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

Abstract

Control of an electric motor and a variable displacement hydraulic pump. A method (100) for controlling a hydraulic system comprising: - controlling the electric motor (3) and the variable displacement actuator according to 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; - in response to a determination that the temperature (T) is above the first temperature threshold (ST1), selecting a first regulated control law (LC1) defining: - a second maximum rotational speed or a second maximum displacement. Figure for the abstract: Fig. 1

Description

Title of the invention: Control of an electric motor and a variable displacement hydraulic pump driven by the electric motor technical field

[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 modified by changing the displacement of the hydraulic pump and / or the rotational speed of the electric motor. Summary

[0003] One idea underlying the invention is to limit the power of the electric motor required to drive the variable displacement hydraulic pump, and thus limit the size and / or cost of the electric motor. To this end, another idea underlying the invention is to control the electric motor and the hydraulic pump in order to prevent a situation in which the electric motor stalls because it cannot provide sufficient torque to drive the hydraulic pump. Yet another idea underlying the invention is to take into account the temperature of the electric motor 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 by based on 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 one speed of electric motor rotation and electric motor temperature;

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

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

[0011] - a second maximum rotational 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 the hydraulic pump is based on the observation that the electric motor heats up more as it is under load, and therefore the higher the temperature of the electric motor at a given moment, the less capacity it has to provide additional torque at that moment. In other words, the control of the electric motor and the hydraulic pump is based on the observation that the temperature of the electric motor is indicative of its capacity to provide additional torque.

[0013] Setting the hydraulic pump displacement to a target value affects both the hydraulic pump 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 electric motor's temperature increases, the hydraulic pump 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 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 greater than a second temperature threshold; the second temperature threshold being greater than 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 rotational speed of the electric motor, the third the maximum rotational speed of the electric motor being less than or equal to the second maximum rotational speed of the electric motor; and

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

[0020] According to one embodiment, the measured operating parameters include a discharge pressure of the hydraulic pump, 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 to better prevent a situation in which 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 rotation speed, so that the first pressure threshold and / or the second pressure threshold decreases as the rotation speed increases.

[0024] This also tends to better avoid a situation in which the electric motor stalls because the electric motor cannot provide a sufficiently high 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 greater than the first pressure threshold, such that the first maximum displacement decreases as the rotational speed increases, and the first The 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 a sufficiently high motor torque to drive the hydraulic pump.

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

[0028] Indeed, it is preferable to limit first the maximum rotational speed of the motor 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 greater than the second pressure threshold than when the discharge pressure is less than 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 a sufficiently high motor torque to drive the hydraulic pump.

[0031] According to one embodiment, as long as a current demand of the operator is not 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 makes it possible to avoid an increase in the speed of movement of a hydraulic actuator powered by the pump without specific demand from the user, i.e. only 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 an electric motor rotation speed, an electric motor temperature;

[0037] - a human-machine interface for receiving 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 further 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 in 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 displacement and / or the rotational speed of the electric motor. Furthermore, the control method does not regulate the hydraulic pump's discharge pressure; only the hydraulic pump displacement and / or the rotational speed of the electric motor can be regulated. This allows the lifting capacity available to a machine operator to be maintained.

[0042] Finally, since the control method ensures that the electric motor does not stall, the power of the electric motor can be limited, which makes it possible 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] [Fig.1] The [Fig.1] is a functional block diagram of a hydraulic unit comprising a variable displacement hydraulic pump and an electric motor.

[0045] [Fig.2] Fig.2 is a diagram illustrating regulated control laws employed by the control unit shown in [Fig.1].

[0046] [Fig.3] The [Fig.3] 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] [Fig.4] [Fig.4] is a graph analogous to [Fig.3], according to another law of regulated control used by the control unit.

[0048] [Fig. 5] Fig. 5 is a block diagram illustrating a control method for order the hydraulic unit according to a specific embodiment

[0049] [Fig.6] Fig.6 is a block diagram illustrating a control method for order the hydraulic unit according to another embodiment. Description of the implementation methods

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

[0051] The functional block diagram in [Fig. 1] is a functional block diagram of a hydraulic unit 1. The hydraulic unit 1 comprises 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 in [Fig. 1] 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. [Fig. 1] is not limiting in this respect. 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] Such a type of pump is known to a person skilled in the art.

