EP2140978B1 - Impact wrench - Google Patents

Description

The invention relates to an impact wrench for screwing and drilling with a rotary impact mechanism wherein such impact wrench are used, inter alia, to produce or solve high-strength threaded connections. Impact wrenches have been known in the art for many years, the function of the rotary impact mechanism being based on the idea of temporarily storing the drive energy of an engine and periodically applying it to an output shaft within a very short working phase. These As a function of the pulse duration, periodically emitted rotational pulses produce a significantly higher resultant drive torque than would be possible given a constant torque curve. From the drive side, the system receives kinetic energy in the form of torque and speed, which is cached in an assembly, for example in a spring or a rotating mass. The storage process takes each time until a control mechanism ensures that the stored energy is delivered via a hammer on an anvil. For this purpose, both the anvil and the hammer of the striking mechanism on impact jaws, wherein the hammer comprises a flywheel, which is formed by the massive part of the hammer, which is accelerated by this mass, the kinetic energy is transferred to the anvil. The anvil is in a rotationally fixed connection to the output, so also for screwing. The control mechanism provides for the temporary delivery of energy to the anvil.

There are two working phases in the striking mechanism, whereby in phase 1 the energy is collected and stored and in phase 2 the stored energy is released again. The energy stored in phase 1 is determined by the input quantities of torque, speed and stroke rate. The higher the stroke rate, the shorter Phase 1 is in terms of time and the less energy can be stored, because the engine can only apply a given torque and thus the duration of the storage process is crucial.

In the second phase also decides the duration of the energy tax. If the stored energy is released to the downforce in a shorter time, the stroke duration is shorter, the resulting torque peak is higher than a longer stroke duration.

Basically, the typical torque curve of an impact wrench is created by temporarily storing energy over a longer period of time, which is delivered abruptly to the output in a very short period of time.

In the case of impact no torque is generated at the output between the torque peaks. Due to this design high tightening and loosening moments in a compact design are possible. Nevertheless, the moment of reaction which the worker has to absorb with the impact wrench is only the moment that is necessary to accelerate the rotating hammer mass in the impact mechanism or to tension the spring. It is comparatively low compared to the output torque.

An impact wrench is for example in the DE 43 01 610 A1 described above. An impact wrench according to the preamble of claim 1 is in the EP 1 714 745 A2 contain.

It may be desirable in an impact wrench to make a torque adjustment e.g. to comply with certain torques that are given. In this case, both the speed and the moment of inertia of the flywheel as well as the spring force and the geometry of the V-groove can be considered as influencing parameters.

It is already known in the art today for preselecting the output torque to provide an electronic speed control. The effect is based on the fact that the torque peaks emitted by the percussion units become lower as the drive speed and thus the angular momentum of the flywheel decreases during impact. In addition, it is planned impact wrench with two-speed transmissions Equip to realize a speed ratio, which are recorded in the stage with lower speeds also significantly lower output torques. However, speed control, whether through a transmission or via electronic speed control, has a number of disadvantages. Thus, in particular in the providence of transmissions usually only a switchable stage are provided. In addition, the general disadvantage of the speed reduction in the slower speeds when screwing without impact function and at the same time caused by the speed reduction, a lower impact frequency, so that the duration of a total screw connection increases. It is therefore also known in the prior art to control the screwdriver until the onset of the impact function at full speed and only then electronically lower. As a result, only the beat frequency is negatively affected, but not the speed when screwing without beat frequency.

In addition, the provision of manual transmissions offers no advantage, since the speed reduction provides a plus in drive torque at low gear ratio, which is not used.

A speed reduction mechanism for transmitting a rotational force in an impact wrench, for example, from DE 102 09 101 A1 previously known, wherein the mechanism is designed here as a planetary gear.

Starting from the prior art, it is an object of the invention to provide an impact wrench, in which a torque adjustment is possible without the aforementioned disadvantages occur and in particular the speed is not reduced to the torque setting.

The invention is achieved by an impact wrench with the features of claim 1.

