GB2286981A

GB2286981A - Impact screwdriver

Info

Publication number: GB2286981A
Application number: GB9502281A
Authority: GB
Inventors: Juergen Gairing
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1994-03-03
Filing date: 1995-02-06
Publication date: 1995-09-06
Anticipated expiration: 2015-02-06
Also published as: ITMI950312A0; ITMI950312A1; GB9502281D0; GB2286981B; DE4406881A1; JPH07251381A; IT1273947B

Description

1 Impact screw driver

Prior art

2286981 The invention proceeds from an impact screw driver of the type according to Claim 1. Already known in the art is an impact screw driver (DE-GM 17 96 182) with a drive shaft having on its circumference a V-shaped recess for an intermediate element. The groove-type recess, which is bounded axially at both ends, can only be produced through an elaborate cutting process which is very costly, particularly in large-scale production.

Advantages of the invention By comparison, the impact screw driver according to the invention, having the characteristics according to Claim 1, offers the advantage that it possesses a recess for guiding the intermediate element which can be produced without cutting. If the recess is produced by, for example, extrusion, then in addition to reduced production costs it is also possible to achieve increased wear resistance.

Advantageous further developments and improvements of the impact screw driver specified in Claim 1 are also possible through the measures stated in the dependent claims.

2 Drawing An embodiment example of the invention is shown in the drawing and explained in greater detail in the following description. Figure 1 shows a section through an impact mechanism of an impact screw driver and Figure 2 shows a view of a drive shaft of the screw driver.

Description of the embodiment example

In Figure 1, reference 10 denotes an electrically powered impact screw driver.with a casing 11 within which there is a drive motor 12. A motor shaft 13 of the drive motor 12 is coupled to a drive shaft 15 through a gear 14. A drive shaft 16, the end of which is equipped with a toolholding fixture 16a for holding, for example, a screw driver bit, connects to the drive shaft 15. Between the drive shaft 15 and the drive shaft 16 there is an impact mechanism 17. The drive shaft 15 is bearing- mounted by means of a journal 18, and with sliding play, within an end of the drive shaft 16 remote from the tool-holding fixture 16a. The drive shaft 15 is also mounted in a rolling bearing 19 so that it is capable of rotation relative to the housing 11. The drive shaft 15 and the drive shaft 16 are in alignment with each other and are caDable of being rotationally coupled by means of an impact element 20. The impact element 20 is approximately tubular in form and is centrally penetrated by the drive shaft 15. The impact element 20 is bearingmounted on the drive shaft 15 so that it is capable of rotation and axial displacement. The impact element 20 is subjected to spring force in the direction of the drive shaft 16 by an impact mechanism spring 21. The other end of the impact mechanism spring 21 is solidly mounted to the casing by means of a disc bearing 22 and an axial bearing 23. The end of the impact element 20 which faces the drive v 3 shaft 16 has two claws 24, disposed at an angle of 180 degrees relative to each other, which engage axially with two wings 25 of the drive shaft 16 which project radially outwards.

Torque is transmitted from the drive shaft 15 to the impact element 20 through two intermediate elements 26, in the form of balls, which are offset at an angle of 180 degrees. The drive shaft 15 possesses a shaft collar 27 with recesses 28 for the intermediate elements 26 located on the end which is remote from the drive shaft 16. The recesses 28 are to be considered as variations of an initial cylindrical shape of the shaft collar 27, which is indicated by the broken line in Figure 2.

The recesses 28, only one of which is shown in Figure 1, each form a guideway 29a, 29b, running axially in an approximate V shape on an annular shoulder of the shaft collar 27, the tip of the V pointing towards the drive shaft 16. Two corresponding guideways 31 forming a V shape in the opposite direction are formed on the inside 30 of the front end of impact element 20. one of these is indicated in Figure 1 by a broken line. Due to the spring force of the impact mechanism spring 21, the impact element 20 is forced against the intermediate elements 26 in such a way that the -atter bear on the guideways 29a, 29b and 31 and prevent further axial displacement of the impact element 20.

