EP2457698A2 - Fastening device - Google Patents

Abstract

The tacker has a tank (5) for storing a fuel, particularly liquefied gas, a combustion chamber (2) connected with the tank and a metering device (4) arranged between the tank and the combustion chamber. The metering device has a thermo mechanical element, by which the defined quantity is changed as a function of temperature.

Description

The invention relates to a tacker, in particular a hand-held tacker, according to the preamble of claim 1.

DE 102 60 703 A1 describes a liquid gas driven driving tool having a metering chamber with an adjustable metering volume. The metering volume can be changed by an electromotive drive, and a discharge of liquid gas into a combustion chamber is initiated by a pneumatic drive by means of compressed air.

It is the object of the invention to provide a fuel-driven tacker that allows adjustment to varying operating conditions.

This object is achieved according to the invention for a drive-in device mentioned above with the characterizing features of claim 1. The temperature-dependent change in the amount of fuel introduced into the combustion chamber ensures in a simple manner a reliable ignition and a uniform function of the tacker, even if ambient temperatures or operating temperatures of the device change. Depending on the requirements, the relevant temperature may be, for example, the temperature in or within the combustion chamber, or the ambient temperature of the tacker.

It is thereby taken into account that, in particular when liquefied petroleum gas is used as the fuel, a phase transformation is required to produce an ignitable gas-air mixture, the kinetics of this process being significantly influenced by the prevailing temperatures. Generally it is known, for example, at low Ambient temperatures to increase the amount of liquid gas introduced into the combustion chamber to provide a sufficiently large amount of ignitable gas-air mixture in a sufficiently short time.

Under a thermo-mechanical element in the context of the invention is understood to mean any component that directly achieves a controlled mechanical effect by changing its temperature, without the thermo-mechanical element resorting to other energy sources such as electric batteries.

In a preferred embodiment, it is provided that the metering volume can be changed by the thermo-mechanical element. This results in a particularly simple and effective embodiment of the invention, which allows, for example, a simple dosing by measuring the fuel in the adjustable dosing as a buffer, for example by opening and closing connected to the variable dosing volume valves. In this case, the thermo-mechanical element can be provided, for example, as a body in the dosing volume or also act as an actuator which alters a limiting wall or membrane of the dosing volume.

In an alternative or supplementary embodiment of the invention, the metering device comprises a movable displacement member for expelling the defined amount of the fuel, wherein preferably a stop position of the displacement member via the thermo-mechanical element is variable. These embodiments generally have the advantage that a particularly fast transport of the fuel is made possible in the combustion chamber via the displacement member. Such a displacement member may in particular, but need not necessarily be designed as a linearly displaceable reciprocating piston or the like. The metered amount of fuel can correspond to the product of piston stroke and its cross-sectional area, wherein the piston stroke is variable over the variable stop.

For the purposes of the present invention, it is preferably assumed that the metering of the fuel takes place predominantly or exclusively in the liquid phase, as a result of which the amount of fuel spent in the combustion chamber is defined particularly precisely. In the case of LPG fuel, such exclusive metering of liquid phase can be ensured, for example, by providing a membrane in the fuel tank is arranged, wherein in the membrane, the liquid gas is held in exclusively liquid phase and outside the membrane, for example, an inert gas is provided under a defined overpressure. In the course of the consumption of the fuel expands while the intergas and keeps due to its overpressure, the liquid gas at any time in the liquid phase. Such a per se known embodiment of a fuel tank is basically accompanied in practice with a certain change in the pressure in the fuel tank in the course of its emptying. This makes a difference to conventional storage tanks for liquefied petroleum gas, in which liquid gas is stored in coexistence of gaseous and liquid phase in a constant volume thus provides a constant pressure.

In a further preferred detailed embodiment of the invention, a drive of the displacement member via a pressure of the fuel, in particular via a connection to the fuel tank, driven. As a result, can be dispensed costly to additional drives, such as electric or pneumatic actuators for the displacement. Ultimately, the stored in the fuel tank mechanical energy is used to make it possible to quickly and accurately the metering of the fuel into the combustion chamber.

In a further detailed design, the displacer can be held in a starting position by force, preferably, but not necessarily, by means of a spring. As a result, a defined starting position of the displacement member is ensured in a simple manner before an initiation of the dosing process.

