Abstract:
The invention relates to a hydropneumatic pressure intensifier comprising a radial seal ( 24, 27 ). Said seal is arranged between working pistons ( 2 ) and the cylinder bore which accommodates said pressure intensifier or in a bore hole ( 15 ) between the working chamber ( 3 ) and a storage area ( 14 ), whereby the radial seals consist of viscoplastic and flexible synthetic material.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a hydropneumatic pressure intensifier of the type categorizing the main claim. Hydropneumatic pressure intensifiers of this type are used mainly for machine tools and function with alternating pressures, i.e. high pressure and low pressure in the working chamber, and having pneumatic and hydraulic working means exhibiting alternating rapid pressure increases and changes between overpressure and underpressure. This affects in particular the sealing rings of the seals between the working piston and the cylindrical wall of the working chamber and/or the sealing ring in the connecting bore between the working chamber and the storage chamber, wherein, at low pressure, the plunger piston is repeatedly introduced into and removed out of the sealing ring. This plunging process requires appropriate design of the sealing ring to ensure that when the plunger piston is immersed, the end face of the plunger piston does not clamp on the sealing ring side facing same, wherein the radial forces produced by the rubber-elastic tensioning ring, which have a corresponding effect on the clearance of the sealing ring, have to be taken into consideration. The sealing ring must have an appropriately large radial stiffness and guarantee static and dynamic sealing. The sealing ring must, of course, have high wear resistance and extrusion resistance with long service life and should facilitate assembly without deformation of the sealing edges. The sealing ring must, in particular, resist extremely high loads, i.e. high pressures and pressure shocks. 
     A known hydropneumatic pressure intensifier of the type categorizing the invention (EP 0 579 073 B1 and DE-PS 32 25 906 C2) provides the optimum preconditions for the expert, in particular for the producer of the patented sealing ring. It is thereby assumed that the high pressure can directly act on the sealing ring from one side. Due to the step provided in the direction of the working chamber on the circumferential surface of the sealing ring facing the piston, this sealing ring is axially loaded and pressed against the end wall, facing away from the working chamber, of the annular groove receiving the sealing ring without producing actual deformation of the sealing ring to thereby provide the intended sealing support of the sealing surface on the piston surface. Other sealing rings produced by this sealing ring manufacturer which are made from softer distortable material would not be used by one of average skill in the art, since their radial stiffness is either too low for immersion or they cannot withstand the high pressures and dynamic wear. 
     Practice has moreover shown that the above-mentioned sealing ring used for hydropneumatic pressure intensifiers consists of a material which is distributed under the trademark Turcon T46 which has metallic inclusions producing increased friction between the sealing ring and piston which act like sanding dust at this location. These metallic inclusions may also be caused by friction on the piston due to the hardness of the sealing material. This has, in end effect, the same result as sanding dust and guarantees good sealing and durability or service life due to the structure of the sealing ring while reducing wear on the piston in the sealing area. 
     SUMMARY OF THE INVENTION 
     In contrast thereto, the inventive hydropneumatic pressure intensifier having the characterizing features of the main claim (in contrast to the expectations of one of average skill in the art and despite the expected relatively easy incorporation of the sealing ring due to the associated pressure and friction acting on the piston) not only advantageously provides good sealing and durability, i.e. service life, but also prevents wear in the frictional area between the sealing ring and piston surface. Moreover, in contrast to the expectations of one of average skill in the art, immersion of the plunger piston into the sealing ring is very easy although, due to the increased softness, the sealing ring can be deformed by the tensioning ring in the direction of the sealing surface. Such a relatively soft sealing ring with corresponding cross-sectional design is known per se (EP 0 670 444) as is the typical deformation of this sealing ring (EP 0 582 593). The material used is distributed by the producer under the trademark Zurcon: the sealing ring itself under the trademark Rimseal. The producer recommends use of this seal only as a secondary seal especially for relatively high pressures. It was developed explicitly as such and only in this way can safe sealing of thin oil films be guaranteed, in particular, with low secondary pressures. The material is polyurethane with Shore D 58. One of average skill in the art uses such a sealing ring in particular if the piston exhibits a slight tilting movement with respect to its cylinder. Immersion of a plunger piston into such a soft material is not considered to be acceptable by one of average skill in the art. The above-mentioned relatively hard sealing ring is recommended for the primary seal and is used in conventional hydropneumatic intensifiers. Due to the relatively soft material, which is also absolutely free from metallic inclusions, the piston surface is not subjected to frictional wear which could lead to the above-mentioned sanding dust effect. 
