Advantageous developments and improvements of the impact screwdriver
specified in Claim 1 are possible by means of the measures outlined in the subclaims.
Drawing An exemplary embodiment of the invention is illustrated in the drawing and is explained in more detail in the following description. Figure 1 shows a section through an impact screwdriver, Figures 2 to 4 each show a schematic illustration of an impact mechanism in various impact mechanism positions, and Figure 5 shows a section through the impact mechanism on the line V-V in Figure 2.
Description of the exemplary embodiment is An impact screwdriver which is designated by 10 in Figure 1 has a housing 11 in which a drive motor 12 is accommodated. A drive shaft 13 of the drive motor 12 is coupled in a rotationally locked manner via a pinion 14 and a gearbox 15 to an input shaf t 16 of an impact mechanism 17. The impact mechanism 17 has an output shaft 18 on the other side, whose end facing away f rom the impact mechanism 17 projects out of the housing 11 of the impact screwdriver 10 and is fitted there with a tool holder 19 for a screwdriver tool, which is not illustrated in more detail.
The drive motor 12 is designed as an electric motor, in particular as an electronically commutated motor, and can be driven via electrical connecting leads 20, 21. The housing 11 forms a handle 23 which points approximately radially away from a drive axis 22. Accom- modated in the handle 23 is a pressure trigger 24 by means of which the drive motor 12 can be switched on and off via a switching device 25. Seated at the end of the handle 23 facing away from the drive motor 12 is an accumulator 26 which supplies the drive motor 12 with electrical drive energy and, for this purpose, is connected via electrical connecting leads, which are not shown in more detail, to the drive motor 12 and to the switching device 25.
The input shaft 16 of the impact mechanism 17 f orms an approximately cylindrical rotation body 13 which is provided with an axial hole 31 for accommodation of the output shaft 18, and with a radial hole 32 for accommodation of a reciprocating- action piston 33. For its part, the reciprocating- action piston 33 has an axial through-hole 34 through which the output shaft 18 passes. A high-pressure chamber 35 and a low- pressure chamber 36 are constructed within the rotation body 30. The interior of the rotation body 30 is filled with a pressure medium, f or example a hydraulic oil. The interior of the rotation body 30 is closed in a scaled manner to the exterior by a cover 38 on an opening of the radial hole 32 and by scaling means 39 on the output shaft 18. There is an operative connection between the reciprocating-action piston 33 and the output shaft 18, via a cam gear 40.
During operation of the drive motor 12. the input shaf t 16 and thus the rotation body 30 are initially driven in a rotating manner via the step-up gearbox 15.
As a result of the friction forces, the output shaft 18 is in this case also driven in a rotating manner. As soon as a screw moment which is picked off on the tool holder 19 exceeds the friction moment, the output shaft 18 and the input shaft 16 or the rotation body 30 can rotate with respect to one another. The output shaft 18, which is connected to the screwdriver tool then rotates more slowly than the rotation body 30, which is rotating, for example, in the direction of the arrow 50 (Figure 2), with the reciprocating-action piston 33.
As can be seen f rom Figure 2, the cam gear 40 comprises a control cam 51, which is firmly connected to the output shaft 18, and a profiled control surface 52, which is arranged within the through-hole 34 on the reciprocating-action piston 33. The profiled control surface 52 is constructed in such a manner that, once per complete relative rotation of the output shaft 18 with respect to the reciprocating-action piston 33, the control cam 51 forces the latter to carry out a displace ment in the direction of reducing the volume of the high pressure chamber 35. In this case, no pressure initially builds up in the high-pressure chamber 35 since the pressure medium can flow via pressure equalizing openings 53, 54 in the direction of the arrows 55, 56 to the low pressure chamber 36.
Arranged on the outer circumference 37 of the reciprocating-action piston 33 are sealing strips 57, 58 which form seal pairs 57, 59 and SS, 60 respectively with sealing projections 59, 60 which are constructed on the rotation body 30 and are likewise in the form of strips. The seal pairs 57, 59; 58, 60 are in this case arranged offset with respect to one another seen in the reciprocating-action direction of the reciprocatingaction piston 33. Seen in the reciprocating-action direction of the reciprocating-action piston 33 in each case, a first sealing strip 57 is located closer to an end 62 of the reciprocating- action piston 33 on the pressure chamber side than is a second sealing strip 58, while in contrast the sealing projections 59, 60 are at the same level. In this way, the seal pairs 57, 59; 58, 60 reach their respective sealing position in mutually offset reciprocating-action positions of the reciprocatingaction piston 33. The seal pairs 57, 59; 58, 60 are correspond- ingly located completely opposite in each case in mutually offset reciprocating-action positions of the reciprocating-action piston 33.
