Control system for controlling a hydraulic actuator

Abstract

The invention relates to a control system which comprises a hydraulic valve and a hydraulic pump, wherein the hydraulic pump feeds the hydraulic valve via a first feed line, the hydraulic pump is driven by an internal combustion engine, the control system comprises a computing unit, the control system further comprises an intermediate feed line, and a load detection line bypassing the intermediate feed line; wherein the valve comprises an open position and a closed position; a pressure of the load detection line controls a resisting torque of the hydraulic pump; the computing unit detects a stalling risk of the engine as a function of an engine speed of the internal combustion engine, and in response, controls a movement of the hydraulic valve towards the closed position; the movement of the hydraulic valve towards the closed position causing a drop in the pressure of the load detection line.

Description

Control system for controlling a hydraulic actuator

[0001] The invention relates to the field of control systems for controlling a hydraulic actuator.

[0002] In particular, the invention relates to the field of control systems for controlling a hydraulic actuator comprising a hydraulic pump mechanically coupled to a thermal engine.

[0003] The invention finds particular application for handling machines comprising a main body mounted on wheels to move on the ground, a handling arm intended to receive a load to be moved, the handling arm being articulated around a horizontal axis relative to the main body, and an actuation device configured to execute a movement of the handling arm relative to the main body, the actuation device comprising a hydraulic lifting cylinder mounted between the handling arm and the main body to execute a movement of the handling arm around the horizontal axis.

[0004] Such a machine can notably be made in the form of a telescopic boom forklift, lifting crane, aerial work platform, bucket loader or other. Technological background

[0005] A control system for operating a hydraulic actuator includes a hydraulic pump suitable for powering the actuator. A power source is required to drive the hydraulic pump, for example, an internal combustion engine. A balance must be struck between the required load and the power capacity supplied by the power source.

[0006] When the power source is an internal combustion engine, it must provide a torque greater than the resisting torque of the hydraulic pump, otherwise the internal combustion engine will stall. This situation is called engine stalling.

[0007] It is desirable to avoid such a situation.

[0008] Indeed, if the internal combustion engine stalls, the hydraulic pump also stops, resulting in a loss of pressure and flow in the hydraulic system, which can compromise the operation of the hydraulic actuator.

[0009] Furthermore, a sudden stall can cause mechanical damage to the internal combustion engine, especially if excessive stress is exerted on the internal combustion engine components during the abrupt stop.

[0010] Engine stalling leads to instability in the control system. Variations in pressure and flow rate can affect actuation accuracy and cause oscillations or unpredictable behavior of the hydraulic actuator.

[0011] A stalled internal combustion engine can create dangerous situations. It is therefore vital to ensure that the engine operates reliably. Furthermore, an internal combustion engine that frequently stalls and restarts consumes more fuel and is less efficient. Preventing stalling thus optimizes the system's energy consumption.

[0012] Therefore, there is a need to prevent a combustion engine driving a hydraulic pump supplying a hydraulic actuator from stalling.

[0013] US6010309A discloses a hydraulic control system comprising a variable displacement pump driven by an internal combustion engine. This system features an anti-stall function, but its structure is complex.

[0014] One idea behind the invention is to reduce the resisting torque of the hydraulic pump in response to the detection of a risk of stalling.

[0015] According to a first aspect, the invention provides a control system for controlling a hydraulic actuator,

[0016] the control system comprising a hydraulic distributor and a hydraulic pump;

[0017] the hydraulic pump being arranged to supply the hydraulic distributor via a first supply line connecting an output of the hydraulic pump to an inlet of the hydraulic distributor, the hydraulic pump being driven by a thermal engine, the hydraulic pump being mechanically coupled to a shaft of the thermal engine;

[0018] the hydraulic distributor being arranged to supply fluid to the hydraulic actuator via a second supply line connecting an output of the hydraulic distributor to an input of the hydraulic actuator; the control system being adapted to command a movement of the hydraulic distributor according to a demand signal,

[0019] the hydraulic distributor comprising an intermediate supply line and being configured to have an open position in which the first supply line is connected to the intermediate supply line by the hydraulic distributor and the intermediate supply line is connected to the second supply line by the hydraulic distributor, and a closed position in which the first supply line is disconnected from the intermediate supply line by the hydraulic distributor and the intermediate supply line is disconnected from the second supply line by the hydraulic distributor;

[0020] the control system further comprising a load sensing line connected in parallel to the intermediate supply line and supplying a torque regulating element, the torque regulating element controlling a resisting torque of the hydraulic pump so that a drop in the pressure of the load sensing line leads to a drop in the resisting torque of the hydraulic pump;

[0021] the control system also includes a computer configured for:

[0022] detect a risk of the internal combustion engine stalling based on the engine speed of the internal combustion engine, and

[0023] in response to the risk of stalling of the internal combustion engine, command a movement of the hydraulic distributor towards or into the closed position;

[0024] the movement of the hydraulic distributor into the closed position resulting in a drop in pressure in the load sensing line.

