Control of a free-wheeling valve

Abstract

The present invention relates to an assembly for a traction assistance hydraulic circuit of a vehicle, the assembly comprising: a free-wheeling valve (1); a hydraulic pilot valve (2) connected to the free-wheeling valve (1) and configured to drive the free-wheeling valve (1); and a directional solenoid valve (3) connected to the hydraulic pilot valve (2) and configured to control the hydraulic pilot valve (2).

Description

[0001] CONTROLLING A FREEWHEEL VALVE

[0002] TECHNICAL FIELD

[0003] This presentation concerns the field of hydraulic assistance for vehicle traction. More specifically, it concerns the control of a freewheeling valve within a hydraulic circuit for vehicle traction assistance.

[0004] STATE OF THE ART

[0005] In a hydraulic traction assistance circuit of a vehicle, at least one hydraulic motor can be engaged with at least one wheel when additional traction is required to drive it, for example when the vehicle is traveling on uneven or slippery terrain. Once the vehicle is moving at a sufficiently high speed or the road conditions are such that traction is sufficient, the motor can be disengaged from the wheel.

[0006] In this regard, the hydraulic circuit is generally equipped with a freewheel valve whose different positions allow the motor to be engaged and disengaged. The different positions are commonly controlled by a pilot valve. The pilot valve is usually a directly operated electrohydraulic directional valve.

[0007] Some engines are designed to be disengaged by retracting the engine pistons. To do this, the engine's intake and / or discharge ports must be connected to a reservoir in the hydraulic circuit, or to a booster circuit, via the freewheel valve and the pilot valve. The engine must be able to be engaged and disengaged quickly enough, especially when the vehicle is moving and the engine continues to run during engagement or disengagement. This speed of execution is useful for minimizing mechanical shocks, torque surges, engine wear, pressure peaks and noise. As a result, the flow rates circulating in the pilot valve are very high, which requires significant energy to switch it.

[0008] Such pilot valves are therefore very heavy and very bulky, in particular because they are equipped with a large solenoid to control their operation. In addition, they are expensive and consume a large amount of energy. For example, such a pilot valve can typically operate with an electrical current greater than 2.5 A and an electrical power greater than 30 W. GENERAL EXPOSE

[0009] One aim of this presentation is to enable the control of a freewheeling valve in a less expensive and less energy-intensive manner.

[0010] For this purpose, according to one aspect of the present disclosure, there is provided an assembly for a hydraulic circuit for assisting the traction of a vehicle, the assembly comprising a freewheeling valve; a hydraulic pilot valve connected to the freewheeling valve and configured to pilot the freewheeling valve; and a directional solenoid valve connected to the hydraulic pilot valve and configured to pilot the hydraulic pilot valve.

[0011] The hydraulic pilot valve may comprise a first inlet port provided to be connected to a reservoir of the circuit; a second inlet port provided to be connected to a booster line of the circuit; and an outlet port connected to a pilot chamber and to a second inlet port of the freewheeling valve.

[0012] The hydraulic pilot valve may further comprise a spool and a body, the spool being movable within the body between a first position in which the spool allows fluid circulation between the first inlet port and the outlet port of the hydraulic pilot valve, and prohibits fluid circulation between the second inlet port and the outlet port of the hydraulic pilot valve; and a second position in which the spool allows fluid circulation between the second inlet port and the outlet port of the hydraulic pilot valve, and prohibits fluid circulation between the first inlet port and the outlet port of the hydraulic pilot valve.

[0013] The hydraulic pilot valve may further comprise a pilot chamber connected to the directional solenoid valve and connected to the spool of the hydraulic pilot valve such that a pressure within the pilot chamber exerts a first force on the spool of the hydraulic pilot valve; and a return element connected to the spool and to the body of the hydraulic pilot valve, such as to exert a second force on the spool of the hydraulic pilot valve; wherein a movement of the spool of the hydraulic pilot valve between the first position and the second position of the hydraulic pilot valve is controlled by a difference between the first force and the second force on the spool of the hydraulic pilot valve.

[0014] The directional solenoid valve may comprise a first inlet port intended to be connected to a reservoir of the circuit; a second inlet port intended to be connected to a booster line of the circuit; and an outlet port connected to a pilot chamber of the hydraulic pilot valve.

[0015] The directional solenoid valve may further comprise a spool and a body, the spool being movable within the body between a first position in which the spool allows fluid flow between the first inlet port and the outlet port of the directional solenoid valve, and prohibits fluid flow between the second inlet port and the outlet port of the directional solenoid valve; and a second position in which the spool allows fluid flow between the second inlet port and the outlet port of the directional solenoid valve, and prohibits fluid flow between the first inlet port and the outlet port of the directional solenoid valve.

[0016] The directional solenoid valve may further comprise a solenoid configured to exert a first force on the spool of the directional solenoid valve; and a return element connected to the spool and to the body of the directional solenoid valve, so as to exert a second force on the second spool of the directional solenoid valve; wherein a movement of the spool of the directional solenoid valve between the first position and the second position of the directional solenoid valve is controlled by a difference between the first force and the second force on the spool of the directional solenoid valve.

[0017] The freewheeling valve may comprise a first inlet port provided to be connected to a first orifice of a hydraulic pump of the circuit; a second inlet port provided to be connected alternatively to a reservoir of the circuit or to a booster line of the circuit, via the hydraulic pilot valve; a third inlet port provided to be connected to a second orifice of the pump; a first outlet port provided to be connected to a first orifice of a hydraulic motor of the circuit; and a second outlet port provided to be connected to a second orifice of the motor.

[0018] The freewheeling valve may further comprise a spool and a body, the spool being movable within the body between a first position in which the spool allows fluid flow between the second inlet port and each of the first outlet port and the second outlet port of the freewheeling valve, and prohibits fluid flow between each of the first inlet port and the third inlet port, and each of the first outlet port and the second outlet port of the freewheeling valve;and a second position in which the spool allows fluid flow between the first inlet port and the first outlet port, and between the third inlet port and the second outlet port of the freewheeling valve, and prohibits fluid flow between the first inlet port and the second outlet port, between the second inlet port and each of the first outlet port and the second outlet port, and between the third inlet port and the first outlet port of the freewheeling valve.;

[0019] The freewheeling valve may further comprise a pilot chamber connected to the hydraulic pilot valve and connected to the slide of the freewheeling valve such that a pressure within the pilot chamber exerts a first force on the slide of the freewheeling valve; and a return element connected to the slide and to the third body of the freewheeling valve, such as to exert a second force on the slide of the freewheeling valve; wherein a movement of the slide of the freewheeling valve between the first position and the second position of the freewheeling valve is controlled by a difference between the first force and the second force on the slide of the freewheeling valve.