The adjustment device according to the invention for adjusting the spring preload a purely mechanical solution for the torque adjustment is achieved without the speed of the drive shaft, which interacts with the hammer, must be varied. In this way, a torque adjustment can be achieved without the impact rate is adversely affected by the reduction of the speed.

It can be provided that the spring is in particular a compression spring and is arranged for example between the hammer and the drive shaft. In this case, the compression spring is mounted so that it rotates in particular together with the hammer.

Stepping disks may in particular be provided as adjusting means, whereby a stepped disk is understood to mean disks in which a step or a stair segment comprising several steps rises on at least one end face over the base surface of the end face. It should be understood under stepped discs and such a disc having only a single run-on slope, which rises above the base of the face. The steps may have step surfaces which run parallel to the base surface of the end face or extend at an angle, ie form a bevel. The steps, stair segments or the run-up slope may extend over the entire circumference or even over a partial circumference of the stepped disk. In this case, it can be provided, in particular, that a plurality of staircase segments comprising one or more steps can be provided, which can be spaced apart in the circumferential direction or can be provided immediately adjacent to one another. If at least two staircase segments with one or more steps are provided on one end face, there is the advantage that the power flow can be made more uniform.

In principle, two or more stepped disks with end faces having their steps can be arranged in such a way that the end surfaces having the steps are arranged towards one another. The stepped disc acts together with a counter-stop in the form of a second stepped disc so that the distance between the discs is changed by turning the stepped discs to each other.

In this case, it can be provided, in particular, that in a first position, the two stepped disks with their stepped end faces lie against one another in such a way that complement the two stepped discs by the stages are fitted into each other. An axial distance between the stepped disks is then given essentially at no point on the stepped disks. The stepped discs are preferably against each other over their entire faces. By rotating one or both stepped disks relative to one another, an axial spacing of the stepped disks relative to one another is then achieved by the steps. The largest axial distance is achieved when the step discs with their highest level, which rise the furthest over the base of the end faces in the axial direction against each other.

The run-on slope on the end faces of the step disc or step surface (including surfaces) of the steps are preferably provided at an angle to the end face of the step discs that the spring force to be overcome during switching is not too large. It is therefore preferred if the slopes are not designed too steep.

It is particularly preferred that at least two stair segments, comprising one or more stages, are provided on the stepped disks, wherein the stair segment can extend in particular over 180 ° of the end face and in particular may have three or more stages. The provision of several stair segments enables the most uniform flow of force possible, with the greater number of stages making several switching stages feasible.

According to a preferred embodiment, one of the discs is fixed against rotation on a housing of the impact wrench and with respect to the housing also not axially displaceable. The other disc is relative to the Housing both rotationally and axially displaceable and thereby performs the adjustment to change the spring preload.

In this case, a switching element, which may be articulated, for example via a lever to the movable step disc, perform an axial and a rotational movement when switching.
If only two switching stages to be provided, instead of the stepped discs and a toothed or a wave washer may be provided, in particular wave troughs and wave crests are alternately provided or has the teeth on the front side, so then depending on whether a mountain with a Wellental the second disc is in contact, the two discs abut against each other or a modified bias of the spring can be achieved when the discs come to rest with two wave crests against each other.

In this case also the axial distance of the discs is adjusted to each other by rotating the discs against each other.

In principle conceivable, however, are also other adjusting devices in which a component, for example in the form of a disk, or a ring or a sleeve, is mounted in the housing in such a way that the sleeve can be displaced axially, wherein an end face of the disk, the sleeve or ., the ring cooperates with the spring and so realizes an adjustment of the biasing force of the spring. In this case, for example, a ring or sleeve in the housing via a toothing of the ring, which cooperates with a toothing of the housing, be guided axially displaceable. The adjustment can be made by a corresponding sliding guide, which is a movement of the ring caused in the housing to be achieved. On the housing can be provided for this purpose a sliding but also a rotary switch.

