Filtration system for electro-hydraulic power steering system

Abstract

The invention relates to a filtration system (100) for an electro-hydraulic power steering system (50) comprising a bidirectional pump (2), the system (100) comprising:- a hydraulic fluid circulation circuit (1) comprising:- a first main branch (A) extending between a first inlet / outlet (3) of the bidirectional pump (2) and a first inlet / outlet (5) of a hydraulic steering mechanism (7),- a second main branch (B) extending between a second inlet / outlet (4) of the pump (2) and a second inlet / outlet (6) of the hydraulic mechanism (7),- a first auxiliary branch (C) extending between the first inlet / outlet (5) of the hydraulic mechanism and a sixth connection point (16) arranged on the first main branch (A),-- a second auxiliary branch (D) extending between the second inlet / outlet (6) of the hydraulic mechanism (7) and an eighth connection point (18) arranged on the second main branch (B), in which the first main branch (A) comprises a first filter (31) and the second main branch (B) comprises a second filter (32). Abstract figure: Figure 1,

Description

Title of the invention: Filtration system for electro-hydraulic power steering system Technical field

[0001] The present invention relates to the field of filtration systems, and in particular filtration systems for electro-hydraulic power steering systems comprising a bidirectional pump. Prior art

[0002] Some power steering systems fitted to motor or industrial vehicles are of the hydraulic type, that is to say that the assistance force provided to reduce the torque that must be applied by the driver to change the orientation of the wheels is generated by a pressurized fluid circulating in a hydraulic circuit. This hydraulic fluid is likely to be contaminated by wear particles coming from the parts in contact with the fluid. It is therefore preferable to filter the hydraulic fluid in order to protect the components of the circuit, such as for example the pump ensuring the pressurization of the hydraulic fluid.

[0003] It is possible to use a bidirectional pump, that is to say a pump where the inlet and outlet of hydraulic fluid can be exchanged selectively, in particular by reversing the direction of rotation of the pump drive motor. This configuration modifies the direction of circulation of the hydraulic fluid according to the operating phases, and poses new constraints for obtaining satisfactory filtration of the hydraulic fluid.

[0004] There is thus a need to have an optimized filtration system for power steering systems using a bidirectional pump. Summary

[0005] To this end, a filtration system for an electro-hydraulic power steering system comprising a bidirectional pump is proposed, the filtration system comprising a hydraulic fluid circulation circuit which comprises: - a first main branch extending between a first connection point configured to be connected to a first inlet / outlet of the bidirectional pump and a second connection point configured to be connected to a first inlet / outlet of a hydraulic steering mechanism, - a second main branch extending between a third connection point configured to be connected to a second input / output of the bidirectional pump and a fourth connection point configured to be connected to a second input / output of the hydraulic steering mechanism, - a first auxiliary branch extending between a fifth connection point configured to be connected to the first input / output of the hydraulic steering mechanism and a sixth connection point arranged on the first main branch, - a second auxiliary branch extending between a seventh connection point configured to be connected to the second input / output of the hydraulic steering mechanism and an eighth connection point arranged on the second main branch, wherein the first main branch comprises a first filter and the second main branch comprises a second filter.

[0006] This circuit structure makes it possible to filter the entire circuit regardless of the discharge direction of the bidirectional pump. In addition, the use of two separate filters makes it possible to adapt the sizing of each filter to the quantity of contaminants to be filtered. Indeed, depending on the arrangement of the internal parts of the hydraulic steering mechanism, the quantity of contaminants emitted at one inlet / outlet may be different from the quantity emitted at the other inlet / outlet. The duration of use before two maintenance operations can thus be increased.

[0007] The features listed in the following paragraphs can be implemented independently of each other or in any technically possible combination:

[0008] The bidirectional pump is configured to be driven by an electric motor.

[0009] According to one aspect of the filtration system, the first main branch comprises a first valve configured to allow circulation of hydraulic fluid from the sixth connection point to the second connection point and configured to block circulation of hydraulic fluid from the second connection point to the sixth connection point.

[0010] According to one aspect of the filtration system, the second main branch comprises a second valve configured to allow circulation of hydraulic fluid from the eighth connection point to the fourth connection point and configured to block circulation of hydraulic fluid from the fourth connection point to the eighth connection point.

[0011] According to one aspect of the filtration system, the first auxiliary branch comprises a third valve configured to allow a circulation of hydraulic fluid from the fifth connection point to the sixth connection point and configured to block a circulation of hydraulic fluid from the sixth connection point to the fifth connection point.

[0012] According to one aspect of the filtration system, the second auxiliary branch comprises a fourth valve configured to allow flow of hydraulic fluid from the seventh connection point to the eighth connection point and configured to block flow of hydraulic fluid from the eighth connection point to the seventh connection point.

[0013] The first valve, the second valve, the third valve and the fourth valve ensure the circulation of the hydraulic fluid in the circuit in both delivery directions of the bidirectional pump.

[0014] The first valve is a passive valve. The second valve is a passive valve. The third valve is a passive valve. The fourth valve is a passive valve.

[0015] According to one embodiment of the filtration system, the first main branch comprises a first differential pressure sensor configured to measure a pressure difference between an inlet and an outlet of the first filter.

[0016] Measuring the pressure drop between the inlet and the outlet of the first filter makes it possible to estimate the degree of clogging of the first filter. In the event of an excessive value revealing clogging of the filter, an alert can be issued to warn the user that the first filter needs to be replaced.

[0017] The differential pressure sensor delivers a first signal level when the applied pressure difference is less than a threshold, and a second signal level when the applied pressure difference is greater than the threshold.

[0018] Optionally, the differential pressure sensor delivers a signal level proportional to the applied pressure difference.

