GB2102718A - Improvements in or relating to rotary percussive drills - Google Patents

Abstract

A rotary percussive hand-held electric drill includes an electric driving motor (18) whose direction of rotation is reversible. The motor (18) is coupled to a drill chuck (2) by rotary drive means including unidirectional drive means (13, 15, 16, 17) operable to permit the rotary drive means to transmit to the chuck rotation of the motor in one direction but not rotation of the motor in the other direction. A percussive drive translates rotation of the motor into movement of a member (29) for imparting percussive blows to a drill bit when located in the chuck (2). <IMAGE>

Description

SPECIFICATION Improvements in or relating to rotary percussive drills This invention relates to rotary percussive drills and has particular reference to hand-held rotary percussive drills fitted with a control enabling the user to disconnect the rotary drive when required to enbable the drill to be used in a percussive, non-rotary mode.

It is well known to provide a rotary percussive drill with a control which enables the user to.disconnect the rotary drive, for example, for the purpose of installing certain types of fastener and for chasing grooves in masonry by chiselling in which operations percussive action only is required. Various arrangements have been proposed for disconnecting the rotary drive and these sometimes involve moving two members of a gear train apart by means of some mechanical contrivance which is actuated by an external knob on the drill.

Such arrangements involve a considerable number of mechanical parts and are consequently expensive.

It is an object of the present invention to provide a rotary percussive drill with an improved arrangement for enabling the user to disconnect the rotary drive.

According to the invention, a rotary percussive drill includes an electric motor, rotary driving means for imparting rotation to a drill bit, a percussive drive for transmitting percussion from the percussive drive to a drill bit, wherein the electric motor is reversible, the percussive drive is operable in both directions of rotation of the motor and the rotary driving means includes a clutch which transmits the rotary drive in the forward direction of rotation of the motor but not in the reverse direction of rotation.

When the motor of the drill runs in the forward direction, the drill operates in the rotary, percussive mode but when the motor is reversed the rotary drive is automatically disconnected and the drill operates in the nonrotary, percussive mode. Thus, the rotary drive is disconnected without the provision of any mechanism connecting an external knob on the drill to a pair of separable members in the gear train.

The electric motor may include an electronic control for effecting the reversing action and may also include an electronic speed control.

With such a control, the power and speed of the motor running in reverse would usually be less than in the forward direction but the power requirement for the motor is also reduced in reverse since the rotary drive is no longer provided.

The reduction in the speed of the motor reduces the frequency of the percussive action but this will not usually have a serious effect and can be taken into account in the design.

The clutch in the rotary drive may be of various forms. In one embodimemt, a sprag clutch may be used.

Means may also be provided for disconnecting the percussive drive to the drill bit. This enables the drill to be used, with the motor running in the forward direction, in a rotary non-percussive mode.

By way of example, an illustrative embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a section of a hammer drill, and Figure 2 is an exploded view of one suitable form of uni-directional clutch that may be included in the hammer drill of Fig. 1.

The percussive drill shown in Fig. 1 has a nose portion 1 in which a bit holder 2 is located. The bit holder comprises the forward end of a tubular sleeve 8 formed with apertures in its curved wall in which are located driving segments and bit holding balls, of which one segment and one ball are shown in Fig. 1 and referenced 3 and 4 respectively.

The balls and segments engage corresponding shaped recesses in the shaft of a bit (not shown) for the purpose of retaining the bit in the holder and imparting rotation to the bit from the sleeve 8 as will be described in more detail below.

The segments and the balls are held releasably in the positions shown in Fig. 1, in which they extend radially inwardly of the sleeve, by the inner flanged portion of a disc-like member 5 screwed to a cylindrical nose portion 6 biassed to the left (as viewed in Fig. 1) by a spring 7 encircling the forward end of the sleeve 8.

