GB2290914A

GB2290914A - Hand-operated machine tool having a commutator motor which is to be operated by mains voltage

Info

Publication number: GB2290914A
Application number: GB9512639A
Authority: GB
Inventors: Martin Summermatter; Hansruedi Ramseier; Beat Schlaefli
Original assignee: Scintilla AG
Current assignee: Scintilla AG
Priority date: 1994-06-28
Filing date: 1995-06-21
Publication date: 1996-01-10
Also published as: DE9410386U1; ITMI950427U1; GB9512639D0; FR2721768A1; IT1276713B1; ITMI951261A1; ITMI950427V0; ITMI951261A0

Abstract

For a hand-operated machine tool having a commutator motor which can be operated by mains voltage, in particular alternating current, and has a rotor 10, which comprises a laminated stack 12, made of laminations, with slots 13, and a rotor shaft 11 and is provided with longitudinal and transverse protective insulation 14 between the rotor shaft 11 and the laminated stack (12) and with operating insulation 15, 16. The coating of the rotor 10, which coating consists of a single material, which can be injected on, is jointly used as the protective and operating insulation. <IMAGE>

Description

Hand-oDerated machine tool having a commutator motor which is to be operated bv mains voltage Prior Art The invention is based on a hand-operated machine tool of the generic type of Claim 1 and on a corresponding commutator motor and rotor.

Hand-operated machine tools which are driven by a commutator motor which can be operated by a mains voltage of about 110 to 230 volts have already been known for a long time. The motor has a rotor, between the laminated stack and the rotor shaft of which a protective insulation consisting of plastic is arranged. This keeps the operator of the hand-operated machine tool safe from a highly dangerous electric shock. The protective insulation is prescribed in Germany by the standard SEV 1059/1981, with a breakdown strength of 5,000 volts for the duration of 3 seconds at 200 mA current intensity.

There are particularly high mechanical strength requirements for the protective insulation of handoperated machine tools, owing to the high powers to be transmitted, of between about 200 and 2,000 watts at rotational speeds of about 30,000 rpm. In addition, intense vibrations, zor example in the case of hammer drills, and the impact load thereof in the case of heavy constructional use must be taken into account. The breakdown strength must be ensured even for an extremely long service life of the hand-operated machine tools.

Tears and ruptures in the protective insulation must not occur. In addition, surface changes, which favour creepage currents, must likewise be precluded.

The rotor of the known hand-operated machine tool has operating insulation in the slots of the laminated stack which are used to accommodate the coil winding.

This operating insulation comprises either prefolded insulating paper placed around the rotor or an elastic, thin-walled plastic sheath placed around the rotor and is intended to prevent a short circuit of the coil windings, which short circuit would lead to the failure of the machine. The commutator of the known hand-operated machine tool motor has protective insulation, just like the rotor laminated stack, due to an extension of the plastic sheath with respect to the rotor shaft.

A lamella made of insulating cardboard and about 3 mm thick is fitted in each case to the end sides of the rotor stack and is used as protective and operating insulation.

In addition, a low-power electric motor, such as is used in motor vehicles, has been disclosed in accordance with DE-A 32 43 212. The rotor of this batterydriven motor has plastic insulation arranged not only between the laminated stack and the rotor shaft but also in the slots of the laminated stack.

A low-power motor of this type does not need any protective insulation, since, in contrast to the mains voltage, the battery voltage of motor vehicles is comparatively safe for people. In addition, low-power motors are lighter and smaller compared with motors operated by mains voltage. Generally, the mechanical load of lowpower motors of this type is likewise low, with the result that the insulation is also exposed to low mechanical loads.

Although any possible tears in the insulation can reduce the power of the low-power motors, they do not represent any danger to the operator of the motor.

Advantages of the invention The hand-operated machine tool, the motor and the rotor according to the invention, having the characterizing features of, Claims 1, 7 and 9, respectively, have in contrast the advantage that the operating insulation and the protective insulation can be introduced from a single material using a single working step, with the result that the laminated stack is thus fixed on the rotor shaft in a particularly reliable and mechanically reinforced manner. In addition, with unchanged tolerances, the slots of the laminated stack have a larger capacity for the coil windings because of the thin-walled plastic insulation. The rotor can therefore be built more compactly. The improved degree to which the slots are filled means that the heat transfer between the coil winding and the laminated stack is greater, resulting in the possibility of more effective cooling of the motor.

The possible power yield is therefore higher in the case of the novel motors.

The fact that the protective and operating insulation are made in one piece, in particular from polyoxymethylene or polyacetal, abbreviated to POM, leads to considerable savings compared with motors having the design which was customary hitherto. This was surprising on account of the initially problematic, large layer thickness differences between the operating insulation and the protective insulation, in particular at their transitions, which required a high development outlay to control in production. Previously, it appeared to a person skilled in .he art to be too complicated and costly to provide common, integral, protective and operating insulation, consisting os a single material, for rotors.

The time, transport and energy outlay for the production of the motors according to the invention is less than according to previous known methods.

Encapsulating the rotor with the protective insulation dispenses with the assembly outlay on end-side cardboard lamellae as well as corresponding stockkeeping outlay or any other consequential outlay.

Drawing An exemplary embodiment of the invention is shown in the associated drawing and explained in more detail in the following description.