In one possible embodiment of the invention, the thermo-mechanical element is designed as a bimetallic element. Preferably, but not necessarily, it may be a bimetallic disc, as known per se. Such bimetallic elements work according to the known principle, two metals or other substances with different thermal expansion coefficients in particular cohesively to each other set. When the temperature changes then it comes to significant and defined deformations, such as bulges of the bimetallic disc, and thus to a thermo-mechanically induced stroke of much greater extent than a pure thermal expansion of a homogeneous piece of metal of the same size.

In an alternative or supplementary embodiment, the thermo-mechanical element may comprise an expansion mass. The wax can, for example, to a liquid or a pasty mass, in particular a wax act. This mass is arranged in a suitable device in which an isotropic volume expansion of the expansion material is converted into a defined stroke or the like. In one of the possible embodiments of the invention, such an expansion mass, optionally enclosed in a membrane, may be arranged in the metering volume, whereby the metering volume which can be filled by the fuel is variable as a function of an expansion of the expansion material. In alternative embodiments, the thermo-mechanical element can preferably be designed as a thermo-actuator, which comprises a temperature-dependent positioned crank pin. Such thermal actuators are known per se and are offered for other applications. The crank pin can be connected, for example, to an adjustable wall of the metering volume or serve as a variable stop for a movable displacement member.

In a generally advantageous detail design, the metering device comprises at least one valve member, wherein the valve member is particularly preferably operated electrically. Further advantageously, the valve member in the interest of a simple and effective implementation as a three-way valve, in particular with two switching positions, be formed. Overall, this allows a simple and reliable control of the metering device. Further advantageously, the two switching positions of the three-way valve can be configured as bistable positions, whereby a particularly low consumption of electrical energy for the valve member is made possible.

Generally, it is provided that a characteristic curve of the defined quantity of fuel has a substantially bilinear course as a function of an ambient temperature. This can be used to advantage that, for example, a change in the metered amount of fuel takes place only in the range of low temperatures, from a certain limit temperature, for example in the range of an ambient temperature of 20 ° C, a constant amount of fuel is metered. By suitable mechanical measures, the thermo-mechanical element can continue to change even at higher temperatures than the limit temperature, without affecting the metered amount of fuel.

In a further possible embodiment of the invention, it is provided that the thermo-mechanical element comprises a remote sensor. As a result, the influencing of the metered amount can be effected as a function of a temperature which is not directly in the Area of mechanical connection of the thermo-mechanical element to the metering occurs. In particular, this may be the temperature in or in the region of the combustion chamber, wherein the remote sensor is arranged on the combustion chamber and the metering device at a distance from the combustion chamber. Such a remote sensor may comprise, for example, a relatively larger container placed in the vicinity of the temperature source and a smaller, deformable container in the region of the metering device, the two containers being connected by a capillary tube. The volume ratios of the two containers then allow the system to substantially respond to the temperature of the larger container.

Depending on the detailed design, a suitable mechanical transmission can be interposed between the thermo-mechanical element, for example an expansion element, and the metering volume in order to achieve a more accurate adaptation of a characteristic of the thermomechanical element to a desired temperature-dependent characteristic of the metering volume. As a result, if necessary, non-linear relations can be achieved, for example by means of link plates or other measures.

Further advantages and features of the invention will become apparent from the embodiments described below and from the dependent claims.

Fig. 1

zeigt eine schematische Gesamtansicht eines erfindungsgemäßen Eintreibgerätes.

Fig. 2

zeigt eine schematische Darstellung einer ersten Ausführungsform der Erfindung bei niedrigen und hohen Temperaturen.

Fig. 3a

zeigt ein zweites Ausführungsbeispiel der Erfindung bei hohen Temperaturen in einem Bereitschaftszustand der Dosiervorrichtung.

Fig. 3b

zeigt das Ausführungsbeispiel aus Fig. 3a während einer Dosierung des Brennstoffs.

Fig. 4a

zeigt das Ausführungsbeispiel aus Fig. 3a bei niedrigen Temperaturen.

Fig. 4b

zeigt das Ausführungsbeispiel aus Fig. 4a während einer Dosierung des Brennstoffs.

Fig. 5

zeigt ein thermomechanisches Element des Ausführungsbeispiels nach Fig. 3a bis Fig. 4b in drei verschiedenen Zuständen.

