A high pressure hydraulic system including a sensor for non-invasive diagnostics

Abstract

A high-pressure hydraulic system comprises: a hydraulic chamber (34) containing a pressurized fluid; a wall (50) surrounding at least a portion of the hydraulic chamber (34) and including an integrated diaphragm (120); a piezoelectric sensor (70) isolated from the pressurized fluid contained in the hydraulic chamber (34) by the diaphragm (120); and an elastic element (102) arranged to apply an elastic force to the piezoelectric sensor (70) between the piezoelectric sensor (70) and the diaphragm (120), wherein deformation of the diaphragm (120) caused by a change in the pressure of the fluid contained in the hydraulic chamber (34) results in a change in the elastic force applied by the elastic element (102) to the piezoelectric sensor (70).

Description

Technical Field

[0001] The present invention relates generally to high pressure hydraulic systems and to a high pressure hydraulic system including a sensor for non-intrusive diagnosis of the operation of the system.

[0002] In particular, the invention has been developed with regard to applications to diagnostics of fuel injection systems for large diesel engines and large dual fuel engines, for example for large naval engines.In the following description reference will be made to this particular field of use, however without loss of generality. Background Art

[0003] In the field of hydraulic systems, in particular in the field of high-pressure injection systems for diesel engines, there is increasing interest in the development of diagnostic systems capable of acquiring important data for diagnosing the operation of the complex systems.

[0004] This has prompted the development of low-cost sensors that can measure characteristic operating parameters such as hydraulic pressure.

[0005] In the field of fuel injection systems, sensors for measuring force and / or pressure and in particular configured to be fixed to a fuel injector for identifying the closing time of an injector needle have been proposed. For example, EP3001167 describes a sensor assembly comprising at least one sensor element of a piezoelectric material having two end faces positioned parallel to each other and each end face having an associated electrode, wherein the electrodes electrically insulated from each other are conceived to be in contact with the sensor element.

[0006] Hydraulic systems have also been proposed in which sensors are integrated in the components to be monitored (eg EP3026254 and EP3034855).

[0007] In common rail fuel injectors, the sensor is usually placed in the area adjacent to the orifice that carries fluid from the pressurized accumulator to the fuel distribution chamber (positioned upstream of the injector needle sealing area). This allows the operating data of the injector to be detected instead of that of its control valve, since the disturbances it generates during operation are not propagated to the line.

[0008] The ideal location for a pressure sensor for diagnostic purposes would be close to the injector control chamber. However, due to the small size of this area and the high pressure of the fluid in the control chamber, small sensor elements must be used, which are therefore limited in the loads and deformations they can withstand. In summary, the problem is that deformations caused by very high pressures (in the order of kilobars) must be managed in a small space.

[0009] US2014027534A1 describes a fuel injector for a common rail injection system, which includes a piezoelectric pressure sensor to detect pressure changes during the opening and closing of the injection needle in order to determine the closing moment of the injector needle. The pressure sensor is arranged in a low-pressure area and is loaded by the axial force generated by the stem of the control valve. The sensor described in US2014027534A1 is used to detect the pressure in a chamber located downstream of the control chamber and connected to it by means of a calibrated orifice. Therefore, the sensor described in this document cannot directly detect a signal representing the pressure in the control chamber. In fact, when the valve is open, the pressure read by the sensor is at an intermediate level between the pressure in the control chamber and the discharge pressure, and this level is also determined by the pressure drop across the valve seat. When the valve is closed, the orifice intermediate chamber system introduces a delay between the pressure signal in the control chamber and the pressure signal detected by the sensor. Summary of the invention

[0010] It is an object of the present invention to provide a high pressure hydraulic system for detecting a signal related to the pressure of a fluid inside the hydraulic system in a cost-effective and non-intrusive manner.

[0011] According to the invention, this object is achieved by a high-pressure hydraulic system having the characteristics of the invention.

[0012] The characteristic element of the invention is the specific arrangement and construction of the sensitive and supporting elements that make up the sensor and allow its integration into different hydraulic systems. The electrical signal provided by the sensor can be used to diagnose the operation of the hydraulic system by conventional techniques or with the aid of artificial intelligence.

