Novel assistance device

Abstract

A closed-circuit hydraulic circuit supplying at least one hydraulic machine (210, 220) comprising a first and a second orifice, comprising a closed-circuit high-pressure pump (110) comprising a first and a second orifice, a high-pressure valve block (300) hydraulically connected to the high-pressure pump and traversed by a first hydraulic line (HP) and a second hydraulic line (BP) respectively connecting the first and the second orifice of the pump and of the hydraulic machine, one of the first or second hydraulic lines being able to be alternately subjected to a high hydraulic pressure, and containing a bypass valve (320) between the supply line and the return line capable of interconnecting the first hydraulic line and the second hydraulic line, and a low-pressure valve block (300) containing valves and shutters, characterized in that the high-pressure valve block and the low-pressure valve block are separated and connected to one another by hydraulic lines, and in that only the high-pressure valve block can receive the high hydraulic pressure, the low-pressure block receiving only the low hydraulic pressure.

Description

NEW SUPPORT DEVICE Description Technical Field

[0001] This presentation concerns a power supply circuit for at least one hydraulic machine. Previous technique

[0002] Typically, a hydraulic machine is powered by a pump that delivers pressurized fluid to a supply line on the machine, which also has an exhaust line. In a closed-loop system, the exhaust line is connected to an outlet on the pump, while in an open-loop system, the exhaust line is connected to a reservoir at atmospheric pressure.

[0003] In particular, a hydraulic machine is a machine comprising a cylinder block with a plurality of cylinders in which pistons can move back and forth. These pistons cooperate with a cam to ensure relative rotation between the cylinder block and the cam. The pistons can be oriented radially with respect to the machine's axis of rotation, in which case the cam can be of the wave type, or axially oriented, in which case the cam can be of the variable-angle cam-plate type. The machine can be of the rotating cam type or of the rotating cylinder block type.

[0004] The pump itself is driven by a drive system that may include, for example, a pump-drive internal combustion engine. To manage the machine's power supply, the circuit generally includes a valve device, allowing, for example, the high and low pressures to be reversed to change the machine's direction of rotation, or enabling auxiliary functions such as deactivating the machine by equalizing the pressure in the supply and exhaust lines, or disengaging the clutch by creating a disengagement pressure within the machine's housing that helps return the machine's pistons to their cylinders. The hydraulic machine has primary and secondary hydraulic power ports, and a housing drain to collect internal leaks. The hydraulic machine may also include a housing pressure port.

[0005] The hydraulic machine may, in particular, be a hydraulic assist motor forming part of a hydraulic transmission that can be used in addition to or instead of a main drive motor, especially for moving a vehicle. Hydraulic circuits including such hydraulic motors are known in particular from the following patent applications: FR 2 956462, FR 2 956461, FR 2 958 886, FR 3 004 148, FR 3 012 543, FR 3 014940, FR 3 026683, FR 3 026811, FR 3 026810, or FR 3 037 354.

[0006] These various patent applications focus in particular on certain functionalities of the transmission circuits they describe. They describe different methods of supplying the hydraulic motor(s) which include at least one main pump driven by a thermal engine type engine, and hydraulic lines conveying the fluid to the various ports of the hydraulic motor(s).

[0007] These technologies are well-established, but the installation of hydraulic circuits can be relatively complex due to the necessary connections and the size of the valves. In particular, to minimize the number of hydraulic lines, it may be desirable to integrate the valves and pump into a single unit. This requires ensuring the pump drive and, on the other hand, proper connection of the lines to the ports of the hydraulic machine(s). However, the valve and pump assembly becomes very bulky, especially since the volume of the valve section can exceed certain dimensions of the pump, such as its length. Alternatively, the valves can be placed in a valve block on one side and the pump on the other. However, the piping between the various circuit components becomes very complex and cumbersome.The various components required for the power supply are presented separately and must be assembled separately. Assembly can be tedious, especially when the hydraulic machine is fitted to a vehicle that already has numerous other components.

