EP2331298B1 - Implement having an overrunning clutch - Google Patents

Description

The invention relates to a working device according to the preamble of claim 1 for generating a beating or pounding working movement, which can be used for example in a hammer, drill or breaker or a rammer for soil compaction use.

Working tools for generating a beating or pounding working movement, in which a drive torque of a drive is transmitted from a drive element to a motion element coupled to the drive element, namely to a percussion or ramming piston, are well known. For example, impact mills that are used in impact, drilling and / or Aufbruchhämmern can be operated on this principle.

In such an impact mechanism, a drive piston is used as the drive element, which is driven by a suitable drive, e.g. a coupled with an electric motor crank mechanism can be placed in an oscillating axial movement. This oscillating axial movement can be transmitted to a tool such as a chisel. In order not to suspend the drive overly strong and thus wear loads and to achieve an improved impact on the tool, a moving element such as a percussion piston can be arranged between the crank mechanism and the tool holder and coupled by a spring device with the drive piston. For example, it is known to use one-sided or double-sided air spring strikes.

• Einseitige Schlagwerke mit durchmessergleichen, in einem Schlagwerksgehäuse geführten Antriebs- und Schlagkolben;
• einseitige Schlagwerke mit hohlem, einseitig offenem Antriebskolben und darin geführtem Schlagkolben;
• einseitige Schlagwerke mit hohlem, einseitig offenem Schlagkolben und darin geführtem Antriebskolben; und
• zweiseitige Schlagwerke mit hohlem, den Schlagkolben umschließenden Antriebskolben.

Basically, air spring impact devices differ by the design and arrangement of a drive piston and a percussion piston. Accordingly, four variants of air spring impact devices are known:

• One-sided striking mechanisms with diametrically identical drive and percussion pistons guided in a percussion mechanism housing;
• one-sided striking mechanisms with hollow, unilaterally open drive piston and percussion piston guided therein;
• one-sided striking mechanisms with a hollow, one-sided open percussion piston and drive piston guided therein; and
• two-sided percussion with hollow, the percussion piston surrounding drive piston.

The drive piston and the percussion piston can be sealed by gap seals or other seals in these arrangements against each other and depending on the variant against the percussion mechanism, so that can form at high relative velocities between the drive piston and the percussion piston by the trapped air volume air springs.

The operation of a conventional percussion mechanism is described below on a percussion cycle.

By means of the crank drive, the drive piston, that is to say the drive element, can be displaced into an oscillating, for example approximately sinusoidal, following axial movement, wherein the extreme position of the drive piston facing the crank drive can be referred to as top dead center, and wherein the extreme position, which is remote from the crank mechanism, can be referred to as bottom dead center.

If the drive piston is moved from the direction of top dead center in the direction of bottom dead center and the percussion piston, ie the movement element, an air spring is formed at least between an end face of the percussion piston and the drive piston due to the enclosed air volume. This generates the movement of the drive piston in the direction of the lower one Dead center due to the inertia of the percussion piston an overpressure of the trapped air volume, through which the percussion piston experiences a thrust in the direction of movement of the drive piston. Here, an impact device can be provided with a tool arranged thereon, which can be formed by an end of the tool or an anvil. By pushing the percussion piston acts on the impact device, while it transmits an impulse to the tool and then bounces back. The recoil depends on the energy of the impact, the geometry of the impact partners, the material of the impactors and the degree of hardness of the machined workpiece. The recoil is particularly great when the tool clamps in the workpiece. The recoil causes the percussion piston to move in the direction of the drive piston and away from the impactor.

The direction of movement of the drive piston connected to the crank drive reverses as soon as the drive piston reaches bottom dead center. If the movement of the now moving in the direction of the crank drive piston is faster than that of the percussion piston, created by the relative movement of the two pistons, a negative pressure in the trapped air volume and thus an air spring which exerts a suction effect on the percussion piston and amplifies its return movement.

After reaching top dead center, the drive piston (drive element) is again moved in the opposite direction by the crank drive, brakes it by the action of the air spring, which is now in compression between the piston, the percussion piston still in the return movement (moving element) and then accelerates it again in the direction of the impact device, whereby the next blow is prepared.

In a percussion mechanism of the known type described above, the recoil of the tool on the percussion piston can adversely affect the relative movement between the drive piston and the percussion piston. So can in a strong recoil, the For example, by a hard surface, a hard workpiece, a jammed tool or by a strong previous impact arises, the percussion piston are repulsed with high kinetic energy.

