FLUSHING OF HYDRAULIC FLUID ON START-UP

The invention relates to a self-maintenance system (1) for a vehicle hydraulic assistance device (2), the said device (2) comprising a hydraulic machine (21, 23), the said hydraulic machine (21, 23) being configured to be brought into operation, or deactivated, alternately, the bringing-into-operation and the deactivation being afforded by movement of bringing-into-operation moving parts (211, 231), and the engagement and disengagement of the assistance being operable on command, the system (1) comprising a control module (11) configured to command the bringing into operation of the hydraulic machine (21, 23) for a predetermined length of time and then command deactivation of the hydraulic machine (21, 23) so as to flush all or part of the hydraulic machine (21, 23), the said commands being independent of a command to engage and disengage the assistance.

TECHNICAL FIELD

The invention relates to a method and a self-maintenance system of a hydraulic assistance device of a vehicle.

The invention more specifically addresses the self-maintenance of a hydraulic assistance device that is little used and/or the hydraulic fluid of which is worn out.

PRIOR ART

For the purpose of proposing an additional drive for one or more wheels of a vehicle, many hydraulic assistance devices with traction, or temporary hydraulic transition, for vehicles have been proposed.

These devices generally implement at least two hydraulic machines put in fluid communication and configured to convert a pressure difference between their inlet and their outlet into a drive torque, and reciprocally.

Typically, such devices comprise a hydraulic pump, the so-called power pump, linked to the powertrain of the vehicle, said power pump outputting into one or more hydraulic motors linked to the non-driving wheels. Thus, it is possible to transition from a propulsion of the vehicle of 4×2 type to propulsion of 4×4 type, for example in environments where the vehicle is at risk of skidding.

Alternatively, the assistance comprises a first hydraulic machine linked to the front axle of the vehicle, and a second hydraulic machine linked to the rear axle of the vehicle. These two machines can alternatively play the role of power pump or hydraulic motor, according to the needs for an additional drive required by one or the other of the axles. This type of device is conventionally referred to as a “chain drive”, and also makes it possible to convert a 4×2 vehicle into a 4×4 one.

In any case, such systems are disengageable, so as to be able to engage or disengage the assistance according to a command of the user and/or the driving conditions of the vehicle, for example at given speed thresholds, or at a skid threshold. Moreover, these devices are controllable on command, by an automaton or a user, such as to constantly monitor the assistance provided to the wheels.

Thus, an assistance system which would only, for example, be engaged to avoid skidding, could stay unengaged for a very long time. For example, a vehicle endowed with such a system which would only activate the assistance in the event of snow. It is thus possible that, in certain countries, the assistance never engages during most of the year.

The hydraulic machines of such systems generally comprise an assembly of movable parts, in relative movement with respect to one another under the action of a hydraulic fluid circulating within the hydraulic machines. However, to ensure the correct operation of such machines, it is necessary to regularly activate the movement of the movable parts, in order to avoid the appearance of wear or corrosion at the level of the contact points, or deposits at different places, in particular in the bottoms and the filters. The contact of immovable parts can cause a localized abrasion when the vehicle receives the vibrations from driving. The deposits can cause a certain polymerization, the sticking of parts, or the clogging of strainers, which risks damaging the surface at the moment when the machines are started again after a long time without activity, and considerably reduces their lifetime.

Furthermore, the high operating temperatures of such machines can cause the premature ageing of the operating fluid by heating of stagnant deposits, at certain particularly hot localized places. A portion of fluid kept immovable in this part of the system would be regularly heated and could then be locally degraded. This degraded fluid could polymerize and create a blockage, or travel through the system at the first starting-up and become placed on a strainer or a small mechanism. This is particularly problematic when the fluid circuits of the assistance devices are equipped with filtering systems with the aim of preventing the ingestion of impurities by the components of the device. Typically, it is usual to endow the feed pump of such circuits with a filtering strainer at the point of suction of hydraulic fluid from the reservoir. The fouling of this strainer can make the assistance system unavailable due to the fact that the feed pump would no longer be capable of sucking through this strainer, and therefore of creating the pressure necessary for the engagement. This considerably reduces the use time between two drainages of the system.

Besides the reduction of the lifetime of hydraulic assistance devices, the previously described drawbacks require regular maintenance by a professional. This maintenance can turn out to be costly and time-consuming for the user.

