Abstract:
A high pressure fluid injection circuit wherein a fluid which may generate pressure waves when flowing therein and generate pressure peaks which may damage the high pressure fluid circuit. To reduce both these pressure waves and the pressure peaks, a pressure wave absorber ( 14 ) including a cylinder, a rod ( 22 ) and a plurality of plates ( 23 ) is connected to the circuit. The plates ( 23 ) are positioned and made in such a way to provide a narrow passageway inside the cylinder that changes a regular movement of the fluid to an irregular movement such that the pressure peaks are reduced by 50% of their initial value.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a high pressure fluid injection circuit. The object of the invention is to enhance the performance of the high pressure fluid injection circuit. The invention is more particularly designed for use in the automobile field but can also be applied in other fields. In the automobile field, this circuit can be used to inject a fluid at high pressure into at least one cylinder of an engine. In this case, the fluid is a fuel.  
         [0002]     A fluid injection circuit comprises a fluid reservoir, a hydraulic pump for fluid injection at low pressure (approximately 10 bars, i.e. approximately 1,000,000 pascals) and at least one pump-injector. The reservoir, the injection pump and the pump-injector are linked by pipes enabling the fluid to flow from the reservoir via the injection pump to the pump-injector and then to continue flowing so that surplus fluid returns to the reservoir. The pump draws in a fluid obtained from the reservoir and increases the pressure of this fluid to a low pressure. In one example, this low pressure is at a pressure of 10 bars. This fluid under low pressure is then expelled from the injection pump through the pipes. A distributor distributes this fluid under low pressure among the different pump-injectors. Each pump-injector then increases the pressure to a maximum of 300 bars and injects it into its own cylinder at a maximum pressure of 2050 bars after a solenoid valve has opened.  
         [0003]     An injection circuit comprising these pump-injectors capable of delivering a fluid at high pressure has the advantage of improved performance by comparison with a circuit comprising an injection pump delivering a lower injection pressure. In one example, a high injection pressure may be approximately 2000 bars. However, at high pressure the pump or pipes of the circuit may be damaged, and the performance of this kind of circuit decreases significantly.  
         [0004]     In the invention, the cause of this deterioration was investigated, and, in particular, an attempt was made to strengthen the various elements of the circuit. This was unsuccessful or, to express it another way, costly. The idea then arose of detecting the transitory temporal variation of the pressure in the circuit during its operation.  
         [0005]     It was then found that the delivery of a fluid at high pressure could cause the formation of a pressure wave. This pressure wave is due to a rapid opening and closing of the solenoid valve of the pump-injector. After the rapid closing of the solenoid valve, a pressure wave may be generated and may be propagated through the fluid, in the opposite direction to the flow of the fluid.  
         [0006]     This pressure wave may also cause the formation of pressure peaks. If these pressure peaks are too high, they may damage elements of the injection circuit, thus decreasing the performance of the injection circuit at high pressure. For example, pressure peaks of 60 bars may be produced when pressure is delivered at 2,000 bars, and may damage the elements of the injection circuit.  
         [0007]     In the prior art, fluid injection circuits were not affected by this pressure wave, since the fluid was pressurized at low pressure and since the elements of the circuits were strong enough not to be damaged by these pressure waves.  
         [0008]     To limit the damage to elements of an injection circuit for pressurized fluid, particularly one for fluid at high pressure, the pipes could have been made wider and thicker. However, this solution would have made such a fluid injection circuit too bulky for use in a vehicle. In any case, it would not have resolved the problem of the pump.  
       SUMMARY OF THE INVENTION  
       [0009]     To attenuate these pressure waves which may potentially generate pressure peaks, the invention proposes a pressure wave absorber interposed in the pipes of the high pressure fluid injection circuit. In one example, this absorber is made in such a way that it forces the fluid to follow several different paths of different lengths. The direction of the fluid is such that the fluid must pass through these narrow passage sections, so that the movement of the fluid is accelerated. The acceleration of this fluid movement creates turbulence. This turbulence disrupts the regular movement of the fluid, thus attenuating the pressure wave and the consequent pressure peaks.  
         [0010]     In this example, the absorber comprises a cylinder within which a rod is positioned. This rod is provided with plates which delimit open compartments. The fluid flows through these compartments via narrow passage sections.  
         [0011]     The object of the invention is therefore a high pressure fluid injection circuit comprising a low pressure fluid injection pump linked by pipes to a reservoir on the one hand, and to at least one pump-injector, designed to deliver the fluid at high pressure, on the other hand, characterized in that it comprises a pressure wave absorber interposed between an output of the pump leading to the pump-injector and the pump-injector itself.  
         [0012]     The invention will be more clearly understood from the following description and the accompanying figures. These figures are provided for guidance only and do not limit the invention in any way. 
