Abstract:
A pressing tool having an electric motor fed by a battery. The electric motor drives a gear pump with two rotor shafts which are accommodated in a hydraulic block. The rotor shafts are mounted in a gear housing on one side of the hydraulic block and in a cylinder housing of a piston cylinder unit which bears on an other side of the hydraulic block. This gear pump uses an extremely simple construction manner and simultaneously achieves a high delivery volume. The high delivery volume leads to an extremely low loading of the battery, by which its operational duration is increased.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a portable, hydraulically functioning pressing tool for the pressing of coupling elements, with a fork-like receiver and with a clamping pincer which is held in the receiver and which is actuatable by a piston cylinder unit with an integrated restoring spring. 
     2. Description of Related Art 
     Portable, hydraulically functioning pressing tools are known and used for pressing coupling elements, such as press sleeves, press fittings, connecting sleeves, tube sections inserted into one another and likewise. The pressing tools have a clamping pincer with clamping jaws which form a pressing space for receiving the coupling elements to be pressed. The pressing force required for the pressing is delivered by a generally hydraulic drive. 
     Because the apparatus of interest here is preferably used on building sites it is an electrically driven apparatus. By way of example, U.S. Pat. No. 5,040,400 shows a pneumatically functioning apparatus. An electrically driven pressing tool apparatus is taught by European Patent Reference EP-A-0&#39;712&#39;696 (Pamag A G). A conventional apparatus is supplied via electricity mains. However the availability of electrical connection sources on building sites is often very limited. For this reason it is desirable to be able to operate independently of the mains electricity, for example by using a battery. However, as is known, a battery-operated apparatus is very heavily dependent on operating in a manner which is economical with regard to energy, so that a reasonable operational duration per battery charging may be achieved. 
     With available hydraulically functioning pressing tools, independently ofthe type of the electrical supply, rotation pumps or piston pumps have been applied. All previously known systems have a relatively low delivery power and accordingly the operational duration per stroke of the piston cylinder unit to be actuated is relatively long. Although this is insignificant with an apparatus which depends on mains electricity, with a battery-operated apparatus this operation time is of underlying importance. 
     U.S. Pat. No. 5,125,324 teaches a mains operated apparatus of the previously mentioned type. The hydraulic pump, which is a piston pump, acts on a piston cylinder unit with an integrated restoring spring, wherein the pump is completely arranged in a hydraulic block between a drive-side gear and a piston cylinder unit. 
     SUMMARY OF THE INVENTION 
     It is one object of this invention to provide a portable, hydraulically functioning pressing tool having an operational duration per pressing procedure as short as possible, so that the operational duration per charging of the battery with the battery-operated apparatus is sufficient for as many pressing procedures as possible. It is another object of this invention to provide a compact pressing tool which is correspondingly light and which is inexpensive to manufacture. 
     A portable hydraulically operated pressing tool with the features described in this specification and in the following claims achieves these objects. The apparatus of this invention can use a gear pump. Because a gear pump with a sufficient power requires a relatively large space, the arrangement in the apparatus is of significant importance in order to achieve the mentioned solution without considerably enlarging the apparatus, to avoid additional weight which may be unwieldy. This invention achieves the objects with a modular construction wherein a gear pump is arranged in the hydraulic block and bears in both neighboring modules on both sides of the hydraulic block. This results also in an extremely compact arrangement with correspondingly short hydraulic conduits and accordingly leads to a relatively light pressing tool, even with the incorporated battery. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantageous embodiments of the hydraulically operated pressing tool according to this invention are deduced from the specification and claims and their significance is explained in the subsequent description with reference to the drawings, wherein: 
     FIG. 1 is a perspective view of a pressing tool according to this invention; 
     FIG. 2 is a vertical longitudinal section view of a function unit of the pressing tool; 
     FIG. 3 is a vertical cross section shown in a simplified representation; and 
     FIG. 4 is a simplified longitudinal section taken through a valve unit, which is shown separately. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A pressing tool  0  is an electrohydraulic apparatus which can be a battery-operated apparatus. The pressing tool  0  has a pressing tool function unit  2  on which there is formed a grip  1 . In the rearward extension on the function unit  2 , a battery housing  6  is formed as a removable part. In the forward extension of the pressing tool function unit  2  there is recognizable a fork-like receiver  3 . In the fork-like receiver  3  is held a clamping pincer  4  in a secured manner in the receiver  3 , with a security bolt  5 . For the actuation of the apparatus there is a release switch  8 . 
     The actual construction of the pressing tool function unit  2  is shown in FIG.  2 . The drive is performed by an electric motor  10  which is supplied by the battery feed  7 . The release switch  8  is arranged between the electric motor  10  and the battery  7 . The electric motor  10  has an output shaft  11  with an end-side output pinion  12  that meshes with a gearwheel  13  which is mounted on a gear output shaft  16 . The gear output shaft  16  is mounted in a gear bearing  14  and in a gear housing  15  which is sealingly passed through by the gear output shaft  16 . A continuation of the gear output shaft  16  forms one of the two rotor shafts  19  of a gear pump  18  (see FIG.  3 ). 
     The lower rotor shaft  19  is mounted in the gear housing  15 . The counter bearing of both rotor shafts  19  are in the cylinder housing  21  of the piston cylinder unit  20  held in suitable sliding bearings. 