There is therefore a need to ensure the long-term availability of the hydraulic assistance devices without compromising the safety of the vehicle.

SUMMARY OF THE INVENTION

One aim of the invention is to provide continuous self-maintenance of a hydraulic assistance device of a vehicle without altering the structure of the device.

Another aim of the invention is to increase the lifetime of a hydraulic assistance device in an inexpensive way.

Another aim of the invention is to increase the time interval separating two drainages of a hydraulic assistance device of a vehicle.

The invention particularly proposes a self-maintenance system of a hydraulic assistance device of a vehicle, said device comprising a hydraulic machine, said hydraulic machine comprising:a fluid inlet,a fluid outlet, andelements movable under the action of a hydraulic fluid circulating within the hydraulic machine.
said hydraulic machine being configured to:convert a pressure difference between the fluid inlet and the fluid outlet into a drive torque, and reciprocally, such as to provide the hydraulic assistance, the conversion being implemented by the movement of movable elements, andbe alternatively:operated such as to engage the hydraulic assistance, ordisabled such as to disengage the hydraulic assistance, the operating and the disabling being provided by the movement of starting movable elements, and the engagement and disengagement of the assistance being controllable on command,
the system comprising a controlling module configured to command the operating of the hydraulic machine during a determined time period, then command the disabling of the hydraulic machine at the end of said time period such as to ensure the flushing of all or part of the hydraulic machine, said operating and disabling commands being independent of a command of engagement and disengagement of the assistance.

In such a self-maintenance system, the controlling module regularly forces the circulation of fluid within all or part of the hydraulic machine, by complete or partial flushing of the hydraulic machine, which avoids the formation of deposits between the parts. This intermittent forcing is furthermore independent of commands of engagement and/or disengagement of the hydraulic assistance. Thus, the conservation of the quality of the hydraulic fluid of the hydraulic assistance system is made possible, reducing and homogenizing its wear over the whole volume of the system, even if the system is not regularly stressed. This is referred to as continuous self-maintenance of the hydraulic system. It should be noted that such self-maintenance is different from the periodic maintenance operation performed by a professional, which consists in changing the hydraulic fluid, and where applicable the filters of the hydraulic assistance system. Furthermore, such a system offers the advantage of not modifying the existing hydraulic assistance device structures, while significantly increasing the lifetime by limiting the damage due to portions of stagnant fluid. Finally, such a system makes it possible to significantly increase the time interval separating two successive drainages of the assistance device.

The system according to the invention can further comprise the following features taken alone or in combination:the device further comprises:a reservoir, anda feed pump, the feed pump comprising:a fluid inlet put in fluid communication with the reservoir, anda fluid outlet put in fluid communication with the hydraulic machine,the pump being configured to circulate the hydraulic fluid alternatively:from the reservoir to the hydraulic machine, through activation of the feed pump, to operate the hydraulic machine, andfrom the hydraulic machine to the reservoir to disable the hydraulic machine.the controlling module being configured to command the feed pump,the starting movable elements are independent, the controlling module being configured to command the operating then the disabling of the hydraulic machine:the vehicle being in movement, the flushing being provided by the circulation of the hydraulic fluid upon the transmission of the movements of the drive torque to the movable elements of the operated hydraulic machine, orthe vehicle being stopped, the flushing being partly provided by the movements of the starting movable elements during the successive operating and disabling of the hydraulic machine,the starting movable elements are dependent, the controlling module being configured to command the operating then the disabling of the hydraulic machine:the vehicle being in movement, the flushing being provided by the circulation of the hydraulic fluid upon the transmission of the movements of the drive torque to the movable elements of the operated hydraulic machine, orthe vehicle being stopped, the flushing being provided by the movements of the starting movable elements during the successive operating and disabling of the hydraulic machine,the hydraulic machine is a hydraulic power pump linked to a powertrain of the vehicle,the hydraulic machine is a hydraulic motor linked to a wheel of the vehicle, andthe hydraulic assistance device comprises:a first hydraulic machine, anda second hydraulic machine,the fluid inlet of the first machine being put in fluid communication with the fluid outlet of the second machine, andthe fluid inlet of the second machine being put in fluid communication at the fluid outlet of the first machine,the controlling module being configured to command the operating then the disabling of the first hydraulic machine independently of the operating then the disabling of the second hydraulic machine.

