54 by a press fit. Moreover, ball bearing 36, with its steel outer ring 86, is mounted via press fit in a bearing seat 102 formed by partition wall 70.

[0033] Introduced into a bearing surface of bearing seat 40 is a pressure-compensation channel 42, formed by a threaded-type recess that opens through, counter to a venting direction of gear compartment 10, into an annular groove 44. Pressure-compensation channel 42 forms a labyrinth seal and, in addition, has a lubricant-recirculating effect during operation. A bearing gap between inner ring 84 and outer ring 86 of ball bearing 36 is sealed airtight and lubricant-tight via a sealing ring 90.

[0034] 10 compartment

[0035] 12 pressure-compensation device

[0036] 14 pressure-compensation device

[0037] 16 bearing

[0038] 18 bearing

[0039] 20 component

[0040] 22 component

[0041] 24 lubricant seal

[0042] 26 lubricant seal

[0043] 28 bearing seat

[0044] 30 bearing seat

[0045] 32 component

[0046] 34 pressure-compensation device

[0047] 36 bearing

[0048] 38 lubricant seal

[0049] 40 bearing seat

[0050] 42 pressure-compensation channel

[0051] 44 annular groove

[0052] 46 filter element

[0053] 48 bearing

[0054] 50 pressure-compensation channel

[0055] 52 pressure-compensation channel

[0056] 54 component

[0057] 56 motor compartment

[0058] 58 drive motor

[0059] 60 tool holder

[0060] 62 bit

[0061] 64 hand grip

[0062] 66 hand grip

[0063] 68 drive shaft

[0064] 70 partition wall

[0065] 72 outer ring

[0066] 74 inner ring

[0067] 76 sealing washer

[0068] 78 shoulder

[0069] 80 fan impeller

[0070] 82 pinion gear

[0071] 84 inner ring

[0072] 86 outer ring

[0073] 88 shoulder

[0074] 90 sealing ring

[0075] 92 bore hole

[0076] 94 recess

[0077] 96 inner ring

[0078] 98 outer ring

[0079] 100 ball bearing

[0080] 102 bearing seat

[0081] 104 housing

[0082] 106 partition wall