In an air spring impact mechanism, this can cause pressure to be built up in the air spring between percussion piston (movement element) and drive piston (drive element), even though the drive piston is still in the direction of top dead center. The percussion piston is slowed down by this pressure and loses kinetic energy, in extreme cases, it can even change its direction of movement. If the drive piston is then moved towards the percussion piston, the movement of the percussion piston has already slowed down and the air spring is no longer sufficiently tensioned, so that the drive piston can transmit only a small push on the percussion piston. It is also possible that the recoil, the air spring is tensioned at a time when the drive piston is indeed already moved in the direction of the percussion piston, but to which it is still near the top dead center, so that it is a low speed having. Also in this case, the air spring is less biased than when the percussion piston and the drive piston with high relative speed in an opposite movement to each other strive. In addition, the drive piston then has too low a speed at the time of maximum air spring compression. Consequently, the subsequent impact is correspondingly weak.

Similar effects can also occur in other implements, in which the drive torque is transmitted from a respective drive element to a respective motion element coupled thereto, and thus weaken a performance or physical effect of the implement.

In the FR 2 493 208 A1 discloses a working device in accordance with the preamble of claim 1 is a portable percussion tool with a built-in transverse to the direction of impact drive motor, a substantially parallel to the motor axis handle and a parallel to the engine axle mounted crankshaft for driving a striking mechanism shown. The crankshaft is set back with respect to the engine center in the rear, opposite to the direction of impact and in the direction of handle area of the striking tool. By a multi-part design of an intermediate gear provided in the drive, the installation of a rotational shock absorption and / or a safety coupling is made possible.

In the EP 1 452 278 A1 shows a control method for an at least partially axially impacting and rotating electric hand tool, in which an electromagnetic clutch is arranged in the force flow between an electric motor and a tool holder. The electromagnetic clutch is controllably connected to a computing means and is repeatedly opened and closed alternately in a process step controlled by the computing means.

The invention has for its object to provide a working device for generating a beating or pounding work movement, in which too early braking of the moving element can be prevented. It is another object of the invention to provide a working device in which the movement behavior of the drive element and moving element is improved.

The object is achieved by a working device according to claim 1. Further developments of the invention can be found in the dependent claims.

A working device for generating a beating or pounding working movement has a drive, a drivable by the drive, axially movable arranged drive element, an axially movable, with the drive element via a coupling device, such as a spring coupled motion element, which is designed as a percussion piston or ram , And arranged in the drive or in a torque flow between the drive and drive element overrunning clutch on. The overrunning clutch is in a locked state when the drive has a faster or equal speed than the drive element. The overrunning clutch is in a freewheeling state when the drive has a slower movement than the drive element. In the locked state, the overrunning clutch closes a torque flow between the drive and the drive element. In the freewheeling state, the overrunning clutch interrupts the torque flow between the drive and the drive element.

The drive may comprise a motor such as an electric or an internal combustion engine. By the drive, a drive torque can be generated, which may include a thrust torque as a translational component and / or a torque as a rotary component. This drive torque can be transmitted to the drive element via other components of the drive, such as flywheels, shafts and / or gears and connected to the drive overrunning clutch. The drive element may be designed, for example, as a drive piston.

The overrunning clutch can assume two different operating states. It is in a locked state when the drive is moving at a faster or faster rate than the drive element. This can for example be the case when the drive accelerates the drive element. In the locked state, the overrunning clutch closes the torque flow between the drive and the drive element, so that the For example, kinetic energy generated by the drive can be transmitted to the drive element in a force-locking or positive-locking manner.

If the movement of the drive is slower than that of the drive element, ie in particular if the drive element is not accelerated by the drive, the overrunning clutch is in a freewheeling state in which the torque flow between the drive and the drive element is interrupted. Due to the interruption of the torque flow, the transmission of the drive torque and / or the driving force of the drive to the drive element is interrupted in the freewheeling state.

When the overrunning clutch is in the locked state, the drive can move the axially movably disposed drive member into motion. This can be, for example, an oscillating, translatory movement of the drive element. This movement of the drive element can now be transmitted, for example by a spring device or an air spring, to the movement element coupled to the drive element. The movement element can also be arranged axially movable and is also offset by the transmission of the movement of the drive element in an oscillating, translational movement, which can be used for example as a beating or pitching motion in a tool.

The overrunning clutch may be arranged in the torque flow between the drive and the drive element. Alternatively, it is also possible that the overrunning clutch is provided operatively directly in the drive. This means that the overrunning clutch can be provided either as an independent component in the drive. Likewise, however, the overrunning clutch can be realized in terms of effect if the drive is controlled such that it can not pass into the generator mode. This is possible in particular in the case of an electric motor in which, by appropriate control of the motor, a generator operation is avoided in the case in which the motor shaft from the outside (here: the moving element) is driven. In the case of an asynchronous motor and synchronous motor with converter, this is possible, for example, because the motor is not subjected to a frequency deviating from the rotor frequency. In this case, when the motor shaft of the motor is externally driven by the fast moving moving member, the rotor in the stator can rotate freely when a current smaller than the no-load current flows in the stator.

