GB2474113A - Power hand tool with switching means comprising a metastable coupling spring - Google Patents

Abstract

A power handtool comprises a switchable mechanism adjustable between a first and second operable position, with resilient means 9 acting on at least one component 11 of the mechanism. The resilient means 9 comprises a metastable coupling spring which adopts a stable position in the first operating position and a quasi-stable position in the second operating position. Coupling spring 9 may comprise a spring ring 13, which may define a full circle or may be conical. Coupling spring 9 may be a sheet metal part, and may have integral or multi-part constructions. Where the spring 9 has a multi-part construction, there may be two co-operating springs, one being a bistable spring element 21 and one element 22 having linear spring characteristics. User force required to maintain a control element 8 in its switching position associated with the spring quasi-stable state is less than the user force needed to attain that switching position.

Description

OPERATING CONTROL IN A POWER HANDTOOL

The present invention relates to a power handtool and has particular reference to operating control, especially of a switchable mechanism, in such a handtool.

A battery-operated screwdriver, which comprises a multi-stage planetary transmission by way of which the drive movement of an electric drive motor is translated into a desired rotational speed with a defined torque of a tool mount for a tool, is described in DE 10 2004 058 809 Al.

The transmissions in power handtools of that kind are typically constructed to be switchable and can, in particular, be switched between a first gear stage providing a slower rotational speed and higher torque and a second gear stage providing higher rotational speed and lower torque. The switching process is executed with the help of a control element adjustable between different switching positions. The control element actuates a switching gear of the planetary transmission and adjusts this between different operating positions. Disposed in the transmission path between the control element and the switching gear is a torsion spring, against the spring force of which the manual setting movement has to be formed.

There remains a need for a power handtool with a mechanism -switchable between at least two operating positions -embodying simple constructional measures by which change between the operating positions can be performed securely and in an ergonomically favourable manner.

According to the present invention there is provided a power handtool comprising a switchable mechanism adjustable between at least a first and a second operating position and resilient means acting on at least one component of the mechanism, the resilient means comprising a metastable coupling spring which in the first operating position adopts a stable position and in the second operating position adopts a quasi-stable position in which it exerts a smaller spring force than in an intermediate position between the first and second operating positions.

A power handtool embodying the invention comprises, in a housing, a drive means, preferably an electric drive motor, providing drive which is transmissible by way of a switchable mechanism to a tool exchangeably held in a tool mount. In the case of an electric drive motor this can be supplied with power by way of a mains cable or, for preference, by way of a rechargeable battery carried at the housing of the handtool; in this case, the handtool is, for example, a battery-operated screwdriver or battery-operated drill.

The switchable mechanism in the power handtool is adjustable between at least two operating positions, with each of which a specific characteristic is associated so that on change between the operating positions a variable of the transmission in the drive train between drive motor and tool mount changes. In a preferred embodiment, a defined rotational speed translation and torque transmission is associated with each operating position. In this manner it is possible, by way of a change between the operating positions, to switch over between a lower rotational speed with higher torque and a higher rotational speed with lower torque.

The adjustment of the mechanism between the at least two operating positions advantageously takes place with the help of a control element adjustable between switching positions associated with the operating positions of the mechanism. Disposed in the transmission path between the control element and a mechanism component of the switchable mechanism is a coupling spring which is constructed as a metastable spring which in a first operating position or switching position of the control element adopts a stable position or state and in a second operating position or switching position of the control element adopts a quasi-stable position or state. In the quasi-stable position the coupling spring exerts a smaller force than in an intermediate position between the two switching positions.

Various advantages can be achieved with this construction. The coupling spring has a double function in that on the one hand it transmits the switching movement of the control element to a component of the switchable mechanism and on the other hand it holds the control element in one switching position in a stable position and in the second switching position in a quasi-stable position. In the stable switching position the control element remains in its position insofar as no external forces, which oppose the spring force of the coupling spring and are sufficiently high in order to move the control element out of the stable switching position, act on the control element. In the quasi-stable position the coupling spring similarly exerts a spring force on the control element; however, this spring force is lower than in the transfer path between the two switching positions. This means that the quasi-stable switching position is perceivable as a switching point, on attainment of which the spring force is lower, which is detectable by the user. The force which the user has to apply in order to maintain the quasi-stable switching position is reduced by comparison with the maximum force between the switching positions. Since, however, the spring force is still effective, the coupling spring causes resetting from the quasi-stable switching position back to the stable switching position as soon as the opposing force exerted by the user is removed.