The invention also relates to a vehicle comprising a hydraulic assistance device, and further comprising a self-maintenance system as previously described.

The invention further relates to a self-maintenance method of a hydraulic assistance device of a vehicle, said device comprising a hydraulic machine, said hydraulic machine comprising:a fluid inlet,a fluid outlet, andelements which are movable under the action of a hydraulic fluid circulating within the hydraulic machine,
said hydraulic machine being configured to:convert a pressure difference between the fluid inlet and the fluid outlet into a drive torque, and reciprocally, such as to provide the hydraulic assistance, the conversion being implemented by the movement of movable elements, andbe alternatively:operated such as to engage the hydraulic assistance, ordisabled such as to disengage the hydraulic assistance, the operating and the disabling being also provided by the movement of starting movable elements, and the engagement and the disengagement of the assistance being controllable on command,
the method comprising the steps consisting inoperating the hydraulic machine for a determined time period, thendisabling the hydraulic machine at the end of said time period so as to provide the flushing of all or part of the hydraulic machine, the steps of operating and disabling being implemented independently of a command of engagement and/or disengagement of the assistance, the method being implemented by a self-maintenance system previously described.

The method according to the invention can further comprise the following features taken alone or in combination:it is implemented for a given range of vehicle speeds, for example the vehicle speed being between 0 and 40 km/h,the steps of operating and disabling are successively repeated with a given frequency,it is implemented starting from a given level of wear of the hydraulic fluid,it is implemented each time the vehicle is started up, andit is implemented at a given rate, said rate beingeither functional, for example each time the vehicle has travelled a given distance, and/ortemporal, for example once every month of operation of the vehicle.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the figures, there now follows a description of a self-maintenance system1of a hydraulic assistance device2of a vehicle.

In the remainder of the text, the term “self-maintenance” is understood to mean all the actions automatically implemented by a system1as described, for the purpose of ensuring the constant availability of the functions of a hydraulic assistance device2of a vehicle. As will be explained in more detail, the self-maintenance of a hydraulic assistance device2comprises the regular defouling of the different elements of the device2, such as the filters101,103or the areas where there are deposits, by circulating the hydraulic fluid within the device2. The self-maintenance also comprises the renewal and the regular homogenization of the hydraulic fluid, by stirring and mixing, for the purpose of avoiding stagnation of fluid, particularly in the portions of elements of the device2which are close to a hot element of the vehicle.

With reference toFIGS. 1ato 1f, 2aand 2b, a hydraulic assistance device2of a vehicle comprises a hydraulic machine21,23.

The hydraulic machine21,23comprises a fluid inlet210,230and a fluid outlet212,232, and mechanical elements movable under the action of a hydraulic fluid circulating within the hydraulic machine21,23. The fluid inlet210,230and outlet212,232are generally put in fluid communication with a hydraulic assistance circuit27. Such a machine21,23is then configured to convert a pressure difference between the fluid inlet210,230and the fluid outlet212,232into a drive torque, and reciprocally, the conversion being implemented by the movement of movable elements of the hydraulic machine21,23. This conversion further makes it possible to provide the function of hydraulic assistance of the device2.
The hydraulic machine21,23is also configured to be alternatively operated or disabled, the operating and the disabling respectively providing the engagement and the disengagement of the hydraulic assistance. With regard to this, the hydraulic machine21,23comprises starting movable elements211,231also movable under the action of a hydraulic fluid circulating within the hydraulic machine21,23. By way of non-limiting example, such movable elements211,231can be clutches211with disks or dogs, for example of the same type as the gearbox state of the art. In this case, the starting movable elements211are linked to a different fluid circuit29from the hydraulic assistance circuit27, and their movement is independent from the other movable elements of the hydraulic machine21. These are referred to as “independent” starting movable elements211. Alternatively such elements can be radial pistons231that disengage from their cam by retraction of the pistons231. In this case, the starting movable elements231are directly linked to the hydraulic assistance circuit27. Their movement is dependent of the other movable elements of the hydraulic machine, or is even the same elements231. These are referred to as “dependent” starting movable elements231. The operating and disabling of such machines21,23are for example described in the patent applications FR 2 996 267 and FR 3 033 529 in the name of the Applicant, and will not be further detailed here. The hydraulic machine21,23generally possesses a casing drain215,235, which collects the internal leaks of all the members of the machine21,23subjected to pressure, and sends them back to an oil reservoir12. More particularly, the hydraulic machine21,23can possess a leak nozzle213,233intended to renew the oil, and to cool certain internal members, which is linked to a drain215,235by which the excess hydraulic fluid can be expelled toward the reservoir12.

