FR2757223A1 - Hydraulic installation used e.g. for vehicle braking system - Google Patents

Abstract

The hydraulic installation having at least one utilisation circuit fed from a single pressure fluid source (11), incorporates an isolator between the source and each circuit and a slide valve (16) with an orifice (29) which is closed when the slide valve is moved by a pressure difference acting on it which is representative of a flow in a corresponding circuit. The slide valve (16) is able to slide in a channel (19) between a first chamber (20) connected to the pressure fluid source and a second chamber (21) connected to the utilisation circuit. The first orifice (29) is normally open into the chamber (29), but is closed by the walls of the channel (19) when the slide valve is moved towards the second chamber against the action of a spring (40).

Description

"Hydraulic installation with at least one circuit
of use of the closed center type "
The invention relates to a hydraulic installation comprising at least one use circuit of the closed center type supplied from a source of pressurized hydraulic fluid; it relates more particularly to protection means associated with this circuit, making it possible to isolate it in the event of operational failure, in particular when a leak or a rupture occurs. The invention also applies to an installation comprising several circuits of this type.

 Such an installation is fitted in particular to civil or military vehicles or to public works vehicles, for example for braking or controlling various movements. The source of pressurized hydraulic fluid comprises a pump and a circuit breaker and feeds one or more closed-center type circuits of use each comprising at least one pressure accumulator, a control member and an operating member.

Such a circuit can power a brake or a power steering system.

 For example, a corresponding number of such circuits can be provided for a motor vehicle equipped with several brakes. The accumulators of the various circuits are all kept under pressure by said source of hydraulic fluid. The fluid displacements in such a circuit are in principle very small in the case of a closed center circuit. However, if a leak or a rupture occurs on one of the use circuits, this obviously becomes inoperative but, moreover, it remains supplied by the source of pressurized hydraulic fluid which is emptied very quickly by the leak or breaking. Such damage has unfortunate, even dangerous consequences. First, the hydraulic fluid, which is oil, can present a danger when it is spilled on a traffic lane. In addition, as the pressure in the defective circuit drops very quickly, the other operating circuits become inoperative, almost instantaneously if they do not have a non-return valve and anyway after exhausting their pressure accumulators.

 The invention makes it possible to solve all these problems linked to the failure of one or more of the circuits. It also makes it possible to keep the operating circuits which have remained healthy in working order and to limit the quantity of hydraulic fluid lost and possibly spilled on the ground, to the clean content of the single damaged circuit.

 More particularly, the invention therefore relates to a hydraulic installation comprising at least one closed-center type use circuit supplied from the same source of pressurized hydraulic fluid, characterized in that an isolation device is inserted between said source and the or each circuit and in that it comprises a drawer comprising a supply duct element of said circuit having a first orifice which can be closed during movement of said drawer under the effect of a pressure difference exerted on it, representative of a leak in the corresponding circuit.

 According to one aspect of the invention, more particularly the abnormal flow of fluid is detected between the source of pressurized hydraulic fluid and the defective circuit, due to the leak or rupture, to cause actuation of the slide. In this case, said drawer is slidably mounted in a bore defined between a first chamber connected to said source and a second chamber connected to said circuit.

 Said first orifice is normally opening into said first chamber but, it is capable of being closed by said bore when the drawer moves towards said second chamber. The drawer is biased back by a spring towards said first chamber.

 According to another variant, said first orifice forms a movable seat defined at one end of the drawer, which comes to cover a shutter located in said second chamber.

 In both cases, a failure in a hydraulic circuit equipped with such an isolation device interrupts the connection between the circuit and the source of pressurized hydraulic fluid. If several circuits are supplied by the source, this keeps the other circuits in working condition.

 Each of these isolation devices can easily be adapted to further constitute a non-return valve making it possible to preserve the corresponding circuit from a pressure drop occurring at the source of pressurized hydraulic fluid.

The invention will be better understood and other advantages thereof will appear more clearly in the light of the following description of several embodiments of part of a hydraulic installation equipped with the means of the invention, made with reference to the accompanying drawings in which:
- Figure 1 is a block diagram illustrating a part of a closed center hydraulic circuit equipped with an isolation device according to the invention;
- Figure 2 is a view similar to Figure 1 illustrating a variant;
- Figure 3 is a view similar to the preceding illustrating another variant;
- Figure 4 is a block diagram of part of a hydraulic installation comprising at least two closed center circuits equipped with a common drawer isolation device;
- Figure 5 is a diagram similar to that of Figure 4 illustrating another variant.