[0008] The invention aims to provide a power supply circuit allowing simplified installation, easy connection to the various components concerned, and limited space at the pump block level, particularly with regard to its length. Description of the invention

[0009] The present invention thus relates to a closed-loop hydraulic circuit supplying at least one hydraulic machine comprising a first and a second orifice, the hydraulic circuit comprising: - a closed-circuit high-pressure pump comprising a first and a second port adapted for fluid intake and discharge - a high-pressure valve block hydraulically linked to the high-pressure pump, through which a first hydraulic line and a second hydraulic line connecting respectively the first and second ports of the pump and the hydraulic machine, one of the first or second power lines being able to be alternately subjected to high hydraulic pressure delivered by the high-pressure pump, and the other of the first or second power lines being able to be alternately subjected to low hydraulic pressure, said high-pressure valve block containing a bypass valve between the first hydraulic line and the second hydraulic line suitable for connecting the first hydraulic line and the second hydraulic line together or for isolating them from each other, and - a low pressure valve block containing valves and flaps, characterized in that the high pressure valve block and the low pressure valve block are arranged in separate housings and connected to each other by hydraulic lines, so that the low pressure valve block is subjected to a pressure strictly lower than the high hydraulic pressure.

[0010] In one example, the high-pressure valve block is mechanically supported by the high-pressure pump.

[0011] As an example, the high-pressure valve block contains a bypass valve configured to: - in a first position, connect the first power line and the second power line, and - in a second position isolate the first power line and the second power line.

[0012] According to one example, in the second position, the first power line and the second power line are connected to a feed or drain port of the high-pressure valve block.

[0013] According to one example, the low pressure valve block is connected to a feed pump and an ambient pressure tank, via a feed port and a tank port.

[0014] According to one example, the low pressure valve block includes a feed pressure relief valve configured to connect the feed pump to the tank, said feed pressure relief valve being a calibrated valve, configured to be passable when the pressure applied to an orifice of said feed pressure relief valve exceeds a calibration value.

[0015] In one example, the low-pressure valve block is connected to a hydraulic machine housing port.

[0016] As an example, the low-pressure valve block includes a feed or drain port

[0017] In one example, the low pressure valve block's feed or drain port is hydraulically connected to the high pressure valve block's feed and drain port.

[0018] According to one example, a non-return valve is hydraulically placed in the low pressure valve block between the feed port and the feed and drain port.

[0019] As an example, a directional valve places the feed or drain port either at the pressure of the feed pump or at the pressure of the unpressurized tank. Brief description of the drawings

[0020] The invention and its advantages will be better understood upon reading the detailed description below of various embodiments of the invention given by way of non-limiting examples.

[0021] [Fig. 1] Figure 1 is a schematic presentation of a hydraulic circuit according to one aspect of the invention. Description of the implementation methods

[0022] We describe an example of this implementation with reference to Figure 1.

[0023] This figure shows a circuit comprising a primary motor M driving a hydraulic pump 110 from a pump unit 100, here via a clutch. The hydraulic pump 110 is coupled to a leakage valve 120, which here comprises a spool 122 coupled to a calibrated valve 124. The leakage valve 120 is known and is configured to provide a calibrated leak of fluid from the branch of the hydraulic circuit with the lowest pressure, thus ensuring fluid renewal, filtration, and cooling.

[0024] The hydraulic pump 110 is typically a radial piston, multi-lobe cam hydraulic pump. The hydraulic pump 110 has a first port 112 and a second port 114, defining a fluid discharge and a fluid inlet respectively, and thus defining a first power line LP1 and a second power line LP2. In this description, for illustrative purposes, the high-pressure line HP will be designated the power line connected to the discharge of the hydraulic pump 110 (here, the first port 112), and the low-pressure line BP will be designated the power line connected to the inlet of the hydraulic pump 110 (here, the second port 114). The hydraulic pump 110 is typically reversible and can operate in reverse; it is understood that the inlet and discharge can be reversed and that the designations HP and BP are arbitrary here. The operation remains unchanged.The high pressure will be established in one of the two power lines, depending on whether the transmission is operating in forward or reverse, or depending on whether the transmission will provide traction or holding torque.

[0025] The first power line LP1 and the second power line LP2 are connected to hydraulic consumers. Figure 1 shows two hydraulic motors 210 and 220 mounted in parallel, which are therefore typically powered by the hydraulic pump 110. In the example shown, the hydraulic motors are wheel motors.

[0026] The 100 pump block is associated with a 300 high-pressure valve block.

[0027] The pump block and the 300 high-pressure valve block are assembled and housed in the same casing or housing. The pipes can therefore be formed directly within the casing, which is advantageous in terms of strength, particularly for pipes carrying high pressure.

[0028] This assembly defines a power supply unit, comprising an outlet port OP1 and an inlet port OP2 for connection to hydraulic consumers. It also includes various outlet ports, notably a leak port 04, a feed port 01, and a drain port 02.

