Patent Publication Number: US-10759032-B2

Title: Fuel gas-operated drive-in device having valve component

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is the U.S. National Stage of International Patent Application No. PCT/EP2016/070938, filed Sep. 6, 2016, which claims the benefit of European Patent Application No. 15185079.9, filed Sep. 14, 2015, which are each incorporated by reference. 
     The invention relates to a nail gun, in particular a manually controlled nail gun according to the preamble of claim  1 . 
     BACKGROUND OF THE INVENTION 
     WO 2009/140728 A1 describes a combustible gas operated nail gun for driving nails into a workpiece, in which a combustion chamber is charged with a combustible gas, wherein after an ignition process, a driving piston is accelerated against the nail. The combustible gas can be charged by combined measures by means of a fan or the stroke of the driving piston against a positive pressure, in order to increase the driving energy. 
     U.S. Pat. No. 8,091,751 B2 describes a combustible gas operated nail gun in which the combustible gas can be charged by means of an electric compression against a positive pressure. A combustion chamber of the device comprises several combustion chamber portions that are movable toward one another and is closed by means of a compression rod when the nail gun is pushed against a workpiece. 
     BRIEF SUMMARY OF THE INVENTION 
     It is the problem of the invention to provide a nail gun that has high operational reliability. 
     This problem is solved for the initially mentioned nail gun with the characterizing features of claim  1 . By provision of the valve element, a combustion chamber that is charged and under a positive pressure can be emptied in a controlled and safe manner if there is no ignition. 
     Generally preferably, the valve element opens automatically when the nail gun is removed from the workpiece. 
     The absence of ignition of the mix can have any number of causes, for example deliberate interruption of the setting process by the operator, or even some sort of operational breakdown. 
     A positive pressure of the combustible gas mix in the sense of the invention means a pressure that is increased using a charging element to raise the driving energy. Also with conventional devices, the pressure of the combustible gas mix usually is somewhat above an ambient pressure, as the combustible gas under pressure is added to the air in the combustion chamber which is under atmospheric pressure. This is only a slight pressure increase. A positive pressure in the sense of the invention preferably is around at least 100 mbar, especially preferably around at least 20 mbar above atmospheric pressure. 
     A charging element in the sense of the invention can be any means that at least raises the air portion of the combustible gas mix above the atmospheric pressure. In particular this can be an electrical compressor. 
     A valve element in the sense of the invention controllably blocks or opens a connection between the combustion chamber and an outer space. In the sense of the invention, the valve element is not understood to be a movable combustion chamber part, the movement of which first forms the combustion chamber. 
     A sensor element in the sense of the invention is understood to be any mechanical, electromechanical, optoelectronic, or other component by means of which a compressed state of the nail gun may be determined. For example, the sensor element can be a moving rod, an electrical switch, an optical sensor, etc. 
     According to the invention, the sensor element is connected to the valve element in such a way that the valve element is controlled depending on a position of the sensor element. In the case of ignition failure of the gas mix, removal of the nail gun can be determined from the sensor element, and the combustible gas mix under positive pressure can escape via the valve element. 
     In a generally advantageous embodiment of the invention, the combustion chamber comprises at least combustion chamber parts movable with respect to one another, wherein the combustion chamber parts are combined into the closed combustion chamber only when the nail gun is in a compressed state. Devices of such design are generally known and due to their construction are quite safe with respect to inadvertent or improper triggering. Although, during charging of such conventional devices with positive pressure, it has been shown that automatic opening or even collapse of the combustion chamber can be disrupted when the device is removed when no ignition occurs. This is basically because such a combustion chamber has large sealing surfaces and sealing systems, on which the correspondingly strong forces act due to the positive pressure. Solutions in which a stronger spring force of a return spring is provided corresponding to the positive pressure are uncomfortable because of the necessary greater pressing force by the operator. The additional valve element according to the invention allows a largely conventional design of the combustion chamber, as the positive pressure initially is reduced in a targeted manner, after which opening or collapsing of the combustion chamber occurs with low spring forces. 