Fig. 6

zeigt einen Thermo-Aktuator bei zwei verschiedenen Temperaturen.

Hereinafter, several embodiments of the invention will be described and explained in more detail with reference to the accompanying drawings.

Fig. 1

shows a schematic overall view of a tacker according to the invention.

Fig. 2

shows a schematic representation of a first embodiment of the invention at low and high temperatures.

Fig. 3a

shows a second embodiment of the invention at high temperatures in a standby state of the metering device.

Fig. 3b

shows the embodiment Fig. 3a during a metering of the fuel.

Fig. 4a

shows the embodiment Fig. 3a at low temperatures.

Fig. 4b

shows the embodiment Fig. 4a during a metering of the fuel.

Fig. 5

shows a thermo-mechanical element of the embodiment according to Fig. 3a to Fig. 4b in three different states.

Fig. 6

shows a thermo-actuator at two different temperatures.

This in Fig. 1 schematically shown tacking device comprises a housing 1, in which a combustion chamber 2 is arranged. Liquefied gas is stored as fuel in a fuel tank 5 and can be injected via a line 3 into the combustion chamber 2. The line 3 connects a metering device 4 with the combustion chamber 2, wherein the metering device 4 in turn is connected to the fuel tank 5 arranged in or on the housing 1. The fuel tank can be designed in particular as a replaceable cartridge.

The tacker also includes an electronic control 6 with an electric accumulator as energy storage. Via the electronic control 6, a spark plug 7 in the combustion chamber 2 is controlled and optionally the metering device 4, provided that it has electrical valves or other electrically controlled components. In a front portion of the tacker, a magazine 8 for storing fasteners, such as nails, is arranged. A pressing member 9 can be pressed against a workpiece to release a triggering of the tacker.

The driving of a fastener member from the magazine 8 via the ignition of a liquid-air mixture in the combustion chamber 2 by means of the spark plug 7, after which a piston (not shown) is driven forward and a Eintreibstößel (not shown), the fastening member or drives the nail into the workpiece. This driving operation is triggered by an operator via a switch 10, which is presently arranged in a grip region 11 of the housing 1.

Fig. 2 shows a first embodiment of the metering device 4. The metering device 4 comprises a metering volume 12 which is connected via an input side, electrically controllable valve 13 to the fuel tank 5 and is connected via an output side, electrically controllable valve 14 to the combustion chamber 2.

In or on the dosing volume is a thermo-mechanical element 15, which in the present case comprises a Dehnstoffmasse. The expansion mass of the thermo-mechanical element 15 expands according to prevailing in the metering volume or the environment Temperature more or less, so that the remaining, fillable by LPG volume at higher temperatures is lower than at low temperatures. This is illustrated by a comparison of the left (low temperature) and the right (higher temperature). For the exact configuration of the arrangement of the Dehnstoffmasse in the dosing different variants are possible. For example, the expansion mass may be enclosed in an inert membrane relative to the liquefied gas and located in the metering volume. But it can also be provided on the metering volume, an elastic or displaceable wall, wherein the Dehnstoffmasse is located on the other side of the wall. In such an arrangement, instead of a Dehnstoffmasse also a bimetallic element such as a bimetallic disc may be provided to change the dosing volume by the displacement or deformation of the wall of the metering volume.

• Zunächst wird mittels der Steuerung 6 das eingangsseitige Ventil 13 geöffnet, so dass Flüssiggas in flüssiger Phase in das Dosiervolumen einströmen kann. Dabei liegt das Flüssiggas in dem Tank 5 ausschließlich in flüssiger Phase vor. Dies wird auf an sich bekannte Weise dadurch erreicht, dass das Flüssiggas in dem Tank in eine Membran eingeschlossen ist und der Raum außerhalb der Membran mit einem Inertgas unter höherem Druck als dem Dampfdruck des Flüssiggases gefüllt ist. Aufgrund dieses Überdrucks findet kein Verdampfungsvorgang im Zuge des Einströmens des Flüssiggases in das Dosiervolumen 12 statt, so dass im Wesentlichen keine Temperaturänderung im Zuge des Einströmens des Flüssiggases erfolgt.

