Pressure limiting device, in particular for an assist system for vehicles

The invention relates to a pressure-limiting device designed to be installed in a system comprising a first line (11) and a second line (12) that can comprise pressurised oil, as well as comprising a discharge and/or booster line (10). The device also comprises a pressure selector (130, 150) in the form of a cage defining two seats (132, 134) and two pressure relief valves (160, 180). The limiting device is characterised in that it further comprises at least one means (170, 172; 190, 192) for regulating a pressure relief valve, disposed on the outside of an axial end of the pressure selector (150), in the form of a cage that allows the loading of the associated pressure relief valve to be regulated.

GENERAL TECHNICAL FIELD

The invention relates to the management of excess pressures of hydraulic circuits, and more particularly to the devices of the “pressure limiter” or “protection valve” type.

The invention applies in particular to hydraulic assistance circuits for a vehicle.

Hydraulic assistance is carried out by means of hydraulic machines which can supply a torque to driving wheels. These machines transform hydraulic energy of oil under pressure into mechanical energy, or the reverse.

PRIOR ART

In a vehicle, a first hydraulic machine M1is mounted on the front axle and a second hydraulic machine M2is mounted on the rear axle. What is meant by machines is that they can operate as a motor or as a pump. Generally, one of the machines is assigned to a mechanically driven axle, while the other is assigned to a carrying axle.

The configuration shown corresponds to a “bicycle chain” (document FR2996176), that is that in its main use, the first machine M1acts as a pump for the second machine M2, which acts as a motor.

The vehicle generally comprises a heat engine (not shown in the figures) which drives, directly or indirectly, the first hydraulic machine M1through a mechanical connection. The second machine M2is connected to the carrying wheels of the vehicle. In this manner, in the event that the mechanically driven wheels skid, the machine M1can transfer torque to the carrying wheels connected to the machine M2. There can be several machines M1or M2on several axles.

To this end, the delivery of the first machine M1is connected to the admission of the second machine M2by a line11, called a high-pressure line, and the delivery of the second machine M2is connected to the intake of the first machine M1by a line12called a low-pressure line.

The terms high and low pressure correspond to use in forward motion with torque addition (“main use”).

Consequently, as pressures can be reversed, the terms first line11and second line12are preferred.

The first and the second line11,12, operate in a closed circuit and can be subjected to excess pressure which can damage the machines M1, M2or the seals present on the circuit. They define a closed loop.

As an example, the pressures are on the order of 400 bars in one line and a few tens of bars, a boost pressure at least, in the other line.

To protect the hydraulic circuit and in particular the first and second lines11,12, it is known to dispose two pressure limiters.

FIG. 1shows a first variant of the prior art: a pressure limiter21is disposed between the first line11and a booster line10, another limiter22is disposed between the second line12and the booster line10.

Each limiter21,22can be calibrated to the desired value. The booster line10is a line allowing a booster pump P, actuated by a motor M, typically an electric motor, which creates an electro-pump unit, to supply with oil the first and second lines11,12through check valves B11, B12so as to activate the hydraulic assistance. Due to a pressure limiter20in parallel with the pump P, the booster circuit10allows the discharge of excess pressure.

This solution uses two protection members (the pressure limiters21,22).

FIG. 2shows a second variant of the prior art: there are still two limiters23,24disposed as before, except that each dumps the excess pressure into the other line of the first and second lines11,12. One line always having a lower pressure, it can tolerate the excess pressure present in the other.

This solution also uses two protection members (the pressure limiters23,24). Also found again inFIG. 2are two check valves B11, B12which are used for boosting.

FIG. 3shows a third variant of the prior art: A high-pressure selector25selects the line with the higher pressure among the first and the second line11,12and sends it to the booster line10via a pressure limiter26. In this manner, a limiter is eliminated but a circuit selector25must be added.

This solution also uses two protection members. Also found again inFIG. 3are two check valves B11, B12which are used for boosting.

Also described in document US 2005/0097887 is another variant of a pressure relief device comprising a pressure selector in the form of a cage associated with two pressure relief valves. During normal operation, the pressure selector allows a connection between a booster line and a low-pressure supply line. In the event of excess pressure on one line, the associated pressure relief valve opens and allows discharge of the excess pressure to the booster line.

The devices previously describe have already made significant contributions.

Nevertheless, they are not always satisfactory.

As has been shown schematically inFIG. 4, in the event of skidding of a wheel associated with one of the motors, an increase in pressure of the line theoretically at low pressure can be observed, due to the opening of an associated pressure relief valve20which short-circuits the motor in question, with the possibility of a pressure rise on both lines11,12as well as, if applicable, on the booster line10, hence the risk of deterioration of the booster pump P, or of an associated filter F. This risk also exists in the case of an installation comprising two machines M1, M2associated respectively with two axles as can be seen inFIG. 4.

In this context, the invention has as its objective to propose a new pressure relief device which makes it possible to improve pressure control, while still allowing the effect of selecting the line to be connected to the booster device.

The present invention also has as its object to propose a pressure relief device which optimizes the space available and reduces the costs of manufacture, with simple members.