[0013] In particular, in the case of application in injection systems, the small size, high temperature resistance and adaptability to integration in components with different stiffness make the sensor suitable for detecting the pressure in the control volume of a common rail injector, from which a series of operating diagnostic parameters for the entire injector can be obtained.

[0014] The claims form an integral part of the disclosure provided herein regarding the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The invention will now be described in detail with reference to the accompanying drawings, given by way of non-limiting example only, in which:

[0016] - Figure 1 is a partial cross section of an injector for a common rail injection system.

[0017] - Figure 2 Is Figure 1 The cross section of the part indicated by arrow II is an enlarged scale,

[0018] - Figure 3 It is along Figure 2 The section along line III-III, and

[0019] - Figure 4 It is along Figure 3 The cross section along line IV-IV. DETAILED DESCRIPTION

[0020] Figure 1 A high pressure hydraulic system is shown. In the example shown, the hydraulic system comprises an injector 10 for a common rail injection system. The injector 10 comprises an atomizer 12 having a fuel distribution chamber 14, which has a valve seat 16. An injector needle 18 extends into the distribution chamber 14 and has a sealing surface 20 cooperating with the valve seat 16. The injector needle 18 is movable along its longitudinal axis A between a closed position, in which the sealing surface 20 abuts against the valve seat 16, and an open position, in which the sealing surface 20 is spaced from the valve seat 16. A spring 22 tends to urge the injector needle 18 towards the closed position. The atomizer 12 has a plurality of injection holes 24, through which the pressurized fuel located in the distribution chamber 14 is atomized when the injector needle 18 is in the open position.

[0021] The distribution chamber 14 is connected to an accumulation volume which is filled with pressurized fuel from a high-pressure pump. The accumulation volume is also connected to a hydraulic chamber 34 via a hydraulic line on which a first calibrated orifice 36 is arranged. The hydraulic chamber 34 is connected to a discharge line leading to a tank. A control valve 42 is arranged on the discharge line. The control valve 42 is an electrically controlled two-position valve which in an open position connects the hydraulic chamber 34 to the discharge line and in a closed position isolates the hydraulic chamber 34 from the discharge line. A second calibrated orifice 44 is arranged upstream of the control valve 42.

[0022] The injector 10 includes a wall 50 arranged in hydraulic sealing contact with a head surface 52 of the sprayer 12. The wall 50 surrounds at least a portion of the hydraulic chamber 34. Calibrated orifices 36, 44 are formed in the wall 50, which are connected to the hydraulic chamber 34 through corresponding holes 54, 56 also formed in the wall 50.

[0023] Reference Figure 2 The wall 50 has a reaction surface 58 on which the pressure of the fluid contained in the hydraulic chamber 34 acts. The holes 54, 56 open on the part of the reaction surface 58 facing the hydraulic chamber 34. In some embodiments, the holes 54 and the orifices 36 can be arranged relative to each other. Figure 2 The arrangement shown in is exchanged.

[0024] The reaction surface 58 of the wall 50 may be formed in a seat 60 of the wall 50 open towards the dispensing chamber 14 of the sprayer 12. A bushing 62 is partially housed in the seat 60 and has a hole 64 in which the head portion of the injector needle 18 slides.

[0025] The hydraulic chamber 34 is delimited by the reaction surface 58 of the wall 50 , the head surface 66 of the injector needle 18 and the annular portion 68 of the guide bushing 62 .

[0026] refer to Figure 2 , Figure 3 and Figure 4 , the injector 10 includes a piezoelectric sensor 70 that provides an electrical signal indicative of the operation of the injector 10 .

[0027] The sensor 70 is completely isolated from the pressurized fluid contained in the hydraulic chamber 34. The electrical signal provided by the sensor 70 is indicative of the deformation of the wall 50 produced by the change in the fluid pressure in the hydraulic chamber 34. The piezoelectric sensor 70 is a pressure transducer that provides an electrical signal related to the pressure of the fluid in the hydraulic chamber 34. The sensor 70 has a detection axis A that constitutes the direction along which the sensor 70 is able to detect pressure changes. The detection axis A may coincide with the longitudinal axis of the injector 10.