Still with reference toFIGS. 1ato 1f, 2aand 2b, a vehicle endowed with such a hydraulic assistance device2comprises a self-maintenance system1for the device2. This system1particularly comprises a controlling module11configured to command the hydraulic assistance. More precisely, the controlling module11is configured to receive a command of engagement or disengagement of the hydraulic assistance and transmit a corresponding command of operating or disabling of the hydraulic machine21,23.

The engagement and the disengagement of the assistance is controllable on command. With regard to this, the command of engagement or disengagement of the hydraulic assistance can be transmitted to the controlling module11directly by a user. Alternatively such a command can be transmitted by an automaton13of the vehicle according to the driving conditions. Typically, the automaton13requires the hydraulic assistance when a skid is detected, for example when the vehicle is tackling snowy or sandy surfaces. In the same way, the automaton13cuts off the hydraulic assistance when the speeds attained by the vehicle are greater than a level permissible by the hydraulic machine21,23.
The controlling module11is further configured to command the operating of the hydraulic machine21,23during a determined time period, then the disabling of the hydraulic machine21,23at the end of the determined operating period, said command being independent of, respectively, an engagement or disengagement command of the assistance. More precisely, the controlling module11is configured to control the operation of the hydraulic assistance device2alternatively in response to a command of engagement or disengagement, or on its own initiative, for self-maintenance purposes, without having received an engagement and/or disengagement command. Specifically, the operating of the hydraulic machine21,23during a determined time period, then the disabling of the hydraulic machine21,23, ensure the setting in movement of movable elements of the hydraulic machine21,23to force the circulation of hydraulic fluid within all or part of the hydraulic machine21,23. This is referred to as complete or partial flushing of the hydraulic machine21,23. The regular self-maintenance of the hydraulic assistance device2is thus advantageously made possible.

With reference toFIG. 2a, the hydraulic machine can be a hydraulic power pump21. In this case, the power pump21is linked, for its drive, to a powertrain31of the vehicle. The movable elements of the power pump21are then configured so that their movements make it possible to convert the torque supplied by the powertrain31into a pressure difference between the fluid inlet210and outlet212of the power pump21.

Alternatively, still with reference toFIG. 2a, the hydraulic machine is a hydraulic motor23. The motor23is linked to a wheel33of the vehicle. The movable elements of the motor23are then configured so that their movements make it possible to convert a pressure difference between the fluid inlet230and outlet232of the motor23into a torque transmitted to the wheel33, when the assistance is engaged. The wheel33is typically a supporting wheel not linked to the mechanical transmission of a 4×2 vehicle. When the assistance is disengaged and the vehicle is in movement, the motor23being moreover operated, the movable elements can be set in movement under the action of the torque exerted by the wheel33in rotation. However, there is in general a vehicle speed limit above which a safety module14of the hydraulic assistance device2automatically disables the hydraulic motor23, to preserve the safety of the motor23.

With reference toFIG. 2a, the hydraulic assistance device can also comprise a first hydraulic machine21and a second hydraulic machine23, the inlet210of the first machine21being put in fluid communication with the outlet232of the second machine23, and the inlet230of the second machine23being put in fluid communication at the outlet212of the first machine21.

Typically, the first machine21can be a hydraulic power pump, whereas the second hydraulic machine23can be a hydraulic motor. The hydraulic circuit linking the power pump21to the motor then advantageously comprises a bypass valve25. The controlling module is thus configured to command the operating then the disabling of the first hydraulic machine21independently of the operating then the disabling of the second hydraulic machine23.
Alternatively, with reference toFIG. 2b, the device2is of “chain drive” type. In this case, the first hydraulic machine21is linked to the front axle35of the vehicle, and the second hydraulic machine23is linked to the rear axle37of the vehicle. The first machine21and the second hydraulic machine23can then be configured to alternatively provide the power pump or motor function, according to the needs for additional drives required by one or the other of the axles35,37. The controlling module11is then configured to implement the operating and/or the disabling of the machines21,23simultaneously.