[0025] Thanks to these features, the control system prevents the internal combustion engine from stalling while having a relatively simple structure, limited cost, and can easily be adapted to different types of pumps, including fixed or variable displacement pumps.

[0026] The control system allows for hydraulic regulation of the hydraulic pump's resistive torque by controlling the torque regulator via the load-sensing line. The intermediate supply line is isolated from the primary and secondary supply lines in the closed position. Therefore, moving the hydraulic distributor to the closed position reduces the fluid supply to the hydraulic actuator and the pressure in both the intermediate supply line and the load-sensing line, thus reducing the hydraulic pump's resistive torque. This prevents the internal combustion engine from stalling.

[0027] According to some embodiments, such a control system may include one or more of the following characteristics.

[0028] Hydraulic pumps can have various designs. In one embodiment, the hydraulic pump has a fixed displacement. With a fixed-displacement pump, it is not possible to reduce the pump's resistive torque by decreasing its displacement. The control system is specifically designed for this type of pump.

[0029] The computer is adapted to detect a risk of the internal combustion engine stalling, depending on the engine. This detection can be done in different ways.

[0030] According to one embodiment, detecting a risk of stalling of the internal combustion engine as a function of an engine speed of the internal combustion engine includes detecting that the engine speed is below a stalling risk value.

[0031] In one embodiment, the stall risk value is between 800 and 1000 rpm, for example, between 900 and 950 rpm. The stall risk value is configurable according to the machine type and is determined by testing. For example, the default stall risk value is 900 rpm.

[0032] When a risk of stalling is detected, the computer commands a movement of the hydraulic distributor towards or into the closed position.

[0033] For example, the stall risk value may correspond to a movement of the hydraulic distributor to the closed position. When the control unit detects that the engine speed is below the stall risk value, it commands the distributor to move to the closed position, regardless of its opening position, in order to cause a rapid drop in the load sensing line pressure and a cut-off of the fluid supply to the hydraulic actuator.

[0034] Hydraulic distributors can have different structures. In one embodiment, the hydraulic distributor is a proportional distributor. In other words, it can assume a multitude of open positions, the opening amplitude of which depends on the properties of a control signal, for example, the amplitude or pulse width of the control signal.

[0035] According to one embodiment, the hydraulic distributor is a closed-center distributor with electro-hydraulic control and spring return.

[0036] According to one embodiment, the control system further includes a safety valve positioned in bypass of the load sensing line, the safety valve including an open position in which the load sensing line is connected by the safety valve to a low-pressure tank, the safety valve including a closed position in which the load sensing line is disconnected by the safety valve from said low-pressure tank.

[0037] The torque control unit regulates the resisting torque of the hydraulic pump so that a drop in pressure in the load-sensing line results in a decrease in the resisting torque of the hydraulic pump. The torque control unit can have various designs.

[0038] In one embodiment, the torque control unit includes a pressure limiter. This pressure limiter can be positioned on different supply lines.

[0039] According to one embodiment, the torque control element includes a pressure limiter positioned in bypass of the first supply line, the pressure limiter having a pilot port connected to the load sensing line and configured to set an opening pressure of the pressure limiter as a function of the pressure of the load sensing line, such that a decrease in the pressure of the load sensing line results in a decrease in the opening pressure.

[0040] Positioning the pressure limiter in bypass of the first supply with a pilot port connected to the load sensing line allows the volume of the pressure limiter to be reduced.

[0041] According to one embodiment, a first pilot line connects the pilot port of the pressure limiter to the safety valve, such that the pilot port is connected to the low-pressure tank in the open position of the safety valve and disconnected from said low-pressure tank in the closed position of the safety valve.

[0042] According to one embodiment, a second pilot line connects the load sensing line to the first pilot line, the second pilot line comprising a flow reducer.

[0043] The pressure limiter is a pilot-operated pressure limiter.

[0044] According to one embodiment, the displacement of the hydraulic pump is variable and the torque control element includes a displacement control actuator configured to control the displacement of the hydraulic pump, the load sensing line controlling the displacement control actuator such that a decrease in the pressure of the load sensing line results in a decrease in the displacement of the hydraulic pump.

