DE102010063148A1 - Method and device for operating an electric motor driven electric hand tool - Google Patents

Abstract

The invention is based on a method for operating an electric motor driven electric hand tool (10) with an overload protection for protecting at least one component (12, 30) of the electric hand tool (10) against thermal overload.
It is proposed that, during operation of the electric hand tool (10), a current thermal energy content of the component (12, 30) is determined from a current energy inflow (E_i) and a current energy outflow (E_o) and compared with a thermal model of the at least one component (12, FIG. 30), wherein the electric hand tool (10) is switched off on reaching and / or exceeding a critical value (T_krit) of the energy content and wherein at least in a region near the critical value (T_krit) the energy flow (E_i) and / or the energy outflow (E_o) is controlled or controlled as a function of at least one operating parameter which influences the thermal energy content of the at least one component (12, 30).

Description

State of the art

The invention is based on a method for operating an electric motor driven electric hand tool with an overload protection for protecting at least one component of the electric hand tool and of a device for carrying out the method according to the preambles of the independent claims.

In power tools, blocking the motor, such as tightening a screw or jamming the saw blade, will overload the motor until it overheats and becomes permanently damaged. In extreme cases, it may lead to smoke and burning of combustible parts of the engine. This can also be the case of improper use of tools such. B. the use of a screwdriver as a mixer.

In the DE 10 2005 038 225 A1 For example, a method for detecting an overload situation in an electric hand tool is described. In such electric hand tools, especially battery-powered electric hand tools such. B. cordless screwdriver or cordless hammer hammers there is a risk that blocked in case of overloading the engine, in which situation the highest possible currents flow, which can be discharged from the battery pack in battery-powered electric hand tools. The high currents have an overheating result, at the same time shut down due to the stationary motor cooling, so that in the case of persistence of this condition within a very short time the risk of thermal failure of one or more involved components such. B. connecting lines, the electric motor, solder joints or the like. The risk of thermal overheating also exists in the event that the electric motor without sufficient cooling phases several times successively occupies the blocked state.

In order to recognize an overload situation in good time and to avoid a thermal failure, according to the DE 10 2005 038 225 AI continuously measured the operating current and compared with a stored limit current, wherein a thermal overload of the power tool is closed, if the accumulated from several cycles and weighted difference of the measured operating current and the stored current limit value exceeds a reference value. Thereafter, the circuit which supplies power to the electric motor is interrupted by a signal from a monitoring device. The electric motor is disabled, overheating is effectively avoided.

The WO 20009/086990 A1 Proposes that in a hand tool with an electric motor, such as cordless screwdrivers, cordless drills, cordless circular saws, cordless saws, cordless planers, cordless rotary hammers or cordless percussion drills or electric hand tools that are connected directly to the mains Temperature or to measure a correlating with the temperature of a component of the electric hand tool current of the electric motor during operation, which is closed in the case of exceeding a reference variable to a thermally increased load. Then, a reduced transient mode is activated, in which the current flow in the circuit supplying the electric motor is modulated, so that the further temperature increase is stopped or at least decelerated. As a result, a measure is taken even before reaching a thermal limit, in which an overload with concomitant destruction of components, which has the consequence that the further increase in temperature is at least attenuated.

Disclosure of the invention

The invention is based on a first aspect of a method for operating an electric motor driven electric hand tool with an overload protection for protecting at least one component of the electric hand tool against thermal overload.

It is proposed that a current thermal energy content of the component is determined during operation of the electric hand tool from a current energy flow and a current energy drain and the electric hand tool is operated at least in an operating range depending on the thermal energy content.

The component may in particular be an electric motor. Alternatively or additionally, the component may also be an electronic component, in particular a power electronics component, of the electric motor. The electric hand tool can be operated by battery or battery or be provided with a mains power supply.

In particular, the energy inflow and the current energy outflow can be derived from a thermal model of the component. From this, a permissible maximum energy content of the component can be determined. The maximum permissible energy content of the component corresponds, for example, to its maximum permissible temperature.

If the component is an electric motor, then in a simple thermal model of the energy input z. B. can be considered as an electrically introduced power to the ohmic resistance of the electric motor, which can then be determined in a simple manner by observing the respective current motor current. For the energy discharge z. B. a certain proportion can be assumed, which can be varied depending on the currently determined temperature and / or engine speed. This can then be concluded that the current thermal energy content of the electric motor. Of course, a more complex model can also be used, or for another component another suitable model of the component, which considers entry mechanisms and discharge mechanisms for heat relative to the component, in particular at its installation location in the electric hand tool.