Different embodiments of a self-maintenance system1of a hydraulic assistance device of a vehicle will now be described, with reference toFIGS. 1ato1f.

A hydraulic assistance device2generally comprises a reservoir12and a feed pump10, the feed pump10comprising:a fluid inlet100put in fluid communication with the reservoir12, anda fluid outlet102put in fluid communication with the hydraulic machine21,23,
The feed pump10can be electrical or be linked to the powertrain31of the vehicle. The feed pump10is moreover configured to make a hydraulic fluid circulate alternatively:from the reservoir12to the hydraulic machine21,23to operate the hydraulic machine21,23such as to set in movement therein the starting movable elements211,231, and to maintain therein a sufficient pressure to maintain the machine21,23in operation, andfrom the hydraulic machine21,23to the reservoir12to disable the hydraulic machine21,23, thus causing a decrease in the pressure inside the hydraulic machine21,23and also setting in movement the starting movable elements211,231.

Typically, with reference toFIGS. 1a, 1dand 1ethe hydraulic machine23,21possesses a fluid inlet230,210put in fluid communication with the fluid outlet102of the feed pump10, and a fluid outlet, for example the leak nozzle233,213, put in fluid communication with the reservoir12, for example by means of the drain235,215. In this case, the controlling module11commands the operating of the hydraulic machine23through activation of the feed pump10which outputs the hydraulic fluid into the hydraulic machine23. In the same way, the controlling module11commands the disabling of the hydraulic machine23by disabling of the feed pump10, which causes the expulsion of the fluid from the hydraulic machine23to the reservoir12, via the drain235.

Alternatively, with reference toFIGS. 1cand 1f, the hydraulic machine23,21possesses a fluid inlet-outlet opening230,210put in fluid communication with the fluid outlet102of the feed pump10, the feed pump10furthermore operating by counter-rotation, i.e. it is configured to output hydraulic fluid from the reservoir12to the hydraulic machine23and reciprocally, by way of a single fluid communication duct. The operation of such a feed pump10is for example described in the patent application FR 3 033 529 in the name of the Applicant. In this case the controlling module11commands the operating of the hydraulic machine23through activation of the feed pump10in a first direction of output, and the disabling through activation of the feed pump10in a second direction of output, opposite to the first direction.

Advantageously, with reference toFIG. 1cto 1f, the feed pump10comprises a strainer101arranged between the reservoir12and the fluid inlet100of the feed pump10, and a main filter103arranged between the outlet102of the feed pump10, and the hydraulic assistance circuit27. The strainer101and the main filter103filter the fluid coming from the reservoir12, so as to preserve the hydraulic assistance device2from the ingestion of particulate contaminants. The strainer101and the main filter103are particularly useful when the hydraulic fluid is worn and/or has been subjected to high temperatures.

However, the strainer101and the main filter103tend to become clogged after the hydraulic assistance device2has been operational for a certain amount of time. The operation of the controlling module11of the self-maintenance system1then makes it possible, in addition to the flushing of the hydraulic machine21,23, to unclog the strainer101and/or the main filter103.

