Abstract:
Fuel injector provided with a piezoelectric actuator, a valve activated by the piezoelectric actuator and regulating a fuel supply that flows in a working direction, and a mechanical transmission placed between the piezoelectric actuator and the valve; an expansion of the piezoelectric actuator displaces the valve in the working direction from a closed position to an open position in an opposite direction to that of the fuel outlet.

Description:
[0001]    The present invention relates to a fuel injector with piezoelectric actuator.  
         BACKGROUND OF THE INVENTION  
         [0002]    Fuel injectors with piezoelectric actuators have been available for many years now, i.e. fuel injectors provided with a valve that is displaced in a working direction between a closed position and an open position for activating a piezoelectric actuator.  
           [0003]    Known piezoelectric actuators, for example of the type described in patent application DE19909451, comprise a fixed frame and an actuator body made of piezoelectric material arranged in alignment with a working direction; the actuator body has a lower base, which is arranged close to the valve, is mechanically linked to the valve itself, and is free to slide with respect to the fixed frame in the working direction, and has an upper base, which is opposite the lower base and is linked to the fixed frame. In use, the actuator body is excited with an electrical field in order to cause it to expand in the working direction and therefore displace the valve in the working direction from the closed position to the open position, in a direction in accordance with the fuel outlet direction. However, such a structure requires that in order for the valve to move from the closed position to the open position, it is displaced towards the outside of the injector putting itself into a configuration that can cause the injector to be soiled, and therefore its functions impaired.  
         SUMMARY OF THE INVENTION  
         [0004]    The objective of the present invention is to produce a fuel injector with piezoelectric actuator, which does not have the drawbacks described above and, in particular, is easy and inexpensive to implement.  
           [0005]    According to the present invention, a fuel injector with piezoelectric actuator is produced in accordance with claim 1. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The present invention will now be described with reference to the attached drawings, which give a non-exhaustive illustration of a few embodiments of the invention, as follows:  
         [0007]    [0007]FIG. 1 is a diagrammatic view, in side elevation and partial section, of a fuel injector produced according to the present invention;  
         [0008]    [0008]FIG. 2 is a section, along the line II-II and with a few portions removed for clarity, of the injector in FIG. 1;  
         [0009]    [0009]FIG. 3 is a diagrammatic view from above and in section of a different embodiment of a fuel injector produced according to the present invention;  
         [0010]    [0010]FIG. 4 is a partial section along the line IV-IV of the injector in FIG. 4 [sic];  
         [0011]    [0011]FIG. 5 is a partial section along the line V-V of the injector in FIG. 4 [sic]; and  
         [0012]    [0012]FIG. 6 is a diagrammatic view, in side elevation and partial section, of another embodiment of a fuel injector produced according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    In FIGS. 1 and 2, the reference number  1  indicates a fuel injector as a whole, which comprises a container  2  substantially cylindrical in shape, having a central axis of symmetry  3  and a circular section; in correspondence with a lower end of the container  2  there is attached an injection pipe  4 , which is in the form of a cylindrical tube and ends in an injection port  5  regulated by a valve  6  that is moveable along the axis  3  between a closed position and an open position. Inside the container  2  there is arranged, coaxially with the axis  3 , a container  7 , which is cylindrical in shape, has a circular section and is provided with an internal chamber  8  that houses a piezoelectric actuator  9  capable of activating the valve  6 , i.e. capable of displacing the valve  6  between the aforementioned closed and open positions.  
         [0014]    The container  7  has a diameter, i.e. a dimension transverse to the axis  3 , that is smaller than the container  2  so as to constitute, between the outer lateral surface  10  of the container  7  and the inner lateral surface  11  of the container  2 , an annular channel  12  through which the fuel can flow freely in a direction parallel to the axis  3  until it reaches the mouth of the injection pipe  4 ; in particular, the fuel is supplied under pressure to an upper portion of the annular channel  12  through a supply pipe  13  ending inside the container  2 .  
         [0015]    The container  7  is integral with the container  2  by way of a contact zone  14  produced by welding or similar, so that the container  7  constitutes a fixed frame for the piezoelectric actuator  9 ; the piezoelectric actuator  9  comprises an actuator body  15  made of piezoelectric material, which is arranged in alignment with the axis  3 , is provided with a central hole  16  in alignment with the axis  3 , has a lower base  17  arranged close to the valve  6  and linked to the container  7 , and has an upper base  18  opposite the lower base  17 , which is free to slide with respect to the container  7  along the axis  3 .  
         [0016]    As illustrated in FIGS. 1 and 2, the actuator body  15  is defined by two components  19  made of piezoelectric material, physically separated from one another and arranged symmetrically about the central axis  3 . According to another embodiment, not illustrated, the actuator body  15  is constituted [by] a single tubular component made of piezoelectric material arranged coaxially to the axis  3 .  