[0029] The high-pressure valve block 300 includes feed valves 310, shown here as two assemblies, each comprising a calibrated valve and a check valve mounted in parallel. These assemblies provide both overpressure protection and feed the hydraulic circuit via a feed pump, which will be described later. The structure of such feed valves is well known. They are connected to the feed port 01 formed in the supply block.

[0030] The high pressure valve block 300 also includes a bypass valve 320, controlled by pneumatic controls connected to the drain port 02.

[0031] The 320 bypass valve has three ports: - a first port connected to the first power line LP1 - a second port connected to the first power line LP2, and - a third orifice connected to the leak orifice 04.

[0032] The 320 bypass valve is controlled between: - a first configuration, in which the first orifice, the second orifice, and the third orifice are connected to each other, - a second configuration, in which the first orifice and the second orifice are connected to each other, and the third orifice is closed, this second configuration being optional, and - a third configuration in which the first orifice, the second orifice and the third orifice are isolated from each other.

[0033] The first and second configurations directly connect the inlet of hydraulic pump 110 to its outlet, bypassing the hydraulic consumers (i.e., hydraulic motors 210 and 220). The pressure within the power lines LP1 and LP2 is then typically zero or equal to the feed pressure. In the third configuration, the system is in operation; hydraulic pump 110 supplies hydraulic motors 210 and 220 (or vice versa in the case of reverse operation, or when hydraulic motors 210 and 220 are braking or holding). One of the power lines is then at high hydraulic pressure, and the other is at low hydraulic pressure.

[0034] The system shown also includes a 400 low pressure valve block. This 400 pressure-passing valve block is formed in a low-pressure housing or enclosure isolated from the power supply unit.

[0035] The 400 low-pressure valve block comprises various components designed for piloting, priming, and draining the hydraulic circuit. It is typically connected to an ambient pressure reservoir (R) and components such as a filter (Fi), a heat exchanger (ET), and a 500 priming pump. The 400 low-pressure valve block is connected to these components via various ports in the low-pressure housing.

[0036] The low-pressure housing of the 400 low-pressure valve block also includes various ports to allow its connection with the power supply unit: - a low-pressure drain port Tl, - a low-pressure T2 feed orifice, and - a low pressure leak orifice T3.

[0037] The low pressure drain port Tl is connected to the drain port 02 of the power supply unit.

[0038] The low pressure leak port T3 is connected to the calibrated valve 124 and allows the oil escaping from the circuit through this calibrated valve 124 to be routed to the filter Fi, the heat exchanger ET and the reservoir R.

[0039] The low pressure feed port T2 is connected to the feed port 01, allowing the feed pump 500 to be connected to the feed valves 310 and to the third port of the bypass valve 320, and thus to perform a feed function of the hydraulic circuit.

[0040] The low-pressure valve block 400, as shown, includes a low-pressure feed valve 410, suitable for connecting or disconnecting the feed pump to the low-pressure feed port T2, and a feed bypass valve 430 suitable for connecting the feed pump 500 to the reservoir R, particularly when the low-pressure feed valve is not open. This allows the flow from the feed pump 500 to be diverted into the reservoir when the pump is running but the feed system is not activated. In conjunction with the bypass valve 320, the low-pressure feed valve 410 also allows the hydraulic circuit to be drained by connecting the high-pressure and low-pressure branches of the hydraulic circuit to the reservoir R.

[0041] In the example shown in Figure 1, valve 320 is depicted with pneumatic control, while valves 410, 420, and 430 are depicted with electrical control. This embodiment is not exhaustive; the various valves can be electrically, hydraulically, or pneumatically controlled. Similarly, the pump clutches can be hydraulically, pneumatically, or electrically controlled.

[0042] The low-pressure valve block 400 also includes a feed pressure relief valve 510, configured to limit the feed pressure to a given pressure and vent the excess to the reservoir R. The feed pressure relief valve 510 is positioned at the outlet of the feed pump 500, in parallel with the low-pressure feed valve 410. The feed pressure relief valve 510 can, for example, be set at a pressure between 20 and 30 bar, for example, around 25 or 26 bar, and thus discharges the excess pressure into the reservoir R.

[0043] Thus, when the hydraulic circuit is in operation—that is, when the bypass valve 320 isolates the first power line LP1 from the second power line LP2 and the hydraulic pump 110 supplies a hydraulic consumer (or vice versa in the case of engine braking)—the feed pump 500 ensures a minimum pressure in the power line with the lower pressure. The low pressure in the hydraulic power lines LP1 and LP2 is therefore equal to, or nearly equal to, the feed pressure defined by the feed pump 500 and limited by the feed pressure relief valve 510.