Figure 1 shows the spatial sectional illustration of a rotor, Figure 2 shows a cross-section of the rotor according to Figure 1, Figure 3 shows an enlarged detail according to Figure 2, Figure 4 shows a complete rotor with a winding and slot closures, and Figure 5 shows a cross-section of the slot of the rotor according to Figure 4.

Description of the exemplary embodiment The rotor 10 shown in Figure 1 comprises a rotor shaft 11 bearing a laminated stack 12 approximately centrally, which comprises individual laminations (not referred to in more detail) and has slots 13 for accommodating a coil winding (not illustrated in the figure).

Protective insulation 14, which encloses the rotor shaft 11 like a tube beyond the end sides of the laminated stack 12, is situated between the laminated stack 12 and the rotor shaft 11. In addition, the protective insulation 14 is shaped at both end sides of the laminated stack 12 50 as to project radially outwards and be flush with the periphery of the laminated stack, in each case in the form of a plastic cover 15 which is about 2.5 mm to 3 mm thick. The protective insulation 14 between the laminated stack 12 and the rotor shaft 11 is about 1.5 mm thick and mergers in each case with the covers 15 at the end sides of the laminated stack 12. Starting from the covers 15, to the walls of the slots 13 the protective insulation 14 abruptly merges, without a break, with film-like operating insulation 16 which is about 0.2 mm thick.

The operating insulation 16 and the protective insulation 14 are secure from tear formation and detachment at the rotational speeds of 30,000 rpm which are customary for universal motors as well as in the case of the high heat evolution of the universal motors which is customary for hand-operated machine tools in continuous operation.

A commutator (not illustrated here), which is shown in Figure 4, is pressed onto the left-hand side (in the observation direction) of the protective insulation 14. The protective insulation 14 extending beyond the end sides of the laminated stack on the side opposite the commutator is provided for accommodating a fan impeller (not illustrated in the figure).

The cross-section, shown in Figure 2, of the rotor 10 without a coil winding (just like in Figure 1) shows the rotor shaft 11 bearing the protective insulation 14 which is arranged concentrically and like a ring and around which, for its part, the laminated stack 12 engages concentrically. The profile of the slot 13 for accommodating the coil winding (not illustrated here) and the operating insulation 16, which lines the inner walls of the slots 13, is clearly visible. A region, emphasized by the reference number 18, of the laminated stack 12 is shown enlarged as a detail in Figure 3.

Figure 3 shows the enlarged region 18 according to Figure 2 with the edge of the laminated stack 12. The thin layer of operating insulation 16 having an oblique end at the upper edge of the slot wall of the slots 13 on the laminated stack 12 is clearly visible.

Figure 4 shows, in a partial lateral section, the rotor 10 with a coil winding 17, a commutator 19 and a rolling bearing 22. The rotor shaft 11, the laminated stack 12, the slots 13 for accommodating the coil winding 17, the protective insulation 14 and the plastic covers 15 can be seen.

Figure 5 shows a slot 13 of the rotor 10 according to Figure 4 with the coil winding 17 and the slot closure 20 made of insulating cardboard, which prevents a displacement of the coil winding 17 in the slots 13 and the penetration of dust, dirt and moisture into the slots 13 between the layers of the winding 17.

Claims

1. Hand-operated machine tool having a commutator motor which can be operated by mains voltage, in particular alternating current, and has a rotor (10), which comprises a laminated stack (12), in particular made of laminations, with slots (13) for a coil winding (17), comprises a rotor shaft (11) and is provided with longitudinal and transverse protective insulation (14) between the rotor shaft (11) and the laminated stack (12) and with operating insulation (15), in particular in the slots (13), which operating insulation at least partially surrounds, in particular, the coil winding (17) of the rotor (10), characterized in that a coating of the rotor (10), in particular of the laminated stack (12) and of the rotor shaft (11), which coating consists of a single material, which can in particular be injected on, is jointly used as the protective and operating insulation.

2. Hand-operated machine tool according to Claim 1, characterized in that a thermoplastic, in particular glass-fibre-reinforced polyoxymethylene or polyacetal, is used as the material.

3. Hand-operated machine tool according to Claim 1, characterized in that the material is a thermosetting plastic.

4. Hand-operated machine tool according to Claim 1, 2 or 3, characterized in that the layer thicknesses of the material on the rotor (10) are between 0.1 mm and 3 mm, and in that the transitions between the thin and the thick layers are continuous, in particular stepless.

5. Hand-operated machine tool according to one of Claims 1 to 4, characterized in that the operating insulation (15) arranged in the slots (13) is at least 0.1 mm thick, and in that the protective insulation is at least 1.5 mm thick.

6. Hand-operated machine tool according to one of the preceding claims, characterized in that the rotor has a weight of at least 300 g and a diameter of at least 20 mm and is intended for a rotational speed of at least 10,000 rpm.

7. Motor for a hand-operated machine tool according to the preamble of Claim 1, characterized in that a coating of the rotor (10), in particular between the laminated stack (12) and the rotor shaft (11), which coating consists of a single material, which can be injected on, is used jointly as the protective and operating insulation.

8. Rotor for the motor of a hand-operated machine tool according to the preamble of Claim 1, characterized in that a coating of the rotor (10), in particular between the laminated stack (12) and the rotor shaft (11), which coating consists of a single material, which can be injected on, is used jointly as the protective and operating insulation.

9. Rotor according to Claim 8, characterized in that the laminated stack (12) is free of insulating material over its periphery, in particular is bare metal.

10. A hand-operated machine tool substantially as herein described with reference to the accompanying drawings.