Rear handle

A power tool comprising: a housing; a handle having two ends, the first being moveably mounted to the housing via a first mounting assembly, the second being moveably mounted to the housing via a second mounting assembly; a biasing mechanism connected between the housing and handle; wherein at least one of the mounting assemblies comprises first and second parts, one being mounted on the housing and the other mounted on the one end of the handle, the first part comprising a passageway, the second comprising a mount and a rod, the rod having a first end and a shaft with a longitudinal axis, the first end being attached to the mount using a bayonet connection, the shaft being located in and capable of axially sliding within the passageway to enable the end of the handle to move towards or away from the housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

FIELD OF THE INVENTION

The present invention relates to a handle for a power tool, in particular for a hammer drill, and in particular, to a mounting assembly for a rear handle on a hammer drill which reduces the amount of vibration transmitted to the handle.

BACKGROUND OF THE INVENTION

Power tools of all types comprise a body attached to which are handles by which an operator can support the tool. Vibrations are generated in the body during the operation of such tools which are transferred to the handles. It is desirable to minimize the amount of transfer.

A hammer drill can operate in one or more of the following modes of operation; hammer only mode, drill only mode and combined hammer and drill mode. EP1157788 discloses such a hammer. During the operation of such hammers, a considerable amount of vibration can be generated. The vibration is caused by the operation of the rotary drive mechanisms and/or the hammer mechanisms, depending on the mode of operation of the hammer drill, combined with the vibratory forces applied to and experienced by the cutting tool, such as a drill bit or chisel when it is being used on a work piece. These vibrations are transferred to the body of the hammer drill, which in turn are transferred to a rear handle being used by the operator to support the hammer drill. The transfer of vibration to the rear handle from the body, and subsequently to the operator's hand can not only be painful but can result in injury, particularly when the hammer drill is used over long periods of time. It is therefore desirable to minimise the amount of vibration transferred from the body to the rear handle.

One solution is to moveably mount the rear handle on the body of the hammer drill to allow relative movement between the two and to locate a vibration dampening mechanism between the body and the rear handle to minimise the amount of vibration transferred to the rear handle from the body.

EP2415561 and EP2415562 both describe two embodiments of such a vibration dampening mechanism for a hammer drill by which the amount of vibration transferred to the rear handle from the body is reduced. In each of the examples, the rear handle is connected via an upper mounting assembly, which enables the upper part of the handle to slide relative to the upper part of the housing, and a lower mounting assembly, which enables a pivoting movement of the lower part of the handle relative to the lower part of the housing.

Accordingly, there is provided three aspects of the present invention in accordance with claims1,5and7respectively.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, which shows an existing design of hammer drill, the hammer drill comprises a main housing2which comprises a motor housing4, in which is mounted an electric motor6, a gear housing8in which is mounted a rotary drive and hammer mechanism10, and a rear housing12. The motor housing4is connected to the gear housing using bolts20. Similarly, the rear housing12is attached to both of the motor housing4and gear housing8using bolts22. A tool holder14is mounted on the front of the gear housing8which is capable of holding a cutting tool16, such as a drill bit. The motor6rotatingly and/or reciprocatingly drives the cutting tool16via the rotary drive and/or hammer mechanism10. The hammer drill can operate in three modes of operation, namely hammer only mode, drill only mode and combined hammer and drill mode. A mode change knob18is rotatably mounted on the top of the gear housing8. Rotation of the knob18to predetermined angular positions activates or deactivates the rotary drive and/or hammer mechanism10to adjust the mode of operation of the hammer drill.

A rear handle24is moveably mounted to the rear housing12as will be described in more detail below. The rear handle24is manufactured from a plastic clam shell which provides a hollow cavity inside of the handle in which component parts of the hammer can located. A trigger switch26is mounted on the rear handle24. An electric cable28enters the base of the rear handle24and connects to the electric motor via the trigger switch26. Depression of the trigger switch26activates the motor. A rubber soft grip50is moulded onto the rear of the rear handle24in well known manner.

The rear handle assembly of the existing design of hammer drill will now be described with reference toFIGS. 2 to 6.