The metering device according to Fig. 2 works like this:

• First, the input-side valve 13 is opened by means of the controller 6, so that liquid gas can flow into the metering volume in the liquid phase. In this case, the liquefied gas in the tank 5 is present exclusively in the liquid phase. This is achieved in a manner known per se by enclosing the liquefied gas in the tank in a membrane and filling the space outside the membrane with an inert gas at a pressure higher than the vapor pressure of the liquefied gas. Due to this overpressure no evaporation process takes place in the course of the inflow of the liquefied gas into the metering volume 12, so that substantially no temperature change takes place in the course of the inflow of the liquefied gas.

If the tacker is triggered, the input-side valve 13 is closed and the output-side valve 14 is opened, so that the liquefied gas can flow into the combustion chamber 2. In this case, the metered into the combustion chamber 2 amount of liquid depending on the extent of the thermo-mechanical element 15 at low temperatures is greater, so that even with a slower evaporation a reasonably fast provision of an ignitable mixture in the combustion chamber 2 takes place.

Fig. 3a to Fig. 4b show a second embodiment of the invention. An essential difference from the preceding embodiment is that the liquid gas is expelled from the metering volume 12 by means of a movable displacement member 16.

The displacement member 16 is formed as a linearly displaceable piston, which in a

Cylinder 17 is located, which is part of the dosing volume 12. The cylinder 17 connects to an electrically operated valve member 18, which in addition to the connection with the cylinder 17 has a connection to the fuel tank 5 and a connection to the combustion chamber 2. A valve spool 19 closes either the connection 18a with the fuel tank 5 or the connection 18b with the combustion chamber 2. Overall, the valve member 18 is formed as a 3-way valve with two valve positions.

Depending on the requirements, the positions of the valve slide 19 can each be stable positions (bistable valve slide), so that only a short, low-energy-requiring electrical pulse is required to switch over the valve. In another embodiment, the valve spool 19 is always in a de-energized rest position as in Fig. 3a arranged, so under closure of the connection 18b with the combustion chamber 2 (monostable valve spool). By applying an electrical voltage, the valve spool is in the opposite position (see Fig. 3b ), in which it closes the connection 18a with the fuel tank 5.

In each of the positions of the valve spool 19, the cylinder 17 of the metering volume 12 remains connected to the valve member 18. The valve member 18 includes a certain own volume, which contributes to the dosing volume 12.

From the connection of the fuel tank 5 to the valve member 18, a branch pipe 20 leads to an end of the cylinder 17 opposite to the valve member 18. The branch pipe 20 connects an upper end of the piston-shaped displacer 16 to the fuel tank 5.

In this upper end region of the cylinder 17, a thermo-mechanical element 15 is also arranged, which provides a temperature-dependent upper stop for the displacement member 16.

As shown in Fig. 3a , which corresponds to a high ambient temperature, the stop is provided by a temperature-dependent movable stop pin 15a. In addition to the stopper pin 15a, a second stop 21, which is fixed depending on the requirements or is provided by other means, for example manual adjustment, is additionally provided. This second stop 21 defines the uppermost position of the displacer 16 at warm temperatures; please refer Fig. 4a and Fig. 4b , A temperature-dependent change of this second stop 21 is therefore not provided.

The piston 16 is also biased by a spring (not shown) in its upper stop position, which is indicated by the upward arrow in Fig. 3a and Fig. 4a is symbolized. At this starting position after Fig. 3a respectively. Fig. 4a is located above and below the piston 16, the pressure of the fuel tank 5 in the cylinder 17 at. The spring force is used only for a defined positioning of the piston 16 in a starting position. Accordingly, the force of the positioning spring can be made relatively small.

A triggering operation of the tacker is now carried out by switching the valve spool 19 of the valve member in the opposite position. As a result, the lower part of the cylinder 17, which is connected to the valve member 18, connected via the port 18 b with the combustion chamber 2, in which a significantly lower pressure (ambient pressure) is present. Above the piston 16, the cylinder 17 is acted upon via the line 20 with the pressure in the fuel tank 5. As a result, the piston 16 is accelerated according to the drawings down or in the direction of the valve member 18, wherein he presses the liquid from the metering volume 12, ie the lower part of the cylinder 17 and the volume in the valve member 18 in the combustion chamber 2. After this operation, the piston 16 has taken a lower stop position, each in Fig. 3b and Fig. 4b is shown. According to this sequence, the drive of the displacer 16 takes place via the pressure of the fuel into the tank 5.