     
    
     BRIEF DESCRIPTION OF THE INVENTION  
       [0013]      FIG. 1  is a schematic representation of a high pressure fluid injection circuit, according to the invention;  
         [0014]      FIG. 2  is a graphic representation of at least one operating command of a solenoid valve as a function of time, according to the invention;  
         [0015]      FIG. 3  is a longitudinal section through a pressure wave absorber according to the invention;  
         [0016]      FIG. 4  is a transverse section through a pressure wave absorber according to the invention;  
         [0017]      FIG. 5  is a three-dimensional representation of a wave absorber according to the invention;  
         [0018]      FIG. 6  is a schematic representation of a pressure wave as a function of the distance traveled, according to the invention; and  
         [0019]      FIG. 7  is a graphic representation of a pressure wave as a function of time. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]      FIG. 1  shows a high pressure fluid injection circuit  1  comprising a low pressure fluid injection pump  2  linked by pipes  3 . 1  and  3  to a reservoir  6  containing fluid  5  and to at least one pump-injector  8  respectively, according to the invention.  
         [0021]     The pump  2  is incorporated in a housing  4 . Fluid is supplied to this circuit in the following way. The pump  2  draws in the fluid  5  contained in the reservoir  6  through the pipe  3 . 1 . In one example, the reservoir may contain fuel such as diesel oil. Having been pressurized in the pump  2 , the fluid  5  is sent through pipes  3 . In one example, the low pressure pump  2  increases the pressure of the fluid by approximately 10 bars. In this case, the pipes  3  comprise a distributor  7  linked to at least one pump-injector  8 . In one example, the distributor  7  is linked to four pump-injectors  8 . The pump-injector  8  is linked to a cylinder  9  of an engine (not shown) within which a piston  9 . 1  slides. The pump-injector is designed to expel a volume of fluid at high pressure through an aperture (not shown) which is blocked in the resting state by an injector needle (not shown). In one example, the pressure of the fluid at the moment of its expulsion from the pump-injector is 2050 bars. The pump-injector  8  is also provided with a solenoid valve  10 , which is made to open  11  and close  12  by a command Oi ( FIG. 2 ). For example, the solenoid valve  10  of each of the pump-injectors  8  is opened  11  and closed  12  by an operating command O 1  to O 4  ( FIGS. 1 and 2 ). The solenoid valve thus enables each pump-injector to be supplied intermittently with fluid. In response to this command, the solenoid valve  10  can be in the opening state  11  or the closing state  12 . The opening can be predetermined during a transitory period  13  to allow fluid to be pre-injected into the pump-injector. The fluid is then compressed inside the pump-injector to 300 bars. At 300 bars, the injector needle is displaced from the aperture of the pump-injector. The fluid is then expelled into the engine cylinder at a pressure of approximately 2050 bars, since the amount of fuel entering the pump-injector is greater than the quantity which can escape through the aperture of the pump-injector.  
         [0022]     Fluid is returned toward the reservoir in the following way. The fluid flows in the opposite direction to that followed by the fluid for the supply of the circuit when the solenoid valve reopens. The excess fluid required for an effective pressure rise inside the pump-injector then returns to the reservoir through pipes (not shown) which are different from the pipes  3 .  
         [0023]     According to the invention, the high pressure fluid injection circuit  1  comprises a pressure wave absorber  14 . The absorber  14  is interposed between an output of the pump  2  leading to the pump-injector  8  and the pump-injector  8  ( FIG. 1 ). More precisely, and preferably, the absorber  14  is positioned inside the housing  4  of the pump  2 , at the location of the output of the pump leading to the pump-injector  8 . However, it could be positioned at another location along the pipes  3 , preferably upstream of the distributor  7 . In one example, this absorber  14  comprises a cylinder  15  ( FIG. 4 ) with a solid outer part  16  and a hollow central part  17 . A transverse section through the absorber shows a cross section  18  of the central part  17  of the cylinder  15  ( FIG. 4 ). A perimeter  19 , a surface  20  and a centre  21  can be distinguished in this cross section  18 . In a preferred example, the cylinder  15  is circular ( FIG. 4 ), but this cylinder  15  can also be rectangular.  
         [0024]     A rod  22  is inserted at the location of the center  21  of this central part  17  ( FIGS. 3 and 5 ). This rod  22  has at least one plate  23 . The transverse section through the absorber  14  also shows a cross section  24  of the plate  23  ( FIG. 4 ). A perimeter  25  and a surface  26  can be identified in this cross section  24 . The rod  22  has a plurality of plates  23  ( FIGS. 3, 4  and  5 ). In  FIG. 3  it is possible to visualize a plate  23  in broken lines located below the plate  23  present in the plane of the drawing. In the preferred example, the rod  22  has six plates  23  and is sixty millimeters long ( FIGS. 3 and 5 ). The plates  23  are positioned on the rod  22  in succession and are spaced apart by the same distance  27 . The plates  23  delimit compartments  28  inside the central part  17  of the cylinder  15 . In the preferred example, the plates  23  are in the shape of a disk cut along a chord, and delimit five compartments  28  ( FIGS. 3, 4  and  5 ).  