PRESENTATION DE L'INVENTION

For this purpose, the invention proposes a pressure relief device suitable to be installed in a system comprising a first line and a second line which can comprise oil under pressure and comprising a discharge and/or booster line, which device comprises a pressure selector in the form of a cage defining two seats and two pressure relief valves, characterized in that the device further comprises at least one adjustment means of a pressure relief valve, disposed on the outside of an axial end of the pressure selector in the form of a cage to allow adjustment of the calibration of the associated pressure relief valve.

As will be understood hereafter, the use of a selector comprising a cage on the ends of which are formed the respective shutters of the two selection valves, allows a constant distance between these two shutters to be guaranteed and consequently allows a guarantee that when one of the selection valves is closed, the other selection valve is automatically opened.

According to one advantageous feature of the invention, the device comprises adjustment means respectively of each pressure relief valve disposed on the outside of the axial ends of the pressure selector in the form of a cage to allow independent adjustment of the calibration of each pressure relief valve.

The pressure relief occurs from now using a single device, which improves the compactness of the system as well as its cost of manufacture, with respect to certain known solutions of the prior art.

The invention also relates to assistance systems and vehicles equipped with a pressure relief device conforming to the invention.

DETAILED DESCRIPTION

FIG. 5shows a system conforming to the invention integrating a pressure relief device100conforming to the invention which integrates means which carry out the function of a pressure selector and of two pressure limiters.

The device100comprises three ports102,104,106: two ports102,104which communicate respectively with the lines11and12and a port106which communicates with the booster line10.

The booster line can be supplied with oil by the booster pump P until it reaches the boost pressure, which makes the machines M1M2operational, or the booster line can be aspirated by the booster pump, which makes the machines M1M2non-operational. The machines M1and M2are of a type which becomes non-operational or disengageable below a pressure threshold in the lines11and12. The selector automatically connects the line with the lower pressure to boost, which allows activation or deactivation of the transmission, which are flexible and orderly.

The pressure relief device100shown inFIG. 6comprises essentially a body110, a selector in the form of a cage150and two pressure relief valves160,180.

The device100is centred on a longitudinal axis of symmetry O-O. The device100is rotationally symmetric overall around the axis O-O.

The body110is formed of a cartridge suitable for being integrated into any support structure, for example on the casing of a hydraulic motor.

The body110is preferably formed by assembling a casing120and a plug112. The plug112can be attached to an axial end of the casing120by any appropriate means, for example by crimping or preferably by screwing of the complementary threads114. The plug112can be equipped with shape113that is not a cylinder of revolution allowing its tightening, as well as a groove115suitable for receiving a fluid-tight seal in contact with the support structure. The axial end of the casing120can be equipped on its exterior surface with a thread121allowing the assembly of the device100on this support structure.

The casing120comprises at least three through passages122,124,126which correspond to the three aforementioned ports102,104,106.

One of the through passages126is formed in the median portion of the length of the casing120and corresponds to the port106. More precisely, preferably, several orifices126are provided evenly distributed around the axis O-O forming the port106.

The passages122and124are formed respectively on either side of the median passage126. More precisely, preferably, the passage122is formed from several orifices122evenly distributed around the axis O-O forming the port102.

The passage124can also be formed from several orifices evenly distributed around the axis O-O forming the port104. However, according to the preferred embodiment, for reasons of manufacture and assembly, the passage124is formed from an orifice which leads axially to the casing120at the end opposite to the plug112.

The casing120preferably comprises on its exterior surface two annular grooves127,128intended to receive respective seals in contact with the support structure allowing the hydraulic connections provided toward the passages122,126and124to be mutually isolated.

The casing120comprises, on its inner surface and at the median passage126, a narrowed portion130which extends axially to either side of the passage126. The narrowed portion130defines respectively on its two axial ends two seats132,134associated with the selector150.

The narrowed portion130which forms the two seats132,134can be formed integrally on the inner surface of the casing120or be formed from a separate part applied to the surface of the casing120and attached by any appropriate means, for example by crimping.

The two seats132,134are oriented respectively toward the axial ends of the casing120.

The selector150has the shape of a diabolo formed from a central cylinder152with a constant cylinder of revolution cross-section provided on its two axial ends with respective protrusions154,156protruding on its outer surface.

The protrusions154,156respectively form two annular shutters, directed respectively toward the median portion of the diabolo150, suitable for cooperating with the seats132,134formed on the casing120.

The outside diameter of the central cylinder152is less than the inner diameter of the narrowed portion130. The outer diameter of the shutters154,156, on the other hand, is greater than the diameter of the seats132,134.

Thus, when one of the shutters154,156rests on the associated seat132,134, the corresponding valve of the selector150is closed. Conversely, when a shutter154,156is separated from the associated seat132,134, the corresponding valve of the selector150is open.

The use of a selector150comprising a cage152on the ends of which are formed the respective shutters154,156of two selection valves, makes it possible to guarantee a constant distance between these two shutters154,156and consequently to make it possible to guarantee that, when one of the selection valves is closed, the other selection valve is automatically opened.