[0019] According to one embodiment of the filtration system, the second main branch comprises a second differential pressure sensor configured to measure a pressure difference between an inlet and an outlet of the second filter.

[0020] Similarly, measuring the pressure drop between the inlet and the outlet of the second filter makes it possible to estimate the degree of clogging of the second filter and an alert can be issued to warn the user that this filter needs to be replaced.

[0021] The first filter and the second filter may be identical.

[0022] The filtration threshold of the first filter is 5 microns for an efficiency of 99.5% filtration. The efficiency [35 of the first filter is equal to 200.

[0023] Similarly, the filtration threshold of the second filter is 5 microns for a filtration efficiency of 99.5%. The efficiency [35 of the second filter is equal to 200.

[0024] Thus, the internal components of the hydraulic steering mechanism are protected.

[0025] According to one embodiment of the filtration system, the first main branch comprises a third filter arranged between the first connection point and the sixth connection point.

[0026] According to one embodiment, the second main branch comprises a fourth filter placed between the third connection point and the eighth connection point.

[0027] The third and fourth filters provide low-pressure hydraulic fluid filtration, which complements high-pressure fluid filtration. This protects the bidirectional pump from contaminants.

[0028] The third filter and the fourth filter may be identical.

[0029] The use of standardized components is thus possible. The risk of reference errors during assembly is also eliminated.

[0030] The filtration threshold of the third filter is for example 5 microns for a filtration efficiency of 99.5%. The efficiency [35 of the third filter is equal to 200.

[0031] Similarly, the filtration threshold of the fourth filter is for example 5 microns for a filtration efficiency of 99.5%. The efficiency [35 of the fourth filter is equal to 200.

[0032] Thus, the internal components of the bidirectional pump are protected.

[0033] The third filter is a metal mesh screen.

[0034] The fourth filter is a metal mesh screen.

[0035] This type of filter allows particles likely to damage the bidirectional pump to be retained.

[0036] According to one embodiment, the first main branch comprises a first bypass branch configured so that the hydraulic fluid bypasses the first filter when the difference between the pressure upstream of the first filter and the pressure downstream of the first filter is greater than a first predetermined threshold.

[0037] The first bypass branch makes it possible to maintain circulation of hydraulic fluid in the circuit when the first filter is clogged and causes a pressure loss incompatible with nominal operation of the system, in particular because the pressure of the hydraulic fluid in the hydraulic mechanism is no longer nominal.

[0038] According to one embodiment, the second main branch comprises a second bypass branch configured so that the hydraulic fluid bypasses the second filter when the difference between the pressure upstream of the second filter and the pressure downstream of the second filter is greater than a second predetermined threshold.

[0039] The second bypass branch has the same role as the first bypass branch, namely to allow circulation of hydraulic fluid in the second main branch when the second filter is clogged.

[0040] The first bypass branch comprises a fifth valve configured to block the flow of hydraulic fluid when the difference between the pressure upstream of the fifth valve and the pressure downstream of the fifth valve is less than a predetermined threshold, and configured to allow the flow of hydraulic fluid when the difference between the pressure upstream of the fifth valve and the pressure downstream of the fifth valve is higher than the predetermined threshold. In other words, as long as the pressure drop caused by the first filter is sufficiently low, all hydraulic fluid flow flows through the first filter. When the first filter is clogged, the hydraulic fluid flow passes through the first bypass branch.

[0041] Similarly, the second bypass branch comprises a sixth valve configured to block the flow of hydraulic fluid when the difference between the pressure upstream of the sixth valve and the pressure downstream of the sixth valve is less than a predetermined threshold, and configured to allow the flow of hydraulic fluid when the difference between the pressure upstream of the sixth valve and the pressure downstream of the sixth valve is greater than the predetermined threshold. In other words, as long as the pressure drop caused by the second filter is sufficiently low, all of the flow of hydraulic fluid can flow through the second filter. When the second filter is clogged, the flow of hydraulic fluid passes through the second bypass branch.

[0042] According to one aspect of the filtration system, the hydraulic fluid circulation circuit comprises a third bypass branch extending between: a thirteenth connection point arranged on the first main branch between the first valve and the second connection point, and a fourteenth connection point arranged on the second main branch between the second valve and the fourth connection point.

[0043] The third bypass branch may include a seventh valve configured to selectively allow or block hydraulic fluid flow in the third bypass branch.

[0044] The fifth valve is an electrically operated valve.

[0045] When a fault is detected on the bidirectional pump and it is no longer functional, the seventh valve can be controlled so as to allow the circulation of hydraulic fluid in the third bypass branch. A blockage of the hydraulic steering mechanism is thus avoided. The mechanism remains manually operable, even if assistance is then no longer available.

[0046] The disclosure also relates to a method of operating an electro-hydraulic power steering system comprising a filtration system as described above, wherein: - according to a first operating mode corresponding to a first delivery direction of the bidirectional pump, the hydraulic fluid is delivered by the first inlet / outlet of the bidirectional pump, circulates in the first main branch and passes successively in this order in: the third filter, the first filter, the hydraulic steering mechanism by entering through the first inlet / outlet and exiting through the second inlet / outlet, the second auxiliary branch, the second main branch passing through the fourth filter, and joins the second inlet / outlet of the bidirectional pump.

[0047] According to another aspect of the operating method: - according to a second operating mode corresponding to a second discharge direction of the bidirectional pump, opposite to the first discharge direction, the hydraulic fluid is discharged through the second inlet / outlet of the bidirectional pump, circulates in the second main branch and passes successively in this order through: the fourth filter, the second filter, the hydraulic steering mechanism by entering through the second inlet / outlet and leaving through the first inlet / outlet, the first auxiliary branch, the first main branch by passing through the third filter, and reaches the first inlet / outlet of the bidirectional pump.