[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 Q 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 dashed lines in [Fig. 1], a control unit 10 is connected to sensors 12, 13, 14 in order to receive measurements from the sensors 12, 13, 14, and the control unit 10 are 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, emitted by a human-machine interface device 20. The human-machine interface device 20 emits 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 the motor 3 is characterized by the rotational speed Q and a motor torque T at the output of the motor 3. The control unit 10 controls the rotational speed Q of the motor 3 according to a control law linking a rotational speed Q of the electric motor 3 to a flow demand signal at the output of the pump 2. The flow demand signal at the output of the pump 2 is determined according to a request from the operator transmitted by the human-machine interface device 20.

[0061] The operation of the pump 2 driven by the motor 3 is characterized by the rotational speed Q, the discharge pressure P, a flow rate Q at the outlet of the pump 2, and a displacement C of the pump 2, where Q = QC. The control unit 10 controls the maximum displacement C of the 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 the 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 rotation speed, i.e. a maximum value of the rotation speed Q of the motor 3, and a maximum displacement, i.e. a maximum value Cmax of the displacement C of the 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 Q 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 Ps with rotation speed ranges Q and maximum rotation speed values ​​with these pressure thresholds Ps.

[0067] First embodiment

[0068] Normal control law

[0069] When the temperature T of the electric motor 3 is below a first temperature threshold STI, the control unit 10 does not perform any regulation and selects a normal control law Ro as said 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 Ro, a first maximum rotation speed and a first maximum displacement are respectively chosen equal to: max = 2600 rpm and Cmax = 63.0 cc / rev.

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

[0073] [Tables 1] a QC | [cc / k] [L / min] 500 63.0 28 600 63.0 34 700 ' 63.0 40 1 800 63.0 46 900 63.0 52 1 1000 63.0 57 | 1100 63.0 63 1200 63.0 69 ] 1300 63.0 75 | 1400 63.0 81 1 1500 63.0 87 | 1600 63.0 93 | 1700 63.0 99 1800 63.0 106 1900 63.0 112 2000 63.0 118 2100 63.0 124 | 2200 63.0 130 | 2300 63.0 137 2400 63.0 143 2500 63.0 149 2000 63.0 156 d

[0074] Regulated control law (LCL 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 Q 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 STI.

[0078] In other words, when the temperature T of the electric motor 3 is greater than the first temperature threshold STI, 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 of the electric motor. This second maximum rotational speed is lower than the first maximum rotational speed of the 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 a 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 STI 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 greater than a second temperature threshold ST2, greater than the first temperature threshold STI.

[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, that is, a threshold value Cr of the displacement C of the hydraulic pump 2, or a maximum displacement. This maximum displacement is smaller than the first maximum displacement specified by the normal control law. In other words, the second regulated control law LC2 defines, as a constraint, a second displacement maximum. 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 provide 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 the pump 2 and / or the maximum rotational speed of the 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 Ps.

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

[0095] According to this second embodiment, the normal control law Ro defines the first maximum rotation speed as a function of the discharge pressure, the first maximum rotation speed being smaller when the discharge pressure is greater than a first pressure threshold Ps than when the discharge pressure is less than the first pressure threshold Ps.

[0096] In the example shown in [Fig.2], the control unit 10 uses at least two control laws: - the normal control law Ro at low temperature, below the first STI temperature threshold; and - the first regulated high temperature control law SH, above the first temperature threshold STI.

[0097] In addition, each of the normal control laws Ro or regulated LC1 defines: - a pressure threshold, i.e. a threshold value Ps of the discharge pressure P of the pump 2; - a maximum rotation speed Q of the motor 3.

[0098] The tables below present examples of the normal control law Ro and the regulated control law LC1 to facilitate understanding. The numerical values ​​listed are provided for illustrative purposes only and are not intended to be limiting.

