Fan and method for operating a fan

Abstract

The invention relates to a fan, particularly a radial fan, having a fan hub with a rotational axis. A plurality of fan blades is disposed about the rotational axis for deflecting an air flow. The invention provides that an adjustment device is provided at the fan blades for the rotational speed-dependant adjustment of an air flow.

Description

PRIOR ART[0001]The invention is based on a fan and a method for operating a fan as generically defined by the preambles to the independent claims.[0002]It is generally known in electric power tools to use fans, especially radial and semiaxial fans. Because of sometimes excessive idling rpm because of an overly low fan moment in idling, interfering vibration of the electric power tool can occur or be increased, which among other things reduces the brush service life of the electric motor and contributes to increased material fatigue.[0003]The fan in an electric power tool performs the task first of cooling the thermally stressed components in the electric power tool, and second, of regulating the idling rpm of the motor by means of a suitable idling moment. In a universal motor, for instance, by means of a fan disposed on the armature shaft, the universal motor is protected against uncontrolled revving during idling. A low load moment is also created by supporting the armature shaft ...

AI Technical Summary

Benefits of technology

[0008]As a result, different goals can be attained. On the one hand, as a first alternative, with increasing rpm of the fan drive, it is possible by a suitable adjustment of the air flow to increase the moment of the fan to beyond the normal rpm-dependent moment characteristic resulting when adjustment is not done. On the other hand, as a second alternative, with decreasing rpm of the fan drive, it is possible by a suitable adjustment of the air flow to improve the flowthrough behavior of the fan and as a result, at low rpm, or in other words as a rule under heavy load, an increased ratio—compared to a normal rpm-dependent flowthrough characteristic without adjustment—can be established between the volume flow and the rpm. The concrete embodiment of the adjusting device may differ for the first and the second alternatives.

[0013]It is also advantageous that the adjustment of the air flow, in the first alternative, can be done such that at high rpm an adequate load moment, which with an unvaried air flow would be less, acts on the motor shaft. In the second alternative, at lower rotary speeds, an increased ratio between the volume flow in the rpm can be established, for optimal cooling performance. Favorably, it can be possible to make the reduction in the volume flow less dependent on the rpm reduction of the electric motor.

[0014]Given a suitable adjustment in the first alternative, the result together with the centrifugal force and the fluid force, that is, the force that is exerted by the air flow, and given a suitable embodiment of the fan blades, leads to a suitable deformation of the fan blades and to an increase in the flow direction, to an increase in the fan moment, and to a reduction in the idling rpm. Because of the lesser blade deformation at the operating point (that is, at a lesser rpm), there are a lesser flow deflection and a lower fan torque, and thus better overall efficiency of an electric power tool in which the fan is disposed.

[0018]Because of the lesser blade deformation at the operating point (that is, at a lesser rpm), there are a lesser flow deflection and a lower fan moment, and thus better efficiency of an electric power tool or electrical appliance in which the fan is disposed. As a result of the utilization of the fluid and centrifugal forces, which are always present, additional fittings, such as an active mechanical adjusting mechanism in the electric power tool or electrical appliance, can be dispensed with.

[0019]In the preferred passive variable-rpm blade deformation in preferred radial fans, for regulating the operating performance of electric power tools, an adaptation of the fan characteristic of the radial fan can advantageously be achieved by means of passive blade deformation, utilizing the incident fluid and centrifugal forces for optimizing the operating performance of electric power tools. In a favorable way, in the first alternative, the idling rpm can be reduced, and as a consequence, component vibration can be lessened. This also increases the brush service life in the AC range and postpones fatigue in the material. Noise emissions from the preferred electric power tool can be reduced as well.

[0021]The fan blades can additionally be adjustable, or can also be embodied rigidly. These movable elements, preferably flaps, can change their position as a function of the centrifugal force of the fan. The flaps may be an integral component of the fan, or separate components that are disposed on the fan. Thus at low rpm, the embodiment can be such that an optimal air flow guidance takes place, with a corresponding high air flow. At higher rotary speeds, by greater deformation or adjustment of the flaps and correspondingly adequate blocking of the cross section and / or a favorable deflection of the flow, a lesser air flow can be delivered.

Problems solved by technology

Because of sometimes excessive idling rpm because of an overly low fan moment in idling, interfering vibration of the electric power tool can occur or be increased, which among other things reduces the brush service life of the electric motor and contributes to increased material fatigue.

At the same time, noise emissions and the vibration load on the component structure both increase because of the high rpm.

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