[0048] According to the first operating mode, the fourth filter collects the impurities circulating downstream of the hydraulic steering mechanism. When the system switches to the first operating mode, the direction of flow of the hydraulic fluid in the fourth filter is reversed. The hydraulic fluid then tends to carry the impurities accumulated on the fourth filter. The impurities removed from the fourth filter are conveyed to the second filter where they remain accumulated. Indeed, the direction of flow of the second filter is not modified between the first operating mode and the second operating mode. The fourth filter is therefore purged of the accumulated impurities at each change of operating mode. Thus, no replacement of this filter is required throughout the lifetime of the filtration system.The same effect also applies to the third filter, which similarly benefits from a phase of purging the accumulated impurities each time the direction of rotation of the flywheel changes.

[0049] The disclosure also relates to an electro-hydraulic power steering system for a vehicle, comprising: - a two-way pump, - a filtration system as described previously. Brief description of the drawings

[0050] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which:

[0051] [Fig.l] is a schematic view of an electro-hydraulic power steering system comprising a filtration system according to the invention,

[0052] [Fig.2] is a schematic view illustrating the operation of the power steering system of [Fig.l], according to a first mode of operation,

[0053] [Fig.3] is a schematic view illustrating the operation of the power steering system of [Fig.l], according to a second mode of operation,

[0054] [Fig.4] is a schematic view of part of a hygienic fluid circulation circuit draulics of the system of [Fig.l]. Description of the embodiments

[0055] In order to facilitate the reading of the figures, the different elements are not necessarily represented to scale. In these figures, identical elements bear the same references. Certain elements or parameters may be indexed, that is to say designated for example by first element, second element, third element or even first parameter, second parameter, third parameter, etc. This indexing is intended to differentiate similar, but not identical, elements or parameters. This indexing does not imply a priority of one element or parameter over another and the names may be interchanged. Some of these elements may be optional, an element of a given rank number may be present while an element of a lower rank number is not present.

[0056] The term "a second element is placed between a first element and a third element" means that the shortest path, along the circuit considered, to go from the first element to the third element passes through the second element.

[0057] When it is specified that a subsystem comprises a given element, this does not exclude the presence of other elements in this subsystem.

[0058] When it is indicated that a connection point of a circuit is connected to another connection point of the fluid circuit, this does not exclude the presence of intermediate elements likely to be crossed by the fluid. The same applies when it is indicated that a connection point of a circuit is connected to an input / output of a component of the circuit.

[0059] The electro-hydraulic power steering system 50 which will be described can equip a motor vehicle, or an industrial vehicle such as for example a truck. [Fig.l] schematically represents the different components of the system as well as its architecture. The power steering system 50 comprises a hydraulic steering mechanism 7 supplied with hydraulic fluid under pressure by a pump 2. The force generated by the pressure of the hydraulic fluid makes it possible to provide an assisting force for the movement of the hydraulic mechanism 7, which is added to the force exerted by the driver via the steering wheel and the steering column.

[0060] The hydraulic steering mechanism 7 thus comprises an actuator configured to move in a translational movement. The actuator is for example linked in translation to a steering rack. The pump makes it possible to circulate the Hydraulic fluid in a closed circuit. The high-pressure hydraulic fluid at the pump outlet powers one or more actuators in the hydraulic mechanism. The hydraulic fluid leaving the hydraulic mechanism returns to the pump inlet and the cycle begins again.

[0061] The angular position of the steering wheel is measured by a position sensor. The rotation speed of the steering wheel can also be determined from the angular information. An electronic control unit 10 receives information relating to the driver's actions. The electronic control unit 10 can also receive instructions, such as the degree of assistance desired by the driver. The electronic control unit 10 implements control laws allowing the various actuators to be controlled, in order to ensure control of the power steering system.

[0062] Each connection point of the circuit allows the hydraulic fluid to pass into one or other of the circuit portions joining at this connection point. The distribution of the hydraulic fluid between the circuit portions joining at a connection point is done according to the opening or closing of the valves arranged on each of the branches. The different valves thus make it possible to selectively direct the hydraulic fluid into the different branches of the hydraulic circuit, in order to ensure different operating modes, as will be described later.

[0063] The hydraulic fluid used in the hydraulic fluid circuit 1 may be a mixture of mineral oil and synthetic oil, to which various additives are added. The hydraulic fluid is incompressible when the system is in its nominal operating state, i.e. without faults or breakdowns.

[0064] The pump 2 is here a bidirectional pump. The bidirectional pump 2 is configured to circulate a hydraulic fluid under pressure. The bidirectional pump 2 is an electric pump. In other words, the bidirectional pump 2 is configured to be driven by an electric motor 8. The moving parts of the bidirectional pump 2 are driven by an electric motor 8 when the pump is in operation.

[0065] The bidirectional pump 2 can selectively discharge the hydraulic fluid in two different discharge directions, designated in [Fig. 2] and in [Fig. 3] by the signs DI and D2. According to a first operating mode corresponding to a first discharge direction DI of the bidirectional pump 2, the hydraulic fluid is discharged at the first inlet / outlet 3 of the bidirectional pump, and is sucked in at the second inlet / outlet 4 of the bidirectional pump 2. In other words, the first inlet / outlet 3 is then a high-pressure hydraulic fluid outlet and the second inlet / outlet 4 is then a fluid inlet low pressure hydraulics.

[0066] According to a second operating mode corresponding to a second delivery direction D2 of the bidirectional pump 2, the hydraulic fluid is delivered at the second inlet / outlet 4 of the bidirectional pump 2 and sucked at the first inlet / outlet 3 of the bidirectional pump 2. The second inlet / outlet 4 is then a high-pressure hydraulic fluid outlet and the first inlet / outlet 3 is a low-pressure hydraulic fluid inlet.

