Open-loop hydraulic circuit for assisting the movement of a vehicle or machine

Abstract

The circuit comprises: - a pump (4); - at least one hydraulic motor (6); and - at least one proportional valve (20) comprising a movable spool, the valve being configured to vary the flow rate of fluid supplied by the pump between non-zero values ​​proportional to a displacement of the spool, the circuit being configured such that the pump supplies the valve with fluid and the valve controls a movement of the motor by means of the fluid flow rate. Figure from the abstract: Fig. 1

Description

Title of the invention: Open-loop hydraulic circuit for assisting the movement of a vehicle or machine. SCOPE OF THE INVENTION

[0001] The invention relates to hydraulic circuits for assisting the drive of vehicles or machinery. STATE OF THE ART

[0002] Open-loop hydraulic circuits are known, in which a hydraulic pump supplying the circuit draws oil from a reservoir and the oil returning from the circuit outlet is sent back to the reservoir. This configuration, called an open loop, contrasts with that of closed circuits, in which a booster pump is generally required to maintain a minimum pressure in the closed circuit. The closed circuit comprises a supply branch and a return branch between the main pump and the hydraulic receivers of the circuit. The closed loop does not pass through the reservoir, while the booster pump draws from the reservoir to maintain the minimum pressure of the closed loop.

[0003] Document FR-3 035 829 in the name of the applicant describes an open-loop hydraulic circuit for assisting the drive of a vehicle.

[0004] One object of the invention is to provide an improved assistance circuit. Description of the invention

[0005] According to the invention, an open-loop hydraulic circuit is provided for assisting the movement of a vehicle or machine, the circuit comprising:

[0006] - a pump;

[0007] - at least one hydraulic motor; and

[0008] - at least one proportional distributor comprising a movable drawer, the distributor being configured to vary the flow rate of fluid supplied by the pump between non-zero values ​​proportional to a displacement of the spool,

[0009] the circuit being configured so that the distributor controls a movement of the motor by means of the fluid flow.

[0010] It is understood that the flow rate supplied by the distributor can also take a value of zero. Furthermore, the distributor is configured to be able to continuously vary the flow rate of the fluid supplied, the position of the spool therefore also varying continuously.

[0011] It can be assumed that the distributor is pressure balanced.

[0012] It is not essential that the distributor be pressure balanced, as it is possible to have only one spool used at a time or a single spool. And if the pump is pressure-regulated, for example of the LS type as will be seen later, a spool A pressure balance may suffice.

[0013] The circuit may also have one or more of the following characteristics:

[0014] . the circuit comprising a reservoir, the distributor includes upstream of the spool a pump-side supply line and a tank-side discharge line connected to the pump-side supply line by a valve allowing fluid communication only from the tank-side discharge line to the pump-side supply line;

[0015] . the circuit comprising a reservoir,

[0016] The distributor includes a discharge conduit on the tank side, and

[0017] the circuit includes on the discharge conduit on the tank side a back pressure valve allowing fluid communication only in the direction of the tank, the valve including a return spring;

[0018] It comprises at least two motors, the distributor(s) being connected to the two motors by a parallel connection;

[0019] It comprises several distributors, the pump being connected to the distributors by a parallel mounting;

[0020] . the distributor being a first distributor and the motor being a first motor, the The circuit includes at least a second motor and a second distributor.

[0021] the circuit being configured so that the second distributor controls a movement of the second motor by means of a fluid flow;

[0022] The first distributor is connected to the first motor without being connected to the second engine and the second distributor is connected to the second engine without being connected to the first engine;

[0023] The circuit comprises several stacked distributors, each distributor is traversed by a supply line having two openings leading to opposite faces of the distributor and by a discharge line having two other openings on the opposite faces;

[0024] . the pump has a fixed displacement;

[0025] The pump has a flow-controlled displacement, and the distributor(s) is capable of supplying a fluid pressure value to the pump, in particular by means of a shuttle valve of the distributor;

[0026] It comprises at least two distributors, the circuit being configured so that the pump receives a higher pressure among the pressures of the distributors;

[0027] The circuit further comprises at least one hydraulic control element for disengagement configured to command a disengagement of the engine or each engine. This arrangement assumes that the engines are of the type allowing disengagement on command by retracting the pistons into the cylinder block, in other words are disengageable;

[0028] The disengagement control element comprises a directional valve and a pressure reducer;

[0029] . the engine or each engine is without a crankcase drain;

[0030] The disengagement control device comprises a proportional distributor, comprising a drawer with a neutral position of the closed center type with vacuum release;

[0031] The disengagement control element includes a power supply port for the motor and a motor discharge port connected to each other by a flow restriction;

[0032] The flow restriction is external or internal to the disengagement control element. pledge;

[0033] The pump is connected to the disengagement control device and to the distributors. by a parallel connection; and

[0034] . it includes a thermal or electric motor for driving the pump;

[0035] The invention also provides for a vehicle or machine comprising a circuit according to the invention for assisting the movement of the vehicle or machine.

[0036] It can be foreseen that the vehicle or machine comprises:

[0037] - at least one hydraulically operated accessory providing an unrelated function to the movement of the vehicle or machine and

[0038] - a main hydraulic circuit capable of actuating the accessory,

[0039] the hydraulic assistance circuit forming a branch of the main circuit, the pump being part of the main circuit.

[0040] The invention also provides a method for assisting the movement of a vehicle or machine, a method in which, in an open-loop hydraulic circuit of the vehicle or machine:

[0041] - a pump supplies fluid to at least one proportional distributor comprising a drawer, and

[0042] - the distributor supplies a fluid flow to at least one assist motor placement of the vehicle or machine and varies the flow rate between non-zero values ​​proportional to a movement of the drawer.

[0043] The proportional distributor may be pressure balanced but this is not mandatory, in particular if the travel assistance is not used at the same time as the accessory.

[0044] The process may also have one or more of the following characteristics:

[0045] The process comprises the following steps:

[0046] - a target displacement magnitude is obtained;

[0047] - a calculator determines a flow rate value aimed at obtaining the target quantity; and

[0048] - the distributor supplies the flow to the motor so that the flow corresponds to the value ;

[0049] The process is such that:

[0050] - the target quantity is a speed of the vehicle or machine at the time of acquisition and forms a first quantity, then

[0051] - a second quantity greater than the first quantity is obtained, and

[0052] - the flow being a first flow, the distributor supplies the motor with a second flow greater than the first flow rate or we increase the pressure of the fluid supplied to the engine;

[0053] The process is such that:

[0054] - the step of supplying the fluid flow to the engine by the distributor is terminated;

[0055] - fluid pressure is then applied in an engine casing so as to retract the engine pistons and drain fluid from the piston housings to a reservoir; and

[0056] - once the pistons are retracted, the application of fluid pressure is interrupted in the crankcase.

