Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1992-07-15
1994-05-24
Stephan, Steven L.
Electrical generator or motor structure
Dynamoelectric
Rotary
310 58, H02K 714, H02K 906
Patent
active
053151933
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a hand-guided electric machine tool with a radial blower.
More particularly, it relates to such a tool which has a motor for driving a tool, and a radial blower with a fan wheel forming a static pressure differential and having an air guide inside the casing.
Hand machine tools, such as drills, angle grinders or hand circular saws comprising radial blowers for cooling the motor, are already known. The air guide ducts in such machines, as for example in the percussion drill according to DE-OS 35 03 172, are disposed more or less in a circular ring around the fan wheel and serve solely to collect the air and discharge it in concentrated form. The air then passes out through cooling air slots provided in the casing. Not least because of the restricted space in hand machine tools, the ducts are not shaped to promote flow, and in particular, depending on the type of fan used, the sometimes very high dynamic pressure fraction is not exploited. In addition, because of the high speed of the outgoing air, this often becomes a nuisance to the operator.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a hand-guided electric machine tool of the above mentioned type, which avoids the disadvantages of the prior art.
In keeping with the above mentioned objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a hand-guidable electric machine tool of the above mentioned type in which the air guide duct continuously widens in cross-section in the direction of its outlet opening, and the cross-section of the inlet opening of the air guide duct as measured in the radial direction is smaller than the cross-section of the outlet opening.
When the hand-guidable electric machine tool is designed in accordance with the present invention, it has in contrast the advantage that the air volume flow delivered by the radial blower is considerably increased and the noise produced is reduced. This is achieved through the fact that the fan wheel-generated dynamic pressure of the air flow delivered is converted in a widening air guide duct into static pressure, that is to say pressure delivering air. The improved air delivery of the radial blower according to the invention may be utilized either to reduce the size of the cooling cross-sections or that of the motor, or else to increase the power output of the motor. With a smaller increase in the amount of cooling air, the noise produced can be reduced to a greater extent.
In view of the restricted space in hand machine tools, it is particularly advantageous for the air guide duct to widen also, or exclusively, axially in the direction of flow, because the diameter of the motor casing is not thereby increased. The arrangement of a plurality of duct portions over the periphery of the fan wheel also permits adaptation of the air guidance, which increases the delivery volume, to restricted space conditions. It is moreover advantageous for the increase in volume flow already achieved to be further augmented by the provision of a diffuser-like mouth downstream of the air guide duct, thereby at the same time reducing the noise produced.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows a machine tool partly in section, FIG. 2 shows a plan view of the air guide casing viewed from the fan wheel, and FIG. 3 shows a view in perspective of the air guide duct. FIG. 4 shows a longitudinal section and FIG. 5 shows a section on the line V--V in FIG. 4 of a second exemplary embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
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Kummer Martin
Prahst Eberhard
Rieker Werner
Strotgen Eckerhard
LaBalle C.
Robert & Bosch GmbH
Stephan Steven L.
Striker Michael J.
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