The drive shaft 15 is shown in greater detail in Figure 2. The end 32 of the drive shaft 15 which faces the gear 14 is toothed, for the purpose of introducing a driving torque. Formed at the opposite end is the shaft journal 18. Located between them is the shaft collar 27 possessing, on the side remote from the journal 18, the recesses 28 forming the guideways 29a, 29b. The guideway 29b shown partially broken in the lower half of the section in Figure 2 has an approximately groove-shaped cross- section with a radius 4 which corresponds approximately to a rolling radius of the intermediate elements 26. Between the two grooves 28 there extends axially a ridge 33 which separates the two guideways 29a, 29b which are offset relative to each other. The recesses 28 thus open axially at one end, in a direction away from the shaft collar 27.

The formation of the recesses 28 according to the invention renders possible the production of the guideways 29a, 29b by means of a noncutting casting-and forming or forming production method, for example precision casting or extrusion. Since the forming production method, in particular, produces a favourahle fibre orientation in the workpiece concerned, the wear resistance of the guideways 29a, 29h can be increased.

The impact mechanism operates as follows. When the impact screw driver 10 is in operation, the drive shaft 15 is driven in continuous rotation by the electric motor 12 through the gear 14. When the drive shaft 16 is unloaded, it is also rotationally driven through the intermediate elements 26, the impact element 20, the claws 24 and the wings 25. When the torque on the drive shaft 16 exceeds a value which depends particularly on the prestress of the impact mechanism spring 21, the drive shaft 15 and the impact element 20 can twist against each other, causing the intermediate elements 26 to roll out of the initial position shown in Figure I along the oppositely disposed V-shaped guideways 29a or 29b and 31, the overlapping sections of the guideways 29a or 29b and 31 being forced apart. The impact element 20 is subjected to a forced axial stroke motion against the spring force of the impact mechanism spring 21. Disengagement of the claws 24 from the wings 25 releases the rotational closure between the imnact element 20 and the drive shaft 16, enabling the impact element 20 and the drive shaft 16 to twist against each other. The claws 24 then move, in the direction of the circumference, past the wings 11 K which project radially outwards. Following passage of the wings 25 the claws 24 of the impact element 20, which are forced axially forward by the impact mechanism spring 21, engage between the wings 25. Due to the difference in rotational speed between the impact element 20 and the drive shaft 16, the claws 24 are brought under momentum to bear laterally on the wings 25, which are now offset by 180 degrees, the centrifugal mass of the impact element 20 causing a rotary impact to be transmitted to the drive shaft 16. The process is then repeated accordingly, with the impact element 20 being again axially displaced by the intermediate elements 26.

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Claims

1. Impact screw driver with an impact mechanism (17), having a drive shaft (15), which is rotationally driven by means of a drive motor (12), and an impact element (20) which is capable of axial displacement on the drive shaft (15) and is guided so as to be capable of rotation relative to it, there being disposed between the drive shaft (15) and the impact element (20) one or more intermediate elements (26) which couple these parts (15, 20) and the impact element (20) being subjected axially at one end by an impact mechanism spring (21) to spring force towards the intermediate element (26), and the one or more intermediate elements (26) being disposed in one or more recesses (28), disposed on the circumference of the drive shaft (15) and forming an axial V shape, characterized in that the drive shaft (15) possesses a shaft collar (27) and the one or more V-shaped recesses (28) of the drive shaft (15) open axially on an annular shoulder of the shaft collar (27).

2. Impact screw driver according to Claim 1, characterized in that the one or more recesses (28) on the annular shoulder of the shaft collar form a guideway (29a,; 29b) for (26).

Lhe one or more intermediate elements

3. Impact screw driver according to Claim 2, characterized in that the guideway (29a; 29b) has a groove-shaped crosssection.

k 7

4. Impact screw driver according to any one of the preceding Claims, characterized in that the one or more intermediate elements (26) are in the form of balls.

5. Impact screw driver according to any one of the preceding Claims, characterized in that the one or more recesses (28) of the drive shaft (15) are produced by means of a non-cutting production process, particularly extrusion.

6. Impact screw driver according to Claim 2, characterized in that there are provided on the shaft collar (27) two recesses (28), disposed at 180 degrees relative to each other, which are constructed as guideways (29a, 29b) for two intermediate elements which are offset by 180 degrees.

7. Impact screw driver according to Claim 6, characterized in that the two guideways (29a, 29b) are separated from each other by a ridge (33) extending axially.

8. An impact screw driver substantially as herein described with reference to the accompanying drawing.