[0028] The wall 50 includes an integrated diaphragm 120 formed by a portion of the wall 50 having a reduced thickness. The diaphragm 120 has a first surface 122 that is in direct contact with the pressurized fluid contained in the hydraulic chamber 34 and a second surface 124 that is opposite the first surface 122 and is not in contact with the pressurized fluid contained in the hydraulic chamber 34. The first surface 122 of the diaphragm 120 includes a portion of the reaction surface 58.

[0029] In the embodiment shown, the diaphragm 120 is located at the bottom of the blind hole 72 in which the sensor 70 is housed. The blind hole 72 is formed in the wall 50 and has a side surface 74 coaxial with the detection axis A of the sensor 70 and a bottom surface forming a second surface 124 of the diaphragm 120.

[0030] The sensor 70 comprises two disk-shaped elements 78, 80. The two disk-shaped elements 78, 80 have respective first faces 78', 80' and respective second faces 78", 80". The first face 78', 80' and the second face 78", 80" of each of the two disk-shaped elements are planes facing parallel to each other and perpendicular to the detection axis A, which may have a circular shape in a plane perpendicular to the axis A ( Figure 4 ).

[0031] At least one of the two disk-shaped elements is a piezoelectric element which, when subjected to a compressive load in the direction of the detection axis A, accumulates a positive charge on the first face 78', 80' and a negative charge on the second face 78", 80". The amount of the electric charge generates a potential difference between the faces 78', 80' and / or 78", 80", which increases in proportion to the increase in pressure in the direction of the detection axis A.

[0032] In one embodiment, both disk-shaped elements 78, 80 are piezoelectric elements. In this case, the first face 78', 80' of the disk-shaped element 78, 80 is the positive terminal face, and the second face 78", 80" of the disk-shaped element 78, 80 is the negative terminal face.

[0033] In a possible variant, only one of the two disk-shaped elements 78 , 80 is a piezoelectric element, and the other of the two disk-shaped elements 78 , 80 may be an insulating element without piezoelectric properties.

[0034] An electrode 82 formed by a thin wall of conductive material is arranged between the two disk-shaped elements 78, 80, said electrode 82 being perpendicular to the detection axis A. The first faces 78', 80' of the two disk-shaped elements 78, 80 are in contact with two opposite faces of the electrode 82. The electrode 82 may have a circular shape with a diameter slightly larger than the diameter of the piezoelectric elements 78, 80.

[0035] The sensor 70 may include two support elements 84, 86 of conductive material. The two support elements 84, 86 have respective support surfaces 88, 90 which rest on respective second surfaces 78", 80" of the disk-shaped elements 78, 80. The side walls of the support elements 84, 86 may be in contact with the side surface 74 of the hole 72.

[0036] An electrode 82 arranged between the two piezoelectric elements 78, 80 constitutes the positive pole of the sensor 70. The negative pole is constituted by supports 84, 86 electrically connected to ground through the wall 50.

[0037] refer to Figure 3 and Figure 4 The electrode 82 may have a protrusion 92 extending outward in a direction perpendicular to the detection axis A, one end of a cable 94 is connected to the protrusion, and an analog electrical signal with an amplitude proportional to the force acting between the two supports 84 and 86 in the direction of the detection axis A is transmitted on the cable.

[0038] The sensor 70 includes an insulating element 96 having an annular shape, which is arranged outside the electrode 82 coaxially with the axis A. The insulating element 96 has an inner surface 98 facing the outer edges of the disk-shaped elements 78, 80 and the outer edges of the electrode 82, and it allows the alignment between the disk-shaped elements 78, 80 and the electrode 82 relative to the detection axis A. The insulating element 96 ensures the electrical insulation of the electrode 82 and the disk-shaped elements 78, 80 from the metal parts of the injector. The insulating element 96 has a size smaller than the distance between the support faces 88, 90 of the support elements 84, 86 in the direction of the detection axis A, and has a base surface 100 resting on the outer peripheral portion of the face 88 of one support element 84.

[0039] The sensor 70 is constrained to the wall 50 in the direction of the detection axis A. For example, an upper surface 110 of the support element 86 of the sensor 70 may be arranged against a lower surface 112 of a body 114 resting on an upper surface 116 of the wall 50 .