[0057] and

[0058] A second distributor supplying fluid flow to a second motor assistance with moving the vehicle or machine:

[0059] - a value for the angle of rotation of the vehicle or machine is determined, and

[0060] - using the value, a computer controls the distributors independently one of the other in order to perform an anti-slip function of the vehicle or machine.

[0061] The invention also provides a method for modifying a vehicle or machine, in which, given a vehicle or machine comprising a main open-loop hydraulic circuit including a pump and at least one hydraulically actuated accessory performing a function unrelated to the movement of the vehicle or machine, a secondary hydraulic circuit is added to the vehicle or machine comprising:

[0062] - at least one hydraulic motor for assisting vehicle movement or the machine, and

[0063] - at least one proportional distributor comprising a movable drawer, the distributor being configured to vary the flow rate of fluid supplied by the pump between non-zero values ​​proportional to a displacement of the spool,

[0064] The circuit is configured so that the pump supplies the distributor with fluid and the distributor controls motor movement by means of the fluid flow. DESCRIPTION OF FIGURES

[0065] We will now present several embodiments of the invention and variants by way of non-limiting examples with reference to the figures in which:

[0066] The [Fig. 1] is a diagram of a circuit according to a first embodiment of the invention;

[0067] The [Fig.2] is a detailed diagram of the distributor of the circuit of the [Fig.1];

[0068] The [Fig.3] is a cross-section of the engine of the [Fig.1];

[0069] [Fig.4]

[0070] [Fig.5]

[0071] [Fig.6]

[0072] [Fig.7]

[0073] [Fig.8]

[0074] [Fig.9]

[0075] Figures 4 to 9 illustrate other respective embodiments of the circuit according to the invention;

[0076] Fig. 10 is a diagram of one of the distributors of the embodiment of Fig. 8

[0077] Figure 11 illustrates variants of the circuit of the invention; and

[0078] Figure 12 illustrates an example of a vehicle according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0079] We will present several embodiments of the invention and variants. These embodiments and variants can be combined with each other so that the characteristics of one are applied to the other. Method of implementation of figure 1

[0080] We describe this mode with reference to Figures 1 to 3.

[0081] Figure 1 is a diagram of an open-loop hydraulic circuit 100 for assisting the movement of a vehicle 1 or a machine according to a first embodiment. The characteristics of such a circuit, other than those presented below, are known in themselves, for example from the aforementioned document FR-3 035 829. In the following, we will consider the case of driving a vehicle 1, it being understood that the same principles apply to a machine. The vehicle is, for example, the crane truck illustrated in Figure 12.

[0082] Circuit 100 comprises:

[0083] - an oil reservoir 2;

[0084] - a hydraulic pump 4, and

[0085] - a hydraulic motor 6.

[0086] As will be seen, several representations of a tank are found in [Fig. 1]. But in fact, all the tanks represented are a single tank. This is a standard for simplifying the drawings.

[0087] In this embodiment, the pump 4 has a fixed displacement and a fixed flow rate. It is driven by an electric or thermal motor 7.

[0088] The hydraulic motor 6 is mounted on a wheel or axle of the vehicle. It is in particular, a motor forming a rotating hydraulic machine such as that shown in cross-section in [Fig. 3] and comprising pistons 8, each having a radial orientation about a central axis XX of rotation of the machine. The pistons 8 are mounted to slide radially in respective housings 10 of a cylinder block 12 and each supported by means of a roller 14 against an inner face of a multilobed cam 16. The cam is rotationally fixed to a housing of the motor 6, and the cylinder block 12 is rotationally fixed to a shaft of the motor. The motor 6 includes an internal distribution system or distributor (not shown) which supplies each housing 10 with fluid and discharges it from the housing through respective conduits.

[0089] Supplying some of the housings 10 with pressurized fluid causes the corresponding roller 14 to roll on the cam 16 in each housing and, given its multilobed shape, causes the corresponding piston 8 to move within the housing, resulting in the rotation of the shaft relative to the casing 17, for operation in motor mode. Conversely, when a driving force causes the shaft to rotate relative to the casing, it causes the pressurized fluid to be discharged from some of the housings 10, the machine thus operating as a pump. Such a machine 6, which can operate as a motor or a pump, is known in itself and will not be described in further detail.

[0090] The circuit 100 of [Fig.1] includes a supply line 15 from the motor 6 from the pump 4 and a discharge line 19 from the motor 6 to the reservoir 2.

[0091] The circuit 100 includes a proportional distributor 20, in this case electrically or electro-proportional. The electrical control is referenced as 21 in [Fig. 2]. The control could, however, be hydraulic or otherwise.

[0092] The distributor 20 is a pressure-balanced valve 23 and includes a movable spool 22. In this case, it is a 5-way, 3-position, reversing spool, so that it controls the forward and reverse movement of the vehicle (i.e., the two directions of rotation of the engine 6) from the flow source. The two ports connected to the application supplied by the spool are labeled A and B. The spool is of the closed-center neutral type, and "applications A and B to T," T designating the unpressurized reservoir 2. The spool 22 connects the engine 6 lines to the reservoir 2 in the central position. The distributor 20 includes springs 25 for returning the spool 22 to the neutral center position when no control signal is present. In the middle or neutral position 34 of the spool 22, the distributor 20 ensures a vacuum of the operating lines A and B so that the pressures respectively supplied to the motor 6 and received from it are zero.The two other positions correspond respectively to forward and reverse. Each includes a pressure drop in the spool necessary for the operation of the pressure balance.

[0093] As illustrated in [Fig. 2], the circuit 100 is configured so that the pump 4 supplies the distributor 20 with fluid through a supply port 24 of the distributor on the pump or upstream side, and that the distributor controls the movement of the motor 6 by means of the fluid flow through a discharge port 26 of the distributor on the motor or downstream side. These two ports are on the supply line 15. The fluid discharged from the motor 6 enters the distributor through an upstream port 28 and is discharged through a port 30, for example, towards the reservoir 2. These two ports are on the discharge line 19.

