Hand-held power tool with grounding

An electrical hand-held power tool (2) includes a housing (4) in which a drive (6) is located, a ventilator (22) for forming a suction region (28) and a pressure region (30) in the housing (4) which provide for an air flow (L) that serves for cooling at least parts of the drive (6), and a separation element (26) arranged between the suction region (28) and the pressure region (30) and fixedly secured in the housing (4), the separation element (46) having an opening for forming a limited wire passage region (46) from the suction region (28) into the pressure region (30).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hand-held power tool including a housing, a drive located in the housing and including a motor, a gear unit and, optionally, a percussion mechanism. The hand-held power tool further includes ventilation means for forming a suction region and a pressure region in the housing which provide for an air flow that serves for cooling at least parts of the drive, and a separation element arranged between the suction region and the pressure region and fixedly secured in the housing.

2. Description of the Prior Art

In the hand-held power tools of the type described above, a constructive separation of the overpressure region in which ventilation means produces a blowing flow, and of the suction region in which the ventilation means produces a suction flow, insures a relatively high cooling capacity.

German Publication DE 42 20 078 A1 discloses a hand-held power tool in which a radial ventilator is located in the tool housing. The ventilator is driven by a motor and aspirates axially cooling air and presses it radially outwardly through air outlet slots from the housing. For increasing pressure and raising the volumetric flow of the radial ventilator, an air conducting element is provided therein and which is held circumferentially in the housing with a concentric cover. The cover separates the pressure region form the suction region.

In some countries, e.g., in some parts of the U.S., electrical tools and, in particular, electrically driven by an electric motor, hand-held tools must be equipped with a protective ground wire which is connected electrically with a ground conductor of the network cable for protection of metallic parts located in the interior of the housing of the electrical hand-held tool. The related metallic parts can be formed, e.g., by housing parts of the gear unit, percussion mechanism, or stator or by bare contact elements for diverting leak currents.

German Patent No. 950,658 discloses an electrical hand-held power tool the motor of which is separated from metal parts of the housing by isolating plastic parts. In addition, in the interior of the tool housing, there is provided two bare annular electrodes which are connected by a protective ground wire to ground or zero point of the network. Further, in the tool housing, there is provided a ventilator wheel that produces, during an operation, a suction region and a pressure region. The protective ground wire is freely mounted in an open transition region between the suction and pressure regions.

The drawback of the known construction consists in that because of the open transition region between the suction and pressure zones, only a relatively weak air flow is produced. In addition, the protective ground wire has a relatively high freedom of movement that can lead to damages during the operation.

Accordingly, an object of the invention is to eliminate the above-mentioned drawbacks in the electrical hand-held power tools of the type discussed above.

Another object of the present invention is to provide an electrical hand-held power tool in which a maximal cooling efficiency is possible independent from requirements in respective countries or use-specific requirement with respect to ground conductors.

SUMMARY OF THE INVENTION

These and other objects of the present invention, which become apparent hereinafter, are achieved by providing a separation element having opening means for forming a wire passage region from the suction region in the pressure region and which is closed in the initial condition and can be optionally open.

In this way, the construction of a hand-held, electrically driven power tool can be adapted or not adapted to the use of a protective ground wire, dependent in which countries it is used or what requirements the hand-held power tool should meet.

If a protective ground wire is used, e.g., because of the corresponding requirement to the power tool in question in the country of use, the wire passage region can be open by a simple secondary treatment. This enables a short connection between the related metallic part and the ground conductor, on one hand, and a simple mounting and a reliable fixation of the protective ground wire. At that, the wire passage region is adapted to the cross-section of the protective wire in order to minimize a possible pressure or temperature imbalance and a resulting reduction in the cooling efficiency.

In case no protective ground wire is needed, the wire passage region remains closed to provide for as complete as possible separation of the suction and pressure regions and a resulting therefrom, maximal cooling efficiency.

Thereby, all of the power tools of a particular type can include both embodiments and be manufactured of the same housing components and, in case of a need in a prescribed additional protective ground wire, be modified by a simple aftertreatment. In both cases, a high cooling efficiency is insured.

According to a particularly advantageous embodiment, the separation element is formed by air conducting means located in the housing, with the wire passage region being formed at an edge of the separation element. Thereby, the separation element and the opening means that is provided therein, can be produced separately from a conventional housing and in a particular simple manner. In addition, in this case, the opening means is particularly easily accessible, which substantially simplifies the secondary treatment for forming the wire passage region.

Advantageously, the opening means provides that a predetermined region of the separation element is irreversibly deformed for forming the wire passage region. Thus, the predetermined region can, e.g., be plastically deformed or broken-through. In both cases, a lasting wire passage region is formed in which the protective ground wire can be easily mounted and reliably held.

Advantageously, the opening means is formed by break-through assist means, which enables a particularly simple and rapid formation of the wire passage region.

Preferably, the break-through assist means is formed by material weakening that, e.g., forms a braking line or a flat region with a reduced material strength in comparison with the remaining portion of the separation element. Thereby, the opening means can be formed in a particular simple way, e.g., by correspondingly shaping a casting of the separation element or by a subsequent embossing.