Thus, in contrast to the prior art, a short current peak, which exceeds the maximum value of the permissible motor current, does not automatically switch off the electric hand tool, but the energy flow into the component is considered by this current peak. Energy is the product of performance and time. If the energy flow into the component is below a permissible limit value of the thermal energy content of the component, the electric hand tool can continue to be operated since the short-term increase in current does not lead to overheating of the component or electric motor.

It can be easily assumed that the component can withstand a certain energy input without damage. In its specified range, the electric hand tool is durable, so that the critical energy input is never reached, provided that the electric hand tool is operated according to its specifications. For example, the electric hand tool can be specified so that it is not thermally overloaded with a battery charge. If the first battery pack is emptied during operation and a new battery pack is used to continue working immediately with the electric hand tool, the thermal load of the component is higher than specified. Accordingly, the electric hand tool for the use of several battery packs can be designed one behind the other, without resulting in the consequent continuous load of the electric hand tool thermal overload, d. H. exceeding the limit of the permissible thermal energy content of the component, occurs.

The current thermal state of the component, such as the electric motor, can be reliably determined. A corresponding thermal model can be known, for example, from the design phase of the electric hand tool. The design of the electric hand tool is carried out for a maximum allowable thermal load corresponding to a maximum allowable thermal energy content, contribute to the various operating parameters, so that their influence on the thermal energy content of the electric motor (or according to another temperature-critical component) can be easily derived.

The component can be reliably protected against damage or destruction without adversely affecting the performance of the electric hand tool. Electrical damage to the electric hand tool due to carelessness of the user can be avoided. At the same time, safe operation of the electric hand tool is also close to the critical energy content, i. H. the limit, possible.

The electric hand tool can be switched off when reaching and / or exceeding a limit value of the energy content. Alternatively or additionally, in the electric hand tool at least in a region close to the limit, the energy supply and / or the energy discharge can be regulated or controlled. Thus, one or more operating parameters can be monitored, which influences the thermal energy content of the at least one component. The term "controlled" may also include shutting off the power hand tool.

According to a favorable development, at least one operating parameter can be used to determine the energy inflow and / or the energy outflow. Expediently, these can be operating parameters which can be derived or are known, for example, from monitoring electronics of a battery management system, as are used in battery-operated electric hand tools.

According to a further embodiment, the at least one operating parameter may include one or more of the following variables: motor current; Duty cycle of a pulse width modulation for controlling the electric motor; Engine speed of the electric motor; Position of a setpoint generator for switching on or off the electric motor; electrical voltage of a battery or a battery for supplying the component; Temperature of the component; Cooling power for cooling the component. The thermal state of the component, such as the electric motor, can be detected more accurately and faster.

The speed of the electric motor can be measured, for example, or derived in a known manner from the duty cycle of the pulse width modulation. Furthermore, the position of the setpoint generator for switching on or off the Show electric motor, whether the electric motor is turned on or off, from which can be derived, for example, whether the component or the electric motor is still actively cooled by an air flow generated by the rotation of the electric motor and / or by a fan of the electric motor, or whether a passive cooling by heat conduction and / or convection takes place.

According to a further development, the motor current can be used with at least one further operating parameter for determining the energy content of the component. The influence of the at least one further operating parameter on the thermal energy content of the component may have previously been determined from the thermal model of the component. Conveniently, by taking into account such influencing parameters in addition to the motor current, the performance and performance of the electric hand tool can be improved. The thermal condition of the component and the electric motor can be detected more accurately and faster. Power reserves of the component, in particular of the electric motor, which otherwise have to be maintained because of the only rough approximation to the thermal overload range, can be used for work purposes. It can advantageously be a holistic view of the dynamic energy balance on the component, for. B. on the electric motor done. In this context, the energy balance is to be understood as comprehensive as possible a holistic consideration of as many influencing parameters as possible on the thermal behavior of the electric motor. Dynamic means the active accumulation and subtraction of the amount of energy as a function of the operating parameters used over time.

In this case, even the addition of a further operating parameter, which influences the thermal state or energy content of the component, represents an improvement and an increase in the performance of the electric hand tool.

Advantageously, the electric motor can be switched off in case of overload, which leads to a decrease in temperature of the component, or it can be a reduced transition operation are activated, in which the current flow in the circuit that supplies the electric motor is modulated, so that prevents further increase in temperature of the component or at least reduced.

Furthermore, a cooling time of the component can be taken into account for determining the current thermal energy content. Here can be taken into account in particular whether an active cooling takes place, for example, in which the electric motor is idling, or a passive cooling, in which the electric hand tool is turned off and the cooling takes place mainly by convection, for example. The distinction between the two states can also be made indirectly via the position of the setpoint generator and the presence of the no-load current.