     In an especially preferred embodiment it is provided that the combustion chamber parts are closed gas-tight in the closed state by means of a self-reinforcing sealing system. With such a system, the compression forces of the seals rise with the pressure in the combustion chamber, so that a maximal positive pressure in principle can be arbitrary and can be selected independently of the force of a compression spring or the like. 
     For a preferred detailed design of the invention, the combustion chamber parts are moved toward each other via a compression rod, wherein the sensor element is additionally provided for the compression rod. This allows reliable control of the valve element when the nail gun is removed regardless of the selected positive pressure and its effect on the compression rod. For other embodiments, however, the valve element can also be controlled directly by the compression rod. 
     Generally advantageously it is provided that the valve element is designed to be low-power with respect to the positive pressure. Preferably this is achieved simply in that a valve rod of the valve element has a direction of motion that runs transversely to a direction of action of the positive pressure of the gas mixture. A low-power design is herein understood to be any valve arrangement in which a normal operating positive pressure alters a necessary actuating force of the valve element at most insignificantly. 
     In a first possible embodiment, the valve element is connected mechanically directly to the sensor element, so that a movement of the sensor element effects an adjustment of the valve. This allows a simple implementation and great reliability against operating disruptions, for example of control electronics. 
     In a second possible embodiment, the valve element can be adjustable via an electrical actuator. Preferably the actuator in this case is connected to an electronic control unit of the nail gun. With this embodiment, the sensor element can be configured as an electrical switch or sensor, by which construction weight is generally saved. In addition, such a solution permits a universal control of the valve element as a safety means. 
     In a structurally simple and generally preferred embodiment of the invention, the charging element comprises an electrical compressor. Alternatively, the charging element can also be a manually actuated compressor, a compressed air reservoir, or the like. Preferably the charging element is integrated into the setting device. Alternatively, the charging element can be separate from the usual setting device. 
     In a generally advantageous further development of the invention, the gas mix escaping via the valve element drives a generator in order to partially convert mechanical pressure energy into electrical energy. The mechanical energy of the charged gas therefore is not completely lost when a setting process is interrupted, but can in part be returned to a battery of the device. In a preferred further development, the generator is configured by changing the operating mode of the charging element. In this way additional structural components can be saved. 
     Further advantages and features of the invention follow from the exemplary embodiments described below, as well as from the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       Below two preferred exemplary embodiments of the invention are described and explained in more detail with reference to the attached drawings. 
         FIG. 1  shows a schematic sectional view of a nail gun according to the invention of a first exemplary embodiment with mechanically controlled valve element in a first operating state. 
         FIG. 2  shows the nail gun of  FIG. 1  in a second operating state. 
         FIG. 3  shows a schematic sectional view of a nail gun according to the invention of a second exemplary embodiment with electrically controlled valve element. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The nail gun from  FIG. 1  is a manually controlled device comprising a housing  1  and a combustion chamber  2  accommodated therein and having a combustion chamber wall. A cylinder  3  abuts the combustion chamber  2  with a driving piston  4  guided therein. 
     A safety mechanism of the device comprises a compression rod with mounting sleeve  5 , which is mounted on a workpiece (not shown) and is pushed against the pressure of a spring (not shown). Only in this state can a driving process be triggered by ignition of a combustible gas in the combustion chamber  2 . The combustion chamber  2  consists of several combustion chamber parts (not shown) that are movable toward one another, which only after pressing of the mounting sleeve  5  via the compression rod are combined into a closed space for receiving an ignitable combustible gas mix. Such designs of combustion chambers with the purpose of safety improvement are generally known, for example from the above-named publications. A detailed representation of these safety mechanisms in the present schematic drawings was therefore dispensed with. 
     An ignitable combustible gas mix is presently fed by means of a charging element  6  and a combustible gas container  7  into the combustion chamber  2 . The charging element  6  is configured as an electrical compressor  9  supplied by a battery  8 . The combustible gas is fed via a dispensing valve  10  from the combustible gas container to the compressed air downstream of the compressor  9 , after which the flow of the combustible gas mix enters the combustion chamber  2  via a supply line. 