It is particularly preferred that the percussion mechanism is designed as a V-groove arrangement, wherein the hammer performs an axial-rotational oscillation with respect to the drive shaft in the case of impact. Under an axial-rotational oscillatory movement is to be understood that the hammer in case of impact performs both an axial relative movement, the hammer on the drive shaft alternately axially towards the drive end of the drive shaft and the output side end of the drive shaft in a groove back and is moved while experiencing a relative rotation to the drive shaft. The groove is in particular V-shaped and arranged the tip of the V in the direction of the output side of the shaft, wherein the axial movement due to the V-shape of the grooves at the same time causes a relative rotational movement of the hammer to the drive shaft with an axial movement, the is coupled with this. The hammer can be guided over a ball guide in the V-grooves, wherein preferably two grooves are arranged diametrically opposite to the drive shaft. To guide the grooves on the hammer corresponding treads can be arranged on the hammer.

An impact wrench and in particular an impact wrench with a V-groove impact works as follows: In a first non-impact case, the hammer, which rotates with the drive shaft, abut against the impact jaws of the anvil over its impact jaws, which overlap in the axial direction and thus in the Engage and drive over this anvil and thus the output shaft and the tool. A corresponding drive takes place until the maximum torque of the screwdriver is achieved without causing a shock case is reached. In this state, there is no relative movement between the hammer and the anvil or between the hammer and the drive shaft.

Concerning a larger torque, that is usually at a first blockage of the screw that is to be tightened or loosened, it comes now that the normal torque of the impact wrench can not apply this greater torque between the hammer and anvil for decoupling the impact baking. The connection of the percussion mechanism and the transition to the impact occurs automatically.

The impact jaws of the hammer and anvil are arranged on mutually facing end faces of the hammer and anvil and lie in the case of impact no longer permanently against each other, as is the case in pure screwing. By temporarily separating the impact jaws of hammer and anvil from each other by locking them and axial movement of the hammer, it comes to a compression of the spring, which cooperates with the hammer and thus to an energy storage in the spring, which then in a second step to a Discharge of energy leads. During the energy discharge then the impact jaws collide again in the circumferential direction and it comes to a short-term greater torque.

It is achieved by the rotation of the drive shaft, which is transmitted to the hammer and the anvil of the anvil, a wandering of the hammer on the drive shaft in the V-grooves, the hammer through the V-grooves at the same time with the rotation relative to the drive shaft in the axial Direction is moved away from the anvil and it comes to a snapping in the axial direction of the impact jaws of the hammer and the anvil. By releasing the hammer from the anvil, the hammer is free to move in a rotational direction and is accelerated by the stored energy stored in the spring by the axial movement of the hammer in the drive direction until at the end of its relative rotational and axial movement impinges against the impact jaws of the anvil with its impact jaws and so performs a blow in the circumferential direction, which leads to a further tightening or loosening of the screw to be machined. After the impact, the tensioning of the percussion mechanism takes place again by the axial and radial movement of the hammer.

Particularly preferred may be provided that the hammer comprises a control part and a flywheel, the flywheel of the hammer performs no oscillating axial movement and the control part is guided axially movable in grooves in the flywheel, but is rotatably coupled to the flywheel. The rotary drive of the flywheel takes place via the control part, wherein the control part interacts with the spring for energy storage and the control part carries the impact jaws of the hammer, which cooperate with the impact jaws of the anvil.

The spring can be provided between the control part and flywheel and the device can act on the flywheel.

According to another preferred embodiment, it can be provided that the impact wrench is a cordless wrench, with cordless tools generally having the advantage of being easier to use at any location and even in difficult applications. In addition, the impact function is particularly advantageous in cordless tools, since in devices with direct electrical connection, the torque design can be done so that higher torques are achieved, so that you can possibly work without an additional impact function.

Further advantages and features of the invention will become apparent from the remaining application documents. The invention will be explained in more detail below with reference to a drawing.