In a favorable development, when the electric motor is switched on again, at least one current temperature of the component can be determined and used to generate a starting value for determining the current thermal energy content of the component.

If the electric hand tool completely switched off, usually its monitoring electronics to prevent self-discharge of the battery or the battery turns off after a relatively short period of time, so that the time in which a passive cooling of the component is difficult to detect. It is favorable if the temperature of the component can be detected. For example, a thermocouple can be attached to the electric motor for this purpose. When re-commissioning so a start value for the current thermal load of the component can be generated by the current temperature of the electric motor is determined. The temperature of the component can be measured and / or (if the duration of the shutdown can be determined) derived from a cooling behavior of the component.

If a shutdown period of the component can be determined, a history of the operation of the electric hand tool can be taken into account in order to better determine the current thermal state or energy content of the component. Additional electronic components or memory can be provided, with which a certain time profile can be stored as a history of operating parameters of the electric hand tool, in order thus to generate a starting value for the determination of the current thermal energy content of the component. In principle, this can be compared with a delayed reset of the monitoring electronics of the electric hand tool, after a critical period for cooling the component has expired, from which the full loadable energy of the component is available again. In the prior art, the monitoring electronics is reset as soon as the electric hand tool is switched off and / or the battery pack is removed, for example, replaced.

This is particularly advantageous for the time of the battery change or battery change, as usually the electric hand tool is immediately put into operation again. If no thermocouple is provided, an electrical buffer may be provided which bridges this short changeover time, such as a capacitor, a button cell, to an unwanted Resetting the monitoring electronics to prevent battery replacement or battery replacement. Thus, the motor protection is also available after the change with the current operating parameters for the thermal condition of the component.

Furthermore, an apparatus for carrying out the method is proposed in which means are provided for determining a current thermal energy content of the component during operation of the electric hand tool from a current energy flow and a current energy outflow and at least in one operating range depending on the thermal energy content operate.

Conveniently, an electrical buffer may be provided to electrically supply a monitoring electronics of the component when disconnecting a power supply from the electric hand tool. Thus, when restarting the electric hand tool, the duration of the shutdown is known, so that from a thermal model of the component, for example, determines the cooling behavior of the component and the temperature can be determined when restarting.

drawing

Further advantages emerge from the following description of the drawing. In the drawing, an embodiment of the invention is shown. The drawing, the description and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them into meaningful further combinations.

It shows:

1 a symbolically illustrated embodiment of an electric hand tool with a monitoring device for detecting a thermal overload situation and for transferring into a transition operation of reduced electrical power or for shutdown, and

2 a visualization of the hand tool 1 with its thermal energy content.

Embodiment of the invention

In the figures, the same or similar components are numbered with the same reference numerals.

This in 1 schematically illustrated embodiment of an electric hand tool 10 has as drive an electric motor 12 on, for example, from a battery pack 14 is fed. In the circuit between battery pack 14 and electric motor 12 is an operating element as a setpoint generator 16 which allows the user to open and close the circuit. The setpoint generator 16 For example, a conventional on-off switch with built-in potentiometer can be used to set a desired engine speed. Furthermore, in the circuit are a device 18 arranged for switching and / or modulating the motor current. The device 18 contains a current measuring device 20 and Z. B. a power electronics of the electric motor 12 , When the circuit is closed, a motor current I_m flows.

The device 18 is from a monitoring electronics 22 controlled, which optionally a temperature measuring device 26 for measuring the temperature of at least one temperature-critical component 12 . 30 in the electric hand tool 10 can be assigned. The temperature-critical component can be the electric motor 12 itself or, for example, its power electronics 30 be. In the following, as a temperature-critical component, for example, only the electric motor 12 However, the considerations can be transferred to other components.

The monitoring electronics 22 also includes a control unit 28 , in which the signal processing and signal generation takes place and, incidentally, also operating parameters of the electric hand tool 10 can be determined or stored. During regular operation of the electric hand tool 10 the circuit is closed, the electric motor 12 is fed with the operating current I_m. In regular operation, the flow meter will continue to run 20 the current operating current I_m and other operating parameters detected, such as the duty cycle of the PWM signal.

With cordless tools, such monitoring electronics are already required to comply with battery management 22 built-in. Therefore, certain signals on operating parameters are already available, such as motor current, speed, duty cycle of the PWM signal, that of the electric motor 12 is fed, switch position of the setpoint generator 16 , Battery voltage and the like. These operating parameters can therefore be used without additional hardware overhead.