[0045] For example, a displacement of the displacement control actuator determines a change in the size of the hydraulic pump's pumping chamber. In this case, an increase in the load-sensing line pressure causes the displacement control actuator to move, increasing the size of the hydraulic pump's pumping chamber, and conversely, a decrease in the load-sensing line pressure causes the displacement control actuator to move, decreasing the size of the hydraulic pump's pumping chamber.

[0046] Thus, the torque control unit commands a resisting torque of the hydraulic pump so that a drop in the pressure of the load sensing line leads to a drop in the resisting torque of the hydraulic pump.

[0047] According to another aspect, the invention provides a handling machine comprising: - a main body mounted on wheels for moving on the ground; - a handling arm for receiving a load to be moved, the handling arm being articulated about a horizontal axis relative to the main body; - an actuation device configured to execute a movement of the handling arm relative to the main body, the actuation device comprising a hydraulic lifting cylinder mounted between the handling arm and the main body to execute a movement of the handling arm about the horizontal axis; - a demand element actuable by a user to produce at least one demand signal; - a thermal engine; - a control system according to one of the embodiments; the hydraulic actuator being the hydraulic lifting cylinder; the hydraulic pump being mechanically coupled to the shaft of the thermal engine.

[0048] According to one embodiment, the handling arm comprises at least two telescopic segments deployable by means of an extension cylinder arranged between the at least two segments.

[0049] According to one embodiment, the handling machine comprising is configured in the form of a telescopic arm forklift. Brief description of the figures

[0050] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent from the following description of several particular embodiments of the invention, given solely by way of illustration and not limitation, with reference to the accompanying drawings.

[0051] This is a schematic representation of a telescopic arm forklift in which embodiments of the invention can be implemented.

[0052] This is a schematic representation of a control system for controlling a hydraulic actuator according to a first embodiment.

[0053] This is a partial representation of a control circuit for a hydraulic lifting cylinder according to the first embodiment.

[0054] This is a view analogous to the one representing the control circuit during an inactive operating phase.

[0055] This is a view analogous to the one representing the control circuit during a lifting operation phase.

[0056] This is a view analogous to the one representing the control circuit during an anti-stall operating phase.

[0057] This is a schematic representation of a control system for controlling a hydraulic actuator according to a second embodiment.

[0058] We will describe below some ways of implementing a control system 1 to control a hydraulic actuator 2.

[0059] The control system 1 is, in particular, suitable for a handling machine in the form of a telescopic boom forklift carrying a handling arm projecting forward of the machine.

[0060] With reference to the, the telescopic arm forklift 1000 comprises a chassis 200 supported on the ground by means of a front axle carrying front wheels 30 and a rear axle carrying rear wheels 40. The handling machine 1 comprises a handling arm 60 of the telescopic type mounted on the chassis 2 by a first end and orientable around an axis of rotation 70 transverse to the chassis 2.

[0061] The handling arm 60 includes a load-carrying tool 140 articulated to a second end of the handling arm 60 by the linkage 150 and configured to carry a payload 90. In the example shown the load-carrying tool 140 is a fork but other tools can be used, for example a bucket.

[0062] The handling arm 60 is rotationally deflectable by a hydraulic lifting cylinder 80 connected to the frame 200 and the handling arm 60. The handling arm 60 comprises at least two telescopic segments that can be extended using an extension cylinder, not shown, arranged between the at least two segments. A slewing actuator, not shown, is arranged to change the orientation of the load-carrying tool 140 around a transverse axis of rotation relative to the frame 200. This slewing actuator may be a hydraulic actuator.

[0063] The 1000 telescopic arm forklift also includes a thermal engine 5 (not shown in the figure) adapted to drive a hydraulic pump 4 (not shown in the figure) of the control system 1. The thermal engine 5 is characterized by an engine speed Ω and a torque C. The instantaneous power of the thermal engine 5 is defined by the following relation: Power = C . Ω.

[0064] The telescopic boom forklift 1000 also includes a demand unit 120 configured to manually control the handling arm 60, the extension cylinder and / or the slewing actuator.

[0065] The demand element 120 allows in particular to raise and lower the handling arm 60, to deploy or retract the handling arm 60 and / or to change the orientation of the load-carrying tool 140 via the control system 1 which will be described below.

[0066] The demand element 120 can be a hydro-proportional manipulator block that delivers a hydraulic demand signal. This hydraulic signal can then be converted into an electrical signal that can be communicated to a computer 7. Alternatively, the demand element 120 can be an electro-proportional manipulator block that delivers an electrical demand signal that can be communicated to the computer 7. The demand element 120 could take other forms, for example, buttons, levers, a touchscreen, etc.