Showing:

FIG. 1

a percussion in assembled representation

FIG. 2

the percussion according to FIG. 2 on average

FIG. 3

a stepped pulley of the device

FIG. 4

the second step disc of the device

FIG. 5

an embodiment of a striking mechanism with divided into control mass and flywheel hammer in section and

FIG. 6

the percussion according to FIG. 5 in a top view.

FIG. 1 shows a striking mechanism of a striking screwdriver comprising an output shaft 10 which is connectable at its output end 12 with a tool, in particular a screwdriver, and at its drive end has an anvil 14 which has two impact jaws 16 which are formed diametrically opposite each other in the radial direction are, wherein the striking surfaces are substantially radially extending surfaces which extend in the radial and axial planes. The impact jaws 16 can as well as impact jaws 18 of a hammer 20 both curved and flat against each other, with curved impact jaws only a linear contact between the impact jaws 16 and 18 may be given. The hammer 20 forms on the one hand a flywheel and serves on the other hand as a control means for the control of the impact process. In addition, the striking mechanism comprises a drive shaft 22 which is coupled via a gear 24 to a drive motor 26. On the drive shaft 22, a spring 28 is provided which serves to store energy, which is then released to produce a rotary impact. The spring is a compression spring and designed in particular as a spiral spring.

The transmission 24 may be configured in particular as a planetary gear to translate the speed of the drive motor 26 and to vary. The spring 28 acts together with its output side end 12 with the hammer 20 and lies with its drive end against a first step plate 30 of the device 32 for adjusting the spring preload. It can be provided between the stepped disc 30 and the spring 28, a bearing 34 to a Allow relative rotation of the spring 28 relative to the device 32.

In addition, the device 32 comprises a second stepped disc 36 which cooperates with the first stepped disc 30, wherein the stepped discs 30 and 36 are aligned with two of their end faces and are formed on the two end faces 38 and 40 stages, each with a plurality of steps a stair segment form and the steps are designed so that by rotation of the step plates 30 and 36 relative to each other there is a varying axial extent of the device 32, depending on which steps abut against each other. For this purpose, the steps rise differently far over the base surfaces of the end faces 38 and 40, wherein the staircase segments continuously increase or decrease.

It can FIG. 1 can be taken that the impact jaws 16 of the anvil 14 overlap in the axial direction with the impact jaws of the hammer 20. By covering a rotary drive of the anvil 14 by means of the hammer 20 and thus a rotary drive of a tool is ensured. A corresponding concern to each other is in the case of a pure screwing, with no impact case, before and at the time of impact.

FIG. 2 now shows a representation of a section through a striking mechanism according to the invention FIG. 1 , The spring 28 is rotatably fixed with the hammer 20 in this, wherein the hammer 20 is guided over balls 52 in V-grooves 42 of the drive shaft 22. The tip of the V of the grooves 42 faces toward the output side end 44 of the drive shaft 22. The V-shaped grooves 42 serve to control the axial-rotational oscillation of the hammer 20 with respect to the drive shaft 22 in impact. There are two V-grooves 42 are provided in the drive shaft 22, which are arranged diametrically opposite one another, whereby a uniform guidance and a favorable force distribution is achieved.

While in the case of a screw, or in non-impact, the impact jaws 18 abut against the striking jaws 16 of the anvil 14 and drive it, it comes in case of impact at a first blockage and thereby holding the tool with the anvil 14 and a simultaneous further rotation of the drive shaft 22, the is further driven by the motor 26, by the anvil of the anvil 14 to a migration of the hammer 20 in the V-grooves 42 by being guided over the balls 52 and thus to a movement in the direction of the arrow 46 and to a relative rotation of the hammer 20 to the drive shaft 22. It then comes to a latching of the impact jaws 18 with the impact jaws 16, if they separate axially from each other. In a further guidance of the hammer 20 in the V-grooves 42 then there is a further relative movement and an axial movement against the direction 46 and by the acceleration of the flywheel in rotational terms to a collision of the impact jaws 16 and the impact jaws 18 of hammer 20 and anvil 14, so that a rotary impact is performed. The impact energy is provided inter alia by the spring 28, which serves for energy storage in a movement of the hammer 20 in the direction 46.

