GB2419170A

GB2419170A - Power tool with three mode overload clutch

Info

Publication number: GB2419170A
Application number: GB0525196A
Authority: GB
Inventors: Michael Stirm; Martin Lauterwald; Stefan D Gensmann
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 2002-09-13
Filing date: 2002-09-13
Publication date: 2006-04-19
Anticipated expiration: 2022-09-13
Also published as: GB2419170B; CN101058153B; GB0221225D0; GB0525196D0; CN1694786A; GB2392966B; GB2392966A; CN101058153A; CN100343025C

Abstract

A power tool, g a hammer drill, has a first mode of operation in which a first set drive balls 113a are urged into engagement with drive pockets 115a of a small diameter driven gear 13c by portion 121a of actuating shaft 121. In a second mode of operation a second set of drive balls 113b are pushed radially outwardly by portion 121a into engagement with large driven gear 13d. When portion 121b of the actuating shaft 21 is radially inward of drive balls 113b the drive balls move radially inwardly disengaging with drive pockets 115d so that no drive is transmitted to drive shaft 5. In a third mode of operation the portion 21b of the actuating shaft 21 is radially inwardly of both sets of drive balls 113a, 113b both sets are disengaged from the drive pockets 115a, 115b and no rotary drive is transmitted between the driven gears 13c, 13d and the drive shaft 5. Thus the overload clutch in the first mode transmits drive to the shaft 5 below a first predetermine torque and stops drive above the first torque while in the second mode it transmits drive below a second predetermined torque and stops torque above the second torque and in the third mode the overload clutch cuts off drive to the shaft 5 in response to a mode change mechanism (126, 128, fig 11A).

Description

1 2419170

ROTARY TOOL

The present invention relates to a hand held power tool with a rotatingly driven tool or bit, in particular the present invention relates to electrically powered rotary hammering tools.

Rotary hammers will normally have a housing and a hollow cylindrical spindle mounted in the housing. The spindle allows insertion of the shank of a tool or bit, for example a drill bit or a chisel bit, into the front end thereof so that it is retained in the front end of the spindle with a degree of axial movement. The spindle may be a single cylindrical part or may be made of two or more co-axial cylindrical parts, which together form the hammer spindle. For example, a front part of the spindle may be formed as a separate tool holder body for retaining the tool or bit.

Such hammers are provided with an impact mechanism which converts the rotational drive from an electric motor to a reciprocating drive for driving a piston, which may be a hollow piston, to reciprocate within the spindle. The piston reciprocatingly drives a ram by means of a closed air cushion located between the piston and the ram. The impacts from the ram are transmitted to the tool or bit of the hammer, optionally via a beatpiece.

Rotary hammers can be employed in combination impact and drilling mode, and also in some cases in a drilling only mode, in which the spindle, or a forwardmost part of the spindle, and hence the bit inserted therein will be caused to rotate. In the combination impact and drilling mode the bit will be caused to rotate at the same time as the bit receives repeated impacts. A rotary drive mechanism transmits rotary drive from the electric motor to the spindle to cause the spindle, or a forwardmost part thereof to rotate.

It is a problem with hand held power tools with a rotating bit that during use of the tool blocking events can sometimes occur, when the bit becomes stuck in the workplace in such a way that the bit can no longer rotate relative to the workpiece. In this case, the rotary drive to the bit causes the housing of the tool to rotate with respect to the stationary bit. It is known to detect blocking events, for example from P- UK-PR OX4B CNSTR US5,914,882, US5,584,619, EP771,619 and GB2,086,277 and then once such an event is detected to arrest the rotary drive to the bit. This can be done by braking the motor, which motor provides rotary drive to the bit via a gear arrangement, but this involves an inherent delay due to the time required to arrest the motor. Alternatively or additionally, the rotating spindle can be braked by engaging the spindle with a part of the hammer housing, in some way. The preferred way of cutting off rotary drive to the bit is by the use of a releasable clutch arrangement in the drive train between the motor of the hammer and the spindle.

The present invention aims to provide an improved design of clutch for cutting off rotary drive to the bit when a blocking event is detected.

According to a first aspect of the present invention, there is provided a hand held, preferably motor driven, power tool, comprising: a spindle for rotatingly driving a tool or bit; a spindle rotary drive train for rotatingly driving the spindle; an overload clutch in the spindle rotary drive train for transmitting rotary drive to the spindle below a predetermined torque and for cutting transmission of rotary drive above the predetermined torque; and an arrangement for detecting blocking events; charactensed in that the overload clutch is arranged to cut off rotary drive to the spindle when a blocking event is detected.

Power tools with a rotatingly driven spindle, in particular if they are highly powered tools, such as rotary hammers, generally have an overload clutch in the drive train for rotatingly driving the spindle. Such an overload clutch can help in the event of a blocking event, if the user has a strong grip on the tool, because when the tool housing begins to rotate, the torque required to rotatingly drive the spindle will increase. If the torque increases to above the predetermined threshold then the overload clutch will stop transmitting rotary drive and drive will no longer be transmitted to the spindle. The overload clutch also acts to reduce damage to components of the tool, for example the motor of the tool, when high torques are experienced. According to the first aspect of the present invention an overload clutch is modified to provide cutting off of rotary drive to the spindle in response to a P UK-PRIOg4R #CNSTR blocking event being detected. The overload clutch may be located in any part of the gear train from the motor of the tool to the spindle, and may for example by the type of overload clutch known in the field which is mounted around the spindle.

In order to cut off rotary drive to the spindle, the predetermined torque of the overload clutch above which transmission of rotary drive is cut off can be reduced in response to the detection of a blocking event. The overload clutch may still provide the function of known overload clutches, depending on the level at which the predetermined torque is set when no blocking event is detected. In accordance with the present invention most types of overload clutch known for use in the drive train of a rotary tool can be adapted to reduce the torque at which they stop transmitting rotary drive in response to the detection of a blocking event. The torque at which the overload clutch stops transmitting rotary drive may be reduced to substantially zero in response to the detection of a blocking event.

The present invention is particularly applicable to rotary hammers as they are generally powerful tools and are known to experience problems from blocking events.

Such rotary hammers generally comprise a hammering mechanism, generally located within the spindle, for generating repeated impacts on a tool or bit mounted at a forward end of the spindle. The spindle is preferably made of as few parts as possible, but it may include a separate tool holder portion located coaxially and forwardly from the portion of the spindle in which the hammering mechanism is mainly located.

It is known to use arrangements for detecting blocking events which are purely mechanical, for example using inertial masses, in which case these arrangements can act mechanically on the overload clutch. Such a mechanical arrangement may include an inertial mass pivotally mounted within the housing of the tool. According to one embodiment of the present invention, the arrangement for detecting blocking events may comprise an inertial mass pivotally mounted within the tool housing and comprising a latch for engaging an actuator of the overload clutch and a spring is provided for urging the actuator of the clutch into a cut off position. These components are arranged such that when a blocking event occurs, the inertial mass pivots in the housing to disengage the latch from the actuator and the spring urges P-UK-PRlOR4B NCNSTR the actuator into the cut off position in which the actuator causes the rotary drive to the spindle to be cut off. This can provide a quick and accurate way of detecting a blocking event.

It is also known to use an electro-mechanical arrangement, which utilises for example, an inertial mass and senses the movement of the mass when a blocking event is occurring to generate an electrical output signal.

It is also known to detect blocking events electronically. For example, the arrangement for detecting blocking events may comprise a sensor, for example an accelerometer, a torque sensor, a motor current or voltage sensor or other types of sensor known in the art for detecting blocking events. The sensor senses an operational condition of the tool, for example an accelerometer will detect vibrations of the tool and a torque sensor may detect a relative torque between components of the tool. The outputs from the sensor are fed into an electronic evaluation unit for analysing the signals from the sensor and for generating an electrical output signal when a blocking event is detected. Examples of such electronic evaluation units are disclosed in US5,914,882, EP771,619 and US5,584,619.

Where the arrangement for detecting blocking events generates an electrical output signal in response to the detection of a blocking event, then the overload clutch may include an electro-mechanical interface, for example an electro-magnet acting on a magnetic element, which interface is responsive to the output signal to reduce the torque at which the overload clutch slips.