[0020] The freewheeling valve may comprise a first inlet port intended to be connected to a first orifice of a hydraulic pump of the circuit; a second inlet port intended to be connected alternatively to a reservoir of the circuit or to a booster line of the circuit, via the hydraulic pilot valve; a third inlet port intended to be connected to a second orifice of the pump; a first outlet port intended to be connected to a first orifice of a hydraulic motor of the circuit; a second outlet port intended to be connected to a second orifice of the motor;a spool and a body, the spool being movable within the body between a first position in which the spool allows fluid flow between the second inlet port and each of the first outlet port and the second outlet port of the freewheeling valve, and prohibits fluid flow between each of the first inlet port and the third inlet port, and each of the first outlet port and the second outlet port of the freewheeling valve;and a second position in which the spool allows fluid flow between the first inlet port and the first outlet port, and between the third inlet port and the second outlet port of the freewheeling valve, and prohibits fluid flow between the first inlet port and the second outlet port, between the second inlet port and each of the first outlet port and the second outlet port, and between the third inlet port and the first outlet port of the freewheeling valve; a pilot chamber connected to the hydraulic pilot valve and connected to the spool of the freewheeling valve such that pressure within the pilot chamber exerts a first force on the spool of the freewheeling valve; and a return element connected to the spool and to the third body of the freewheeling valve, such as to exert a second force on the spool of the freewheeling valve;wherein a movement of the slide of the freewheeling valve between the first position and the second position of the freewheeling valve is controlled by a difference between the first force and the second force on the slide of the freewheeling valve. The hydraulic pilot valve may comprise a first inlet port provided to be connected to the reservoir of the circuit; a second inlet port provided to be connected to the feed line of the circuit; an outlet port connected to the pilot chamber and to the second inlet port of the freewheeling valve; and a slide and a body, the slide being movable within the body between a first position in which the slide allows fluid circulation between the first inlet port and the outlet port of the hydraulic pilot valve, and prohibits fluid circulation between the second inlet port and the outlet port of the hydraulic pilot valve;and a second position in which the spool allows fluid flow between the second inlet port and the outlet port of the hydraulic pilot valve, and prohibits fluid flow between the first inlet port and the outlet port of the hydraulic pilot valve; and wherein, in the first position of the spool of the freewheeling valve and in the second position of the spool of the hydraulic pilot valve, the freewheeling valve and the hydraulic pilot valve are configured to connect the feed line to the pilot chamber of the freewheeling valve and to the motor.;

[0021] The freewheeling valve may comprise a first inlet port intended to be connected to a first orifice of a hydraulic pump of the circuit; a second inlet port intended to be connected alternatively to a reservoir of the circuit or to a booster line of the circuit, via the hydraulic pilot valve; a third inlet port intended to be connected to a second orifice of the pump; a first outlet port intended to be connected to a first orifice of a hydraulic motor of the circuit; a second outlet port intended to be connected to a second orifice of the motor;a spool and a body, the spool being movable within the body between a first position in which the spool allows fluid flow between the second inlet port and each of the first outlet port and the second outlet port of the freewheeling valve, and prohibits fluid flow between each of the first inlet port and the third inlet port, and each of the first outlet port and the second outlet port of the freewheeling valve;and a second position in which the spool allows fluid flow between the first inlet port and the first outlet port, and between the third inlet port and the second outlet port of the freewheeling valve, and prohibits fluid flow between the first inlet port and the second outlet port, between the second inlet port and each of the first outlet port and the second outlet port, and between the third inlet port and the first outlet port of the freewheeling valve; a pilot chamber connected to the hydraulic pilot valve and connected to the spool of the freewheeling valve such that pressure within the pilot chamber exerts a first force on the spool of the freewheeling valve; and a return element connected to the spool and to the third body of the freewheeling valve, such as to exert a second force on the spool of the freewheeling valve;wherein a movement of the slide of the freewheeling valve between the first position and the second position of the freewheeling valve is controlled by a difference between the first force and the second force on the slide of the freewheeling valve. The hydraulic pilot valve may comprise a first inlet port provided to be connected to the reservoir of the circuit; a second inlet port provided to be connected to the charge line of the circuit; and an outlet port connected to the pilot chamber and to the second inlet port of the freewheeling valve; and wherein the assembly further comprises a line connecting the outlet port of the pilot valve to the pilot chamber of the freewheeling valve, the line comprising a nozzle provided to adjust a flow rate from the charge line.;

[0022] The hydraulic pilot valve may further comprise a spool and a body, the spool being movable within the body between a first position in which the spool allows fluid circulation between the first inlet port and the outlet port of the hydraulic pilot valve, and prohibits fluid circulation between the second inlet port and the outlet port of the hydraulic pilot valve; and a second position in which the spool allows fluid circulation between the second inlet port and the outlet port of the hydraulic pilot valve, and prohibits fluid circulation between the first inlet port and the outlet port of the hydraulic pilot valve.

[0023] The hydraulic pilot valve may further comprise a pilot chamber connected to the directional solenoid valve and connected to the spool of the hydraulic pilot valve such that a pressure within the pilot chamber exerts a first force on the spool of the hydraulic pilot valve; and a return element connected to the spool and to the body of the hydraulic pilot valve, such as to exert a second force on the spool of the hydraulic pilot valve; wherein a movement of the spool of the hydraulic pilot valve between the first position and the second position of the hydraulic pilot valve is controlled by a difference between the first force and the second force on the spool of the hydraulic pilot valve.

[0024] The directional solenoid valve may comprise a first inlet port intended to be connected to a reservoir of the circuit; a second inlet port intended to be connected to a booster line of the circuit; and an outlet port connected to a pilot chamber of the hydraulic pilot valve.

[0025] The directional solenoid valve may further comprise a spool and a body, the spool being movable within the body between a first position in which the spool allows fluid flow between the first inlet port and the outlet port of the directional solenoid valve, and prohibits fluid flow between the second inlet port and the outlet port of the directional solenoid valve; and a second position in which the spool allows fluid flow between the second inlet port and the outlet port of the directional solenoid valve, and prohibits fluid flow between the first inlet port and the outlet port of the directional solenoid valve.

[0026] The directional solenoid valve may further comprise a solenoid configured to exert a first force on the spool of the directional solenoid valve; and a return element connected to the spool and to the body of the directional solenoid valve, so as to exert a second force on the second spool of the directional solenoid valve; wherein a movement of the spool of the directional solenoid valve between the first position and the second position of the directional solenoid valve is controlled by a difference between the first force and the second force on the spool of the directional solenoid valve.

[0027] According to another aspect of the present disclosure, there is provided a hydraulic circuit for assisting traction of a vehicle, the circuit comprising a hydraulic motor intended to be coupled to a wheel of the vehicle; a hydraulic pump; and an assembly according to the present disclosure; in which the freewheeling valve is configured to control the circulation of fluid between the pump and the motor.

[0028] The pump may comprise a first orifice and a second orifice and the hydraulic motor may comprise a first orifice and a second orifice, the circuit further comprising a communication circuit connecting the first orifice of the pump to the first orifice of the motor, and the second orifice of the pump to the second orifice of the motor, the communication circuit comprising the freewheeling valve; a reservoir; a booster pump comprising an inlet orifice connected to the reservoir and a discharge orifice; and a booster line connected to the discharge orifice of the booster pump and to the communication circuit; wherein the freewheeling valve and the hydraulic pilot valve are configured to control the circulation of fluid between, on the one hand, the motor and, on the other hand, the pump, the booster line and / or the reservoir.

[0029] The hydraulic pilot valve can be configured to allow fluid flow between the engine and the feed line and / or the tank at a flow rate of between 50 and 100 liters per minute.

[0030] An engagement time and / or a disengagement time of the motor may be less than 1 second, preferably less than 0.5 seconds.

[0031] The directional solenoid valve can be configured to consume less than 20 W of electrical power for controlling the hydraulic pilot valve.

[0032] According to another aspect of the present disclosure, there is provided a vehicle comprising a primary axle adapted to support at least one drive wheel of the vehicle; a secondary axle, distinct from the primary axle; a wheel mounted on the secondary axle; and a circuit according to the present disclosure, in which the motor is coupled to the wheel.

[0033] According to another aspect of the present disclosure, there is provided a method for steering a vehicle, the vehicle comprising a primary axle provided to support at least one drive wheel of the vehicle, a secondary axle, separate from the primary axle, and a wheel mounted on the secondary axle, method in which: a directional solenoid valve controls a hydraulic pilot valve; and the hydraulic pilot valve controls a freewheeling valve of a hydraulic motor of the vehicle coupled to the wheel; in which an activation of the directional solenoid valve causes an activation of the hydraulic pilot valve so as to activate the freewheeling valve to establish a circulation of fluid first between the motor and a fuel line of the vehicle then between a hydraulic pump of the vehicle and the motor;and wherein deactivation of the directional solenoid valve causes deactivation of the hydraulic pilot valve so as to deactivate the freewheel valve to isolate the pump from the engine and connect the engine to a reservoir of the vehicle, via the hydraulic pilot valve.;

[0034] DESCRIPTION OF FIGURES

[0035] Other characteristics, aims and advantages will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the attached figure 1 which schematically illustrates a hydraulic circuit for assisting the traction of a vehicle.