[0099] Normal control law R e

[0100] According to the normal control law Ro, the pressure condition is satisfied when the discharge pressure P is greater than the first pressure threshold Ps i.

[0101] The first pressure threshold is defined by the normal control law Ro with respect to the rotational speed Q of the motor 3. In other words, the pressure threshold Ps is variable as a function of the rotational speed Q of the motor 3.

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

[0103] The value of the first maximum displacement is also variable depending on the rotational speed Q, as shown in Table 2 below. The first maximum displacement thus varies with 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.

[0104] Furthermore, the first maximum displacement is defined as a function of 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 Ps L

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

[0107] [Tables2] Ps O ........c...... Q....... Bar 270.0 .......500""" [cc / rev] " ^63^0...... (Üminj 28 270.0 600 63.0 34 270.0 700 63.0 hU 270.0 800 63.0 46 270.0 900 63.0 52 270.0 1000 63.0 57 270.0 1100 63.0 63 270.0 270.0 1200 1300 63.0 63.0 69 75 270.0 1400 63.0 81 270.0 1500 63.0 87 270.0 270.0 1600 1700 63.0 63.0 93 99 260.0 1800 63.0 104 250.0 1900 63.0 105 240.0 2000 56.0 105

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

[0109] Conversely, the first maximum displacement is independent of the rotation 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 Ps 2.

[0112] The second pressure threshold Ps2 is defined by the regulated control law LC1 with respect to the rotational speed Q of the motor 3. In other words, the second pressure threshold Ps2 is variable as a function of the rotational speed Q of the 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 Ps 2 is smaller than the first pressure threshold Ps i.

[0115] Furthermore, the second pressure threshold Ps 2 depends on the rotational speed of the motor 3, so that the second pressure threshold Ps 2 decreases when the rotational speed Q of the motor 3 increases.

[0116] Thus, for the same rotational speed Q of the motor 3, the second pressure threshold Ps 2 is smaller than the first pressure threshold Ps i.

[0117] As long as the discharge pressure P is less than the second pressure threshold Ps 2., the values ​​of the second maximum rotation speed and the second maximum displacement are respectively chosen to be equal to: Qmax = 2600 rpm (revolutions per minute) and Cmax = 40.0 cc / rev (cubic centimeters per revolution).

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

[0119] Table 5 indicates the value of the second maximum displacement when the pressure is below the second pressure threshold Ps 2.

[0120] [Tables5] [rpm [Umsn] bar 500 1 40.0 i 18 200.0 600 | 40.0 [ 22 200.0 700 40.0 1 25 200.0 600 1 40.0 [ 29 200.0 900 40.0 i 33 200.0 AH A 1 40.0 ] 36 200.0 * îv'v î 40.0 [ 40 200.0 0 0 CM ] 40.0 [ 44 200.0 1300 40.0 ] 48 200.0 1400 I 40.0 52 ..... 200.0 S Uvv | 40.0 ] $6 200.0 1600 ] 40.0 1 59 200.0 1700 î 40.0 1 63 190.0 S VW 1 40.0 ...]........67......... 190.0 1900 ] 40.0 | 71 190.0 2000 1 40.0 î 75 180.0 2100 î 40.0 ] 79 18Ô.Ô 2200 1 40.0 I 83 180.0 2300 40.0 [ 87 180.0 2400 40.0 I 91 180 0 2500 40.0 [ 95 180.0 20 S <5 ÔA

[0121]

[0122]

[0123] The value of the second maximum rotation speed chosen is equal to Qr = 2000 rpm when the discharge pressure P is less than the second pressure threshold PS 2 - Table 6 indicates the value of the second maximum displacement when the pressure is above the second pressure threshold Ps 2. [Tableauxô] ZZ5ZZDQ o™ Bar hr / minj | p / bj | pmin) .....Mo.....r'loo........I......Mo......j.........ï4...... 200,0 i 600 30,0 | 16 200.0 700 | 30.0 19 200,0 800 | 30,0 22 200,0 900 I 30,0 25 200^0 1 1000 I 30.0 | 27 200,0 ] 1100 | 30,0 !......30...... 200.0 ] 1200 I 30.0 | 33 200.0 1 1300 | 30.0 | 36 200,0 | 1400 [ 29.0 ......37...... 200,0 ] 1500 I 29.0 * 40 200.0 ï 1600 | 29:0 { 43 190.0 [ 1700 [ 29,0 I 46 190,0 ] 1800 I 29.0 | 49 190,0 1900 29.0 î 51 .....180'0.....1.....2000......1......28,0.....S.........52......