[0040] The injector 10 may include at least one elastic element 102, for example formed by a cup spring, which is coaxial with the detection axis A and is arranged to exert an elastic force between the sensor 70 and the diaphragm 120 in the direction of the detection axis A. The elastic element 102 and the sensor 70 are arranged so that in the direction of the detection axis A, the sensor 70 is only subjected to the elastic force generated by the elastic element 102.

[0041] In the example shown, the resilient element 102 is axially compressed between the second surface 124 of the diaphragm 120 and the lower surface 104 of the support element 84. The support element 84 may have an axial protrusion 106 that protrudes from the lower surface 104 in the direction of the detection axis A and engages the central hole 108 of the resilient element 102. The resilient element 102 compresses the sensor 70 against the lower surface 112 of the body 114 in the direction of the detection axis A.

[0042] The sensor 70 generates an electrical signal related to the elastic force exerted by the elastic element 102 between the piezoelectric sensor 70 and the diaphragm 120 along said detection axis A. During operation, periodic pressure variations of the fluid in the hydraulic chamber 34 result in periodic deformations of the diaphragm 120 in the direction of the detection axis A. The deformation of the diaphragm 120 caused by the pressure variations of the fluid results in a deformation of the second surface 124 of the diaphragm 120 in the direction of the detection axis A. The deformation of the second surface 124 in the direction of the detection axis A in turn results in a variation of the elastic force exerted by the elastic element 102 on the sensor 70 and, therefore, in a variation of the electrical signal generated by the sensor 70. The electrical signal generated by the sensor 70 is therefore directly related to the instantaneous value of the pressure of the fluid contained in the hydraulic chamber 34.

[0043] The force due to the deformation of the diaphragm 120 is transmitted to the sensor only by means of the elastic element 102 , and this prevents the deformation of the diaphragm 120 (under the effect of the pressure in the hydraulic chamber 34 ) from generating an excessive load on the sensor 70 .

[0044] The stiffness of the elastic element 102 is sized according to the thickness of the diaphragm 120 and the pressure in the hydraulic chamber 34. By means of appropriate selection of the size and geometry of the elastic element 102, the stiffness of the elastic element 102 can be adapted so that the deformation of the diaphragm 120 generates a force that is compatible with the working range of the piezoelectric elements 78, 80.

[0045] The possibility of varying the stiffness of the elastic element 102 at the design stage allows ensuring a sufficient thickness of the diaphragm 120 .

[0046] In the case where both disk-shaped elements 78, 80 are piezoelectric elements, the facing and relative arrangement of the piezoelectric elements 78, 80 doubles the sensitivity of the sensor 70 relative to a sensor using a single piezoelectric element and simplifies its construction because it uses the same piezoelectric element 78, 80 as an electrical insulating element between the positive and negative poles and avoids introducing additional elements of insulating material in the series of elements supporting the loads to which the sensor 70 is subjected.

[0047] The sensor 70 has very small dimensions and can be easily accommodated between the calibrated orifices 36, 44 of the wall 50. The sensor 70 is able to provide an indirect measurement of the hydraulic pressure in the hydraulic chamber 34 without requiring any contact with the fluid and without in any way modifying the geometry of the hydraulic chamber 34. Deformations of the diaphragm 120 can be detected by the sensor 70 with an excellent signal / noise ratio.

[0048] The hydraulic pressure inside hydraulic chamber 34 detected by sensor 70 may be processed to obtain diagnostic information regarding the operation of injector 10 .

[0049] The accompanying drawings show by way of example the use of a sensor 70 according to the invention in a common rail injector. However, it is understood that the sensor 70 according to the invention may be used in any other type of high pressure hydraulic system, such as, for example, an accumulator, a pipe, a pump, a valve element, etc.

[0050] In general, sensor 70 may be mounted in any component of a hydraulic system that has a surface that is exposed to a pressurized fluid and that deforms due to changes in the pressure of the fluid.

[0051] The sensor 70 is thus able to detect the pressure of the fluid without direct contact with the pressurized fluid because of the deformation of the diaphragm separating the sensor 70 from the volume containing the pressurized fluid.