[0067] The electronic control unit 10 makes it possible to control the operation of the electric drive motor 8. Thus, the direction of rotation of the electric motor 8 can be selected. Similarly, the rotation speed and the mechanical torque provided by the electric motor 8 can be controlled according to the needs of the power steering system 50, for example according to the speed of the vehicle and the driver's preferences regarding the degree of assistance provided by the power steering system 50.

[0068] The hydraulic fluid circulation circuit 1 forms a closed circuit. The circuit can be traveled in two opposite directions, depending on the delivery direction selected for the bidirectional pump 2.

[0069] [Fig.l] shows a filtration system 100 for an electro-hydraulic power steering system 50 comprising a bidirectional pump 2, the filtration system comprising a hydraulic fluid circulation circuit 1 which comprises: - a first main branch A extending between a first connection point 11 configured to be connected to a first inlet / outlet 3 of the bidirectional pump 2 and a second connection point 12 configured to be connected to a first inlet / outlet 5 of a hydraulic steering mechanism 7, - a second main branch B extending between a third connection point 13 configured to be connected to a second inlet / outlet 4 of the bidirectional pump 2 and a fourth connection point 14 configured to be connected to a second inlet / outlet 6 of the hydraulic steering mechanism, - a first auxiliary branch C extending between a fifth connection point 15 configured to be connected to the first input / output 5 of the hydraulic steering mechanism and a sixth connection point 16 arranged on the first main branch A, - a second auxiliary branch D extending between a seventh connection point 17 configured to be connected to the second input / output 6 of the hydraulic steering mechanism 7 and an eighth connection point 18 arranged on the second main branch B, wherein the first main branch A comprises a first filter 31 and the second main branch B comprises a second filter 32.

[0070] This circuit structure makes it possible to filter the entire circuit 1 regardless of the delivery direction of the bidirectional pump 2. In addition, the use of two separate filters 31, 32 makes it possible to adapt the sizing of each of the filters to the quantity of contaminants to be filtered. Indeed, depending on the arrangement of the internal parts of the hydraulic steering mechanism 7, the quantity of contaminants emitted at one inlet / outlet may be different from the quantity emitted at the other inlet / outlet. The capacity of the filter capable of receiving the most particles can thus be chosen to be greater than the capacity of the filter receiving the fewest particles. The duration of use between two maintenance operations of the power steering system 50 can thus be increased.

[0071] This circuit structure thus makes it possible to have two loops each capable of providing fluid communication with the hydraulic steering mechanism 7. The two loops consist respectively of a first loop including the first main branch A, the second auxiliary branch D, as well as a portion of the second main branch B, and a second loop including the second main branch B, the first auxiliary branch C as well as a portion of the main branch A. A set of valves makes it possible to connect the hydraulic mechanism and the pump respectively by arranging them in each auxiliary branch and each main branch in order to selectively form the loop corresponding to one or the other of the two operating modes of the pump.

[0072] The first filter 31 is configured to be traversed by a flow of hydraulic fluid and to retain particles, in particular solid particles, contained in the hydraulic fluid. The components located downstream of the filter thus receive a flow of purified hydraulic fluid, that is to say freed from solid particles originating in particular from the wear of the metal components in contact with the hydraulic fluid. The flow of hydraulic fluid circulates from one to the other between the bidirectional pump 2 and the hydraulic steering mechanism 7.

[0073] As illustrated in [Fig.l], the first main branch A comprises a first valve 41 configured to allow a circulation of hydraulic fluid from the sixth connection point 16 to the second connection point 12 and configured to block a circulation of hydraulic fluid from the second connection point 12 to the sixth connection point 16. The second main branch B comprises a second valve 42 configured to allow a circulation of hydraulic fluid from the eighth connection point 18 to the fourth connection point 14 and configured to block a circulation of hydraulic fluid from the fourth connection point 14 to the eighth connection point 18.

[0074] The first auxiliary branch C comprises a third valve 43 configured to allowing a circulation of hydraulic fluid from the fifth connection point 15 to the sixth connection point 16 and configured to block a circulation of hydraulic fluid from the sixth connection point 16 to the fifth connection point 15. The second auxiliary branch D comprises a fourth valve 44 configured to allow a circulation of hydraulic fluid from the seventh connection point 17 to the eighth connection point 18 and configured to block a circulation of hydraulic fluid from the eighth connection point 18 to the seventh connection point 17.

[0075] The first valve 41, the second valve 42, the third valve 43 and the fourth valve 44 ensure the circulation of the hydraulic fluid in the circuit 1 in the two delivery directions D1, D2 of the bidirectional pump 2.

[0076] The first valve 41 is a passive valve. The second valve 42 is also a passive valve. Similarly, the third valve 43 is a passive valve, and the fourth valve 44 is a passive valve. In other words, each of the valves 41, 42, 43, 44 is devoid of an electromagnetic actuator controllable by an electronic control unit. Each valve 41, 42, 43, 44 is actuated by the pressure of the hydraulic fluid. Each valve 41, 42, 43, 44 has exactly one inlet and one outlet.

[0077] Each valve 41, 42, 43, 44 has an inlet channel and an outlet channel. Each valve comprises a shutter that is movable under the effect of the pressure of the hydraulic fluid. The movable shutter receives a thrust from the hydraulic fluid upstream of the valve, and also receives a thrust in the opposite direction from the hydraulic fluid downstream of the valve. The inlet channel ends with a seat on which the movable shutter can rest. The passage of fluid in the valve is blocked when the shutter rests on the seat. A prestressed elastic spring exerts a force tending to press the movable shutter against the seat. When the pressure at the inlet of the valve is greater than the pressure at the outlet of the valve, the pressure difference tends to reduce the force applied by the spring and tends to move the movable shutter. When the movable shutter leaves its seat, the hydraulic fluid can flow from the inlet to the outlet of the valve.When the pressure at the valve outlet is higher than the pressure at the valve inlet, the pressure difference tends to force the movable shutter against the seat. The flow of fluid is thus blocked.