[0094] The distributor 20 is configured to vary the flow rate of fluid supplied by the pump between non-zero values ​​proportional to a displacement of the spool 22. Such a distributor ensures control of the delivered flow rate that is independent of load variations experienced by the distributor. It therefore supplies the receiver formed by the motor 6 with a flow rate independent of the pressure returned by the latter. As the distributor 20 contains a pressure balance 23, it maintains a constant pressure drop or pressure difference across the distribution spool 22 regardless of the load variations experienced by the distributor. Indeed, such a distributor operates with a constant pressure difference. Consequently, each position of the spool 22 corresponds to a flow rate regardless of the load. The distributor 20 is therefore characterized by a flow rate / spool position relationship.It operates with a position control system for the spool 22 using a closed-loop spool position control system that provides position feedback. This allows for flow control of the motor 6 and thus speed control. In another embodiment, this also enables the implementation of an anti-slip function. The pressure difference is set by adjusting a spring in the balance 23 and is, for example, 3 bar. Figure 2 illustrates the pressure feedback line 31 from the receiver to the pressure balance 23.

[0095] In the present example, the distributor 20 is of the load sensing type (or load sensing in English, abbreviated as "LS") but this function is not used in this mode, the corresponding port 36 of the distributor 20 being closed for example by a plug.

[0096] The circuit in [Fig. 1] represents the simplest circuit where the pump has a fixed displacement and the excess flow in the supply line 15 is discharged by means of a valve 37 illustrated in [Fig. 1]. This valve discharges this flow from a branch on the line 15 located between the distributor 20 and the pump 4 to a pressureless reservoir. The valve 37 protects the pump 4 against overpressure if it has a fixed displacement. Alternatively, this valve can be calibrated with the LS signal as will be described later. This prevents the system from remaining at high pressure when it is not supplied.

[0097] It can be observed here in passing that, in the case where the pump is load-sensing, and if the spool 22 is unique, since the delta P (or difference of pressure) across the spool terminals, a pressure balance is not needed. A simple proportional spool without a pressure balance is sufficient.

[0098] The circuit 100 includes a control unit 40 capable of receiving a command from the vehicle driver 42. This command may be a request to activate the assistance system with a speed that can vary between different non-zero values. The control unit actuates the distributor 20 according to the command received.

[0099] This assistance circuit is part of the vehicle 1 and serves to assist its movement. The vehicle may be provided with at least one hydraulically operated accessory 44 performing a function unrelated to the vehicle's movement. This accessory is, for example, a jack stand, a hydraulic crane 44, or a tipper lifting device. Referring to [Fig. 12], the vehicle also includes a main hydraulic circuit 50 capable of actuating the accessory 44 shown in Figures 8 and 12. The hydraulic assistance circuit 100 forms, in this case, a branch of the main circuit 50, the pump 4 being part of the main circuit. The invention thus makes it possible, where appropriate, to use an open-loop circuit not initially intended for movement assistance to provide this assistance.An existing vehicle with an open-loop 50 circuit not used for assistance can therefore be easily adapted to also serve this purpose.

[0100] The circuit 100 enables the implementation of a vehicle movement assistance method, in which the pump 4 supplies fluid to the distributor 20, and the latter provides a flow of fluid to the motor 6 and varies the flow between non-zero values ​​proportional to the movement of the spool 22.

[0101] The following engagement sequence can be foreseen:

[0102] - the driver 42 determines a target displacement quantity such as a speed of the vehicle on the ground;

[0103] - the calculator 40 determines a flow rate value aimed at obtaining the target quantity; and

[0104] - the distributor 20 supplies the flow to the motor 6 so that the flow corresponds to the value.

[0105] The following sequence can also be predicted:

[0106] - the target quantity is a speed of vehicle 1 at the time of acquisition and forms a first magnitude, then

[0107] - a second quantity greater than the first is obtained, and

[0108] - the flow being a first flow, the distributor 20 supplies the motor 6 with a second flow rate greater than the first or we increase the pressure of the fluid supplied to the engine 6.

[0109] This is a hydraulic freewheeling mode followed by an active traction mode. Indeed, since the first quantity in this case is the current speed of the vehicle, which can be zero, the flow rate obtained provides no assistance to movement. The The system is then in a hydraulic freewheeling or speed-replication mode, and traction only occurs if the mechanical wheels are already slipping. This state also synchronizes the hydraulic motors for smooth engagement of the wheels. It is the second flow rate that begins to provide this assistance, creating traction in all driving conditions. Variant 1

[0110] A variant of this embodiment is illustrated in [Fig. 1].

[0111] This time, the motor 6 can be disengaged or unhooked under the effect of fluid pressure in its casing 17.

[0112] For this purpose, the engine preferably has retractable pistons. The structure of such engines is well known to those skilled in the art and will therefore not be described in detail hereafter. Such an engine is described, for example, in document WO 2018 / 077829, which is incorporated herein by reference.

[0113] As indicated above and with reference to [Fig.3], the pistons 8 are guided by radial sliding in the respective housings or cylinders 10 of the cylinder block 12 and bear against the lobes of the cam 16, preferably by means of rollers 14.

[0114] The internal distribution system of the engine is adapted to successively apply in a controlled manner a pressurized fluid into the housings 10 and consequently onto the pistons 8, so that the successive support of the pistons by means of the rollers on the lobes of the cam 16 causes the relative rotation of the cylinder block 12 and the elements which are connected to it with respect to the crankcase 17.

[0115] To be disengageable, the pistons 8 and the associated rollers 14 must be retracted into the housings 10 so that the rollers escape the cam 16. This retraction, to obtain the disengagement of the engine, is carried out by the application of an adequate pressure in its crankcase, i.e. in the chamber between the multi-lobe cam 16 and the external space of the cylinder block 12. The pressure thus exerted by the fluid is applied to the pistons and retracts them into the cylinders 10.

[0116] This retraction, which corresponds to a disengagement operation, can also be assisted by springs 39 illustrated in [Fig. 3]. These are generally placed on the side of the pistons to pull them towards the center of the cylinder block. The structure, position, and operation of such springs 39, which exert force on the retracted position of the pistons, are known to those skilled in the art and will therefore not be described in further detail. For guidance and not limitation, information can be found in documents FR 2 426 812, FR 2 651 836, and FR 2 504 987. [Fig. 3] illustrates only one example of the general positioning of the springs 39, which are the same number as the pistons 8. Reference may be made to these latter documents for more details on their arrangement and assembly.

