Electromechanical gear selection device comprising a stepping motor

A method for selecting a gear in the transmission of a power tool having an electric motor. The method includes the following steps of changing an operating device from a first position to a second position in order to select a gear in the transmission; detecting a signal via at least one sensor corresponding to the second position of the operating device; sending the signal to a controller; changing the rotational speed of the electric motor from a first value to a second value via the controller; changing the operating device from the second position to a third position; changing the stepping motor from a first position to a second position corresponding to the third position of the operating device; and changing a shift fork from a first position to a second position in order to change from a first gear to a second gear.

The present invention relates to a method for selecting a gear in the transmission of a power tool, particularly a core drilling machine, whereby the power tool has an electric motor for generating and transmitting a torque to the transmission as well as a controller for setting the rotational speed of the electric motor, and the transmission has an operating device for selecting a gear in the transmission, a shift fork for engaging a gear in the transmission as well as a stepping motor for transmitting a movement of the operating device to the shift fork, whereby the operating device has at least one signal transmitter as well as at least one sensor for receiving at least one signal from the at least one signal transmitter.

The invention also relates to a power tool for carrying out the method according to the invention. Moreover, the invention relates to a transmission for a power tool, especially a core drilling machine, for carrying out the method according to the invention.

BACKGROUND

A precise coordination of the rotational speed of the power tool with the tool bit being employed is particularly important when it comes to power tools, especially power tools with a rotating tool bit.

In this context, especially the size, the volume and the weight of the tool bit being employed constitute important factors. If the tool bit is too large and the rotational speed is too low, the progress of the work is too slow and inefficient, thereby slowing down the work process altogether. In contrast, if the rotational speed is too high, the power tool or the tool bit can become damaged.

When it comes to core drilling machines, a precise coordination or adaptation of the rotational speed of the tool bit, that is to say, of the core bit, to the size of the core bit or to the diameter of the core bit is of great importance.

Core drilling machines make use of cylindrical core bits that can cut into mineral materials, for example, concrete or masonry, using a diamond-tipped cutting edge. In order for the rotational speed and the torque of the core bit to be varied for various applications, core drilling machines normally also have a transmission comprising at least two gears. Thanks to the different gears, the rotational speed as well as the torque of the core bit can be set. Maintaining the most constant possible circumferential speed of the core bit during the core drilling procedure is very important for a proper and efficient core drilling process and especially in order to ensure that the core bit and the core drilling machine are used in a manner that is gentle on the material. For this purpose, however, it is often necessary to undertake a relatively fine coordination of the device to the diameter of the core bit that is being used. The correct coordination of the rotational speed, the torque and the correct gear to the diameter of the core bit being used often poses major problems for the user of the core drilling machine if the consistency (e.g. the degree of hardness) of the material to be worked is constantly changing. This can render the core drilling procedure either inefficient and slow or else it can cause damage to the core bit.

When it comes to the commercially available core drilling machines or the core drilling machines according to the state of the art, however, such a fine coordination between the size (diameter), the rotational speed, the torque of the core bit or the gear selected for the core drilling machine is either not an option at all or else it is very complicated for the user of the core drilling machine.

SUMMARY OF THE INVENTION

Before this backdrop, one objective of the present invention is to solve the above-mentioned problem.

The present invention provides a method for selecting a gear in the transmission of a power tool, particularly a core drilling machine, whereby the power tool has an electric motor for generating and transmitting a torque to the transmission as well as a controller for setting the rotational speed of the electric motor, and the transmission has an operating device for selecting a gear in the transmission, a shift fork for engaging a gear in the transmission as well as a stepping motor for transmitting a movement of the operating device to the shift fork, whereby the operating device has at least one signal transmitter as well as at least one sensor for receiving at least one signal from the at least one signal transmitter.

The present invention also provides a power tool for carrying out the method according to the invention as well as a transmission for a power tool, especially a core drilling machine, for carrying out the method according to the invention.

According to the invention, it is provided that the method comprises the following steps:changing the operating device from a first position to a second position in order to select a gear in the transmission;detecting a signal by means of at least one sensor corresponding to the second position of the operating device;sending the signal to the controller;changing the rotational speed of the electric motor from a first value to a second value by means of the controller;changing the operating device from the second position to a third position;changing the stepping motor from a first position to a second position corresponding the third position of the operating device; andchanging the shift fork from a first position to a second position in order to change from a first gear to a second gear.