[0036] DETAILED DESCRIPTION

[0037] A vehicle is generally provided with at least one primary axle which supports at least one drive wheel of the vehicle. The drive wheel allows the vehicle to move, for example on land. Of course, the vehicle may comprise a plurality of primary axles and a plurality of drive wheels. In addition, the vehicle may comprise at least one secondary axle supporting at least one other, non-drive wheel 42 of the vehicle. Of course, the vehicle may comprise a plurality of secondary axles and a plurality of non-drive wheels 42. The wheels 42, although non-drive, may nevertheless play a role in driving the vehicle, for example by supporting a load of the vehicle, or by ensuring the steering of the vehicle.

[0038] The vehicle may be an agricultural machine or a construction machine, for example a combine harvester or a grader. The vehicle may be an articulated vehicle, or a hitch, comprising a tractor part, and a towed (or pushed) part, for example a trailer or a tool with towed (or pushed) wheels.

[0039] Figure 1 illustrates that the vehicle may further comprise a hydraulic circuit comprising a hydraulic pump 43. The hydraulic pump 43 may be driven, directly or indirectly, by the primary engine of the vehicle, typically via a power take-off connected to the primary engine, the power take-off being able to be connected to the hydraulic pump 43 via a clutch. The primary engine of the vehicle may comprise a heat engine and / or an electric motor. The hydraulic pump 43 comprises at least two ports 431, 432 connected to a communication circuit 40. The communication circuit 40 comprises a high pressure line, in the flow direction of the hydraulic pump 43, and a low pressure line, in the suction direction of the hydraulic pump 43. The flow direction within the communication circuit 40 may be modified.This modification can be implemented by reversing the drive direction of the pump 43, by using a pump 43 with reversing flow direction and / or by providing a direction reversing valve within the communication circuit 40.

[0040] In operation, the pressure which is established within the communication circuit 40 can be between 0 and 600 bar (i.e. 600.10 5 Pa), typically between 0 and 500 bar (i.e. 500. 10 5Pa). To supply the communication circuit 40 with fluid and compensate for the numerous losses, a booster line 400 is connected to the communication circuit 40. This booster line 400 is, for example, connected to the communication circuit 40 via non-return valves 46 visible in FIG. 1, typically with a non-return valve 46 arranged at the interface between the booster line 400 and the high pressure line and a non-return valve 46 arranged at the interface between the booster line 400 and the low pressure line. As described in more detail below, the pressure established within the booster line 400 is also used as hydraulic pilot pressure to actuate valves 1, 2 of the circuit. This booster pressure is between 5 and 20 bar (i.e. between 5.0.10 5 and 20.10 5 Pa), and is typically worth 15 bar (i.e. 15.10 5Pa). The booster line 400 is itself supplied via a booster pump 45, which draws fluid through its inlet port from a hydraulic reservoir 44 and delivers the fluid through its discharge port into the booster line 400. The hydraulic reservoir 44, or pressureless reservoir 44, is substantially at atmospheric pressure and defines the zero pressure reference of the circuit. The booster pump 45 may also be driven by the prime mover of the vehicle via a power take-off, for example the same drive as for the hydraulic pump 43, as seen in FIG. 1. The booster pump 45 may also be integrated into the hydraulic pump 43. Alternatively, the booster pump 45 may be driven by an electric pump unit. The hydraulic reservoir 44 is provided in particular to collect the fluid from all leaks in the circuit.Figure 1 also illustrates a pressure regulating valve 47 provided to regulate the pressure within the booster line 400, regardless of the operating mode of the booster pump 45, typically regardless of the speed of the primary engine of the vehicle.

[0041] The circuit is used in particular for traction assistance of the non-driven wheels 42. More specifically, the circuit can be used to temporarily provide additional torque to at least one of the non-driven wheels 42 of the vehicle. This additional torque may be necessary in particular when the vehicle is traveling on uneven or slippery terrain. In fact, in such situations, slippage of the driven wheels may occur which, associated with a reduction in the torque provided by the primary axle, leads to a reduction in the traction of the vehicle. In other words, the circuit makes it possible to temporarily increase the number of driven wheels of the vehicle. The circuit is further configured to deactivate its assistance when it is no longer necessary to provide additional traction to the wheels of the vehicle.The vehicle may comprise at least one, or even several, secondary axle(s) assisted by the circuit, or even by several circuits similar to that illustrated in FIG. 1, typically one circuit per non-driven wheel 42 or one circuit per secondary axle. In any event, the vehicle may thus comprise a secondary axle which is assisted in a working mode of the vehicle, for example in a field or on a construction site, and the assistance of which is disengaged in a road mode, for example when the vehicle is traveling on the roadway.

[0042] The excess torque is provided via a hydraulic motor 41 of the circuit, which is connected (or coupled) to the wheel 42, as seen in Figure 1. The hydraulic motor 41 is capable of providing excess torque to the wheel 42 by means of the hydraulic pump 43. The hydraulic pump 43 may be of a structure and operation similar to the hydraulic motor 41, or not. The hydraulic motor 41 comprises at least two ports 411, 412, the ports 431, 432 of the hydraulic pump 43 being connected to the ports 411, 412 of the hydraulic motor 41 via the communication circuit 40. In this way, the hydraulic pump 43 can deliver a fluid into the hydraulic motor 41, via the communication circuit 40, which allows the hydraulic motor 41 to develop excess torque to be transmitted to the wheel 42.Figure 1 illustrates that the portion of the communication circuit 40 which connects the hydraulic pump 43 to the hydraulic motor 41 is closed, that is to say that all the fluid delivered by the hydraulic pump 43 which circulates through the hydraulic motor 41, returns to the hydraulic pump 43 before being returned again to the hydraulic motor 41. If necessary, the direction reversing valve within the communication circuit 40 is arranged between the hydraulic pump 43 and the hydraulic motor 41, upstream or downstream of the freewheeling valve 1, described in more detail below. The direction of fluid flow within this portion of the communication circuit 40 and the determination of the high pressure line and the low pressure line, depends on the direction of rotation of the wheel 42, i.e. whether the vehicle is moving forward or backward, and / or on the type of force transmitted to the wheel 42, i.e. traction or restraint.Typically, returning to Figure 1, if the forward movement corresponds to a clockwise circulation of fluid within the communication circuit 40, then, in traction, the high pressure line will be connected to the inlet port 113 of the freewheel valve 1 and the low pressure line will be connected to the inlet port 111 of the freewheel valve 1, and vice versa in retention, the inlet ports 111, 113 being described in more detail below. In reverse, in the event that the hydraulic pump 43 could see its direction of rotation reversed, the circulation of the fluid would be in the counterclockwise direction within the communication circuit 40, and the high pressure and low pressure lines would be reversed, in traction and retention, compared to what has been described concerning the forward movement.

[0043] The traction assistance of the wheel 42 must be able to be activated or deactivated according to the needs of the vehicle, typically at the command of the driver, for example depending on the traveling conditions of the vehicle. Therefore, it may be provided that the assistance is activated and / or deactivated by the engagement and / or disengagement of the hydraulic motor 41, which also remains connected to the wheel 42. The engagement and / or disengagement can be achieved by deployment and / or retraction of pistons in their respective housings, when the hydraulic motor 41 is provided with them, typically when the hydraulic motor 41 is a multi-lobed cam and radial piston motor.