The cylinder152defines an axial through passage intended to slidably receive shutters162,182and their associated support rods164,184of the pressure relief valves160,180. The cylinder152also comprises a plurality of radial through orifices158.

The orifices158also allow free filling of the inner volume of the selector152and the discharge of fluid during the opening of a pressure relief valve, as will be seen hereafter.

The aforementioned protrusions154,156also protrude on the inner surface of the cylinder152to define two annular seats155,157directed axially toward the median portion of the selector150and intended to cooperate respectively with the shutters162,182.

The shutters162,182are formed with protrusions on one end of the rods164,184. The shutters are place on the inside of the seats155,157in the volume of the inner chamber of the cylinder152.

The rods164,184emerge axially on each end of the selector150. Each rod164,184and its associated shutter162,182is biased toward a respective axial end of the casing120by a respective spring170,190.

Thus, the shutters162,182are urged respectively against the seats155,157.

The springs170,190are interspersed on the rods164,184, between the protrusions154,156and stops172,192in the form of rings carried by the rods164,184.

Preferably, the stops172,192are adjustable in position over the length of the rods164,184to define the force exerted by each spring170,190and consequently the calibration of the opening pressure of each pressure relief valve.

The stops172,192can be attached in position on their respective rod164,184by any appropriate means, for example by screwing or crimping.

The protrusions154,157and the cylinder152are advantageously formed from at least two parts, preferably three parts, initially separate and assembled by any appropriate means, for example by screwing or crimping.

To assemble the pressure relief device previously described, the procedure is essentially as follows:

First of all, the shutters162,182and their rods164,184are assembled, equipped with springs170,190and with stops172,192on the respective protrusions154,156. The stops172,192are adjusted in position for the desired calibration.

The pressure relief valve sub-assemblies thus formed are introduced into the casing120, respectively by each end of it, and the protrusions154,156are attached to the cylinder152of the selector.

To this end, the exterior surface of the cylinder of the selector can be equipped with gripping shapes accessible by the passages126to facilitate assembly.

Then, the plug112is attached to the end of the casing120. The fluid-tight seals are placed in their respective grooves.

The operation of the relief device is essentially the following:

At rest, in the absence of pressure on the port106and therefore in the booster line10and consequently on the parts102,104and therefore in the supply lines11,12, the selector150is capable of free movement in the casing120facing the seats132,134. The shutters162,182biased by the springs170,190rest on their respective seats155,157and the pressure relief valves are consequently closed.

In operation, during activation of the booster pump P and selection of the direction of rotation of the machine M1, one of the ports102,104is subjected to a high pressure while the other port104,102is subjected to a low return pressure.

The selector150is thus urged by the high pressure.

If, as illustrated inFIG. 7, the high pressure is applied to port102corresponding to the passage122. The protrusion154of the selector150is urged in contact against the seat132. The corresponding selection valve is closed. Conversely, a low pressure is applied to the port104corresponding to the passage124. The protrusion156of the selector150is separated from the seat134. The corresponding selection valve is open.

As can be seen inFIG. 8, in the case of a reversal of the direction of rotation, the high pressure is applied to port104corresponding to the passage124. The protrusion156of the selector150is urged in contact against the seat134. The corresponding selection valve is closed. Conversely, a low pressure is applied to port102corresponding to the passage122. The protrusion154of the selector150is separated from the seat132. The corresponding selection valve is open.

The operation of the selector is identical at the time of activation or of deactivation of the hydraulic machines, through the use of the booster pump in the sense of making oil enter into the closed loop or making oil leave the closed loop.

When the pressure in a line11,12, exceeds the calibration threshold of the pressure relief valve defined by the springs170,190, this excess pressure applied to the shutters162,182ensures respectively the opening of the pressure relief valves, as illustrated inFIGS. 9 and 10by the separation of the shutters162,182with respect to their seats155,157. The corresponding excess pressure is then discharged to the booster line10as well as to the other supply line.

InFIGS. 7 to 10, the closed valves are denoted Fe while the open valves are denoted Ou.

It will be observed that the distance which separates, at rest, the facing ends of the two shutters162,182must be sufficient to allow a sufficient movement of this shutter to allow an opening of the corresponding pressure relief valve suitable for not creating considerable head losses.

Preferably, this distance is sufficient to allow, in the case of simultaneous excess pressure on the two lines11and12, a simultaneous opening of the two pressure relief valves.

In this manner, it is possible to protect the two lines11and12with respect to overpressure, in the case where the system has been in traction at a high torque, and therefore with an elevated pressure. In this case, in the case of skidding of the two axles, by decompression, one of the lines11,12could expand into the other of the lines11,12. The two lines would be in excess pressure, which would damage the booster pump. For this particular case, it is necessary that the two pressure relief valves be able to open simultaneously.

A person skilled in the art will understand that the implementation conforming to the invention will allow all the functions to be integrated into a component in the form of a cartridge while still allowing simple and reliable adjustment, as well as independently, of the calibration of each pressure relief valve.

The invention can also be integrated or juxtaposed to one of the machines M1, M2.

Of course, the present invention is not limited to the particular embodiments which have just been described, but extends to all variants within its spirit.