The coupling of drive element and movement element, for example, by a spring means leads to an elastic transmission of the kinetic energy and thus to a dynamic relative movement between the drive and moving element, as will be explained below. The arrangement of the spring device between the drive and the moving element can continue to dampen the recoil of the moving member on the drive after a shock such that the drive is not excessively loaded.

Energy transfer and damping can be influenced by the design of the spring device. For example, mechanical or hydraulic spring devices can be used. Common is the use of air springs, which can form in cavities between drive and moving element by the relative movement of the elements to each other with a corresponding sealing of the cavities.

In the following, the operation of a working device according to the invention will be explained with reference to the dynamic movement of its components. For this purpose, it is assumed that the overrunning clutch is set by a movement of the drive in the locked state. This allows the drive element in a translational movement, for example, away from the moving element, are added. This movement can be transmitted by the spring device to the moving element, which, delayed by its inertia, is also placed in a movement directed to the movement of the drive element in the same direction.

At the top dead center of the movement of the drive element, the direction of movement of the drive element is reversed. At this time, the moving member continues to move in the direction of the driving member due to its inertia. By the opposite relative movement of the two elements, the spring device biases until the direction of movement of the moving element reverses and the moving element is set in a movement to the side facing away from the drive element side. This movement is amplified by the movement of the drive element towards the movement element and by a relaxation of the spring device, so that the movement element is moved away from the drive element with high kinetic energy. The high kinetic energy can be used for one work step of the implement. If the implement is designed as a percussion, for example, a strike against a whipping device, such as a tool, are performed. If the implement is designed as a rammer, the kinetic energy can move a ramming plate, so that, for example, a soil compaction can be effected.

Depending on the impact conditions, e.g. the degree of hardness of the impactor and / or under the impactor or the ramming board located substrate, the energy of the impact is now partially released to the impactor or the ramming plate and / or the substrate and partially returned to the moving element. As a result, the moving element experiences a recoil, whose energy can vary depending on the degree of hardness of the substrate.

With a strong recoil, the movement element bounces back with high kinetic energy. The drive element may still be in a movement on the moving element at this moment before it reaches the bottom dead center, or it may already have been offset by the drive in a movement away from bottom dead center. By the acceleration of the moving element, the spring device can be biased, so that the high kinetic energy of the moving element can be transferred to the drive element.

In this case, the drive torque acting on the drive element can be stronger than the drive torque of the drive, so that the drive element transmits a faster movement to the over-hollow clutch than the drive. The overrunning clutch is thereby in the freewheeling state, so that the torque flow between the drive and the drive element is interrupted. The movement of the drive element and the movement element is thus decoupled from the drive, so that the movement element can cause a thrust on the drive element in the direction of top dead center. By decoupling the drive element, the drive element can be accelerated freely, the acceleration is not braked by a coupling to the drive, so for example. in an electric motor drive by the transition to the generator mode.

As a result of the energy to be expended, the speed of the moving element and thus also of the drive element decreases on the way to top dead center. As soon as the speed of the drive element is equal to or less than the speed of the drive, the overrunning clutch can assume the locked state and close the torque flow between the drive and the drive element. The drive element and the motion element coupled thereto can be moved by the drive again.

As soon as the drive element reaches the top dead center, its direction of movement is reversed by the drive. In this case, first the moving element continues to move by its inertia towards the drive element until the direction of movement of the moving element is reversed by the increase of the bias of the spring device. The drive element may have already moved away from its top dead center at that time and have been accelerated by the drive in the direction of the movement element. Due to the kinetic energy of the drive element and the stored energy in the spring device, the moving element then with high energy are moved away from the drive element in the next working movement.

Due to the freewheeling state of the overrunning clutch, the moment of inertia of the drive can be decoupled from the drive and moving element in the manner described above. Thus, the moving element can convert the energy of a strong recoil in an acceleration on the drive element. Movement element and drive element can thus use the energy of the recoil to move in an accelerated movement in the direction of top dead center. Deceleration of the drive and moving elements by the drive, which draws kinetic energy from the elements, is reduced.