Generally an overload clutch will comprise a driven gear and a driving gear and a coupling element, for example a resilient element or clutch balls biased by a resilient element, for coupling the driven gear and driving gear below the predetermined torque and for enabling de-coupling of the driven gear and the driving gear above the predetermined torque. According to one embodiment of the present invention the arrangement for detecting blocking events acts on the coupling element to cut off rotary drive to the spindle when a blocking event is detected. The coupling element may be a resilient element which couples the driven gear and the driving gear via a set of locking elements mounted on one of the driven gear and the driving P-UK-PRI084B #CNS rR gear and engageable with the other of the driven gear and the driving gear in order to transmit rotary drive therebetween. The arrangement for detecting blocking events may act to move the coupling element, such as a resilient element, with respect to the driven and driving gears in order to vary the torque at which the overload clutch slips. Alternatively, the driven gear can be coupled to the output of the overload clutch by a drive coupling and the arrangement for detecting blocking events acts on the drive coupling to cut off the transmission of rotary drive in response to the detection of a blocking event.

Sometimes it is desirable, in particular in a rotary hammer, to have different torques at which the rotary drive to the spindle is cut off, in different applications of the hammer. Therefore, in one embodiment of the present invention the overload clutch may have a first mode of operation in which the overload clutch transmits rotary drive to the spindle below a first predetermined torque and stops transmission of rotary drive above the first predetermined torque, a second mode of operation in which the overload clutch transmits rotary drive to the spindle below a second predetermined torque, different from the first predetermined torque and stops transmission of rotary drive above the second predetermined torque, and a third mode of operation in which the overload clutch cuts off rotary drive to the spindle when a blocking event is detected.

The powered tool may be a rotary hammer, having a non-rotary mode and a mode change mechanism of the hammer may be arranged to cause the overload clutch to cut off rotary drive to the spindle, for example by reducing the torque at which the overload clutch stops transmitting rotary drive, when the non-rotary mode is selected. Thus, the overload clutch according to the present invention, when incorporated in a rotary hammer can additionally be used as part of the mode change mechanism of the hammer for stopping rotary drive to the hammer spindle when the mode is switched to the non-rotary mode.

According to a second aspect of the present invention there is provided a hand held, preferably motor driven electrically powered rotary hammer, comprising: a spindle for rotatingly driving a tool or bit; P-UK-PRIO84B #CNSTR a hammering mechanism for generating repeated impacts on a tool or bit mounted at a forward end of the spindle; a spindle rotary drive train for rotatingly driving the spindle; a mode change mechanism for selectively disengaging a clutch in the spindle rotary drive train so as to cut off the rotary drive to the spindle; and an arrangement for detecting blocking events; characterized in that the clutch is arranged to disengaged when a blocking event is detected.

Rotary hammers are well known with mode change mechanisms which are used to selectively provide rotary drive to a spindle of the hammer. For example, in a drilling only mode or a rotary hammering mode of the hammer, the mode change mechanism acts to engage a clutch in the spindle rotary drive train so that rotary drive is transmitted to the spindle. In hammering only mode the mode change mechanism acts to disengage the clutch. Many such mode change mechanisms for selectively cutting off drive to the spindle are known in the art and would be suitable for use in the present invention. In addition rotary hammers may also have a part of the mode change mechanism for selectively disengaging the hammering mechanism, as is well known in the art. According to the second aspect of the present invention the clutch in the spindle drive train acted on by the mode change mechanism to disengage rotary drive to the spindle is also utilised to disengage rotary drive to the spindle when a blocking event is detected. Thus, the present invention has the advantage of utilising the clutch for two purposes, mode change and cutting off rotary drive when blocking events occur.

The comments above in relation to the arrangement for detecting blocking events also apply to this second aspect of the present invention.

In one embodiment the clutch includes a spindle drive gear arrangement axially slideably mounted on the spindle and selectively engageable with part of the spindle drive train in order to rotatingly drive the spindle. In this case the arrangement for detecting blocking events acts on the spindle drive gear arrangement to move the spindle drive gear arrangement axially along the spindle and out of engagement with the part of the spindle drive train when a blocking event is detected. According to P'UKPRiOh4B a('NSTR this embodiment, the mode change arrangement can also act on the spindle drive gear arrangement to move the spindle drive gear arrangement axially along the spindle and out of engagement with the part of the spindle drive train, when a non- rotary mode is selected.

The clutch may additionally be an overload clutch of the type described above in relation to the first aspect of the present invention.

According to a third aspect of the present invention there is provided a hand held, preferably motor driven electrically powered rotary hammer, comprising: a spindle for rotatingly driving a tool or bit; a hammering mechanism for generating repeated impacts on a tool or bit mounted at a forward end of the spindle; a spindle rotary drive train for rotatingly driving the spindle; an overload clutch in the spindle rotary drive train for transmitting rotary drive to the spindle below a predetermined torque and for cutting transmission of rotary drive above the predetermined torque; a mode change mechanism for selectively cutting off the rotary drive to the spindle; characterized in that the overload clutch has: a first mode of operation in which the overload clutch transmits rotary drive to the spindle below a first predetermined torque and stops transmission of rotary drive above the first predetermined torque; a second mode of operation in which the overload clutch transmits rotary drive to the spindle below a second predetermined torque, different from the first predetermined torque, and stops transmission of rotary drive above the second predetermined torque; and a third mode of operation in which the overload clutch cuts off rotary drive to the spindle in response to the mode change mechanism.

In one embodiment of this third aspect of the present invention overload clutch may comprise a driven gear and a driving gear and a coupling element for coupling the driven gear and driving gear below the predetermined torques and for enabling de-coupling the driven gear and the driving gear above the predetermined torques P-UK-PRl08413 #CNSTR and a drive coupling for coupling the driven gear to the output of the clutch, wherein the mode change arrangement acts on the drive coupling to alter the predetermined torque and to stop the transmission of rotary drive. There may be two driven gears and one of the driven gears can be coupled to the output of the clutch via the drive coupling so that the overload clutch has a first predetermined torque, the other or both of the driven gears can be coupled to the output of the clutch via the drive coupling so that the overload clutch has a second predetermined torque, different from the first or neither of the driven gears can be coupled to the output of the clutch via the drive coupling so that the transmission of rotary drive is stopped.

One form of rotary hammer according to the present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a partially cutaway longitudinal cross section through a first embodiment of a rotary hammer according to a first aspect of the present invention; Figure 2 shows a longitudinal cross-section through a first embodiment of the overload clutch of the rotary hammer of Figure 1; Figure 3 shows a longitudinal cross-section through a second embodiment of the overload clutch of the rotary hammer of Figure 1; Figure 4 shows a partially cutaway longitudinal cross section through a rotary hammer according to a second aspect of the present invention; Figure 5 shows a longitudinal cross-section through a rotary hammer according to a second embodiment of the first aspect of the present invention; Figure 6 shows a from a front view, a transverse cross-section of the mechanical blocking event detection arrangement of the rotary hammer of Figure 5; Figure 7 shows a longitudinal cross-section through a first embodiment of the overload clutch of the rotary hammer of Figure 5; Figure 8 shows a longitudinal cross-section through a second embodiment of the overload clutch of the rotary hammer of Figure 5; Figure 9 shows a longitudinal cross-section through a third embodiment of an overload clutch suitable for use in the rotary hammer of Figures 1 or 5; Figure 10 shows a broken apart perspective view of the components of the overload clutch of Figure 10; and P-UK-PRI084B CNSTR Figure 11 shows a fourth embodiment of an overload clutch suitable for use in the rotary hammer of Figures 1 or 5.

In the Figures like parts are identified by like numerals.

The hammer shown in Figure 1 comprises an electric motor (2), an spindle drive train and a crank drive arrangement which are housed within a metal gear housing (not shown) surrounded by a plastic housing (4). A rear handle housing incorporating a rear handle (6) and a trigger switch arrangement (8) is fitted to the rear of the housing (4). A cable (not shown) extends through a cable guide and connects the motor to an external electricity supply. Thus, when the cable is connected to the electricity supply and the trigger switch arrangement (8) is depressed the motor (2) is actuated to rotationally drive the armature of the motor.

The metal gear housing is made from magnesium with steel inserts and rigidly supports the components housed within it.