 In Figure 1, there is shown a part of a hydraulic installation comprising a source of pressurized hydraulic fluid 11 and part of a closed-center use circuit 12 supplied from this source of pressurized hydraulic fluid. The latter includes a pump and a circuit breaker. The hydraulic circuit being of the closed center type, it comprises a pressure accumulator 13. The rest of the operating circuit is not shown. It may include, as mentioned above, a control member and an operating member such as a braking device.

 The improvement of the invention is interposed between the source of hydraulic fluid under pressure 11 and the pressure accumulator 13.

 Indeed, an isolation device 15 is interposed between said source of hydraulic fluid, possibly common to several circuits and the or each circuit 12. This isolation device comprises a drawer 16 comprising a supply duct element 18 of the circuit corresponding. This drawer here consists of a generally cylindrical element subject to sliding movement in a bore 19 defined between a first chamber 20 connected to the source of pressurized hydraulic fluid 11 and a second chamber 21 connected to the corresponding circuit 12, more particularly to accumulator 13.

 Said second chamber is defined in a cavity 24 adjacent to the bore 19 (with which it communicates) and closed by a plug 26 provided with a threaded connection ensuring the connection with the rest of the circuit 12. The conduit element supply 18 contained in the drawer 16 comprises a first orifice 29 which can be closed during movement of the drawer, under the effect of a pressure difference exerted on said drawer and representative of a leak in the corresponding circuit 12.

 In the example, this first orifice 29 is double and formed by the ends of a transverse bore 30 normally in communication with said first chamber 20. This transverse bore communicates in its middle with an axial bore 32 of the drawer plugged at its end by an insert 33. Another transverse bore 35, normally opening into the second chamber 21 connected to the circuit 12 is in communication with the axial bore 32. Thus, in normal operation, pressurized fluid can be delivered by the source 11 to maintain the accumulator 13 charged.

 In the second chamber 21, the drawer has a shoulder 38. A connecting washer 39 is mounted on the drawer, coaxial therewith. It normally rests on the shoulder. The drawer is biased by a spring 40 in the direction of the first chamber. This spring is mounted in said second chamber 21 and bears on said connecting washer 39.

 It is understood that said first orifice 29, which normally opens into the first chamber, in normal operation, is capable of being closed by the bore 19 of the drawer when the latter moves towards said second chamber 21. The spring 40 is tared at a value slightly higher than the thrust it receives from the drawer during feeding in the case of maximum consumption provided for in the operating circuit.

The washer 39 normally takes support, under the effect of the spring, on a peripheral shoulder 44 of said second chamber.

 It is evident from the above description, that if the pressure difference between supply and use becomes greater than the calibration value, (that is to say when this pressure difference becomes representative of an anomaly due to a leak or broken pipe) the spring compresses more under the thrust of the drawer, which allows the movement of the latter, and causes the interruption. This interruption of the supply is maintained as long as the source of pressurized hydraulic fluid remains active.

 In the example described, the connecting washer 39 can be fixed to the end of the drawer, that is to say in permanent support against the shoulder thereof. However, it is advantageous for said washer 39 to be slidably mounted on the end portion 46 of small diameter of said drawer. Indeed, it is clear that the transverse bore 35 located on the side of the second chamber defines a second orifice 48 normally opening into this second chamber, but which is also capable of being closed by the bore 19 if the drawer moves towards said first chamber 20. The fact of mounting the sliding washer on the drawer, transforms the latter into a non-return valve.

 Indeed, if a pressure drop is recorded on the side of said first chamber 20, for example due to a failure of the source of hydraulic fluid under pressure, it is advantageous to keep the accumulator 13 charged so that the hydraulic circuit can continue to operate. In this case, the pressure difference exerted between the two ends of the drawer, tends to move the latter towards the first chamber and consequently, momentarily isolate the circuit 12 by closing said second orifice 48.

 In the embodiment of Figure 2, the structural elements similar to those described with reference to Figure 1 have the same reference numerals and will not be described again in detail. There are therefore said first and second chambers 20, 21 between which the slide 16 moves inside a bore 19 formed between these two chambers. The second chamber 21 contains a connecting washer 39 and a spring 40. The latter urges said washer towards a peripheral shoulder 44 of the second chamber.