[0044] In a multi-lobed cam and radial piston engine, disengagement is typically implemented by isolating the hydraulic motor 41 from the hydraulic pump 43, and by connecting the ports 411, 412 of the hydraulic motor 41 to the reservoir 44. In doing so, when the wheel 42 drives the hydraulic motor 41, the pistons are pushed, by the cam and / or by the pressure established in the housing of the hydraulic motor 41, into a retracted position, and the fluid located under the pistons is ejected towards the reservoir 44. Once in the retracted position, and as long as they remain isolated from the hydraulic pump 43 and connected to the reservoir 44, the pistons do not deploy and the cam is decoupled from the pistons. The hydraulic motor 41 is then disengaged.Conversely, the engagement is typically implemented by deploying the pistons so that they come into contact with the cam, and thus engage the hydraulic motor 41 with the wheel 42 so as to be able to transmit a torque and a rotational movement. In the circuit illustrated in FIG. 1, the activation and / or deactivation of the assistance are implemented using a freewheeling valve 1, which is arranged within the communication circuit 40 so as to provide the interface between the hydraulic motor 41 and the hydraulic pump 43, that is to say to control the circulation of fluid between the hydraulic pump 43 and the hydraulic motor 41, but also between the hydraulic motor 41 and the reservoir 44 and between the hydraulic motor 41 and the feed line 400.More precisely, it is the configuration of the freewheeling valve 1 which controls the activation and / or deactivation of the traction assistance of the wheel 42, by placing the hydraulic motor 41 in communication with the feed line 400, then with the hydraulic pump 43 (activation) and / or by placing the hydraulic motor 41 in communication with the reservoir 44 (deactivation). Thus, the hydraulic reservoir 44 is not only designed to collect the fluid from all the leaks in the circuit, but also the excess fluid from the communication circuit 40 when the assistance is deactivated.

[0045] The freewheeling valve 1 comprises a plurality of inlet ports 111, 112, 113, in this case three inlet ports 111, 112, 113, and a plurality of outlet ports 121, 122, in this case two outlet ports 121, 122, as well as a slide 13 movable within a body (not shown) between different positions P5, P6, each position P5, P6 making it possible to establish and / or prohibit the circulation of fluid between inlet ports 111, 112, 113 and outlet ports 121, 122. Furthermore, the freewheeling valve 1 comprises a pilot chamber 14 and a return element 15. The pilot chamber 14 is provided to receive fluid so that a pressure is established within the pilot chamber 14 produces a force on the drawer 13. In the same way, the return element 15 connects the drawer 13 to the body so as to exert on the drawer 13 a force antagonistic to the force exerted by the pressure established in the control chamber 14.Therefore, a movement of the slide 13 within the body is controlled by the difference between these opposing forces of the pressure within the control chamber 14 and the return element 15. Figure 1 also illustrates that any fluid leak between the slide 13 and the body of the freewheeling valve 1 is redirected to the reservoir 44. Of course, all other leaks in the circuit, for example internal leaks from the hydraulic pump 43 and the hydraulic motor 41 and leaks from the other components 3, 47 can also be drained to the reservoir 44.

[0046] In a rest position P5, or default position, in which the pressure within the pilot chamber 14 of the freewheeling valve 1 is negligible compared to the force exerted by the return element 15 of the freewheeling valve 1, the slide 13 of the freewheeling valve 1 allows a circulation of fluid between its two outlet ports 121, 122, each connected to one of the orifices 411, 412 of the hydraulic motor 41, and one of its inlet ports 112, provided to be connected to the reservoir 44, the other two inlet ports 111, 113, each connected to one of the orifices 431, 432 of the hydraulic pump 43, remaining blocked. In this way, the hydraulic motor 41 can empty at least part of its fluid into the reservoir 44 and, if necessary, the pistons retract, then remain in their housings, as long as the orifices 411, 412 of the hydraulic motor 41 are at the pressure of the reservoir 44.Therefore, even if the hydraulic motor 41 continues to rotate, given its coupling to the wheel 42 via its cam, no resistive torque is transmitted from the hydraulic motor 41 to the wheel 42, the cam no longer being in contact with the pistons. The traction assistance is then deactivated.

[0047] In an operating configuration, a pressure has been established within the pilot chamber 14 of the freewheeling valve 1 and this is sufficiently high to counteract the force exerted by the return element 15 on the slide 13 of the freewheeling valve 1, so that the freewheeling valve 1 passes from the rest position P5 to an active position P6, in which it allows circulation of fluid between the hydraulic pump 43 and the hydraulic motor 41. More precisely, in the active position P6, circulation of fluid is allowed between each of the inlet ports 111, 113 connected to the orifices 431, 432 of the hydraulic pump 43 and each of the outlet ports 121,

[0048] 122, the inlet port 112 intended to be connected to the reservoir 44 remaining blocked.

[0049] Traction assistance is then activated.

[0050] Figure 1 illustrates that the freewheel valve 1 is controlled by a hydraulic pilot valve 2, connected to the freewheel valve 1.

[0051] The hydraulic pilot valve 2 is a hydraulically controlled directional valve and has a structure similar to that of the freewheeling valve 1, except that it has only two inlet ports 211, 212, one intended to be connected to the reservoir 44, and the other to the feed line 400, and an outlet port 221 intended to be connected to the pilot chamber 14 of the freewheeling valve 1, preferably via a line comprising a nozzle 48 provided to adjust the flow rate from the feed line 400, as will be described in more detail below.

[0052] In a rest position P1, or fault position, in which the pressure within the pilot chamber 24 of the hydraulic pilot valve 2 is negligible compared to the force exerted by the return element 25 of the hydraulic pilot valve 2 on the slide of the hydraulic pilot valve 2, the slide 23 of the hydraulic pilot valve 2 allows circulation of fluid between its outlet port 221 and its inlet port 211 connected to the reservoir 44, the other inlet port 212 remaining blocked. In this way, the pilot chamber 14 of the freewheeling valve 1 can empty itself of at least part of its fluid and the pressure established there becomes negligible compared to the force exerted by the return element 15 of the freewheeling valve 1 on the slide 13 of the freewheeling valve 1. Thus, the freewheeling valve 1 can move from its active position P6 to its rest position P5.Furthermore, once the freewheel valve 1 is in its rest position P5, the hydraulic motor 41 can empty itself of its fluid, via the hydraulic pilot valve 2 and thus the traction assistance can be deactivated. More precisely, the deactivation of the hydraulic pilot valve 2 makes it possible to deactivate the freewheel valve 1. From there, the hydraulic motor 41 is isolated from the hydraulic pump 43 and is connected to the reservoir 44, via the freewheel valve 1 and the hydraulic pilot valve 2, which causes the pistons of the hydraulic motor 41 to retract and the wheel 42 to disengage.

[0053] In an operating configuration, a pressure has been established within the pilot chamber 24 of the hydraulic pilot valve 2 and this is sufficiently high to counteract the force exerted by the return element 25 of the hydraulic pilot valve 2 on the slide 23 of the hydraulic pilot valve 2, so that the slide 23 of the hydraulic pilot valve 2 passes from the rest position P1 to an active position P2, in which it allows a circulation of fluid between the feed line 400 and the hydraulic motor 41 as long as the freewheel valve 1 is still in its rest position P5, but also between the feed line 400 and the pilot chamber 14 of the freewheel valve 1.More precisely, in the active position P2, a circulation of fluid is authorized between the inlet port 212 connected to the feed line 400 and the outlet port 221, the inlet port 211 intended to be connected to the reservoir 44 remaining blocked.

[0054] This active position P2 of the hydraulic pilot valve 2 ultimately makes it possible to establish and maintain a pressure in the pilot chamber 14 of the freewheeling valve 1, so as to counteract the force exerted on the slide 15 of the freewheeling valve 1 by the return element 15 of the freewheeling valve 1, thus causing the freewheeling valve 1 to move from its rest position P5 to its active position P6. More precisely, the activation of the hydraulic pilot valve 2 makes it possible to activate the freewheeling valve 1.