In an embodiment of the self-maintenance system1illustrated inFIG. 1c, it is the operating and the successive disabling of the hydraulic machine21,23, by successive activation of the feed pump10in two opposite directions of output, which provides the circulation of the hydraulic fluid through the strainer101successively in two opposite directions of circulation. At the moment of disabling of the hydraulic machine21,23, the reverse flow of hydraulic fluid makes it possible to unclog the strainer101by releasing the impurities that it has accumulated into the reservoir. In another embodiment illustrated inFIG. 1d, the feed pump10operates conventionally, and the self-maintenance system1further comprises a vacuum valve104commanded by the controlling module11. The vacuum valve24is used to drain all or part of the hydraulic assistance circuit27, preferably by being linked to the high-pressure branch of the most likely hydraulic assistance circuit27(i.e. as illustrated inFIG. 1d, when driving forwards), and/or the independent movable elements211. To do this, the vacuum valve104is movable between a passing position and an insulating position, on the command of the controlling module11. In this case, the controlling module11commands the operating of the hydraulic machine21,23through activation of the feed pump10which outputs the hydraulic fluid into the hydraulic machine21,23, the vacuum valve104being insulating. In the same way, the controlling module11commands the disabling of the hydraulic machine21,23by disabling of the feed pump10and commands the vacuum valve104in passing mode, which causes the expulsion of the fluid from the hydraulic machine23,21toward the reservoir12, via the drain215and the fluid circuit29, both linked to the strainer101. The return flow of hydraulic fluid makes it possible to unclog the strainer101by releasing into the reservoir the impurities that it has accumulated. Alternatively, the feed pump10is of counter-rotation type, and the operating as well as the successive disabling of the hydraulic machine21,23, by successive activation of the feed pump10in two opposite directions of output provides the circulation of the hydraulic fluid through the strainer101and the main filter103successively, in two opposite directions of circulation.
In an alternative embodiment illustrated inFIG. 1e, the self-maintenance system1comprises, in addition to the vacuum valve104, a low pressure selector switch270(or “inverse shuttle valve”) linking the two lines of the hydraulic assistance circuit27to the feed line. This makes it possible to feed the line of the hydraulic assistance circuit27which always has the lowest pressure. The selector switch270leaves permanently open the lowest pressure line with the feed line. Such a selector switch270is for example described in application FR 3 033 529 in the name of the Applicant and will not be further detailed here. Thus, the controlling module11commands the operating of the hydraulic machine21,23through activation of the feed pump10which outputs the hydraulic fluid into the hydraulic machine21,23, the vacuum valve being insulating. In the same way, the controlling module11commands the disabling of the hydraulic machine21,23by disabling of the feed pump10and commands the vacuum valve104in passing mode. On the one hand, this causes the expulsion of the fluid from the high pressure line of the hydraulic assistance circuit27and from the hydraulic machine21,23toward the reservoir12, via the fluid circuit29and the drain215respectively, both linked to the strainer101. On the other hand, this causes the expulsion of the fluid from the low pressure line of the hydraulic assistance circuit27toward the reservoir12, via the main filter103. An unclogging of the main filter103and the strainer101is then advantageously obtained by these return flows. Alternatively, the feed pump10is of counter-rotation type, and the operating as well as the successive disabling of the hydraulic machine21,23, by successive activation of the feed pump10in two opposite directions of output provides the circulation of the hydraulic fluid through the strainer101and the main filter103successively, in two opposite directions of circulation.
In an embodiment illustrated inFIG. 1f, the self-maintenance system1comprises, further to the low pressure selector switch270, a secondary filter105arranged between the main filter103and the outlet102of the feed pump10. Parallel to the secondary filter105is a by-pass valve107. Furthermore, the fluid circuit29for placing the independent movable elements211in a vacuum is linked to the outlet of the main filter103. Thus, when the controlling module11commands the operating of the hydraulic machine21,23through activation of the feed pump10which outputs the hydraulic fluid into the hydraulic machine21,23, the flow passes through the valve107. Then, when the controlling module11disables the feed pump10, the fluid flows back from the fluid circuit29and the low pressure line via the selector switch270through the main filter103which then discharges its impurities into the secondary filter105. Alternatively, the feed pump10is of counter-rotation type, and the operating as well as the successive disabling of the hydraulic machine21,23, by successive activation successive of the feed pump10in two opposite directions of output, provides a circulation of the hydraulic fluid through the main filter103successively, in two opposite directions of circulation, with the retention of the impurities on return by the secondary filter105.

In any case, in a system1configured to provide continuous self-maintenance of the hydraulic assistance device2, the controlling module11commands the feed pump10and/or the vacuum valve104preferably independently of a command of engagement or disengagement of the traction assistance of the vehicle. This permits the fluid flushing of all or part of the hydraulic machine21,23and/or the unclogging of the strainer101and of the main filter103which are regular, even if the assistance is not moreover required. Furthermore, for the operating and the rapid disabling of the hydraulic assistance, it is preferable that the self-maintenance system1comprises the vacuum valve104and/or the feed pump of counter-rotation type 10.

In a first embodiment, with reference toFIGS. 1band 1cto 1f, the starting movable elements211are independent, for example constitute a disk clutch211, making it possible to engage or disengage the machine21from its drive shaft (not shown).

