Abstract:
An accumulator fuel injection apparatus is provided which may be employed in a common rail system for diesel engines. The fuel injection apparatus includes a pressure relief valve designed to relieve an unwanted rise in pressure of the fuel within an accumulator. The pressure relief valve includes a pressure pulsation minimizing mechanism designed to minimize pressure pulsations which are generated in a drain line and propagated to a valve mechanism of the pressure relief valve, causing a valve-opening pressure of the pressure relief valve to change. The pressure pulsation minimizing mechanism may be implemented by an orifice or a check valve.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Technical Field of the Invention  
           [0002]    The present invention relates generally to an accumulator fuel injection system for internal combustion engines, and more particularly to an improved structure of such a system designed to avoid a failure in operation of a pressure relief valve caused by pressure pulsations of a drain line.  
           [0003]    2 Background Art  
           [0004]    Accumulator fuel injection systems are known which supplies a high-pressure fuel to an accumulator of a common rail through a supply pump and distributes the fuel stored in the accumulator to a plurality of fuel injectors installed one in each cylinder of an internal combustion engine. The accumulator fuel injection systems usually have a pressure relief valve connected to the accumulator of the common rail. FIG. 7 shows an example of such a pressure relief valve.  
           [0005]    The pressure relief valve  100  works as a pressure limiter and consists essentially of a valve  101 , a cylindrical housing  102 , and a hollow screw  103 . The valve  101  is made up of a valve body having a valve hole  111  formed therein and a valve ball  105  selectively opening and closing the valve hole  111 .  
           [0006]    The housing  102  has an inlet side fuel hole  112 , a small-diameter hole  113 , and an outlet side fuel hole  114 . Within the inlet side fuel hole  112 , a spring guide  107  and a spring  108  are disposed which urge the valve ball  105  to close the valve hole  111  at all times. The hollow screw  103  has formed therein a longitudinal hole  115  communicating with the outlet side fuel hole  114  and a lateral hole  116  extending perpendicular to the longitudinal hole  115 . The lateral hole  116  communicates with a fuel passage  117  in a low-pressure pipe  109  (i.e., a drain line) through which the fuel is returned back to a fuel tank (not shown).  
           [0007]    A valve-opening pressure at which the ball valve  105  is to be opened is determined by a contact area between the valve body  104  and the valve ball  105  and a set load produced by the spring  108 . The valve-opening pressure may be adjusted by changing the thickness of shims  118  and  119 . The lateral hole  116  of the hollow screw  103  has a fuel-flowing sectional area substantially identical with that between the valve  101  and the longitudinal hole  115  of the hollow screw  103 .  
           [0008]    If some flow resistance exists in the low-pressure pipe  109 , it may cause pressure pulsations of the fuel returned from the supply pump or the fuel injector back to the fuel tank through the low-pressure pipe to be transmitted to the valve  101  of the pressure relief valve  100 , so that the valve ball  105  bounces within the valve body  104 , thereby resulting in a change in valve-opening pressure of the pressure relief valve  100 .  
         SUMMARY OF THE INVENTION  
         [0009]    It is therefore a principal object of the invention to avoid the disadvantages of the prior art.  
           [0010]    It is another object of the invention to provide an improved structure of an accumulator fuel injection system capable of avoiding a failure of a pressure relief valve caused by pressure pulsations occurring in a drain line.  
           [0011]    According to one aspect of the invention, there is provided an accumulator fuel injection apparatus which may be employed in a common rail system for diesel engines. The accumulator fuel injection apparatus comprises: (a) a high-pressure supply pump pumping fuel out of a fuel tank, the high-pressure supply pump pressuring and discharging the fuel; (b) an accumulator storing therein the fuel discharged from the high-pressure supply pump; (c) a fuel injector injecting the fuel stored in the accumulator into an internal combustion engine; (d) a high-pressure fuel line extending from the high-pressure supply pump to the fuel injector through the accumulator; (e) a relief valve having an inlet communicating with the high-pressure fuel line, an outlet, and a valve mechanism disposed between the inlet and the outlet, the valve mechanism being responsive to a rise in pressure of the fuel within the high-pressure fuel line beyond a given level to establish communication between the inlet and the outlet for relieving the rise in pressure of the fuel within the high-pressure fuel line; and (f) a pressure pulsation absorbing mechanism disposed between the valve mechanism of the relief valve and a pressure pulsation source existing downstream of the outlet of the relief valve. The pressure pulsation absorbing mechanism works to absorb a pressure pulsation propagated from the pressure pulsation source to the valve mechanism of the relief valve, thereby avoiding an undesirable change in a valve-opening pressure at which the valve mechanism opens the inlet to drain the fuel within the accumulator.  
