EP1258322B1 - Power driven Screwdriver with torque limiting clutch - Google Patents

Abstract

The power screwdriver has a torque limiting coupling, coupling the screwdriver's drive to a spindle which drives the tool receiver up to a preset release torque. The torque limiting coupling is connected to the spindle by a free-play coupling (86), which may connect the reaction part (70) of the transmission to the spindle.

Description

The invention relates to a power screwdriver for screwing and loosening of screws, with a torque limiting coupling which couples a drive of the screwdriver with a spindle driving a tool holder until reaching a preset triggering torque, wherein the torque limiting coupling is connected to the spindle via a backlash.

Such a screwdriver is from the US-A-5,738,177 known.

Power-driven screwdrivers for screwing in and loosening screws have increasingly replaced conventional manual screwdrivers in the past. In the commercial sector mainly power-driven screwdrivers are used with a torque-dependent triggering torque limiting clutch, since there screws are usually screwed with well-defined torques. Under screws are understood in the broadest sense, all types of threaded fasteners, ie in particular also nuts.

Torque limiting clutches are placed in a drive train between a driver of the screwdriver and a tool holder. The torque limiting clutch breaks the connection between the drive and the tool holder as soon as a screwed-in screw is clamped with the desired force in a screw-receiving thread. The torque with which the drive of the screwdriver then acts on the stuck screw is called the tripping torque and can usually be set on the torque limiting clutch. So that the drive does not idle after loosening the torque limiting clutch, the torque limiting clutch usually acts on an additional switch, upon actuation of the drive is turned off. When changing the direction of rotation, ie for loosening screws, a higher torque than when screwing must be applied so that this suitable torque limiting clutches often show an asymmetric tripping behavior.

From the above US-A-5,738,177 a screwdriver is known, the torque-dependent triggering torque limiting clutch is connected via a backlash with the spindle. As a result, a more accurate Abschaltmoment the screwdriver is to be achieved, since the clearance clutch absorbs kinetic energy when braking the engine.

However, the structure of the known screwdriver is very complicated. It has also been shown that the release torque can nevertheless be subject to a certain scatter.

From the WO 99/16585 Furthermore, a screwdriver is known, which is formed with a planetary gear and has a torque-limiting coupling which is arranged between a ring gear and the tool housing, wherein the ring gear has a spring-loaded pressure element which cooperates with cam elements via balls and a cam surface. To trigger a REED relay is used, which is actuated by a swivel lever with permanent magnets.

The invention has for its object to improve a power screwdriver of the type mentioned in such a way that results in a simple and compact design and that a preset release torque is maintained as accurately as possible.

This object is achieved by a screwdriver according to claim 1.

The object of the invention is completely solved in this way. Namely, since the reaction part is a ring gear of a planetary gear which receives a plurality of planetary gears, the reaction part can be accommodated in a compact screwdriver in a particularly space-saving manner. Since the backlash between a planet carrier of the last gear stage of the planetary gear and the spindle is arranged so any reaction moments that are exerted directly by the spindle, neutralized via the backlash. This results in a particularly high precision in terms of compliance with a preset release torque.

With the invention, inter alia, the knowledge is exploited that the inaccurate compliance with the preset triggering torque is due to the effect of torque limiting clutch. Namely, if this triggers after screwing a screw, so it exerts on the spindle in the opposite direction (release direction) acting torque on the screw, ie the screw is always easily solved after reaching the trigger torque. Since the value of the torque acting in the release direction is unknown, the actual tightening torque with which the screw is screwed in can not be accurately predicted. The torque acting in the release direction arises when the torque limiting clutch is triggered by the pressure spring continuing to exert pressure on the two clutch parts involved, namely the ring gear and the ring gear, after they have moved apart in the axial direction when the torque limiting clutch is released. This pressure now acts on the rolling elements on the likewise inclined rear side of the cam, whereby a torque is exerted on the ring gear on which the cams are formed. This torque on the ring gear causes a release torque exerted on the spindle via the planetary gear and thus the screw is released again.