[0117] It can be foreseen that the retraction of the pistons 8 is done solely by a crankcase pressure, or jointly by a crankcase pressure and the activation of the springs 39, for example by applying a crankcase pressure at the time of the retraction of the pistons, while the springs 39 are then sufficient to keep the pistons retracted in a hydraulic shutdown situation of the circuit.

[0118] Disengagement occurs here by crankcase pressure. Disengagement corresponds to the disengagement of the pistons from the hydraulic motor cam, typically by retracting the pistons into the cylinder block, which has the effect of disengaging the motor from the wheels. As illustrated by the disengagement line 45 in dashed lines connecting the pump 4 to the motor housing, the circuit 100 controls the disengagement of the motor. It includes for this purpose a component 43 configured to control the disengagement by means of a fluid flow. The disengagement line 45 pressurizes the hydraulic machine housing, which, if the hydraulic supply pressure is zero, causes the pistons 8 to retract into the cylinder block, and thus disengage them from the cam. This disengagement line is separate from the supply line 15 and the discharge line 19.In this case, component 43 includes a disengagement control valve 48 for motor 6 located on line 45. Valve 48 is a 2-way, 2-position, electrically actuated directional control valve. Component 43 also includes a pressure reducing valve 49 interposed between pump 4 and valve 48, ensuring, for example, a pressure reduction over a range of 0.5 to 20 bar.

[0119] The engine 6 also includes a crankcase drain 54, equipped with a flow restriction 56. The latter can be a calibrated valve.

[0120] It is recalled that each engine 6 comprises two isolated but connected oil volumes:

[0121] - the internal volume of the crankcase, normally at drain pressure, or low pressure, for piston retraction; and

[0122] - the volume of the piston housings, at high working pressure, for example between 20 and 600 bar.

[0123] This variant allows for the implementation of a motor disengagement sequence as follows:

[0124] - by means of distributor 20, the flow rate is reduced in lines 26 and 28 coming from the line 15 and we place drawer 22 in the neutral position towards T,

[0125] - this position of the drawer then results in a decrease in pressure in the piston housings that are no longer supplied by the supply line 15. These housings are at zero supply pressure and are not closed,

[0126] - fluid pressure is then applied in the crankcase 17 of the engine by means of the disengagement line 45, which causes the pistons 8 to retract into their housings. During this retraction of the pistons into the cylinder block, a volume Oil is expelled through ports A and B of the engine, which remain connected to reservoir 2, while an equivalent volume of oil enters the crankcase, and

[0127] - once the pistons have retracted, the application of pressure is stopped fluid is drawn into the crankcase via line 45. The engine is then disengaged. Variant 2

[0128] Alternatively, instead of the engine disengagement capability of variant 1, a clutch assembly (not shown) can be positioned between the engine and the wheels. This eliminates the need to create crankcase pressure in the engine. A crankcase drain to the reservoir is sufficient.

[0129] The clutch can be hydraulically operated and controlled by the same means as those already described, but for example by reversing the control, i.e. by sending hydraulic pressure to engage the clutch. An electrically operated clutch can also be considered.

[0130] If a clutch is used, it is not necessary to retract the pistons. However, during clutch operation, synchronizing the flow is preferable to avoid jerking if the vehicle is in motion. Part of the control process may therefore include the following successive steps for producing the assistance:

[0131] 1. Start pump 4,

[0132] 2. Synchronize the pump flow rate so that the motor runs at the speed of current rotation of the wheels

[0133] 3. Engage, and

[0134] 4. Adjust the flow rate to achieve the desired thrust.

[0135] When disengaging the clutch, there is less resistance to opening the clutch, but it is still possible to eliminate the thrust and restore equal speeds to avoid wearing the clutch. Simply reverse the procedure until the pump stops, if necessary.

[0136] In all cases, the motors can be supplied with the proportional drawers.

[0137] Method of implementation of figure 4

[0138] This embodiment differs from that of [Fig. 1] only in the following characteristics, the common characteristics not being described again.

[0139] In this circuit 400, the pump 4 has a variable displacement controlled by the load, which can, for example, present a pressure of 20 to 220 bar or more. It has a pump standby pressure "LS", here of 20 bar, in the absence of a load. It It provides a higher pressure if it receives a load signal LS from a load. The load signal is typically the pressure present in the load. Here, a load control line 60, shown as a dashed line, connects the LS port 36 of the valve 20 to the pump 4 for this control. The valve 20 is therefore capable of supplying a fluid pressure value to the pump. This supply occurs, in particular, by means of a shuttle valve 61 of the valve. The pump thus receives the load signal from the valve 20. In turn, it modulates its displacement to reach the pressure it receives (corresponding to the load) plus a delta. It thus forms a follower pump.

[0140] If the disengagement line 45 conforming to the variant is present, it is not necessary to provide it with a return charge line LS to the pump 4 because, being set at a low pressure, in particular less than 20 bar and consuming little, it does not disturb the outlet pressure of the pump.

[0141] The restriction 56 formed by the nozzle or the calibrated valve is found on the drain 54. For example, the latter is calibrated at 1.5 bar while the pressure reducer 49 is calibrated at 1 bar. Method of implementation of figure 5

[0142] This embodiment differs from that of [Fig. 1] only in the following characteristics, the common characteristics not being described again.

[0143] In this circuit 500, the disengagement of the motor 6 is achieved by different means than in [Fig. 1]. The control valve 47 of the disengagement control line 45 is a 3-way, 2-position directional valve with electrical control. In the valve's rest position, as illustrated in the figure, the line 45 is isolated from the pump 4 and communicates with a reservoir 2 for draining the fluid from the line. This is the default position of the valve 47, under the effect of a return spring, in the absence of a control signal. The motor 6 is engaged. The valve therefore has one port for zero pressure.

[0144] When a disengagement command is present, the electrical control is activated and causes the valve 47 to move to the other position against the spring. The line 45 is then isolated from the reservoir 63 and communicates with the pump 4, via the pressure reducer 49, from which it receives the pressurized fluid. This causes the pistons 8 to retract into their housings 10. The motor 6 is disengaged.

[0145] As illustrated in [Fig. 5], on the right, the circuit can be provided to include the drain line 54 with its restriction 56. Alternatively, the circuit can be provided to not include an engine crankcase drain line 6 and that the pressure reducer 49 includes a third channel connected to the reservoir 2, as illustrated on the left. Both of these possibilities have been illustrated in [Fig. 5].

[0146] Valve 37 is also found connected to the supply line 15. Method of implementation of figure 6

[0147] This embodiment differs from that of [Fig. 1] only in the following characteristics, the common characteristics not being described again.