[0067] Lamontre the handling arm 60 carrying the payload 90 in a high and retracted position in continuous line and in several lower and more deployed positions in broken line.

[0068] With reference to figures 2 to 6, a first embodiment of the control system 1 will be described.

[0069] Lare represents schematically the control system 1 for controlling a hydraulic actuator 2 according to the first embodiment.

[0070] Hydraulic actuator 2 can be hydraulic lifting cylinder 80, extension cylinder or slewing actuator.

[0071] The control system 1 includes the hydraulic pump 4 and a hydraulic distributor 3. The hydraulic pump 4 ensures the supply of fluid to the hydraulic actuator 2 and a sufficient pressure rise in the control system 1.

[0072] The hydraulic pump 4 is mechanically coupled to a shaft 6 of the internal combustion engine 5. The hydraulic pump can be directly coupled to the shaft 6 of the internal combustion engine 5 or mechanically coupled to the shaft 6 via one or more gears. Thus, the internal combustion engine 5 drives the hydraulic pump 4.

[0073] Furthermore, with reference to the hydraulic pump 4, it is a fixed displacement pump. Therefore, the size of the pumping chamber of hydraulic pump 4 is fixed.

[0074] The fluid flow rate in the control system 1 depends on the rotational speed of the hydraulic pump 4 and the fixed displacement of the hydraulic pump 4. Since the displacement of the hydraulic pump 4 is fixed, an increase in the flow rate in the control system 1 is obtained by increasing the rotational speed of the hydraulic pump 4.

[0075] However, the hydraulic pump 4 is mechanically coupled to a shaft 6 of the internal combustion engine 5. Thus, the rotational speed of the hydraulic pump 4 is proportional or equal to the engine speed Ω of the internal combustion engine 5.

[0076] Thus, an increase in flow rate in control system 1 is obtained by an increase in engine speed Ω of the internal combustion engine 5.

[0077] The power required from the internal combustion engine 5 also depends on the pressure at the outlet of the hydraulic pump 4. The internal combustion engine 5 stalls when it is no longer able to supply the power required by the hydraulic pump 4.

[0078] Conversely, a drop in pressure at the outlet of the hydraulic pump 4 leads to a drop in the resisting torque of the hydraulic pump 4 and therefore a drop in the power required from the internal combustion engine 5, all other things being equal.

[0079] The hydraulic pump 4 is arranged to supply the hydraulic distributor 3 via a first supply line 11. The first supply line 11 extends from an outlet P of the hydraulic pump 4 to a first inlet A of the hydraulic distributor 3.

[0080] In addition, a pressure relief valve 9 is positioned in bypass of the first supply line 11. The pressure relief valve 9 limits the pressure of the first supply line 11 to an opening pressure P max which is variable depending on a control signal provided by a load sensing line LS.

[0081] As illustrated in Figures 3 to 6, the pressure relief valve 9 is a pilot-operated valve: the fluid in the first supply line 11 is applied to a section of a valve in the pressure relief valve 9. The force produced by the pressure of the fluid in the first supply line 11 opposes a closing force generated, on the one hand, by the spring rate of a spring 91 and, on the other hand, by a pressure force generated in a pilot port 92 by pressure in a pilot line 21. When the pressure at the inlet of the pressure relief valve 9 reaches the value of the generated closing force, the valve is pushed back and the fluid can be discharged to the reservoir T, which is at atmospheric pressure or at least at a low pressure. Thus, the opening pressure of the pressure relief valve 9 is P ouv is defined by the spring 91 and the pilot line 21.

[0082] As illustrated in Figure 1, the pilot line 21 is connected to the load-sensing line LS via a pilot line 22. The opening pressure P ouv is therefore fixed on the one hand by the spring setting and on the other hand by the pressure of the load detection line LS.

[0083] In addition, the pilot line 22 includes a flow reducer 23.

[0084] The spring setting defines the minimum value of the opening pressure P ouv For example, this minimum value is between 5 and 25 bars, for example 14 bar.

[0085] The hydraulic distributor 3 is arranged to supply the hydraulic actuator 2 via a second supply line 10. The second supply line 10 extends from a first output D of the hydraulic distributor 3 to an input B1 of the actuator 2.

[0086] The control system 1 also includes the load sensing line LS connected to an intermediate supply line 13 of the hydraulic distributor 3.

[0087] The intermediate supply line 13 extends between a second outlet F of the hydraulic distributor 3 and a second inlet C of the hydraulic distributor 3. The representation is functional but the intermediate supply line 13 is actually integrated into the structure of the hydraulic distributor 3.

[0088] The load detection line LS is positioned in bypass of the intermediate line 13. It extends from a bypass point G to the pressure limiter 9.