The rear handle is mounted to the rear housing12at its two ends30,32. The top end30is mounted to the rear housing12via an upper mounting assembly34. The upper mounting assembly34allows the top end30of the handle12to move towards or away from (Arrow D) the rear housing12over a large range of movement, whilst allowing limited movement in the directions of Arrows E and F relative to rear housing12. The lower end32is mounted to the rear housing12via a lower mounting assembly36. The lower mounting assembly36allows the lower end32of the handle to pivot (Arrow G—seeFIG. 4) about a horizontal axis58relative to the rear housing12, whilst allowing limited linear movement in the directions of Arrows D and E.

The upper mounting assembly34will now be described with reference toFIGS. 2 and 6. The upper mounting assembly34comprises a metal rod38which is rigidly attached to the rear housing12using a bolt40. The bolt40passes through a hole46in the rear housing12and through the length of the rod38. The head42of the bolt40abuts the rear housing12. A nut44is screwed on the end of the bolt40and sandwiches the rod38and the part of the rear housing12with the aperture46between the head42of the bolt and the nut44thus locking the rod38to the rear housing12.

The free end of the rod38comprises a rectangular portion52, the height (vertically) of which is the same as the rod38(as seen inFIG. 2), but the width (horizontally) of which is greater than the rod38(seeFIG. 6).

Rigidly mounted inside the cavity at the top end30of the rear handle24is a plastic tubular sleeve54. The shaft of the rod38passes through the length of the tubular aperture56formed by the sleeve54. The length of the shaft of the rod38is greater than the length of the sleeve54. The dimensions of the cross section area of the tubular aperture56of the sleeve are slightly greater than the dimensions of the cross section area of the rod38so that a small gap is formed between the outer surface of the shaft of the rod38and the inner wall of the tubular aperture56. The rectangular portion52of the rod38locates at one end of the sleeve54. The width of the rectangular end of the rod38is greater than the width of the tubular aperture56and the sleeve54(seeFIG. 6). As such, it is too wide for it to pass through the tubular aperture56. The other end of the rod38which is attached to the rear housing is located at the other end of the sleeve and is prevented from entering the tubular aperture56by the rear housing12. The rod38can freely slide in an axial direction (Arrow D) within the sleeve54, the range of axial movement being limited at one end of the range by the rear housing12engaging with one end of the sleeve54and at the other end of the range by the rectangular portion52engaging with the other end of the sleeve54. As the dimensions of the cross section area of the tubular aperture56of the sleeve are slightly greater than the dimensions of the cross section area of the rod38to produce a small gap between the outer surface of the shaft of the rod38and the inner wall of the tubular aperture56, limited movement of the rod38inside of the sleeve is allowed in the directions of Arrows E and F relative to rear housing12.

Connected between the rear housing12and top end30of the rear handle24is a helical spring60which surrounds the rod38. The spring biases the top end30of the rear handle24away from the rear housing12. When the spring60biases the top end of the rear handle away by the maximum amount, the rectangular portion52engages with the end of the sleeve54, preventing further movement of the top end30of the handle24away from the rear housing12. The spring60is under a small compression force in this state. When the top end30of the rear handle is moved towards the rear housing12against the biasing force of the spring60by the application of an external force, the spring60becomes further compressed and shortens in length as the rod38axially slides within the sleeve54until the rear housing engages with the other end of the sleeve54. When the external force is removed, the top end30of the rear handle24moves away from the rear housing due to the biasing force of the spring60, the rod38axially sliding within the sleeve54until the rectangular portion52engages the end of the sleeve54. The spring60also applies a biasing force on the rod38in a direction of Arrows E and F, urging the rod38to a central position within the sleeve54. As such, when no external forces are applied to the rear handle24, the spring60also locates the rod38centrally within the tubular aperture56so that a gap is formed around the whole of the outer surface of the rod and the inner wall of the sleeve54. Movement of the rod in directions of Arrows E or F causes the rod38to move towards an inner wall of the tubular aperture56against a side way biasing force generated by the spring60.

A set of bellows62connects between the rear housing12and the top30of the handle and surrounds the rod38and spring60.