         [0017]    Between the mobile upper base  18  and the valve  6  there is placed a mechanical transmission  20  provided with mobile equipment  21 , which is arranged in contact with the upper base  18  and is connected rigidly to the valve  6 ; in particular, the mobile equipment  21  comprises a plate  22 , which is transverse to the axis  3 , bears against the upper base  18  and is kept bearing against the upper base  18  itself by the pressure exerted along the axis  3  by a spring  23  compressed between the plate  22  and an upper portion  24  of the container  7 . A rod  25  is integral with the plate  22 , which rod is arranged inside the hole  16  along the axis  3  and is connected rigidly to the valve  6 .  
         [0018]    Between the plate  22  and the upper base  18  there is placed an annular body  26  provided with a spherical contact surface  27 , so as to make the plate  22  floating with respect to the base  18  in order to be free to perform small oscillations about an axis perpendicular to the axis  3 ; these small free oscillations are necessary in order to allow the plate  22  to absorb without deformation, and therefore without breaking due to fatigue, any expansion differences in the components  19  made of piezoelectric material.  
         [0019]    In order to drive the actuator body  15 , electric voltage is supplied to the actuator body  15  itself via an electric cable  28 , which passes through an appropriate open hole  29  in the upper portion  24  of the container  7 , through the central zone of the spring  23 , and through an open hole (not illustrated) in the plate  22 ; the electric cable  28  passes through the open hole (not illustrated) in the plate  22  with a certain amount of play to allow movement of the plate  22  along the axis  3  with respect to the electric cable  28 .  
         [0020]    In use, when the actuator body  15  is non-excited, i.e. is not subject to an electrical field, the valve  6  is in the aforementioned closed position in that it is pushed downwards along the axis  3  by the pressure exerted by the spring  23  and transmitted to the valve  6  by the plate  22  and the rod  25 .  
         [0021]    When the actuator body  15  is excited, i.e. is subject to an electrical field, the actuator body  15  itself expands along the axis  3 ; for the purposes of this expansion the lower base  17  stays still, since it is linked to the container  7 , while the upper base  18  performs an upward displacement along the axis  3 , which displacement is transmitted to the valve  6  by the plate  22  and the rod  25  and causes a displacement of the valve  6  along the axis  3  from the aforementioned closed position to the aforementioned open position.  
         [0022]    As stated above, it is clear that the valve  6  is displaced along the axis  3  from the aforementioned closed position to the aforementioned open position in an opposite direction V 1  to that V 2  in which fuel leaves the supply pipe  13 ; therefore, in order to move from the closed position to the open position, the valve  6  is displaced towards the inside of the supply pipe  13 , putting itself in a configuration that reduces the soiling, and therefore impairment of the functions, of the injector  1 .  
         [0023]    The internal chamber  8  of the container  7  is produced in such a way that it is isolated from the fuel; for this purpose the outer lateral surface  10  of the container  7  is continuous and has no opening, and the hole  30  in the lower portion  31  of the container  7 , to allow connection between the valve  6  and the rod  25 , is provided with a deformable holding component  32 .  
         [0024]    The container  7  is made of sheet metal with a high thermal transmission coefficient; furthermore, the container  7  is provided with exchange means  33  capable of increasing heat exchange between the fuel and the piezoelectric actuator  9 .  
         [0025]    As illustrated in FIGS. 1 and 2, the actuator body  15  has smaller dimensions than the dimensions of the chamber  8 , and the exchange means  33  comprise a plurality of transmission means  34  made of heat-conducting material, which have a shape and dimensions so as to be arranged between the actuator body  15  and an inner lateral surface  35  of the container  7  so as to increase heat transmission between the actuator body  15  and the container  7 . In particular, each transmission body  34  is arranged in contact with either the actuator body  15  or the inner lateral surface  35  of the container  7 .  
         [0026]    In an embodiment not illustrated, the exchange means  33  also comprise finning of the outer lateral surface  10  of the container  7  bathed in the fuel.  
         [0027]    As stated above, it is clear that the piezoelectric actuator  9  is arranged inside the chamber  8 , which is isolated from the fuel and has its outer lateral surface  10  bathed in the fuel itself; this configuration is particularly advantageous, since it makes it possible either to keep the piezoelectric actuator  9  isolated from the fuel, protecting the piezoelectric actuator  9  itself from the corrosive and soiling action of the fuel, or to ensure, in a simple and extremely economical manner, continuous cooling of the piezoelectric actuator  9  by transmitting the heat produced by the piezoelectric actuator  9  inside the chamber  8  to the fuel lapping the outer lateral surface  10 .  
         [0028]    Furthermore, the use of the transmission bodies  34  makes it possible either to increase heat transmission from the piezoelectric actuator  9  to the container  7 , or to ensure correct positioning of the piezoelectric actuator  9  inside the chamber  8 , since the transmission bodies  34  also have the function of filling the empty spaces inside the chamber  8  itself.  