Due to the free movement of the drive element early compression of the spring device can be prevented. The time of the strongest compression of the spring device can therefore be done later, for example, at a moment in which the drive element has already changed its direction of movement and in which it is moved at a high speed in the direction of the moving element. In this case, since the energy of the moving member is determined by the thrust of the driving member and the energy stored in the spring means, the shock may be stronger.

Consequently, the freewheel makes it possible to use the energy of recoil for the subsequent work movement. Furthermore, the overall performance of the work tool can be increased by the freewheel, since on the one hand, the movement of the moving element after a high recoil stronger, and there on the other by the acceleration of the drive and the moving element by the recoil, the number of working movements at a same remaining drive power increases. In addition, the drive is protected by the decoupling of the movement of the drive and the moving element after a strong recoil.

To support the operation of the overrunning clutch, This can be suitably arranged in the torque flow between the drive and drive element. In principle, any arrangement in the effective path between the source of the drive torque and the drive element is possible, which allows a decoupling of the drive torque of the drive from the drive element. In particular, the overrunning clutch can be arranged close to the drive element in order to decouple as many elements of the drive train, which exert an inertial effect on the drive element, from the drive element. As a result, the thrust of the recoil can be used as comprehensively as possible for a movement of the drive and the movement element.

In one embodiment, the drive is a rotary drive. Furthermore, in the torque flow between the rotary drive and the drive element, a rotational movement-changing device, such as a crank mechanism, is provided for converting a rotary movement of the rotary drive into an oscillating translational movement. Here, the drive element is movable by the rotary motion converting means.

The rotary drive may comprise an electric motor, such as a high-frequency three-phase motor, or also an internal combustion engine, which sets a shaft in rotation. By way of further mechanical devices, such as a gearbox, this rotational movement can be transmitted to the overrunning clutch and further to the rotary motion converting device. This can convert the rotational movement of the rotary drive into the oscillating, axial translational movement of the drive element.

Depending on the design of the rotary motion conversion device, for example, a translational movement of the drive element between the upper and lower dead center can result, which approximately corresponds to a sine function over time. In this case, the drive element has its highest speed when it is halfway between the top and bottom dead center. The temporal and Spatial displacement of the occurrence of the maximum compression of the spring means may cause the maximum compression to occur at a time when the driving member is moved by the drive at a relatively high speed in the direction of the bottom dead center in this case. This can lead to an effective acceleration of the moving element by the drive element.

In a variant of this embodiment, the overrunning clutch is arranged in the torque flow between the rotary drive and the rotational movement-changing device. As a result, in the locked state of the overrunning clutch, the rotational movement of the drive can be transmitted to the rotary motion converter, for example the crank drive. In the freewheeling state, the torque flow can be interrupted, so that the rotary motion conversion device can be decoupled from the rotational movement of the drive.

In one embodiment, a spring means arranged as a coupling device is arranged between the drive element and the movement element. This allows an elastic coupling of the movements of the drive and the moving element and thus an elastic transmission of kinetic energy between drive and moving element. The spring device may, for example, comprise springs which are arranged between the drive element and the movement element on opposite end faces of the movement element.

In a further embodiment, the overrunning clutch is formed by a freewheel. The freewheel changes according to the relative direction of rotation on its drive side or its output side between the blocking and the freewheeling state. The drive side refers to the side of the freewheel facing the drive, from which the drive torque of the drive is transmitted to the freewheel. At the same time, the output side refers to the side connected to the drive element, via which the drive torque of the drive is transmitted to the drive element. In the locked state, the freewheel couples the on - and output side positive or positive. When freewheeling, the freewheel decouples the input and output side.

In a variant of this embodiment, the freewheel is formed by a sprag freewheel, a clamping roller freewheel, a pawl freewheel and / or a tooth freewheel. In a sprag freewheel clamp body, which have a non-circular, so not circular or spherical shape, arranged between circular cylindrical races. The races can be arranged circular cylindrical around the axes of rotation to be coupled. In the locked state input and output side can be coupled by a positive coupling of the races through the clamp body. When using a clamping roller freewheel, an inner star can be provided in the inner race, which has individually sprung rollers in wedge-shaped indentations. Depending on the relative direction of rotation, the rollers can move freely and thus decouple the inner and outer race, or they are pressed into the wedge-shaped pockets, whereby a coupling of the races formed by a clamping of the pinch rollers. When using a pawl freewheel, as used for example in ratchets and ratchets, a positive connection between the input and the output side is made in the locked state. When using a gear freewheel teeth are used to transmit a torque. The toothed freewheel automatically shifts when a coupling sleeve shifts due to a speed difference between the drive and output side.