Preferably, the material weakening has a U-shaped delimitation extending to the edge of the separation element. This provides for an exact predetermined limitation of the break-through region and an easy breaking-through a region designed for forming the wire passage region with a suitable tool, e.g., flat nose pliers.

According to an alternative embodiment, the opening means provides for an elastical deformation of a predetermined region of the separation element for forming the wire passage region. E.g., the opening means can be formed by an elastic diaphragm provided on the separation element. The diaphragm is deformed during mounting of the protective ground wire by its cross-section, with the diaphragm applying pressure to the surface of the protective ground wire. In this way, the wire passage region is sealed particularly well during insertion of the wire.

It is advantageous when the opening means includes a film hinge that pivotally supports a predetermined region. The film hinge can be elastically or plastically deformed. In each case, the wire passage region can be formed without use of any tool, which substantially simplifies mounting of the protective ground wire.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A hand-held power tool2according to the present invention, which is shown inFIG. 1, has a housing4in which there is arranged a drive6for driving a working tool10receivable in a chuck8. The drive6includes a motor12, a gear unit14located in a gear unit housing16, and a percussion mechanism18arranged in a percussion mechanism housing20. Alternatively, there can be provided a hand-held power tool2without the percussion mechanism18.

The motor12drives ventilation means22in form of a ventilator supported on a separation element26, arranged on an opening24in the housing4and serving as air conducting means. The separation element26is form- or forcelockingly held on the housing4, in a manner not shown in the drawing in detail, in the condition of the hand-held power tool2after the final assembly. Alternatively, the separation element can be formed as one-piece with a part of the housing4. In each case, during rotation of the ventilation means22in the housing4in the direction shown with arrow D, a suction region28is formed on one side of the separation element26and a pressure region30is formed on another side of the separation element26. Thereby, there is produced an air flows in the directions indicated with arrows L. The air enters the housing4through inlet openings32in a bottom34, flows along the motor12for cooling the same, and then flows through the opening24out of the suction region28and into the pressure region30where it flows along the gear unit14and the percussion mechanism18for cooling them. The air flows out of the pressure region through outlet openings36in the direction of the chuck8.

For its power supply, the motor12is connected, in a manner not shown in detail, by a network connector38with a network cable40. In certain countries, in hand-held power tools2, there is provided, as shown with dash-dot lines, a ground wire44secured to the network connector38which, in turn, is connected with a protective conductor42of the network cable40. The protective ground wire44forms an electrical contact with a metallic element of the hand-held power tool2such as, e.g., the gear unit housing16, as shown in the drawing. Alternatively, the protective ground wire44can be connected with any other or additional element such as, e.g., the percussion mechanism housing18or a common housing part of the drive unit14and the percussion mechanism18. The electrical connection of the metallic element with the protective conductor permits to divert current applied to the metallic element, without any damage of the metallic element. In some countries, such protective ground wires are not required.

In order to be able to use the same components for the hand-held power tools2independent on the country in which they will be used, there is provided on the separation element26, as shown inFIGS. 1-2, a limited wire passage region46which is closed in its initial condition and, if needed, enables insertion of the protective ground wire44in a predetermined position of the separation element26. In hand-held power tools2that do not require any protective ground wire, the wire passage region remains closed.

Thereby, independent from whether use of the protective ground wire is required or note, unnecessary, separate from the air flow L, pressure or temperature balance between the suction region28and the pressure region30is prevented, whereby favorable flow characteristics and an adequate cooling efficiency can be insured.

As shown inFIG. 3a, the separation element26has, for an optional opening of the wire passage region46, opening means in form of a plane embossing48. The embossing48forms a U-shaped limited material weakening of the separation element26and that extends up to the edge50thereof. The embossing48serves as break-through assistance means, whereby the material in the wire passage region46can be broken through with e.g., a flat nose pliers, not shown.

FIG. 3bshows a separation element in a mounted condition with an open wire passage region. There, a ground wire44is located. As shown inFIG. 3b, the size of the open wire passage region46corresponds to the cross-section of the protective ground wire.

FIGS. 4a-4bshow an alternative embodiment of the wire passage region4b. In the embodiment ofFIGS. 4a-4b, the opening means formed by U-shaped, arranged in row recesses52such as through-or blind bores, as shown inFIG. 4b. The material in the wire passage region46is weakened by the recesses52and is broken therethrough. Alternatively, to the shown embodiment, the recesses can be formed as elongate recesses.

In the embodiment according toFIGS. 5aand5b, an elastic diaphragm54is provided in the wire passage region46, closing the same in the initial condition. As shown inFIG. 5b, upon insertion of the protective ground wire44, the diaphragm54is pressed sidewise, providing for a particularly good sealing of the wire passage region46as a result of action of recovery deformation forces.

In the embodiment according toFIGS. 6a-6b, the wire deformation region46is formed by two parallel incisions56at the edge50and a film hinge58. In this way, the material of the separation element26forms a flap50in the wire passage region46. For insertion of the protective ground wire44, the flap60can be elastically or plastically deflected over the film hinge58, as shown inFIG. 6b.