Control of an electric motor and of a variable displacement hydraulic pump driven by the electric motor

Abstract

The invention relates to a method (100) for controlling a hydraulic system, which comprises: - controlling the electric motor (3) and the displacement variation actuator while complying with a control law; - measuring (104) a rotational speed (Ω) of the electric motor (3) and a temperature (T) of the electric motor (3); - detecting (105) that the temperature (T) is below a first temperature threshold (ST1), selecting a normal control law (R0), the normal control law (R0) defining a first maximum rotational speed and a first maximum displacement; and - in response to determining that the temperature (T) is greater than the first temperature threshold (ST1), selecting a first regulated control law (LC1) defining: - a second maximum rotational speed or a second maximum displacement.

Description

Control of an electric motor and a variable displacement hydraulic pump driven by the electric motor

[0001] The invention relates to the control of an electric motor and a variable displacement hydraulic pump driven by the electric motor. Technological background

[0002] Work machines comprising an electric motor and a variable displacement hydraulic pump are known, for example from document EP 2 141 361 A1. In such work machines, the flow rate at the outlet of the hydraulic pump can be changed by changing the displacement of the hydraulic pump and / or the rotational speed of the electric motor. Summary

[0003] One key idea of ​​the invention is to limit the power of the electric motor required to drive the variable displacement hydraulic pump, thereby reducing the size and / or cost of the electric motor. Another key idea of ​​the invention involves controlling the electric motor and the hydraulic pump to prevent the electric motor from stalling because it cannot provide sufficient torque to drive the pump. Yet another key idea of ​​the invention is to take the electric motor's temperature into account when controlling the electric motor and the hydraulic pump.

[0004] According to one embodiment, the invention provides a control method for controlling a hydraulic system comprising an electric motor, a variable displacement hydraulic pump driven by the electric motor, and a displacement variation actuator configured to modify the displacement of the variable displacement hydraulic pump according to a feedback signal dependent on the discharge pressure of the variable displacement hydraulic pump, the control method comprising:

[0005] - control the electric motor and the displacement variation actuator according to a request from an operator and respecting constraints defined by a control law, each control law linking a rotation speed of the electric motor to a request from the operator;

[0006] - measure operating parameters including at least the rotational speed of the electric motor and the temperature of the electric motor;

[0007] - in response to a detection that the temperature of the electric motor is below a first temperature threshold, select a normal control law as said control law,

[0008] the normal control law defining as constraints, a first maximum rotation speed of the electric motor and a first maximum displacement of the variable displacement hydraulic pump;

[0009] - in response to a determination that the electric motor temperature is above the first temperature threshold, select a first regulated control law as said control law,

[0010] the first regulated control law defining, as constraints:

[0011] - a second maximum rotation speed of the electric motor or a second maximum displacement, the second maximum rotation speed being smaller than the first maximum rotation speed, the second maximum displacement being smaller than the first maximum displacement.

[0012] The control of the electric motor and hydraulic pump is based on the observation that the electric motor heats up more as it is under load, and therefore, the higher the electric motor's temperature at any given moment, the less capacity it has to deliver additional torque at that moment. In other words, the control of the electric motor and hydraulic pump is based on the observation that the electric motor's temperature is an indicator of its capacity to deliver increased torque.

[0013] Setting the hydraulic pump displacement to a target value affects both the pump's output flow rate and the torque required from the electric motor. By selecting a characteristic curve based on the electric motor's temperature, such that the target displacement value decreases as the motor's temperature increases, the hydraulic pump's output flow rate decreases when the electric motor is hot, but conversely, less torque is required from the electric motor. This helps prevent situations where the electric motor stalls because it cannot provide sufficient torque to drive the hydraulic pump.

[0014] According to some embodiments, such a control method may include one or more of the following characteristics.

[0015] According to one embodiment, in which the first regulated control law defines the second maximum rotational speed of the electric motor, the second maximum rotational speed being lower than the first maximum rotational speed, the method further comprises the steps of:

[0016] - in response to a determination that the temperature of the electric motor is above a second temperature threshold; the second temperature threshold being above the first temperature threshold, select as said control law a second regulated control law,

[0017] the second regulated control law defining:

[0018] - a third maximum rotation speed of the electric motor, the third maximum rotation speed of the electric motor being less than or equal to the second maximum rotation speed of the electric motor; and

[0019] - the second maximum displacement, the second maximum displacement being smaller than the first maximum displacement.

[0020] According to one embodiment, the measured operating parameters include a hydraulic pump discharge pressure, and in which the normal control law defines the first maximum rotational speed as a function of the discharge pressure, the first maximum rotational speed being smaller when the discharge pressure is above a first pressure threshold than when the discharge pressure is below the first pressure threshold, and in which the first regulated control law defines the second maximum rotational speed as a function of the discharge pressure, the second maximum rotational speed being smaller when the discharge pressure is above a second pressure threshold than when the discharge pressure is below the second pressure threshold.

[0021] Thus, when the discharge pressure exceeds the pressure threshold, the maximum motor speed is reduced. This helps prevent situations where the electric motor stalls because it cannot provide sufficient torque to drive the hydraulic pump.

[0022] According to one embodiment, the second pressure threshold is smaller than the first pressure threshold.