[0044] In the illustrated example, the low-pressure valve block 400 also includes a crankcase pressure valve 420, adapted to be connected to the crankcases of the hydraulic motors 210 and 220 via a crankcase pressure port T3. This allows for a pressure increase in the crankcases of the hydraulic motors 210 and 220 to selectively cause their pistons to retract into their housings, thus switching them to a freewheel configuration with zero displacement, or connecting them to the pressure of the reservoir R. Pressurizing the crankcases of the hydraulic machines allows the pistons to retract into the cylinder block, removing them from contact with the cam, and thus disengaging the hydraulic machine shaft from its cam, allowing it to rotate without parasitic drag.

[0045] This presentation concerns a circuit composed of a first power unit 100, comprising a pump 110 and a high-pressure valve block 300, and a second unit 400, comprising low-pressure valves, intended to power at least one hydraulic machine 200. The power unit therefore contains a high-pressure pump 110 and a high-pressure valve block 300. The second valve block 400 is designated as the low-pressure unit and is physically separate from the power unit 100. Typically, such a circuit is used to provide temporary traction assistance on an axle not driven by the main transmission of a machine or vehicle, for example, a truck steering axle or a trailer axle. The vehicle will therefore include at least one power unit, one low-pressure unit, and a source of mechanical motion, for example, a combustion or electric motor to drive the power pump.

[0046] Thus, the present exposition relates to a high-pressure power unit for at least one hydraulic machine, the power unit comprising a housing containing a power pump device and having a motion input for the mechanical drive of the pump device, and a first and a second hydraulic power port, the housing containing a hydraulic valve device for selective connection between the power pump device and said hydraulic power ports, designated as a bypass valve, bearing the reference 320 in Figure 1,the power supply being configured to be connected to control means of the hydraulic valve device and to adopt a rest state in which the first and second hydraulic power ports are set to a common rest pressure and an activated state in which the first and second hydraulic power ports are respectively set to a high pressure and a low pressure of the pump device.

[0047] The high-pressure power supply unit described herein comprises, on the one hand, a mechanical port constituting the motion input for the mechanical drive of the pump device 110. This port is, in particular, a force input and may be in the form of a drive shaft segment that can be connected to the output of a drive motor, specifically a thermal or electric motor M. This motion input may be male, capable of being mechanically coupled to a female output of the drive motor, or it may also be a female segment that can be mechanically coupled to a male output of the drive motor. A pilot-operated clutch, as schematically illustrated in Figure 1, may be interposed.

[0048] The power unit houses both the pump and the high-pressure hydraulic valve within the same casing. In addition to the previously mentioned mechanical input port, the casing features first and second hydraulic ports, OP1 and OP2, which are outputs of the hydraulic valve and can be connected to the main ports of a 210 and / or 220 hydraulic machine.

[0049] A "same casing" makes it possible, in particular, to avoid hydraulically connecting the blocks with conduits or hydraulic hoses.

[0050] The hydraulic pump with a power rating of 100 has a first port and a second power port, 112 and 114 respectively. The valve block has at least two hydraulic power lines: a first line connecting the first power port of the pump to the first port of the hydraulic machine, and a second line connecting the second port of the power pump to the second port of the hydraulic machine, thus creating a closed hydraulic circuit. The bypass valve 320 is located between the first and second hydraulic power lines.

[0051] The power pump can be of the fixed displacement type. In particular, it can be of the multi-lobe cam and radial piston type.

[0052] Thanks to the control means of bypass valve 320, the pressures at the first and second hydraulic ports can be set either to a common pressure, so that a hydraulic machine whose main ports are connected to the first and second hydraulic ports is in a neutral state, or to different pressures, allowing the machine to operate with different supply and exhaust pressures. This is achieved by actuation of the valve, which has at least two positions. Furthermore, in the common pressure position, the bypass valve is also connected to a feed or drain line, which will be detailed below. This allows the first and second power lines to be set to either a feed pressure or zero pressure for draining the high-pressure lines.The common pressurization position of the bypass valve can be connected to a feed and drain port to the low pressure group.