A driving gear (9) is press fitted onto the motor pinion (3) and has teeth which engage the teeth of a driving gear (12) of an overload clutch arrangement (14) to rotatingly drive the driving gear (12). The driving gear (12) rotatingly drives a driven gear (13) of the overload clutch arrangement (14) when the torque transmitted between the two gears (12,13) is below a predetermined threshold and if no blocking event is detected. The driven gear (13) is press fit onto a spindle drive shaft (5), formed with a bevel pinion (7) at its end remote from the driven gear wheel (13). The bevel pinion meshes with a beveled spindle drive gear (10) which drive gear is non rotatably mounted on the spindle (40). The overload clutch arrangement (14) is described in more detail below with respect to Figures 2 and 3.

The teeth of the driving gear (9) also engage the teeth of a crank drive gear (20) to rotatingly drive the drive gear (20). The drive gear (20) is non- rotatably mounted on a crank drive spindle (22) which spindle is rotatably mounted within the gear housing. A crank plate (30) is nonrotatably mounted at the end of the drive spindle remote from the drive gear (20), which crank-plate is formed with an eccentric bore for housing an eccentric crank pin (32). The crank pin (32) extends from the crank plate into a bore at the rearward end of a con-rod or crank arm (34) so that the P-IJK-PRI084B dCNSTR con-rod (34) can pivot about the crank pin (32). The opposite forward end of the con- rod (34) is formed with a bore through which extends a trunnion pin (36) so that the con-rod (34) can pivot about the trunnion pin. The trunnion pin (36) is fitted to the rear of a piston (38) by fitting the ends of the trunnion pin (36) into receiving bores formed in a pair of opposing arms, which arms extend to the rear of the piston (38).

The piston is reciprocally mounted in a cylindrical hollow spindle (40) so that it can reciprocate within the hollow spindle. An O-ring seal is fitted in an annular recess formed in the periphery of the piston (38) so as to form an air tight seal between the piston (38) and the internal surface of the hollow spindle (40).

Thus, when the motor (2) is actuated, the armature pinion (3) rotatingly drives the driving gear (9) and the driving gear rotatingly drives the crank drive spindle (22) via the drive gear (20). The drive spindle rotatingly drives the crank plate (30) and the crank arm arrangement comprising the crank pin (32), the con-rod (34) and the trunnion pin (36) convert the rotational drive from the crank plate (30) to a reciprocating drive to the piston (38). In this way the piston (38) is reciprocatingly driven back and forth along the hollow spindle (40), when the motor (2) is actuated by depression of the trigger switch (8). The driving gear (9) also drives the driving gear (12) of the clutch arrangement (14) which drives the driven gear (13) of the clutch arrangement. The driven gear (13) of the clutch arrangement rotatingly drives the spindle drive shaft (5) which rotatingly drives the spindle drive gear (10) and thus the spindle (40) via the bevel pinion (7) .

A ram (58) is located within the hollow spindle (40) forwardly of the piston (38) so that it can also reciprocate within the hollow spindle (40) . An O-ring seal is located in a recess formed around the periphery of the ram (58) so as to form an air tight seal between the ram (58) and the spindle (40). In the operating position of the ram (58), with the ram located rearward of venting bores (not shown) in the spindle a closed air cushion (44) is formed between the forward face of the piston (38) and the rearward face of the ram (58). Thus, reciprocation of the piston (38) reciprocatingly drives the ram (58) via the closed air cushion (44). When the hammer enters idle mode (ie. when the hammer bit is removed from a workpiece), the ram (58) moves forwardly, past the venting bores. This vents the air cushion and so the ram (58) is P-UK-PR 1 084B #CNS I R no longer reciprocatingly driven by the piston (38) in idle mode, as is well known in the art.

A beatpiece (64) is guided so that it can reciprocate within forward portion of the spindle. A bit or tool (68) can be releasably mounted within a tool holder (66) so that the bit or tool (68) can reciprocate to a limited extent within a tool holder portion of the spindle. When the ram (58) is in its operating mode and is reciprocatingly driven by the piston (38) the ram repeatedly impacts the rearward end of the beatpiece (64) and the beatpiece (64) transmits these impacts to the rearward end of the bit or tool (68) as is known in the art. These impacts are then transmitted by the bit or tool (68) to the material being worked.

In the arrangement in Figure 1, an operational condition of the rotary hammer is monitored by a sensor, such as an angular accelerometer (16). The signals from the sensor (16) are transmitted via an input interface to an electronic evaluation unit, which may be formed as a microcontroller (17). The micro-controller analyses the signals from the accelerometer (16) and is programmed to generate an output signal when a blocking event is about to occur. For example, the arrangement of the type described in US5,584,619, US5,914,882 or EP 771,619 can be used to generate an output signal when a blocking event is about to occur. The warning signal triggers a circuit (18) powered by the power supply to the motor (2) of the hammer. The circuit (18), when triggered supplies electric current to an electromagnet (19) which causes the clutch arrangement (14) to disengage in order to interrupt the drive from the driving gear (9) to the spindle drive shaft (5).

One embodiment of an overload clutch arrangement suitable for use in the arrangement of Figure 1 is shown in Figure 2. The driving gear (12) of the overload clutch arrangement (14) is rotationally mounted within the hammer housing via a bearing (15). The driving gear (12) is mounted to rotate about an actuating shaft (21), which actuating shaft is axially slideable with respect to the driving gear. The driven gear (13) of the overload clutch arrangement (14) is rotationally mounted within the hammer housing via a bearing (23). The driven gear (13) is also mounted to rotate about the axially slideable actuating shaft (21) and is formed with a bore (24) for axially slidably receiving a first end of the actuating shaft (21).

P-UK-PR1084H #CNSTR Rotary drive is transmitted between the driving gear (12) and the driven gear (13) of the overload clutch arrangement (14) via a plurality of locking balls (25). The driving gear (12) is formed with a cylindrical sleeve portion (12a) which extends within a cylindrical sleeve portion (13a) of the driven gear (13). The locking balls (25) are mounted in corresponding holes radially formed through the cylindrical sleeve portion (12a). The balls are mounted so as to be shiftable in a radial direction. The actuating shaft (21) has an increased diameter portion (21a) which is slideable within the cylindrical sleeve portion (12a) of the driving gear (12). A cylindrical sleeve (26) is mounted on the increased diameter portion (21a) of the actuating shaft, co-axial with and in the space between the actuating shaft (21) and the cylindrical sleeve portion (12a). The cylindrical sleeve (26) is resilient and acts to bias the locking balls (25) into a radially outward position in which the locking balls engage a corresponding set of pockets (13b) formed in the radially inwardly facing surface of the cylindrical sleeve portion (13a) of the driven gear. The pockets (13b) (see left hand side of Figure 2) are separated by a set of sloped ridges. When the locking balls (25) engage the pockets (13b) rotary drive is transmitted between the driving gear (12) and the driven gear (13) and rotational drive is transmitted via the spindle drive shaft (5) to the spindle (40).

When the actuating shaft (21) is the position shown in Figure 2, the clutch arrangement (14) acts as an overload clutch. Below a predetermined torque, the resilient sleeve (26) biases the locking balls (25) into engagement with the pockets (13b) in the driven gear (13) to thereby transmit rotation from the driving gear (12) to the driven gear (13). Thus, rotary drive is transmitted to the spindle (40) via the spindle drive shaft (5). However, above the predetermined torque, the biasing force from the resilient sleeve (26) becomes insufficient to bias the locking balls (25) into the pockets (13b) in the driven gear (13) and the balls can move radially inwardly to ride up the slopes and over the ridges between the pockets (13b) (see right hand side of Figure 2). Thus, the driven gear (13) rotates with respect to the driving gear (12) and rotary drive to the spindle drive shaft (5) and thus to the spindle (40) is cut off.

