LIQUID PRESSURE DETECTOR

Description

[0001] The present invention relates to a pressure detector intended to be associated with a hydraulic or pneumatic circuit to deliver an electrical signal in response to crossing a pressure threshold in the circuit. BACKGROUND OF THE INVENTION

[0002] Generally, pressure detectors are designed to react to a pressure difference between the pressure of one circuit and a reference pressure, which can be atmospheric pressure or the pressure of another circuit.

[0003] Pressure detectors are known to consist of a body dividing two chambers, each sealed against the other, and each capable of being connected to a pressurized fluid source. A sliding assembly is mounted within the body, subjected to opposing pressures in each chamber. This sliding assembly actuates, directly or indirectly, a microswitch that detects at least one position of the sliding assembly, representing a pressure difference threshold between the two chambers, and emits a signal in response to this detection.

[0004] The microswitch is the source of several problems. The travel of the moving parts can be very small (on the order of a few tenths of a millimeter), making the microswitch assembly and adjustment extremely delicate and therefore very expensive. Furthermore, the internal forces within the microswitch, as well as the forces between the microswitch and the moving parts, are difficult to control and disrupt the accuracy of position detection, particularly when measuring low pressures. Both the microswitch and the moving parts are also susceptible to wear due to contact and friction during operation, which limits the normal operating life of such a pressure sensor. Finally, the vibration resistance of a microswitch is limited.

[0005] Other types of pressure sensors exist in which the position of the moving assembly is detected by a permanent magnet carried by the moving assembly and by an inductive cell sensitive to the permanent magnet's magnetic field, fixed to the body facing the permanent magnet. The use of an inductive cell avoids any mechanical contact between the moving assembly and the cell, thus reducing wear, the risk of mechanical misalignment, and detection interference due to friction.

[0006] However, this type of pressure sensor is designed so that the moving assembly uses a flexible diaphragm subjected to the differential pressures in the two chambers. The flexible diaphragm is clamped between an O-ring and a bearing screwed into the body. Therefore, such a pressure sensor cannot reliably detect significant pressure differences between the two chambers, as the risks of diaphragm rupture or O-ring leakage are high.

[0007] Documents WO 2009 / 135612 A1, EP 1 319 936 A1 and WO 2005 / 059343 A1 disclose examples of pressure detectors. SUBJECT OF THE INVENTION

[0008] The invention therefore aims to provide an inductive pressure detector that does not use a flexible membrane to detect a pressure differential. SUMMARY OF THE INVENTION

[0009] For this purpose, a pressure detector is proposed comprising a body delimiting a chamber into which open two channels each capable of being connected to a source of pressurized fluid, a movable assembly extending inside the chamber and fixed to a rod mounted to slide in one of the channels, defining with it a leak passage for the fluid, and a detector of at least one position of the movable assembly significant of a determined threshold of pressure difference between the two fluid sources.

[0010] The moving assembly is subjected to the action of an elastic element which pulls said moving assembly back towards the channel in which the rod slides.

[0011] According to a particular feature of the invention, the rod is equipped, at an end opposite to that receiving the moving assembly, with a stop arranged to limit the sliding of the rod towards the chamber.

[0012] In particular, the stop is equipped with a sealing gasket arranged to block the leak passage when the stop is in contact with the body.

[0013] According to another particular feature of the invention, the position detector emits a logic-type signal that can take two distinct values ​​in response to the detection of the position of the moving crew.

[0014] According to another particular feature of the invention, the position detector comprises a permanent magnet carried by the moving assembly and an inductive cell sensitive to the magnetic field of the permanent magnet carried in a fixed manner by the body opposite the permanent magnet.

[0015] In particular, the position detector also includes a counter-magnet fixedly mounted on the body in opposition to the permanent magnet of the moving assembly relative to the inductive cell.

[0016] According to another particular feature of the invention, the elastic element is a helical spring.

[0017] The invention also relates to a hydraulic actuation system comprising at least one such pressure detector.