This construction has the advantage that the control element has to be moved by the user against the force of the coupling spring in only one direction in order to produce a transfer between the switching positions and, in company therewith, between the operating positions of the switchable mechanism. In the opposite direction, movement takes place by the force of the coupling spring without requiring active intervention by the user. By virtue of the construction as a metastable coupling spring, however, the holding force which has to be applied by the user in the quasi-stable switching position is reduced, so that holding in the quasi-stable position is more comfortable and is thus performed in ergonomically favourable manner.

Various constructional forms of the coupling spring as a metastable spring element are possible. In a preferred embodiment the coupling spring is constructed as a spring ring which advantageously has the form, at least approximately, of a complete circle. For preference, the spring ring forms a closed full circle, wherein in principle interrupted circles or partly circular forms, for example a semicircular form, are also possible. However, the construction as a closed full circle has the advantage that the coupling spring is formed to be particularly stable and in addition may be less susceptible to wear or fatigue.

The spring ring can have a frusto-conical form which, in the absence of bias, represents the stable position of the spring ring. With deformation of the spring ring, the conicity is reduced by application of a force, such that on attainment of a metastable position of the spring ring a reduced spring force, which is oriented in the direction of the initial setting, is generated. Advantageously, the spring ring in the installed position does not exert any spring force in its initial setting, so that the initial position representing the stable switching position is free of force. However, the spring force of the spring ring counteracts changes out of the stable initial position, wherein the spring force on attainment of the second, quasi-stable switching position diminishes again so that this switching position can be maintained with reduced expenditure of force by the user. On removal of the opposing force by the user the spring ring automatically again adopts its first, stable initial position.

In principle, however, biasing of the spring ring into the stable position is also possible.

This spring behaviour of the spring ring can, if so desired, be achieved by spring arms which, for preference, are constructed integrally with the spring ring and extend outwardly at the outer circumference of the spring ring with radial and/or axial components. The spring arms are, for example, of angular construction and in the installed position are supported at a part of the power handtool. As a result, a spring force action keeping the switchable mechanism in the stable initial position is already present in the initial position, which represents the stable switching position. The spring arms can be combined with a conical form of the spring ring, by way of which a metastable spring behaviour can similarly be achieved. However, in principle, a construction of the spring ring as a disc or washer is also possible.

Moreover, it is advantageous to provide at the spring ring at least one support element, preferably two support elements, by way of which the spring ring is supported at a part of the handtool, particularly at the control element. The support elements are, for example, constructed as radially projecting, diametrically opposite support straps. The afore-mentioned spring arms also form support elements.

In addition, it is advantageous to provide at the spring ring radially outwardly projecting connecting elements which are formed at the annular body of the spring ring. The connecting elements serve for connecting and retaining the spring ring by one or more parts of the handtool.

The mechanism, which is to be adjusted by way of the control element between the at least two operating positions, is preferably a transmission with at least two gear stages which respectively represent the operating positions. The control element forms a gear change switch by way of which the different gear stages of the transmission can be engaged. In this connection, the transmission can be a planetary transmission, preferably a multi-stage planetary transmission, wherein the transmission can have at least two gear stages between which switching can be made. Each gear stage of the transmission in this regard represents an operating position. The control element acts as a change switch by way of which the gear stages of the transmission are selected, thus engaged. An adjustable switching element can be provided, which is acted on by the coupling spring and constructed as, for example, a switching internal gear which in one switching position of the change switch is coupled with a pinion cage of the planetary transmission.

The coupling spring is preferably a metal part, particularly a sheet metal part. In principle, however, construction from other materials, particularly plastics material, are possible.

In one advantageous embodiment the metastable coupling spring is executed as an integral component, for example a metal part. In another advantageous embodiment, the coupling spring is of multi-part construction and comprises at least two co-operating individual springs, which are each constructed from metal or another material, for example plastics material. The individual springs are so constructed with respect to the spring characteristics thereof that the metastable spring characteristic is achieved in the co-operation of the individual springs. By comparison with an integral construction, this has the advantage that the individual springs do not necessarily have to intrinsically have a metastable spring behaviour; rather the metastable behaviour results only from the co-operation of the individual springs. Accordingly, the individual springs can be of comparatively simple construction or produced in simple manner.