To preset the spring preload while the device 32 already described is provided, which is formed of two stepped discs 30, 36, each with their stepped faces 38, 40 abut against each other. In addition, the stepped disk 30 has a Actuator 48, which in FIG. 1 is shown, whereas the stepped pulley 36 is fixed against rotation on the gear of the impact wrench and can not be moved in the axial direction.

FIG. 3 shows the stepped pulley 36, which is fixed with attachment means, here via a screw 50, the transmission housing and thus with respect to the housing of the electric hand tool device rotationally fixed and axially immovable. On an end face 40 of the stepped disk 36, there are provided here two stairways 54 'and 54 "which each comprise five steps 56, each stair segment 54' and 54" extending over approximately 180 ° of the end face 40. The steps 46 are in this case inclined with respect to their step surfaces or surfaces 58 to the end face 40 of the stepped disk 36 and rise within a stair segment 54 on or off depending on the consideration.

FIG. 4 now shows the second stepped disc 30, which has an actuating element 48 which is attached via a lever 60 to the step disc 30 has. The stepped pulley 30 also has two staircase segments 62 'and 62''which also extend over approximately 180 ° of the stepped pulley 30 and also have five steps 64 which also have an inclined step surface and rising from the base of the end face 38, depending on which of the stages 54 cooperates with a corresponding step 64, this leads to a different axial extent of the device 32 with the step plates 30, 36th

In the case of the minimum set spring preload, the stepped discs 30, 36 with their stair segments 54 and 62 against each other so that it is approximately full-surface contact of the stepped discs 30 and 36 against each other. Rotational movement via the adjusting element 48 of the stepped disk 30 then causes the steps 56 and 64 to move relative to one another, so that, due to the step-like design, overcoming the spring force of the spring 28 results in an axial movement of the stepped disk 30 with respect to the stepped disk 36.

In this way, the spring bias of the spring 28 and thus the torque can be adjusted in the case of shock.

FIG. 5 shows an alternative embodiment of the impact mechanism, in which case the same components are provided with the same reference numerals. Again, a drive shaft 22 via a drive motor 26 which is coupled to the drive shaft via a gearbox 24, driven and it is a device 32, as shown in the FIGS. 1-4 has been described. Unlike a striking mechanism, like the FIGS. 1 and 2 show, here is a two-piece hammer 20 is provided, comprising a flywheel 70 and a control part 72, wherein the control part 72 carries the impact jaws 18 of the hammer 20.

Between control part 72 and flywheel 70, the spring 28 is arranged, which serves the energy storage to enable the impact of the control part 72 against the impact jaws 16 of the anvil 14. A bearing 74 is located between the stepped disc 30 and the flywheel 70, wherein the flywheel mass includes the essential mass of the hammer 20 and the control part 72 may have a comparatively lower mass.

In the case of impact, the control part 72 is now guided in the axial direction in grooves of the flywheel 70, in which the Control part 72 engages with corresponding ribs. The control part 72 is rotatably connected to the flywheel 70 and drives these rotationally. By this design it is achieved that the flywheel 70 has no oscillating axial movement component and thus causes no vibration excitation of the machine in this direction. Due to the much smaller mass of the control part 72 lower vibrations are caused, so that the machine is generally more pleasant to lead. However, the flywheel 70 is still the necessary mass for the rotary blow available. The control part 72 is further guided in the V-grooves 42 of the drive shaft 22 and therefore make a movement corresponding to the hammer in the FIGS. 1 and 2 , The impact jaws 18 of the control part can protrude in the direction of the anvil 14 in the axial direction over the end face 76 of the flywheel 70 in the case of a rotary drive and thus a covering with the impact jaws 16 of the anvil 14. Alternatively, a design may be provided in which the end face 78 of the impact jaws 18 of the control part 72 is flush with the end face 76 of the flywheel 70 and immerse the impact jaws 16 of the anvil 14 in the flywheel 70.