[0055] This active position P2 of the hydraulic pilot valve 2 also makes it possible to delay the switching from the rest position P5 to the active position P6 of the freewheeling valve 1, thanks to the nozzle 48, and this to promote the engagement of the hydraulic motor 41 with the wheel 42. Indeed, by adjusting the flow rate from the feed line 400, the nozzle 48 makes it possible not only to take into account the properties of the pilot chamber 14 of the freewheeling valve 1, but also to favor, at least in a first sequence of the switching, a circulation of fluid towards the inlet port 112 of the freewheeling valve 1 by which the hydraulic motor 41 is supplied, rather than towards the pilot chamber 14 of the freewheeling valve 1.This allows the pistons of the hydraulic motor 41 to be deployed, the pressure in the line connecting the inlet port 112 of the freewheeling valve 1 to the hydraulic motor 41 remaining low as long as the pistons have not come into contact with the cam. Once the pistons are resting on the cam, the pressure increases in the line connecting the inlet port 112 of the freewheeling valve 1 to the hydraulic motor 41, until it reaches a level equivalent to that established in the feed line 400. From then on, the flow rate of fluid circulating towards the hydraulic motor 41 becomes lower, and a significant pressure is established downstream of the nozzle 48, that is to say within the control chamber 14 of the freewheeling valve 1, so as to switch the slide 13 of the freewheeling valve 1 from the rest position P5 to the active position P6.Once in the active position P2, the hydraulic motor 41 is put into communication with the hydraulic pump 43, this communication being implemented only once the pistons have been deployed. From then on, in a sequential manner, the pistons are, in a first step, deployed, which allows the hydraulic motor 41 to engage the wheel 42, then the freewheeling valve 1 is switched, in a second step, which allows the pressure of the hydraulic pump 43 to be transmitted to the hydraulic motor 41.

[0056] Thus, the combination of the freewheel valve 1, the nozzle 48 and the hydraulic pilot valve 2 makes it possible to guarantee a significant fluid flow rate to supply the hydraulic motor 41 at the feed pressure and thus deploy its pistons more quickly.

[0057] Figure 1 illustrates that the hydraulic pilot valve 2 is piloted by a directional solenoid valve 3, connected to the hydraulic pilot valve 2, and more precisely to the pilot chamber 24 of the hydraulic pilot valve 2. Indeed, the behavior of the directional solenoid valve 3 determines the pressure established within the pilot chamber 24 of the hydraulic pilot valve 2 and, therefore, the passage of the hydraulic pilot valve 2 from its rest position P1 (deactivation of the freewheeling valve 1 and, therefore, of the traction assistance) to its active position P2 (activation of the freewheeling valve 1 and, therefore, of the traction assistance).

[0058] The directional solenoid valve 3 has a structure similar to that of the hydraulic pilot valve 2, except that its outlet port 321 is intended to be connected to the pilot chamber 24 of the hydraulic pilot valve 2 and that it is not a pressure established in a pilot chamber which counteracts the force exerted by the return element 35 of the solenoid valve on the slide 33 of the directional solenoid valve 3, but the action of a solenoid 34.

[0059] In a rest position P3, or fault position, in which the solenoid 34 is deactivated, the spool 33 of the directional solenoid valve 3 allows fluid to circulate between its outlet port 321 and its inlet port 311 connected to the reservoir 44, the other inlet port 312 remaining blocked. In this way, the pilot chamber 24 of the hydraulic pilot valve 2 can empty at least part of its fluid and the pressure established there becomes negligible compared to the force exerted by the return element 25 of the hydraulic pilot valve 2 on the spool 23 of the hydraulic pilot valve 2. Thus the hydraulic pilot valve 2 can move from its active position P2 to its rest position P1 to deactivate the freewheel valve 1 and the traction assistance. More specifically, deactivating the directional solenoid valve 3 makes it possible to deactivate the hydraulic pilot valve 2 and, therefore, to deactivate the traction assistance.

[0060] In an operating configuration, the solenoid 34 has been activated, for example by means of a remote control implemented by the driver of the vehicle, and the force that the solenoid 34 exerts on the slide 33 of the directional solenoid valve 3 has become sufficiently large to counteract the force exerted by the return element of the directional solenoid valve 3 on the slide 33 of the directional solenoid valve 3, so that the slide 33 of the directional solenoid valve 3 passes from the rest position P3 to an active position P4, in which it allows a circulation of fluid between the feed line 400 and the pilot chamber 24 of the hydraulic pilot valve 2. More precisely, in the active position P4, a circulation of fluid is allowed between the inlet port 312 connected to the feed line 400 and the outlet port 321, the inlet port 311 intended to be connected to the reservoir 44 remaining blocked.This active position P4 of the directional solenoid valve 3 makes it possible to establish and maintain a pressure in the pilot chamber 24 of the hydraulic pilot valve 2, so as to counteract the force exerted on the slide 23 of the hydraulic pilot valve 2 by the return element 25 of the hydraulic pilot valve 2, thus causing the hydraulic pilot valve 2 to move from its rest position P1 to its active position P2. The traction assistance can thus be activated. More precisely, the activation of the directional solenoid valve 3 makes it possible to activate the hydraulic pilot valve 2 and, therefore, to activate the traction assistance.

[0061] To deactivate the assistance, the hydraulic motor 41 must be disengaged.

[0062] To do this, the solenoid 34 is deactivated, so that the directional solenoid valve 3 switches from its active position P4 to its rest position P3, causing the reservoir 44 of the pilot chamber 24 of the hydraulic pilot valve 2 to be pressurized, which then switches from its active position P2 to its rest position P1. In its rest position P1, the hydraulic pilot valve 2 makes it possible to establish a pressure at the orifices 411, 412 of the hydraulic motor 41 which is identical to the pressure in the reservoir 44. As the wheel 42 continues to drive the hydraulic motor 41, the cam and / or the pressure within the casing of the hydraulic motor 41 pushes the pistons back, which retract.As long as all the pistons are not in the retracted position, the flow of fluid which is discharged from the hydraulic motor 41 to the reservoir 44, via the freewheel valve 1 and the hydraulic pilot valve 2 is a flow of the same order as the flow circulating within the hydraulic motor 41 when the assistance is activated, the hydraulic motor 41 is connected to the hydraulic pump 43 and the rotation speed of the wheel 42 is nominal. Once all the pistons are retracted and disengaged from the cam, the flow circulating from the hydraulic motor 41 to the reservoir 44 becomes, on the other hand, zero.

[0063] It should be noted that, in a variant, a system of return members can be provided to maintain the pistons in the retracted position by default as long as the orifices 411, 412 of the hydraulic motor 41 are not exposed to the pressure of the fluid discharged by the hydraulic pump 43.

[0064] Thus, whether in its rest position P1 or in its active position P2, the hydraulic pilot valve 2 is sized to allow the circulation of fluid at a high flow rate, that is to say of the same order of magnitude as the nominal flow rate of the hydraulic motor 41, once engaged and put into communication with the hydraulic pump 43.

[0065] In fact, the flow rate of fluid ejected from the pistons to retract them is equivalent to the flow rate to which the hydraulic motor 41 was exposed until the moment when its orifices 411, 412 were suddenly put into communication with the reservoir 44, the hydraulic pilot valve 2 having switched from its active position P2 to its rest position P1. In fact, at this precise moment, the cam is still connected to the wheel 42 and the pistons are in contact with the cam. However, this flow rate to which the hydraulic motor 41 was exposed may turn out to be the full admissible flow rate of the hydraulic motor 41 at its maximum rotation speed. Similarly, the flow rate of fluid intended to deploy the pistons may also be very high, typically between 0.33 and 0.5 times the maximum admissible flow rate by the hydraulic motor 41.

[0066] On the other hand, the pilot flow rate of the freewheeling valve 1, i.e. the flow rate of fluid flowing from the outlet port 222 of the hydraulic pilot valve 2 to the pilot chamber 14 of the freewheeling valve 1 to switch the freewheeling valve 1, is of the order of a few milliliters for a fraction of a second. Consequently, a ratio between the pilot flow rate of the freewheeling valve 1 and the supply flow rate of the hydraulic motor 41 from the feed line 400 to deploy the pistons (hydraulic piloting valve 2 in active position P2), or the discharge flow rate from the hydraulic motor 41 to the reservoir 44 to retract the pistons (hydraulic piloting valve 2 in rest position P1), when the freewheeling valve 1 is in rest position P5, is between 80 and 120, and is preferably 100.