[0053] In one particular embodiment, the bypass valve 320 is a three-position, three-port valve (this three-position valve includes a return spring and two controls, these controls being either electrical or pneumatic and actuated by a vehicle computer). However, it could fulfill the functions of the invention with an alternative design that includes at least one position with three ports closed (corresponding to the uppermost position of the valve 320) and one position with the three ports communicating with each other (corresponding to the uppermost position of the valve 320).

[0054] The 300 high-pressure valve block is designed to handle the high hydraulic pressure required for power transmission. For example, it can withstand pressures ranging from 100 to 600 bar when the transmission is activated. When the hydraulic power transmission is started, depending on the direction of rotation and the direction of the load—that is, whether the hydraulic machine is operating in traction or compression—one of the two power lines is at high hydraulic pressure, while the other is at low pressure. The high pressure can be established alternately in either of the two hydraulic power lines, depending on the direction of the load.

[0055] The power unit can be easily mounted to a support such as a fixed part of a vehicle, particularly the engine block, transmission, or chassis. The power unit allows for compact mechanical and high-pressure hydraulic connections. Because its housing contains the power pump and the high-pressure hydraulic valve assembly, the use of external high-pressure lines and fluid fittings is minimized, contributing to overall compactness and ergonomics, and reducing pressure losses that can occur with external fluid connections. This design reduces pressure losses and improves the efficiency of the hydraulic transmission.Furthermore, this assembly optimizes the overall dimensions by relocating the 400 low-pressure valve block while minimizing the size of the hydraulic lines required to connect it to the power supply unit due to the reduced pressure within it. It is clear that housing all the components in a single casing is not feasible due to space constraints. The proposed invention thus provides an optimized structure.

[0056] Optionally, the housing also features a third and fourth hydraulic power port. The first, second, third, and fourth hydraulic power ports are set to a common resting pressure in the off state, while the third and fourth hydraulic power ports are set to the high and low pressures of the pump device, respectively, in the activated state. The third port is supplied in parallel with the first port, and the fourth port is supplied in parallel with the first port, allowing multiple outputs to be supplied to hydraulic machines, for example, connecting two hydraulic machines in parallel.

[0057] The power unit may include other components subjected to high hydraulic pressure. For example, a pressure relief valve and a check valve, and a pressure and safety group comprising a pressure relief valve and a check valve for each of the high-pressure and low-pressure lines. Each pressure and safety group is connected to a port leading to the low-pressure group.

[0058] The power pack also includes a drain line to collect internal leaks to a pressureless tank, and a low-pressure exchange (also called "rinsing" or "flushing") line.

[0059] The supply circuit also includes a second separate valve block, designated as the low pressure valve block 400. When the hydraulic pump 110 is in operation, the low pressure valve block is never supplied with high hydraulic pressure without the intermediary of elements enabling the pressure delivered by the hydraulic pump to be isolated or reduced.In other words, when the bypass valve 320 does not connect the inlet of the hydraulic pump 110 to its outlet by short-circuiting the hydraulic consumers (here the hydraulic motors 210 and 220), that is to say when the bypass valve 230 is in a configuration not connecting its first orifice connected to the first power line to its second orifice connected to the second power line, the pressure in the various lines of the low pressure valve block 400 is always less than or equal to the set pressure of the feed valve 510, that is to say less than or equal to the lowest pressure among the pressure in the first power line LP1 and the second power line LP2.Since the pressure in the low pressure line of the hydraulic circuit is typically equal to or substantially equal to the pressure delivered by the feed pump 500, which is itself limited by the feed valve 510, the pressure within the low pressure valve block 400 is thus typically less than or equal to the set pressure of the feed valve 510.

[0060] The low-pressure valve block is connected to a non-pressurized reservoir (R) and a 500-liter fuel pump. The 500-liter fuel pump can be either mechanically or electrically driven. The 500-liter fuel pump provides a low-pressure supply, typically between 3 and 30 bar. The low-pressure unit contains a set of valves designed to distribute the fuel pressure or connect to zero pressure for various functions.

[0061] The low pressure valve block has a port to the 500 feed pump, a port to the unpressurized R reservoir, a port to the hydraulic machine housings 210, 220, and a port to the high pressure valve block 400.

[0062] The low-pressure block includes a pressure relief valve for limiting the feed pressure, for example set at 26 bar, and its leak return to the unpressurized tank.

[0063] A non-return valve is connected to the outlet of the fuel pump 500, supplying the fuel and drain ports to the high-pressure valve block 300. A directional valve 410, used for fuel pressure control or vacuuming, allows the fuel or vacuum line to be set to either the fuel pressure or the pressure of the unpressurized tank. This pressure control valve allows the closed-loop circuit, i.e., the high-pressure circuit, to be filled or emptied when the transmission circuit needs to be activated or deactivated.