     The hydraulic block  17  is completely passed through by the two rotors or rotor shafts  19  of the gear pump  18 . In the same hydraulic block  17  right at the bottom there is mounted an outlet peg  27  which communicatingly is connected to a reservoir  28  variable in volume and via suitable lead bores in the hydraulic block  17 , via a valve unit  31 , is connected to the gear pump  18 . In the hydraulic block  17  there is a lead line  29  and a pressure line  30 , acting as bores, via which the outlet peg  27  is in communicating connection with the gear pump  18  and the gear pump  18  with the piston cylinder unit  20 . The hydraulic block  17  has a piston space return travel  26  via which hydraulic oil displaced during the load stroke via the outlet peg  27  may be led back to the reservoir  28  which is changeable in volume or with the return travel of the piston accordingly hydraulic oil may be led back into the piston space. 
     With the arrangement according to this invention and the use of the gear pump  18 , a particularly simple design solution is achieved and with the relatively large gear pump a large delivery output may be achieved which accordingly has a short operational duration per stroke. The arrangement according to this invention and the use of a gear pump provides simple and short delivery paths for hydraulic oil. Thus sealing problems are minimized and the conduits are manufactured as bores with a relatively large cross section. Thus, flow losses are minimized. 
     The piston cylinder unit  20  with the cylinder housing  21 , with the exception of the integrated sliding bearing for the rotor shafts of the gear pump  18 , is configured conventionally. In the cylinder housing  21  there is mounted the piston  20  on which there acts a restoring spring  25 . The piston  22  via the piston rod  23  displaces a roller bearing  24  for actuating the clamping pincer  4 . 
     A further advantage of the solution according to this invention is that there is not a multitude of valves which could lead to considerable flow losses, but rather a single valve unit  31  is sufficient. This valve unit permits large flow rates in the lead direction, by which the mentioned losses are kept very low. 
     With regard to the construction of the valve unit  31 , FIG. 4 shows the construction in a simplified manner. The valve unit  31  has two housing parts which are screwable to one another, wherein the one housing part accommodates the first lead change-over valve  32 , and the second, larger housing part accommodates a ball valve  38  as a second valve. The first valve  32  is separated from the second valve  38  by a valve plate  37 . In the housing of the first, lead change-over valve  32  there is an axially displaceable mounted hollow piston  33 . The displacement of the hollow piston  33  is at the inlet side limited by a securing ring  52  and limited on the other side by the valve plate  37 . The hollow piston  33  is at the side directed towards the valve plate  37  completely open, while in the closed end on the side of the piston head there is arranged a relatively small relieving bore  34 . The housing part  33 ′ forms the cylinder of the valve in which the hollow piston  33  is axially movably mounted. Into the hollow piston  33  there engages a restoring spring  36  which rests on the inside on the piston head and is supported on the valve plate  37 . The prevailing oil pressure D displaces the hollow piston  33  against the force of the restoring spring  36  until the hollow piston  33  opens the lateral lead bores  35  to the pressure line. Via the pressure line  30  the hydraulic oil enters the piston cylinder unit  20  and displaces the piston  22  which with the piston rod  23  displaces the roller bearing  24  and thus leads to the actuation of the clamping pincer  4 . 
     The second valve  38  supports the case of a ball valve which via the return travel bore  39  is in communicating connection with the pressure conduit and via the passage bore  40  through the valve plate  37  in connection with the cylinder  33 ′ of the first valve  32 . This connection, by way of the valve ball  41 , is closed or opened depending on the pressure. The second valve  38  has a valve body  42  with a valve body foot  43 . The valve body foot  43  has the shape of a circular disk which is connected as one piece to the valve body  42  and in which centrally there is a ball receiver  53  in which the valve ball  41  is partly mounted. The valve plate  37  forms the valve seat for the valve ball  41 . In the housing  54  of the second valve  38  there is screwed-in a spring counter bearing  45  in the form of a ring. Between the spring counter bearing  45  and the valve body foot  43  there is arranged a compression spring  46 . The characteristics of the compression spring  46  determines the change-over pressure. If the change-over pressure is reached the valve ball  41  is lifted, onto the hollow piston and there arises a counter pressure and the hollow piston  33  with the help of the restoring spring  36  is displaced back to the securing ring  52 , wherein the lead openings  35  are closed. This is independent of whether or not the gear pump  18  continues to deliver. 
     If for reasons which are not explained a blocking or an incomplete stroke release occurs, then via manual actuation of a push button  48  the pressure may be built up. The push button  48  can be a restoring spring  47  held in the original position. With pressure on the push button  48  a rounded head  49  of the valve body  42  moves in an eccentric bore which is indicated as a tilt surface  50 . The head  49  is simultaneously pivoted to the side, wherein the whole valve body  42  takes part in this pivot movement. Thus the valve body foot  43  with a tilting edge  44  bears on the valve plate  37  on one side and pivots about the point of bearing. As a result the valve body foot  43  in the middle lifts slightly and the valve ball  41  is relieved of pressure. The pressure may now be relieved through the passage bore  40  in the valve plate  37  and the first valve  32  again closes. 
     On closing the first valve  32  the hollow piston  33  travels back in a jolted manner. For the user the knocking of the valve may be heard. As soon as the user hears the closing of the valve the user releases the release switch  8 . It is possible in the cylinder  33 ′ of the first valve  32  in the lower region to arrange a sensor  51  which acts on the release switch  8 , or interrupts the feed conduit from the battery  7  to the electric motor  10 . This sensor is activated, time-delayed so that it is activated when the hollow piston  33  is in the open condition and thus only then realizes the closure procedure. By way of such a sensor  51  it may be ensured that the user does not unnecessarily load the energy source after the completion of a stroke movement. 
     The embodiment shown has a battery-operated apparatus. The enormous advantages, specifically the short operational period per working stoke, the extremely economical manufacturability and the weight saving which can be achieved by way of the compact arrangement are desirable with mains electricity pressing tools. This invention relates to mains electricity pressing tools.