     When the combustion chamber is charged, ignition of the combustible gas mix can be actuated via a manually activated trigger  11 , so that the driving piston  4  is driven forward and via a driving member  12 , a nail element (not shown) is driven into the workpiece. The exhaust gases of the ignited and expanded combustible gas can exit to the external space via outlet openings  14  at the end of the path of the driving piston. 
     A return of the driving piston  4  after the driving process occurs in the conventional way, for example by means of a return spring. 
     In the present examination, the combustion chamber parts in mounted state of the device are sealed by means of a sealing system such that a pressure increase in the combustion chamber  2  leads to an increase in the forces acting on the seals (self-reinforcing sealing system). The result is that when the setting process does not take place and the nail gun is removed, the combustion chamber remains in the charged state. 
     To reduce the positive pressure in the combustion chamber, according to the invention a valve element  15  is provided that connects the combustion chamber  2  to the external spaced. The valve element  15  has a valve slide  16 , which moves transversely to the pressure direction or the outflow direction of the combustible gas mix. In this way a resistance of the valve slide is scarcely dependent on the amount of positive pressure in the combustion chamber  2 . 
     The valve slide  16  is connected via a mechanical rod  17  to a sensor element  18 . The sensor element  18  is in the region of the mounting sleeve  5  and is shown in the schematic drawing as a depressible probe tip. 
     The rod  17  is acted on by the force of a spring  19 , so that the sensor element  18  is driven forward when the nail gun is in unmounted state, and the valve element  15  is in an opened state (see  FIG. 2 ). 
     When the nail gun is mounted on the workpiece, the sensor element  18  is pushed against the spring pressure. The valve slide  16  is hereby displaced by the rod  17  and the valve element  15  is closed. The valve function is shown in the drawings by the covering or displaced openings in the valve slide  16  and in the combustion chamber wall. 
     For the mounted status of the nail gun shown in  FIG. 1 , the combustion chamber  2  with the combustible gas mix is acted on by the positive pressure. The mounting sleeve  5  and sensor element  18  are pushed inward. 
     If the device is now removed from the workpiece without triggering, the mounting sleeve  5  initially remains in its position, as the combustion chamber parts cannot be displaced. The sensor element  18  on the other hand, based on the spring force of the spring  19 , moves forward, so that the valve element  15  is opened via the rod  17 . In this way the combustible gas mix can escape and the positive pressure in the combustion chamber  2  can be reduced (intermediate status according to  FIG. 2 ). 
     After a reduction of the positive pressure, the combustion chamber parts can be moved by engaging spring forces, so that the mounting sleeve is also returned to the forward position (not shown). 
     It is understood that the valve element according to the invention then also represents an advantageously further development and a gain in safety when the sealing system of the combustion chamber is not designed as self-reinforcing or when the return spring force of the combustion chamber parts are also designed for opening under positive pressure. An operating fault in connection with a charged combustion chamber can thus be reliably avoided. 
       FIG. 3  shows a second exemplary embodiment of the invention in which, in contrast to the first exemplary embodiment, the valve element  15  is electrically actuated. 
     Toward this end the valve element  15  has an electrical actuator  20 , which is connected to an electronic control unit  21 . The sensor element is configured as an electrical sensor element  22  on the end of the mounting sleeve  5 . The sensor element  22  is likewise connected to the control unit  21 . 
     As a further embodiment, the nail gun has a manually operated switch  23 , which is readily reachable on the housing  1  of the nail gun. 
     A valve element so designed can be configured for example as currentless open so as to ensure a maximum of safety. Opening of the closed valve element of the present example occurs in operation when the sensor element  22  is not seated on a workpiece. But opening also occurs when the manually operated switch  23  is pushed. In this way, the operator can discharge the combustion chamber at any time, or ensure the discharged state of the device.