In another embodiment, a fluid coupling may take over the function of the overrunning clutch. If e.g. integrated into the pump circuit a check valve, creates a high resistance for the blocking effect and a low resistance for the freewheel.

The implement may - as already stated above - be designed such that the overrunning clutch is provided directly in the drive. The drive is then, for example, to realize that he in an operating condition in which a drive shaft of the drive is driven by a torque from the outside, is not operated as a generator, so can not deliver power. The drive shaft and, for example, a rotor coupled thereto, when the moving element has a tendency to overtake the drive element, rotate freely, without acting electrical or magnetic fields between the rotor and a stator of the drive. For example, in an asynchronous motor, the excitation field can be switched off when the drive shaft is to be turned faster by external action, as the engine dictates. In this way, it is not necessary to provide the overrunning clutch by an independent component. Rather, by skillful control of the engine, the overrunning clutch is realized directly by the interaction between the rotor and stator.

In one embodiment, the moving element is a percussion piston. The implement may in this embodiment include a striking mechanism, which may, for example, drive a hammer, drill and / or breaker.

In a variant of this embodiment, the spring device may be formed by at least one or more air springs. The air springs may form, for example, in the trapped by the drive element and the percussion piston air volumes in a relative movement of the drive element and the percussion piston. You can transmit relative movements between the drive element and the percussion piston by a pressure or suction.

In a further embodiment, an impact device which can be acted upon by the percussion piston is provided. The impact device can be arranged so that it is regularly acted upon by the percussion piston in its oscillating translational movement. It may be formed for example by an anvil or the insertion end of a tool. It is possible that the tool holder holds a tool such that the percussion piston acts on the tool directly.

An inventive implement can be used differently become. In one embodiment, it has a tool which is arranged on the impact device. The tool may for example be a chisel in a breaker, which is actuated by the regular action by the percussion piston, so the moving element. Furthermore, a hammer or hammer drill can be arranged on the impact device and operated by the percussion piston.

In a further embodiment, the implement is designed as a vibratory rammer, wherein the moving element is formed by a ramming piston. At the ram can be arranged a ramming plate, which can be offset by the movement of the ram in pounding movements. These movements can be used, for example, for soil compaction.

In a variant of this embodiment, the spring device is formed by a helical spring, which couples the movements of drive element and ramming piston and transmits mutually. By the coil spring, the high kinetic energy, which can be transmitted by the movement of the ramming piston and the ramming plate, which may have a high mass, suitably between the drive element and ramming piston. Other types of springs, such as gas springs or E-lastomerfedern, can be used alternatively or additionally.

In a further variant of this embodiment, the ramming piston has a cavity in which the helical spring, gas pressure spring and / or elastomer spring is arranged and coupled to the drive element. In this way, a suitable coupling of the movements of the drive element and the ramming piston can be achieved, an axial guidance of the movements supported and at the same time space can be saved.

Fig. 1

ein Schlagwerk mit Freilauf und einfacher Luftfeder;

Fig. 2

ein Schlagwerk mit Freilauf und doppelter Luftfeder;

Fig. 3A

schematisch einen Klemmkörperfreilauf;

Fig. 3B

ein Segment des Klemmkörperfreilaufs im Freilaufzustand; und

Fig. 3C

ein Segment des Klemmkörperfreilaufs im Sperrzustand.

Fig. 4

einen Stampfer mit Freilauf und doppelt wirkender Schraubenfeder;

These and other features of the invention will now be described by way of example with the aid of the accompanying drawings explained in more detail. Show it:

Fig. 1

a percussion with freewheel and simple air spring;

Fig. 2

a percussion with freewheel and double air spring;

Fig. 3A

schematically a sprag freewheel;

Fig. 3B

a segment of the sprag freewheel in the freewheeling state; and

Fig. 3C

a segment of the sprag freewheel in the locked state.

Fig. 4

a rammer with freewheel and double-acting coil spring;

This in Fig. 1 The striking mechanism shown schematically is operated by a motor 1 whose torque is transmitted via a gear 2 to a freewheel 3.

Depending on the operating state, the freewheel 3 can transmit the torque, which is transmitted to it via its drive side, to a rotational movement changing device arranged on its output side, which in FIG Fig. 1 is formed by a crank mechanism 4 and a connecting rod 5. The crank mechanism 4 and the connecting rod 5 convert the torque transmitted via the freewheel 3 into an oscillating translational movement of a drive piston 6 connected to the connecting rod 5.

The drive piston 6 is arranged movably in a hollow guide cylinder 7. In the guide cylinder 7 a cylindrically shaped percussion piston 8 is further arranged on the side facing away from the connecting rod 5 side of the drive piston 6 movable. The percussion piston 8 is arranged so that it can apply a tool 10 held by a tool holder 9 to the side of the guide cylinder 7 facing away from the crank drive 4.