[0078] According to one embodiment of the filtration system, the first main branch A comprises a first differential pressure sensor 35 configured to measure a pressure difference between an inlet 31a and an outlet 31b of the first filter 31.

[0079] Measuring the pressure drop between the inlet 31a and the outlet 31b of the first filter 31 makes it possible to estimate the degree of clogging of the first filter 31. In the event of an excessive value revealing clogging of the first filter 31, an alert can be issued, in order to warn the user that replacement of the first filter 31 is to be expected.

[0080] According to an exemplary embodiment, the first differential pressure sensor 35 delivers a first signal level when the applied pressure difference is less than a predetermined threshold, and a second signal level when the applied pressure difference is greater than the predetermined threshold. The predetermined threshold is chosen to correspond to a value representative of a state where the first filter 31 is sufficiently clogged to justify an alert and replacement.

[0081] According to another exemplary embodiment, the first differential pressure sensor 35 delivers a signal level proportional to the applied pressure difference. In other words, the first differential pressure sensor 35 delivers continuous information, which makes it possible to measure a progressive drift in the pressure drop across the first filter 31. More precise monitoring of the state of the first filter 31 can be carried out.

[0082] According to the illustrated example, the second main branch B comprises a second differential pressure sensor 36 configured to measure a pressure difference between an inlet 32a and an outlet 32b of the second filter 32.

[0083] Similarly, measuring the pressure drop between the inlet 32a and the outlet 32b of the second filter 32 makes it possible to estimate the degree of clogging of the second filter 32 and an alert can be issued, in order to warn the user that a replacement of this filter is to be expected.

[0084] The first filter 31 and the second filter 32 may be identical. The use of standardized components is thus possible. The risk of reference error during assembly is also eliminated.

[0085] The first filter 31 is for example a hydraulic type filter. The filtration threshold of the first filter 31 is here 5 microns for a filtration efficiency of 99.5%. The efficiency [35 of the first filter 31 is thus equal to 200.

[0086] Similarly, the second filter 32 is for example a hydraulic type filter. Similarly, the filtration threshold of the second filter 32 is here 5 microns for a filtration efficiency of 99.5%. The efficiency [35 of the second filter 32 is equal to 200. Thus, the internal components of the hydraulic steering mechanism 7 are protected. The first filter 31, as well as the second filter 32 may respectively have a cartridge, removably mounted in a filter housing having a rigid external side wall, for example made from at least one perforated metal sheet, which envelops a filter medium. The perforated wall and the filter medium may be held between two opposite flanges constituting axial ends of the cartridge.

[0087] The first main branch A comprises a third filter 33 arranged between the first connection point 11 and the sixth connection point 16. Similarly, the second main branch B comprises a fourth filter 34 arranged between the third connection point 13 and the eighth connection point 18.

[0088] The third filter 33 and the fourth filter 34 provide filtration of the low-pressure hydraulic fluid, which complements the filtration carried out on the high-pressure fluid. The bidirectional pump 2 is thus protected from contaminants.

[0089] The third filter 33 and the fourth filter 34 may be identical. The use of standardized components is thus possible, and the risk of reference error during assembly is eliminated.

[0090] The filtration threshold of the third filter 33 is for example 5 microns for a filtration efficiency of 99.5%. The efficiency [35 of the third filter 33 is equal to 200. Similarly, the filtration threshold of the fourth filter 34 is for example 5 microns for a filtration efficiency of 99.5%. The efficiency [35 of the fourth filter 34 is equal to 200. Thus, the internal components of the bidirectional pump 2 are protected.

[0091] The third filter 33 is here a metal mesh screen. The fourth filter 34 is also a metal mesh screen. This type of filter makes it possible to retain particles likely to damage the bidirectional pump.

[0092] According to one embodiment, detailed in [Fig.4], the first main branch A comprises a first bypass branch BPI configured so that the hydraulic fluid bypasses the first filter 31 when the difference between the pressure upstream of the first filter 31 and the pressure downstream of the first filter 31 is greater than a first predetermined threshold Pmaxl.

[0093] The first bypass branch BPI makes it possible to maintain a circulation of hydraulic fluid in the circuit 1 when the first filter 31 is clogged and causes a pressure loss incompatible with nominal operation of the system, in particular because the pressure of the hydraulic fluid in the hydraulic mechanism 7 is no longer nominal.

[0094] Similarly, the second main branch B here comprises a second bypass branch BP2 configured so that the hydraulic fluid bypasses the second filter 32 when the difference between the pressure upstream of the second filter 32 and the pressure downstream of the second filter 32 is greater than a second predetermined threshold Pmax2.

[0095] The second bypass branch BP2 has the same role as the first bypass branch BPI, namely to allow circulation of hydraulic fluid in the second main branch B when the second filter 32 is clogged.

[0096] The first bypass branch BPI comprises a fifth valve 45 configured to block the circulation of hydraulic fluid when the difference between the pressure upstream of the fifth valve 45 and the pressure downstream of the fifth valve 45 is less than a predetermined threshold Pmaxl, and configured to authorize the circulation of hydraulic fluid when the difference between the pressure upstream of the fifth valve 45 and the pressure downstream of the fifth valve 45 is greater than the predetermined threshold Pmaxl. In other words, as long as the pressure drop caused by the first filter 31 is sufficiently low, all the hydraulic fluid flow flows through the first filter 31. When the first filter 31 is clogged, the hydraulic fluid flow passes through the first bypass branch BPI. The fifth valve 45 is a one-way valve. In other words, the hydraulic fluid can only pass in one direction of circulation.