[0023] According to one embodiment, the first pressure threshold and / or the second pressure threshold depends on the rotational speed, so that the first pressure threshold and / or the second pressure threshold decreases as the rotational speed increases.

[0024] This also tends to better avoid a situation in which the electric motor stalls because the electric motor cannot provide enough motor torque to drive the hydraulic pump.

[0025] According to one embodiment, the normal control law defines the first maximum displacement as a function of the discharge pressure, the first maximum displacement being variable as a function of the rotational speed when the discharge pressure is above the first pressure threshold, so that the first maximum displacement decreases as the rotational speed increases, and the first regulated control law defines the second maximum displacement as a function of the discharge pressure, the second maximum displacement being variable as a function of the rotational speed when the discharge pressure is above the second pressure threshold, so that the second maximum displacement decreases as the rotational speed increases.

[0026] This also tends to better avoid a situation in which the electric motor stalls because the electric motor cannot provide enough motor torque to drive the hydraulic pump.

[0027] According to one embodiment, the first maximum displacement is independent of the rotational speed when the discharge pressure is below the first pressure threshold, and / or the second maximum displacement is independent of the rotational speed when the discharge pressure is below the second pressure threshold.

[0028] Indeed, it is preferable to limit the maximum rotational speed of the motor first rather than the maximum displacement of the pump in order to benefit from a better efficiency of the hydraulic unit.

[0029] According to one embodiment, the first regulated control law defines the second maximum displacement as a function of the discharge pressure, the second maximum displacement being smaller when the discharge pressure is above the second pressure threshold than when the discharge pressure is below the second pressure threshold.

[0030] This also tends to better avoid a situation in which the electric motor stalls because the electric motor cannot provide enough motor torque to drive the hydraulic pump.

[0031] According to one embodiment, as long as a current demand of the operator is non-zero, the method includes a step of inhibiting the step of selecting a control law when the selected control law would have the effect of linking to the current demand of the operator a rotation speed of the electric motor higher than a current speed.

[0032] This prevents an increase in the speed of movement of a hydraulic actuator powered by the pump without a specific user request, i.e. solely related to a change in control law.

[0033] According to one embodiment, the temperature of the electric motor is an internal temperature of the electric motor.

[0034] According to another aspect, the invention provides a working machine comprising:

[0035] - an electric motor and a variable displacement hydraulic pump driven by the electric motor;

[0036] - sensors configured to measure operating parameters including electric motor rotation speed and electric motor temperature;

[0037] - a human-machine interface to receive a request from the operator, and

[0038] - a control unit connected to the sensors and the human-machine interface and configured to implement the control method according to the invention.

[0039] According to one embodiment, the sensors are configured to also measure a discharge pressure of the hydraulic pump.

[0040] According to one embodiment, the working machine includes a lifting mechanism and a hydraulic lifting circuit associated with the lifting mechanism, the hydraulic pump supplying the hydraulic lifting circuit with hydraulic fluid.

[0041] The control method described above is particularly applicable to such a work machine. Indeed, the control method ensures that the electric motor does not stall during a lifting operation; the lifting speed is only reduced due to a decrease in the hydraulic pump's displacement and / or the electric motor's rotational speed. Furthermore, the control method does not regulate the hydraulic pump's discharge pressure; only the hydraulic pump's displacement and / or the electric motor's rotational speed can be regulated. This allows the lifting capacity available to the machine operator to be maintained.

[0042] Finally, since the control process ensures that the electric motor does not stall, the power of the electric motor can be limited, which helps to limit the size and / or cost of the electric motor. Brief description of the figures

[0043] 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.

[0044] This is a functional block diagram of a hydraulic unit comprising a variable displacement hydraulic pump and an electric motor.

[0045] This is a diagram illustrating regulated control laws used by the control unit shown on the.

[0046] Laest is a graph including torque-speed curves, showing the motor torque supplied by the electric motor to the hydraulic pump, according to a regulated control law used by the control unit.

[0047] La is a graph analogous to the one, according to another regulated control law used by the control unit.

[0048] This is a block diagram illustrating a control method for controlling the hydraulic unit according to an embodiment

[0049] This is a block diagram illustrating a control method for controlling the hydraulic unit according to another embodiment.

[0050] The numbering adopted in the detailed description below (“first”, “second”, “third” etc.) is solely for the purpose of naming the control laws, maximum rotation speeds and maximum displacements planned and not for counting them.

[0051] The functional block diagram of the is a functional block diagram of a hydraulic unit 1. The hydraulic unit 1 includes a variable displacement hydraulic pump 2 (hereinafter "the pump 2") and an electric motor 3 (hereinafter "the motor 3").

[0052] Pump 2 is driven by motor 3. Reference numeral 4 designates a rotating shaft that drives pump 2 via motor 3. Shaft 4 can be an output shaft of motor 3 or a drive shaft driven by the output shaft of motor 3. Pump 2, shaft 4, and motor 3 can be arranged relative to each other in various ways. This is not a limiting case. Furthermore, a distributor (not shown) is positioned at the outlet of pump 2 and supplies one or more hydraulic actuators.

[0053] Pump 2 is a load-sensing pump whose displacement C is variable and depends on a feedback signal dependent on the discharge pressure of pump 2.