           [0012]    In the preferred mode of the invention, the valve mechanism includes a valve body in which the inlet of the relief valve is formed and a valve member movable to open and close the inlet selectively. The relief valve includes a hollow cylindrical housing having a fuel hole formed between the inlet and the outlet. The pressure pulsation absorbing mechanism includes a hollow screw which is fitted in an open end of the housing as defining the outlet of the relief valve and has formed therein an orifice working to absorb the pressure pulsation to be propagated from the pressure pulsation source to the valve mechanism. A valve-urging mechanism is disposed in the fuel hole of the housing which urges the valve member to close the inlet constantly.  
           [0013]    The hollow screw includes a sleeve and a flange head. The sleeve is retained within the open end of the housing and has formed therein a longitudinal chamber communicating with the fuel hole of the housing through an end of the sleeve. The flange head is formed on an end of the sleeve opposite the housing.  
           [0014]    The orifice is implemented by a hole formed in the sleeve which extends perpendicular to the longitudinal chamber of the sleeve. The hole is smaller in diameter than the fuel hole of the housing and the longitudinal chamber of the sleeve.  
           [0015]    The relief valve communicates at the inlet thereof with the accumulator for relieving a rise in pressure of the fuel within the accumulator beyond the given level to keep the pressure in the accumulator constant.  
           [0016]    The relief valve may alternatively communicate at the inlet thereof with an outlet of the high-pressure supply pump for relieving a rise in pressure of the fuel flowing into the accumulator beyond the given level to keep the pressure of the fuel supplied to the accumulator constant.  
           [0017]    The relief valve may alternatively communicate at the inlet thereof with a portion of the high-pressure fuel line extending from the accumulator to the fuel injector for relieving a rise in pressure of the fuel supplied to the fuel injector beyond the given level to keep the pressure of the fuel supplied to the fuel injector constant.  
           [0018]    According to another aspect of the invention, there is provided an accumulator fuel injection apparatus which comprises: (a) a high-pressure supply pump pumping fuel out of a fuel tank, the high-pressure supply pump pressuring and discharging the fuel; (b) an accumulator storing therein the fuel discharged from the high-pressure supply pump; (c) a fuel injector injecting the fuel stored in the common rail into an internal combustion engine; (d) a high-pressure fuel line extending from the high-pressure supply pump to the fuel injector through the accumulator; (e) a relief valve having an inlet communicating with the high-pressure fuel line, an outlet, and a valve mechanism disposed between the inlet and the outlet, the valve mechanism being responsive to a rise in pressure of the fuel within the high-pressure fuel line beyond a given level to establish communication between the inlet and the outlet for relieving the rise in pressure of the fuel within the high-pressure fuel line; and (f) a check valve disposed between the valve mechanism of the relief valve and a pressure pulsation source existing downstream of the outlet of the relief valve. The check valve works to block transmission of a pressure pulsation from the pressure pulsation source to the valve mechanism of the relief valve.  
           [0019]    In the preferred mode of the invention, the valve mechanism includes a valve body in which the inlet of the relief valve is formed and a valve member movable to open and close the inlet selectively. The relief valve includes a hollow cylindrical housing having a fuel hole formed between the inlet and the outlet. A hollow screw is provided which is fitted in an open end of the housing as defining the outlet of the relief valve and has disposed therein the check valve. A valve-urging mechanism is disposed in the fuel hole of the housing which urges the valve member to close the inlet constantly.  
           [0020]    The check valve includes a valve body, a check valve member, and a check valve-urging mechanism. The valve body has an orifice formed downstream of the fuel hole of the housing of the relief valve in communication therewith. The check valve-urging mechanism urges the check valve member into constant engagement with the orifice of the valve body.  