[0097] The first bypass branch BPI extends between a ninth connection point 19 arranged on the first main branch A upstream of the first filter 31 to a tenth connection point 20 arranged on the first main branch A downstream of the first filter 31.

[0098] Similarly, the second bypass branch BP2 comprises a valve, here called sixth valve 46 configured to block the circulation of hydraulic fluid when the difference between the pressure upstream of the sixth valve 46 and the pressure downstream of the sixth valve 46 is less than a predetermined threshold Pmax2, and configured to allow the circulation of hydraulic fluid when the difference between the pressure upstream of the sixth valve 46 and the pressure downstream of the sixth valve 46 is greater than the predetermined threshold Pmax2. In other words, as long as the pressure loss caused by the second filter 32 is sufficiently low, all the flow of hydraulic fluid can flow through the second filter 32. When the second filter 32 is clogged, the flow of hydraulic fluid passes through the second bypass branch BP2. The sixth valve 46 is a one-way valve.In other words, the passage of hydraulic fluid can only be done in one direction of circulation. Valve 46 can be associated with a variable number of valves used in other sections of the circuit. The same is true for valve 45. Valve 45 and valve 46 are presented in combination with a seventh valve 47 which will be described, and these names are arbitrary.

[0099] The sixth valve 46 is for example identical to the fifth valve 45. The sixth valve 46 can also be different from the fifth valve 45.

[0100] The second bypass branch BP2 extends between an eleventh connection point 21 arranged on the second main branch B upstream of the second filter 32 to a twelfth connection point 22 arranged on the second main branch B downstream of the second filter 32. The first bypass branch BPI and the second bypass branch BP2 are not shown in Figures 1 to 3, in order to simplify these figures.

[0101] The hydraulic fluid circulation circuit 1 comprises a third bypass branch E extending between: a thirteenth connection point 23 arranged on the first main branch A between the first valve 41 and the second connection point 12, and a fourteenth connection point 24 arranged on the second main branch B between the second valve 42 and the fourth connection point 14.

[0102] The thirteenth connection point 23 can be confused with the second connection point 12. Similarly, the fourteenth connection point 24 can be confused with the fourth connection point 14.

[0103] The third bypass branch E comprises a seventh valve 47 configured to selectively allow or block a circulation of hydraulic fluid in the third bypass branch E. The seventh valve 47 is an electrically controlled valve. In other words, the seventh valve 47 comprises an electromagnetic actuator controlled by an electronic control unit. The valve 47 is here presented in combination with a fifth valve 45 and a sixth valve 46, these names are arbitrary. Similarly, the names first, second, third bypass branch are arbitrary.

[0104] When a fault is detected on the bidirectional pump 2 and the latter is no longer functional, the seventh valve 47 can be controlled so as to allow the circulation of hydraulic fluid in the third bypass branch E. A hydraulic blockage of the hydraulic steering mechanism 7 is thus avoided. The hydraulic mechanism 7 remains manually operable, even if no assistance is then provided.

[0105] The disclosure also relates to a method of operating an electro-hydraulic power steering system 50 comprising a filtration system 100 as previously described, in which: - according to a first operating mode corresponding to a first delivery direction DI of the bidirectional pump 2, the hydraulic fluid is delivered by the first inlet / outlet 3 of the bidirectional pump 2, circulates in the first main branch A and passes successively in this order: the third filter 33, the first filter 31, the hydraulic steering mechanism 7 by entering through the first inlet / outlet 5 and leaving through the second inlet / outlet 6, the second auxiliary branch D, the second main branch B by passing through the fourth filter 34, and joins the second inlet / outlet 4 of the bidirectional pump 2.

[0106] The circulation of the hydraulic fluid in the circuit 1 when the power steering system 50 operates according to the first operating mode is shown diagrammatically in [Fig.2]. In [Fig.2] as well as in [Fig.3], the circuit portions in which the hydraulic fluid circulates are in thick lines. The circuit portions in which the hydraulic fluid does not circulate are in thin lines.

[0107] In [Fig.2], the arrow DI indicates the first discharge direction. The high-pressure hydraulic fluid is discharged through the first inlet / outlet 3, reaches the first connection point 11, and circulates in the first main branch A passing successively through the third filter 33, the sixth connection point 16, the first filter 31, the first valve 41, the thirteenth connection point 23, the second connection point 12. The seventh valve 47 is in the closed position, so that the high-pressure hydraulic fluid cannot circulate in the third bypass path E. The third valve 43 prevents circulation of high-pressure hydraulic fluid in the first auxiliary branch C. The high-pressure hydraulic fluid coming from the second connection point 12 joins the first inlet / outlet 5 of the hydraulic steering mechanism 7 so as to provide assistance to a movement of the steering wheel in the direction of rotation marked RL The hydraulic fluid leaves the hydraulic mechanism 7 through the second inlet / outlet 6.The fourth valve 44 allows hydraulic fluid to flow in the second auxiliary branch D, while the second valve 42 prevents flow in the second main branch B. The hydraulic fluid leaving the hydraulic mechanism 7 reaches the seventh connection point 17, passes through the fourth valve 44, and reaches the eighth connection point 18. The second valve 42 prevents the hydraulic fluid from flowing from the eighth connection point 18 to the fourth connection point 14, because the pressure at the fourth connection point 14 is higher than the pressure at the eighth connection point 18. The hydraulic fluid flows through the portion of the second main branch B between the eighth connection point 18 and the third connection point 13 by passing through the fourth filter 34.The hydraulic fluid then circulates in the portion of the circuit between the third connection point 13 and the second inlet / outlet 4 of the bidirectional pump 2, and joins the bidirectional pump 2 where it is discharged in the direction DI.