The co-operation of the individual springs can be realised particularly by the individual springs being in contact with one another, the individual springs preferably being connected in parallel. In principle, however, a series connection of the individual springs is also possible. In an advantageous embodiment at least two individual springs, but preferably all individual springs, forming the coupling spring are supported by respective sections at the handtool housing and advantageously are in mutual contact or are mutually supporting by a further section. For example, in the case of a coupling spring composed of two individual springs a first individual spring can contact the switchable component of the mechanism and subject it to force loading, whereagainst the second individual spring, which is supported just like the first individual spring at the housing, subjects the first individual spring to direct force loading without directly contacting the switchable component. A parallel connection of the individual springs to provide an overall spring characteristic differing from the spring characteristics of the individual springs thereby results.

In a further advantageous embodiment one of the individual springs is constructed as a bistable spring element and a further individual spring as a spring element with a linear spring characteristic. The desired metastable spring characteristic results from the series connection. In constructional terms this can be executed in the manner that the first individual spring, which has the bistable spring characteristic, is constructed as a spring ring and the second individual spring with linear spring characteristic is constructed as a spring lever.

Preferred embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. I is a schematic side view of an electric power handtool in the form of a battery-operated screwdriver, which comprises, in a housing, a planetary transmission adjustable between two gear stages, wherein the switching process takes place by actuation of a switch connected by way of a coupling spring with a switching element of the transmission; Fig. 2 is a detail view of a gear change switch which actuates a metastable coupling spring coupled with a switching gear of the transmission; Fig. 3 is a perspective view of a coupling spring in the form of a closed spring ring; Fig. 4 is a perspective view of an annular coupling spring; Fig. 5 is a diagram showing a spring characteristic of the coupling spring; Fig. 6 is a perspective view of part of an electric power handtool with a coupling spring composed of two individual springs; and Fig. 7 is a perspective view of two individual springs co-operable to provide the coupling spring in Fig. 6.

Referring now to the drawings there is shown in Fig. 1 a power handtool I in the form of a battery-operated screwdriver which comprises a housing 2 accommodating an electric drive motor 3, which is supplied with current by way of a changeable battery 4 arranged at a handle 5 of the handtool casing. The drive motor 3 is coupled with a planetary transmission 6 which drives a drive output spindle 7 provided for reception of a tool mount for a tool. The planetary transmission 6 is of multi-stage construction and is switchable between at least two operating positions, which can be engaged with the help of a control element or pawl 8 at the handle 5. The control element 8 actuates a switch in the handle 5 for switching on and switching off the electric drive motor. In addition, the control element 8 has the task of switching back and forth between the operating positions of the transmission. This takes place by way of pressing the control element 8 into the handle 5 of the housing. The control element 8 thus serves to transfer the transmission 6 between the different operating positions. The control element 8 in this connection adopts different switching positions corresponding with the operating positions of the transmission.

Serving for transmission of the switching movement of the control element 8 to the planetary transmission 6 is a coupling spring 9, which is connected with a switch element, in the form of a switching internal gear, of the transmission 6. The coupling spring 9 is constructed as a metastable spring element adjustable between a stable position or state, which corresponds with the first switching position of the control element 8 and thus the first operating position of the planetary transmission, and a quasi-stable position or state, which corresponds with the second switching position of the control element 8 and thus the second operating position of the planetary transmission. The stable, first switching position is advantageously the initial setting of the control element 8. The quasi-stable, second switching position is preferably the depressed setting of the control element 8. In the stable initial position the force of the coupling spring 9 opposes changing of the position of the control element 8 so that the control element has to be adjusted against the force of the coupling spring 9 for transfer of the transmission from the first to the second operating position. In the quasi-stable position corresponding with the second switching or operating position the force of the coupling spring is reduced, but not as far as zero, and is oriented in direction towards the initial position, which has the advantage that the control element 8 has to be held by the user with only a reduced expenditure of force. On reaching the quasi-stable depressed switching position, however, a maximum force produced by the coupling spring has to be overcome by the user.