[0018] The invention also relates to a method for detecting the crossing of a pressure difference threshold using such a pressure detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention will be better understood in light of the following description, which is purely illustrative and not limiting, and should be read in conjunction with the accompanying figures, among which: [ Fig.1A ] there figure 1A is a view of a pressure detector according to a particular embodiment of the invention; [ Fig.1B ] there figure 1B is a view showing the operation of the pressure detector illustrated in the figure 1A ; Fig.2A ] there figure 2A is a view of a variant of the pressure detector illustrated in the figure 1A ; Fig.2B ] there figure 2B is a view showing the operation of the pressure detector illustrated in the figure 2A ; Fig.3 ] there figure 3 is a graph representing the behavior of the inductive cell equipping the pressure detectors illustrated in figures 2A And 2B . DETAILED DESCRIPTION OF THE INVENTION

[0020] With reference to the figure 1 A pressure detector 1, according to a particular embodiment of the invention, comprises a hollow body 2 of revolution about an axis X. The body 2 consists of an upper part 2a, generally tubular in shape, and a lower part 2b forming the base of the body 2, the upper part 2a and the lower part 2b being welded together. The lower part 2b is a part of revolution about axis X having a stepped outer surface comprising: a first end section, of larger diameter, fixed to the upper part 2a to close one end of said upper part 2a; a second end section, of smaller diameter, intended to be placed in the circuit whose pressure is to be measured; and an intermediate section, of intermediate diameter between the two preceding diameters, connected to the first end section by a first shoulder and to the second end section by a second shoulder.The intermediate and second end sections are arranged to be inserted into a stepped fitting connected to the circuit whose pressure is to be measured. The first end section acts as a stop against the insertion of the intermediate and second end sections into the fitting. The upper part 2a has a separator 3 screwed into the body 2, as well as a cover 4. The separator 3 and the cover 4 define a compartment housing the electrical components of the pressure sensor, which will be described in more detail later.

[0021] The body 2 delimits with the separator 3 a chamber 5 of generally cylindrical shape into which a first channel 6 and a second channel 7 open, passing through the lower part 2b of the body 2.

[0022] The first channel 6 has a circular cross-section of diameter D. It extends along an axis coinciding with the X-axis and is intended to be connected to a high-pressure (HP) hydraulic (or pneumatic) circuit in which a fluid circulates, changing almost instantaneously from a rest pressure to a working pressure and vice versa. The rest pressure and working pressure are approximately 10 bar and 200 bar, respectively. Under such a pressure difference, the leakage criterion in equipment acceptance testing, also called the ATP leakage criterion, on the high-pressure (HP) circuit is generally approximately 800 cm³ / min.

[0023] The second channel 7 extends along an oblique axis relative to the X-axis and is intended to be connected to a low-pressure hydraulic (or pneumatic) circuit BP to form a leakage path. To this end, the second channel 7 has one end opening into chamber 5 and an opposite end opening onto the second shoulder of the external surface of the lower part 2b. The intermediate section and the second end section are each provided with at least one O-ring to ensure a seal with the walls of the branch into which they are inserted, so as to ensure a seal for the low-pressure circuit BP which is located between the two seals (between the second shoulder and a shoulder of the branch extending opposite said second shoulder).

[0024] In the first channel 6, a rod 8 is mounted to slide along the X axis, the upper end of which is fixed to a moving assembly 9, shaped like a piston, extending inside the chamber 5. The moving assembly 9 is fixed relative to the rod 8 and is subjected to the action of a helical spring 10 bearing against an internal shoulder of the upper part 2a of the body 2 and on an upper face of the moving assembly 9. The spring 10 extends coaxially with the X axis and tends to press the moving assembly 9 against the bottom of the body 2, which forms a stop to the movement of the moving assembly, and therefore to the sliding of the rod 8.

[0025] One lower end of the rod 8 is designed to be subjected to the pressure of the fluid in the high-pressure (HP) circuit and, together with the first channel 6, defines a leak passage 11 for the fluid. For this purpose, the rod is cylindrical and has a diameter d slightly smaller than the diameter D of the first channel 6. The diameter d of the rod 8 is approximately 2.5 millimeters, and the first channel 6 has a diametral clearance with the rod 8 of approximately 0.03 millimeters.