[0124] When the discharge pressure P is greater than the second pressure threshold Ps 2., the value of the second maximum rotation speed is chosen to be: Qmax = 2000 rpm (revolutions per minute)

[0125] Furthermore, when the pressure is above the second pressure threshold PS2, the second maximum displacement is variable depending on the rotation speed so that the second maximum displacement decreases when 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 rotation speed when the discharge pressure is below the second pressure threshold Ps 2 as 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 Ps 2 than when the discharge pressure is below the second pressure threshold Ps 2* Indeed, the second maximum displacement is 40 cc / rev when the discharge pressure is below the second pressure threshold Ps 2 whereas it is 30 cc / rev at most when the discharge pressure is above the second pressure threshold Ps 2.

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

[0130] Regulated control law - intermediate

[0131] Similarly, according to the second embodiment, it is possible to provide 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 an STI temperature interval defines constraints on the maximum displacement of the pump 2 and / or the maximum rotational speed of the 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 STI to STn. Each regulated control law provides a pressure threshold PS, therefore a plurality of pressure thresholds PS2 to PSn+ can be respectively associated with the plurality of regulated control laws LC1 to LCn.

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

[0135] When the discharge pressure of the pump 2 is below a third pressure threshold PS3, the values ​​of a third maximum rotational speed and of a The third maximum engine displacements are respectively chosen to be equal to: Qmax = 2600 rpm and Cmax = 51.5 cc / rev. Table 3 below shows the observed flow rate Q of the pump.

[0136] [Tables3] Q pr / rnh] C (cc / tr) | Ps(bar] «nn tJVU 51.5 ( 23 235.0 600 515 I 28 235.0 ■F UU 51.5 ( 33 ! 235.0 80Û 51.5 | 37 235.0 900 51.5 |. 42 235.0 1000 1100 1200 1300 1400 1500 51.5 51.5 51.5 51.5 51.5 51.5 | 47 S 52 | 57 | 62 66 71 235.0 235.0 235.0 235.0 51.5 sec 235.0 1700 51.5 | 81 230.0 1800 51.5 1 86 225.0 1900 51.5 91: 220.0 r 2000 51.5 | 96 i 210.0 2100 51.5 101 205.0 2200 51.5 107 | 190.0 2300 51.5 112 185.0 2400 51.5 1 117 i 175.0 2500 ( W 51.5 l 51.5 122 [ 127 170.0 ..,.....1 ^0.0... j

[0137] When the discharge pressure of the pump 2 is greater than a third pressure threshold PS3, the value of the speed threshold Qr is chosen to be equal to Qr = 2000 rpm.

[0138] The third pressure threshold PS3 is variable depending on the rotational speed Q 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 Ps 3, the third maximum displacement is variable depending on the rotational speed so that the third maximum displacement decreases as the rotational speed increases.

[0140] For example, when the discharge pressure of the pump 2 is greater than a third pressure threshold PS3, the maximum displacement value is chosen to be equal to Cmax = 46.5 cc / rev.