[0067] The hydraulic pilot valve 2 is sized to allow the circulation of fluid through its slide valve 23 at such high flow rates without generating significant pressure loss, so that the disengagement and engagement of the hydraulic motor 41 can be done quickly.

[0068] In an exemplary embodiment of the circuit, the hydraulic motor 41 is designed to consume 100 liters per minute at 45 revolutions per minute, which requires the hydraulic pump 43 to be designed to deliver 200 liters per minute, assuming that the secondary axle comprises two wheels 42, each coupled to a hydraulic motor 41. Furthermore, the volume of fluid necessary to deploy the pistons of the hydraulic motor 41 is typically 150 cm 3 . In operation, the hydraulic motor 41 is designed to operate at a pressure between the charge pressure and 600 bar (i.e. 600.10 5 Pa), typically 300 bar (i.e. 300.105 Pa). Furthermore, the fluid flow rate required to control the control chamber 14 of the freewheeling valve 1 is between 2 and 3 liters per minute, and the freewheeling valve 1 is designed to switch from its rest position P5 to its active position P6 when a pressure of at least 12 bar (i.e. 12.10 5 Pa) is established within the pilot chamber 14 of the freewheeling valve 1. Finally, the fluid flow rate required to pilot the pilot chamber 24 of the hydraulic pilot valve 2 is 1 liter per minute, and the hydraulic pilot valve 2 is designed to switch from its rest position P1 to its active position P2 when a pressure of at least 7 bar (i.e. 7.10 5Pa) is established within the pilot chamber 24 of the hydraulic pilot valve 2. The directional solenoid valve 3 is, for its part, sized to provide a limited pilot flow rate in the direction of the hydraulic pilot valve 2. Typically, the flow rate required for this piloting is of the order of 2 liters per minute, preferably 1 liter per minute, at the boost pressure. In addition, the directional solenoid valve 3 operates with an electrical intensity of less than 2 Å, typically 1.4 Å, and an electrical power of less than 20 W, typically 17 W. The joint use of the directional solenoid valve 3 and the hydraulic pilot valve 2 therefore makes it possible to limit the electrical power required to pilot the circuit. When the hydraulic motor 41 is engaged, the flow rate of the boost pump 45 is typically 50 liters per minute.The time to engage the pistons is 0.5 seconds, i.e. a flow rate of the order of 20 liters per minute for the hydraulic motor 41, and 40 liters per minute for a secondary axle comprising two wheels 42, each coupled to a hydraulic motor 41. Furthermore, the time to switch the slide valve 13 of the freewheel valve 1 is 0.2 seconds.

[0069] When the hydraulic motor 41 is disengaged, the drain flow rate of the cylinders of the hydraulic motor 41 corresponds to the operating flow rate of the hydraulic motor 41 at its rotational speed, for example 100 liters per minute. The drain time is 0.5 seconds at the nominal speed of the hydraulic motor 41.

[0070] This embodiment shows that the flow rate required to control the valves 1, 2 is of the order of 1 to 2 liters per minute, while the flow rate to supply the hydraulic motor 41 is of the order of 100 liters per minute. The hydraulic control valve 2 is therefore sized to circulate a fluid flow rate of 2 liters per minute for controlling the freewheeling valve 1, and between 50 and 100 liters per minute to supply the hydraulic motor 41 during expansion or retraction of the pistons. Thus, the hydraulic motor 41 is capable of being engaged and disengaged very quickly, in a time of less than 1 second.In this way, it is possible to engage or disengage the assistance to the wheel 42 even when the vehicle is in motion, and the hydraulic motor 41 is driven by the wheel 42, while minimizing noise, torque surges, pressure peaks, and mechanical shocks at the pistons.

[0071] Thus, using a hydraulically controlled directional valve 2 to control the freewheeling valve 1 makes it possible to pass a large fluid flow between the hydraulic motor 41 and, respectively, the reservoir 44 or the feed line 400. From there, the engagement and / or disengagement of the hydraulic motor 41 is facilitated. To pass such a large fluid flow using a directional solenoid valve, instead of the hydraulically controlled directional valve 2 illustrated in FIG. 1, it would have been necessary to oversize the solenoid 34, which would have resulted in excessive bulk and cost of the circuit.On the contrary, the directional solenoid valve 3 illustrated in FIG. 1, insofar as it only controls the hydraulic pilot valve 2, and no longer directly the freewheel valve 1, can be smaller, in particular because it only needs to see a low flow of fluid pass through it, and therefore be less bulky and less energy-intensive.

[0072] The circuit illustrated in Figure 1 can be used solely for assisting the vehicle's traction. If necessary, the primary axle is driven by the vehicle's primary engine, by means of a primary transmission, which may include a clutch, a gearbox and / or a drive shaft line. In this case, the assembly formed by the power take-off, the possible clutch, and the circuit, constitutes a secondary transmission by which a torque supplied by the primary engine is capable of being transmitted to the non-driven wheel 42, when the assistance is activated. The secondary transmission is then independent of the primary transmission. In fact, the secondary axle is not driven by the primary transmission, but by the secondary transmission.

[0073] Alternatively, the circuit illustrated in Figure 1 is also used to transmit the mechanical power of the primary motor to the drive wheels of the primary axle. Where appropriate, each of the low pressure line and the high pressure line of the communication circuit 40 is further connected, in parallel with the hydraulic motor 41, to the ports of at least one other hydraulic motor (not shown), this connection to the other hydraulic motor being made upstream of the freewheel valve 1, that is to say directly at the ports 431, 432 of the hydraulic pump 43. The other hydraulic motor is, for its part, coupled to the primary axle, which may be a differential axle-bridge equipped, or not, with a reduction mechanism.

[0074] In any case, the direction of flow within the communication circuit 40 is modified according to the desired direction of advancement (forward or backward) of the wheels, whether they are driven or not.

Claims

CLAIMS 1. Assembly for a hydraulic circuit for assisting the traction of a vehicle, the assembly comprising: a freewheeling valve (1); a hydraulic pilot valve (2) connected to the freewheeling valve (1) and configured to pilot the freewheeling valve (1); and a directional solenoid valve (3) connected to the hydraulic pilot valve (2) and configured to pilot the hydraulic pilot valve (2).

2. Assembly according to claim 1, in which the hydraulic pilot valve (2) comprises: a first inlet port (211) intended to be connected to a reservoir (44) of the circuit; a second inlet port (212) intended to be connected to a feed line (400) of the circuit; and an outlet port (221) connected to a pilot chamber (14) and to a second inlet port (112) of the freewheeling valve (1).

3. The assembly of claim 2, wherein the hydraulic pilot valve (2) further comprises a slide valve (23) and a body, the slide valve (23) being movable within the body between: a first position (P1) in which the slide valve (23) allows fluid circulation between the first inlet port (211) and the outlet port (221) of the hydraulic pilot valve (2), and prohibits fluid circulation between the second inlet port (212) and the outlet port (221) of the hydraulic pilot valve (2); and a second position (P2) in which the slide valve (23) allows fluid circulation between the second inlet port (212) and the outlet port (221) of the hydraulic pilot valve (2), and prohibits fluid circulation between the first inlet port (211) and the outlet port (221) of the hydraulic pilot valve (2).