FIG. 6 now shows a design of a corresponding impact mechanism according to FIG. 5 in a non-sectional view, wherein the means 32 for presetting the torque of in FIG. 1 and 2 shown corresponds. The flywheel 70 may be formed as a substantially cylindrical sleeve, wherein on its inner side, the spring 28 is supported against a drive-side end face 80 of the flywheel 70.

The device then interacts in particular with the flywheel 70 and moves it axially, whereby the change in bias is transmitted to the spring 28.

By the present invention, the advantage is achieved that without sacrificing speed in a torque adjustment can be realized in a purely mechanical way, so that a total of one screw can be completed faster due to the lack of speed reduction. In addition, a speed control can be done via a gearbox regardless of the torque setting. A corresponding embodiment is structurally simple and includes only compared to a conventional design only a few other components.

In addition, if the hammer is divided into a flywheel and a control part, the vibrations in the axial direction can be reduced.

Claims (13)

1. Impact screwdriver having a driving motor (26) for driving a driving shaft (22) and an output shaft (10) that can be coupled to a tool-holder, and also having a striking mechanism; wherein said striking mechanism comprises an anvil (14) coupled to the output shaft (10) and having first striking jaws (16), and also comprises a hammer (20) which is guided on the driving shaft (22) and rotates with the latter in non-percussive situations and which, in percussive situations, performs an axial movement relative to said driving shaft (22); wherein the hammer (20) has second striking jaws (18) which are in engagement with the first striking jaws (16) of the anvil (14) for rotation-transmitting purposes; wherein there is provided, for generating the percussive energy, a spring (28) which, in percussive situations, is alternately compressed and relieved of tension as a result of the axial movement of the hammer (20); and wherein pre-tensioning of the spring (28) can be set continuously or in stages via a setting apparatus (32) and said apparatus (32) is arranged between the spring (28) and the driving shaft, characterised in that a bearing is provided between the apparatus (32) and the driving shaft (22) and also between said apparatus (32) and the spring (28).
2. Impact screwdriver according to claim 1, characterised in that the spring (28) is a compression spring.
3. Impact screwdriver according to either of the preceding claims, characterised in that the setting apparatus (32) comprises at least two stepped discs (30, 36) which bear against one another via end faces (38, 40) that comprise their steps (56, 64), wherein the axial distance between the discs (30, 36) can be set by twisting said discs (30, 36) in relation to one another.
4. Impact screwdriver according to one of the preceding claims, characterised in that the striking mechanism is constructed as a V-groove striking mechanism, wherein the hammer (20) performs, in percussive situations, an axially rotatory oscillation with respect to the driving shaft (22).
5. Impact screwdriver according to claim 3, characterised in that the driving shaft (22) has at least one V-groove (42) and the hammer (20) is guided in the V-grooves (42) of said driving shaft (22).
6. Impact screwdriver according to one of the preceding claims, characterised in that the hammer (20) and the anvil (14) each have two diametrically opposed striking cams (16, 18).
7. Impact screwdriver according to one of the preceding claims, characterised in that the stepped discs (30, 36) have two or more steps (56, 64).
8. Impact screwdriver according to one of the preceding claims, characterised in that the steps (56, 64) extend at an angle to the end faces (38, 40) of the stepped discs (30, 36).
9. Impact screwdriver according to one of the preceding claims, characterised in that there are provided, for each stepped disc (30, 36), at least two stepped segments (54, 62) comprising one or more steps (56, 64).
10. Impact screwdriver according to one of the preceding claims, characterised in that one of the discs (36) is constructed so as to be axially immovable in relation to a housing of the impact screwdriver and the other stepped disc (30) is constructed so as to be axially movable with respect to said housing.
11. Impact screwdriver according to one of the preceding claims, characterised in that the movable disc (30) is coupled to a switching element (48, 60).
12. Impact screwdriver according to claim 11, characterised in that the switching element (48, 60) undergoes a rotatory and axial component of motion on switching.
13. Impact screwdriver according to one of the preceding claims, characterised in that said impact screwdriver is a battery appliance.

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