Based on the existing operating parameters can be reliably derived, in which operating state that is the electric hand tool 10 in particular, whether the electric motor 12 idling is whether that of the electric motor 12 driven tool (not shown) is engaged with a workpiece, whether the tool is blocked. Furthermore, it can be deduced how the current operating mode on the thermal state of the electric motor 12 and thus affects its temperature, so that its current thermal state can be detected with good approximation.

The monitoring electronics 22 recorded during operation of the electric hand tool 10 a current energy inflow E_i and a current energy outflow E_o ( 2 ) and determines a current thermal energy content of the electric motor 12 , This comes with a critical thermal energy content (limit) of the electric motor 12 that in a memory of the surveillance electronics 22 filed, compared. This can be the electric hand tool 10 upon reaching and / or exceeding a critical value T_crit ( 2 ) of the energy content are turned off. At least in an area close to the critical value T_krit, the energy supply E_i and / or the energy drain E_o can be regulated or controlled, wherein at least one operating parameter which determines the thermal energy content of the electric motor 12 influenced, is influenced accordingly.

When switching on the electric hand tool 10 generates the monitoring electronics 22 (eg in unit 28 ) a starting value, such as the current temperature of the electric motor 12 and thus a size that reflects its current thermal energy content.

Based on the actual, actual thermal energy content, energy can be supplied to the electric motor 12 and / or energy drain from the electric motor 12 be dynamically adjusted. So can for the respective application, for which the user his electric hand tool 10 used, a maximum power from the electric motor 12 be retrieved. The actual thermal state of the electric motor 12 can be estimated much better than in the prior art.

Optionally, it may be provided to perform a first shutdown after a certain thermal energy content or after a defined period of time. Thus, after switching off the blocking of the tool or during operation at the power limit or other borderline applications, a certain reserve of energy reserves is kept available. Such a boundary application provides, for example, an application with a high torque requirement at low speed, ie with high motor current and low ventilation by the correspondingly slowly rotating fan wheel of the electric motor 12 Thus, even after such a shutdown several times a re-commissioning is possible again, without thereby immediately the critical value T_krit ( 2 ) of the energy content. Ie. an example blocked tool of the electric hand tool 10 , such as a screwing tool or a saw blade or the like, can also several times in succession with full torque, that is to be charged with full motor current, without being damaged.

If the monitoring electronics 22 is switched off, usually when not operating the electric hand tool 10 or when changing the battery pack, the stored in the memory current energy content of the electric motor goes 12 lost.

Also in this case, the above-mentioned lead can contribute to damage to the electric hand tool 10 to avoid multiple times in succession deletion of the memory.

In a further variant, in addition, a temperature sensor 26 , z. As an NTC resistor or the like, be provided to turn on the monitoring electronics 22 generate a starting value of the current temperature to a reference for the current thermal energy content of the electric motor 12 to have. The temperature sensor 26 thus serves as a "memory" and can simultaneously the energy flow during the cooling time of the electric motor 12 describe. This can also favorably a distinction between active and passive cooling of the electric motor 12 omitted. Active cooling means that the electric motor 12 and / or a motor fan is running and generates a cooling air flow. Passive cooling means that the electric motor 12 cooled only by convection and heat conduction. For a dynamic control is the detection of the current temperature of the electric motor 12 with the temperature sensor 26 However, too sluggish, since this can usually only be mounted away from critical areas, such as the housing of the electric motor 12 ,

Optionally, a non-volatile read and write memory may be provided with an internal clock, for example in the monitoring electronics 22 so that common monitoring electronics can be used with little change. Advantageously, the non-volatile memory can be supplied with the clock module via an electrical buffer when the battery pack or battery pack is replaced, such as a battery button cell, a capacitor or the like.

It is also conceivable a "non-dormant" electronics, even in the dormant state of the electric hand tool 10 is supplied electrically, for example via the battery 14 or via a charging station where the electric hand tool 10 can be practically permanently connected in the idle state.

Additionally or alternatively, other sensors can be used, which detect parameters such as speed sensors and the like.

2 shows a simplified representation of the thermal state of the component, such as the electric motor 12 , The component experiences an energy supply E_i and an energy discharge E_o and can absorb energy up to a critical energy input (reaching or exceeding a critical energy content (limit value) corresponding to a maximum temperature T_crit) without being damaged. In the example shown, the current energy content is represented by a dashed area, which is far below the threshold value.