[0108] In this first operating mode, the high-pressure hydraulic fluid is filtered by the third filter 33 then by the first filter 31 which are passed through in series. The low-pressure hydraulic fluid downstream of the hydraulic mechanism 7 is filtered by the fourth filter 34. Double filtration is thus ensured, which improves the cleanliness of the hydraulic fluid circulating in the circuit 1.

[0109] According to another aspect of the operating method: - according to a second operating mode corresponding to a second delivery direction D2 of the bidirectional pump 2, opposite to the first delivery direction D1, the hydraulic fluid is delivered through the second inlet / outlet 4 of the bidirectional pump 2, circulates in the second main branch B and passes successively in this order: the fourth filter 34, the second filter 32, the hydraulic steering mechanism 7 by entering through the second inlet / outlet 6 and leaving through the first inlet / outlet 5, the first auxiliary branch C, the first main branch A by passing through the third filter 33, and joins the first inlet / outlet 3 of bidirectional pump 2.

[0110] In [Fig.3], arrow D2 indicates the second direction of discharge. The fluid high pressure hydraulic fluid is discharged through the second inlet / outlet 4, reaches the third connection point 13, and circulates in the second main branch B passing successively through the fourth filter 34, the eighth connection point 18, the second filter 32, the second valve 42, the fourth connection point 24. The seventh valve 47 is in the closed position, so that the high pressure hydraulic fluid cannot circulate in the third bypass path E. The high pressure hydraulic fluid reaches the fourth connection point 14 and joins the second inlet / outlet 6 of the hydraulic steering mechanism 7 so as to provide assistance to a movement of the steering wheel in the direction of rotation marked R2. The hydraulic fluid leaves the hydraulic mechanism 7 through the first inlet / outlet 5.The first valve 41 prevents the circulation of hydraulic fluid in the first main branch A, while the third valve 43 allows circulation in the first auxiliary branch C. The hydraulic fluid leaving the hydraulic mechanism 7 reaches the fifth connection point 15, passes through the first valve 41, and reaches the sixth connection point 16. The first valve 41 prevents the hydraulic fluid from circulating from the sixth connection point 16 to the second connection point 12, because the pressure at the second connection point 12 is higher than the pressure at the sixth connection point 16. The hydraulic fluid flows through the portion of the first main branch A between the sixth connection point 16 and the first connection point 11 by passing through the third filter 33.The hydraulic fluid then circulates in the portion of the circuit between the first connection point 11 and the first inlet / outlet 3 of the bidirectional pump 2, and joins the bidirectional pump 2 to be discharged in the direction D2.

[0111] In this second mode of operation, the high-pressure hydraulic fluid is filtered by the fourth filter 34 and then by the second filter 32 which are passed through in series. The low-pressure hydraulic fluid downstream of the hydraulic mechanism 7 is filtered by the third filter 33.

[0112] The portion of the first main branch A between the first connection point 11 and the sixth connection point 16 is traversed by hydraulic fluid in both operating modes. The direction of travel in this portion is reversed between the two operating modes. In the same way, the portion of the second main branch B between the third connection point 13 and the eighth connection point 18 is traversed by hydraulic fluid in both operating modes, and the direction of travel is reversed between the two operating modes.

[0113] According to the first operating mode illustrated in [Fig. 2], the fourth filter 34 is traversed in the direction indicated by the arrow F1, and collects the impurities circulating downstream of the hydraulic steering mechanism 7. When the system switches to the second operating mode, the direction of travel of the hydraulic fluid in the fourth filter 34 is reversed, as shown diagrammatically by the arrow F2 in [Fig. 3]. In addition, the pressure upstream of the fourth filter 34 in the second operating mode is higher than the pressure upstream of the fourth filter 34 in the first operating mode, because the fourth filter is then on the high pressure side of the circuit 1. The hydraulic fluid then tends to carry the impurities previously accumulated on the fourth filter 34. The impurities removed from the fourth filter 34 are then conveyed to the second filter 32 where they remain permanently accumulated.Indeed, the direction of travel of the second filter 32 is not modified between the first operating mode and the second operating mode. The fourth filter 34 is thus purged of accumulated impurities at each change of operating mode. Thus, no replacement of the fourth filter 34 is required throughout the duration of use of the filtration system.

[0114] In the same way, the third filter 33 collects, in the second operating mode illustrated in [Fig. 3], the impurities circulating downstream of the hydraulic steering mechanism 7. When the system switches to the first operating mode, the direction of travel of the hydraulic fluid in the third filter 33 is reversed. The hydraulic fluid then tends to carry the impurities previously accumulated on the third filter 33. The impurities removed from the third filter 33 are then conveyed to the first filter 31 where they remain permanently accumulated. The third filter 33 thus also benefits, each time the direction of rotation of the steering wheel changes, from a phase of purging the accumulated impurities. The third filter 33 therefore does not require any replacement, since it is periodically purged of the accumulated impurities.

[0115] The disclosure also relates to an electro-hydraulic power steering system 50 for a vehicle, comprising: - a two-way pump 2, - a filtration system 100 as described previously.

[0116] The present disclosure is not limited to the embodiments described above, only by way of example, but it encompasses all the variants that may be envisaged by those skilled in the art within the framework of the protection sought. Thus, the particular structures for the realization of the circuit are not specifically limited. The branches which have been schematically illustrated as separated from each other may, if necessary, be arranged in neighboring channels or lines, included in a system of conduits isolating the flows circulating in the branches or passageways. The term "branch" is not intended to be restrictive and can mean a simple line or passageway through which fluid flows. The same applies to the terms "connection" or "connection point".