The controlling module11is then configured to command the operating then the disabling of the hydraulic machine21:the vehicle being in movement, the flushing being provided by the circulation of the hydraulic fluid upon the transmission of the movements of the drive torque of the powertrain31or of the wheel33to the elements of the operated machine21, orthe vehicle being stopped, the flushing being partly provided by the sole movements of the starting movable elements211during the successive operating and disabling of the hydraulic machine21.
The controlling module11commands the operating and/or the disabling of the hydraulic machine21in particular independently of a command of engagement and/or disengagement of the assistance. This permits the partial or complete flushing of the hydraulic machine21, even if the assistance is not moreover required.

In a second embodiment, with reference toFIGS. 1aand 1cto 1f, the starting movable elements231are dependent, and for example comprise retractable radial pistons231.

The controlling module11is then configured to command the operating then the disabling of the hydraulic machine23:the vehicle being in movement, the flushing being provided by the circulation of the hydraulic fluid upon the transmission of the movements of the drive torque of the powertrain31or of the wheel33to the movable elements of the operated hydraulic machine23, orthe vehicle being stopped, the flushing being provided by the movements of the starting movable elements231during the successive operating and disabling of the hydraulic machine23.
In the same way as in the first embodiment, the controlling module11commands the operating and/or the disabling of the hydraulic machine23in particular independently of a command of engagement and/or disengagement of the assistance. This permits the more complete flushing of the hydraulic machine23, in particular if the assistance is required and the machine performs a full revolution.

In any case, with reference toFIG. 1b, the controlling module11can advantageously comprise an automaton13configured to automatically implement a self-maintenance method E of a hydraulic assistance device2.

Furthermore, still with reference toFIG. 1b, the controlling module11can comprise a module15for estimating the level of wear of the hydraulic fluid. This module15can for example measure the amperage of the current consumed by the feed pump10. This is because the wear of the hydraulic fluid is directly correlated with the power needed to pressurize the hydraulic assistance circuit27. Alternatively, this module15can estimate the level of wear of the hydraulic fluid based on the condition of ageing thereof. The condition of ageing of a hydraulic fluid is characterized by several parameters, including the shearing of the fluid, the oxidization of the fluid, and its particulate contamination. The knowledge of all these parameters, alone or in combination, and their variation during the operation of the hydraulic assistance device2, in particular makes it possible to estimate the viscosity of the hydraulic fluid as a function of its temperature. The viscosity of the hydraulic fluid can also be determined directly by sensors configured for this purpose. In any case, the controlling module11is always configured to receive an item of information relating to the condition of wear of the hydraulic fluid.

With reference toFIG. 3, there now follows a description of a self-maintenance method E of a hydraulic assistance device2of a vehicle, the self-maintenance method E being implemented by a self-maintenance system1as claimed in any one of the previously described embodiments.

Such a method E comprises the steps consists in:operating E1the hydraulic machine21,23during a determined time period, thendisabling E2the hydraulic machine21,23at the end of said time period.
This ensures the flushing of all (complete flushing) or part (partial flushing) of the hydraulic machine21,23by the setting in movement of the movable elements to force the circulation of hydraulic fluid, the steps of operating E1and disabling E2being furthermore implemented independently of the command of engagement and/or disengagement of the assistance. This provides the regular self-maintenance of the hydraulic assistance device2, even if the assistance is not moreover required, particularly if it is rarely required.

Advantageously, the step of disabling E2can also be implemented by the safety module14for the purpose of preserving the safety of the hydraulic machine21,23when the vehicle reaches too high a speed.

Even more advantageously, the alternating of the steps of operating E1and disabling E2is repeated successively with a given frequency, for example ten times in a row, such as to homogenize the flushing of the hydraulic machine21,23. This alternating can be preset by a user or the manufacturer.

The duration of the step of operating E1can be preset by the manufacturer of the self-maintenance system1. Alternatively, if the hydraulic machine23is linked to a vehicle wheel33, the hydraulic machine23is operated during a time period corresponding to one wheel revolution23.