The tubular sleeve 8 is rotatable coupled to a gear member with teeth 9 which engage a bevel gear 10 through which rotation about its longitudinal axis can be imparted to the sleeve 8. The bevel gear 10 is mounted on a shaft 11 driven by a gear 1 2 which in turn meshes with a gear 1 3 freely mounted on a shaft 14. The gear 13, together with a gear 15, a disc spring 1 6 and spring steel washer 1 7 form a unidirectional drive means which will be described in more detail later with reference to Fig. 2. The gear 1 5 is fixed to the shaft 14 and is driven by an electric motor 1 8 via a pinion 1 9 on the armature shaft of the motor.

The motor 1 8 is provided with an electronic speed control indicated diagrammatically by block ESC, a trigger 20 on a handle 21 which controls the energisation of the motor and a reversing switch RS. Electronic speed controls for tools of this kind are now well known to those skilled in the art. European Patent Specification No. 34822 describes a suitable electronic speed control incorporating a reversing switch that is suitable for use as ESC and RS.

The speed of rotation of the motor 1 8 is controlled by ESC, a rotatable knob 22 being provided to enable a user to select a required speed of rotation. The switch RS may be mounted in the handle 21 adjacent the trigger 20 as shown in Fig. 1. Preferably, switch RS is a slide switch because this form of switch is less likely to be inadvertently operated by a user than a push-button switch. Alternatively, the switch RS may be positioned at some other location remote from the trigger 20.

The shaft 1 4 is secured at its upper end to a crank drive including a pin 23 which engages a guideway 24. The guideway 24 is mounted transversely of the longitudinal axis of a hollow piston 25 whose end wall 26 has an extension 27 in which the guideway 24 is mounted.

The hollow piston 25 is guided for linear movement in a guide cylinder 28.

Housed within the hollow piston 25 for movement relative thereto is a hammer element 29 formed with a noise 30 which, as will be described later imparts blows to a beat piece 31 reciprocable in the tubular sleeve 8 and which transfers the blows to a bit held in the bit holder 2 but not shown in the drawing.

In operation, energisation of the motor 1 8 in the forward direction by squeezing the trigger 20 with the reversing switch RS set for forward rotation, rotates the sleeve 8 and thus a bit in the bit holder 2. Additionally, the hollow piston 24 is reciprocated in the guide cylinder 28 by the crank drive. Such reciprocation results, in known manner, in reciprocation of the hammer element 29 within the hollow piston 25 and the imparting of a series of impacts to the bit via the beat piece 31.

The speed of rotation of the motor is selected by means of the knob 22 before operation of trigger 20.

With the reversing switch RS set for reverse rotation, the unidirectional clutch is disengaged and the sleeve 8 does not rotate, but the piston 25 continues to be reciprocated so that impacts are imparted to the bit.

The power and speed of the motor running in reverse is less than in the forward direction but disengagement of the rotary drive reduces the power requirement by between 1 5 and 20 per cent.

The unidirectional drive means shown in more detail in Fig. 2 is a simple sprag clutch.

The washer 1 7 has a central aperture 32 mounting the washer freely on shaft 14, four downwardly projecting half shear teeth 33 and four peripheral locating teeth 35 which engage in corresponding slots (not shown) in the underneath of the gear 1 3 so that the washer 1 7 rotates with the gear 1 3. The gear 1 5 is formed with four spaced teeth 36 on its upper surface. The disc spring 1 6 biasses the gear 1 3 and washer 1 7 down towards the gear 15.

In the forward direction of rotation of the motor the gear 1 5 is rotated clockwise (as seen from above) as indicated by arrow "DRIVE" and the edges of the teeth 33 engage the flanks of the teeth 36 so that the washer 1 7 and gear 1 3 rotate with the gear 1 5 and rotary drive is imparted to a tool bit via gear 1 2. In the reverse direction of rotation of the motor, the gear 1 5 is rotated anticlockwise (as seen from above) as indicated by arrow "SLIP" and the teeth 33 ride up onto the top of the teeth 36 against the bias of the spring disc 1 6 and, accordingly, the washer 1 7 and gear 1 3 do not rotate and there is no rotary drive to the tool bit.