The impact mechanism 17 does not reach its impact position until the highpressure chamber 35 is completely sealed off, that is to say until both seal pairs 57, 59; 58, 60 assume their closed position, as is illustrated in Figure 3. in the reciprocating- action position of the reciprocatingaction piston 33 illustrated there, a first seal pair 57, 59 is shown shortly before leaving its sealed position, and a second seal pair 58, 60 has just reached its sealed position. The pressure chamber 35 is thus sealed and the pressure medium has pressure applied to it on further displacement of the reciprocating- action piston. Since the pressure medium, for example hydraulic oil, is virtually incompressible, a very high pressure resistance is then built up in the impact mechanism 17 so that, as a result of the flywheel mass of the rotation body 30, an impact moment is transmitted to the output shaft 18. In order to prevent the impact mechanism 17 locking up, the high-pressure chamber 35 can additionally be connected to the low-pressure chamber 36 via a pressure equalizing line, which is not illustrated in more detail and has a variable restriction resistance.
Figure 4 shows a subsequent reciprocating-action position in which the first seal pair 57, 59 is open again, so that pressure equalization between the highpressure chamber 35 and the low- pressure chamber 36 is made possible in accordance with an arrow 61, although the second seal pair 58, 60 is still in its sealed position. The reciprocating-action position range in which the seal pairs 57, 59; 58, 60 seal the pressure chamber 35 can be fixed by the choice of the axial separation and the thickness of the two mutually offset seal pairs 57, 59; 58, 60. This reciprocating- action position range can also be called the seal travel or with respect to the relative rotation of the control cam 18 with respect to the rotation body 30 - the sealing angle. It is critical in this case that the distance A between a lower sealing edge 63 of the first sealing strip 57 and an upper sealing edge 64 of the second sealing strip 58 is not greater than a distance B between an upper sealing edge 66 of the first sealing projection 59 and a lower sealing edge 67 of the second sealing projection 60.
Figure 3 illustrates a limit case in which the seal travel is virtually zero, that is to say A is approximately equal to B. The sealing projections 59, 60 are in this case arranged at the same level, opposite one another, on the inner wall of the rotation body 30. The sealing strips 57, 58 are likewise diametrically opposite one another and are mutually offset seen in the reciprocating-action direction. If the sealing strips 57, 58 were further offset with respect to one another in the reciprocating-action direction, as is illustrated in Figure 3, that is to say A were greater than B, then simultaneous closing of both seal pairs would not be possible. Conversely, the seal travel or the sealing angle can be correspondingly enlarged by reducing the distance A between the sealing edges 63, 64 of the sealing strips 57, 58 or by enlarging the distance B between the upper sealing edge 66 of the first sealing projection 59 and the lower sealing edge 67 of the second sealing projection 60.
The plan view, which is illustrated in Figure 5, of the end of the reciprocating-action piston 33 illustrates the predominantly circular shape of the reciprocating-action piston 33 which has a shoulder 65, in the form of a step, only on its side facing the pressure equalizing opening 54. The pressure equalizing openings 53, 54 are cut out of an inner wall 38 of the rotation body 30, approximately in the form of sickles. However, these cutouts do not exist at the level of the. sealing projections 59, 60 (indicated by dashed-dotted lines in Fig. 5), so that the inner wall 38a of the rotation body 30 has an approximately cylindrical cross- section there.
- a - Claims 1. Impact screwdriver having an input shaft (16) which can be driven in a rotating manner via a drive shaf t (13) by means of a drive motor (12), having an output shaft (18) which can be connected in a rotationally locked manner to a tool holder (19) for a screwdriver tool, and having a hydraulic impact mechanism (17) via which the input shaf t (16) is coupled to the output shaft (18) and which has a rotation body (30) in which at least one reciprocating- action piston (33) is guided, which piston carries out a forced reciprocating movement when the input shaf t (16) rotates relative to the output shaft (18), as a result of which a pressure medium which is located in a pressure chamber (35) in the rotation body (30) has pressure applied to it from at least one reciprocating- action piston (33), characterized in that the reciprocating-action piston (33) is provided with at least two sealing strips (57, 58), of which in each case one sealing strip (57, 58) forms a seal pair (57,59; 58,60) with a sealing projection (59, 60) which is fixed to the rotation body (30) and extends in a limited manner in the reciprocating- action direction, the seal pairs (57,59; 58,60) being arranged offset with respect to one another, seen in the reciprocating-action direction of the reciprocating- action piston (33), in such a manner that they are in each case completely opposite in mutually offset reciprocating- action posi tions of the reciprocatingaction piston (33), and in that the pressure chamber (35) is sealed in a specific reciprocating- action position range by all the sealing strips (57, 58) being covered radially by all the associ ated sealing projections (59, 60).