[0054] For example, the displacement C is modified by a displacement variation actuator 21 as a function of a pressure balance dependent on the discharge pressure of the pump 2.

[0055] The displacement C can be limited to a value Cmax. For example, the stroke of the displacement variation actuator 21 can be limited.

[0056] This type of pump is familiar to anyone in the trade.

[0057] The hydraulic unit 1 further includes sensors 12, 13, 14. Sensor 12 is a pressure sensor associated with the outlet of pump 2 and measures a discharge pressure P of pump 2. Sensor 13 is a temperature sensor and measures a temperature T of motor 3. Sensor 14 measures a rotational speed Ω of motor 3, in other words the motor speed of motor 3, for example by measuring the rotational speed of shaft 4.

[0058] As indicated by the dotted lines on the diagram, a control unit 10 is connected to sensors 12, 13, 14 in order to receive measurements from sensors 12, 13, 14, and the control unit 10 is associated with motor 3 and pump 2 in order to control the operation of motor 3 and pump 2.

[0059] Furthermore, the control unit 10 is configured to receive a flow rate request signal from the pump 2 outlet, transmitted by a human-machine interface device 20. The human-machine interface device 20 transmits the flow rate request signal from the pump 2 outlet in response to an actuation request received from a user. The human-machine interface device may include, for example, a joystick, a foot pedal, a touchscreen, etc.

[0060] The operation of motor 3 is characterized by the rotational speed Ω and a motor torque Γ at the output of motor 3. The control unit 10 controls the rotational speed Ω of motor 3 according to a control law linking a rotational speed Ω of the electric motor 3 to a flow demand signal at the output of pump 2. The flow demand signal at the output of pump 2 is determined according to a request from the operator transmitted by the human-machine interface device 20.

[0061] The operation of pump 2, driven by motor 3, is characterized by the rotational speed Ω, the discharge pressure P, the flow rate Q at the outlet of pump 2, and the displacement C of pump 2, where Q = Ω·C. The control unit 10 controls the maximum displacement C of pump 2 in a known manner. For example, the control unit 10 defines the maximum stroke of the displacement control actuator 21 and thus sets a maximum displacement value. The control unit 10 also controls the opening of the spools of the hydraulic distributor at the outlet of pump 2.

[0062] Thus, the control unit 10 controls the operation of the motor 3 and the pump 2 according to the actuation requests of a user interacting with the human-machine interface device 20.

[0063] Each of the control laws (normal or regulated) defines a maximum rotational speed, that is, a maximum value M axof the rotational speed Ω of the motor 3, and a maximum displacement, i.e. a maximum value C max of the displacement C of pump 2.

[0064] The control laws (normal or regulated) are stored in the control unit 10.

[0065] According to a first embodiment, the normal or regulated control laws are stored in the form of a table associating maximum displacement values ​​and / or maximum rotation speed Ω with temperature thresholds ST.

[0066] According to a second embodiment detailed below, the normal or regulated control laws are stored in the form of a table associating maximum displacement values ​​and pressure thresholds P s at rotational speed ranges Ω and maximum rotational speed values ​​at these pressure thresholds P s .

[0067] First method of implementation

[0068] Normal control law

[0069] When the temperature T of the electric motor 3 is below a first temperature threshold ST1, the control unit 10 does not perform any regulation and selects a normal control law R0 as its control law. Indeed, in such a situation, it is considered that the electric motor 3 can provide a sufficiently high motor torque to drive the hydraulic pump 2.

[0070] For example, the first temperature threshold can be set at 130°C.

[0071] According to this normal control law R0, a first maximum rotational speed and a first maximum displacement are respectively chosen to be equal to: m ax = 2600 rpm and C max = 63.0 cc / rev.

[0072] Table 1 below shows the observed flow rate Q of pump 2.

[0073]

[0074] Regulated control laws (LC1, LC2)

[0075] When the control unit 10 determines that a regulation condition is satisfied, it controls the electric motor 3 and the hydraulic unit 2 according to a regulated control law.

[0076] A regulated control law imposes constraints on the hydraulic unit 1. The constraints may concern the rotational speed Ω of the motor 3 and / or the maximum value of the displacement C of the pump 2, in other words a maximum displacement.

[0077] According to a first embodiment, the regulation condition includes at least one temperature condition and this is satisfied when the temperature T of the electric motor 3 is greater than the first temperature threshold ST1.

[0078] In other words, when the temperature T of the electric motor 3 is above the first temperature threshold ST1, the control unit 10 selects as said control law a first regulated control law LC1.

[0079] The first regulated control law LC1 defines, as constraints, a second maximum rotational speed for the electric motor. This second maximum rotational speed is lower than the first maximum rotational speed of motor 3 defined by the normal control law. Thus, the control of the electric motor 3 by the control unit 10 according to the regulated control law LC1 clearly constitutes regulation.

[0080] For example, the first maximum rotation speed according to the first regulated control law LC1 is set at 1700 rpm.

[0081] Alternatively, the first regulated control law LC1 defines, as a constraint, a second maximum displacement. This second maximum displacement is smaller than the first maximum displacement predicted by the normal control law.

[0082] Thus, the control of the displacement variation actuator by the control unit 10 according to the regulated control law LC1 does indeed represent regulation.