[0026] The rod / moving assembly 8, 9 is thus subjected in an antagonistic manner to the action of the spring 10 and that of the pressure prevailing in the high pressure circuit HP.

[0027] The pressure detector 1 is equipped with an inductive position detector comprising a permanent magnet 12 carried by the moving assembly 9, as well as a Hall effect type inductive cell 13 and a counter magnet 14 both fixed on the separator 3 opposite the permanent magnet 12. The inductive cell 13 is connected to an electronic board (not shown) which is itself connected to an electrical connector 19 extending outward from the cover 4.

[0028] The inductive cell 13, the counter-magnet 14 and the electronic board are contained in the compartment defined by the separator 3 and the cover 4, and are therefore physically separated from the chamber 5. The compartment is made sealed with respect to the chamber 5 by means of a sealing gasket 15 placed between the separator 3 and the body 2.

[0029] The operation of pressure detector 1 will now be detailed.

[0030] Starting from a race C with zero points, as illustrated in the first part of the figure 1B The moving assembly 9 only begins to move if the fluid pressure in the high pressure (HP) circuit is high enough to overcome a threshold force imposed by the spring 10.

[0031] When the fluid circulating in the high-pressure (HP) circuit transitions from its resting to its working state, the moving assembly 9 moves towards the separator 3 until it reaches a stable equilibrium position. This position corresponds to the equilibrium between the force exerted by the spring 10 and the pressure exerted by the fluid in the HP circuit on the lower end of the rod 8. Simultaneously, some of the fluid in the HP circuit passes through the leakage passage 11 and enters chamber 5, encountering initial hydraulic resistance. It then flows through the second channel 7 to escape from chamber 5, encountering a second hydraulic resistance. This effect is primarily due to the narrowness of the leakage passage 11 and the leakage path formed by the second channel 7.

[0032] It is then understood that the force of the spring 10 associated with the working pressure of the fluid prevailing in the high-pressure circuit corresponds to a maximum stroke C max of the moving assembly 9 and a minimum clearance j between the permanent magnet 12 and the separator 3 ( figure 1B ).

[0033] It will be noted that the minimum play j can here be defined by an adjustment shim 16 inserted between a shoulder of the separator 3 and an upper end of the body 2.

[0034] It should also be noted that chamber 5 can be subjected to a pressure close to the working pressure of the fluid in the high-pressure (HP) circuit, so separator 3 must be able to withstand such a pressure. In particular, the wall thickness e of separator 3, highlighted on the figure 1A , must be properly chosen to avoid any damage to the inductive cell 13.

[0035] When the stroke C of the moving assembly 9 is at its maximum, only part of the rod 8 is in the first channel 6. The leak passage 11 then has a length along the X axis here approximately equal to 15 millimeters, which, combined with the values ​​of the diameter d of the rod 8 and the diametral clearance, generates a leak flow rate of the order of 40 cm3 / min equivalent to 5% of the ATP leak criterion of the high pressure circuit HP.

[0036] The behavior of inductive cell 13 is illustrated on the graph of the figure 3 where the x-axis represents the intensity of the magnetic field influencing the inductive cell 13, and the y-axis represents the value of the signal produced by the inductive cell 13 in response to the magnetic field. This is an inductive cell delivering a signal that can only take two values, V1 and V2, according to the following modalities.

[0037] If the magnetic field influencing the inductive cell 13 is weak, the signal produced by the inductive cell 13 is V1. When the magnetic field influencing the inductive cell increases and exceeds an influence threshold Ssup, the signal abruptly changes value to V2. When the magnetic field decreases and falls below an influence threshold Sinf, which is lower than the influence threshold Ssup, the signal value returns to V1. The influence thresholds Sinf and Ssup define a detection range P and are subject to shifting due to temperature variations.

