Drive cylinder unit for a power tool, and power tool

Abstract

A drive cylinder unit (1) for a power tool (2) with an impact mechanism (3), in particular a pneumatic impact mechanism (3), comprising a drive cylinder (4) axially movably mounted in a guide tube (23) between a front and a rear end position, the drive cylinder being fork-shaped at one end and forming two arms (5) each with a bearing bore (6) in which a bearing pin (7) is rotatably mounted, the bearing pin (7) being penetrated perpendicular to its longitudinal axis by a bore (8) for receiving a pin (9) of a swashplate bearing (10). The drive cylinder (4) is axially pre-tensioned towards the rear end position by means of a spring element (11). A power tool (2) with an impact mechanism (3), in particular a pneumatic impact mechanism (3), comprising a drive cylinder unit (1) according to the invention.

Description

[0001] The invention relates to a drive cylinder unit for a power tool with an impact mechanism, in particular a pneumatic impact mechanism, according to the preamble of claim 1. Furthermore, the invention relates to a power tool with an impact mechanism comprising a drive cylinder unit according to the invention.

[0002] The invention is primarily applicable to handheld power tools, in particular rotary hammers and / or demolition hammers. These tools have an impact mechanism for applying the necessary impact energy to the respective tool. State of the art

[0003] Power tools with an impact mechanism are well known. In a pneumatic impact mechanism, a drive cylinder and an impact piston are operatively connected via an air spring, so that an axial displacement of the drive cylinder causes an axial displacement of the impact piston. For this purpose, the drive cylinder and the impact piston are guided axially within a guide tube, which together with the drive cylinder forms a drive cylinder unit.

[0004] The axial displacement of the drive cylinder is achieved via an electrically driven shaft. To convert the rotary motion of the shaft into a translational motion of the drive cylinder, the drive cylinder is connected to the shaft via a coupling device.

[0005] An example of such a coupling device is described in DE 10 2020 207 591 A1. It comprises a pendulum rod which is connected at one end to a drive shaft via a pendulum bearing. At the other end, the pendulum rod is connected to a piston pin of a piston assembly, which is rotatably mounted in two spaced-apart piston arms of a piston body of the piston assembly. During operation, the pendulum rod moves relative to the piston arms.

[0006] Coupling devices of the aforementioned type are subject to wear and thus limit the service life of the power tool. Wear occurs particularly in the contact area between the moving parts of the coupling device and the drive cylinder unit due to friction. This can lead to defects, resulting in increased play. The increased play, in turn, causes vibrations and increases the stress in the contact areas, further accelerating wear. Particles, such as dust particles, that penetrate the contact area also exacerbate wear. As a consequence of progressive wear, the power tool eventually fails.

[0007] Based on the aforementioned prior art, the present invention aims to provide a drive cylinder unit for a power tool with an impact mechanism that is less prone to wear, thus increasing the service life of the power tool.

[0008] To solve the problem, the drive cylinder unit with the features of claim 1 is proposed. Advantageous embodiments of the invention are described in the dependent claims. Furthermore, a power tool with a coupling device according to the invention is specified. Disclosure of the invention

[0009] A drive cylinder unit for a power tool with an impact mechanism, in particular a pneumatic impact mechanism, is proposed. The unit comprises a drive cylinder axially movably mounted in a guide tube between a front and a rear end position. The drive cylinder is fork-shaped at one end and forms two arms, each with a bearing bore in which a bearing pin is rotatably mounted. The bearing pin is penetrated perpendicular to its longitudinal axis by a bore for receiving a pin of a swashplate bearing. According to the invention, the drive cylinder is axially preloaded towards the rear end position by means of a spring element.

[0010] The axial preload of the drive cylinder towards the rear end position eliminates play between the moving parts of the drive cylinder unit. As a result, vibrations and the high loads caused by these vibrations in the contact areas are reduced. Consequently, wear is minimized and the service life of the power tool incorporating the drive cylinder unit is extended.

[0011] The spring element used for axial preloading of the drive cylinder can, in principle, be of any design. This means that virtually any elastic component can be used as a spring element. For example, the spring element can be a coil spring or a leaf spring.

[0012] According to a preferred embodiment of the invention, the spring element is designed as a tension spring, in particular as a helical tension spring. Such spring elements are simple and inexpensive to manufacture, so that the invention can be implemented cost-effectively. In addition, the axial preload force can be very easily adjusted by the design of the helical tension spring.

[0013] Furthermore, it is proposed that the spring element be connected to the drive cylinder via a sheet metal part. This sheet metal part facilitates the connection between the spring element and the drive cylinder. Preferably, the sheet metal part is arranged between the two arms of the drive cylinder and held in place by the bearing pin in the drive cylinder. This eliminates the need for additional connecting or fastening means to fix the sheet metal part to the drive cylinder, thus simplifying its assembly. In this arrangement, the sheet metal part can also replace two washers that are typically placed between the drive cylinder and the pin held in the bearing pin to reduce wear in the contact area.