           [0021]    The relief valve communicates at the inlet thereof with the accumulator for relieving a rise in pressure of the fuel within the accumulator beyond the given level to keep the pressure in the accumulator constant.  
           [0022]    The relief valve may alternatively communicate at the inlet thereof with an outlet of the high-pressure supply pump for relieving a rise in pressure of the fuel flowing into the accumulator beyond the given level to keep the pressure of the fuel supplied to the accumulator constant.  
           [0023]    The relief valve may alternatively communicate at the inlet thereof with a portion of the high-pressure fuel line extending from the accumulator to the fuel injector for relieving a rise in pressure of the fuel supplied to the fuel injector beyond the given level to keep the pressure of the fuel supplied to the fuel injector constant. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.  
         [0025]    In the drawings:  
         [0026]    [0026]FIG. 1 is a block diagram which shows an accumulator fuel injection system according to the invention;  
         [0027]    [0027]FIG. 2 is a sectional view which shows a pressure limiter according to the first embodiment of the invention which is designed to relieve a rise in fuel pressure within an accumulator;  
         [0028]    [0028]FIG. 3 is a schematic illustration which shows an internal structure of the pressure limiter of FIG. 2;  
         [0029]    [0029]FIG. 4 is a sectional view which shows a pressure limiter according to the second embodiment of the invention;  
         [0030]    [0030]FIG. 5 is a schematic illustration which shows an internal structure of the pressure limiter of FIG. 4;  
         [0031]    [0031]FIG. 6 is a block diagram which shows modifications of a pressure limiter; and  
         [0032]    [0032]FIG. 7 is a sectional view which shows a conventional pressure limiter installed in typical accumulator fuel injection systems. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    Referring to the drawings, wherein like reference numbers refer to like parts in several views, particularly to FIG. 1, there is shown an accumulator fuel injection system according to the first embodiment of the invention.  
         [0034]    The shown system is also called a common rail system and consists of a supply pump  2 , a common rail  3 , and a plurality of fuel injectors  4  (only one is shown for the brevity of illustration) each of which is connected to one of output ports of the common rail  3 . The supply pump  2  pumps fuel out of a fuel tank  1  and supplies the fuel to the common rail  3  at a given high pressure. The fuel stored in an accumulator provided in the common rail  3  is supplied to each of the fuel injectors  4 . Each of the fuel injectors  4  injects the high-pressure fuel into one of cylinders of an internal combustion engine  7  such as a diesel engine.  
         [0035]    The supply pump  2  has disposed therein a feed pump working as a low-pressure pump which is rotated in synchronism with rotation of a crankshaft of the engine  7  to pump the fuel out of the fuel tank  1 . The supply pump  2  pressurizes the fuel pumped by the feed pump and supplies it to the common rail  3  through a fuel pipe. The supply pump  2  works to control the quantity of fuel to be sent to the common rail  3  to adjust the internal pressure of the accumulator in the common rail  3  (i.e., a common rail pressure).  
         [0036]    The common rail  3  is one of surge tanks and designed to store therein the fuel under high pressure. The common rail  3 , as described above, connects with each of the fuel injectors  4  through a fuel pipe. The fuel injectors  4  are installed in a cylinder block of the diesel engine  7 , one for each cylinder, and supply a spray of fuel into combustion chambers at a high pressure. A pressure limiter  6  is installed in a low-pressure pipe  5  (i.e., a drain line) through which the fuel is returned from the supply pump  2 , the common rail  3 , and the fuel injectors  4  back to the fuel tank  1 . The pressure limiter  6  works as a pressure relief valve which relieves a fuel pressure in the accumulator of the common rail  3  beyond a specified limit to keep it at all the time. In this embodiment, the pressure limiter  6  is disposed between the accumulator of the common rail  3  and a fuel passage  10  of the low-pressure pipe  5 , but may alternatively be installed between the low-pressure pipe  5  and an outlet of the supply pump  2  to keep the fuel pressure to be supplied to the common rail  3  at a constant level.  
         [0037]    The pressure limiter  6  consists, as shown in FIGS. 2 and 3, of a valve  11  connected to the accumulator of the common rail  3  in a liquid tight seal, a hollow cylindrical housing  12  joined to a downstream side of the valve  11  in a liquid tight seal, a spring  13  disposed within the housing  12 , a spring guide  14  retaining an end of the spring  13 , and a hollow screw  16  fitted in an opened end  15  (i.e., an outlet) of the housing  12 .  