Furthermore, the present invention provides a power tool for carrying out the method according to the invention, whereby the power tool has a transmission, an electric motor for generating and transmitting a torque to the transmission, a controller for setting the rotational speed of the electric motor, an operating device for selecting a gear in the transmission, a shift fork for engaging a gear in the transmission and a stepping motor for transmitting a movement of the operating device to the shift fork for engaging a gear in the transmission, whereby the operating device has at least one signal transmitter as well as at least one sensor for receiving at least one signal from the at least one signal transmitter.

According to another advantageous embodiment of the present invention, it is possible for the signal transmitter to be configured in the form of a magnet and for the sensor to be configured in the form of a Hall sensor. However, it is likewise possible to use any other suitable type of signal transmitter and sensor.

According to an advantageous embodiment of the present invention, it is also possible for the transmission to contain a shifting energy storage means, as a result of which a force can be applied onto the shift fork in order to pretension the shift fork to make a transition from a first position to a second position. In this context, the shifting energy storage means can be configured as a spring element. Consequently, a new gear can be preselected during a gear selection procedure so that the new gear is engaged as soon as the transmission is able to do so. This is particularly advantageous if the constellation of the gear wheels with respect to each other inside the transmission does not immediately allow a new gear to be engaged.

Moreover, the present invention also provides a transmission for a power tool, especially a core drilling machine, for carrying out the method according to the invention.

Additional advantages can be gleaned from the figure description below. The figures show several embodiments of the present invention. The figures, the description and the claims contain numerous features in combination. The person skilled in the art will advantageously also consider the features individually and merge them to form additional meaningful combinations.

DETAILED DESCRIPTION

FIG. 1shows an embodiment of a power tool1according to the invention, configured as a core drilling machine.

The power tool1configured as a core drilling machine essentially comprises a housing2, an electric motor3, a transmission4, a controller18, a driven shaft6, an operating device7and a tool bit socket8. As can be seen inFIG. 1, the electric motor3, the transmission4, the controller18and the driven shaft6are situated inside the housing2. The operating device7is situated on the housing2, so that it can be operated from the outside by a user. A power cable9that supplies the power tool1with electric power is indicated on the housing2.

The electric motor3serves to generate a torque that is transmitted to the tool bit socket8via the driven shaft6and the transmission4. The tool bit socket8serves to receive and hold a tool bit with which a material (e.g. concrete) can be worked. The tool bit in the case of the embodiment of the power tool1in the form of a core drilling machine can be a core bit. Neither the tool bit nor the material is shown in the figures.

The controller18serves, among other things, to set and monitor the rotational speed of the electric motor3. For this purpose, the controller18is connected to the operating device7, to the transmission4and to the electric motor3; seeFIG. 1.

The transmission4contains three gear wheels so that transmission ratio of the torque introduced by the electric motor3into the transmission4can be varied. Even though the transmission4shown in the figures only has three gear wheels10, it is possible to select more than three gears in the transmission4, as will be shown in detail below. However, it is also possible for the transmission4to have more than or fewer than three gear wheels10.

An embodiment of the transmission4according to the invention is shown inFIGS. 3 to 6. The transmission4is connected to the operating device7and it essentially comprises a housing11, part of the driven shaft6, a stepping motor12, the three gear wheels10as well as a shift fork13. The stepping motor12and part of the shift fork13are located in the housing. The stepping motor12can be configured as a shifting cylinder or as a Geneva drive.

The operating device7, in turn, serves to allow the user of the power tool1to select a gear in the transmission4or to set a rotational speed value for the electric motor3. Setting the rotational speed value by means of the operating device7by using the present method according to the invention does not bring about a mechanical gear change but rather an electronic one. In other words, setting or changing the rotational speed value by means of the operating device7appears as a mechanical gear change in which a change is made from one gear wheel constellation to another gear wheel constellation.

The operating device7also comprises a rotary switch14that can be rotated relative to a numerical display in the C or D rotational direction. On the basis of the numerical display, the user of the core drilling machine1can see which gear has been or can be engaged. The rotary switch14can also be referred to as a gear selection switch.

According to an alternative not shown in the figures, the operating device7can also be connected to an electronic display so that the gear that is currently engaged can be shown to the user on a screen (display).

The stepping motor12serves essentially to convert the rotational movement of the rotary switch14in the C or D rotational direction into a linear movement of the shift fork13in the A or B direction. For this reason, the stepping motor12is connected to the shift fork13. A special feature of the stepping motor12is the fact that not every rotational movement of the rotary switch14results in a corresponding rotational movement of the stepping motor12. In other words, only every other rotational movement carried out over certain sections or else only every other rotational movement along a sector causes a rotational movement of the stepping motor12. The shift fork13, in turn, serves to actually align the gear wheels10relative to each other inside the transmission4in order to set a given transmission ratio or gear wheel constellation.