Claims

Claims

1. A filtration system (100) for an electrohydraulic power steering system (50) comprising a bidirectional pump (2), the filtration system comprising: - a hydraulic fluid circulation circuit (1) comprising: — a first main branch (A) extending between a first connection point (11) configured to be connected to a first inlet / outlet (3) of the bidirectional pump (2) and a second connection point (12) configured to be connected to a first inlet / outlet (5) of a hydraulic steering mechanism (7), — a second main branch (B) extending between a third connection point (13) configured to be connected to a second inlet / outlet (4) of the bidirectional pump (2) and a fourth connection point (14) configured to be connected to a second inlet / outlet (6) of the hydraulic steering mechanism, — a first auxiliary branch (C) extending between a fifth connection point (15) configured to be connected to the first input / output (5) of the hydraulic steering mechanism and a sixth connection point (16) arranged on the first main branch (A), — a second auxiliary branch (D) extending between a seventh connection point (17) configured to be connected to the second input / output (6) of the hydraulic steering mechanism (7) and an eighth connection point (18) arranged on the second main branch (B), wherein the first main branch (A) comprises a first filter (31) and the second main branch (B) comprises a second filter (32), wherein the first main branch (A) comprises a third filter (33) arranged between the first connection point (11) and the sixth connection point (16), and wherein the second main branch (B) comprises a fourth filter (34) disposed between the third connection point (13) and the eighth connection point (18).

2. A filtration system (100) according to claim 1, wherein: - the first main branch (A) comprises a first valve (41) configured to allow a circulation of hydraulic fluid from the sixth connection point (16) to the second connection point (12) and configured to block a circulation of hydraulic fluid from the second connection point (12) to the sixth connection point (16), - the second main branch (B) comprises a second valve (42) configured to allow a circulation of hydraulic fluid from the eighth connection point (18) to the fourth connection point (14) and configured to block a circulation of hydraulic fluid from the fourth connection point (14) to the eighth connection point (18), - the first auxiliary branch (C) comprises a third valve (43) configured to allow a circulation of hydraulic fluid from the fifth connection point (15) to the sixth connection point (16) and configured to block a circulation of hydraulic fluid from the sixth connection point (16) to the fifth connection point (15),- the second auxiliary branch (D) comprises a fourth valve (44) configured to allow circulation of hydraulic fluid from the seventh connection point (17) to the eighth connection point (18) and configured to block circulation of hydraulic fluid from the eighth connection point (18) to the seventh connection point (17).,

3. A filtration system (100) according to claim 1 or 2, wherein the first main branch (A) comprises a first differential pressure sensor (35) configured to measure a pressure difference between an inlet (31a) and an outlet (31b) of the first filter (31), and wherein the second main branch (B) comprises a second differential pressure sensor (36) configured to measure a pressure difference between an inlet (32a) and an outlet (32b) of the second filter (32).

4. Filtration system (100) according to one of the preceding claims, wherein the filtration threshold of the third filter (33) is 5 microns for a filtration efficiency of 99.5% and the filtration threshold of the fourth filter (34) is 5 microns for a filtration efficiency of 99.5%.

5. Filtration system (100) according to one of the preceding claims, in which the first main branch (A) comprises a first bypass branch (BPI) configured so that the hydraulic fluid bypasses the first filter (31) when the difference between the pressure upstream of the first filter (31) and the pressure downstream of the first filter (31) is greater than a first predetermined threshold (Pmaxl), and wherein the second main branch (B) comprises a second bypass branch (BP2) configured so that the hydraulic fluid bypasses the second filter (32) when the difference between the pressure upstream of the second filter (32) and the pressure downstream of the second filter (32) is greater than a second predetermined threshold (Pmax2).

6. Filtration system (100) according to one of the preceding claims in combination with claim 2, wherein the hydraulic fluid circulation circuit (1) comprises a third bypass branch (E) extending between: a thirteenth connection point (23) arranged on the first main branch (A) between the first valve (41) and the second connection point (12), and a fourteenth connection point (24) arranged on the second main branch (B) between the second valve (42) and the fourth connection point (14).

7. Filtration system (100) according to the preceding claim, wherein the third bypass branch (E) comprises a seventh valve (47) configured to selectively allow or block a circulation of hydraulic fluid in the third bypass branch (E), the seventh valve (47) being an electrically controlled valve.

8. Method of operating an electrohydraulic power steering system (50) comprising a filtration system (100) according to one of the preceding claims, wherein: - according to a first operating mode corresponding to a first delivery direction (Dl) of the bidirectional pump (2), the hydraulic fluid is delivered through the first inlet / outlet (3) of the bidirectional pump (2), circulates in the first main branch (A) and passes successively in this order: the third filter (33), the first filter (31), the hydraulic steering mechanism (7) by entering through the first inlet / outlet (5) and leaving through the second inlet / outlet (6), the second auxiliary branch (D), the second main branch (B) by passing through the fourth filter (34), and joins the second inlet / outlet (4) of the bidirectional pump (2).

9. Method of operation according to the preceding claim, in which : - according to a second operating mode corresponding to a second discharge direction (D2) of the bidirectional pump (2), opposite to the first discharge direction (D1), the hydraulic fluid is discharged through the second inlet / outlet (4) of the bidirectional pump (2), circulates in the second main branch (B) and passes successively in this order through: the fourth filter (34), the second filter (32), the hydraulic steering mechanism (7) by entering through the second inlet / outlet (6) and leaving through the first inlet / outlet (5), the first auxiliary branch (C), the first main branch (A) by passing through the third filter (33), and joins the first inlet / outlet (3) of the bidirectional pump (2).

10. Electro-hydraulic power steering system (50), comprising: - a bidirectional pump (2), - a filtration system (100) according to one of claims 1 to 7.

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