The overload clutch arrangement of Figure 2, also acts to cut-off rotary drive to the spindle (40) when a blocking event is detected. When the signals from the P-UK-PR1084B fi('NSTR accelerometer (16) are analysed by the microprocessor (17) so that the microprocessor determines that ablocking event is occurring, an output signal is output from the microprocessor into the circuit (18). This causes the circuit (18) to apply current to an electromagnet (19). The electromagnet is mounted in the hammer housing (4) so that it surrounds an end of the actuating shaft (21) remote from the end received in the bore (24) of the driven gear (13) . A magnetic element (27) is mounted on the end of the actuating shaft (21) surrounded by the electromagnet (19). When current is supplied to the electromagnet (19) a magnetic force is created between the electromagnet (19) and the magnetic element (27) which draws the magnetic element downwardly in the direction of the arrow A of Figure 2. The actuating shaft (21) moves downwardly until the increased diameter portion (21a) of the actuating shaft (21) abuts the base of the cylindrical sleeve (12a) of the driving gear (12). This movement of the actuating shaft (21) moves the resilient sleeve (26) downwardly in the direction of the arrow A until only the upper edge of the resilient sleeve engages the locking balls (25). Thus, the radially outwardly biasing force on the locking balls (25) from the biasing sleeve (26) is significantly reduced and the locking balls move radially inwardly, out of the pockets (13a) in the cylindrical sleeve (13a) of the driven gear (13). Thus, rotary drive to the driven gear (13) and so to the spindle (40) via the spindle drive shaft (5) is cut off.

Accordingly, as soon as current is supplied to the electromagnet (19) from the circuit (18), the clutch arrangement (14) is disengaged and no further rotary drive is transmitted via the clutch arrangement (14) to the spindle (40). In this way the potentially dangerous consequences of a blocking event are avoided. A return spring can be provided to return the actuating shaft (21) to its original position.

It should be noted that disengagement of the clutch arrangement (14) of Figure 2 could also be used to switch the hammer into its hammering only mode position in which no rotary drive is transmitted to the spindle (40). This mode change could be performed electromechanically using the electromagnet (19) to move the actuating shaft (21) or could be done mechanically by utilising mechanical means to shift the actuating shaft.

A second embodiment of an overload clutch arrangement suitable for use in the arrangement of Figure 1 is shown in Figure 3. The driving gear (12), driven gear (13) P-UK-PRIOR4D #CNSTR and actuating shaft (21) are mounted in the housing as described for the Figure 2 embodiment. Rotary drive is transmitted between the driving gear (12) and the driven gear (13) of the overload clutch arrangement (14) via a plurality of locking balls (25). The driving gear (12) is formed with a cylindrical sleeve portion (12a) which extends within a cylindrical sleeve portion (13a) of the driven gear (13). The locking balls (25) are mounted in corresponding holes formed through the cylindrical sleeve portion (12a) so as to be shiftable in a radial direction. The actuating shaft (21) has an increased diameter portion (21a) which is slideable within the cylindrical sleeve portion (12a) of the driving gear (12). A cylindrical sleeve (26) is located within the cylindrical sleeve portion (12a), co-axial with and in the space between the actuating shaft (21) and the cylindrical sleeve portion (12a). The cylindrical sleeve (26) is resilient and the increased diameter portion (21a) of the actuating shaft bears on the internal surface of the resilient sleeve (24) to reinforce a biasing force from the resilient sleeve which biases the locking balls (25) into a radially outward position in which the locking balls engage a corresponding set of pockets (13b) formed in the radially inwardly facing surface of the cylindrical sleeve portion (13a) of the driven gear. The pockets (13b) are separated by a set of sloped ridges. When the locking balls (25) engage the pockets (13b) (see left hand side of Figure 3) rotary drive is transmitted between the driving gear (12) and the driven gear (13) and rotational drive is transmitted via the spindle drive shaft (5) to the spindle (40).

When the increased diameter portion (21a) of the actuating shaft (21) is the position shown in dotted lines (a) Figure 3, the clutch arrangement (14) acts as an overload clutch. Below a predetermined torque, the resilient sleeve (26), reinforced by the increased diameter portion (21a) of the actuating shaft (21) biases the locking balls (25) into engagement with the pockets (13b) in the driven gear (13) to thereby transmit rotation from the driving gear (12) to the driven gear (13). Thus, rotary drive is transmitted to the spindle (40) via the spindle drive shaft (5). However, above the predetermined torque, the biasing force from the resilient sleeve (26) becomes insufficient to bias the locking balls (25) into the pockets (13b) in the driven gear (13) and the balls can move radially inwardly (see right hand side of Figure 3) to ride up the slopes and over the ridges between the pockets (13b). Thus, the driven gear (13) rotates with respect to the driving gear (12) and rotary drive to the spindle drive shaft (5) and thus to the spindle (40) is cut-off.

P-UK-PRI084B#CNSIR The overload clutch arrangement of Figure 3, also acts to cut-off rotary drive to the spindle (40) when a blocking event is detected. An electromagnet (19) is mounted in the hammer housing (4) so that it surrounds an end of the actuating shaft (21) remote from the end received in the bore (24) of the driven gear (13) . A magnetic element (27) is mounted on the end of the actuating shaft (21) surrounded by the electromagnet (19). When current is supplied to the electromagnet (19) a magnetic force is created between the electromagnet (19) and the magnetic element (27) which draws the magnetic element downwardly in the direction of the arrow A of Figure 3 into the position shown in dotted lines (b) in Figure 3. The actuating shaft (21) moves downwardly until the increased diameter portion (21a) of the actuating shaft (21) abuts a rim of the base of the cylindrical sleeve (12a) of the driving gear (12). This movement of the actuating shaft (21) moves the increased diameter portion (21a) of the actuating shaft (21) downwardly in the direction of the arrow A until it bears against only the lower edge of the resilient sleeve (26). Thus, the radially outwardly biasing force on the locking balls (25) from the biasing sleeve (26) is significantly reduced and the locking balls move radially inwardly (see right hand side of Figure 3), out of the pockets (13a) in the cylindrical sleeve (13a) of the driven gear (13). Thus, rotary drive to the driven gear (13) and so to the spindle (40) via the spindle drive shaft (5) is cut off. Accordingly, as soon as current is supplied to the electromagnet (19) from the circuit (18), the clutch arrangement (14) is disengaged and no further rotary drive is transmitted via the clutch arrangement (14) to the spindle (40). In this way the potentially dangerous consequences of a blocking event are avoided. A return spring can be provided to return the actuating shaft (21) to its original position.

It should be noted that disengagement of the clutch arrangement (14) of Figure 3 could also be used to switch the hammer into its hammering only mode position in which no rotary drive is transmitted to the spindle (40). This mode change could be performed electromechanically using the electromagnet (19) to move the actuating shaft (21) or could be done mechanically by utilising mechanical means to shift the actuating shaft.

The cut off of rotary drive to the spindle (40) is achieved by utilising an already existing component in the drive train to the hammer mechanism, ie. the overload P-UK-PRI084H #CNSTR clutch. In the embodiments of Figures 1 to 3, the overload clutch arrangement is altered to enable it also to cut off rotary drive to the spindle (40) by reducing the torque at which the overload clutch slips when a blocking event is detected.

A rotary hammer according to a second aspect of the present invention is shown in Figure 4. The hammer in Figure 4 differs from that in Figure 1 in that the rotary drive train from the motor (2) to the spindle (40) is different. The drive from the driving gear (9) is transmitted to the spindle drive shaft (5) via a gear wheel (41) press fit onto the spindle drive shaft. At its end remote from the gear wheel (41) the spindle drive shaft (5) is formed with a pinion (7) which is engageable with a spindle drive gear (10). The spindle drive gear (10) is mounted on a sliding sleeve (43), which sliding sleeve is axially slideably but rotationally fixedly mounted on the spindle (40). The mounting of the spindle drive gear (10) on the slider sleeve (43) may be a rotationally and axially fixed mounting, as shown in Figure 4, arranged such that rotation of the spindle drive gear (10) rotatingly drives the sliding sleeve (43) and so rotatingly drives the spindle (40). Alternatively, this mounting may be via an overload clutch as is known in the art, arranged such that rotation of the spindle drive gear (10) rotatingly drives the sliding sleeve (43) to rotatingly drive the spindle (40) below a predetermined torque and slips relative to the sliding sleeve above a predetermined torque, so that above the predetermined torque the spindle (40) is no longer rotatingly driven.