4. Assembly according to claim 3, wherein the hydraulic pilot valve (2) further comprises: a pilot chamber (24) connected to the directional solenoid valve (3) and connected to the spool (23) of the hydraulic pilot valve (2) so that a pressure within the pilot chamber (24) exerts a first force on the spool (23) of the hydraulic pilot valve (2); and a return element (25) connected to the spool (23) and to the body of the hydraulic pilot valve (2), so as to exert a second force on the spool (23) of the hydraulic pilot valve (2); wherein a movement of the spool (23) of the hydraulic pilot valve (2) between the first position (P1) and the second position (P2) of the hydraulic pilot valve (2) is controlled by a difference between the first force and the second force on the spool (23) of the hydraulic pilot valve (2).

5. Assembly according to any one of claims 1 to A, in which the directional solenoid valve (3) comprises: a first inlet port (311) intended to be connected to a reservoir (44) of the circuit; a second inlet port (312) intended to be connected to a feed line (400) of the circuit; and an outlet port (321) connected to a pilot chamber (24) of the hydraulic pilot valve (2).

6. An assembly according to claim 5, wherein the directional solenoid valve (3) further comprises a slide (33) and a body, the slide (33) being movable within the body between: a first position (P3) in which the slide (33) allows fluid circulation between the first inlet port (311) and the outlet port (321) of the directional solenoid valve (3), and prohibits fluid circulation between the second inlet port (312) and the outlet port (321) of the directional solenoid valve (3); and a second position (P4) in which the slide (33) allows fluid circulation between the second inlet port (312) and the outlet port (321) of the directional solenoid valve (3), and prohibits fluid circulation between the first inlet port (311) and the outlet port (321) of the directional solenoid valve (3).

7. An assembly according to claim 6, wherein the directional solenoid valve (3) further comprises: a solenoid (34) configured to exert a first force on the spool (33) of the directional solenoid valve (3); and a return element (35) connected to the spool (33) and to the body of the directional solenoid valve (3), so as to exert a second force on the second spool (33) of the directional solenoid valve (3); wherein a movement of the spool (33) of the directional solenoid valve (3) between the first position (P3) and the second position (P4) of the directional solenoid valve (3) is controlled by a difference between the first force and the second force on the spool (33) of the directional solenoid valve (3).

8. Assembly according to any one of claims 1 to 7, in which the freewheeling valve (1) comprises: a first inlet port (111) intended to be connected to a first orifice of a pump (43) hydraulic of the circuit; a second inlet port (112) provided to be connected alternately to a reservoir (44) of the circuit or to a feed line (400) of the circuit, via the hydraulic pilot valve (2); a third inlet port (113) provided to be connected to a second port of the pump (43); a first outlet port (121) provided to be connected to a first port of a hydraulic motor (41) of the circuit; and a second outlet port (122) provided to be connected to the second port of the motor (41).

9. An assembly according to claim 8, wherein the freewheeling valve (1) further comprises a slide valve (13) and a body, the slide valve (13) being movable within the body between: a first position (P5) in which the slide valve (13) allows fluid circulation between the second inlet port (112) and each of the first outlet port (121) and the second outlet port (122) of the freewheeling valve (1), and prohibits fluid circulation between each of the first inlet port (111) and the third inlet port (113), and each of the first outlet port (121) and the second outlet port (122) of the freewheeling valve (1);and a second position (P6) in which the slide (13) allows fluid circulation between the first inlet port (111) and the first outlet port (121), and between the third inlet port (113) and the second outlet port (122) of the freewheeling valve (1), and prohibits fluid circulation between the first inlet port (111) and the second outlet port (122), between the second inlet port (112) and each of the first outlet port (121) and the second outlet port (122), and between the third inlet port (113) and the first outlet port (121) of the freewheeling valve (1).; 10. The assembly of claim 9, wherein the freewheeling valve (1) further comprises: a pilot chamber (14) connected to the hydraulic pilot valve (2) and connected to the slide (13) of the freewheeling valve (1) so that pressure within the pilot chamber (14) exerts a first force on the slide (13) of the freewheeling valve (1); and a return element (15) connected to the slide (13) and to the third body of the freewheeling valve (1), so as to exert a second force on the slide (13) of the freewheeling valve (1); wherein a movement of the slide (13) of the freewheeling valve (1) between the first position (P5) and the second position (P6) of the freewheeling valve (1) is controlled by a difference between the first force and the second force on the slide (13) of the freewheel valve (1).

11. Assembly according to any one of claims 1 to 10, wherein: the freewheeling valve (1) comprises: a first inlet port (111) provided to be connected to a first orifice of a hydraulic pump (43) of the circuit; a second inlet port (112) provided to be connected alternately to a reservoir (44) of the circuit or to a feed line (400) of the circuit, via the hydraulic pilot valve (2); a third inlet port (113) provided to be connected to a second orifice of the pump (43); a first outlet port (121) provided to be connected to a first orifice of a hydraulic motor (41) of the circuit; a second outlet port (122) provided to be connected to a second orifice of the motor (41);a spool (13) and a body, the spool (13) being movable within the body between: a first position (P5) in which the spool (13) allows fluid circulation between the second inlet port (112) and each of the first outlet port (121) and the second outlet port (122) of the freewheeling valve (1), and prohibits fluid circulation between each of the first inlet port (111) and the third inlet port (113), and each of the first outlet port (121) and the second outlet port (122) of the freewheeling valve (1);and a second position (P6) in which the slide (13) allows fluid circulation between the first inlet port (111) and the first outlet port (121), and between the third inlet port (113) and the second outlet port (122) of the freewheeling valve (1), and prohibits fluid circulation between the first inlet port (111) and the second outlet port (122), between the second inlet port (112) and each of the first outlet port (121) and the second outlet port (122), and between the third inlet port (113) and the first outlet port (121) of the freewheeling valve (1); a pilot chamber (14) connected to the hydraulic pilot valve (2) and connected to the slide (13) of the freewheeling valve (1) so that a pressure within the pilot chamber (14) exerts a first force on the slide (13) of the freewheeling valve (1);and a return element (15) connected to the slide (13) and to the third body of the freewheeling valve (1), so as to exert a second force on the slide (13) of the freewheeling valve (1); wherein a movement of the slide (13) of the freewheeling valve (1) between the first position (P5) and the second position (P6) of the freewheeling valve (1) is controlled by a difference between the first force and the second force on the slide (13) of the freewheeling valve (1); the hydraulic pilot valve (2) comprises: a first inlet port (211) provided to be connected to the reservoir (44) of the circuit; a second inlet port (212) provided to be connected to the feed line (400) of the circuit; an outlet port (221) connected to the pilot chamber (14) and to the second inlet port (112) of the freewheeling valve (1);and a spool (23) and a body, the spool (23) being movable within the body between: a first position (P1) in which the spool (23) allows fluid circulation between the first inlet port (211) and the outlet port (221) of the hydraulic pilot valve (2), and prohibits fluid circulation between the second inlet port (212) and the outlet port (221) of the hydraulic pilot valve (2); and a second position (P2) in which the spool (23) allows fluid circulation between the second inlet port (212) and the outlet port (221) of the hydraulic pilot valve (2), and prohibits fluid circulation between the first inlet port (211) and the outlet port (221) of the hydraulic pilot valve (2);and wherein, in the first position (P5) of the slide (13) of the freewheeling valve (1) and in the second position (P2) of the slide (23) of the hydraulic pilot valve (2), the freewheeling valve (1) and the hydraulic pilot valve (2) are configured to connect the feed line (400) to the pilot chamber (14) of the freewheeling valve (1) and to the motor (41).; 12. Assembly according to any one of claims 1 to 11, wherein: the freewheeling valve (1) comprises: a first inlet port (111) provided to be connected to a first orifice of a hydraulic pump (43) of the circuit; a second inlet port (112) provided to be connected alternately to a reservoir (44) of the circuit or to a feed line (400) of the circuit, via the hydraulic pilot valve (2); a third inlet port (113) provided to be connected to a second orifice of the pump (43); a first outlet port (121) provided to be connected to a first orifice of a hydraulic motor (41) of the circuit; a second outlet port (122) provided to be connected to a second orifice of the motor (41); a spool (13) and a body, the spool (13) being movable within the body between: a first position (P5) in which the spool (13) allows fluid circulation between the second inlet port (112) and each of the first outlet port (121) and the second outlet port (122) of the freewheeling valve (1), and prohibits fluid circulation between each of the first inlet port (111) and the third inlet port (113), and each of the first outlet port (121) and the second outlet port (122) of the freewheeling valve (1);and a second position (P6) in which the slide (13) allows fluid circulation between the first inlet port (111) and the first outlet port (121), and between the third inlet port (113) and the second outlet port (122) of the freewheeling valve (1), and prohibits fluid circulation between the first inlet port (111) and the second outlet port (122), between the second inlet port (112) and each of the first outlet port (121) and the second outlet port (122), and between the third inlet port (113) and the first outlet port (121) of the freewheeling valve (1); a pilot chamber (14) connected to the hydraulic pilot valve (2) and connected to the slide (13) of the freewheeling valve (1) so that a pressure within the pilot chamber (14) exerts a first force on the slide (13) of the freewheeling valve (1);and a return element (15) connected to the slide (13) and to the third body of the freewheeling valve (1), so as to exert a second force on the slide (13) of the freewheeling valve (1); wherein a movement of the slide (13) of the freewheeling valve (1) between the first position (P5) and the second position (P6) of the freewheeling valve (1) is controlled by a difference between the first force and the second force on the slide (13) of the freewheeling valve (1); the hydraulic pilot valve (2) comprises: a first inlet port (211) provided to be connected to the reservoir (44) of the circuit; a second inlet port (212) provided to be connected to the feed line (400) of the circuit; and an outlet port (221) connected to the pilot chamber (14) and to the second inlet port (112) of the freewheeling valve (1);and wherein the assembly further comprises a line connecting the outlet port (221) of the pilot valve (2) to the pilot chamber (14) of the freewheeling valve (1), the line comprising a nozzle (48) provided for adjusting a flow rate from the feed line (400).; Tl 13. The assembly of claim 12, wherein the hydraulic pilot valve (2) further comprises: a slide valve (23) and a body, the slide valve (23) being movable within the body between: a first position (P1) in which the slide valve (23) allows fluid circulation between the first inlet port (211) and the outlet port (221) of the hydraulic pilot valve (2), and prohibits fluid circulation between the second inlet port (212) and the outlet port (221) of the hydraulic pilot valve (2); and a second position (P2) in which the slide valve (23) allows fluid circulation between the second inlet port (212) and the outlet port (221) of the hydraulic pilot valve (2), and prohibits fluid circulation between the first inlet port (211) and the outlet port (221) of the hydraulic pilot valve (2).