 In addition, the duct element 18 of said drawer comprises, on the side of the source of pressurized hydraulic fluid, two transverse parallel bores 30, 45 capable of establishing communication between said first chamber 20 and the axial bore 32 of the drawer . The bore 30 defines said first orifice 29 as in the previous example.

 On the other hand, the bore 45, of smaller diameter, opens into said first chamber 20 through an auxiliary orifice 47 of smaller section. The auxiliary orifice 46 is placed so as to be closed after said first orifice 29, when the drawer 16 moves towards said second chamber 21. In the latter, the drawer cooperates with the connecting washer 39 by means of a auxiliary washer 48 itself urged by an auxiliary spring 49, of lower stiffness than the spring 40, tending to push the drawer towards said first chamber. An axial clearance is defined between the washers 39 and 47.

 With this embodiment, if moderate and momentary consumption is recorded, the drawer moves first until the auxiliary washer 47 comes into contact with the connecting washer 39 by compressing the spring of low stiffness 49. During this operating phase, said first orifice 29 is closed and the pressurized hydraulic fluid can circulate (between the pump and the accumulator) only through the second transverse bore 45, of small diameter, of the drawer. If the hydraulic fluid flow disappears again and the pressure in the operating circuit rises, the slide valve returns to its normal position automatically.

 On the other hand, if the pressure imbalance increases, due to an anomaly, the slide 16 moves towards the second chamber by compressing the spring 40 even more and said auxiliary orifice 46 ends up being closed in turn, causing isolation of the circuit.

 FIG. 3 represents another variant of FIG. 1 with the same main structural elements.

However, it is noted that the drawer 16 mainly comprises two portions of different sections 50A, 50B admitting a common axis. The portion of larger section 50A is located on the side of the source of hydraulic fluid under pressure 11 and opens into said first chamber 20. The portion of smaller section 50B is located on the side of the use circuit 12 and opens into the second chamber 21. The connection of these two portions defines an annular shoulder 52. The latter is located in a cavity 53 connected to a hydraulic cover 54. The sensitivity of the drawer is increased, all other things being equal.

 In the following embodiments, the installation comprises at least two aforementioned circuits of use, the isolation devices of which are aligned and antagonistic with a common double drawer 116.

 Consequently, the isolation of one of the two defective circuits causes the common slide to be in a position such that the other circuit necessarily remains in communication with the source of pressurized fluid.

 In these embodiments, the structural elements similar to those which have been described previously, bear the same numerical references supplemented by the indices a and d depending on whether they belong to the circuits 12a, 12b respectively.

 In the embodiment of Figure 4, the aforementioned first orifice 29a, 29b of each part of the double drawer 116 opens into said corresponding second chamber 21a, 21b. It is formed at the end of a longitudinal bore 132 of the drawer and it defines a seat cooperating with a shutter 60a, 602b arranged opposite in said second chamber 21a, 21b, respectively. The source 11 communicates with said first chamber 20 into which opens a transverse bore 133 communicating with the bore 132. The drawer which carries the seat moves towards the shutter when the corresponding circuit 12a, 12b is isolated. The shutter 60a, 60b comprises a hemispherical head capable of closing the corresponding orifice 29a, 29b forming a seat.

 In this example, said shutter 60a, 60b is, on the one hand, biased by a spring 62a, 62t in the direction of the seat and, on the other hand, secured to a movable piston in a bore 65a, 65b communicating with side with said second chamber 21a, 21b and on the other side with the hydraulic tank 54. The arrangement is therefore such that the pressure of the second chamber 21a, 21b is exerted on the piston and acts in the opposite direction to the spring. The shutter 60a, 60k and the seat or first orifice 29a, 29b thus further define a non-return valve.

 In fact, if the pressure upstream of the drawer decreases below a certain value, the spring 62a, 62b causes the shutter 60a, 60b to move in the direction of the seat and, consequently, the isolation of the circuit 12a, 12b corresponding.

 Of course, the same arrangement is possible with a simple drawer supplying only one circuit.

 In the embodiment of Figure 5, there are the same structural elements as in the embodiment of Figure 4; they have the same reference numbers. The main difference lies in the fact that each shutter is constituted by a ball 70a, 70b which is held captive with clearance opposite the first orifice 29a, 29b forming a seat, opening into said second chamber.