The hammer shown in Figure 4, has two modes hammering only mode and rotary hammer mode. Figure 4 shows the rotary hammer mode in which the pinion (7) of the spindle drive shaft (5) engages the spindle drive gear (10), which is a bevel gear, to rotatingly drive the spindle (40) via the sliding sleeve (43). Thus, a tool (68) mounted within the forward end of the spindle is rotatingly driven via the spindle and simultaneously receives repeated impacts from the beatpiece (64) of the hammering mechanism. A mode change knob (45) is rotationally mounted within the hammer housing (4) and is formed with an eccentric pin (47), which pin extends into the hammer housing (4). The eccentric pin (47) is received within a recess at the first rearward end of a mode change linkage (49). The forward end of the mode change linkage is formed with a finger (49a) which finger is engageable with a raised peripheral rim at the forward end of the sliding sleeve (43). In the position shown in P-UK-PR1084B #CNSTR 1 1 Figure 4, the mode change knob is turned to its rotary hammer mode position and the finger (49a) of the linkage (49) does not engage the sliding sleeve (43). The sliding sleeve is thus biased by a helical spring (50) into its rearward rotary hammer mode position, as shown in Figure 4. The helical spring (50) is mounted around the spindle (40) and acts between a circlip (51) on the spindle at the forward end of the spring and the sliding sleeve (43) at the rearward end of the spring, in order to bias the sliding sleeve rearwardly.

The hammer can be changed into a hammering only mode by rotating the mode change knob (45) so that the eccentric pin (47) moves to the left in Figure 4.

The eccentric pin (47) engages the mode change linkage (49) to move it towardly (to the left in Figure 4). The finger (49a) of the mode change linkage engages the rim of the sliding sleeve (43) to urge it forwardly against the biasing force of the spring (50).

The spindle drive gear (10) is axially fixed on the sliding sleeve and so the spindle drive gear (10) moves forwardly with the sliding sleeve (43) out of engagement with the pinion (7) of the spindle drive shaft, and so rotary drive to the spindle is shut off.

In the forward position of the spindle drive gear (10) the spindle drive gear can engage a set of cooperating teeth mounted within the housing (4) to lock the spindle against rotation in its hammering only mode, as is well known in the art.

On turning the mode change knob back into rotary hammering mode position, as shown in Figure 4, the sliding sleeve (43) is urged rearwardly back into the Figure 4 position by the spring (50).

The rotary hammer shown in Figure 4 has the same blocking event detecting arrangement comprising an accelerometer (16), a microprocessor (17), circuit (18) and electromagnet (19), as described above in relation to Figure 1, except that the electromagnet (19) surrounds the spindle drive gear (10), and the circuit (18) is repositioned between the microprocessor and the electromagnet. The spindle drive gear (10) and/or the sliding sleeve (43) are formed at least partly of a magnetic material. Thus, when a blocking event is detected the circuit (18) supplies current to the electromagnet (19) and this causes a magnetic force between the electromagnet (19) and the magnetic material in the spindle drive gear and/or sliding sleeve in order to move the sliding sleeve (43) and spindle drive gear (10) forwardly (to the left in P-UK-PR Og4B #CNSTR Figure 4) against the biasing force of the spring (50) and out of engagement with the pinion (7) of the spindle drive shaft (5). In this way, when a blocking event is detected rotary drive is cut-off between the motor (2) and the spindle (40) by disengaging the driving connection between the spindle drive shaft (5) and the spindle drive gear (10). This arrangement requires only the addition of the electromagnet (19) and of magnetic material to the spindle drive gear (10) and/or sliding sleeve (43) in order to cut off rotary drive to the spindle. No further components or changes are required to be made to components already existing rotary hammer components. In the Figure 4 embodiment, this is achieved by using the already existing mode change components for switching the rotary drive to the hammer spindle (40) on and off.

Alternatively, the rotary hammer of Figure 4 can be designed to have an additional drilling only mode in which the hammer drive mechanism is shut off, as is well known in the art.

The rotary hammer shown in Figure 5 is similar to that of Figure 1, except that it has a purely mechanical arrangement for detecting blocking events, as opposed to an electro-mechanical arrangement for detecting blocking events. Instead of the accelerometer (16), micro-controller (17), circuit (18) and electromagnet (19) of the Figure 1 embodiment, the hammer of Figure 5 has the mechanical arrangement shown, from the front, in Figure 6.

The arrangement for detecting blocking events shown in Figures 5 and 6 comprises an inertial mass (72) which is formed at the lower end of a lever (74), the upper end of which lever (74) is pivotally mounted with respect to the hammer housing, via pivot pin (76) so that the mass (72) and lever (74) are pivotal about an axis (80) extending parallel to the spindle axis (78). The mass is connected via a spring (82) to a mounting block (84) which mounting block is rigidly mounted with respect to the hammer housing (4). A first end of the spring (82) is fixed to the mounting block (84) and a second end of the spring (82) is fixed to the mass (72). As the hammer is operated, the mass vibrates, and so pivots about the pivot pin (76) due to the vibrations occurring from the operation of the hammer. The spring (82) is arranged to damp the vibration of the mass (72) and so minimise the extent of the P-UK-PR1084B #CNS7'R pivoting of the mass (72) about the pivot pin (76) during normal operation of the hammer. The upper end of the lever (74), above the pivot pin (76) is formed with a latching ledge (86), which during normal operation of the hammer engages with a facing latching ledge (88) formed at the lower end of an actuating shaft (21) of a clutch arrangement (14), discussed below in relation to Figures 7 and 8. The actuating shaft (21) of the clutch arrangement (14) is slideably mounted for movement in the direction of arrow (X) within components of the clutch and within a bushing (90). The actuating shaft (21) is biased by a strong spring (92), upwards, in the direction of the clutch arrangement (14).

During normal operating of the hammer, the pivoting movement of the mass (72) about the pivot pin (76) is limited by the damping action of the spring (82).

However, when a blocking event occurs, the bit (68) becomes rotationally fixed in the material being worked and the hammer housing is rotatingly driven about the bit (68) by the motor (2) via the spindle rotary drive arrangement. This causes the lower part of the hammer housing (4a) to rotate, with a very high acceleration, about the spindle axis (78) so that said lower part moves in a direction out of the paper of Figure 5.

The inertia of the mass (72) causes the mass to pivot about the pin (76) in a direction into the paper in Figure 5, ie. in the direction of the arrow (Y) in Figure 6, so as to compress the spring (82). The upper end of the lever (74) above the pin (76) pivots in the direction of the arrow (Z) with respect to the pivot pin (76), which causes the latching ledge (86) of the lever (74) to disengage the latching ledge (88) of the actuating shaft (21). The strong spring (92) is then able to urge the actuating shaft (21) to move upwardly to cause the clutch (14) to disengage, as is described below in relation to Figures 7 and 8, and so rotary drive from the motor (2) to the spindle (40) is cut off and the housing (4) is not rotatingly driven any further.

A lever (94) is provided on the actuating shaft (21) to re-set the blocking event detection arrangement of Figure 6 after the rotary drive has been cut off in response to the detection of a blocking event. The lever (94) can extend outside of the hammer housing (4) or can engage a sliding knob actuable from the outside of the housing (4), so that the lever (94) and thus the actuating shaft can be pulled downwardly. As the shaft (21) is pulled downwardly, against the force of the strong spring (92), chamfered outer edges (96, 98) formed on the actuating shaft (21) and P-UK-PR1084B #CNSTR the upper end of the lever (74) engage to pivot the lever (74) about the pivot pin (76) in the direction of the arrow (Z) against the biasing force of the spring (82) so as to re-engage the latching ledges (86, 88) of the actuating shaft (21) and the lever (74).

An overload clutch arrangement suitable for use in the hammer of Figure 5 is shown in Figure 7. The driving gear (12), driven gear (13) and actuating shaft (21) are mounted in the housing as described for the Figure 2 embodiment, with an extra guiding bushing (90) for slideably guiding the actuating shaft (21) as described above in relation to Figures 5 and 6. Rotary drive is transmitted between the driving gear (12) and the driven gear (13) of the overload clutch arrangement (14) via a plurality of locking balls (25). The driving gear (12) is formed with a cylindrical sleeve portion (12a) which extends within a cylindrical sleeve portion (13a) of the driven gear (13).

