GB2121717A - Improvements in or relating to rotary percussive drills - Google Patents

Abstract

A rotary percussive drill has means for positively disconnecting the rotary drive (7) and also means for positively disconnecting the drive (6,10) for the percussion mechanism (16). The disconnections may be controlled by separate operating members (38,41) or by a common member (90). The positive disconnection ensures that very little power is wasted in driving a disconnected drive; in particular no part of the percussion mechanism (16) is driven in the non-percussive mode. <IMAGE>

Description

SPECIFICATION Improvements in or relating to rotary percussive drills This invention relates to rotary percussive drills.

In a known form of rotary percussive drill a motor imparts rotation to a drill bit via one gear train and also imparts percussive blows to the bit with a percussive mechanism driven via another gear train by the motor. In order to enable the drill to operate in a percussive non-rotary mode means for interrupting the gear train for the rotary drive have been provided in certain drills. Also in order to enable the drill to operate in a non-percussive rotary mode means for disabling the percussive mechanism have been provided in certain drills. Where the percussive mechanism comprises interengaging teeth that ride over one another the mechanism is disabled by separating the interengaging teeth.Where the percussive mechanism is a pneumatic system with a ram driven by an air cushion, the mechanism may be disabled by allowing the ram to advance forwards to a position in which the air cushion is vented.

In the non-percussive mode of the forms of drill described above the gear train for the percussive mechanism and also part of the percussive mechanism itself continues to operate. The percussive mechanism therefore still consumes some of the motor power leaving less available for the rotary drive. In the case of a pneumatic mechanism there is a possibility that the ram will continue to oscillate and if the ram is held in the forward position to prevent this the pneumatic mechanism may require even more power from the motor in this non-percussive mode than it takes in the percussive mode.

It is an object of the invention to provide a rotary percussive drill that mitigates the disadvantages mentioned above.

According to the invention a rotary percussive drill includes a motor, a rotary drive drivingly connected to the motor for imparting rotation to a drill bit, a percussion mechanism for transmitting percussive blows to a drill bit and a percussive drive drivingly connected to the motor for driving the percussion mechanism wherein means are provided for enabling the rotary drive to be disconnected by an operator for operating the drill in a non-rotary percussive mode and means are provided for enabling the percussive drive to be disconnected by an operator for operating the drill in a rotary non-percussive mode.

By providing disconnection means in the rotary and percussive drives it is ensured that when the rotary or percussive action of the drill is terminated very little power is required for the disconnected drive and almost all the power of the motor remains available for the connected drive. In particular, in a non-percussive mode no part of the percussion mechanism is operated. Also the actual disconnection of the rotary or percussive drive provides a very positive method of disabling.

The drill may have a pneumatic percussion mechanism. The invention is of particular advantage in this case since a pneumatic percussion mechanism when disabled in the known manner referred to above may continue to operate after disablement and is likely to consume a considerable amount of power even when disabled.

A safety overload clutch may be provided in the rotary drive (or the percussive drive). Such a clutch operates automatically, when the torque transmitted by the drive reaches a predetermined maximum safe level, to disconnect the drive. The clutch should not be confused with the means for enabling the rotary drive to be disconnected by an operator, which is means under the direct control of the operator.

In one embodiment of the invention each operator controlled disconnection means comprises a pair of toothed members spring biased into engagement with one another and interposed in the drive path, and means actuable by an operator for separating the toothed members to interrupt the drive path. The toothed members have confronting toothed faces and are mounted for rotation about an axis perpendicular to the toothed faces.

By way of example, certain illustrative embodiments of the invention will now be described with reference to the accompanying drawings, of which: Figure 1 is a partly sectional side view of a hammer drill embodying the invention, Figure 2A is a sectional side view to a larger scale than Fig. 1 of a part of Fig. 1, Figure 2B is an exploded view of the parts shown in Fig. 2A, Figure 3A is a sectional side view corresponding to Fig. 2A and illustrating a modification to the drill, Figure 3B is an exploded view of the parts shown in Fig. 3A, Figure 4 is an exploded perspective view of an actuating means forming part of the drill of Fig. 1, Figure 5 is a perspective view of part of the drill housing in which the actuating means of Fig. 4 is located, Figure 6 is a sectional side view illustrating a modification which may be made to the embodiment of Fig. 1, Figure 7 is an exploded view of some of the parts shown in Fig. 6, and Figure 8 is a perspective, somewhat, schematic view of an actuating means for the modified arrangement shown in Figs. 6 and 7.