Moreover, the operating device7comprises a signal transmitter15in the form of a magnet. As an alternative, the operating device7can also comprise more than one signal transmitter15in the form of several magnets. However, it is also possible for any other suitable type of signal transmitter15to be used. Thus, for instance, according to an alternative embodiment, a metal ring can also be provided as the signal transmitter15and so can an appropriate induction sensor that matches the metal ring.

The signal transmitter15is permanently positioned on the rotary switch14and it serves to emit signals corresponding to the location or rotational position of the rotary switch14of the operating device7.

Furthermore, the operating device7has several sensors16in the form of Hall sensors corresponding to the configuration of the signal transmitter15as a magnet. However, it is also possible to employ any other suitable type of sensor. The sensor16serves to receive the signal from the signal transmitter15. The arrows shown on the signal transmitter inFIG. 2depict magnetic fields.

As shown inFIG. 2, four sensors16are permanently positioned in a circle on the operating device7so as to detect the magnetic field of the signal transmitter15configured as a magnet on the rotary switch14. It should be noted that a sensor16is only provided on every other possible rotational position of the rotary switch14(seeFIGS. 8 and 9). If the rotary switch14is oriented towards one of these four rotational positions fitted with a sensor16, the sensor16can detect the signal transmitter15on the rotary switch14and can associate the position of the rotary switch14with one of the four rotational positions. However, it is also possible for sensors16to be positioned at more than or fewer than four rotational positions.

Each sensor16is connected to a control unit5via a line17in order to transmit the signals received from the signal transmitter15to the control unit5(seeFIGS. 2, 8 and 9). The control unit5, in turn, is connected to a controller18of the electric motor3(seeFIG. 1). As an alternative, the control unit5is also connected directly to the electric motor3. The connection serves to transmit an appropriate signal from the control unit5of the transmission4to the controller18of the electric motor3. The controller18can regulate the power supply to the electric motor3and can thus control the rotational speed value of the electric motor3. The rotational speed value is the target rotational speed value.

Since (as already elaborated upon above) the stepping motor12can convert a continuous rotational movement of the rotary switch14into an intermittent rotational movement, not every rotational movement of the rotary switch14causes an activation of the shift fork13and thus a mechanical gear change or a change in the gear wheel constellation.

If, as shown inFIG. 8, the rotary switch14is rotated in the C direction from a first position to a second position in order to move the operating device7from a first position to a second position for purposes of selecting a gear in the transmission4, the stepping motor12moves the shift fork13in the A direction so that the gear wheels10in the transmission4are moved to a different constellation. In other words, a higher gear is engaged by means of the stepping motor12and the shift fork13. In this process, no signal to change the rotational speed of the electric motor3is transmitted from the sensor16to the controller18via the control unit5. Here, the gear change takes place purely mechanically.

If, however, as shown inFIG. 9, the rotary switch14is rotated further in the C direction from the second position to a third position in order to change the operating device7from the second position to a third position for purposes of selecting a different gear in the transmission4, a signal from the signal transmitter15(that is to say, from the magnet) to the appropriate sensor16is detected. The sensor16sends a signal to the control unit5. The control unit5detects the rotational position of the rotary switch14and, in turn, sends an appropriate signal to the electric motor3via the controller18in order to set a target value for the rotational speed. In the present case, the target value for the rotational speed is raised. In this process, the shift fork13is not activated by the stepping motor12, and thus the gear is changed purely electronically. Therefore, due to the change in the target value for the rotational speed of the electric motor3, an additional spread can be attained for the transmission4without a mechanical gear change, that is to say, without a new gear wheel constellation.

According to an alternative embodiment, the transmission4can also contain a shifting energy storage means. The shifting energy storage means here can be configured as a spring mechanism or as a spring. The shifting energy storage means configured as a spring mechanism applies a force onto the shift fork13in order to pretension the shift fork13to make a transition from a first position to a second position. The shifting energy storage means is not shown in the figures.

If the shift fork13cannot make a linear movement, then the shifting energy storage means configured as a spring mechanism is activated and it stores the movement energy in a pretension or spring pretension so that a gear is preselected. In other words, the selected gear can only be actually engaged at the time of a re-start or when the rotational speed is low. As soon as the movement of the shift fork13has become possible, the gear preselected by the shifting energy storage means is engaged by means of the shift fork13and the shifting energy storage means once again assumes the initial position, that is to say, the non-tensioned position. The mechanism of the gear preselection is configured in such a way that it is possible to shift from the first to the highest selectable gear without bringing about an alignment inside the shifting mechanism.

REFERENCE NUMERALS