[0089] Hydraulic distributor 3 is a proportional distributor configured to assume a closed position and a multitude of open positions. Alternatively, it could be an on / off distributor.

[0090] In the closed position, the hydraulic distributor 3 disconnects the second output F from the first input A and the first output D from the second input C. Thus, in the closed position, the first supply line 11 is disconnected from the intermediate supply line 13 by the distributor 3 and the intermediate supply line 13 is disconnected from the second supply line by the distributor 3. In figures 3, 4 and 6, the hydraulic distributor 3 is in the closed position.

[0091] In each open position, the hydraulic distributor 3 connects the second output F with the first input A and the first output D with the second input C. Thus, in the open position, the first supply line 11 is connected to the intermediate supply line 13 via the hydraulic distributor 3, and the intermediate supply line 13 is connected to the second supply line 10 via the hydraulic distributor 3. At position A, the hydraulic distributor 3 is in an open position.

[0092] As illustrated in Figures 3 to 6, the hydraulic distributor 3 is a closed-center, electro-hydraulically controlled distributor. Solenoid valves E1 and E2 can control the movement of the hydraulic distributor 3 from the closed position to open positions in either the lifting or lowering direction. The transition from the open to the closed position is also ensured by a return spring 31.

[0093] Solenoid valves E1 and E2 are controlled by the computer 7 as indicated by the command line 71 on the.

[0094] As illustrated in Figures 3 to 6, the control system further includes a safety valve 14 positioned in bypass of the load sensing line LS. The safety valve 14 has an open position and a closed position.

[0095] The pilot line 21 connects the safety valve 14 and the pilot port 92. Thus, the safety valve 14 is positioned in bypass of the load sensing line LS via the pilot line 22.

[0096] The pilot port 92 is connected to the low-pressure tank in the open position of the safety valve 14 and disconnected from said low-pressure tank in the closed position of the safety valve 14.

[0097] Thus, in the open position, the load sensing line LS is connected via the safety valve 14 to a reservoir T. The relative pressure in the load sensing line LS is then zero or at least negligible compared to the pressures of the other supply lines of the control system. Generally, when the safety valve is in the open position, the absolute pressure in the load sensing line LS is equal to atmospheric pressure. The flow restrictor 23 smooths the fluid flow to the low-pressure reservoir when the safety valve 14 is opened.

[0098] In the closed position, the LS load sensing line is disconnected from the tank T by the safety valve 14.

[0099] As illustrated in figures 3 to 6, the control system further includes a safety pressure limiter 15 positioned in bypass of the load sensing line LS.

[0100] The safety pressure limiter 15 sets the maximum pressure of the load sensing line LS to prevent damage to the load sensing circuit and the hydraulic circuit in case of overpressure

[0101] The safety pressure relief valve 15 is a direct-acting pressure relief valve. The opening pressure of the safety pressure relief valve 15 is determined by the spring setting. For example, the opening pressure of the safety pressure relief valve 15 is between 200 and 250 bar. The spring setting can be either variable or fixed.

[0102] The control system 1 includes the calculator 7.

[0103] The control unit 7 is adapted to control the movement of the hydraulic distributor 3 from the open position to the closed position and from the closed position to the open position. The control unit 7 controls the movement of the hydraulic distributor 3 via the solenoid valves E1 and E2. For example, the control unit 7 can control the movement of the hydraulic distributor 3 based on a demand signal transmitted by the demand device 120, as indicated by the control line 72 on the diagram, in order to perform handling movements under the direction of an operator.

[0104] The control unit 7 is also adapted to receive or determine the engine speed Ω of the internal combustion engine 5 as indicated by the control line 73. The engine speed of the internal combustion engine 5 can be measured from the rotational speed of the shaft 6 of the internal combustion engine 5. In addition, the control unit 7 is adapted to detect a risk of stalling of the internal combustion engine 5 based on its engine speed. For example, the control unit 7 detects that the engine speed is below a stall risk value: there is then a risk that the internal combustion engine 5 will stall.

[0105] The calculator 7 is also adapted to control a movement of the safety distributor 14 from the open position to the closed position to avoid a risk of stalling, as will be described below.

[0106] We will now describe the operation of control system 1 to avoid a risk of stalling.

[0107] Laillustrates the state of the control system 1 when no demand signal has been transmitted by the demand unit 120 to the computer 7.

[0108] Since calculator 7 has not received any demand signal, the hydraulic distributor 3 is in its default position, i.e. the closed position.

[0109] Furthermore, the safety valve 14 is in its safe position, i.e., the open position. Therefore, the pressure in the load sensing line LS is zero.