The components participating in the gear changing are shown in Fig. 2 in individual illustration. The control element 8 is mounted to be pivotable, but can in a given case also be arranged at the housing to be translationally displaceable or slidable, thus as indicated in Fig. 1, wherein a corresponding rotational or translational setting movement has to be performed for transfer between the different switching positions.

The control element 8 is connected by way of a first connecting element 10 with the coupling spring 9, which is coupled by way of a second connecting element 11 with a switching element 12, preferably a switching internal gear, of the transmission 6. The initial position is illustrated by a solid line, this initial position corresponding with the stable position of the coupling spring 9. The adjusted position of the control element 8 as well as of the first connecting element 10 is illustrated by a dashed line, this adjusted position, which corresponds with a setting travel, denoting the quasi-stable second position of the coupling spring 9. In the initial position the planetary transmission 6 is disposed in the first operating position and, in the adjusted position, in the second operating position.

In a variant the control element 8 is directly connected with the coupling spring 9 so that it is possible to dispense with the connecting element 10. In a further variant the control element 8 is directly connected with the connecting element 11, which in turn is coupled with the coupling spring 9; it is again possible to dispense with the connecting element 10 in this embodiment.

A coupling spring 9 in the form of a spring ring is illustrated in Fig. 3. The coupling spring 9 consists of a closed ring 13, which is conically arched, and radially outwardly protruding, diametrically opposite support straps 14 and 15 for coupling to the handtool housing or to a casing of the transmission. The coupling spring 9 constructed in this form represents a metastable spring element which is adjustable between a stable initial position and a quasi-stable, second position.

Another form of the metastable coupling spring 9 is illustrated in Fig. 4, in this case consisting of a closed ring 13 which, by contrast with the first form, is of flat washer-shaped construction. Integrally constructed spring arms 16 and 17, which are each of angular form and in the installed position are supported at a part of the handtool, are formed at the outer circumference of the ring 13. In the case of adjustment of the coupling spring in the manner illustrated in Fig. 2 the spring arms 16, 17 as well as the ring 13 generate a spring force which in the transition between the stable initial position and the quasi-stable position exceeds a maximum.

Radially outwardly projecting, diametrically opposite support straps 14 and 15 are formed at the coupling spring 9 of Fig. 4 similarly to the spring of Fig. 3. The two spring arms 16 and 17 are both disposed in the same, upper half of the ring 13 and lie at an angular spacing of approximately 300 from the upper support strap 14.

Connecting elements 18 serving for connection of the coupling spring 9 with further parts of the handtool are formed at the ring 13 of the coupling spring 9, in particular at its outer circumference. For example, a possibility of coupling to the control element 8 or the connecting element 10 (Fig. 2) can be provided by way of the connecting elements 18 at the top and the connection into the transmission by way of the connecting elements 18 disposed thereunder.

The force/travel spring characteristic of a metastable coupling spring is illustrated in the diagram of Fig. 5. The lefthand starting point 20 corresponds with the stable initial position of the coupling spring and the region 21 recorded on the right corresponds with the quasi-stable position. On transfer between the positions 20 and 21 a force maximum has to be overcome. In the quasi-stable position 21 the spring characteristic has a force level significantly reduced by comparison with the force maximum, but higher than in the stable initial position 20. As soon as the opposing force by the user is removed, the spring characteristic returns, as recorded by the arrows, from the quasi-stable position 21 to the

stable position 20.

A further embodiment is illustrated in Figs. 6 and 7. The power handtool 1 is again a battery-operated screwdriver with a housing 2, which serves as a transmission housing and in which a transmission, which is to be driven by way of an electric drive motor, for transmission of the drive movement of the motor to the drive output spindle is accommodated. The transmission 6 is constructed as, for example, a multi-stage planetary transmission switchable between different operating positions. The switching between the operating positions takes place manually with the help of a control element or pawl 8, wherein the switching movement of the control element 8 is transmitted to the coupling spring 9 by way of a connecting or transmission element 10. The spring 9 has a metastable spring characteristic and is adjustable between a stable position corresponding with a first operating position of the transmission and a quasi-stable position corresponding with a second operating position of the transmission. To that extent, the embodiment of Figs. 6 and 7 corresponds with the first embodiment.