[0014] Preferably, the sheet metal part is essentially U-shaped and has an opening in each of its two parallel side walls for receiving the bearing bolt. The essentially U-shaped sheet metal part can be inserted between the two arms of the drive cylinder in such a way that the two parallel side walls of the sheet metal part abut the arms of the drive cylinder and the openings formed in the side walls cover the bearing bores formed in the arms. The sheet metal part can then be fixed in the drive cylinder by subsequently inserting the bearing bolt into the bearing bores of the arms and into the openings in the side walls of the sheet metal part. In this arrangement, the two parallel side walls also eliminate the need for the two washers that are usually required.

[0015] Furthermore, the parallel side walls of the sheet metal part preferably have additional openings at their end facing the spring element for inserting, in particular screwing in, a spring end of the spring element. Advantageously, these additional openings are formed in sections of the two side walls that are recessed relative to the outer surface of the two parallel side walls. This ensures that the spring end of the spring element does not protrude laterally beyond the sheet metal part and come into contact with the arms of the drive cylinder.

[0016] Furthermore, preferably, the two parallel side walls of the sheet metal part are connected by a rear wall which has a recess at the level of the spring element for inserting a tool through the sheet metal part to or into the spring element. Inserting the tool facilitates the mounting of the spring element to the housing. For example, the housing-side mounting can be achieved using a screw as a fastener. A screwdriver can then be inserted through the rear recess of the sheet metal part into the spring element to screw the screw into a receptacle on the housing.

[0017] Furthermore, a power tool with an impact mechanism, in particular a pneumatic impact mechanism, is proposed, wherein the impact mechanism comprises a drive cylinder unit according to the invention. The drive cylinder unit according to the invention reduces vibrations and thus wear in the contact areas of the moving parts. Accordingly, the service life of the power tool is increased. Preferably, the spring element is attached to a housing at its end facing away from the drive cylinder by means of a screw, with a washer preferably arranged between the screw and the housing. The washer allows the spring end to be clamped between the screw and the housing, so that it is securely held against the housing. Alternatively, the spring element can be connected to the drive cylinder via a sheet metal part.The sheet metal part can be U-shaped and have two parallel side walls, each with an opening for receiving a bearing bolt of the drive cylinder unit. The sheet metal part can then be fixed in the drive cylinder via the bearing bolt.

[0018] Preferably, a pin of a swashplate bearing is received in the bore of the bearing pin, via which the drive cylinder is operatively connected to a shaft arranged parallel to the drive cylinder. The rotary motion of the shaft can thus be converted into a translational motion of the drive cylinder.

[0019] Furthermore, the swashplate bearing preferably comprises an inner ring arranged on the shaft and an outer ring supported on the inner ring by bearing balls, with the pin arranged on the outer circumference of the outer ring. The bearing of the outer ring on the inner ring by bearing balls allows the outer ring to wobble relative to the inner ring, so that the pin connected to the outer ring performs a kind of pendulum motion. This pendulum motion moves the drive cylinder back and forth.

[0020] A preferred embodiment of the invention is described in more detail below with reference to the accompanying drawings. These show: Fig. 1 a longitudinal section through a power tool according to the invention with a drive cylinder unit according to the invention, Fig. 2 an exploded view of the spring element for axial preloading of the drive cylinder of the drive cylinder unit including sheet metal part and fastening means, Fig. 3 a side view of the sheet metal part of the Figure 2 with mounted spring element, Fig. 4 a perspective view of the sheet metal part including spring element during connection with the drive cylinder of the drive cylinder unit and Fig. 5 a perspective view of the drive cylinder after connection with the sheet metal part including spring element. Detailed description of the drawings

[0021] The Figure 1A section of an electric tool 2 according to the invention with a pneumatic impact mechanism 3 is shown. The pneumatic impact mechanism 3 has a drive cylinder unit 1 according to the invention, comprising a guide tube 27 in which a drive cylinder 4 is axially movably mounted between a front and a rear end position. The drive cylinder 4 is operatively connected to an impact piston 24 via an air spring 23, so that an axial displacement of the drive cylinder 4 causes an axial displacement of the impact piston 24. The impact piston 24 in turn acts on a striker 25 and this on a [missing element] in the Figure 1 tool not shown.

[0022] The axial displacement of the drive cylinder 4 is effected by means of an electrically driven shaft 19, which is an intermediate shaft connected to a motor shaft 26. To convert the rotary motion of the shaft 19 into a translational motion of the drive cylinder 4, a swashplate bearing 10 with a pin 9 is arranged on the shaft 19. The pin 9 is received at its end facing away from the swashplate bearing 10 in a bore 8 of a bearing bolt 7, which is rotatably mounted in the drive cylinder 4 via bearing bores 6. For this purpose, the drive cylinder 4 has a forked end, forming two arms 5 in which the bearing bores 6 are arranged. The swashplate bearing 10 has an inner ring 20, which is arranged on the shaft 19 and non-rotatably connected to the shaft 19.An outer ring 22 is mounted on the inner ring 20 via bearing balls 21, and the pin 9 is attached to the outer ring 22, so that the pin 9 is arranged radially with respect to the outer ring 22. Via the swashplate bearing 10, the pin 9 is set into a pendulum motion when the shaft 19 rotates, which in turn moves the drive cylinder 4 back and forth axially between its front and rear end positions.