         [0038]    The valve  1   1  is made up of a valve body  21  joined to an outlet pipe (not shown) of the common rail  3  in a liquid tight seal and a valve ball  23 . The valve body  21  has formed in an end surface thereof a valve hole  22  communicating with the accumulator of the common rail  3  through the outlet pipe. The valve body  21  has formed therein a valve chamber within which the valve ball  23  is disposed for selectively opening and closing the valve hole  22 . A valve seat  24  is formed on an inner wall of the valve chamber of the valve body  2   1 . The valve ball  23  rests on the valve seat  24  to close the valve hole  22 . The valve body  21  also has a sliding chamber  25  formed downstream of the valve chamber which supports the spring guide  14  slidably.  
         [0039]    The housing  12  is made of a metallic hollow cylinder and has fitted therein annular shims  17  and  18  for achieving fine adjustment of a valve-opening pressure. The housing  12  defines therein an inlet side fuel hole  31 , a fuel hole  34  smaller in diameter than the inlet side fuel hole  31 , and an outlet side fuel hole  35 . The shims  17  and  18  have fuel holes  32  and  33  formed therein, respectively, which are smaller in diameter than the inlet side fuel hole  31 . The housing  12  has formed in an outer surface of an end thereof an external thread  36  which is fitted in a limiter mount (not shown) of the common rail  3 . The housing  12  also has an internal thread  67  formed in the outlet side fuel hole  35  with which the hollow screw  16  engages.  
         [0040]    The spring  13  is a coil spring disposed within the inlet side fuel hole  31  of the housing  12  to produce a set load urging the valve ball  23  into constant engagement with the valve seat  24  to close the valve hole  22  of the valve body  21 . The spring  13  is retained at an end thereof on a rear end surface of a large-diameter portion  42  of the spring guide  14  and at the other end on a front surface of the shim  17 . The seat diameter of the valve ball  23  (i.e., a contact area between the valve body  21  and the valve ball  23 ) and the set load of the spring  13  defines the valve-opening pressure acting on the valve ball  23  at which the valve hole  22  of the pressure limiter  6  is to be opened when the fuel pressure within the common rail  3  exceeds a specified limit. Fine adjustment of the valve-opening pressure may be accomplished by changing the thickness of the shim  17  and/or the shim  18 .  
         [0041]    The spring guide  14  is disposed within the inlet side fuel hole  31  of the housing  12  and the sliding chamber  25  of the valve body  21 . The spring guide  14  is made up of a small-diameter portion  41  working as a cylindrical slider, the large-diameter portion  42 , and a small-diameter portion  43  working as a spring-retaining boss. The small-diameter portion  41  is fitted to be slidable within the sliding chamber  25  of the valve body  21 . The large-diameter portion  42  is fitted to be slidable within the inlet side fuel hole  31 . The small-diameter portion  43  projects from the large-diameter portion  42  opposite the small-diameter portion  41 .  
         [0042]    The small-diameter portion  41  of the spring guide  14  has formed on an outer peripheral surface thereof two flat areas  44  which define fuel passages between themselves and an inner wall of the sliding chamber  25  of the valve body  21  which establish fluid communications between the inlet side fuel hole  31  and the valve hole  22  when the valve ball  23  and the spring guide  14  are moved away from the valve seat  24  over a preselected distance. The flat areas  44  are formed by grinding diametrically opposed portions of the outer peripheral surface of the small-diameter portion  41 . The large-diameter portion  42  is disposed within the housing  12  and defines an annular gap between the outer periphery of the large-diameter portion  42  and the inner wall of the inlet side fuel hole  31  which serves as a fuel passage communicating with the valve hole  22 .  
         [0043]    The hollow screw  16  functions to absorb pulsation of fuel pressure and is installed downstream of the valve  11  and the outlet side fuel hole  35  of the housing  12 . The hollow screw  16  closes the open end  15  of the housing  12  and consists of a sleeve  52  and a flanged head  53 . The sleeve  52  has formed therein an external thread  51  engaging the internal thread  67  of the housing  12 . The head  53  which is hexagonal and greater in diameter than the sleeve  52  is formed on an end of the sleeve  52 .  