 More precisely, the ball 70a, 70b is held captive in a space defined between said first orifice forming a seat, the connecting washer 39a, 39b and an axial stop opposite to said second orifice and defined at the end of a plug 26a, 26b closing said second chamber. The arrangement of the ball 70 and the seat defined at the corresponding end of the double drawer 116 also constitutes a non-return valve. However, a rod 74 is inserted into the axial bore 132 of the drawer between the two balls. This rod is of a length such that the first non-return valve which closes due to a drop in pressure of the hydraulic fluid source 11, prevents the closure of the other non-return valve so that at least one circuit remains in communication with the source of pressurized hydraulic fluid 11 and prevents inadvertent operation of the contactor-circuit breaker associated with this source.

Claims (12)

 1- Hydraulic installation comprising at least one closed-center type use circuit supplied from the same source of pressurized hydraulic fluid (11), characterized in that an isolation device is inserted between said source and each circuit and in that it comprises a drawer (16, 116) comprising a supply duct element of said circuit having a first orifice (29, 29a, 29b) closable during the movement of said drawer under the effect of a pressure difference exerted on it, representative of a leak in the corresponding circuit.  2- Installation according to claim 1, characterized in that said drawer (29) is slidably mounted in a bore (19) defined between a first chamber (20) connected to said source and a second chamber (21) connected to said circuit and in that said first orifice is normally opening into said first chamber but is capable of being closed by said bore (19) when said drawer moves towards said second chamber and in that said drawer is biased by a spring (40) in the direction of said first chamber.  3- Installation according to claim 2, characterized in that said spring (40) is mounted in said second chamber (21) and is supported on a connecting washer (39) mounted on said drawer (16) coaxially therewith.  4- Installation according to claim 3, characterized in that said duct member comprises a second orifice (35) normally opening into said second chamber (21), but is capable of being closed by said bore (19) when said drawer moves towards said first chamber and in that said connecting washer (39) is slidably mounted on a corresponding end of said drawer, provided with an abutment shoulder, the arrangement thus forming a non-return valve.  5- Installation according to claim 3 or 4, characterized in that said conduit member of said drawer (16) comprises, on the side of said source of hydraulic fluid under pressure, two transverse bores (30, 45) in parallel, one defining said first orifice (29) and the other, of smaller section, defining an auxiliary orifice (46) placed to be closed after said first orifice when said drawer (16) moves towards said second chamber (21).  6- Installation according to claim 5, characterized in that said drawer cooperates with said connecting washer by means of an auxiliary washer (47) itself urged by an auxiliary spring (49), to push the drawer towards of said first chamber.  7- Installation according to one of the preceding claims, characterized in that said drawer (16) comprises two portions (50A, 50B) of different sections admitting a common axis, the portion of larger section being on the side of said source of pressurized hydraulic fluid (11).  8- Installation according to claim 7, characterized in that the shoulder (52) for connection between the two portions is located in a cavity (53) connected to a hydraulic tank (54).  9- Installation according to claim 1, characterized in that said first orifice (29a, 29b) of said drawer (116) opens into said second chamber (21a, 2lb) and in that it forms a seat cooperating with a shutter (60a , 60b) arranged opposite in said second chamber, said drawer carrying said seat moving towards said shutter at the time of isolation of the corresponding circuit.  10- Installation according to claim 9, characterized in that said shutter (60a, 60t) is, on the one hand, biased by a spring (62a, 62b) towards said seat and, on the other hand, secured to a piston (64a, 64b) movable in a bore communicating on one side with said second chamber and on the other side with a hydraulic tank (54), the arrangement being such that the pressure of said second chamber being exerted on said piston acts in the opposite direction to said spring, said shutter and said seat thus defining a non-return valve.  11- Installation according to claim 9, characterized in that said shutter is constituted by a ball (70a, 70b) held captive with clearance opposite said first orifice, in said second chamber.  12- Installation according to one of the preceding claims, characterized in that it comprises at least two aforementioned circuits (12a, 12b) whose isolation devices are aligned and antagonistic, with a common double drawer (116), so that the isolation of one of the two faulty circuits causes the common slide in a position such that the other circuit remains in communication with said source of pressurized fluid (11)