Both the drive piston 6 and the percussion piston 8 are axially movable along the central axis of the guide cylinder 7 and sealed against the guide cylinder 7 by means of gap seals. The gap seals enable an air spring 11 to be formed at high relative speeds between the drive piston 6 and the percussion piston 8 by compression or decompression of the air volume trapped between the drive piston 6 and the percussion piston 8, permitting an elastic momentum transfer between the drive piston 6 and the percussion piston 8.

The operation of the in Fig. 1 described hammer mechanism with freewheel and simple air spring described on the basis of a beating cycle:

When transmitting a torque from the engine 1 via the transmission 2 to the drive side of the freewheel 3, the freewheel 3 assumes a blocking state, if the crank mechanism 4 has a lower speed on the output side of the freewheel 3 at this time. In the locked state, the freewheel 3 transmits the torque to the crank mechanism 4, which is thereby set in rotation. The rotational movement is converted via the connecting rod 5 in the oscillating translational movement of the drive piston 6 along a central axis of the guide cylinder 7. In the in Fig. 1 shown position of the components of the impact mechanism, this can for example lead to a movement of the drive piston 6 in the direction of the percussion piston 8. As a result, the trapped in the guide cylinder 7 between the drive piston 6 and the percussion piston 8 air spring 11 is compressed and the motion impulse of the drive piston 6 is elastically transmitted to the percussion piston 8. The percussion piston 8 is, delayed by its inertia, also offset in a movement corresponding to the direction of movement of the drive piston 6 and moved toward the tool 10. He hits the tool 10 at a stroke, which forwards the pulse transmitted in this case to a substrate, not shown, or an unillustrated workpiece. Depending on the hardness of the workpiece and the tool 10 experiences the impact piston 8 while a recoil in the direction of the drive piston 6. The drive piston 6 may be at this time, depending on the speed of the motor 1 in a movement in the direction of the percussion piston 8, or he can after reaching a bottom dead center by the crank mechanism 4 and the connecting rod 5 are already moved in a movement in the opposite direction.

Due to the energy contained in the recoil of the percussion piston 8 is accelerated in the direction of the drive piston 6, wherein the trapped between the drive piston 6 and the percussion piston 8 air spring 11 is compressed. As a result, the acceleration energy of the percussion piston 8 can be elastically transmitted to the drive piston 6. By the connecting rod 5, the axial movement of the drive piston 6 is now converted into a rotational movement of the crank mechanism 4 and transmitted to the output side of the freewheel 3. If the rotational movement of the crank mechanism is faster transmitted through the engine 1 and the transmission 2 from the drive side to the freewheel 3, the freewheel 3 assumes a freewheeling state in which a torque flow between its arrival and its output side is interrupted. The movement of the drive piston 6 is thus decoupled from the drive of the motor 1, and the percussion piston 8 can accelerate the drive piston 6 in the direction of the recoil.

With decreasing speed of the percussion piston 8, the movement of the drive piston 6 and thus also of the crank drive 4 slows down. As soon as the rotational movement transmitted through the crank drive 4 to the output side of the freewheel 3 slows down or is the same as that through the engine 1 via the transmission 2 On the drive side of the freewheel 3 transmitted rotary motion, the freewheel 3 again assumes the blocking state and the motor 1 can drive the movement of the drive piston 6.

If the drive piston 6 at this time is still in a movement away from the percussion piston 8, the air spring 11 is decompressed. Due to the resulting suction the movement impulse becomes of the drive piston 6 elastically transmitted to the percussion piston 8.

As soon as the movement direction transmitted by the crank drive 4 and the connecting rod 5 to the drive piston 6 reverses, an opposite relative movement between the drive piston 6 and the percussion piston 8 occurs. As a result, the air spring 11 is again compressed and the next impact cycle is initiated.

Since the drive piston 6 can be decoupled from the drive torque of the motor 1 by the action of the freewheel 3 and can be accelerated unhindered by the action of the recoil, he is in an advanced position at the beginning of the next beat cycle. The maximum air spring compression can therefore take place at a time when the drive piston 6 is already displaced and accelerated in a movement in the direction of the percussion piston 8. The drive piston 6 therefore has at the time of maximum air compression high speed in the direction of the percussion piston 8, so that the percussion piston 8 can be effectively accelerated and the subsequent impact of the percussion piston 8 on the tool 10 correspondingly strong.