[0083] When the first regulated control law LC1 defines, as constraints, a second maximum rotational speed of the electric motor, the control unit 10 employs the first regulated control law LC1, i.e., controls the motor 3 respecting the constraints defined by the first regulated control law LC1 from this first temperature threshold ST1 up to a second temperature threshold ST2

[0084] In other words, a second temperature condition is satisfied when the temperature of the electric motor 3 is above a second temperature threshold ST2, which is above the first temperature threshold ST1.

[0085] From this second temperature threshold ST2, i.e. when the temperature T of the electric motor 3 is greater than a second temperature threshold ST2, the control unit 10 selects as said control law a second regulated control law LC2.

[0086] The second regulated control law LC2 sets a displacement threshold, i.e., a threshold value C r of the hydraulic pump 2's displacement C, or a maximum displacement. This maximum displacement is smaller than the first maximum displacement predicted by the normal control law. In other words, the second regulated control law LC2 defines, as a constraint, a second maximum displacement. This second maximum displacement is smaller than the first maximum displacement predicted by the normal control law.

[0087] For example, the second maximum displacement provided for by the second control law LC2 is set at 50 cc / rev.

[0088] In addition, the second regulated control law LC2 can also define a third maximum rotational speed of the electric motor, the third maximum rotational speed being less than or equal to the second maximum rotational speed defined by the first regulated control law LC1.

[0089] It is possible to define more than two temperature thresholds and a regulated control law associated with each temperature range. Each regulated control law associated with a temperature range defines constraints on the maximum displacement of pump 2 and / or the maximum rotational speed of motor 3.

[0090] Second embodiment

[0091] The second embodiment will now be detailed below.

[0092] According to a second embodiment, the regulation condition further includes less a pressure condition.

[0093] The pressure condition is satisfied when the discharge pressure P is greater than the first pressure threshold P S .

[0094] The regulation condition is thus satisfied when the temperature T of the electric motor 3 is greater than the first temperature threshold ST1 and / or when the discharge pressure P is greater than the first pressure threshold P S .

[0095] According to this second embodiment, the normal control law R0 defines the first maximum rotational speed as a function of the discharge pressure, the first maximum rotational speed being lower when the discharge pressure is greater than a first pressure threshold P S that when the discharge pressure is below the first pressure threshold P S .

[0096] In the example shown on the diagram, the control unit 10 uses at least two control laws: - the normal control law R0 at low temperature, below the first temperature threshold ST1; and - the first regulated control law at high temperature SH, above the first temperature threshold ST1.

[0097] Furthermore, each of the normal R0 or regulated LC1 control laws defines: - a pressure threshold, i.e., a threshold value P s of the discharge pressure P of the pump 2; - a maximum rotation speed Ω of the motor 3.

[0098] The tables below present examples of the normal control law R0 and the regulated control law LC1 to aid understanding. The numerical values ​​listed are provided for illustrative purposes only and are not exhaustive.

[0099] Normal control law R0

[0100] According to the normal control law R0, the pressure condition is satisfied when the discharge pressure P is greater than the first pressure threshold P S 1.

[0101] The first pressure threshold is defined by the normal control law R0 with respect to the rotational speed Ω of motor 3. In other words, the pressure threshold P s is variable depending on the rotational speed Ω of motor 3.

[0102] The value of the maximum rotational speed B r is chosen equal to C r = 2000 rpm as shown in Table 2 below.

[0103] The value of the first maximum displacement also varies with the rotational speed Ω, as shown in Table 2 below. The first maximum displacement thus varies with the rotational speed when the discharge pressure exceeds the first pressure threshold, so that the first maximum displacement decreases as the rotational speed increases.

[0104] Furthermore, the first maximum displacement is defined according to the discharge pressure when the discharge pressure is greater than the first pressure threshold.

[0105] Table 2 shows the value of the first maximum displacement when the pressure is above the first pressure threshold P S 1.

[0106] Table 2 also shows the observed flow rate Q of pump 2.

[0107]

[0108] Thus, as illustrated by Tables 1 and 2, the first maximum rotational speed is smaller when the discharge pressure is above a first pressure threshold than when the discharge pressure is below the first pressure threshold.

[0109] Conversely, the first maximum displacement is independent of the rotational speed when the discharge pressure is below the first pressure threshold.

[0110] Regulated control law LC1

[0111] Similarly, according to the regulated control law LC1, the pressure condition is satisfied when the discharge pressure P is greater than the second pressure threshold P S 2.

[0112] The second pressure threshold P s2 is defined by the regulated control law LC1 with respect to the rotational speed Ω of motor 3. In other words, the second pressure threshold P s2is variable depending on the rotational speed Ω of motor 3.

[0113] According to this second embodiment, the first regulated control law LC1 defines the second maximum rotation speed as a function of the discharge pressure: the second maximum rotation speed is smaller when the discharge pressure is greater than a second pressure threshold than when the discharge pressure is less than the second pressure threshold as illustrated in Tables 5 and 6.

[0114] As illustrated by Tables 1 and 2 relating to the normal control law R0 and Tables 5 and 6 relating to the regulated control law LC1, the second pressure threshold P S 2 is smaller than the first pressure threshold P S 1.