The lower mounting assembly36will now be described with reference toFIGS. 2 to 5.

The lower mounting assembly36comprises a metal pin70of circular cross section which is mounted inside the lower end32of the handle. The pin70has a longitudinal axis58. The pin70extends sideways (generally in the direction of Arrow F) relative to the handle24. The pin70is rigidly connected to the side walls72of the lower end32of the handle24and traverses the cavity inside of the handle24.

The rear housing12comprises a projection74which extends rearwardly and projects into the cavity of the handle24at the lower end of the handle24in the vicinity of the pin70. Formed through projection is a hollow passage76. The hollow passage76similarly extends sideways (in the direction of Arrow F). The pin70passes through the length of the hollow passage76, each end of the pin70extending beyond an end of the hollow passage76and connecting to the side wall72of the handle24. The cross sectional area of the hollow passage76is greater than the cross sectional area of the pin70, allowing the pin70to move sideways (in the direction of Arrows D and E) inside of the passageway76, as well as being able to feely pivot (in the direction of Arrow G) within the hollow passage76.

Located inside each end of the hollow passage76is an insert78. Each insert78is of identical size and is rigidly connected to the inner wall of the hollow passage76to prevent movement of the insert78relative to the projection74. An aperture80, with an oval cross section, is formed through each insert78(seeFIGS. 5A and 5B) and which extends in the same direction as the hollow passage76. The pin70passes through each of the apertures80. The two apertures80are aligned with each other inside of the projection74.

The width82of the aperture80is marginally greater that the diameter of the pin70. The length84of the aperture is twice the size of the diameter of the pin70. As such, the pin can side sideways in a lengthwise direction84in the aperture80.

The pin70is prevented from sliding sideways88through the aperture80by the side walls72of the lower end32of the handle24, to which the pin70is rigidly attached, abutting directly against the sides of the inserts78.

The hammer drill (excluding the rear handle24) has a centre of gravity86. A centre of gravity axis120passes through the centre of gravity. The centre of gravity axis is horizontal and extends width ways in the direction of Arrow F. The inserts are mounted inside the hollow passage76with aperture80orientated so that the lengthwise direction84of the aperture80extends tangentially to a circle (with radius R) centered on the centre of gravity axis120of the hammer drill (seeFIG. 1) in a plane which extends in the directions of Arrows D and E (It should be noted that a plane which extends in the directions of Arrows D and E is a lengthwise vertical plane. A plane which extends in the directions of Arrows F and E is width way vertical plane).

When no force is applied to the rear handle24by an operator, the pin70is biased to the centre, in the lengthwise direction84, of the aperture80of each insert78, with equal space within the aperture80being left on either side of the pin70in the lengthwise direction84. The biasing force acting on the pin70is generated by the spring60in the upper mounting assembly34which urges the pin70to the central position. Sliding movement of the pin70in the aperture, in the lengthwise direction84, towards either of the ends of the oval aperture, is against the biasing force of the spring60.

A set of bellows90connects between the rear housing12and the lower end32of the handle24.

During use, the operator supports the hammer drill using the rear handle24. When the operator places the cutting tool against a work piece, the operator applies a pressure to the rear handle24, causing the rear handle24to move towards the rear housing12of the hammer. The top end30moves towards the rear housing12by the rod38axially sliding within the sleeve54against the biasing force of the spring60, reducing the length of the spring60as it becomes compressed. The lower end32pivots about the pin70. Depression of the trigger26activates the motor6which drives the cutting tool16.

During the operation of the hammer, vibrations are generated by the operation of the motor6and the rotary drive and hammer mechanism10. These vibrations are transferred to the rear housing12. Significant vibrations are generated in two directions in particular. The first direction is in a linear direction (Arrow D) parallel to a longitudinal axis92of the cutting tool16. The second direction is in a circular direction (Arrow H) about the centre of gravity axis120of the hammer. This is caused by the centre of gravity86being located away from the longitudinal axis92of the cutting tool16, in this case, below the longitudinal axis92.