[0110] Therefore, the opening pressure P ouv The pressure of the pressure limiter 9 is fixed by the setting of its spring. Thus, the pressure at the outlet of the hydraulic pump 4 and the pressure in the first supply line 11 is substantially equal to the pressure defined by the setting of the spring of the pressure limiter 9, as represented by the dashed lines on the.

[0111] Laillustrates the state of the control system 1 when a demand signal is transmitted by the demand device 120 to the computer 7.

[0112] The control unit 7 commands the hydraulic distributor 3 to move from the closed position to the open position in the direction requested by the operator, which in this case is the lifting direction to raise a load 90 onto the handling arm 60. The intermediate supply line 13 is connected to the first supply line 11 by the hydraulic distributor 3, and the second supply line 10 is connected to the intermediate supply line 13 by the hydraulic distributor 3. Thus, the first supply line 11, the intermediate supply line 13, and the second supply line are interconnected. The pressure in these lines rises to a high pressure, as shown in bold on the diagram. The value of the high pressure depends, of course, on the actual load on the lifting cylinder 80, for example, 100 to 200 bar.

[0113] Furthermore, the load sensing line LS is also connected to the first supply line 11, as shown by the dashed lines on the diagram. The opening pressure of the pressure relief valve 9 is therefore determined by the spring tension and the pressure of the load sensing line LS. This opening pressure is higher than the pressure of the load sensing line LS due to the spring force. Thus, the pressure relief valve 9 remains closed despite the high pressure in the first supply line 11.

[0114] Thus, a flow of fluid at high pressure is transmitted through the outlet of the hydraulic pump 4 to the hydraulic actuator 2. This results in a movement of the hydraulic actuator 2.

[0115] The movement of the hydraulic actuator continues as long as the internal combustion engine 5 is able to supply the resisting torque consumed by the hydraulic pump 4.

[0116] When the internal combustion engine 5 is no longer able to supply the resistive torque consumed by the hydraulic pump 4, the engine speed of the internal combustion engine 5 decreases. When the control unit 7 detects that the engine speed is below the stall risk threshold, the internal combustion engine 5 is likely to stall.

[0117] In this case, as illustrated in the figure, the calculator 7 commands a movement of the hydraulic distributor 3 into the closed position, which cuts off the lifting movement.

[0118] The intermediate supply line 13 is then disconnected from the first supply line 11 by the hydraulic distributor 3 and the second supply line 10 is disconnected from the intermediate supply line 13 by the hydraulic distributor 3.

[0119] The intermediate supply line 13 and the load sensing line LS are then disconnected from the input B1 of the hydraulic actuator 2. The pressure in the load sensing line LS therefore drops since the intermediate supply line 13 and the load sensing line LS are no longer subjected to the weight of the load 90 and are not completely sealed.

[0120] Consequently, the opening pressure of the pressure relief valve 9 drops as the pressure in the load sensing line LS decreases. The pressure at the outlet of the hydraulic pump 4 and the pressure in the first supply line 11 therefore become greater than the opening pressure of the pressure relief valve 9, and the valve of the pressure relief valve 9 opens. The pressure at the outlet of the hydraulic pump 4 and the pressure in the first supply line 11 then immediately drop to the target pressure of the pressure relief valve 9, as represented by the dashed lines on the diagram.

[0121] Thus, the resisting torque of the hydraulic pump 4 decreases, and therefore the power demanded from the internal combustion engine 5 also decreases. This prevents the internal combustion engine 5 from stalling.

[0122] In parallel, the second supply line 10 is isolated from the rest of the control system 1 by the hydraulic distributor 3. The pressure in the second supply line 10 is maintained, and the hydraulic actuator 2 is held in position, since stopping the lifting movement must not, of course, cause the handling arm to suddenly lower under its own weight. The pressure in the second supply line 10 can be maintained by check valves.

[0123] The movement of the hydraulic distributor 3 from the open position to the closed position therefore prevents the internal combustion engine 5 from stalling while maintaining the load 90 in position.

[0124] The first embodiment of control system 1 has just been described with a fixed-displacement hydraulic pump. However, the hydraulic pump can also be a variable-displacement pump.

[0125] In the case of a variable displacement pump, it is also possible to reduce the hydraulic pump's displacement to reduce the resisting torque of the hydraulic pump 4 and thus prevent the internal combustion engine 5 from stalling. A corresponding embodiment of the control system 1 will be described below.