[0115] Furthermore, the second pressure threshold P S 2 depends on the rotational speed of motor 3, so that the second pressure threshold P S2 decreases when the rotational speed Ω of the motor 3 increases.

[0116] Thus, for the same rotational speed Ω of motor 3, the second pressure threshold P S 2 is smaller than the first pressure threshold P S 1.

[0117] As long as the discharge pressure P is below the second pressure threshold P S 2. The values ​​of the second maximum rotational speed and the second maximum displacement are respectively chosen to be equal to: Ω max = 2600 rpm (revolutions per minute) and C max = 40.0 cc / rev (cubic centimeters per revolution).

[0118] Table 5 below shows the observed flow rate Q of pump 2.

[0119] Table 5 shows the value of the second maximum displacement when the pressure is below the second pressure threshold P S 2.

[0120]

[0121] The value of the second maximum rotational speed chosen is equal to Ω r = 2000 rpm when the discharge pressure P is less than the second pressure threshold P S 2. .

[0122] Table 6 shows the value of the second maximum displacement when the pressure is above the second pressure threshold P S 2.

[0123]

[0124] When the discharge pressure P is greater than the second pressure threshold P S 2. The value of the second maximum rotational speed is chosen to be equal to: Ω max = 2000 rpm (revolutions per minute)

[0125] Furthermore, when the pressure is above the second pressure threshold P S2 The second maximum displacement is variable depending on the rotation speed, so the second maximum displacement decreases as the rotation speed increases.

[0126] For example, at 500 rpm, the second maximum displacement is 30 cc / rev while at 1900 rpm, the second maximum displacement is 29 cc / rev.

[0127] Conversely, the second maximum displacement is independent of the rotational speed when the discharge pressure is below the second pressure threshold P S 2as shown in Tables 5 and 6.

[0128] Finally, as shown in Tables 5 and 6, the second maximum displacement is smaller when the discharge pressure is above the second pressure threshold P S 2. that when the discharge pressure is below the second pressure threshold P S 2. Indeed, the second maximum displacement is 40 cc / rev when the discharge pressure is below the second pressure threshold P S 2 whereas it is 30 cc / rev at most when the discharge pressure is greater than the second pressure threshold P S2.

[0129] Table 6 also shows the observed flow rate Q of pump 2.

[0130] Intermediate regulated control law

[0131] Similarly, according to the second embodiment, it is possible to foresee more than two temperature thresholds ST and therefore more than two control laws (the normal control law R0 and the first regulation law LC1 presented above).

[0132] In this case, a regulated control law is associated with each temperature interval. Each regulated control law associated with a temperature interval ST1 defines constraints on the maximum displacement of pump 2 and / or the maximum rotational speed of motor 3.

[0133] In other words, a plurality of regulated control laws LC1 to LCn can be respectively associated with a plurality of temperature thresholds ST1 to STn. Each regulated control law includes a pressure threshold PS, therefore a plurality of pressure thresholds PS2 to PS n+1 can be respectively associated with the plurality of regulated control laws LC1 to LCn.

[0134] As an indication, a third intermediate regulated control law associated with a third ST3 temperature threshold lower than the first ST1 temperature threshold is presented in Tables 3 and 4 below.

[0135] When the discharge pressure of pump 2 is below a third pressure threshold P S3 The values ​​of a third maximum rotational speed and a third maximum displacement are respectively chosen to be equal to: Ω max = 2600 rpm and C max= 51.5 cc / rev. Table 3 below shows the observed flow rate Q of the pump.

[0136]

[0137] When the discharge pressure of pump 2 is greater than a third pressure threshold P S3 , the value of the velocity threshold Ω r is chosen to be equal to Ω r = 2000 rpm.

[0138] The third pressure threshold P S 3 is variable depending on the rotational speed Ω as shown in Table 4 below. Table 4 also shows the observed flow rate Q of pump 2.

[0139] Similarly, as shown in Table 4, when the pressure is above the third pressure threshold P S 3, the third maximum displacement is variable depending on the rotation speed so that the third maximum displacement decreases as the rotation speed increases.

[0140] For example, when the discharge pressure of pump 2 is greater than a third pressure threshold P S3 , the maximum displacement value is chosen to be Cmax = 46.5 cc / rev.

[0141]

[0142] Figures 3 and 4 show torque-speed curves illustrating the motor torque Γ supplied by motor 3 to pump 2 as a function of the motor 3's rotational speed Ω, when the control unit 10 controls the operation of motor 3 and pump 2 according to the normal control law ( ) and the first regulated control law LC1 ( ), respectively. The MA curves indicate the motor torque Γ supplied by motor 3 when the discharge pressure P is not above the pressure threshold P S (respectively first pressure thresholds P S 1st and second pressure threshold P S2) The MB curves indicate the motor torque Γ supplied by the motor 3 when the discharge pressure P is greater than the pressure threshold P S (respectively first pressure thresholds P S 1st and second pressure threshold P S 2) and the MP curves indicate a peak value of the motor torque Γ that the motor 3 is capable of supplying for 1 second without stalling.