[0141] [Tables4] Ps [bar] p Ct [cc / tr] |Q 235.0 235^0 235.0 235.0 235.0 235:0 235.0 235.0 235.0 235.0 235 0 205.0 235.0 ] [ 6 22 ss | , 800 [ 900 ] |1QQO| s ïï 1 | 1200 | j 1300 ] [ 1400 1 î 1500 1600 ] î 1700 I î 1800 I 1900 ] 46.5 46.5 46.5 45.5 44.0 | 21 | ........É 1 34 : 38 | 42 : 47 51 or : 59 | ........64 : 68 .......73........] 76 : [ 7g ] 210,0 ] 2000 1 42.0 1.........79 |

[0142] Figures 3 and 4 show torque-speed curves showing the motor torque F supplied by the motor 3 to the pump 2 as a function of the rotational speed Q of the motor 3, when the control unit 10 controls the operation of the motor 3 and the pump 2 respectively according to the normal control law ([Fig.3]) and the first regulated control law LC1 ([Fig.4]). The MA curves indicate the motor torque F supplied by the motor 3 when the discharge pressure P is not greater than the pressure threshold Ps (respectively first pressure threshold Ps and second pressure threshold Ps 2), the MB curves indicate the motor torque F supplied by the motor 3 when the discharge pressure P is greater than the pressure threshold Ps (respectively first pressure threshold Ps and second pressure threshold Ps 2) and the MP curves indicate a peak value of the motor torque F that the motor 3 is able to supply for 1 second without stalling.

[0143] Regulation

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

[0145] Similarly, with reference to [Fig. 4], Table 5, and Table 6, according to the regulated control law LC1, when the discharge pressure P exceeds the second pressure threshold Ps2, the value of the second maximum displacement decreases as the rotational speed Q increases, and the rotational speed Q is regulated to remain below the second maximum rotational speed. Consequently, as shown by the MB curve in [Fig. 5], the motor 3 provides a reduced motor torque T, lower than the peak value indicated by the MP curve. Thus, like the regulated control law SC, the first regulated control law LC1 prevents the motor 3 from stalling.

[0146] According to the second embodiment, with reference to Tables 2, 5 and 6, for a given rotational speed Q, the pressure threshold Ps defined by the normal control law is greater than the pressure threshold Ps defined by the regulated control law LC1. Thus, the pressure threshold Ps leading to the adjustment of the maximum displacement and the regulation of the rotational speed Q to remain below the maximum rotational speed value decreases as the temperature T of the motor 3 increases.

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

[0148] Processes

[0149] According to the first embodiment illustrated in [Fig. 6], a process is described order 100 according to the first embodiment.

[0150] In a 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 Q 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 a step 104, the temperature T of the motor 3 and the rotational speed Q of the motor 3 are measured. Specifically, the control unit 10 acquires a measurement of T taken by the temperature sensor 13, and a measurement of Q taken by the sensor 14.

[0153] Preferably, a timing step 103, of 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 the normal control law R0 or a regulated control law from among the plurality of regulated control laws LC1 to LCn.

[0155] Thus, in step 105, the control unit 10 selects as said control law the control law (normal or regulated) corresponding to the temperature T measured in 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, of a duration of 2 seconds for example; and after the timing step 112, the process 100 returns to step 104.

[0158] A control method 100 for controlling the hydraulic unit 1 according to the second embodiment is now described with reference to [Fig. 5]. The control method 100 is implemented by the control unit 10.

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

[0160] In a step 102, the control unit 10 increases the rotational speed Q 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 the pump 2, the temperature T of the motor 3, and the rotational speed Q of the 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 Q taken by the sensor 14.

[0162] Preferably, a timing step 103, of 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 the normal control law R0 or a regulated control law from among the plurality of regulated control laws LC1 to LCn.

[0164] Thus, in step 105, the control unit 10 selects as said control law the control law corresponding to the temperature T measured in 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 (Q) of the electric motor 3 higher than a speed measured in step 104.

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

[0167] If the discharge pressure P measured in step 104 is not greater than the pressure threshold Ps (F on the [Fig.5]), process 100 returns to step 104.

[0168] Conversely, if the discharge pressure P measured in step 104 is greater than the pressure threshold Ps (V on [Fig.5]), the process 100 proceeds to a step 111 in which the control unit 10 adjusts the displacement C of the pump 2 and regulates the rotational speed Q 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 Q by a second predetermined increment towards the maximum rotation speed value if the rotation speed Q is greater than the maximum rotation speed; - Step 111 is followed by a delay step 112, lasting for example 2 seconds; and - after the time-delay step 112, process 100 returns to step 104.