[0148] The circuit 600 includes a valve 65 forming a bridge between the supply line 15 upstream of the distributor 20 on the pump side and the discharge line 19 on the reservoir side 2. The valve 65 allows fluid communication only from the discharge line 19 to the supply line 15. It is a freewheel or overspeed valve, which opens only if the vehicle is going faster than the flow rate of the pump 4. This valve is therefore upstream of the spool 22.

[0149] In addition, the circuit 600 includes, on the discharge line 19 on the reservoir 2 side, a backpressure valve 66 allowing fluid communication only towards the reservoir 2, the valve 66 including a return spring. This is a low-pressure backpressure valve so that the motor 6 always has a minimum pressure on the discharge line 19. This prevents the pistons 8 from leaving the cam, which can generate noise and may damage or destroy the motor 6.

[0150] The valves 65 and 66 can be provided independently of each other. They can also be incorporated into one or the other of the components of the distributor 20 or of one of the distributors 20, or of the components forming the stack delimited by the connection block 78 and the terminal plate 80 by reference to the embodiments which will follow. Method of implementation of figure 7

[0151] This embodiment is compatible with each of the preceding ones and the representation has been deliberately simplified.

[0152] Here, the circuit 700 comprises at least two hydraulic assist motors 6 and a single valve 20 connected to the two motors 6 in parallel. It therefore controls both motors simultaneously and identically, although the flow rate may be distributed between the two motors in an unmeasured manner. This circuit has the advantage of being easy to control. For example, the motors are associated respectively with the left and right wheels of the same axle of the vehicle. It requires that the valve 20 be sized to supply both motors at the same time. Alternatively, at least two valves can be used in parallel to supply both motors. In this case, the two valves must be controlled identically.

[0153] This arrangement allows several motors 6 to be supplied with inexpensive, commercially available distributors if a single large distributor does not exist for this purpose. Furthermore, if a disengagement function (not shown) is provided, the control of the decoupling of the 6 motors by crankcase pressure can take place by a single component 43 because it consumes little flow.

[0154] The case where the motors are supplied in parallel by one or more distributors allows for a variation of speed between the right and left wheels without differentiated control of the distributors, which allows for turning if the motors are on the same axle, or a variation of speed between axles if the motors are on different axles. This arrangement is inexpensive for enabling turning. The control is simplified in that it is not necessary to determine a flow law during turning for each motor. It is sufficient to specify the flow rate required for the average speed of the wheels considered. Indeed, by being connected in parallel, the motors distribute the flow rate according to their speed and their adhesion. A difference in speed between the motors can thus occur. The arrangement of [Fig.[7] This allows, without any special control, for different speeds to be obtained on the two motors 6, because they are connected in parallel and, in a way, draw what they need. The resulting assistance is supplied with the flow rate corresponding to the average speed of the vehicle's wheels, and this flow rate is freely distributed between the wheels. There is no need to calculate the flow rate for each wheel. This arrangement is simple and performs the turn on its own. However, if one wheel slips, it can consume most of the flow rate, leading to a loss of traction, because the other wheels no longer deliver torque.

[0155] Two or more axles can also be powered in this way. For example, if there are two axles, each equipped with its own motor, the two axles are powered in parallel. Alternatively, two axles can have a total of four motors, all connected in parallel. Method of implementation of figure 8

[0156] This embodiment is compatible with each of the preceding ones and the representation has been deliberately simplified.

[0157] The circuit 800 comprises two hydraulic assist motors 6, as in the previous embodiment. It includes several proportional valves 20. The first is connected to the first motor 6 but not to the second motor 6, and the second is connected to the second motor but not to the first motor. The valves 20 are thus associated with the motors 6 in a bijective manner. Each valve 20 controls the movement of its associated motor by means of a fluid flow. The valves are stacked and form layers arranged against each other. This configuration can be reproduced with a larger number of valves and motors. In this circuit, one motor can also be replaced by a group of motors so that one valve supplies a group of motors.

[0158] The circuit 800 may further include one or more hydraulic accessories 44, here two in number, not performing a function related to the movement of the vehicle. It also includes control devices 68 for these accessories, such as proportional distributors, including electro-proportional ones, which are dedicated to these accessories. In this example, this brings the number of proportional distributors 20, 68 to four. The pump 4 is connected to all the distributors 20, 68 by a parallel connection.

[0159] It can therefore be seen that the power supply for the hydraulic motors 6 can be integrated with that of the other hydraulic consumers 44 in an open-loop system of a vehicle. However, in this case, if a freewheel valve 65 is to be provided as in the mode of [Fig. 6], it can be included on the side of each motor 6.

[0160] Unit 40 controls each distributor 20 independently of the others for individual flow control of each motor 6 (or group of motors). This arrangement makes it possible to control the speed of each motor (or group of motors) separately and, for example, to provide an anti-slip function between the left and right wheels 69 of the same axle by giving them different speeds when cornering (inside or outside the corner).

[0161] To this end, during a turn, unit 40 can implement the following steps:

[0162] - determine, by means of an angle sensor, a value of the angle of rotation of the vehicle 1, and

[0163] - using the value, control the distributors 20 associated with the 6 independent motors interlocking to achieve a traction control function for vehicle 1 by delivering different flow rates to the two motors 6 to obtain different wheel rotation speeds. This therefore provides a traction control function between the motors 6 during cornering. Method of implementation of figure 9

[0164] The embodiment illustrated in Figures 9 and 10 is compatible with each of the preceding ones. It is similar to that of [Fig. 8] because it includes the two proportional distributors 20 controlling the two respective motors 6. This type of distributor, as before, includes a movable spool 22B with a neutral position of the closed center type and uses A and B to T, as illustrated in the upper left part of [Fig. 9]. The pressure balance 23 is also included.

[0165] The circuit 900 further includes two other proportional distributors 46, which may be identical to the previous two and serve to control the engagement and disengagement of the respective motors 6. In each of these two distributors 46, the motor-side supply port 26 is connected to the motor housing 17, the latter being equipped with a drain 54 with a nozzle 56 (illustrated only on the left-hand motor) as in the previous configurations. Alternatively, since the flow rates are minimal, a single distributor 46 is sufficient to perform this function for several motors 6. These engagement distributors 46 here include a 5-way movable spool 22A and 3 positions with neutral position at closed center and uses A and B closed, for pressure control in the crankcase, as illustrated in the upper right of [Fig.9]. The outlets B are closed, for example by a plug as shown on the left-hand spool 46.