         [0025]     The plates  23  are identical and the perpendiculars to their chords are oriented at an angle  29  differing from one plate to the next with respect to an axis  30  defined by the rod  22  and passing through the center  21 . Preferably, the plates  23  are oriented alternately at an angle of 180° to each other with respect to the axis  30  of the rod  22  ( FIGS. 4 and 5 ). The plates  23  are positioned perpendicularly to the axis  30  ( FIG. 3 ). In another example, it would be possible to provide an orientation at an angle other than 180°, thus producing a helical progression of these orientations.  
         [0026]     According to the invention, the surface  26  of the plate  23  is equal to at least half of the surface  20  of the section  18  of the central part  17  of the cylinder  15 . Additionally, the perimeter  25  of the plate  23  partially follows the perimeter  19  of the central part  17  of the section  18  of the cylinder  15  ( FIG. 4 ).  
         [0027]     The perimeter  25  of the plate  23  has a portion  31  and a portion  32 . The portion  31  follows the perimeter  19  of the cylinder  15 , whereas the portion  32  does not follow it ( FIG. 4 ).  
         [0028]     The perimeter  19  of the cylinder  15  also has a portion  33  which follows the plate  23  and a portion  34  which does not follow it. Thus the portion  32  of the plate  23  and the portion  34  of the cylinder  15  delimit an opening  35  which is lateral with respect to the axis  30  formed by the rod  22  ( FIG. 4 ). Because of the presence of this lateral opening  35  in each plate  23 , the compartments  28  are open inside the cylinder  15  ( FIG. 3 ).  
         [0029]     The plate  23  is made in such a way that, along an axis  38  perpendicular to the axis  30  formed by the rod  22 , a point on the portion  31  of the perimeter  25  of the plate  23  is separated from another point on the portion  32  of the perimeter  25  by a distance  36 .  
         [0030]     Additionally, a point on the portion  32  is separated from a point on the portion  34  along the axis  38  perpendicular to the axis  30  of the rod  22  by a distance  37 . In the preferred example, the distance  36  is 4.5 millimeters and the distance  37  is 1.5 millimeters, giving a diameter of 6 millimeters plus or minus 20%. Thus a good compromise is achieved between size and robustness.  
         [0031]     When the fluid  5  at low pressure is injected into the pipes  3 , the fluid  5  undergoes a slight pressure drop during its flow ( FIG. 6 ). This slight pressure drop, or loss of head, is represented by a linear curve  39  decreasing as a function of the distance covered within the pipes  3 . The moving fluid  5  strikes the solenoid valve  10  at the moment when the valve is closing. The fluid  5  is injected into the cylinder  9  by the rapid-opening and closing of the solenoid valve  10 . The rapid closing  12  of the solenoid valve  10  operated by the command O creates a pressure wave  40  ( FIG. 6 ). This wave  40  moves in the opposite direction to the movement of the fluid  5  when the circuit is supplied with fluid. This movement in the opposite direction takes place from the pump-injector  8  to the location of the pump  2 .  
         [0032]     This pressure wave  40  moves in space and in time ( FIGS. 6 and 7 ). This pressure wave  40  emits at least one pressure peak  41  following the closing of the solenoid valve  10  ( FIG. 7 ). For example,  FIG. 7  shows four pressure peaks  41  of a pressure wave  40  caused by the successive opening  11  and closing  12  of the solenoid valve  10  of each of the four fluid pump-injectors  8 . These pressure peaks  41  can reach a pressure of 60 bars.  
         [0033]     The lateral openings  35  and the arrangement of the plates  23  with one above the next create restrictions and enlargements of section inside the cylinder  15  of the absorber  14 . These restrictions and enlargements of sections disrupt the rectilinear trajectory of the fluid. The reverse wave must pass through the same areas.  
         [0034]     The fluid  5  leaving the pump  2  enters the inside of the absorber  14 . The trajectory  42  of the fluid inside the cylinder  15  has a sinusoidal shape ( FIG. 3 ). At the opposite end to that at which the fluid  5  enters, the pressure wave  40  penetrates into the cylinder  15  and describes an identical trajectory  43 , shown in broken lines in  FIG. 3 . The pressurized fluid  5  creates turbulence inside the compartments  28  after its passage through the lateral openings  35 , thus significantly attenuating the pressure peaks of the pressure wave to as little as 50% of their maximum value.