According to the present invention, the torque limiting clutch having a first and a second coupling part, which engage with closed torque limiting clutch, wherein the first coupling member rotatably with a housing of the screwdriver and the second coupling member rotationally fixed with a reaction torque against a spindle receiving and with respect to the housing freely rotatable reaction part of a transmission is connected.

Opposite torque limiting clutches, which are arranged directly between two sections of a drive train, this has the advantage that no rotational movement of the two coupling parts takes place when the torque limiting clutch is closed. As a result, acting on the coupling parts and possibly provided balls that cause the coupling between the coupling parts, no significant centrifugal forces that contribute to their wear. The clearance clutch then connects the reaction part of the transmission to the spindle.

Further, the reaction part is a planetary gear receiving a ring gear of a planetary gear.

Due to their distribution of forces, planetary gearboxes are particularly reliable and long-lasting, making them particularly suitable for power-driven screwdrivers in the commercial sector.

According to the invention, the backlash is not arranged directly between the ring gear, but between a planet carrier of a final gear stage of the planetary gear and the spindle.

This measure makes it possible to design a play coupling between the spindle and the reaction part of the transmission that is structurally particularly simple, since the planet carrier is in the immediate vicinity of the spindle driven by the transmission; the ring gear, however, would be further away from the spindle and less accessible to parts of a backlash. In addition, can be largely integrated in this way, the game clutch in the planetary gear.

In a preferred embodiment, this integration takes place in that the play clutch has a rotatably connected to the spindle driving wheel, from which several wings extend radially outward, which abut in a coupled state to lugs of the planet carrier.

For the game clutch thus only a few additional components are required, in particular the driving wheel. The lugs on the planet carrier can be designed as simple pins or projections, which can engage the wings of the driving wheel.

Preferably, however, the approaches are formed by stubs of Planetenradachsen that carry planetary gears and enforce the planet.

This measure makes it possible to dispense with even the formation of lugs on the planet carrier, as they are formed by the already required Planetenradachsen. The entire game clutch is thus feasible with minimal design effort.

Fig. 1

einen vorderen Teil eines erfindungsgemäßen Schraubers, wobei durch einen Gehäuseausschnitt schematisch angedeutete Teile im Inneren des Schraubers erkennbar sind;

Fig. 2

einen axialen Schnitt durch einen Abschnitt eines Antriebsstrangs des in Fig. 1 dargestellten Schraubers, in dem ein Planetenradgetriebe und eine Drehmomentbegrenzungskupplung in teilgeschnittener Darstellung erkennbar sind;

Fig. 3

eine in dem Schrauber nach den Fig. 1 und 2 verwendete Spielkupplung in einer perspektivischen Darstellung.

Further advantages and features of the invention will become apparent from the following description of an embodiment of the invention with reference to the drawing. Show:

Fig. 1

a front part of a screwdriver according to the invention, wherein through a housing cutout schematically indicated parts are visible in the interior of the screwdriver;

Fig. 2

an axial section through a portion of a drive train of the in Fig. 1 shown screwdriver in which a planetary gear and a torque limiting clutch are recognizable in a partially sectioned view;

Fig. 3

one in the screwdriver after the Fig. 1 and 2 used game clutch in a perspective view.

In Fig. 1 an inventive screwdriver is shown in a side view with partially removed housing part and designated 10 in total. The screwdriver 10 has a housing 11 with a main housing part 12 on which a handle portion 16 is formed. From there, a main switch 18 is conveniently operated by an operator. At the front end of the main housing part 12, an angle head housing 19 of an angle head 20 is rotatably mounted, from which a tool holder 22 protrudes at right angles to a longitudinal axis of the screwdriver 10. Such screwdrivers are commonly referred to as rod angle screwdrivers and have the advantage over conventional power driven screwdrivers that the torque absorbed by the screwdriver when screwing screws not to a twisting of the screwdriver about its longitudinal axis, but to a pivoting of the screwdriver at right angles angled, through the tool holder 22 fixed axis leads. Such pivotal movements can be more easily absorbed by an operator than rotations of the screwdriver about its longitudinal axis.