[0143] Regulation

[0144] With reference to Table 1 and Table 2, according to the normal control law R0, the value of the first maximum displacement decreases when the discharge pressure P is greater than the first pressure threshold P S1. And when the rotational speed Ω is greater than 1700 rpm. Consequently, as shown by curve MB, motor 3 provides a reduced motor torque Γ, lower than the peak value indicated by curve MP. This prevents a situation in which motor 3 stalls because it cannot provide a sufficiently high motor torque Γ to drive pump 2. For the same reason, the value of the first maximum displacement decreases as the rotational speed Ω increases, and the rotational speed Ω is regulated to remain below the first maximum rotational speed.

[0145] Similarly, with reference to Table 5 and Table 6 according to the regulated control law LC1, when the discharge pressure P is greater than the second pressure threshold P S2. The value of the second maximum displacement decreases as the rotational speed Ω increases, and the rotational speed Ω is regulated to remain below the second maximum rotational speed. Consequently, as shown by curve MB on the graph, motor 3 provides a reduced motor torque Γ, lower than the peak value shown by curve MP. Thus, like the regulated control law SC, the first regulated control law LC1 prevents motor 3 from stalling.

[0146] According to the second embodiment, with reference to Tables 2, 5 and 6, for a given rotational speed Ω, the pressure threshold P S defined by the normal control law is greater than the pressure threshold P S defined by the regulated control law LC1. Thus, the pressure threshold P Sleading to adjusting the maximum displacement and regulating the rotation speed Ω to stay below the maximum rotation speed value decreases when the temperature T of the motor 3 increases.

[0147] Similarly, and still with reference to Tables 2, 5 and 6, the maximum engine displacement C max decreases when the temperature T of engine 3 increases.

[0148] Processes

[0149] According to the first embodiment illustrated in the figure, a control process 100 is described according to the first embodiment.

[0150] In step 101, the control unit 10 receives a flow request signal from the outlet of the pump 2 issued by the control device 20.

[0151] In a step 102, the control unit 10 increases the rotational speed Ω of the motor 3 in response to the flow demand signal at the output of the pump 2 and opens the distributor spool proportionally to the flow demand signal.

[0152] In step 104, the temperature T of motor 3 and the rotational speed Ω of motor 3 are measured. Specifically, the control unit 10 acquires a measurement of T taken by the temperature sensor 13, and a measurement of Ω taken by the sensor 14.

[0153] Preferably, a timing step 103, with a duration of 1 second for example, is implemented between step 102 and step 104. This tends to prevent the measurements carried out in step 104 from being distorted by a transient regime phenomenon.

[0154] In a step 105, the control unit 10 selects as said control law either the normal control law R0 or a regulated control law from among the plurality of regulated control laws LC1 to LCn.

[0155] Thus, at step 105, the control unit 10 selects as said control law the control law (normal or regulated) corresponding to the temperature T measured at step 104.

[0156] In a step 106, the control unit 10 controls the electric motor 3 and the displacement variation actuator 21 according to the demand of an operator while respecting constraints defined by the control law selected in step 105.

[0157] Step 106 is followed by a timing step 112, for a duration of 2 seconds for example; and after the timing step 112, process 100 returns to step 104.

[0158] We now describe, with reference to the diagram, a control method 100 for controlling the hydraulic unit 1 according to the second embodiment. The control method 100 is implemented by the control unit 10.

[0159] In step 101, the control unit 10 receives a flow request signal from the outlet of the pump 2 issued by the control device 20.

[0160] In a step 102, the control unit 10 increases the rotational speed Ω of the motor 3 in response to the flow demand signal at the output of the pump 2.

[0161] In step 104, the discharge pressure P of pump 2, the temperature T of motor 3, and the rotational speed Ω of motor 3 are measured. Specifically, the control unit 10 acquires a measurement of P taken by the pressure sensor 12, a measurement of T taken by the temperature sensor 13, and a measurement of Ω taken by the sensor 14.

[0162] Preferably, a timing step 103, with a duration of 1 second for example, is implemented between step 102 and step 104. This tends to prevent the measurements carried out in step 104 from being distorted by a transient regime phenomenon.

[0163] In a step 105, the control unit 10 selects as said control law either the normal control law R0 or a regulated control law from among the plurality of regulated control laws LC1 to LCn.

[0164] Thus, at step 105, the control unit 10 selects as said control law the control law corresponding to the temperature T measured at step 104.

[0165] In a preferred embodiment, the control unit 10 inhibits the step of selecting a control law when the selected control law would have the effect of linking to the current operator demand a rotational speed (Ω) of the electric motor 3 higher than a speed measured in step 104.

[0166] In step 110, the control unit 10 checks whether the discharge pressure P measured in step 104 is greater than the pressure threshold P S , more precisely at the pressure threshold P S which is associated by the control law selected in step 105 with the rotational speed Ω measured in step 104.

[0167] If the discharge pressure P measured in step 104 is not greater than the pressure threshold P S (F on the), process 100 returns to step 104.

[0168] Conversely, if the discharge pressure P measured in step 104 is greater than the pressure threshold P S(V on the), process 100 passes to a step 111 in which the control unit 10 sets the displacement C of the pump 2 and regulates the rotational speed Ω of the motor 3.