     In accordance with an advantageous embodiment of the invention, the opposite walls of the annular groove or the like extend essentially parallel to one another. As a result thereof, the sealing ring is loaded with unilateral forces produced by the conical travel of the end wall and acting in the direction of the piston. 
     In accordance with a further advantageous embodiment of the invention, the plastic material of the sealing ring does not have any metallic inclusions. This has the principal advantage of preventing mechanical wear of the piston surface. 
     In accordance with another advantageous embodiment of the invention, the sealing ring consists of a plastic material produced by the company Busak and Shamban under the name Zurcon with the trademark Rimseal and made from a special polyurethane 58 Shore B. 
     In accordance with another advantageous embodiment of the invention, the working piston comprises a pneumatically loaded collar for its fast stroke drive, wherein the rear side of the seal is alternately loaded with pneumatic working pressure and with the lowermost pressure. 
     In accordance with another advantageous embodiment of the invention, the sealing ring is directly loaded at the working chamber side with the pressure of the working chamber, without any other intermediate sealing elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Further advantages and advantageous embodiments of the invention can be extracted from the following description, the drawing and the claims. 
     One embodiment of the subject matter of the invention is shown in the drawing and explained in more detail in the following: 
     FIG. 1 shows a longitudinal section through a hydropneumatic pressure intensifier; 
     FIG. 2 shows each a section in the area of a radial seal of FIG. 1, in an enlarged scale 
     FIG. 3 shows a section in the area of a radial seal of FIG. 1, in an enlarged scale. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the hydropneumatic pressure intensifier shown in FIG. 1, a working piston  2  is disposed in a casing  1  in an axially displaceable and radially sealed manner and delimits therewith a working chamber  3  filled with hydraulic oil. A piston rod  4  is disposed on the working piston  2  and projects beyond the casing  1 . The working piston  2  further comprises an auxiliary piston  5  shaped as a collar which is radially sealed towards the tubular shell  6  and thereby separates two pneumatic chambers  7  and  8  which are supplied alternately with air pressure for the fast stroke of the working piston  2 . As soon as the air pressure in the pneumatic chamber  7  is sufficiently high and the pressure in the pneumatic chamber  8  is sufficiently low, the working piston  2  is pushed downward. Conversely, with corresponding high pressure in the pneumatic chamber  8  and reduced pressure in the pneumatic chamber  7 , the piston  2  is displaced again in the initial position shown. 
     The working chamber  3  is closed on the side facing away from the piston  2  by a casing part  9  to which a tubular shell  11  is attached which, in turn, is closed by a casing lid  12 . A storage piston  13  is disposed in the tubular shell in an axially movable fashion and delimits a storage chamber  14  along with the tubular shell  11  and casing part  9 . This storage chamber  14  is hydraulically connected to the working chamber  3  via a plunger bore  15  disposed in the casing part  9 . A drive piston  16  is also disposed in the tubular shell  11  in a radially sealed fashion for actuating a plunger piston  17  and is loaded by a storage spring  18  which is supported on the storage piston  13  on the side facing away from the drive piston  16  and thus determines the storage pressure present in the storage chamber  14  and serves as a restoring force for the drive piston  16 . The spring chamber  19  accommodating the spring  18  is pressure-relieved. A driving chamber  21  is disposed on the side of the drive piston  16  facing away from the spring chamber  19  and can be supplied, via a connection  22 , with pressurized air to drive the drive piston  16 . 
     The plunger piston  17  is axially displaceably guided in a central bore  23  of the storage piston  13 , wherein a radial seal  24  prevents hydraulic oil from passing from the storage chamber  14  into the spring chamber  19 . A radial seal  25  is disposed in an annular groove  26  in the surface region of the plunger piston  13  and seals towards the tubular shell  11  to also prevent hydraulic oil from reaching the spring chamber  19 . 
     During its driving motion in the direction of the arrow I, effected by the pressurized air in the driving chamber  21 , the plunger piston  17  penetrates the plunger bore  15  thereby separating the storage chamber  14  from the working chamber  3 . To achieve absolute separation, a radial seal  27  is disposed in the wall of the plunger bore  15 . (Shown in FIG. 2 in an enlarged scale). As soon as the plunger piston  17  is immersed in the working chamber  3 , the hydraulic fluid therein is displaced, thereby producing corresponding pressure intensification of the air pressure prevailing in the driving chamber  21  relative to the hydraulic pressure prevailing in the working chamber  3  in accordance with the cross-sectional ratio between the drive piston  16  and plunger piston  17 . Due to the relatively large cross-sectional surface of the working piston  2 , a correspondingly large actuating force for the piston rod  4  is produced in accordance with the hydraulic pressure in the working chamber  3 . To be able to maintain the pressure in the working chamber  3 , and to prevent hydraulic fluid from passing from the working chamber  3  into the pneumatic chamber  7 , a radial seal  29  is disposed in an annular groove  28  in the casing  1 . (Shown in FIG. 3 in an enlarged scale). The casing  1  further comprises two annular toroidal sealing rings  31  which seal towards the working piston  2 . 