Vibrations in the first direction are mainly absorbed by the upper mounting assembly34, and by the spring60in particular. As the rear housing12vibrates in the first direction, the rod38can axially slide in and out of the sleeve54under the influence of the vibrations, the spring60expanding and compressing as it does so. The dampening action of the spring60results in a reduction in the amount of vibration transferred to the rear handle24from the rear housing12. As the rod38axially slides in and out of the sleeve54under the influence of the vibrations, the rear handle12pivots about the pin70in the lower mounting assembly36as it engages with the side walls of the oval aperture80as the pin70is urged by the vibrations in the first direction to move in a direction parallel to the longitudinal axis92of the cutting tool16.

If the operator applies more pressure to the rear handle24, the spring60becomes more compressed, thus transferring the additional force to the rear housing12of the hammer drill. However, its compression and expansion due to the vibration continues to result in a reduction of vibration being transferred to the rear handle24from the rear housing12.

Vibrations in the second direction result in a twisting movement of the housing2, motor6and the rotary drive and hammer mechanism10about the centre of gravity axis120(Arrow H). These vibrations are mainly absorbed by the lower mounting assembly36. As the pin70is located in the oval slot80of the insert78which is orientated so that the lengthwise direction84of the aperture80extends tangentially to a circle centered on the centre of gravity axis120which extends in a lengthwise vertical plane, the pin70can slide tangentially relative to the centre of gravity axis120, allowing housing2, motor6and the rotary drive and hammer mechanism10to twist about the centre of gravity axis120relative to the rear handle24. This twisting movement is then damped due to the action of the spring60in the upper mounting mechanism34which biases the pin70to the centre of the oval slot80. The twisting movement of the housing2, motor6and the rotary drive and hammer mechanism10about the centre of gravity axis120relative to the rear handle24is accommodated by the top mounting assembly34by the gap formed between the outer surface of the rod38and the inner wall of the sleeve54. As the rod38being urged to a central position within the sleeve54by the spring60, when vibrations in the second direction are applied, the rod38can move sideways (Arrow E) within the sleeve54. The spring60, which biases the rod38centrally within the tubular aperture36, also dampens the movement of the rod38in the sleeve54.

An embodiment of the invention will now be described with reference toFIGS. 7 to 15. Where the same features shown in the embodiment are present in the design of the rear handle assembly of the existing design of hammer drill are present, the same reference numbers have been used.

The upper mounting assembly34in the embodiment is the same as the upper mounting assembly in the existing design of hammer except for method by which the metal rod38is attached to rear housing, the location of the helical spring60, the sleeve54has been replaced by a structure integrally formed within the clam shell of the handle.

The upper mounting assembly34will now be described with reference toFIGS. 7 to 15. The upper mounting assembly34comprises a metal rod38which is attached at a first end200to the rear housing12using a bayonet type connection. The rear housing comprises a plastic housing800mounted onto a magnesium transmission housing802. The first end200forms a T shape with two arms202,204projecting sideways from the longitudinal axis of the rod38. Formed by the rear plastic housing800and magnesium housing802is a chamber206formed by walls211of the plastic housing800. A rectangular entrance208is formed through the rear wall of the plastic housing800which has dimensions slightly larger than those of the cross section of the T shaped first end200in a direction perpendicular to the longitudinal axis of the rod38. The orientation of the rectangular entrance208is such that the longer sides of the entrance208extend vertically. The T shaped first end200is able to pass through the entrance208from behind the rear housing12and locate within the chamber206, the two arms202,204being capable of being located entirely within the chamber206. The shape and dimensions of the chamber206are such that it allows for the first end200of the rod38with the two arms202,204to be rotated through 90 degrees within the chamber206in an anti-clockwise direction as shown inFIG. 9(prior to the plastic housing800being attached to the magnesium housing802). Once rotated through 90 degrees, the first end200of the rod38is prevented from being removed from the chamber206as the arms202,204extend perpendicularly to the longer sides of the entrance208of the chamber206and therefore abut against the rear wall of the plastic housing800within the chamber206as shown inFIG. 9. The T-shaped first end200is passed through the entrance208, rotated through 90 degrees and located within the chamber206prior to the plastic housing800being attached to the magnesium transmission housing802. The angular position of the rod can be locked in this orientation using a latch as best seen inFIGS. 9 and 18. When the first end200is rotated through 90 degrees, one arm202passes over a ridge804formed in the plastic housing and locates on the other side. When the plastic housing800is attached to the magnesium transmission housing802, the first end200is prevented from passing back over the ridge804. The magnesium housing802comprises a stop806integrally formed with the housing802. When the magnesium housing802is attached to the plastic housing800, the stop806locates adjacent one of the arms204and prevents it from being rotated clockwise. The ridge804and the stop806lock the first end200in the chamber206by preventing it from rotating within the chamber206. The dimensions of the chamber206are such that, when the arms202,204are extended perpendicularly to the longer sides of the entrance208of the chamber206as shown inFIG. 9, the first end200of the rod38is held rigidly with the chamber206with the remainder of the rod38protruding rearwardly away from the rear housing12towards the rear handle. This provides a bayonet connection between the rod38and the rear housing12. To remove the first end200from the chamber206, the magnesium housing802is disconnected from the plastic housing800, the first end200of the rod38with the two arms202,204is then rotated through 90 degrees in a clockwise direction as shown inFIG. 9and then passed through the entrance208. This provides a simpler method of assembly and avoids the need for the use of bolts or screws.