[0023] In the illustrated drive cylinder unit 1 according to the invention, the drive cylinder 4 is axially preloaded towards the rear end position by means of a spring element 11. The preload eliminates the play between the moving parts, thus reducing vibrations and consequently wear in the contact areas. For the axial preloading of the drive cylinder 4 towards the rear end position, the spring element 11 is designed as a helical tension spring. The helical tension spring is connected to the drive cylinder 4 via a sheet metal part 12 on one side and to a housing 17 via a screw 16 and a washer 18 on the other.

[0024] As in particular the Figure 2As can be seen, the sheet metal part 12 is essentially U-shaped. The sheet metal part 12 thus has two parallel side walls 13 and a rear wall 28 connecting them. A recess 29 is provided in the rear wall 28 through which a tool (not shown) can be inserted into the spring element 11. With the aid of the tool, the screw 16 can be screwed into a corresponding receptacle in the housing 17. The spring end of the spring element 11 facing the housing 17 is clamped between the screw 16 and the housing 17 by the washer 18 (see also Figure 3 The other end of the spring element 11 is inserted or screwed into openings 15 in the sheet metal part 12. Furthermore, the sheet metal part 12 has openings 14 in the area of ​​the two parallel side walls 13, which, during assembly of the sheet metal part 12, can be aligned with the bearing bores 6 of the two arms 5 of the drive cylinder 4 (see Figure 4 ). By subsequently inserting the bearing bolt 7 into the bearing bores 6 of the arms 5 and into the openings 14 of the two side walls 13 of the sheet metal part 12, the sheet metal part 12 can then be fixed in the drive cylinder 4. Figure 5 shows the drive cylinder 4 with the sheet metal part 12 inserted and fixed. Reference symbol list

[0025] 1 Drive cylinder unit 2 Power tool 3 Impact mechanism 4 Drive cylinder 5 Arm 6 Bearing bore 7 Bearing bolt 8 Bore 9 Pin 10 Swash plate bearing 11 Spring element 12 Sheet metal part 13 Side wall 14 Opening 15 Opening 16 Screw 17 Housing 18 Washer 19 Shaft 20 Inner ring 21 Bearing ball 22 Outer ring 23 Air spring 24 Impact piston 25 Bump stop 26 Motor shaft 27 Guide tube 28 Back panel 29 Recess

Claims

1. Drive cylinder unit (1) for a power tool (2) with an impact mechanism (3), in particular a pneumatic impact mechanism (3), comprising a drive cylinder (4) axially movable between a front and a rear end position in a guide tube (27), which is fork-shaped at one end and forms two arms (5) each with a bearing bore (6) in which a bearing pin (7) is rotatably mounted, wherein the bearing pin (7) is penetrated perpendicular to its longitudinal axis by a bore (8) for receiving a pin (9) of a swashplate bearing (10), characterized by the fact that the drive cylinder (4) is axially pre-tensioned in the direction of the rear end position by means of a spring element (11).

2. Drive cylinder unit (1) according to claim 1, characterized by the fact that the spring element (11) is designed as a tension spring, in particular as a helical tension spring.

3. Drive cylinder unit (1) according to claim 1 or 2, characterized by the fact thatthe spring element (11) is connected to the drive cylinder (4) via a sheet metal part (12), wherein preferably the sheet metal part (12) is arranged between the two arms (5) of the drive cylinder (4) and is held in the drive cylinder (4) via the bearing bolt (7).

4. Drive cylinder unit (1) according to claim 3, characterized by the fact that the sheet metal part (12) is essentially U-shaped and has an opening (14) in the area of ​​two parallel side walls (13) for receiving the bearing bolt (7).

5. Drive cylinder unit (1) according to claim 4, characterized by the fact that the parallel side walls (13) of the sheet metal part (12) have further openings (15) at their end facing the spring element (11) for inserting, in particular for screwing in, a spring end of the spring element (11).

6. Drive cylinder unit (1) according to claim 4 or 5, characterized by the fact thatthe two parallel side walls (13) of the sheet metal part (12) are connected via a rear wall (28) which has a recess (29) at the level of the spring element (11) for inserting a tool through the sheet metal part (12) to or into the spring element (11).

7. Power tool (2) with a percussion mechanism (3), in particular a pneumatic percussion mechanism (3), comprising a drive cylinder unit (1) according to one of the preceding claims, wherein preferably the spring element (11) is attached to a housing (17) at its spring end facing away from the drive cylinder (4) by means of a screw (16), wherein furthermore preferably a washer (18) is arranged between the screw (16) and the housing (17).

8. Power tool (2) according to claim 7, characterized by the fact thatin the bore (8) of the bearing bolt (7) a pin (9) of a swashplate bearing (10) is received, via which the drive cylinder (4) is operatively connected to a shaft (19) arranged parallel to the drive cylinder (4).

9. Power tool (2) according to claim 7 or 8, characterized by the fact that the swashplate bearing (10) has an inner ring (20) arranged on the shaft (19) and an outer ring (22) mounted on the inner ring (20) via bearing balls (21), on the outer circumferential side of which the pin (9) is arranged.

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