[0064] The low-pressure valve block also includes a directional valve 420 for pressurizing the hydraulic machine housings, capable of connecting the hydraulic machine housing to the feed pressure or to the pressure in the unpressurized reservoir. Pressurizing the hydraulic machine housings allows the pistons to retract into the cylinder block, disengaging the hydraulic machine from its shaft and thus allowing it to rotate freely relative to the shaft without parasitic drag. The low-pressure valve block also includes a directional valve 430 for bypassing the feed pump, capable of connecting the feed pump outlet to the unpressurized reservoir in one position, bypassing the feed pump and thus canceling the feed pump pressure even if the pump is operating and supplying flow, and in another position, closing this connection and restoring the feed pressure.

[0065] The low-pressure block may also include an outlet and a return for circulating fluid through a cooler. It has a return port to the reservoir where a filter can be installed. The low-pressure block also includes a drain port for collecting internal leaks, connected to the unpressurized reservoir.

[0066] The hydraulic machine typically drives a wheel of a vehicle.

[0067] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0068] It is also evident that all the characteristics described with reference to a process are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a process.

Claims

Demands

1. Closed-loop hydraulic circuit supplying at least one hydraulic machine (210, 220) comprising a first and a second orifice, the hydraulic circuit comprising: - a closed-circuit high-pressure pump (110) comprising a first (112) and a second (114) orifice adapted to achieve fluid intake and discharge, respectively defining a high-pressure (HP) line and a low-pressure (LP) line - a high-pressure valve block (300) hydraulically linked to the high-pressure pump (110), through which a first power line and a second power line connecting respectively the first and second ports of the pump and the hydraulic machine, one of the first or second power lines being able to be alternately subjected to high hydraulic pressure delivered by the high-pressure pump, and the other of the first or second power lines being able to be alternately subjected to low hydraulic pressure, said high-pressure valve block containing a bypass valve (320) between the first hydraulic line and the second hydraulic line capable of connecting the first hydraulic line and the second hydraulic line together or of isolating them from each other, and - a low-pressure valve block (400) containing valves and check valves, characterized in that the high pressure valve block (300) and the low pressure valve block (400) are arranged in separate housings and connected to each other by hydraulic lines, so that the low pressure valve block (400) is subjected to a pressure less than or equal to the lowest pressure among the pressures within the first power line (LP1) and the second power line (LP2).

2. Circuit according to claim 1, characterized in that the high pressure valve block (300) is mechanically carried by the high pressure pump (110).

3. Circuit according to claim 1, characterized in that the high-pressure valve block (300) contains a bypass valve (320) configured to: - in a first position, connect the first power line (LP1) and the second power line (LP2), and - in a second position isolate the first power line (LP1) and the second power line (LP2).

4. Circuit according to claim 3 characterized in that in the second position, the first power line (LP1) and the second power line (LP2) are connected to a feed port (01) or drain port of the high pressure valve block (300).

5. Circuit according to any one of the preceding claims, characterized in that the low pressure valve block (400) is connected to a feed pump (500) and to a reservoir (R) at ambient pressure, by a feed port and a reservoir port.

6. A circuit according to claim 5, wherein the low-pressure valve block (400) comprises a feed pressure relief valve (510) configured to connect the feed pump (500) to the reservoir (R), said feed pressure relief valve (510) being a calibrated valve configured to be open when the pressure applied to an orifice of said feed pressure relief valve (510) exceeds a calibration value.

7. A circuit according to any one of claims 4 to 6, characterized in that the low-pressure valve block (400) is connected to a hydraulic machine housing port

8. Circuit according to any one of claims 4 to 7, characterized in that the low-pressure valve block (400) comprises a feed port (T2) or a drain port

9. Circuit according to claim 8, characterized in that the feed port (T2) or drain port of the low pressure valve block (400) is hydraulically connected to the feed port (01) and drain port of the high pressure valve block (300).

10. Circuit according to any one of claims 5 to 9 characterized in that a check valve is hydraulically placed in the low pressure valve block (400) between the feed port and the feed and drain port.

11. Circuit according to any one of claims 8 to 10 characterized in that a directional valve (410) places the feed port (T2) or drain port either at the pressure of the feed pump (500), or at the pressure of the unpressurized tank (R).

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