[0169] In a preferred embodiment, - at step 111, the control unit 10 modifies the value of the displacement C by a first predetermined increment towards the maximum displacement value if the displacement C is greater than the maximum displacement value and / or modifies the rotation speed Ω by a second predetermined increment towards the maximum rotation speed value if the rotation speed Ω is greater than the maximum rotation speed; - step 111 is followed by a timing step 112, of a duration of 2 seconds for example; and - after the timing step 112, the process 100 returns to step 104.

[0170] In this way, the displacement C of pump 2 and the rotational speed Ω of motor 3 are adjusted gradually, which helps to avoid undesirable phenomena of hydraulic oscillation, jerking or resonance in a hydraulic circuit in which pump 2 is integrated.

[0171] Alternatively, the control unit 10 sets the maximum displacement of the pump 2 to the value defined by the control law and regulates the rotational speed Ω of the motor 3 to remain below the maximum rotational speed in other ways in step 111 if desired.

[0172] If motor 3 is subjected to a relatively long operating period, its temperature T tends to increase, and steps 104 and 105 may lead to a change in the regulated control law over time. For example, the normal control law R0 could be selected initially, followed by the first regulated control law LC1.

[0173] Thus, the control of motor 3 and pump 2 by control unit 10 is based on the observation that motor 3 heats up more as it is under load, and therefore the higher the temperature T of motor 3 at a given instant, the less capacity motor 3 has to provide an additional motor torque Γ at that instant. In other words, the control of motor 3 and pump 2 by control unit 10 is based on the observation that the temperature T of motor 3 is indicative of its capacity to provide an additional motor torque Γ. This is why, with the normal control law R0 and the plurality of regulated control laws LC1 to LCn, the pressure threshold P S and the value of the maximum displacement decreases when the engine temperature T increases.

[0174] In this regard, it is preferable that the temperature T measured by the temperature sensor 13 be an internal temperature of the motor 3. Indeed, in this case, the temperature sensor 13 is less disturbed by factors external to the hydraulic unit 1, in particular the ambient air temperature, the ambient air circulation, etc., so that the temperature T measured by the temperature sensor 13 is more representative of the operating state of the motor 3.

[0175] On the other hand, during operation, motor 3 must provide a sufficiently high motor torque Γ to drive pump 2; otherwise, motor 3 will stall. Therefore, with both normal and regulated control laws, the displacement C of pump 2 is limited—based on the maximum displacement value—when the discharge pressure P of pump 2 exceeds the pressure threshold P. S The value of the pressure threshold P Sis chosen according to the respective characteristics of the motor 3 and the pump 2. Preferably, the value of the pressure threshold P S is chosen equal to or slightly less than the discharge pressure P of pump 2 corresponding to the maximum motor torque Γ that can be supplied by motor 3.

[0176] The maximum rotation speed is also chosen according to the respective characteristics of the motor 3 and the pump 2. Preferably, the maximum rotation speed is chosen equal to the rotation speed Ω which allows a maximum flow rate Q to be obtained at the outlet of the pump 2.

[0177] In a very simple variant, only the normal control laws and the regulated control law LC1 are used. However, it is preferable to use several intermediate regulated control laws (analogous to the intermediate regulated control law presented as an example). Each of the intermediate regulated control laws is associated with a temperature sub-interval T included within the interval between T C and T H and vice versa. In this case, with the intermediate regulated control laws, the pressure threshold P S , the maximum engine displacement C max and the maximum rotational speed value decreases as the temperature T of motor 3 increases. By employing more intermediate regulated control laws, it is better possible to ensure that the flow rate Q at the outlet of pump 2 corresponds to the maximum motor torque Γ that can be supplied by motor 3.

[0178] Various applications are possible for the hydraulic unit 1. For example, the pump 2 can supply hydraulic fluid to a hydraulic circuit in various types of work machines, including earthmoving equipment, material handling equipment, etc. The hydraulic circuit can have various functions, such as propulsion or lifting. The motor 3 can be powered by various means, including an on-board battery, an on-board generator, etc.

[0179] In one example, the hydraulic unit 1 and the control unit 10 are mounted on a material handling machine, and the pump 2 supplies hydraulic fluid to a hydraulic circuit associated with a lifting mechanism of the material handling machine. In this case, the control described above for the hydraulic unit 1 ensures that the motor 3 does not stall during a lifting operation; the lifting speed is only reduced due to the decrease in the displacement C of the pump 2 and / or the rotational speed Ω of the motor 3. Furthermore, the control described above for the hydraulic unit 1 does not regulate the discharge pressure P of the pump 2; only the displacement C of the pump 2 and / or the rotational speed Ω of the motor 3 can be regulated. This allows the lifting capacity available to a user of the material handling machine to be maintained.Finally, since the control of the hydraulic unit 1 ensures that the motor 3 does not stall, the power of the motor 3 can be limited, which helps to limit the size and / or cost of the motor 3.

[0180] Some of the elements shown, particularly control unit 10, can be implemented in various forms, either individually or in a distributed manner, using hardware and / or software components. Usable hardware components include ASICs (Automatic System Integrated Circuits), FPGAs (Field Programmable Gate Arrays), and microprocessors. Software components can be written in various programming languages, such as C, C++, Java, or VHDL. This list is not exhaustive.

[0181] 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.

[0182] 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.

[0183] In claims, any reference sign in parentheses shall not be interpreted as a limitation of the claim.