For clarity, in Fig. 3a to Fig. 4b in each case those volume areas in which liquid gas is in equilibrium in the liquid phase or under high pressure, represented by a hatching.

The temperature-dependent change in the amount of fuel injected into the combustion chamber takes place over the variable length of the stop part 15a of the thermo-mechanical element 15. In this case, the thermo-mechanical element 15 comprises an expansion element actuator 22 which is filled with an expansion material mass. Such expandable actuators are commercially available and exemplary in Fig. 6 shown.

Fig. 5 shows a particularly preferred arrangement of the thermo-mechanical element 15, through which a bilinear characteristic of the metering volume with respect to the temperature can be achieved, in particular by simple means. In this case, the Dehnstoffaktuator 22 is supported on the one hand via a first support spring 23 against a housing 1, wherein its linearly displaceable crank pin 22a is connected to an extension 22b, which in turn is supported by a second spring 24 against the housing 1 to a return of the crank pin at to ensure a cooling of the wax.

Via a stroke control range HR (see left figures Fig. 5 ) can now be a temperature-dependent change in the dosing volume. From a certain temperature, the extension 22b abuts on a housing-fixed stop, whereby a maximum reduction of the dosing volume is reached. A further expansion of the expansion material or a further extension of the crank pin 22a is subsequently absorbed by a compression of the first spring 23, which has the function of an overstroke spring. The extension 22b and the crank pin 22a remain stationary relative to the housing.

The over the stop position (middle illustration in Fig. 5 ) outgoing stroke is thus no longer used as excess lift HU for controlling the metering volume. In this range, the characteristic of the dosing volume as a function of the temperature is thus a horizontal or the dosing volume is constant from this temperature.

In practice and when using conventional liquid gas such as propane or propane-butane mixtures shows that a change in the dosing volume or introduced into the combustion chamber amount of liquefied gas in areas below about 20 ° C to 25 ° C is useful. At higher temperatures, such a control is no longer very effective and preferably the dosing volume is kept constant in these temperature ranges.

A variation of the metering volume in the range between -10 ° C and + 20 ° C for hand-driven tackers is typically about 15 mm ³ , which corresponds to a technically easy to implement stroke of 1 to 1.5 mm for the thermo-mechanical element in appropriate embodiments.

Claims (12)

A tacker comprising
a tank (5) for storing a fuel, in particular LPG,
a combustion chamber (2) connected to the tank (5), the combustion chamber (2) having a movable piston for driving a driving ram, and
a metering device (4) arranged between the tank (5) and the combustion chamber (2),
wherein by means of the metering device (4) a defined amount of the fuel from a metering volume (12) can be brought into the combustion chamber (2),
characterized,
that the metering device (4) comprises a thermo-mechanical element (15), by means of which the amount varies depending on a temperature defined is variable. A tacker according to claim 1, characterized in that the metering volume (12) by the thermo-mechanical element (15) is variable. A tacker according to claim 1 or 2, characterized in that the metering device (4) comprises a movable displacement member (16) for expelling the defined amount of the fuel, wherein a stop position of the displacement member (16) via the thermo-mechanical element (15) is variable. A tacker according to claim 3, characterized in that a drive of the displacement member (16) via a pressure of the fuel, in particular via a connection to the tank (5), can be driven. A tacker according to claim 3 or 4, characterized in that the displacement member (16) is subjected to force in an initial position, in particular by means of a spring. A tacker according to one of the preceding claims, characterized in that the thermo-mechanical element (15) comprises a bimetal member, in particular a bimetal disc. A tacker according to any one of the preceding claims, characterized in that the thermo-mechanical element (15) comprises a Dehnstoffmasse. A tacker according to claim 7, characterized in that the thermo-mechanical element (15) is designed as a thermo-actuator, which comprises a temperature-dependent positioned crankpin (22a). A tacker according to one of the preceding claims, characterized in that the metering device (4) comprises at least one valve member (13, 14, 19), wherein the valve member is in particular electrically operated. A tacker according to claim 9, characterized in that the valve member is designed as a 3-way valve, in particular with two switching positions. A tacker according to one of the preceding claims, characterized in that a characteristic of the defined amount of fuel in dependence on an ambient temperature has a substantially bilinear course. A tacker according to any one of the preceding claims, characterized in that the thermo-mechanical element (15) comprises a remote sensor.

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