The second end of the rod38comprises a circular flange210and a projection212which extends in the same direction as the longitudinal axis of the rod38as seen inFIG. 8. Integrally formed within the plastic clam shells214,216of the rear handle are a plurality of ribs218which extend horizontally towards a passageway220formed, in part, by the ends of the ribs218. The ends222of the ribs218form the vertical sides of the passageway220. Integrally formed within the plastic clam shells214,216of the rear handle are two walls224,226which extend horizontally. The walls224,226form the top and bottom horizontal sides228,230of the passageway220. The shaft of the rod38passes through the passageway220. The length of the shaft of the rod38is greater than the length of the passageway220. The ends222of the ribs218are designed so that they form a convex curved support surface which can engage with the vertical sides of the shaft of the rod38. The surfaces228,230of the walls224,226which are capable of engaging with the top and bottom sides of the shaft of the rod38are curved in a convex manner.

The diameter of the circular flange210of the rod38is greater than the width and height of the passageway220(seeFIG. 11). As such, it is too wide for it to pass through the passageway220. The first end of the rod38which is attached to the rear housing by the bayonet connection is on the other side of the passageway220and is prevented from entering the passageway220by the rear housing12engaging the clam shells214,216of the rear handle.

The rod38can freely slide in an axial direction (Arrow M) within the passageway220the range of axial movement being limited at one end of the range by the rear housing12engaging with clam shells214,216of the rear handle and at the other end of the range by the flange210engaging with the other end of the passageway220. The dimensions of the cross section area of the passageway220at the narrowest section are slightly greater than the dimensions of the cross section area of the shaft of the rod38to produce a small gap between the outer surface of the shaft of the rod38and the inner walls of the passageway220. This allows limited movement of the rod38inside of the passageway in the directions of Arrows N and O relative to rear housing12. The convex curved support surface formed by the ends222of the ribs218and the convex curved surfaces228,230of the walls224,226enable the shaft of the rod38to pivot over a limited range of movement about an approximate point232within the passageway about a vertical axis234and a horizontal axis236which is perpendicular to the longitudinal axis of the rod38.

It will be appreciated that the rear clam shells214,216of the handle may be designed so that either the support surface formed by the ends222of the ribs218or the support surfaces228,230of the walls224,226only are curved to restrict the pivotal movement to one direction, either about the vertical axis234or the horizontal axis236which is perpendicular to the longitudinal axis of the rod38.