     As shown in FIG. 2, the plunger bore  15  has a step  32  facing the working chamber  3  into which a support ring  33  is introduced and axially secured by a retaining ring  34 . The radial seal  27  is disposed between the support ring  33  and the end wall  35  of the step and consists of a sealing ring  36  and a tensioning ring  37  pressing the sealing ring  36  against the plunger piston  17 . The tensioning ring  37  is an annular toroidal sealing ring which assumes an oval shape in the installed position. The sealing ring  36  consists of special, relatively soft polyurethane with  58  Shore D. Viewed in cross-section, the circumference  38  extends parallel to the plunger piston  17 . The pressing force of the tensioning ring  37  produces a sealing surface  39  towards the surface area of the plunger piston  17 . A gradation  41  is provided in the sealing ring  36  facing the pressure chamber  3 , thereby pressing the sealing ring  36  against the end wall  35  when the working chamber  3  is at high pressure, wherein the associated element flank  42  abuts against the end wall  35  although it extends, in the pressure-less condition or at low pressures in the working chamber  3 , at an angle with respect to the end wall  35 . This deformation at high pressures effects increased pressing in the area of the sealing surface  39 . The sealing ring has a conical surface  43 , having a small wedge angle, between element flank  42  and sealing surface  39  which serves mainly to ensure that, with low storage pressure and largely undeformed sealing ring  36 , the plunger piston  17  can easily penetrate through the sealing ring  36  when passing through the plunger bore  15 . When the plunger piston  17  first contacts the conical surface  43 , the sealing ring  36  is displaced in the direction of the support ring  33  and largely without deformation of the sealing ring  36  since, at the beginning of immersion, the hydraulic pressure on both sides of the sealing ring is approximately equal. Subsequently, the pressure in the working chamber  3  rapidly increases to thereby move the sealing ring  36  into the position shown and then into the deformation position. During the return stroke of the plunger piston  17 , the pressure in the working chamber may be lower than that in the storage chamber  14  such that the sealing ring  36  is displaced into the position shown due to the frictional engagement between plunger piston  17  and sealing ring  36 . Also in this case, no substantial deformation occurs. 
     The radial seal  29 , disposed in the annular groove  28 , between working piston  2  and casing  1  of FIG. 3 is basically of the same construction. A tensioning ring  44  acts radially on a sealing ring  45 . The sealing ring  45  has a nearly rhombic cross-section with a gradation  46  facing the working chamber  3  and is supported, with a sealing surface  47 , on the surface area of the piston  2 . As soon as the pressure in the working chamber  3  is high enough, the element flank  48  of the sealing ring  45  is pressed against the end wall  49  of the annular groove  28  thereby increasing the pressing force of the sealing surface  47  and enhancing performance through the frictional engagement between piston  2  and sealing ring  45 . The sealing ring  45  is thereby deformed considerably due to its relatively soft material, wherein, in particular, the circumferential area  51 , parallel to the piston, is also displaced into a slightly conical disposition. As soon as the working piston  2  starts its return stroke and the pressure in the working chamber  3  is low or even at underpressure, the sealing ring  45  assumes its previous shape due to frictional engagement and is displaced in the direction of the working chamber  3  up to the other end wall of the annular groove  28 . The sealing ring  45  assumes its initial shape and is not deformed again, since the underpressure is too low. 
     All the features mentioned in the description, the following claims and shown in the drawing may be essential to the invention either individually or in any arbitrary combination. 
     LIST OF REFERENCE NUMERALS 
       1  casing 
       2  working piston 
       3  working chamber 
       4  piston rod 
       5  auxiliary piston 
       6  tubular shell 
       7  pneumatic chamber 
       8  pneumatic chamber 
       9  casing part 
     
       10 
     
       11  tubular shell 
       12  casing lid 
       13  storage piston 
       14  storage chamber 
       15  plunger bore 
       16  drive piston 
       17  plunger piston 
       18  storage spring 
       19  spring chamber 
     
       20 
     
       21  driving chamber 
       22  connection 
       23  central bore 
       24  radial seal 
       25  radial seal 
       26  annular groove 
       27  radial seal 
       28  annular groove 
       29  radial seal 
     
       30 
     
       31  annular toroidal sealing ring 
       32  step 
       33  support ring 
       34  retaining ring 
       35  end wall 
       36  sealing ring 
       37  tensioning ring 
       38  circumferential surface 
       39  sealing surface 
     
       40 
     
       41  gradation 
       42  element flank 
       43  cone surface 
       44  tensioning ring 
       45  sealing ring 
       46  gradation 
       47  sealing surface 
       48  element flank 
       49  end wall 
     
       50 
     
       51  circumferential surface 
     I driving direction