14. An assembly according to any one of claims 11 to 13, wherein the hydraulic pilot valve (2) further comprises: a pilot chamber (24) connected to the directional solenoid valve (3) and connected to the spool (23) of the hydraulic pilot valve (2) so that a pressure within the pilot chamber (24) exerts a first force on the spool (23) of the hydraulic pilot valve (2); and a return element (25) connected to the spool (23) and to the body of the hydraulic pilot valve (2), so as to exert a second force on the spool (23) of the hydraulic pilot valve (2); wherein a movement of the spool (23) of the hydraulic pilot valve (2) between the first position (P1) and the second position (P2) of the hydraulic pilot valve (2) is controlled by a difference between the first force and the second force on the spool (23) of the hydraulic pilot valve (2).

15. Assembly according to any one of claims 11 to 14, in which the directional solenoid valve (3) comprises: a first inlet port (311) intended to be connected to a reservoir (44) of the circuit; a second inlet port (312) intended to be connected to a feed line (400) of the circuit; and an outlet port (321) connected to a pilot chamber (24) of the hydraulic pilot valve (2).

16. Assembly according to claim 15, in which the directional solenoid valve (3) further comprises a spool (33) and a body, the spool (33) being movable within the body between: a first position (P3) in which the spool (33) allows circulation of fluid between the first inlet port (311) and the outlet port (321) of the directional solenoid valve (3), and prohibits a circulation of fluid between the second inlet port (312) and the outlet port (321) of the directional solenoid valve (3); and a second position (P4) in which the slide (33) allows a circulation of fluid between the second inlet port (312) and the outlet port (321) of the directional solenoid valve (3), and prohibits a circulation of fluid between the first inlet port (311) and the outlet port (321) of the directional solenoid valve (3).

17. An assembly according to claim 16, wherein the directional solenoid valve (3) further comprises: a solenoid (34) configured to exert a first force on the spool (33) of the directional solenoid valve (3); and a return element (35) connected to the spool (33) and to the body of the directional solenoid valve (3), so as to exert a second force on the second spool (33) of the directional solenoid valve (3); wherein a movement of the spool (33) of the directional solenoid valve (3) between the first position (P3) and the second position (P4) of the directional solenoid valve (3) is controlled by a difference between the first force and the second force on the spool (33) of the directional solenoid valve (3).

18. Hydraulic circuit for assisting the traction of a vehicle, the circuit comprising: a hydraulic motor (41) intended to be coupled to a wheel (42) of the vehicle; a hydraulic pump (43); and an assembly according to any one of claims 1 to 17; in which the freewheel valve (1) is configured to control the circulation of fluid between the pump (43) and the motor (41).

19. Circuit according to claim 18, wherein the pump (43) comprises a first orifice (431) and a second orifice (432) and the hydraulic motor (41) comprises a first orifice (411) and a second orifice (412), the circuit further comprising: a communication circuit (40) connecting the first orifice (431) of the pump (43) to the first orifice (411) of the motor (41), and the second orifice (432) of the pump (43) to the second orifice (412) of the motor (41), the communication circuit (40) comprising the freewheeling valve (1); a reservoir (44); a booster pump (45) comprising an inlet orifice connected to the reservoir (44) and a discharge orifice; and a feed line (400) connected to the discharge port of the feed pump (45) and to the communication circuit (40); in which the freewheel valve (1) and the hydraulic pilot valve (2) are configured to control the circulation of fluid between, on the one hand, the motor (41) and, on the other hand, the pump (43), the feed line (400) and / or the tank (44).

20. Circuit according to claim 19, in which the hydraulic pilot valve (2) is configured to allow circulation of fluid between the motor (41) and the feed line (400) and / or the tank (44) at a flow rate of between 50 and 100 liters per minute.

21. Circuit according to any one of claims 18 to 20, wherein an engagement time and / or a disengagement time of the motor (41) is less than 1 second, preferably less than 0.5 seconds.

22. Circuit according to any one of claims 18 to 21, in which the directional solenoid valve (3) is configured to consume an electrical power of less than 20 W for controlling the hydraulic pilot valve (2).

23. A vehicle comprising: a primary axle provided to support at least one drive wheel of the vehicle; a secondary axle, separate from the primary axle; a wheel (42) mounted on the secondary axle; and a circuit according to any one of claims 18 to 22, wherein the motor (41) is coupled to the wheel (42).

24. A method of steering a vehicle, the vehicle comprising a primary axle provided to support at least one drive wheel of the vehicle, a secondary axle, separate from the primary axle, and a wheel (42) mounted on the secondary axle, a method in which: a directional solenoid valve (3) controls a hydraulic pilot valve (2); and the hydraulic pilot valve (2) controls a freewheeling valve (1) of a hydraulic motor (41) of the vehicle coupled to the wheel (42); in which an activation of the directional solenoid valve (3) causes an activation of the hydraulic pilot valve (2) so as to activate the freewheeling valve (1) to establish a circulation of fluid first between the motor (41) and a feed line (400) of the vehicle then between a hydraulic pump (43) of the vehicle and the motor (41);and wherein deactivation of the directional solenoid valve (3) causes deactivation of the hydraulic pilot valve (2) so as to deactivate the freewheel valve (1) to isolate the pump (43) from the engine (41) and connect the engine (41) to a reservoir (44) of the vehicle, via the hydraulic pilot valve (2).;

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