         [0029]    In a preferred embodiment, the injector  1  is provided with at least one compensation component  36  having thermal expansion capable of compensating for the various heat expansions of the actuator body  15  and the mechanical transmission  20 ; in other words, through the combined effect of its own dimensions and thermal expansion coefficient (positive or negative), the compensation component  36  has heat expansion that cancels out all the various heat expansions of the actuator body  15  and the mechanical transmission  20 .  
         [0030]    The compensation component  36  can be integrated into the container  7 , can be placed between the container  7  and the actuator body  15  (as illustrated in FIG. 1), or can be integrated into the mobile equipment  21 .  
         [0031]    In a preferred embodiment, the compensator component  36  is made of metal with a low thermal expansion coefficient, particularly Invar.  
         [0032]    In FIGS. 3, 4 and  5  the reference number  101  indicates a fuel injector as a whole, which comprises a container  102  substantially cylindrical in shape, having a central axis of symmetry  103  and a circular section; in correspondence with a lower end of the container  102  there is attached an injection pipe  104 , which is in the form of a cylindrical tube and ends in an injection port  105  regulated by a valve  106  that is moveable along the axis  103  between a closed position and an open position. Inside the container  102  there is arranged, coaxially with the axis  103 , a container  107 , which is cylindrical in shape, has an elliptical section and is provided with an internal chamber  108  that houses a piezoelectric actuator  109  capable of activating the valve  106 , i.e. capable of displacing the valve  106  between the aforementioned closed and open positions.  
         [0033]    The container  107  has a dimension transverse to the axis  103  that is smaller than the container  102  so as to constitute, between the outer lateral surface  110  of the container  107  and the inner lateral surface  111  of the container  102 , an annular channel  112  through which the fuel can flow freely in a direction parallel to the axis  103  until it reaches the mouth of the injection pipe  104 ; in particular, the fuel is supplied under pressure to an upper portion of the annular channel  112  through a supply pipe  113  ending inside the container  102 .  
         [0034]    The container  107  is integral with the container  102  by way of a contact zone  114  produced by welding or similar, so that the container  107  constitutes a fixed frame for the piezoelectric actuator  109 ; the piezoelectric actuator  109  comprises an actuator body  115  made of piezoelectric material, which is arranged in alignment with the axis  103 , has a lower base  117  arranged close to the valve  106  and linked to the container  107 , and has an upper base  118  opposite the lower base  117  and free to slide with respect to the container  107  along the axis  103 . The actuator body  115  is constituted by a single component  119  made of piezoelectric material arranged coaxially to the central axis  103 .  
         [0035]    Between the mobile upper base  118  and the valve  106  there is placed a mechanical transmission  120  provided with mobile equipment  121 , which is arranged in contact with the upper base  117  and is connected rigidly to the valve  106 ; in particular, the mobile equipment  121  comprises a ring component  122  substantially rectangular in shape, which is moveable along the axis  3 , is arranged around the actuator body  115  and the container  107 , has an upper transverse side  123  arranged in contact with the upper base  118 , and a transverse side  124  opposite the transverse side  123  and connected rigidly to the valve  106 .  
         [0036]    In particular, the ring component  122  is arranged so as to bear against the upper base  118  by means of the interposition of a cylindrical body  125 , and is kept bearing against the upper base  118  itself by the pressure exerted along the axis  103  by a spring  126  compressed between the upper transverse side  123  and an upper portion  127  of the container  102 . The cylindrical body  125  is arranged so as to pass through a hole  128  in the upper portion  129  of the container  107  and is coupled to the hole  128  itself by means of a holding component  130 .  
         [0037]    In order to drive the actuator body  115 , electric voltage is supplied to the actuator body  115  itself via an electrical cable  131 , which passes through an appropriate open hole  132  of the container  102  and through an appropriate open hole  133  of the container  107 , which is coupled in a fluid-tight manner with the hole  132 . In use, when the actuator body  115  is non-excited, i.e. is not subject to an electrical field, the valve  106  is in the aforementioned closed position in that it is pushed downwards along the axis  103  by the pressure exerted by the spring  126  and transmitted to the valve  106  by the ring component  122 .  
         [0038]    When the actuator body  115  is excited, i.e. is subject to an electrical field, the actuator body  115  itself expands along the axis  103 ; for the purposes of this expansion the lower base  117  stays still, since it is linked to the container  107 , while the upper base  118  performs an upward displacement along the axis  103 , which displacement is transmitted to the valve  106  by the cylindrical body  125  and the ring component  122  and causes a displacement of the valve  106  along the axis  103  from the aforementioned closed position to the aforementioned open position.  