         [0044]    The sleeve  52  has a longitudinal chamber  54  and an orifice  56  formed therein. The chamber  54  extends along a longitudinal center line of the sleeve  52  and communicates with the outlet side fuel hole  35  of the housing  12 . The orifice  56  extends perpendicular to the chamber  54  and establishes fluid communication between the chamber  54  and the fuel passage  10  of the low-pressure pipe  5 . The orifice  56  is smaller in diameter (i.e., a fuel flow sectional area) than the inlet side fuel hole  31 , the fuel hole  34 , the outlet side fuel hole  35 , and the chamber  54  and works to absorb the pulsation of fuel pressure transmitted from a pulsation source to the valve  11  and the spring guide  14 . Seal washers  57  and  58  are installed between the end of the housing  12  and the low-pressure pipe  5  and between the screw head  53  and the low-pressure pipe  5 , respectively, to seal gaps formed among the sleeve  52 , the low-pressure pipe  5 , and the housing  12 .  
         [0045]    In operation, when the fuel pressure in the accumulator of the common rail  3  exceeds the valve-opening pressure of the pressure limiter  6 , it will cause the valve ball  23  to be moved out of engagement with the valve seat  24  of the valve body  24  against the spring pressure produced by the spring  13 , so that the valve hole  22  is opened. This causes the fuel stored within the common rail  3  to flow from the valve hole  22  to the orifice  56  through the sliding chamber  25 , the inlet side fuel hole  31 , the fuel hole  34 , the outlet side fuel hole  35  of the housing  12 , and the longitudinal chamber  35  of the hollow screw  16  and back to the fuel tank  1  through the fuel passage  10  of the low-pressure pipe  5 . Specifically, the pressure limiter  6  works to relieve an excess pressure of the fuel stored in the accumulator of the common rail  3 , thereby keeping the fuel pressure within the common rail  3  at a desired level.  
         [0046]    Usually, when the fuel is discharged from the supply pump  2  or the injectors  4  and returned back to the fuel tank  1  through the low-pressure pipe  5 , pressure pulsations are generated which may be propagated to the hollow screw  16  of the pressure limiter  6 . If the pressure pulsations are transmitted to the spring guide  14  or the valve  11  of the pressure limiter  6 , it will cause the valve ball  23  to bound in the valve body  21 , which may result in an undesirable change in valve-opening pressure of the pressure limiter  6 . The pressure limiter  6  of this embodiment, however, has the orifice  56  formed between the valve  11  and the low-pressure pipe  5  which works to absorb or block the transmission of the pressure pulsations from the low-pressure pipe  5  to the spring guide  14  and the valve  11 , thereby avoiding the undesirable change in valve-opening pressure of the pressure limiter  6 .  
         [0047]    The orifice  56  is formed in the sleeve  52  of the hollow screw  16 , but may alternatively be provided in an end portion of the fuel passage  10  of the low-pressure pipe  5  connecting with the hollow screw  16  or the housing  12 . The orifice  56  may also be formed in the sleeve  52  longitudinally.  
         [0048]    [0048]FIGS. 4 and 5 show a pressure limiter  6  according to the second embodiment of the invention. The same reference numbers as employed in the first embodiment will refer to the same parts, and explanation thereof in detail will be omitted here.  
         [0049]    The hollow screw  16 , like the first embodiment, consists of the sleeve  52  and the screw head  53 . The sleeve  52  has formed therein the longitudinal chamber  54  within which a check valve  70  is disposed for blocking transmission of pressure pulsations from the fuel passage  10  of the low-pressure pipe  5  to the spring guide  14  and the valve  11 . The check valve  70  consists of an orifice  71 , a ball  72 , and a coil spring  74 . The orifice  71  is formed in the end of the sleeve  52  and establishes fluid communication between the inlet side fuel hole  31  and the fuel passage  10  of the low-pressure pipe  5 . The orifice  71  is smaller in diameter than the inlet side fuel hole  31 , the fuel hole  34 , the outlet side fuel hole  35 , and the longitudinal chamber  54 . The spring  74  is disposed within the longitudinal chamber  54  and urges the ball  72  into constant engagement with a valve seat  73  formed on an inner wall of the sleeve  52  to close the orifice  71 .  