[0170] In this way, the displacement C of the pump 2 and the rotational speed Q of the motor 3 are adjusted gradually, which makes it possible to avoid undesirable phenomena of hydraulic oscillation, jerking or resonance in a hydraulic circuit in which the 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 Q 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 period of operation, the temperature T of motor 3 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 Ro 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 motor 3 is under load, and therefore the higher the temperature T of motor 3 at a given instant, the less motor 3 is able to provide an additional motor torque F 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 motor 3's ability to provide an additional motor torque T. This is why, with the law of normal control Ro and the plurality of regulated control laws LC1 to LCn, the pressure threshold Ps and the maximum displacement value decrease as 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 circulation of ambient air, 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, the motor 3 must provide a sufficiently high motor torque T to drive the pump 2; otherwise, the motor 3 will stall. Therefore, with both normal and regulated control laws, the displacement C of the pump 2 is limited—based on the maximum displacement value—when the discharge pressure P of the pump 2 exceeds the pressure threshold Ps. The value of the pressure threshold Ps is chosen according to the respective characteristics of the motor 3 and the pump 2. Preferably, the value of the pressure threshold Ps is chosen to be equal to or slightly less than the discharge pressure P of the pump 2 corresponding to the maximum motor torque T that can be supplied by the 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 Q allowing a maximum flow rate Q to be obtained at the outlet of the pump 2.

[0177] According to 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 shown as an example). Each of the intermediate regulated control laws is associated with a sub-range of temperature T included in the range between Tc and TH, and vice versa. In this case, with the intermediate regulated control laws, the pressure threshold Ps, the maximum displacement Cmax, and the maximum rotational speed decrease as the temperature T of the motor 3 increases. By using more intermediate regulated control laws, it is better possible to ensure that the flow rate Q at the outlet of the pump 2 corresponds to the maximum motor torque T that can be supplied by the motor 3.

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

[0179] According to 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 Q of the motor 3. Furthermore, the control described above for the hydraulic unit 1 does not implement regulation of the discharge pressure P of the pump 2; only the displacement C of the pump 2 and / or the rotational speed Q of the motor 3 can be regulated. This makes it possible to maintain the lifting capacity available to a user of the material handling machine.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, in particular the 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, FPGAs, or microprocessors. Software components can be written in various programming languages, for example, 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 "comprise", "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 the claims, any reference sign in parentheses shall not be interpreted as a limitation of the claim.

Claims

1. Demands 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 change the 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: - control 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 (Q) of the electric motor (3) to a request from the operator; - measure (104) operating parameters including at least one rotational speed (Q) of the electric motor (3) and one temperature (T) 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 (STI), select as said control law a normal control law (R0), the normal control law (R0) defining as constraints, a first maximum rotation speed of the electric motor and a first maximum displacement of the hydraulic pump (2) with variable displacement; - in response to a determination that the temperature (T) of the electric motor (3) is above the first temperature threshold (STI), select as said control law a first regulated control law (LC1), the first regulated control law (LC1) defining, as constraints: - 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.

2. A 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.;

3. A 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 (Ro) defines the first maximum rotational speed (Q) 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.

4. Control method (100) according to claim 3, wherein the second pressure threshold is smaller than the first pressure threshold.

5. A 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.

6. A control method (100) according to any one of claims 3 to 5, wherein the normal control law (RO) 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, such 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, such that the second maximum displacement decreases as the rotational speed increases.

7. 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.

8. 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.

9. 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 rotational speed (Q) of the electric motor (3) higher than a current speed.

10. Control method (100) according to any one of claims 1 to 9, wherein the temperature (T) of the electric motor (3) is an internal temperature of the electric motor (3).

11. A 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 (Q) 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 10.

12. Working machine according to claim 11, wherein the sensors (12, 13, 14) are configured to further measure a discharge pressure (P) of the hydraulic pump (2).

13. Working machine according to claim 11 or 12, 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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