Whereas in the first embodiment the coupling spring 9 is of integral construction, the coupling spring 9 in the second embodiment of Figs. 6 and 7 comprises two individual springs 21 and 22 which co-operate and together form the coupling spring 9 with the metastable spring characteristic.

The first individual spring 21 is constructed as a spring ring and comprises a closed ring 13 (Fig. 7) at which connecting elements 18 as well as supporting or holding elements 14 and angularly offset relative to and disposed between the connecting elements 18 are arranged, by way of which a coupling to the housing 2 and a connection with the element and the switching element of the transmission takes place. The annular individual spring 21 has a bistable spring behaviour.

The second individual spring 22 is constructed as a spring lever or spring yoke and comprises a carrier plate 23, by way of which the spring 22 is connected with the housing 2, and two spring arms or yokes 24 and 25, which project angularly from the carrier plate 23 and are constructed integrally with the carrier plate and which in the installed state according to Fig. 6 bear against the first individual spring 21 and, in particular, are coupled with the connecting elements 18 in the lateral region of the spring 21. The two spring yokes 24 and 25 are curved and together describe approximately a semicircle.

The two individual springs 21 and 22 are functionally connected in parallel, whereby an overall spring characteristic results differing from the characteristics of the individual springs results. The overall spring characteristic corresponds with a metastable spring behaviour, whereagainst the annular individual spring 21 is constructed as a bistable spring element and the second individual spring, which is constructed as a spring yoke, has a linear spring behaviour.

In the mounted position, the yokes 24 and 25 of the second individual spring 22 bear against the ring 13 of the first individual spring 21, which on the one hand is acted on by the connecting or transmission element 10 and on the other hand is supported at the switching element of the transmission.

Claims (21)

1. CLAIMS1. A power handtool comprising a switchable mechanism adjustable between at least a first and a second operating position and resilient means acting on at least one component of the mechanism, the resilient means comprising a metastable coupling spring which in the first operating position adopts a stable position and in the second operating position adopts a quasi-stable position in which it exerts a smaller spring force than in an intermediate position between the first and second operating positions.
2. 2. A power handtool according to claim 1, comprising a control element for producing the operating positions, the control element being adjustable between two switching positions respectively corresponding with the first and second operating positions and acting by way of the coupling spring on the component of the mechanism.
3. 3. A power handtool according to claim 1 or claim 2, wherein the coupling spring comprises a spring ring.
4. 4. A power handtool according to claim 3, wherein the spring ring substantially defines a full circle.
5. 5. A power handtool according to any one of claims 3 to 5, wherein the spring ring is substantially conical.
6. 6. A power handtool according to any one of claims 3 to 6, wherein the spring ring has at least one protruding support element in contact with a part of the handtool.
7. 7. A power handtool according to claim 6, wherein the part is a casing of the handtool.
8. 8. A power handtool according to claim 6 or claim 7, wherein the support element comprises a support strap.
9. 9. A power handtool according to any one of claims 6 to 8, wherein the support element comprises a spring arm.
10. 10. A power handtool according to claim 9, wherein the spring arm is angular.
11. 11. A power handtool according to any one of claims 3 to 10, wherein radially outwardly projecting connecting elements are formed at the spring ring.
12. 12. A power handtool according to any one of the preceding claims, wherein the mechanism comprises a transmission
13. 13. A power handtool according to claim 12, wherein the transmission is a planetary transmission.
14. 14. A power handtool according to any one of the preceding claims, wherein the coupling spring is a metal part
15. 15. A power handtool according to claim 13, wherein the coupling spring is a sheet metal part.
16. 16. A power handtool according to any one of the preceding claims, wherein the coupling spring is of integral construction.
17. 17. A power handtool according to any one of claims 1 to 15, wherein the coupling spring is of multi-part construction and comprises at least two co-operating springs.
18. 18. A power handtool according to claim 17, wherein one of the co-operating springs comprises a bistable spring element.
19. 19. A power handtool according to claim 17 or claim 18, wherein one of the co-operating springs comprises a spring element with a linear spring characteristic.
20. 20. A power handtool according to any one of claims 17 to 19, wherein one of the co-operating springs comprises a spring ring and the other comprises a spring lever.
21. 21. A power handtool according to any one of claims 17 to 20, wherein each of the co-operating springs is supported at a casing of the handtool.