[0126] The control system 100 according to the second embodiment differs from the control system 1 according to the first embodiment in that the hydraulic pump is a variable displacement hydraulic pump 104 and the load sensing line LS extends from the bypass point G to a displacement control actuator 12. Thus, the control system 100 according to the second embodiment does not necessarily include the pressure limiter 9.

[0127] The 104 hydraulic pump is a variable displacement hydraulic pump. Therefore, it is possible to change the amount of fluid pumped with each rotation of the 104 hydraulic pump.

[0128] The displacement adjustment actuator 12 is adapted to modify the size of a pumping chamber of the hydraulic pump 104. A position of the displacement adjustment actuator 12 determines a value for the size of the pumping chamber of the hydraulic pump 4. Similarly, a displacement of the displacement adjustment actuator 12 determines a change in the size of the pumping chamber of the hydraulic pump 104.

[0129] The pressure in the load sensing line LS controls the position of the displacement adjustment actuator 12 so that an increase in the pressure in the load sensing line LS results in an increase in the displacement of the hydraulic pump 104. Conversely, a decrease in the pressure in the load sensing line LS results in a decrease in the displacement of the hydraulic pump 104.

[0130] In particular, an increase in the pressure of the load sensing line LS causes a displacement of the displacement adjustment actuator 12 increasing the size of the pumping chamber of the hydraulic pump 104 and conversely, a decrease in the pressure of the load sensing line LS causes a displacement of the displacement adjustment actuator 12 decreasing the size of the pumping chamber of the hydraulic pump 104.

[0131] In a manner analogous to the operation of the control system 1 according to the first embodiment, when the computer 7 detects that the engine speed is below the stall risk value, it commands a movement of the hydraulic distributor 3 from the open position to the closed position.

[0132] The intermediate supply line 13 and the load sensing line LS are then disconnected from the input B1 of the hydraulic actuator 2. The pressure in the load sensing line LS therefore drops since the intermediate supply line 13 and the load sensing line LS are no longer subjected to the weight of the load 90 and are not completely sealed.

[0133] The drop in pressure in the load-sensing line LS causes a decrease in the displacement of the hydraulic pump 104. Consequently, the resistive torque of the hydraulic pump 104 decreases, and therefore the power demanded from the internal combustion engine 5 also decreases. This prevents the internal combustion engine 5 from stalling.

[0134] Similar to the control system 1 of the first embodiment, the second supply line 10 is isolated from the rest of the control system 100 by the hydraulic distributor 3. The pressure in the second supply line 10 is maintained and the hydraulic actuator 2 is held in position.

[0135] The movement of the hydraulic distributor 3 from the open position to the closed position therefore prevents the internal combustion engine 5 from stalling while maintaining the load 90 in position.

[0136] Furthermore, when the control system 1 includes a hydraulic pump 104 with variable displacement according to one of the two embodiments, the load sensing line LS also allows a load signal to be sent to the hydraulic pump 104 so that it maintains its displacement which will allow a constant pressure to be obtained.

[0137] The hydraulic pump 104 then automatically adjusts its pressure and flow rate in order to deliver a constant pressure maintained between the inlet of the hydraulic distributor 3 and the supply of the hydraulic actuator 2.

[0138] Finally, the hydraulic distributor 3 of the first and second embodiments is a proportional hydraulic distributor. However, the hydraulic distributor 3 can also be an on / off hydraulic distributor, i.e., comprising an open position in which the pressure at the outlet of the hydraulic pump 4 is transmitted to the hydraulic actuator 2 and a closed position in which the pressure demand is removed.

[0139] When the hydraulic distributor 3 is a proportional hydraulic distributor, the control unit 7 can command the hydraulic distributor 3 to move towards the closed position to prevent stalling, without necessarily reaching a fully closed position. In this case, the pressure in the load sensing line LS gradually decreases as the proportional hydraulic distributor closes.

[0140] Although the invention has been described in connection with several particular embodiments, it is clearly evident that it is by no means limited to them and that it includes all technical equivalents of the means described as well as their combinations if these fall within the scope of the invention.

[0141] The use of the verb "comporter", "comprendre" or "include" and its conjugated forms does not exclude the presence of other elements or steps than those stated in a claim.

[0142] In claims, any reference sign in parentheses shall not be interpreted as a limitation of the claim.