Referring first to Fig. 1 the hammer drill has a casing 1 in a lower portion of which an electric motor 2 with a pinion 3 on its armature shaft is provided. The pinion 3 meshes with a gear 4 which is an interference fit around a member 6. As will be described in more detail later, a rotary drive 7 extends via a safety overload clutch from the member 6 to a sleeve 8 to impart rotation via a beat piece 13 to a chuck 14 in which a bit 1 5 is held and a percussive drive is formed by the member 6 and a crank 10 having a pin 11 which engages in a guideway 1 2 of a percussion mechanism 1 6.

The percussion mechanism 1 6 comprises a hollow piston 1 7 which is mounted for reciprocating movement in a guide tube 20 and on the rear end of which the guideway 1 2 is formed, and a ram 1 8 having a nose 1 9 mounted in the piston 1 7.

The nose 1 9 of the ram is shown in the drawing in engagement with the rear end of the beat piece 1 3. Adjacent to its rear end the beat piece 1 3 has a pair of diametrically opposite grooves 20 (one being visible in Fig.

1) in each of which a ball 21 is partly received. The balls 21 are also partly received in diametrically opposite grooves 22 in the rotatable sleeve 8. The grooves 20, 22 and balls 21 together define a coupling between the sleeve 8 and the beat piece 1 3 that transmits rotation from the sleeve to the beat piece but allows axial movement of the beat piece 1 2 relative to the sleeve 8. In Fig. 1 the beat piece 13, chuck 14 and ram 18 are shown in different positions above and below their common axis.

The chuck 14 has a body 23 with a pair of diametrically opposite bores 24 in each of which balls 25 are received, the balls also extending into a pair of diametrically opposite grooves 26 in the beat piece 1 3 (only one of each pair being visible in Fig. 1). The bores 24, balls 25 and grooves 26 define a coupling between the beat piece and the chuck body 23 which allows axial movement of the beat piece relative to the chuck body but transmits rotation from the beat piece to the chuck body.

The chuck body 23 has two further pairs of diametrically opposed bores 29 in which balls 27 are received engaging in diametrically opposite grooves 28 (only the upper bores 29, balls 27 and grooves 28 being visible in Fig.

1) in the bit 15. The bores 29, balls 27 and grooves 28 define a coupling allowing limited axial movement of the bit in the chuck body but preventing relative rotation of the bit and the chuck body. An outer sleeve 30 with a plastics insulating sleeve 31 fixed thereto is slidably mounted over the chuck body 23 and biased by a compression spring 32 to the position shown in the drawing where the balls 27 are pressed into the grooves 28. If an operator retracts the outer sleeve assembly 30, 31 to the right (as seen in Fig. 1) a recess 33 in the outer sleeve assembly comes into register with the bores 29 and the balls 27 are able to move outwardly clear of the grooves 28 so that the bit 1 5 can be removed or replaced.

The percussive drive is transmitted from the member 6 to the crank 10 by toothed portions 34 and 35 on the confronting faces of the member 6 and crank 10 respectively.

Referring also now to Figs. 2A and 2B, the member 6 is a running fit on a lay shaft 36 while the crank 10 is a high interference fit on the lay shaft. The member 6 is also slidably mounted on the shaft 36 and is biased away from the crank 10 by a compression spring 37. In the position shown in Fig. 1, however, the member 6 is held adjacent the crank 10 with the confronting toothed portions 34, 35 in engagement by an operator controlled actuator that will now be described with reference to Figs. 1,4and5.

The actuator comprises generally an operating member having a generally circular cam face 38 mounted in the inner end of a recess 39 formed in a lower part 40 of a gear casing and an integral operating lever 41 which projects beyond the recess 39 outside the drill housing, and an annular cam element 42 mounted on top of the cam face 38. The cam face 38 is generally flat but has two sector shaped raised portions 43 at diametrically opposite sides of the cam face and, midway between the raised portions two diametrically opposite ridges 44 are provided on the cam face. The cam element 42, which is non rotatably but slidably mounted has a pair of diametrically opposite downward (as seen in Fig. 1) projections 45 on its periphery and the bottom face of each projection has a recess 46.

Mounted on top of the cam element 42 is the outer race of a bearing 47 in which the lay shaft 36 is slidably journalled. A collar 48 rests on the top of the inner race of the bearing 47 and supports the member 6.

The rotary drive 7 is transmitted via a clutch member 49 (forming part of an overload clutch to be described later) with a toothed periphery meshing with a gear member 50. The member 50 is a running fit on a lay shaft 51 on the top of which a bevel gear 52 is fixed, the bevel gear 52 meshing with teeth formed on the end of the sleeve 8.

Toothed portions 53 and 54 on the confronting faces of the bevel gear 52 and the member 50 transmit the rotary drive. The two faces are biased away from one another by a compression spring 55 but in the position shown in Fig. 1, the toothed faces are held in engagement by an operator controlled actuator, the components of which are the same as those described above with reference to Figs.

4 and 5 and which are designated by the same reference numerals. As shown in Fig. 5 the actuator controlling the rotary drive is housed in a recess 56 in the part 40 of the gear casing.