[0166] When the distributor 46 is energized, a flow is established towards the crankcase via line A, while the fluid outlet returning to the reservoir via drain 54 establishes pressure equilibrium in the crankcase. In this way, by adjusting the flow rate of the distributor 46, the crankcase pressure can be adjusted. For this purpose, the drain line 54 is designed to provide a certain pressure drop. It may incorporate a means for increasing the pressure, for example, a restriction or a calibrated valve 56 as shown in the left-hand motor diagram.

[0167] Alternatively, line B has no plug and is connected to the crankcase 17 as shown on the right-hand engine. The drain line 54 is then calibrated to evacuate the leakage flow from the running engines, while the distributor 46 has an additional fluid outlet via line B, only when the distributor 46 is actuated. In this case, the restriction 56 is located on line B.

[0168] As a replacement for the aforementioned drawer 22, it is possible to use in the distributors 46 a drawer 22B with neutral position at closed center and uses A and B connected to the reservoir as illustrated in the upper left part of [Fig.9].

[0169] The circuit 900 may also include a backpressure device 71, such as a nozzle, on the discharge line 19, connected to the central position of the spool via this flow restriction 71. The flow restriction 71 has a similar effect to the restriction 56 of the previous modes and can replace it. Flow / pressure equilibrium is then achieved in the crankcase through the pressure drop 71 if the spool delivers a flow. In this way, the desired crankcase pressure is determined.

[0170] In this example, in order to be stackable with identical dispensers, each dispenser 20, 46 is traversed by:

[0171] - the power supply line 15 having two openings 72 (one forming the port 24) leading to opposing main faces 73 of the distributor,

[0172] - the discharge line 19 having two other openings 74 (one forming the port 30) on faces 73, and

[0173] - a pressure tracking line 60 having two further openings 76 (one forming port 36) on faces 73.

[0174] The distributors 20, 46 are connected to each of these lines by parallel connections.

[0175] When the distributors 20, 46 are stacked, for example by placing them side by side as in [Fig. 9], the openings of the supply line 15 coincide in order to constitute the supply line passing through the stack from side to side In part, the same applies to the discharge lines 19 and pressure monitoring lines 60. At one end of the stack, on the left in the figure, the circuit 900 includes a connecting block 78 placed against the face 73 of the first distributor in the stack and ensuring the connection of these three lines to the pump 4, which here has a variable displacement. At the other end of the stack, on the right in [Fig. 9], the circuit includes a terminal plate 80 placed against the face 73 of the last distributor and which closes the openings on this face.

[0176] As illustrated in [Fig. 10], each distributor 20, 46 includes a shuttle valve 61 (see mode 1) communicating with:

[0177] - the pressure balance 23,

[0178] - the pressure detection line 60 for the section of this line going towards the dis contiguous downstream tributary (if it exists), to the right on the [Fig. 10] and

[0179] - with the pressure detection line 60 for the section of this line going towards the upstream contiguous distributor (if it exists), on the left in the figure.

[0180] The valve 61 therefore receives the pressure from the pressure balance of its own distributor and that from the downstream section, i.e. from the distributor(s) 20 located on the right, if there are any. It communicates the higher of these pressures upstream.

[0181] Each shuttle valve 61 sends the pressure at its highest terminals to the next valve. In this way, the circuit 900 transmits to the pump 4 the highest pressure among those appearing in the distributors 20, 46 on the line 60. This creates a high-pressure selector on this line. The pump therefore receives the load signal from the distributor 20 with the highest load. This valve is also visible in Figures 4 and 5. Variants of Figure 11

[0182] Figure 11 illustrates variants of the embodiment of Figure 9 which differ from the latter by the following characteristics depending on the variants considered. Variant 1

[0183] In a first embodiment, shown on the left-hand motor, the disengagement control element includes a proportional distributor 46 such that the crankcase pressure for disengaging the motor 6 is controlled by this distributor. The motor(s) include two crankcase drains 54.

[0184] The distributor spool 46 is of type 22A with closed neutral center with evacuation of uses A and B to T. Variant 2

[0185] In a second variant also shown on the left-hand engine, again the disengagement control element comprises a distributor pro Portion 46. On this component, the motor supply port 26 and the motor discharge port 28 are connected to each other by a flow restrictor or nozzle 82, which can be external or internal to the distributor, both cases being illustrated in [Fig. 11]. The flow restrictor establishes a suitable flow rate so that the distributor can balance and regulate pressure when a crankcase pressure increase is requested, while the drain 54 only serves to evacuate motor leaks when no crankcase pressure increase is requested. In this case, the motor 6 can have a single crankcase drain 54 corresponding to port B of the spool; the drain 54 with its nozzle 56 connected to the reservoir is no longer necessary because, in continuous operation, they are replaced by port B, which is evacuated by the spool (neutral position with A and B towards T).

[0186] The distributor spool 46 is of type 22A with closed neutral center with evacuation of uses A and B to T. Variant 3

[0187] In a third variant, shown on the right-hand motor, the disengagement control member 46 does not include a proportional distributor. It comprises a 2-way, 2-position directional valve 84 for supplying the crankcase 17, connected to the supply line 15 with an interposed pressure reducer 49. The valve 84 and the pressure reducer 49 can be separate units. A typical drain conduit 53 for such a valve is shown in dashed lines in [Fig. 11] for the valve spools. It opens into the discharge line 19. It drains only the valve mechanism and is not connected to the ports. Each motor 6 is provided with a crankcase drain as in the configuration of [Fig. 4]. Alternatively, a three-way valve and a three-way pressure reducer are provided as in [Fig. 5].

[0188] This is the simplest and cheapest variant with regard to the cost of the crankcase pressure control. Variant 4

[0189] In a fourth variant, the valve 84 can be a three-way, two-position pressure reducing valve, identical to valves 47 and 49 in [Fig. 5], thus providing a reservoir supply of the drain via the discharge line 19. In this variant, the motor 6 can be without a crankcase drain, and the drain 54 located to the left of the motor can therefore be eliminated. The motor mounting is thus less bulky at the wheel. Example sequences

[0190] In each of the circuits of the invention allowing independent control of two motors 6, the following sequences can be provided. Indeed, the invention proposes improved control for engaging or disengaging the vehicle 1 drive.

[0191] It is assumed that the vehicle 1 comprises, for example, a main axle and a secondary load-bearing axle, on which a temporary assistance circuit such as one of those just described is installed. The circuit provides hydraulic assistance to the secondary axle as opposed to the primary axle driven by a primary motor of the vehicle. The circuit can be engaged continuously, intermittently, or under predetermined conditions, for example, when the vehicle speed is less than or equal to a predetermined speed. The operation described thereafter remains unchanged regardless of the application.