The locking balls (25) are mounted in corresponding holes formed through the cylindrical sleeve portion (12a) so as to be shiftable in a radial direction. The actuating shaft (21) has an reduced diameter portion (21b) which is slideable within the cylindrical sleeve portion (12a) of the driving gear (12). A plurality of spring elements (100) are circumferentially spaced around the actuating shaft (21) and are pivotably mounted with respect to the reduced diameter portion (21b) via balls (102).

Each spring element comprises a helical spring (106) mounted within a guide jacket (104) and extends radially with respect to the actuating shaft (21) between the balls (102) and the locking balls (25). Each ball (102) is received within an associated pocket in the reduced diameter portion (21b) and a pocket formed at the radially inner end of the resilient jacket (104) of an associated spring element (100). This enables the locking elements (100) to pivot between the positions shown on the left hand side and the right hand side of Figure 7. In the position shown in the left hand side of Figure 7, the spring elements (100) bias the locking balls (25) into a radially outward position in which the locking balls engage a corresponding set of pockets (13b) formed in the radially inwardly facing surface of the cylindrical sleeve portion (13a) of the driven gear. The pockets (13b) are separated by a set of sloped ridges.

When the locking balls (25) engage the pockets (13b) rotary drive is transmitted between the driving gear (12) and the driven gear (13) and rotational drive is transmitted via the spindle drive shaft (5) to the spindle (40).

P-UK PRIOX4B #CNSTR When the reduced diameter portion (21b) of the actuating shaft (21) is the position shown in the left hand side of Figure 7, the clutch arrangement (14) acts as an overload clutch. Below a predetermined torque, the spring elements (100) bias the locking balls (25) into engagement with the pockets (13b) in the driven gear (13) 5to thereby transmit rotation from the driving gear (12) to the driven gear (13). Thus, rotary drive is transmitted to the spindle (40) via the spindle drive shaft (5). However, above the predetermined torque, the biasing force from the spring elements (100) become insufficient to bias the locking balls (25) into the pockets (13b) in the driven gear (13) and the balls can move radially inwardly to ride up the slopes and over the 10ridges between the pockets (13b). Thus, the driven gear (13) rotates with respect to the driving gear (12) and rotary drive to the spindle drive shaft (5) and thus to the spindle (40) is cut-off.

The overload clutch arrangement of Figure 7, also acts to cut-off rotary drive to 15the spindle (40) when a blocking event is detected. As described above in relation to Figures 5 and 6, when a blocking event occurs, the inertial mass (72) pivots in the direction (Y) causing the upper end of the lever (74) to pivot in direction (Z) thus causing the latching ledges (86, 88) on the lever (74) and actuating shaft (21) to disengage. The strong spring (92), which is axially fixed at its lower end to an 20increased diameter portion (21c) and is axially fixed at its upper end to the driving gear (12), acts to pull the increased diameter portion (21c) of the actuating shaft, upwardly and so pulls the actuating shaft upwardly into the position shown on the right hand side of Figure 7. This movement of the actuating shaft (21) moves the decreased diameter portion (21 b) of the actuating shaft (21) upwardly and causes the 25spring elements to pivot about the pivot balls (102). This pivoting of the spring elements (100) leads to an extension of the springs (104) which reduces the biasing forces from the spring elements (100) on the locking balls (25). In this way, the radially outwardly biasing force on the locking balls (25) from the spring elements (100) is significantly reduced and the locking balls move radially inwardly, out of the 30pockets (13a) in the cylindrical sleeve (13a) of the driven gear (13). Thus, rotary drive to the driven gear (13) and so to the spindle (40) via the spindle drive shaft (5) is cut off. Accordingly, as soon as the latching ledges (86, 88) of the lever (74) and clutch actuating shaft (21) are disengaged no further rotary drive is transmitted via P-UK-PR1084B #CNSTR the clutch arrangement (14) to the spindle (40). In this way the potentially dangerous consequences of a blocking event are avoided.

A second embodiment of an overload clutch arrangement suitable for use in the hammer of Figure 5 is shown in Figure 8. The driving gear (12), driven gear (13) and actuating shaft (21) are mounted in the housing as described for the Figure 2 embodiment, with an extra guiding bushing (90) for slideably guiding the actuating shaft (21) as described above in relation to Figures 5 and 6. Rotary drive is transmitted between the driving gear (12) and the driven gear (13) of the overload clutch arrangement (14) via a plurality of locking balls (25). The driving gear (12) is formed with a cylindrical sleeve portion (12a) which extends within a cylindrical sleeve portion (13a) of the driven gear (13). The locking balls (25) are mounted in corresponding holes formed through the cylindrical sleeve portion (12a) so as to be shiftable in a radial direction. The actuating shaft (21) is formed with three increased diameter annulae (121a to 121c), the middle of which (121b) is of reduced diameter, as compared to the others. The annulae (121a to c) are slideable within the cylindrical sleeve portion (12a) of the driving gear (12). A first plurality of springs (110) are circumferentially spaced around the actuating shaft (21) and extend radially with respect to the actuating shaft (21) between the lower two annulae (121c and 121b) from the actuating shaft to an associated guide element (112). A second plurality of springs (114) are circumferentially spaced around the actuating shaft (21) and extend radially with respect to the actuating shaft (21) between the upper two annulae (121a and 121b) from the actuating shaft to the associated guide element (112). The radially outer end of each spring is mounted around an associated radially inwardly extending peg (116) formed on the associated guide element (112).

Each guide element is formed with two pegs (116), an upper peg for engaging the end of one of the springs (114) and a lower peg for engaging the end of one of the springs (110) directly below said one of the springs (114). The first plurality of springs (110) extort a weaker radially outward biasing force than the second plurality of springs (114). Depending on the axial position of the actuating shaft (21), either the strong springs (114) or the weak springs (110) bias the locking balls (25) radially outwardly via the guide elements (112).

P-UK-PR 084B #CNS I R When the latching ledges (86, 88) are engaged and the spring (92) is extended the annulus (121c) is moved downwardly from its position in Figure 8 and abuts the base of the driving gear sleeve (12). In this position the strong springs (114) are radially inwardly of the locking balls (25) and the clutch arrangement (14) acts as an overload clutch. Below a predetermined torque, the strong springs (114) bias the locking balls (25) into engagement with the pockets (13b) in the driven gear (13) to thereby transmit rotation from the driving gear (12) to the driven gear (13). Thus, rotary drive is transmitted to the spindle (40) via the spindle drive shaft (5). However, above the predetermined torque, the biasing force from the springs (114) become insufficient to bias the locking balls (25) into the pockets (13b) in the driven gear (13) and each guide element (112) pivots inwardly and the balls can move radially inwardly to ride up the slopes and over the ridges between the pockets (13b). Thus, the driven gear (13) rotates with respect to the driving gear (12) and rotary drive to the spindle drive shaft (5) and thus to the spindle (40) is cut-off.

The overload clutch arrangement of Figure 8, also acts to cut-off rotary drive to the spindle (40) when a blocking event is detected. As described above in relation to Figures 5 and 6, when a blocking event occurs, the inertial mass (72) pivots in the direction (Y) causing the upper end of the lever (74) to pivot in direction (Z) thus causing the latching ledges (86, 88) on the lever (74) and actuating shaft (21) to disengage. The strong spring (92), which is axially fixed at its lower end to an increased diameter portion (21c) and is axially fixed at its upper end to the driving gear (12), acts to pull the increased diameter portion (21c) of the actuating shaft, upwardly and so pulls the actuating shaft upwardly into the position shown in Figure 8. This movement of the actuating shaft (21) moves the weaker springs (110) radially inwardly of the locking balls (25). In this way, the radially outwardly biasing force on the locking balls (25) from the springs (110) is significantly reduced, as compared from the biasing force from the springs (114) and the locking balls move radially inwardly, out of the pockets (13a) in the cylindrical sleeve (13a) of the driven gear (13). Thus, rotary drive to the driven gear (13) and so to the spindle (40) via the spindle drive shaft (5) is cut off. Accordingly, as soon as the latching ledges (86, 88) of the lever (74) and clutch actuating shaft (21) are disengaged no further rotary drive is transmitted via the clutch arrangement (14) to the spindle (40). In thisway the potentially dangerous consequences of a blocking event are avoided.