Advantageously, the method E is implemented at a given rate, said rate being either functional and/or temporal, for example once every month of operation of the vehicle. The term “functional rate” is understood to mean that the method E is implemented at a rate that depends on the way in which the hydraulic assistance device2is used, for example each time the vehicle has travelled a given distance, when the vehicle reaches a defined rate of use or rate of load, or when pressure thresholds are reached in the hydraulic assistance circuit27.

Advantageously, the method E is implemented based on a given level of wear of the fluid.

In a first embodiment of the method E, with reference toFIG. 4a, the assistance is moreover not required.

In this case, if the vehicle is in movement, then the method is implemented for a given range of vehicle speed, for example the speed of the vehicle being between 0 and 40 km/h. Beyond a certain level of vehicle speed, operating the hydraulic machine on a wheel can cause said machine to deteriorate.
Alternatively, the method E can be implemented while the vehicle is stopped, typically at traffic lights, preferably each time the vehicle is started up. This has the advantage of not interfering with the driving of the vehicle. In this case, if the starting movable elements211are independent, then the flushing is only partial.
Preferably, the step of operating E1is implemented over a time period corresponding to a complete rotation of a hydraulic machine21,23of the vehicle, which makes it possible to make all the parts move, and to entirely renew the hydraulic fluid contained in the cylinders of the machine21,23, but also to make the hydraulic fluid circulate in the ducts more completely. In particular if one rotation of a machine21,23corresponds to one revolution of a wheel33, the time period will correspond to one complete rotation of a wheel33.

In a second embodiment of the method E, still with reference toFIG. 4a, the assistance is moreover required.

In this case, if the vehicle is in movement, the method E is not implemented, and the flushing is provided by the nominal operation of the hydraulic assistance device2.

Alternatively, the method E can be implemented while the vehicle is stopped, typically at traffic lights, preferably each time the vehicle is started up. In this case, if the starting movable elements211are independent, then the flushing is only partial.

In a third embodiment of the method E, with reference toFIG. 4b, the assistance device comprises a reservoir12, a feed pump, preferably with counter-rotation10and a set of filters, for example a strainer101and a main filter103, as previously described. In this embodiment, besides the flushing of the hydraulic machine, the unclogging of the filters101,103is advantageously obtained.

The method E then comprises the steps consisting in operating E1the hydraulic machine21,23during a determined time period, for example through activation of the feed pump10, and in disabling E2the hydraulic machine21,23, at the end of the step of operating E1, such as to make hydraulic fluid circulate through the filters101,103successively, in two opposite directions of circulation. As previously described, the disabling E2can be implemented by disabling of the feed pump10, and backflow of the hydraulic fluid to the reservoir12, or through activation of the feed pump10in the opposite direction, if it is of counter-rotation type. Furthermore, as previously described, the steps of operating E1and disabling2are implemented independently of a command of engagement and/or disengagement of the assistance.

Advantageously, the method E can then be implemented with the assistance being moreover required. In this case, if the vehicle is in movement, the step of disabling E2momentarily cuts off the assistance. The method E then makes provision for a step of operating again E3following the step of disabling E2, such as to ensure the safety of the vehicle. Preferably, the step of disabling E2is implemented over a time period corresponding to one rotation of the wheel33of the vehicle. In particular if one rotation of a machine21,23corresponds to one revolution of a wheel23, the time period will correspond to one complete rotation of a wheel23.

The method E allows the regular setting in movement of the parts of the hydraulic assistance device2, even if it is not used, which prevents wear or corrosion localized at the points of contact of immovable parts, avoids the existence of immovable hydraulic fluid which could undergo repeated heat cycles, and prevents the sedimentation or polymerization of the hydraulic fluid. Also, it allows the unclogging of filters101,103. By its effects, it makes it possible to keep the hydraulic assistance device2operational for longer, between two intervals of drainage of the hydraulic fluid. It can furthermore make it possible to space the drainage dates apart, and therefore reduce the operating costs of the system.

The self-maintenance system1can be used for the benefit of any hydraulic assistance traction device, particularly to convert a 4×2 vehicle into a 4×4 vehicle, or to assist the supporting wheels of a vehicle, for example the drive wheels of a truck, the supporting axles of trucks or trailers, the supporting axles of building site or agricultural machinery, of low-speed temporary hydraulic transmissions for service or work vehicles, designated by the name of “creep drive”, or road/rail convertible vehicles or machinery.