In this way, the energy of the recoil can be used for the subsequent blow. In addition, the impact performance of the percussion is increased, because by the use of the freewheel 3, the stroke rate of the percussion increases at a constant speed of the engine 1.

Fig. 2 shows a percussion with freewheel and double air spring. The functions of the engine 1, the transmission 2, the freewheel 3, the crank mechanism 4 and the connecting rod 5 correspond to the functions already described above.

In Fig. 2 the drive piston 6a is cylindrical and has a cavity in which a percussion piston 8a is inserted axially movable along the central axis of the drive piston 6a. Of the Percussion piston 8a protrudes on the side facing away from the connecting rod 5 side of the drive piston 6a out of this, so that it can act on the fixed by the tool holder 9 tool 10 in a striking motion. The drive piston 6a and the percussion piston 8a are sealed relative to each other by means of gap seals such that upon a relative movement of the two pistons to one another, the air volumes enclosed within the drive piston 6a on both sides of the percussion piston 8a are compressed or decompressed. Here, a first air spring 11a is formed on the side facing away from the tool 10 side of the percussion piston 8a and a second air spring 11b on the tool 10 side facing the percussion piston 8a. The two air springs 11a and 11b allow effective transmission of kinetic energy between the drive piston 6a and the percussion piston 8a.

As in the in Fig. 1 can also be seen in the in Fig. 2 shown striking mechanism after acceleration of the percussion piston 8a by a transmitted by the tool 10 on the percussion piston 8a recoil the freewheel 3 interrupt the flow of torque between the engine 1 and the drive piston 6a, so that the percussion piston 8a can accelerate the drive piston 6a unhindered.

In addition, in the in Fig. 2 shown percussion movement of the drive piston 6a are decoupled from the motor 1 when the percussion piston 8a moves with high kinetic energy in the direction of the tool 10 and thereby accelerates the drive piston by compression of the second air spring 11b. Thus, it can be prevented that the percussion piston 8a is braked shortly before the impact by the coupling to the torque flow of the drive.

In this way, in the in Fig. 2 with hammer and freewheel and double air spring, the energy of the recoil is used for the preparation of the next stroke and the stroke rate is increased while the engine speed remains the same.

Fig. 3A schematically shows a sprag freewheel with an inner drive ring 12 and a concentrically arranged, outer output ring 13, wherein between the drive ring 12 and the output ring 13 non-circular clamping body 14a, 14b, 14c, ... are arranged. Depending on the orientation of a section through one of the clamping bodies 14a, 14b, 14c,..., The diameter along the section is different. Depending on a relative movement and thus of a relative rotational speed between the drive ring 12 and the output ring 13 of the sprag freewheel assumes a freewheeling state or a blocking state in which the clamp body 14a, 14b, 14c, ... align differently.

The freewheeling state and the locked state are in the FIGS. 3B and 3C and are described below.

Fig. 3B shows the sprag freewheel Fig. 3A in the freewheeling state, in which the drive ring 12 has a lower rotational speed than the output ring 13 and thus a negative relative movement to the output ring 13. In this case, the clamping body 14a, 14b and 14c are oriented so that a smaller diameter between the drive ring 12 and the output ring 13 comes to rest, so that the movement of the output ring 13 is decoupled from that of the drive ring 12.

Fig. 3C shows the sprag freewheel Fig. 3A in the locked state. Here, the drive ring 12 has a higher speed than the output ring 13, whereby the clamping body 14 a, 14 b and 14 c are aligned so that a larger diameter between the drive ring 12 and the output ring 13 comes to rest. This results in a positive connection, via which the torque of the drive ring 12 can be transmitted to the output ring 13.

Fig. 4 shows a rammer with freewheel and double-acting coil spring. The functions of the engine 1, the transmission 2, the freewheel 3, the crank mechanism 4 and the connecting rod 5 correspond to the functions already described above and will not be repeated described.

In the in Fig. 4 The rammer shown is a ramming piston 15 is provided, which has at its lower end a ramming plate or a padfoot. The rammer can be used, for example, for soil compaction.

Furthermore, the rammer on a drive element 6b, which is elongated and coupled to the connecting rod 5. It is partially embedded in a cavity of the ramming piston 15 such that the drive element 6b and the ram 15 are movable relative to each other axially along a common center axis.

Within the cavity of the ramming piston 15, the drive element 6b has a collar 16 serving as a holding device, with which it is coupled between two helical springs 17a and 17b, which are provided in the cavity of the ramming piston 15. The coil springs 17a, 17b are aligned along the common center axis of the ramming piston 15 and the drive element 6b and can touch end faces of the cavity of the ramming piston 15. This ensures that the coil springs 17a, 17b can transmit an axial relative movement of the drive element 6b and ram 15 elastic. The coil springs 17a, 17b thus enable an effective transmission of the kinetic energy between the drive element 6b and the ram 15.