[0192] The hydraulic motors 6 are of the type that allow, on command, disengagement by retracting the pistons in the cylinder block; in other words, they are disengageable. For example, they are equipped with return elements such as springs, which tend to position the pistons 8 in their retracted configuration. Thus, in the absence of pressure applied to the inlet and outlet ports of the hydraulic motors that causes the pistons to extend from their housings 10, the pistons are retracted, and the hydraulic motors have zero displacement, while the wheels are disengaged from the motor torque. Engagement sequence

[0193] The instruction applied to the assistance circuit typically aims to synchronize the rotational speed of the secondary axle with that of the primary axle.

[0194] Consider an initial situation in which the entire power assistance circuit is at rest. The pump drive motor 4 is stopped, and the pressure in the circuit is zero. The motors 6 are disengaged from the wheels, particularly if they are disengagement motors by retracting the pistons 8. The pistons are advantageously held in the retracted position by springs. The wheels 69 are in a freewheeling state.

[0195] The hydraulic pump 4 is activated. This causes it to rotate. If it is a fixed-displacement pump, a pressure is established and a relief valve releases the excess pressure. The hydraulic circuit operates at the pressure of this valve. If the pump 4 is a pressure-sensing type, the pump displacement is established and guarantees a standby pressure, typically 20 bar.

[0196] A target displacement quantity is determined, for example, the speed of the main axle wheels, or the ground speed of the vehicle 1. The control unit 40 determines a target quantity for the secondary axle wheels, for example, the speed of the main wheels plus a speed delta, for example, 5%. The target quantity is equivalent to a hydraulic flow rate to be supplied to the secondary axle motors 6.

[0197] The proportional distributor(s) 20 are actuated to provide the target flow rate according to the position / flow law of the spool valve 22. The motors 6 are supplied by the pump 4, which starts them up and, if necessary, extends the pistons of motor 6 from their housings 10. The excess pressure in the motor housing is then purged. With the motors engaged and the flow rate supplied being substantially proportional to the speed of the vehicle or the wheels of the main axle if it slips, the hydraulic circuit delivers a traction force.

[0198] This control can be refined by adjusting the pressure sensor data. For example, during engagement, a flow rate can be requested that closely matches the wheel speed, resulting in zero or moderate traction, and a low pressure, for example 80 bar, which constitutes a standby situation. Then, when the assistance is called upon, a setpoint slightly higher than the vehicle's forward speed or a pressure control towards higher pressures provides a noticeable traction effort, thus putting the assistance into effective traction mode. The pressure can typically reach up to 400 bar. Depending on the need, the setpoint can be varied to adapt to the vehicle's movement, for example, increasing the speed delta to provide more traction, even when wheel slippage has not occurred.

[0199] We are therefore dealing with a flow control of the hydraulic motors 6, based on a target flow rate which corresponds to a speed to be reached on the wheels 69, and which can be modulated by a pressure measurement on the pressure line 15 which supplies the motors.

[0200] Alternatively, the aggressiveness of the assistance can be modulated by limiting the available pressure, either by derating the pressure limiting valve in the case of a fixed displacement pump 4, or by limiting the return pressure for a load-controlled variable displacement pump. Disengagement sequence

[0201] A sequence for disengaging the assistance system is now described.

[0202] An initial situation is considered in which the motors 6 are engaged, and the wheels are driven by the motors, it being understood that the speed may be zero.

[0203] Initially, as an option, the rotational speed of the motors 6 can be controlled to lower the pressure in the hydraulic circuit to a resting pressure. This is done, for example, by reducing the target speed and controlling the pressure, or by reducing the difference between the vehicle or vehicle wheel speed and the target speed. This resting or standby position corresponds to a driving mode where the hydraulic motors are engaged but do not provide any torque. The pressure in the circuit is very low, typically 80 bar.

[0204] Next, the crankcases 17 are pressurized using the unit Order 40. The target crankcase pressure is in the range of 10 to 20 bar.

[0205] Then the flow setpoint on the proportional motor supply valve(s) is reduced towards zero. Each valve 22 of the closed-center neutral position type, with uses A and B to T, is placed in the zero or mid-position to perform a vacuum. It should be noted that this valve is such that the supply and discharge lines of each motor are then connected to the reservoir. This causes a pressure drop in the circuit and retracts the pistons 8 into their housings. Indeed, after the shutdown, the motor is driven in rotation by the drive components, typically the wheels or axles, but is no longer supplied with pressure. This then causes a pressure increase at the discharge of the hydraulic motor. The fluid discharged by the rotating motor 6 is discharged through line 19 until all the pistons remain in the retracted position, and the motor is disengaged from the wheel.

[0206] Here, for example, a timer can be used to ensure the retraction of the pistons 8. Then, the pressurization of the crankcase can be stopped, the pistons being held in the retracted position by the return springs. The pump 4 can be kept in operation to maintain the system in standby mode. If there is no other use of the assistance or any other hydraulic use, for example on hydraulic accessories of the vehicle, the pump can be stopped. Other considerations

[0207] A disengagement control device can be provided for each motor housing or group of motor housings if it is desired to engage or disengage motors at different times. If the motors are to be engaged simultaneously, a single device is suitable for several housings. For example, several axles associated with their respective motors can be engaged or disengaged at different times.

[0208] Each of these embodiments can be achieved by assembling commercially available components. For distributor 20, for example, a proportional hydraulic distributor from Danfoss, reference PVG32 or PVG120, can be used. The operation of such a distributor is explained, for example, in the video available online at the following link: https: / / www.youtube.com / watch?v=GtvOOZoGfHY. Detailed documentation is available at the following link: https: / / assets.danfoss.com / documents / 187048 / BC152886483664fr-001401.pdf. This is the Hydrokit website: https: / / www.hydrokit.com / distribution / distribution-pvg-danfoss / pvg-32-xrpl0056.html

[0209] It can be seen that the invention allows control of the flow rate supplied to each motor 6 which is independent of load variations. The flow rate to each receiver is in- depending on the pressure of this one and the pressure of others, if applicable.

[0210] In the absence of implementation of the load detection and control function, a pressure limiter can be provided in the connection block to regulate the aggressiveness of the assistance. The pressure limiter can be placed on the LS pilot line of the pump to limit the load signal from the loads.