         [0039]    In FIG. 6, the reference number  201  indicates a fuel injector as a whole, which comprises a container  202  substantially cylindrical in shape, having a central axis of symmetry  203  and a circular section; in correspondence with a lower end of the container  202  there is attached an injection pipe  204 , which is in the form of a cylindrical tube and ends in an injection port  205  regulated by a valve  206  that is moveable along the axis  203  between a closed position and an open position. Inside the container  202  there is arranged, coaxially with the axis  203 , a container  207 , which is cylindrical in shape, has an circular section and is provided with an internal chamber  208  that houses a piezoelectric actuator  209  capable of activating the valve  206 , i.e. capable of displacing the valve  206  between the aforementioned closed and open positions.  
         [0040]    The container  207  has a diameter, i.e. a dimension transverse to the axis  203 , that is smaller than the container  202  so as to constitute, between the outer lateral surface  210  of the container  207  and the inner lateral surface  211  of the container  202 , an annular channel  212  through which the fuel can flow freely in a direction parallel to the axis  203  until it reaches the mouth of the injection pipe  204 ; in particular, the fuel is supplied under pressure to an upper portion of the annular channel  212  through a supply pipe  213  ending inside the container  202 .  
         [0041]    The container  207  is integral with the container  202  by way of a contact zone  214  produced by welding or similar, so that the container  207  constitutes a fixed frame for the piezoelectric actuator  209 ; the piezoelectric actuator  209  comprises an actuator body  215  made of piezoelectric material, which is arranged in alignment with the axis  203 , has a lower base  217  arranged close to the valve  206  and free to slide with respect to the container  207  along the axis  203 , and has an upper base  218  opposite the lower base  217  and linked to the container  207 . The actuator body  215  is constituted by a single component  219  made of piezoelectric material arranged coaxially to the central axis  203 .  
         [0042]    Between the mobile lower base  217  and the valve  206  there is placed a mechanical transmission  220 , which is capable of inverting the direction of displacement produced by the expansion of the piezoelectric actuator  209  along the axis  203  so that, to a first displacement produced by the expansion of the piezoelectric actuator  209  along the axis  203 , there corresponds a second displacement of the valve  206  along the axis  203  in the opposite direction to the first displacement.  
         [0043]    The mechanical transmission  220  is provided with mobile equipment  221 , which is linked to the lower base  217  and connected to the valve  206 , and is provided with a system  222  for inverting the rocking movement, which is capable to transforming a first displacement produced by the expansion of the piezoelectric actuator  209  along the axis  203  into a second displacement of the valve  206  along the axis  203  in the opposite direction to the first displacement.  
         [0044]    The system  222  for inverting movement comprises a pair of rockers  223  arranged symmetrically on either side of the axis  203 ; each rocker  223  is supported on a respective fixed fulcrum  224  constituted by a spherical body projecting from a lower portion  226  of the container  202 , and is provided with an arm  226  arranged in contact with the mobile equipment  221  and by an arm  227  arranged in contact with a counterpart component  228  integral with the valve  206 .  
         [0045]    The arms  226  and  227  of each rocker  223  bear against either the mobile equipment  221  or the counterpart component  228 , and are held in that condition by the pressure exerted along the axis  203  by a spring  229  compressed between the mobile equipment  221  and the counterpart component  228 .  
         [0046]    In particular, the mobile equipment  221  comprises a plate  230  transverse to the axis  203  and integral with the lower base  217 ; integral with the plate  230  is a cylindrical body  231 , which passes through an open hole  232  of a lower portion  233  of the container  207  with the interposition of a holding component  234 . The body  231  supports a fork  235 , with two symmetrical branches  236 , each of which is held so as to bear against the end of a respective arm  226 .  
         [0047]    In order to drive the actuator body  215 , electric voltage is supplied to the actuator body  215  itself via an electrical cable  237 .  
         [0048]    In use, when the actuator body  215  is non-excited, i.e. is not subject to an electrical field, the valve  206  is in the aforementioned closed position in that it is pushed downwards along the axis  203  by the pressure exerted by the spring  229 .  
         [0049]    When the actuator body  215  is excited, i.e. is subject to an electrical field, the actuator body  215  itself expands along the axis  203 ; for the purposes of this expansion the upper base  218  stays still, since it is linked to the container  207 , while the lower base  217  performs a downward displacement along the axis  203 , which displacement is transmitted to the valve  206  by the mechanical transmission  220  and causes a displacement of the valve  206  along the axis  203  from the aforementioned closed position to the aforementioned open position.  
         [0050]    On the basis of the dimensional relationship between the arms  226  and  227  of each rocker  223 , it is possible to impose a given transmission ratio less than, greater than or equal to unity on the mechanical transmission  220 ; in particular, as illustrated in FIG. 6, the mechanical transmission  220  has an amplification factor that amplifies the displacement produced by the expansion of the actuator body  15 .