It can be easily assumed that the electric motor 12 a certain energy input (E_i) can survive unscathed. In the specified area of the target application is the electric hand tool 10 durable, so that the critical energy input (T_krit) is never reached. The specified range corresponds for example to the use of a trained as a screwdriver electric hand tool 10 for a specific bolt class.

Will the electric hand tool 10 operated in borderline applications (for example, more battery packs are used in sequence, as the specification of the electric hand tool 10 corresponds to, for example, the work with the electric hand tool 10 do not have to interrupt long), so the introduced energy increases in the component 12 , the electric motor, depending on various operating parameters, such. B. Motor current and speed (ie also fan power). However, working with the electric hand tool 10 interrupted or the electric hand tool 10 only operated at idle, the electric motor cools 12 Over time, ie energy is released (E_o). Up to the shutdown limit T_krit can therefore now be an increased energy input, ie the electric hand tool 10 can be operated longer in a range near and below the cut-off limit T_krit.

However, if the shutdown limit T_krit is reached, the electric motor switches 12 protects against overheating. Depending on the underlying model, it is also conceivable to allow an immediate further processing, but only if the resulting energy input is negative, ie in this further work the electric motor 12 cools; at a renewed increased energy input E_i, such as blocking the electric motor 12 powered tool, the electric hand tool switches 10 again very fast.

This initially creates no waiting for the user to cool the electric hand tool 10 , which favorably the impression can be avoided, the electric hand tool 10 be defective or would suspend.

For this purpose, the energy supply E_i and the energy drain E_o can be controlled in particular in the range A_lim near the switch-off limit T_crit. On further cooling, d. H. As the distance to the switch-off threshold T_crit increases, one arrives from the area A_lim in the area A_norm. In the A_norm area, you can work uncontrolled or if required under control.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102005038225 A1 [0003, 0004]
• WO 20009/086990 A1 [0005]

Claims (11)

Method for operating an electric motor driven electric hand tool ( 10 ) with an overload protection for protecting at least one component ( 12 . 30 ) of the electric hand tool ( 10 ) against thermal overload, characterized in that during operation of the electric hand tool ( 10 ) from a current energy inflow (E_i) and a current energy outflow (E_o) a current thermal energy content of the component ( 12 . 30 ) and the electric hand tool ( 10 ) is operated at least in an operating range depending on the thermal energy content. Method according to claim 1, characterized in that the electric hand tool ( 10 ) is switched off when reaching and / or exceeding a critical value (T_krit) of the thermal energy content. A method according to claim 1 or 2, characterized in that at least in an area (A_lim) near the critical value (T_krit) the energy flow (E_i) and / or the energy drain (E_o) is controlled or controlled. Method according to one of the preceding claims, characterized in that at least one operating parameter for determining the current energy flow (E_i) and / or the current energy flow (E_o) is used, wherein the at least one operating parameter is one of the following variables: - Motor current (I_m) ; - Duty cycle of a pulse width modulation for controlling the electric motor ( 12 ); - engine speed of the electric motor ( 12 ); - Position of a setpoint generator ( 16 ) for switching the component on or off ( 12 . 30 ); - electrical voltage of a battery or a battery for supplying the component ( 12 . 30 ); - temperature of the component ( 12 . 30 ); - cooling capacity for cooling the component ( 12 . 30 ). A method according to claim 4, characterized in that the motor current (I_m) with at least one further operating parameter for determining the energy content of the component ( 12 . 30 ) is used. Method according to one of the preceding claims, characterized in that for determining the energy content, a cooling time of the component ( 12 . 30 ) is taken into account. Method according to one of the preceding claims, characterized in that when the electric motor ( 12 ) at least one actual temperature of the component ( 12 . 30 ) and for generating a starting value for determining the current thermal energy content of the component ( 12 . 30 ) is used. Method according to claim 7, characterized in that the temperature of the component ( 12 . 30 ) and / or from a cooling behavior of the component ( 12 . 30 ) is derived. Method according to claim 7 or 8, characterized in that a switch-off duration of the component ( 12 . 30 ) is determined. Device for carrying out a method according to one of the preceding claims, characterized in that means ( 18 . 22 ) are provided to in the operation of the electric hand tool ( 10 ) from a current energy supply (E_i) and a current energy discharge (E_o) a current thermal energy content of the component ( 12 . 30 ) and the electric hand tool ( 10 ) operate at least in an operating range depending on the thermal energy content. Device according to claim 10, characterized in that an electrical buffer is provided in order to disconnect (a) 14 ) from the electric hand tool ( 10 ) a monitoring electronics ( 22 ) of the component ( 12 . 30 ) to supply electrically.

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