[0038] In the application illustrated here, the magnetic field influencing the inductive cell 13 is that of the permanent magnet 12, while the variations in said magnetic field are due to the movement of the moving assembly 9 and therefore of the permanent magnet 12 under the effect of the fluid pressure in the high-pressure circuit HP. A correspondence can thus be established between a given stroke Cinf of the moving assembly 9 and the lower influence threshold Sinf, as well as between a given stroke Csup of the moving assembly 9 and the upper influence threshold Ssup. sup Equivalently, the detection range P will denote a stroke interval between the determined stroke Cinf and the determined stroke Csup.

[0039] The inductive cell 13 is arranged in relation to the moving assembly 9, so that the detection range P of the inductive cell 13 corresponds to a stroke substantially equal to half of the maximum stroke C max of the moving assembly 9, which itself corresponds here to a pressure of the fluid circulating in the high pressure circuit HP substantially equal to 100 bars.

[0040] As is known in itself, the presence of the counter-magnet 14 mounted in opposition to the curve of the magnetic field tightens the magnetic field lines of the permanent magnet 12, which has the effect of improving the accuracy of the position detector and allowing the use of an inexpensive inductive cell 13.

[0041] There figure 2A illustrates a pressure detector 1' which is none other than a variant of the pressure detector 1 illustrated in the figure 1A .

[0042] The pressure detector 1' differs from the pressure detector 1 in that the lower end of the rod 8 is equipped with a stop 17 arranged to limit the movement of said rod 8 towards the chamber 5, and therefore the stroke C of the moving assembly 9.

[0043] The stop 17 includes a sealing gasket 18 housed in an annular groove of said stop 17 and intended to be in contact with a lower end of the body 2 into which the first channel 6 opens when the stroke C of the moving assembly is at its maximum, so as to prevent the fluid in the high pressure circuit HP from using the leak passage 11 and thus to limit the leakage rate of said fluid.

[0044] It should be noted that the leak passage 11 of the pressure device 1' has a length along the X axis that is shorter than that of the pressure device 1 illustrated in the figure 1A .

[0045] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0046] In particular, the pressure detector may have a different structure than that described in relation to the figures.

[0047] The helical spring 10 can be replaced by an elastic membrane.

[0048] The number and type of joints may differ from those indicated.

[0049] The use of a counter-magnet is optional.

[0050] Although the contactless detection sensor here is inductive, it can be of a different nature (optical, etc.)

Claims

1. Pressure detector (1; 1') comprising a body (2) delimiting a chamber (5), wherein two channels (6, 7) open into, arranged to each be connected to a source of pressurised fluid (BP, HP), a mobile unit (9) extending inside the chamber and fixed to a rod (8) mounted slidably in one (6) of the channels, by defining with it an escape passage (11) for the fluid, and a detector (12, 13) of at least one position of the mobile unit signifying a determined threshold of pressure difference between the two sources of fluids, the mobile unit being subjected to the action of an elastic element (10) returning said mobile unit towards the channel wherein the rod slides, characterized in that the rod (8) is equipped, at an end opposite that receiving the mobile unit (9), with an abutment (17) arranged to limit the sliding of the rod towards the chamber (5).

2. Pressure detector (1') according to claim 1, wherein the abutment is equipped with a seal (18) arranged to block the escape passage (11) when the abutment is in contact with the body (2).

3. Pressure detector (1; 1') according to any one of the preceding claims, wherein, in response to the detection of the position of the mobile unit (9), the position detector emits a signal of the logic type, being able to take two distinctive values (V1, V2).

4. Pressure detector (1; 1') according to any one of the preceding claims, wherein the position detector comprises a permanent magnet (12) carried by the mobile unit and an inductive cell (13) sensitive to the magnetic field of the permanent magnet fixedly carried by the body facing the permanent magnet.

5. Pressure detector (1; 1') according to claim 4, wherein the position detector further comprises a counter-magnet (14) fixedly mounted on the body (2) opposite the permanent magnet (12) of the mobile unit (9) with respect to the inductive cell (13).

6. Pressure detector (1; 1') according to any one of the preceding claims, wherein the elastic element (10) is a helical spring.

7. Hydraulic actuation system comprising at least one pressure detector (1, 1') according to any one of the preceding claims.

8. Method for detecting the crossing of a pressure different threshold implementing a pressure detector (1, 1') according to any one of claims 1 to 6.