[0211] The invention makes it possible to implement assistance systems using open-loop circuits already installed on vehicles, such as trucks. The assistance can relate to the traction of a motor vehicle or a trailer.

[0212] In the entire demand, one bar is worth 105 Pa.

Claims

Demands

1. An open-loop hydraulic circuit for assisting the movement of a vehicle (1) or machine, the circuit comprising: - a pump (4); - a reservoir (2); - at least one hydraulic motor (6); and - at least one proportional distributor (20) comprising a movable spool (22), the distributor being configured to vary a flow rate of fluid supplied by the pump between non-zero values ​​proportional to a displacement of the spool, the circuit being configured so that the distributor controls a movement of the motor by means of the fluid flow, in which the distributor (20) comprises upstream of the spool a supply conduit on the pump side (24) and a discharge conduit on the reservoir side (30).

2. Circuit according to the preceding claim in which the distributor (20) is pressure balanced.

3. Circuit according to any one of the preceding claims wherein the tank-side discharge line (30) is connected to the pump-side supply line by a valve (65) permitting fluid communication only from the tank-side discharge line to the pump-side supply line.

4. Circuit according to any one of the preceding claims wherein the circuit comprises on the discharge conduit on the tank side a back pressure valve (66) permitting fluid communication only in the direction of the tank (2), the valve comprising a return spring.

5. Circuit according to any one of the preceding claims comprising at least two motors (6), the distributor or each distributor (20) being connected to the two motors by a parallel arrangement.

6. Circuit according to any one of the preceding claims comprising several distributors (20), the pump (4) being connected to the distributors by a parallel arrangement.

7. A circuit according to any one of the preceding claims, wherein, the distributor (20) being a first distributor and the motor (6) being a first motor, the circuit comprises at least a second motor (6) and a second distributor (20), the circuit being configured so that the second distributor controls a movement of the second motor by means of a fluid flow.

8. Circuit according to the preceding claim in which the first distributor (20) is connected to the first motor (6) without being connected to the second motor (6) and the second distributor (20) is connected to the second motor without being connected to the first motor.

9. Circuit according to any one of the preceding claims wherein the circuit comprises several stacked distributors (20, 68), and each distributor is traversed by a supply line (15) having two openings (72) opening onto opposite faces (73) of the distributor and by a discharge line (19) having two further openings (74) on the opposite faces.

10. Circuit according to any one of the preceding claims wherein the pump (4) has a fixed displacement.

11. Circuit according to any one of claims 1 to 9 in which the pump (4) has a flow-controlled displacement, and the distributor or each distributor (20) is capable of supplying a fluid pressure value to the pump, in particular by means of a shuttle valve (61) of the distributor.

12. Circuit according to the preceding claim, which includes at least two distributors (20), the circuit being configured so that the pump (4) receives a higher pressure among the pressures from the distributors.

13. Circuit according to any one of the preceding claims further comprising at least one hydraulic disengagement control element (46) configured to control disengagement of the or each motor (6).

14. Circuit according to the preceding claim in which the disengagement control member (46) comprises a directional valve (48) and a pressure reducer (49).

15. Circuit according to the preceding claim in which the motor or each motor (6) is devoid of a crankcase drain.

16. Circuit according to claim 13 in which the disengagement control member (46) comprises a proportional distributor having a spool (22) with neutral position of the closed centre type with vacuum.

17. Circuit according to the preceding claim in which the disengagement control member (46) comprises a motor supply port (6) and a motor discharge port (6) connected to each other by a flow restriction (82).

18. Circuit according to the preceding claim in which the flow restriction (82) is external or internal to the disengagement control member.

19. Vehicle (1) or machine comprising a circuit according to at least one of the preceding claims for assisting in the movement of the vehicle or machine.

20. Vehicle (1) or machine according to the preceding claim comprising: - at least one hydraulically operated accessory (44) performing a function not related to the movement of the vehicle or machine and - a main hydraulic circuit capable of operating the accessory (44), the hydraulic assistance circuit forming a branch of the main circuit, the pump (4) forming part of the main circuit.

21. A method for assisting the movement of a vehicle (1) or machine, a method in which, in an open-loop hydraulic circuit of the vehicle or machine: - a pump (4) supplies fluid to at least one proportional distributor (20) comprising a spool (22), and - the distributor provides a flow of fluid to at least one motor (6) assisting the movement of the vehicle or machine and varies the flow between non-zero values ​​proportional to a movement of the spool, and - the distributor (20) discharges fluid into a discharge conduit communicating with a reservoir (30).

22. A method according to the preceding claim wherein: - a target displacement quantity is obtained; - a computer (40) determines a flow value aimed at obtaining the target quantity; and - the distributor (20) supplies the flow to the motor (6) so that the flow corresponds to the value.

23. Method according to the preceding claim wherein: - the target quantity is a speed of the vehicle (1) or machine at the time of obtaining and forms a first quantity, then - a second quantity greater than the first quantity is obtained, and - the flow being a first flow, the distributor (20) supplies the motor (6) with a second flow greater than the first flow or a pressure of the fluid supplied to the motor (6) is increased.

24. A method according to any one of claims 21 to 23 wherein: - the step of supplying the fluid flow to the engine by the distributor is terminated; - then fluid pressure is applied in a crankcase (17) of the engine so as to retract pistons (8) of the engine and fluid is evacuated from the piston housings to a reservoir; and - once the pistons have retracted, the application of fluid pressure in the crankcase is stopped.

25. A method according to any one of claims 21 to 24 wherein a second distributor (20) supplying a fluid flow to a second motor (6) assisting the movement of the vehicle (1) or machine: - a value of the angle of rotation of the vehicle or machine is determined, and - by means of the value, a computer controls the distributors independently of each other in order to perform an anti-slip function of the vehicle or machine.

26. A method of modifying a vehicle (1) or machine, a method in which, in the presence of a vehicle or machine comprising a main open-loop hydraulic circuit including a pump (4) and at least one hydraulically actuated accessory (44) performing a function not related to the movement of the vehicle or machine, a secondary hydraulic circuit is added to the vehicle or machine comprising: - at least one hydraulic motor (6) for assisting the movement of the vehicle or machine and - at least one proportional distributor (20) including a movable spool (22), the distributor being configured to vary a flow rate of fluid supplied by the pump between non-zero values ​​proportional to a movement of the spool, the circuit being configured so that the pump supplies the distributor with fluid and the distributor controls a movement of the motor by means of the flow rate of fluid.

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