Mounted within the clam shells of the rear handle within a tubular passageway240is a helical spring242. One end of the spring242surrounds the projection212, which holds the end of the spring242in place, and abuts against the flange210. The other end of the spring242abuts against an internal wall244of the clam shells. The spring biases the top end30of the rear handle24away from the rear housing12. When the spring242biases the top end of the rear handle away by the maximum amount, the flange210engages with the entrance to the passageway220preventing further movement of the top end30of the handle24away from the rear housing12. The spring242is under a small compression force in this state. When the top end30of the rear handle is moved towards the rear housing12against the biasing force of the spring242by the application of an external force, the spring242becomes further compressed and shortens in length as the rod38axially slides within the passageway220until the rear housing12engages with the clam shells214,216of the rear handle. When the external force is removed, the top end30of the rear handle24moves away from the rear housing due to the biasing force of the spring242, the rod38axially sliding within the passageway220until the flange210engages the entrance of the passageway. The spring242also applies a biasing force on the rod38in a direction of Arrows N and O, urging the rod38to a central position within the passageway220. As such, when no external forces are applied to the rear handle24, the spring242also locates the rod38centrally within the passageway220so that a gap is formed around the whole of the outer surface of the rod and the inner walls of the passageway220. Movement of the rod in directions of Arrows N or O causes the rod38to move towards an inner wall of the passageway against a side way biasing force generated by the spring242.

A set of bellows250connects between the rear housing12and the top30of the handle and surrounds the part of the rod38located between the two.

The bellows250comprises a corrugated portion500with a L shaped stop502formed at one end and a U shaped stop504formed at the other. The U shaped stop504is attached to top30of the handle by a lip506formed in the handle housing locating within the groove508formed in the U shaped stop504and a side510of the U shaped stop504locating within a groove512in the handle housing. The L shaped stop502locates in close proximity to the rear housing12.

The bellows250are made from rubber. When the top of handle is moved to its maximum extent towards rear housing12, the U shaped stop504engages the L shaped stop502, preventing further movement. The top of handle and the rear housing are prevented from coming into direct contact with each other. Therefore, due to resilient nature of the material of the bellows250, the amount of vibration transferred is reduced as the ends502,504of the rubber bellow250are sandwiched between the rear housing12and the top30of the handle.

The lower mounting assembly36in the embodiment is exactly the same as the lower mounting assembly in the existing design except for the construction of the passageway76for the pin70and the mounting of the ends of the pin70within the handle.

The lower mounting assembly36comprises a metal pin70of uniform circular cross section along its length which is mounted inside the lower end32of the handle. The pin70has a longitudinal axis290and extends sideways relative to the handle24. The ends260of the pin70locate within pockets262formed the inner walls of the clam shells214,216, the ends260being loosely held within the side walls72of the lower end32of the handle24to allow limited movement within the pockets262. The pin70traverses the cavity264inside of the handle24.

The rear housing12comprises a projection74which extends rearwardly and projects into the cavity264of the handle24at the lower end of the handle24in the vicinity of the pin70. Formed through projection is a hollow passage266. The hollow passage266similarly extends sideways. The pin70passes through the length of the hollow passage266, each end of the pin70extending beyond an end of the hollow passage266and connecting to the side wall72of the handle24. The cross sectional shape of the passage266along the full length of the passage is that of an oval, the oval being long in a first direction268(length) and shorter in a second direction270(width). The length268of the oval cross section of the hollow passage76is of a constant value along the full length of the hollow passage76. The width270varies along the length of the hollow passage76to produce two symmetrical curved convex surfaces272which are capable of engaging the side of the pin70. The narrowest point is at the centre of the hollow passage76where it is just slightly larger than the diameter of the pin70.

The lower mounting assembly of the embodiment is capable of functioning in the same manner as the example described above with reference toFIGS. 1 to 6. However, in addition, the curved walls of the passageway allow the lower end of the handle to pivot about an axis274which extends parallel to the lengthwise direction268of the oval cross section. The loose fitting ends260of the pin70also assist in such movement.

The overall embodiment of the rear handle is capable of functioning in the same manner as that of the example described above with reference toFIGS. 1 to 6. However the use of the combination of the passageway with curve support surfaces222,238,230in relation to the rod38and the hollow passage76with curved side walls272with the pin70additionally allows the rear handle an overall limited amount of twisting movement (up to 10 degrees) approximately about the longitudinal axis of the rear handle providing addition vibration damping.