The screwdriver 10 has an example designed as an electric motor drive 32 which is rotatably attached to a fixed relative to the main housing part 12 support sleeve 34. The drive 32 drives via an intermediate shaft 36 to a reduction gear in the form of a planetary gear 38, which on the output side, a spindle 40 is rotated. The spindle 40 drives a tool spindle 44 via a bevel gear arrangement 46 arranged in the angle head 20, which tool holder carries the tool holder 22 at its free end.

Furthermore, in Fig. 1 a torque limiting clutch 50 is shown schematically, which couples a reaction torque with respect to the spindle 40 receiving reaction part of the planetary gear 38 with a control sleeve 52. The adjusting sleeve 52 is integrally formed with an angle head housing 19 or rotatably connected via one or more intermediate parts with this. To turn the angle head 20, for example in the in Fig. 1 Dashed position shown, the entire angle head 20, ie, the angle head housing 19 with housed bearings 55 and 56 for the spindles 40 and 44 and the adjusting sleeve 52, relative to the housing-fixed support sleeve 34 along a running here as a screw adjustment device 58 is rotated. When the torque limiting clutch 50 is closed, the reaction part of the planetary gear 38 is fixed against rotation relative to the angle head 20 and coupled to the drive 32 via the adjusting device 58.

Fig. 2 shows in an axial section details of in Fig. 1 only schematically illustrated parts in the interior of the screwdriver 10th

On a rotor neck 60 of in Fig. 2 only indicated drive 32 is an intermediate shaft 62 rotatably pushed, which is integrally formed with a first sun gear 64 of the two-stage planetary gear 38. The first sun gear 64 meshes with three first planetary gears 66 of a first planetary gear stage, of which in Fig. 2 only two are recognizable. The first planetary gears 66 are rotatably mounted on a first planet carrier 68 and mesh simultaneously with a ring gear 70 which extends over the entire axial length of the planetary gear 38. The first planet carrier 68 is integrally formed with a second sun gear 72 or rotatably connected, which meshes with second planetary gears 74. The second planet gears 74 are in turn rotatably mounted on a second planet carrier 76 and also mesh with the ring gear 70. Planetenradachsen 82 on which the second planetary gears 74 are guided, enforce the second planet 76 and form on the gear side facing away from neck 80th These engage on wings of a driving gear 84, which drives the spindle designed as a hexagon 40 and is supported in the axial direction on a ring 87 held by a snap ring 85. The nozzle 80 and the driving wheel 84 together form a further below with reference to Fig. 3 explained in more detail game clutch 86th

The ring gear 70, which assumes a reaction torque relative to the intermediate shaft 62 and the spindle 40 and thus represents the reaction part of the planetary gear 38, is rotatable via a bearing 88 in the carrier sleeve 34 bolted to the drive 32 and the adjusting sleeve 52 connected thereto via the adjusting device 58 added. The ring gear 70 is on the adjusting sleeve 52 (or a non-rotatably connected part) via set the torque limiting clutch 50. This comprises a rotatably screwed into the ring gear 70 cam ring 90, which projects beyond the ring gear 70 shoulder 92 is also supported on the bearing 88 on the adjusting sleeve 52, and a switching ring 96 which is clamped by a compression spring 94 against the cam ring 90. The switching ring 96 is axially, ie in the longitudinal direction 95 of the spindle 40, slidably, but rotatably received in an associated with the adjusting sleeve 52 intermediate sleeve 98. The rotationally fixed, but axially displaceable arrangement of the switching ring 96 is achieved by means of first and second longitudinal grooves 100 and 101, which are arranged on a peripheral surface of the switching ring 96 and the inside of the intermediate sleeve 98 and cooperate with guide balls 102, via the first and second longitudinal grooves 100 and 101 rolling guide balls 102, the switching ring 96 and the intermediate sleeve 98 can be moved to each other in the axial direction, wherein a snap ring 105 inserted into the intermediate sleeve 98 prevents falling out of the guide balls 102.

On the cam ring 90 side facing the switching ring 96 three rollers 104 are rotatably mounted on axles 106 circumferentially. The rollers 104 can roll on a cam track 108, which is formed on a switching ring 96 facing the end face of the cam ring 90. At the cam ring 90 facing end side of the switching ring 96 also three projections 109 are formed.