The overload clutch in the rotary drive is formed between the clutch member 49 and the gear 4. The confronting faces of these parts define the two operative faces of a friction clutch and are biased into contact by a belville washer 57 compressed between a shoulder 58 on the member 6 and a recess in the clutch member 49. In the event of overloading the clutch member 49 and the gear 4 slip relative to one another.

Actuation of the motor 2 is controlled by a trigger switch 59 on the handle 60 of the tool. In the embodiment illustrated an electronic control of the motor is provided and a printed circuit board is incorporated and a torque control knob 61 also provided. If desired the motor may also be reversible and a reversing switch included.

In operation of the device when the trigger 59 is squeezed with the toothed portions 34, 35 and 53, 54 in engagement the drill operates in the rotary percussive mode. The pinion 3 drives the member 6 via the gear 4 so that the percussion mechanism 1 6 is driven by the crank 10 and the sleeve 8 is rotated via the clutch member 49, gear 50 and bevel gear 52. The crank 10 reciprocates the piston 1 7 which in turn reciprocates the ram 1 8 which imparts blows via the beat piece on to the bit 1 5. The sleeve 8 rotates the beat piece 1 3 through the balls 21 and this rotation is imparted through the balls 25 to the chuck which in turn rotates the bit through the balls 27.In this percussive mode of the tool, the chuck, bit and beat piece are in a forward position as shown above their common axis in Fig. 1.

In order to hold the toothed portions 34, 35 and 53, 54 in engagement the respective operating lever 41 is in the position shown in Fig. 4 but it can be moved to a position rotated through ninety degrees from that shown in Fig. 4. As each lever 41 is rotated, the projections 45 cammingly engage the side walls of the recesses 43 and drop down onto the face 38; as the lever completes its ninety degree rotation the recesses 46 in the projections locate over the ridges 44 and the lever ciicks into position.

If on the one hand it is desired to operate the drill in the rotary non-percussive mode, the cam face 38 associated with the recess 39 is rotated to the position ninety degrees from that shown in Fig. 4. The spring 37 presses down the member 6, clutch member 49 and gear 4 so that the toothed portions 34, 35 move out of engagement and the crank 10 and percussion mechanism 1 6 ceases to be driven. The rotary drive continues to be transmitted through the overload clutch as before and the bit 1 5 continues to rotate. Since the percussion mechanism is no longer operating, when the bit 1 5 is pressed against a workpiece, the bit, the chuck 14 and the beat piece 1 3 move back into the drill to the position shown below their common axis in Fig. 1.In this position ball 21 is located at the forward end of the groove 20 in the beat piece 1 3. It will be seen that in this mode of the drill none of the percussion mechanism 1 6 nor the crank 10 is driven so that all the power of the motor is available to rotate the bit.

If on the other hand it is desired to operate the drill in the non-rotary percussive mode, the cam face 38 associated with the recess 56 is rotated to the position ninety degrees from that shown in Fig. 4. In this case the spring 55 presses down the gear 50 so that the toothed portions 53, 54 move out of engagement and the bevel gear 52, sleeve 8, beat piece 13, chuck 1 4 and bit 1 5 cease to rotate. The percussive drive continues to operate as before. In this case it will be seen that only the gear 50 and overload clutch arrangement of the rotary drive continues and almost all of the power of the motor is available to drive the percussion mechanism.

Figs. 3A and 3B illustrate a modification that may be made to the parts of the drill shown in Figs. 2A and 28. The modification involves elimination of the overload clutch by replacing the clutch member 62. The other parts of the arrangement are substantially unchanged and are designated by the same reference numerals. Particularly if the motor 2 is protected electronically against overloading, it may be desirable to omit the mechanical overload clutch shown in Figs. 2A and 2B.

Figs. 6 to 8 illustrate a modification to the rotary drive and percussive drive and also to the actuating means for controlling operation therefor.

Referring first to Figs. 6 and 7 the motor pinion 3 meshes with a gear 70 mounted for rotation around the lower part of a crank member 71 having a crank pin 72 and mounted on a lay shaft 73 slidably journalled in a bearing 84. A compression spring 74 in a bore of the crank member bears against the top of the shaft 73 and biases it downwardly.

The shaft 73 has a waisted portion which in the position shown in Fig. 6 accommodates portions of a pair of balls 75 received in holes 76 in the crank member 71. The internal bore of the gear 70 has a series of longitudinal grooves 77 around its periphery, the grooves being sized to accommodate portions of the balls 75.