[0052] If the sensor 70 is only subjected to the elastic force generated by the elastic element 102 in the direction of the detection axis A, the elastic element 102 may be arranged differently from that shown in the drawings. For example, the elastic element may be arranged between the surface 112 of the body 114 and the upper surface 110 of the second support element 84 .

[0053] Of course, without prejudice to the principle of the invention, the details of construction and of the embodiments may vary widely with respect to those described and illustrated, without therefore departing from the scope of the invention as defined by the appended claims.

Claims

1. A high pressure hydraulic system comprising: - a hydraulic chamber (34) containing a pressurized fluid, a wall (50) surrounding at least a portion of the hydraulic chamber (34) and comprising an integrated diaphragm (120), a piezoelectric sensor (70) isolated from the pressurized fluid contained in the hydraulic chamber (34) by the diaphragm (120) and having a detection axis (A), wherein the piezoelectric sensor (70) generates an electrical signal related to a force compressing the piezoelectric sensor (70) along the detection axis (A), and - an elastic element (102) arranged to exert an elastic force between the piezoelectric sensor (70) and the diaphragm (120) along the detection axis (A), wherein the elastic element (102) and the piezoelectric sensor (70) are arranged so that a deformation of the diaphragm (120) in the direction of the detection axis (A) caused by a change in the pressure of the fluid contained in the hydraulic chamber (34) causes a change in the elastic force exerted by the elastic element (102) between the piezoelectric sensor (70) and the diaphragm (120) along the detection axis (A), wherein the diaphragm (120) is formed directly in the wall (50), the wall (50) having a surface delimiting an upper portion of the hydraulic chamber (34), Wherein, the piezoelectric sensor (70) comprises: two disk-shaped elements (78, 80), the disk-shaped elements having respective first faces (78', 80') and respective second faces (78", 80") parallel to each other and perpendicular to the detection axis (A); an electrode (82) formed by a thin plate of a conductive material perpendicular to the detection axis (A), wherein the first faces (78', 80') of the two disk-shaped elements (78, 80) are in contact with two opposite faces of the electrode (82), two support elements (84, 86) formed of an electrically conductive material, wherein support surfaces (88, 90) of the two support elements (84, 86) rest on respective second surfaces (78", 80") of the two disk-shaped elements (78, 80); and An annular insulating element (96) is arranged coaxially with the detection axis (A) on the outside of the electrode (82), wherein the insulating element (96) has a size smaller than the distance between the support surfaces (88, 90) of the two support elements (84, 86) in the direction of the detection axis (A), and has a base surface (100) placed on the outer peripheral portion of the support surface (88) of the first support element (84) of the two support elements (84, 86).

2. The hydraulic system according to claim 1, wherein: The elastic element (102) and the piezoelectric sensor (70) are arranged so that in the direction of the detection axis (A), the piezoelectric sensor (70) is subjected only to the elastic force generated by the elastic element (102).

3. A hydraulic system according to claim 1 or claim 2, wherein: The membrane (120) is formed by a portion of the wall (50) having a reduced thickness.

4. The hydraulic system according to claim 3, wherein: The diaphragm (120) is positioned at the bottom of a blind hole (72) formed in the wall (50), and the piezoelectric sensor (70) is received in the blind hole.

5. The hydraulic system according to any one of the preceding claims 1-2, wherein: in, At least one of the disk-shaped elements (78, 80) is a piezoelectric element.

6. The hydraulic system according to claim 5, wherein: The elastic element (102) is compressed between the diaphragm (120) and a surface (104) of the first support element (84) in the direction of the detection axis (A).

7. The hydraulic system according to claim 5, wherein: The insulating element (96) has an inner surface (98) facing the electrode (82) and the outer edge of the disk-shaped element (78, 80).

8. The hydraulic system according to claim 5, wherein: Both disk-shaped elements (78, 80) are piezoelectric elements, wherein the first surface (78', 80') of the disk-shaped elements (78, 80) is a positive terminal surface, and the second surface (78", 80") of the disk-shaped elements (78, 80) is a negative terminal surface.

9. The hydraulic system according to claim 5, wherein: The first support element (84) has an axial projection (106) which projects from its lower surface (104) in the direction of the detection axis (A) and engages with a central hole (108) of the elastic element (102).

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