During the screwing of a screw, the rollers 104 are formed on the cam track 108 cams such that the force exerted on the ring gear 70 reaction torque on the cams, the rollers 104 and the switching ring 96 on the intermediate sleeve 98th and thereby is transmitted to the rotatably associated adjusting sleeve 52, so that the ring gear 70 rests during the screwing of a screw. When the torque increases, the torque acting on the cam ring 90 increases until, finally, the cam ring 90 begins to rotate, lifting the rollers 104 and thus the switching ring 96 counter to the force of the compression spring 94 with its cams. Upon further rotation of the cam ring 90, this then runs with its cams under the rollers 104, so that the rollers 104 with the switching ring 96 finally lower again under the pressure of the compression spring 94.

During rotation of the cam ring 90 and the associated ring gear 70, the planetary gear 38 is no longer fixed against rotation, so that the torque exerted by the drive 32 on the spindle 40 is reduced to virtually zero.

In Fig. 3 the play clutch 86 between the output of the planetary gear 38 and the spindle 40 is shown in perspective. The play clutch comprises the three stubs 80, which are formed by the Planetenradachsen 82 passing through the second planet carrier 76, and the carrier wheel 84, which is rotatably guided in a central recess of the second Planetenradträgers 76. The entrainment wheel 84 has a central, executed as a hexagon socket passage 130, in the assembled state, an end of the cross-sectionally also hexagonal spindle 40 is inserted. From the center of the entraining wheel 84, three wings 132 extend radially outward, and indeed so far that they can get into contact with the nozzle 80. When screwing a screw, the nozzle 80 rotate with this receiving second planet carrier 76 about the longitudinal axis 95 of the spindle 40 and thereby engage the wings 132 of the driving wheel 84 at. In this way, guided in the entrainment wheel 84 spindle 40 is coupled to the output of the planetary gear 38.

If the rotation limiting coupling 50 then releases when the triggering torque is reached, the force exerted by the compression spring 94 causes the connecting pieces 80 to reverse their direction of rotation, as has already been explained in the introduction. During this movement in the direction indicated by an arrow 134, the sockets 80 are not in contact with the wings 132 of the carrier wheel 84, so that no torque is transmitted to the spindle 40. Since the movement of the nozzles 80 caused by the torque limiting clutch 50 is short, they remain in an intermediate position between the vanes 132. In a subsequent screwing the play clutch 86 therefore couples with a short delay.

Claims (3)

1. Power screwdriver (10) for tightening and loosening of screws, having a torque limiting coupling (50) which couples a drive (32) of the screwdriver (10) with a spindle (40) driving a tool receptacle (22), until a preset release moment is reached, wherein the torque limiting coupling (50) is coupled to the spindle (40) via a loose coupling (86), characterized in that the torque limiting coupling (50) comprises a first (96) and a second coupling part (90) which engage each other when the torque limiting coupling (50) is closed, wherein the first coupling part (96) is connected non-rotatably with a housing (11) of the screwdriver (10) and the second coupling part (90) is connected non-rotatably with a freely rotatable reaction part of a gear (38) which is configured for receiving a reaction moment with respect to the spindle (40), in that the loose coupling connects the reaction part (70) of the gear (38) with the spindle (40), in that the reaction part is a hollow wheel (70) of a planetary gear (38) which receives several planetary wheels (66, 74), and in that the loose coupling (86) is arranged between a planetary wheel carrier (76) of a last gear stage of the gear (38) and the spindle (40).
2. Screwdriver according to any of the preceding claims, characterized in that the loose coupling comprises a tappet wheel (84) which is connected non-rotatably with the spindle (40), wherein several wings (132) extend from the tappet wheel radially outwardly and rest against dock points (80) of the planetary wheel carrier (76).
3. Screwdriver according to claim 2, characterized in that the dock points are formed by connecting pieces (80) of planetary wheel axes (82) which carry planetary wheels (74) and which extend through the planetary wheel carrier (76).

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