The gear 70 also meshes with a gear 78 freely mounted for rotation on sleeve 79. A safety overload clutch is provided by plates 80 sandwiching the gear 70, the plates 80 being rotatably coupled to the sleeve 79 and the sandwich being biased upwards (as seen in Fig. 6) by a spring (not shown) between the lower plate and a member 81. The sleeve 79 is mounted for rotation around the lower part of a bevel gear member 81 having a bevel gear at its top corresponding to the bevel gear 52 in Fig. 1. The bevel gear 81 is mounted on a lay shaft 82 slidably mounted in a journal 85 and a compression spring 83 in a bore of the member 81 bears against the top of the lay shaft and biases it downwardly.

The shaft 82 has a waisted portion which in the position shown in Fig. 6 accommodates portions of a pair of balls 86 received in holes 87 in the bevel gear member 81. The internal bore of the sleeve 79 has a series of detents 88 around its periphery, the dentents being sized to accommodate portions of the balls 86.

The shafts 73 and 82 can both be displaced longitudinally by operation of a lever 89 of a cam member 90 which is mounted in the drill housing for rotation about the pinion 3 of the motor. The cam member 90 has a flat upper face and flour bosses 91, 92, 93 and 94 with inclined sides on its face.

In use, with the cam member 90 in a central position, the shafts 73 and 82 stand on the bosses 91 and 92 respectively and are displaced upwards (as seen in Fig. 6) from the position shown in Fig. 6. Upward displacement of the shaft 73, 82 forces the balls 75, 86 outwardly into the grooves 77 and 88 rotatably coupling the crank member 71 to the gear 70 and the bevel gear member 81 to the sleeve 79 so that both the rotary drive and the percussive drive are connected.

If the cam member is now rotated clockwise (as seen from above) the shaft 73 stands on the boss 93 and is therefore maintained in the same position while the shaft 82 stands on the flat face of the cam member and returns to the position shown in Fig. 6. In this position, the balls 86 are able to move inwardly out of the grooves 88 and the coupling between the bevel gear member 81 and the sleeve 79 is broken so that the rotary drive is disconnected.

If the cam member is rotated anti-clockwise (as seen from above) the shaft 82 stands on the boss 94 and is therefore maintained in a raised position while the shaft 73 stands on the flat face of the cam member and returns to the position in Fig. 6. In this position the balls 75 are able to move inwardly out of the grooves 77 and the coupling between the crank member 71 and the gear 70 is broken so that the percussive drive is disconnected.

Thus it will be seen that the drill can operate in the rotary and percussive, rotary only or percussive only modes. In the modification shown in Figs. 6 and 8 a single member is provided to control which of these modes is adopted and it is not possible to disconnect both drives at once. The modification also avoids the need to displace during mode changing and therefore enables a more compact design to be achieved.

Claims (11)

1. A rotary percussive drill including a motor, a rotary drive drivingly connected to the motor for imparting rotation to a drill bit, a percussion mechanism for transmitting percussive blows to a drill bit and a percussive drive drivingly connected to the motor for driving the percussion mechanism wherein means are provided for enabling the rotary drive to be disconnected by an operator for operating the drill in a non-rotary percussive mode and means are provided for enabling the percussive drive to be disconnected by an operator for operating the drill in a rotary nonpercussive mode.

2. A drill as claimed in claim 1 in which the percussion mechanism is a pneumatic mechanism.

3. A drill as claimed in claim 1 or 2 in which a safety overload clutch is provided in the rotary drive.

4. A drill as claimed in any preceding claim in which a safety overload clutch is provided in the percussive drive.

5. A drill as claimed in any preceding claim in which a respective operating member is provided to enable the rotary drive to be disconnected and to enable the percussive drive to be disconnected.

6. A drill as claimed in any preceding claim in which a common operating member is provided to enable the rotary drive to be disconnected and to enable the percussive drive to be disconnected.

7. A drill as claimed in any preceding claim in which the drill is able to operate in a rotary, non-percussive mode, a percussive, non-rotary mode and a rotary percussive mode.

8. A drill as claimed in any preceding claim in which each enabling means comprises a pair of toothed members spring biased into engagement with one another and interposed in the drive path, and means actuable by an operator for separating the toothed members to interrupt the drive path.

9. A drill as claimed in claim 8 in which the toothed members have confronting toothed faces and are mounted for rotation about an axis perpendicular to the toothed faces.

10. A drill as claimed in any of claims 1 to 7 in which each enabling means comprises a pair of members drivingly connected by a plurality of balls, and means actuable by an operator for switching from an arrangement in which the balls are held in a driving position to an arrangement in which the balls are able to move to a position in which the driving connection is terminated.

11. A rotary percussive drill substantially as herein described with reference to and as illustrated by Figs. 1, 2A, 2B, 4 and 5 of the accompanying drawings.

1 2. A drill as claimed in claim 11 modified substantially as herein described with reference to Figs. 3A and 3B, or Figs. 6,7 and 8 of the accompanying drawings.