Alternatively, the coil springs 17a, 17b can also be replaced by only one coil spring, which can be coupled to the drive element in a central region with respect to its longitudinal axis.

As in the in Fig. 2 can also be seen in the in Fig. 4 shown rammer after acceleration of the ramming piston 15 by a transmitted via the ramming plate on the ramming piston 15 recoil the freewheel 3, the torque flow between the motor 1 and the drive element 6b interrupt, so that the ramming piston 15 can accelerate the drive element 6b unhindered.

In addition, the movement of the drive element 6 b can be decoupled from the motor 1 when the ram 15 moves with high kinetic energy in the direction of the ramming plate, thereby accelerating the drive element 6 b by compression of the first coil spring 17 a. Thus it can be prevented that the ram 15 is braked shortly before the impact of the ramming plate by the coupling to the torque flow of the drive.

In this way, in the in Fig. 4 shown rammer with freewheel and double-acting coil spring the energy of the recoil used for the preparation of the next stamping and the number of tamping strokes are increased at a constant engine speed.

Claims (14)

1. Working unit for producing a percussion or stamping working movement, having

   - a drive (1);

   - a drive element (6) which is disposed in an axially movable manner and can be driven by the drive (1);

   - a movement element which is disposed in an axially movable manner, is coupled to the drive element (6, 6a, 6b) via a coupling device and is formed as a percussion piston (8, 8a) or stamping piston (15); and

   - an overrunning clutch (3) which is disposed in the drive (1) or in a torque flow between the drive (1) and the drive element (6, 6a, 6b);

   characterised in that

   - the overrunning clutch (3) is in an engaged state when the drive (1) has the same or quicker movement than the drive element (6, 6a, 6b), and is in a free state when the drive (1) has a slower movement than the drive element (6, 6a, 6b), and in that

   - the overrunning clutch completes the torque flow between the drive (1) and the drive element (6, 6a, 6b) in the engaged state and interrupts said torque flow in the free state.
2. Working unit as claimed in Claim 1, characterised in that

   - the drive (1) is a rotary drive (1); and in that

   - a rotary movement converting device (4, 5) disposed in the torque flow between the rotary drive (1) and the drive element (6, 6a, 6b) is provided for converting a rotary movement of the rotary drive (1) into an oscillating translational movement of the drive element (6, 6a, 6b).
3. Working unit as claimed in Claim 2, characterised in that

   - the overrunning clutch (3) is disposed in the torque flow between the rotary drive (1) and the rotary movement converting device (4, 5).
4. Working unit as claimed in any one of the preceding claims, characterised in that a spring device (11) used as a coupling device is disposed between the drive element (6, 6a, 6b) and the movement element (8, 8a, 15).
5. Working unit as claimed in any one of the preceding claims, characterised in that the overrunning clutch (3) is formed by a free-wheel clutch (3).
6. Working unit as claimed in Claim 5, characterised in that the free-wheel clutch (3) is formed by a sprag free-wheel clutch, a grip roller free-wheel clutch, a racheting free-wheel clutch and/or a toothed free-wheel clutch.
7. Working unit as claimed in any one of the preceding claims, characterised in that

   - the overrunning clutch (3) is disposed in the drive (1);

   - the drive (1) can be controlled such that it cannot be operated as a generator in an operating state in which a drive shaft of the drive (1) is driven in a rotating manner from the outside.
8. Working unit as claimed in any one of Claims 1 to 7, characterised in that the movement element (8, 8a) is a percussion piston (8, 8a).
9. Working unit as claimed in Claim 8, characterised in that the spring device (11) is formed by at least one air spring (11, 11 a, 11b) which is produced during relative movement of the drive element (6, 6a) and the percussion piston (8, 8a).
10. Working unit as claimed in Claim 9, characterised in that an impact apparatus is provided which can be influenced by the percussion piston (8, 8a).
11. Working unit as claimed in Claim 10, characterised in that a tool (10) is disposed on the impact apparatus.
12. Working unit as claimed in any one of the Claims 1 to 7, characterised in that the movement element is formed by a stamping piston (15).
13. Working unit as claimed in Claim 12, characterised in that the spring device is formed by a helical spring (17a, 17b), a gas spring and/or an elastomer spring.
14. Working unit as claimed in Claim 13, characterised in that the stamping piston (15) comprises a hollow chamber in which the helical spring (17a, 17b) is disposed and is coupled to the drive element (6, 6a, 6b).

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