Claims

Control system (1; 100) for controlling a hydraulic actuator (2), the control system comprising a hydraulic distributor (3) and a hydraulic pump (4); the hydraulic pump (4) being arranged to supply the hydraulic distributor (3) via a first supply line (11) connecting an outlet of the hydraulic pump (4) to an inlet of the hydraulic distributor (3), the hydraulic pump being driven by a thermal engine (5), the hydraulic pump being mechanically coupled to a shaft (6) of the thermal engine; the hydraulic distributor (3) being arranged to supply fluid to the hydraulic actuator (2) via a second supply line (10) connecting an outlet of the hydraulic distributor (3) to an inlet of the hydraulic actuator (2);the control system being adapted to control a movement of the hydraulic distributor (3) according to a demand signal, the hydraulic distributor (3) comprising an intermediate supply line (13) and being configured to have an open position in which the first supply line (11) is connected to the intermediate supply line (13) by the hydraulic distributor (3) and the intermediate supply line (13) is connected to the second supply line (10) by the hydraulic distributor (3), and a closed position in which the first supply line (11) is disconnected from the intermediate supply line (13) by the hydraulic distributor (3) and the intermediate supply line (13) is disconnected from the second supply line by the hydraulic distributor (3);the control system (1) further comprising a load sensing line (LS) connected in parallel to the intermediate supply line (13) and supplying a torque regulating element (9, 12), the torque regulating element (9, 12) controlling a resisting torque of the hydraulic pump (4) such that a decrease in the pressure of the load sensing line (LS) results in a decrease in the resisting torque of the hydraulic pump; the control system (1) further comprising a computer (7) configured to: detect a risk of stalling of the internal combustion engine (5) as a function of an engine speed of the internal combustion engine, and in response to the risk of stalling of the internal combustion engine (5), command a movement of the hydraulic distributor (3) towards or into the closed position; the movement of the hydraulic distributor (3) towards or into the closed position resulting in a decrease in the pressure of the load sensing line. Control system (1) according to claim 1, wherein the torque regulating member includes a pressure limiter (9) positioned in bypass of the first supply line (11), the pressure limiter having a pilot port connected to the load sensing line (LS) and configured to set an opening pressure of the pressure limiter as a function of the pressure of the load sensing line, such that a decrease in the pressure of the load sensing line (LS) results in a decrease in the opening pressure. Control system (1) according to any one of claims 1 to 2, wherein the hydraulic pump (4) has a fixed displacement. Control system (100) according to claim 1, wherein a displacement of the hydraulic pump (4) is variable, wherein the torque regulating member includes a displacement adjusting actuator (12) configured to adjust the displacement of the hydraulic pump, the load sensing line controlling the displacement adjusting actuator such that a decrease in the pressure of the load sensing line results in a decrease in the displacement of the hydraulic pump. Control system (1) according to any one of claims 1 to 4, wherein detecting a risk of stalling of the internal combustion engine as a function of an engine speed of the internal combustion engine includes detecting that the engine speed is below a stalling risk value. Control system (100) according to claim 5, wherein the stall risk value is between 800 and 1000 rpm. Control system (1) according to any one of claims 1 to 6, wherein the hydraulic distributor (3) is a closed-center distributor with electro-hydraulic control and spring return. Control system (1) according to any one of claims 1 to 7, further comprising a safety valve (14) positioned in bypass of the load sensing line (LS), the safety valve (14) comprising an open position in which the load sensing line (LS) is connected by the safety valve to a low-pressure tank, the safety valve (14) comprising a closed position in which the load sensing line (LS) is disconnected by the safety valve from said low-pressure tank. Control system (100) according to claim 8 taken in combination with claim 2, wherein a first pilot line (21) connects the pilot port of the pressure limiter to the safety valve, such that the pilot port is connected to the low-pressure tank in the open position of the safety valve (14) and disconnected from said low-pressure tank in the closed position of the safety valve (14). Control system (100) according to claim 9, wherein a second pilot line 22) connects the load sensing line (LS) to the first pilot line (21), the second pilot line (22) comprising a flow reducer. Handling machine (1000) comprising: - a main body (200) mounted on wheels (30, 40) for moving on the ground; - a handling arm (60) for receiving a load (90) to be moved, the handling arm being articulated about a horizontal axis (70) relative to the main body; - an actuating device configured to perform a movement of the handling arm relative to the main body, the actuating device comprising a hydraulic lifting cylinder (80) mounted between the handling arm (60) and the main body (200) for performing a movement of the handling arm about the horizontal axis; - a request element (120) actuable by a user to produce at least one request signal; - a thermal engine (5); - a control system (1) according to any one of claims 1 to 10; the hydraulic actuator (2) being the hydraulic lifting cylinder (80);the hydraulic pump (4) being mechanically coupled to the shaft of the internal combustion engine (5).; Handling machine (1000) according to claim 11, wherein the handling arm (60) comprises at least two telescopic segments deployable by means of an extension cylinder arranged between the at least two segments. Handling machine (1000) according to claim 12, configured in the form of a telescopic arm forklift.

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