P-IJK-PRl084B #CNSTR It should be noted that with modification to the actuating shaft (21) the clutch arrangements of Figures 2 and 3 are suitable for use in the hammer of Figure 5 and that the clutch arrangements of Figures 7 and 8 are suitable for use in the hammer of Figure 1.

Figures 9 and 10 show a further embodiment of a clutch arrangement suitable for use in the hammer of Figure 1, if a lower portion of the actuating shaft (21) is made of a magnetic element. The Figure 9 and 10 embodiment is also suitable for use in the arrangement of Figure 5, if a spring arrangement is added for biasing the actuating shaft into an upper position.

The drive shaft (5) is formed with a pinion (7) at its upper end for meshing engagement with spindle drive gear (10). The shaft is rotatably mounted within the housing via bearings (23) and (15). The drive shaft (5) is hollow and the actuating shaft (21) is mounted within the drive shaft so as to be axially slideable within the drive shaft (5), with the lower end of the actuating shaft extending beyond the end of the drive shaft (5) remote from the pinion (7). The driving gear (12) is rotatably mounted on the drive shaft (5).

A first small diameter driven gear (13c) is mounted on the drive shaft (5) for selective rotation therewith, depending on the position of the actuating shaft (21). A first set of clutch balls (25a) are located within an associated set of through holes (103a) in the driving gear (12), which through holes are radially inwardly of a second set of through holes (103b). A conical spring (107) biases the clutch balls (25) axially downwardly, towards the driven gears (13c, 13d) via a washer (105). The spring extends from its radially inner end, which bears against a shoulder formed on the drive shaft (5) to a radially outer end which bears against the washer (105). The washer (105) is located with a cooperating annular recess formed in the upper side of the driving gear (12). The spring (107) biases each of the first set of four clutch balls (25a) into one of a set of four pockets (109) formed in the upper surface of the small diameter driven gear (13c). In this way, below a first predetermined torque, the first set of clutch balls (25a) transmit rotatary drive from the driving gear to the small diameter driven gear (13c). Above the first predetermined torque, the first set of clutch balls (25a) will ride out and over the pockets (109) formed in the small P-UK-PRI084B flCNSTK diameter driven gear (13c) and so will cut off drive between the driving gear (12) and the small diameter driven gear (13c). The rotary drive from the small diameter driven gear (13c) can be transmitted to the drive shaft (5) depending on the position of the actuating shaft (21), as is described below.

A first pair of drive balls (113a) are located within an associated pair of upper holes (105a) in the drive shaft. The drive balls are engageable with two of a set of four drive pockets (115a) formed in the radially inner edge of the small diameter driven gear (13c), to rotatingly drive the drive shaft (5) when an increased diameter portion (121a) is radially inwardly of the drive balls (113a) and so pushes the drive balls (113a) into a radially outward position. When a reduced diameter portion (121 b) of the actuating shaft (21) is radially inwardly of the drive balls (113a) the drive balls can move radially inwardly and out of engagement with the drive pockets (115a) of the small diameter driven gear (13c) so that no rotary drive can be transmitted to the drive shaft (5).

A second large diameter driven gear (13d) is mounted on the drive shaft (5) for selective rotation therewith, depending on the position of the actuating shaft (21).

The second large diameter driven gear is located on the drive shaft (5) below and extends radially outwardly of the small diameter driven gear (13a). A peripheral rim of the large diameter driven gear (13d) extends axially towards the driving gear (12) around the periphery of the small diameter driven gear (13c). A second set of clutch balls (25b) are located within an associated set of through holes (103b) in the driving gear (12), which through holes are radially outwardly of the first set of through holes (103a). The conical spring (107) biases each of the second set of four clutch balls (25a), via the washer (105), into one of a set of four pockets (111) formed in the upper surface of the peripheral rim of the large diameter driven gear (13d). In this way, below a second predetermined torque, the second set of clutch balls (25b) transmit rotatory drive from the driving gear to the large diameter driven gear (13b).

Above the second predetermined torque, the second set of clutch balls (25b) will ride out and over the pockets (111) formed in the large diameter driven gear (13d) and so will cut off drive between the driving gear (12) and the large diameter driven gear (13d). The second predetermined torque will be higher than the first due to the greater radial distance between the axis of the drive shaft (5) and the second set of P-IJK-PR 1 084B #CNSTR clutch balls (25b) than the radial distance between the axis of the drive shaft and the first set of clutch balls (25a). The rotary drive from the large diameter driven gear (13d) can be transmitted to the drive shaft (5) depending on the position of the actuating shaft (21), as is described below.

A second pair of drive balls (113b) are located within an associated pair of lower holes (105b) in the drive shaft. The drive balls are engageable with two of a set of four drive pockets (115b) formed in the radially inner edge of the large diameter driven gear (13d), to rotatingly drive the drive shaft (5) when an increased diameter portion (121a) of the actuating shaft is radially inwardly of the drive balls (113b) and so pushes the drive balls (113b) into a radially outward position. When a reduced diameter portion (121b) of the actuating shaft (21) is radially inwardly of the drive balls (113b) the drive balls can move radially inwardly and out of engagement with the drive pockets (115b) of the large diameter driven gear (13d) so that no rotary drive can be transmitted to the drive shaft (5).

In a first position of the actuating shaft (21) of the clutch of Figures 9 and 10 shown on the right hand side of Figure 9, only the small diameter driven gear (13c) can rotatingly drive the drive shaft (5) via the first set of drive balls (113a). The drive balls (113a) in the first position as shown in the right hand side of Figure 9 are urged into engagement with the drive pockets (115a) of the small diameter driven gear (13c). This is because the increased diameter portion (121a) of the actuating shaft is radially inward of the first set of drive balls (113) and so urge the drive balls radially outwardly. The second set of drive balls (113b) are able to move radially inwardly into the reduced diameter portion (121b) of the actuating shaft (21) and out of the drive pockets (115b) in the large diameter driven gear (13d), and so no rotary drive can be transmitted between the large diameter driven gear (13d) and the drive shaft (5). In this first position, of the clutch of Figures 9 and 10, below a first relatively low predetermined torque, the first set of clutch balls (25a) transmit rotatory drive from the driving gear to the small diameter driven gear (13c). Above the first predetermined torque, the first set of clutch balls (25a) will ride out and over the pockets (109) formed in the small diameter driven gear (13c) and so will cut off drive between the driving gear (12) and the small diameter driven gear (13c). Accordingly, P-UK-PKIOX4B #CNSTR in the first position, the clutch arrangement of Figures 9 and 10 acts as an overload clutch which slips at a first relatively low predetermined torque.

In a second position of the actuating shaft (21) of the clutch of Figures 9 and 10 shown on the left hand side of Figure 9, both the small diameter driven gear (13c) and the large diameter driving gear (13d) can rotatingly drive the drive shaft (5) via the first and second sets of drive balls (113a, 113b). The drive balls (113a, 113b) in the second position as shown in the left hand side of Figure 9 are urged into engagement with the drive pockets (115a, 115b) of the small diameter driven gear (13c) and of the large diameter driven gear (13d). This is because the increased diameter portion (121a) of the actuating shaft is radially inward of the both sets of drive balls (113a, 113b) and so urge both sets of drive balls radially outwardly. In this second position, of the clutch of Figures 9 and 10, below a second predetermined torque, higher than the first predetermined torque, each sets of clutch balls (25a, 25b) transmit rotatary drive from the driving gear (12) to their associated driven gear (13c, 13d). Above the second predetermined torque, the clutch balls (25a, 25b) will ride out and over the pockets (109, 111) formed in the associated driven gears (13c, 13d) and so will cut off drive between the driving gear (12) and the associated driven gears (13c, 13d). Accordingly, in the second position, the clutch arrangement of Figures 9 and 10 acts as an overload clutch which slips at a second predetermined torque, which is higher than the first.