The drill is also provided with a mechanism to allow it to be operated with the motor running in the forward direction in a nonpercussive mode, i.e. without the percussive action of the hammer element 29 and the beat piece 31.

The mechanism comprises balls 37 that locate in diametrically opposed longitudinal slots 38 in the curved wall of the sleeve 8.

The beat piece 31 has a central portion 39 of reduced diameter as compared with the remainder of the element, the balls 37 engaging portion 39 as shown.

The balls 37 locate in a seating ring 40 secured to an outer ring 41 spring biassed into the position shown in Fig. 1 by the spring 7. In that position, the balls 37 are located at the right-hand (as viewed in Fig. 1) end of the slots 38.

Spring 7 also maintains a cam face 42 on ring 41 in contact with a cammed flange 43 of a mode change ring 44 rotatably mounted on the nose 1. When the mode change ring 44 is rotated from the position shown in Fig.

1, co-operation between the cam face 42 and cammed ring 43 produce movement of the setting ring 40 and support ring 41 to the left (as viewed in Fig. 1) and similar movement of the beat piece 31. Rotation of the mode change ring 44 is sufficient to cause balls 37 to travel to the extreme left-hand (as viewed in Fig. 1) end of the slots 38 and the resultant movement of the beat piece 31 take the latter out of the range of movement of the hammer element 29 so that the latter can no longer contact the beat piece 31.

When the beat piece is held in that position, the hammer element 29 is capable of slightly greater movement to the left (as seen in Fig. 1) an this allows the hammer element 29 to move into a position in which holes (not shown) in the wall of the hollow piston 25 are uncovered. This allows air to leak into and out of that part of the hollow piston 25 between the end wall 21 and the hammer element 29 and thus minimises movement of the hammer element 29 in the hollow piston 25.

When the mode change ring 44 is rotated back to its percussive position, the balls 37 return to the positions shown in Fig. 1, the beat piece is released and when the bit is next pressed against a work piece the beat piece moves to the right (as seen in Fig. 1) into a position in which it can be impacted by the hammer element 29. Movement to the left of the ram is thus restricted with the result that the leakage of air referred to above ceases.

Claims (9)

1. A rotary percussive drill including a drill chuck and comprising an electric driving motor, rotary driving means for imparting rotation from the motor to the drill chuck, a percussive drive for translating rotation from the motor into movement of a member for imparting percussive blows to a drill bit when located in the drill chuck, and in which means are provided for reversing the direction of rotation of the driving motor, the rotary drive means further including unidirectional drive means operable to permit the rotary drive means to transmit to the drill chuck rotation of the driving motor in one direction but not rotation of the motor in the other direction.

2. A drill as claimed in claim 1 in which the unidirectional drive means comprises a clutch.

3. A drill as claimed in claim 2 in which the clutch is a sprag clutch.

4. A drill as claimed in claim 1 or 2 in which the driving motor has an aramture shaft carrying a drive gear, in which there is a first gear in mesh with the drive gear, a second gear, unidirectional drive means interconnecting the first and second gears, and in which the rotary drive means includes a gear wheel meshed with the second gear wheel.

5. A drill as claimed in claim 4 in which the first gear wheel is fixed to a rotatably mounted shaft forming part of the percussive drive.

6. A drill as claimed in claim 4 or 5 in which the unidirectional drive means comprises driving teeth on the first gear, a washer having half shear teeth for engagement with the driving teeth only when the motor is rotated in one direction, the washer also having locating teeth, driven teeth on the second gear wheel in meashing engagement with the locating teeth, and spring means for urging the washer towards the first gear.

7. A drill as claimed in any one of the preceding claims in which the means for reversing the direction of rotation of the motor form part of a motor speed control unit.

8. A drill as claimed in any one of the preceding claims and further comprising releasable means for preventing the member from imparting percussive blows.

9. A hand-held, electric, rotary percussive drill substantially as herein described with reference to and as illustrated by the accompanying drawings.