         [0050]    The hollow screw  16  also includes an adjustor screw  75  which is fitted in a threaded hole formed in an end of the bolt head  53  in alignment with the spring  74  and works to adjust the pressure produced by the spring  74  which defines a valve-opening pressure at which the ball  72  is to be moved away from the valve seat  73  to open the orifice  71 . The sleeve  52  also has formed therein a radial hole  86  which traverses the longitudinal chamber  54  to establish fluid communication between the fuel passage  10  and the longitudinal chamber  54 .  
         [0051]    In operation, when the fuel pressure in the accumulator of the common rail  3  exceeds the valve-opening pressure of the pressure limiter  6 , it will cause the valve ball  23  to be moved out of engagement with the valve seat  24  of the valve body  24  against the spring pressure produced by the spring  13 , so that the valve hole  22  is opened. This causes the fuel stored within the common rail  3  to flow from the valve hole  22  to the outlet side fuel hole  35  through the sliding chamber  25 , the inlet side fuel hole  31 , and the fuel hole  34 . When the fuel pressure in the outlet side fuel hole  35  exceeds the valve-opening pressure of the check valve  70  set by the spring  74 , it will cause the ball  72  to be moved away from the valve seat  73  against the valve-opening pressure, thereby opening the orifice  71 . The fuel within the outlets side fuel hole  35 , thus, flows into the longitudinal chamber  54  of the hollow screw  16  and is discharged to the fuel passage  10  from the radial hole  86 , thereby keeping the fuel pressure within the common rail  3  at a desired level.  
         [0052]    When pressure pulsations are generated in the low-pressure pipe  5  and enter the pressure limiter  6 , the check valve  70  works to block the propagation of the pressure pulsations to the spring guide  14  and the valve  11 , thereby avoiding, like the first embodiment, an undesirable change in valve-opening pressure of the pressure limiter  6 .  
         [0053]    The pressure limiter  6  in each of the first and second embodiments may also be used with a common rail fuel injection system in which the fuel stored in a common rail is injected to a diesel engine using a single fuel injector. In this case, instead of the common rail  3 , a high-pressure pipe working as an accumulator may alternatively be installed between the supply pump  2  and the injector.  
         [0054]    The supply pump  2  used in the above embodiments is a distributor type pump designed to distribute fuel to a plurality of cylinders of the engine using a single or two pairs of plungers or less, but may alternatively be implemented by an in-line pump which has as many plungers as the cylinders of the engine and supplies the pressurized fuel through each of the plungers every turn of a cam shaft.  
         [0055]    The valve ball  23  and the spring guide  14  may alternatively be made of a one-piece member. The housing  12  and the valve body  21  may also be of one-piece construction. Instead of the spring  13 , an air cushion, a rubber, or an elastic plate may alternatively be used to urge the valve ball  23  into constant engagement with the valve seat  24  through the spring guide  14 .  
         [0056]    The check valve  70  is installed in the sleeve  52  of the hollow screw  16 , but may alternatively be provided in an end portion of the fuel passage  10  of the low-pressure pipe  5  connecting with the hollow screw  16  or the housing  12 .  
         [0057]    The pressure limiter  6  in each of the first and second embodiments is joined directly to the accumulator in the common rail  3 , but however, may alternatively be installed, as shown in FIG. 6, between an outlet of the supply pump  2  and the low-pressure pipe  5 . In this case, the inlet (i.e., the valve hole  22 ) of the pressure limiter may be connected to a downstream side of a check valve  2   a  of the supply pump  2  or an upstream side of the check valve  2   a , as indicated by a broken line, to keep the pressure of the fuel flowing into the common rail  3  at a desired level. Further, the pressure limiter  6  may alternatively be installed, as indicated by a broken line on the right side of the drawing, between a portion of a high-pressure fuel line  90  between the outlet of the common rail  3  and the inlet of the fuel injector  4  to keep the pressure of the fuel supplied to the fuel injector  4  at a desired level.  
         [0058]    While the present invention has been disclosed in terms of the preferred embodiments in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments witch can be embodied without departing from the principle of the invention as set forth in the appended claims.