Claims

Control method (100) for controlling a hydraulic system comprising an electric motor (3), a variable displacement hydraulic pump (2) driven by the electric motor (3), and a displacement variation actuator configured to modify a displacement of the variable displacement hydraulic pump (2) according to a feedback signal dependent on the discharge pressure of the variable displacement hydraulic pump (2), the control method (100) comprising:- controlling the electric motor (3) and the displacement variation actuator according to a request from an operator and respecting constraints defined by a control law, each control law linking a rotation speed (Ω) of the electric motor (3) to a request from the operator;- measure (104) operating parameters including at least a rotational speed (Ω) of the electric motor (3) and a temperature (T) of the electric motor (3), the temperature (T) of the electric motor (3) being an internal temperature of the electric motor (3); - in response to a detection (105) that the temperature (T) of the electric motor (3) is below a first temperature threshold (ST1), select as said control law a normal control law (R0), the normal control law (R0) defining as constraints, a first maximum rotational speed of the electric motor and a first maximum displacement of the variable displacement hydraulic pump (2);- in response to a determination that the temperature (T) of the electric motor (3) is above the first temperature threshold (ST1), select as said control law a first regulated control law (LC1), the first regulated control law (LC1) defining, as constraints: - a second maximum rotational speed of the electric motor or a second maximum displacement, the second maximum rotational speed being smaller than the first maximum rotational speed, the second maximum displacement being smaller than the first maximum displacement.; Control method (100) according to claim 1, wherein the first regulated control law (LC1) defines the second maximum rotational speed of the electric motor, the second maximum rotational speed being less than the first maximum rotational speed, the method further comprising the steps of: - in response to a determination that the temperature (T) of the electric motor (3) is greater than a second temperature threshold (ST2); the second temperature threshold (ST2) being greater than the first temperature threshold (ST1), selecting as said control law a second regulated control law (LC2), the second regulated control law (LC2) defining: - a third maximum rotational speed of the electric motor, the third maximum rotational speed of the electric motor being less than or equal to the second maximum rotational speed of the electric motor;and - the second maximum displacement, the second maximum displacement being smaller than the first maximum displacement. Control method (100) according to any one of claims 1 to 2, wherein the measured operating parameters include a discharge pressure (P) of the hydraulic pump (2), and wherein the normal control law (R0) defines the first maximum rotational speed (Ω) as a function of the discharge pressure, the first maximum rotational speed being smaller when the discharge pressure is above a first pressure threshold than when the discharge pressure is below the first pressure threshold, and wherein the first regulated control law (LC1) defines the second maximum rotational speed as a function of the discharge pressure, the second maximum rotational speed being smaller when the discharge pressure is above a second pressure threshold than when the discharge pressure is below the second pressure threshold. Control method (100) according to claim 3, wherein the second pressure threshold is smaller than the first pressure threshold. Control method (100) according to claim 3 or 4, wherein the first pressure threshold and / or the second pressure threshold depends on the rotational speed, such that the first pressure threshold and / or the second pressure threshold decreases as the rotational speed increases. Control method (100) according to any one of claims 3 to 5, wherein the normal control law (R0) defines the first maximum displacement as a function of the discharge pressure, the first maximum displacement being variable as a function of the rotational speed when the discharge pressure is above the first pressure threshold, so that the first maximum displacement decreases as the rotational speed increases, and wherein the first regulated control law (LC1) defines the second maximum displacement as a function of the discharge pressure, the second maximum displacement being variable as a function of the rotational speed when the discharge pressure is above the second pressure threshold, so that the second maximum displacement decreases as the rotational speed increases. Control method (100) according to claim 6, wherein the first maximum displacement is independent of the rotational speed when the discharge pressure is below the first pressure threshold, and / or the second maximum displacement is independent of the rotational speed when the discharge pressure is below the second pressure threshold. Control method (100) according to any one of claims 3 to 7, wherein the first regulated control law (LC1) defines the second maximum displacement as a function of the discharge pressure, the second maximum displacement being smaller when the discharge pressure is above the second pressure threshold than when the discharge pressure is below the second pressure threshold. Control method (100) according to any one of claims 1 to 8, as long as a current demand of the operator is non-zero, the method comprises: inhibiting the step of selecting a control law when the selected control law would have the effect of linking to the current demand of the operator a rotation speed (Ω) of the electric motor (3) higher than a current speed. Work machine comprising: - an electric motor (3) and a variable displacement hydraulic pump (2) driven by the electric motor (3); - sensors (12, 13, 14) configured to measure operating parameters including a rotational speed (Ω) of the electric motor (3), a temperature (T) of the electric motor (3); - a human-machine interface (20) for receiving a request from the operator, and - a control unit (10) connected to the sensors (12, 13, 14) and to the human-machine interface and configured to implement the control method (100) according to any one of claims 1 to 9. Working machine according to claim 10, wherein the sensors (12, 13, 14) are configured to further measure a discharge pressure (P) of the hydraulic pump (2). Working machine according to claim 10 or 11, wherein the working machine comprises a lifting mechanism and a hydraulic lifting circuit associated with the lifting mechanism, the hydraulic pump (2) supplying the hydraulic lifting circuit with hydraulic fluid.

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