To move between the first and second position of the clutch of Figures 9 and the actuating shaft is moved downwardly in the direction of arrow (W). This can be facilitated, for example as is shown in Figure 11a, by connecting the lower end of the actuating shaft (21c) to a linkage (120), which linkage is operated via a knob (122) actuatable by a user of the hammer to slideably move the actuating shaft (21) within the drive shaft (5) adjust the slipping torque of the overload clutch between the first and second predetermined torques. In the arrangement of Figure 11a, an eccentric pin (122a) acts to pull the linkage (120) upwardly and to thereby pull the actuating shaft (21) upwardly from its position in Figure 11a, against the biasing force of a spring (124) on rotation of the knob (122) out of the position shown in Figure 11 a. On movement of the knob (122) back into the position shown in Figure 11 a, the spring (124) returns the linkage and thus the actuating shaft to the position shown in P-UK-PR I ()84B #CNS l'R Figure 11a. The Figure 11a position would be the higher torque position shown in the left hand side of Figure 9 and the linkage (120) and actuating shaft (21) would be pulled upwardly out of the Figure 11a position into the lower torque position shown in the right hand side of Figure 9. Alternatively, the lower end of the actuating shaft (21) could be connected directly to the knob.

The clutch arrangement of Figures 9 and 10 has a third position in which the reduced diameter portion (21 b) of the actuating shaft is radially inwardly of both sets of drive balls (113a, 113b). Thus, the drive balls are able to move radially inwardly and out of engagement with the drive pockets (115a, 115b) of the driven gears (13c, 13d) and no rotary drive can be transmitted between the driven gears (13c, 13d) and the drive shaft. In this third position, in which the actuating shaft (21) is moved upwardly, in the opposite direction to the arrow (W) from the low torque position shown in the right hand side of Figure 9, the rotary drive to the drive shaft (5) and thus to the spindle (40) is cut off.

The clutch arrangement of Figure 9 and 10 can be moved into the third position via a mode change linkage (126), shown in Figures 11a and 11b. The mode change linkage can be actuated between it positions in Figures 11a and 11b by a mode change knob actuable by a user of the hammer. In the Figure 11 a position the mode change linkage (126) is out of engagement with the actuating shaft (21), this position would be a drilling only or a rotary hammering position of the mode change linkage.

Thus the linkage (126), maintained in the position of Figure 11a by a spring (128) does not interfere with the arrangement for altering the predetermined torque, discussed above in relation to Figure 11a, in the drilling and/or rotary hammering modes. In the Figure 11b position, the linkage (126) has been moved, against the biasing force of the spring (128) by a mode change knob into its hammering only mode position, in which the linkage (126) engages the lower portion (21c) of the actuating shaft (21) to move it upwardly from the position shown in the right hand side of Figure 9. This cuts off drive form the driving gear (12) to the drive shaft (5) and so there is no rotational output of the spindle (40) or the bit (68) mounted therein.

The linkage arrangement (120, 122) for switching between low torque and high torque position in rotary modes of the hammer does not interfere with the operation of the mode change linkage (126) to move the hammer into its non-rotary mode. On P-UK-PRIOX4B #CNSrR return of the mode change knob to a rotary mode position the biasing force of the spring (128) will return the mode change linkage (126) to its position of Figure 11a.

The third position of the clutch arrangement can also be used to cut off rotary drive to the spindle (40) when a blocking event is detected. If the blocking event is detected electronically, then an electromagnet surrounding the lower portion of the actuating shaft (21) can be energised to react against a magnetic element fitted to the lower portion of the actuating shaft and to move the actuating shaft upwardly into its third position against the biasing forces of the springs (124) and (128). It should be noted that neither the arrangement (120, 122) for switching between the first and second positions, not the mode change linkage arrangement (126, 128) for switching to the third position hinder the movement of the actuating shaft to its upper position in response to the energisation of the electromagnet.

As an alternative to an electromagnet, the mechanical arrangement for detecting blocking events of Figure 6, could be used in conjunction with the clutch arrangement of Figures 9 and 10. Here the latching ledge (86) of the linkage (74) would engage the lower portion (21c) of the actuating shaft (21) and the shaft would be biased to move upwardly into the third position should the latching ledge and lower portion (21c) become disengaged in the event of a blocking event.

Figure 12 shows an additional design of overload clutch (14) which can be used for selectively cutting of rotary drive between the driving gear (12) and the driven gear (13) for mode change or in response to a blocking event. The driving gear (12) is rotatably mounted on the drive shaft (5) and has clutch balls (25) mounted in holes extending axially through the driving gear. A driven gear (13) is non-rotatably mounted on the drive shaft (5) and is formed with a set of pockets (13b) on its face facing the driving gear (12) for receiving the clutch balls (25). A conical spring (107) urges the driven gear (13) towards the driving gear (12). An actuating ring (130) is located below the driving gear (12) and in a first position shown on Figure 12, the ring (130) pushes the clutch balls (25) into engagement with the pockets (13b) in the driven gear (13). The actuating ring (130) can be moved downwardly in direction (V) into a position in which it no longer urges the clutch balls into engagement with the pockets (13b) in the driven gear (13).

P-UK PR I Oh4B #CNSTR In the position shown in Figure 12 the clutch acts as an overload clutch. Below a predetermined torque, the conical spring (107) biases the clutch balls (25) into engagement with the pockets (13b) in the driven gear (13) to thereby transmit rotation from the driving gear (12) to the driven gear (13). Thus, rotary drive is transmitted to the spindle (40) via the spindle drive shaft (5). However, above the predetermined torque, the biasing force from the conical spring (107) becomes insufficient to bias the clutch balls (25) into the pockets (13b) in the driven gear (13) and the driven gear (13) can move axially against the force of the spring (107) to ride over clutch balls (25). Thus, the driven gear (13) rotates with respect to the driving gear (12) and rotary drive to the spindle drive shaft (5) and thus to the spindle (40) is cutoff. When the actuating ring is moved to the second position no rotary drive can be transmitted between the driving gear (12) and the driven gear (13) because the clutch balls (25) cannot engage the pockets (13b) in the driven fear (13). Therefore, on detection of a blocking event the guide ring is moved to the second position to disengage rotary drive. This can be done by mechanical or electromechanical means, as described above in relation to Figures 1, 5 and 6. Additionally or alternatively, the locking ring (130) can be moved to the second position by a mode change arrangement on switching to a non-rotary mode of the hammer.

P-IJK-PK I ()84B ACES l R

Claims

CLAlMs rid held rotary hammer comprising a spindle (40) for rotatingly

driving a tool or bit (68); a hammering mechanism (38, 58, 64) for generating repeated impacts on a tool or bit (68) mounted at a forward end of the spindle; a Spindle rotary drive train (14, 5, 10) for rotatingly driving the spindle (40); an overload clutch (14) in the spindle rotary drive train for transmitting rotary drive to the spindle below a predetermined torque and for cutting transmission of rotary drive above the predetermined torque; a mode change mechanism (126, 128) for selectively cutting off the rotary drive to the Spindle (40); sed in that the overload clutch (14) I I a first mode of operatic n in which th e overload Clutch transmits rotary drive to the spindle below a first predetermined torque and stops transmission of rotary above the first predetermined torq a second mode of operati the overload clutch transmits rota d i to the Spindle below a s P determined torque, different from th predetermined torque P transmission of rosary drive abov th predetermined torque; and a third mode of oper ch the overload clutch cuts on rot d the spindle in response to the mode change mechanism (126, 128).
A hammer aCcordin t 9 o claim 1 in the Overload Clutch (14) compels driven gear (13) and a driving gear (12) and a coupling element (105, 107) for coupling the driven ear g and drivin el w the Predetermined torque a d f enabling de- couplin the 9 driven gear and t driving gear above the predetermi d torque and a drive coupling (21, 113, 115) for coupling the driven gear to the output Of the clutch, wherein the mode change err cement (126, 128) acts on the dri Coupling (21, 113 115) to stop the transmission of rotary drive.
3. A hammer according to claim 1 or claim 2 wherein there are two driven gears (13c, 13d) and one of th e driven gears Candied to the output of the clutch j the drive coupling (21, 113, 115) so that the overload clutch has a first predetermined -l]K-PRlo848 RCNSIR torque, the other or both of the driven gears can be coupled to the output of the clutch via the drive coupling (21, 113, 115) so that the overload clutch has a second predetermined torque, different from the first or neither of the driven gears can be coupled to the output of the clutch via the drive coupling (21, 113, 115) so that the transmission of rotary drive is stopped.

P-UK-PR1084B #CSTR