Method for controlling an electrohydraulic actuator

Abstract

Method for controlling an electro-hydraulically operated actuator (1) with two pressure lines (4, 5) supplied with pressure medium depending on a direction of rotation of an electric motor (3) operating a pump (2), wherein a pressure sensor (8, 9) is arranged in each pressure line (4, 5) and a double pressure valve (7) is connected between a pressure medium reservoir (6) and the pressure lines (4, 5), wherein an offset of each of the pressure sensors (8, 9) is determined and compensated only when the associated pressure line (4, 5) is connected to the pressure medium reservoir (6) without pressure, characterized in that the offset of a first pressure sensor (8, 9) in a first pressure line (4, 5) is determined when a pressure above a predetermined threshold value is detected at the second pressure line (5, 4).

Description

[0001] The invention relates to a method for controlling an electro-hydraulically operated actuator with two pressure lines supplied with pressure medium depending on a direction of rotation of an electric motor operating a pump, wherein a pressure sensor is arranged in each pressure line and a double pressure valve is connected between a pressure medium reservoir and the pressure lines.

[0002] DE 10 2016 216 136 A1 discloses a method for adjusting a volume flow or a conveyed volume of a hydraulic actuator arrangement.

[0003] DE 10 2009 056 673 B4 discloses a hydraulic system, a torque transmission device and a method for calibrating a pressure sensor.

[0004] From publication EP 2 851 277 A1, an electro-hydraulic actuator for adjusting the height of a vehicle is known, in which an electric motor drives a pump in two directions of rotation. An adaptation or determination of the time- or temperature-dependent offset of pressure sensors is not known from this publication.

[0005] Furthermore, clutch actuators are known that serve for the automated actuation of friction clutches, particularly in the drive trains of motor vehicles, for example, to disconnect an internal combustion engine from a transmission or to connect them frictionally. For this purpose, clutch actuators are known in which the friction clutch is actuated along an actuation path by a clutch cylinder piston acting on an actuating element, for example, a disc spring or lever elements, along the actuating element. The system pressure required for displacing the clutch cylinder piston is provided by means of a hydrostatic clutch actuator, as is known from German patent application DE 10 2010 047 800 A1.In this system, an electric motor moves a master cylinder piston, which, via a hydrostatic system, acts on the clutch cylinder. Thus, the displacement of the master cylinder piston, or the rotation angle of the electric motor's rotor, can be correlated with the actuation path of the friction clutch, provided the gear ratio between the rotor and the master cylinder piston is known. A clutch characteristic curve then allows the corresponding torque transmitted via the friction clutch to be assigned to this actuation path.

[0006] A clutch actuator is known from publication WO 95 / 26472 A1, in which the clutch cylinder piston is actuated by means of a hydraulic pump, wherein at least one hydraulic valve is provided between the pump and the clutch cylinder for controlling the flow rate of the hydraulic fluid. The actuation stroke is detected by means of a separate sensor.

[0007] From publication WO 2015 / 120846 A1, a clutch actuator is known in which a clutch cylinder actuating the friction clutch along an actuation path is directly supplied with pressure medium from an electrically driven pump without the interposition of valves.

[0008] The object of the invention is the further development of a method for controlling an electrohydraulic actuator. In particular, the object of the invention is to propose a method for controlling an electrohydraulic actuator in which an offset of existing pressure sensors is robustly determined and compensated.

[0009] The problem is solved by the subject matter of claim 1. The dependent claims describe advantageous embodiments of the subject matter of claim 1.

[0010] The proposed method serves to control an electro-hydraulically operated actuator with two pressure lines supplied with pressure medium, depending on the direction of rotation of an electric motor driving a pump. The actuator and the method controlling it are intended, in particular, for a motor vehicle powertrain. The actuator can, for example, be used to actuate two friction clutches. For instance, it can be configured as two friction clutches of a dual-clutch transmission, or as one friction clutch between an internal combustion engine and a transmission, and another friction clutch for engaging an electric motor in a hybrid powertrain.For example, two actuators can be connected in series, with one actuator using one pressure line to actuate a friction clutch of a dual clutch, and the other pressure line alternately actuating, for example, the friction clutch for engaging the electric motor. The friction clutches can be closed, for example, by applying pressure to each of the pressure lines.

[0011] A pressure sensor is installed in each pressure line to control the electro-hydraulic actuator. A dual-pressure valve is connected between a pressure medium reservoir and the pressure lines to supply the pump with hydraulic fluid. Depending on the direction of rotation of the electric motor driving the pump and the position of the dual-pressure valve, the pump draws in hydraulic fluid, such as oil, hydraulic fluid, or the like, through one pressure line and supplies the other pressure line with hydraulic fluid, thereby generating hydraulic pressure.

[0012] The control of devices actuated by the pressure lines, such as friction clutches, brakes, hydraulic cylinders, and the like, is achieved by a control unit that controls the electric motor based on pressure signals detected by pressure sensors located in the pressure lines. For example, the pressure sensors determine whether a pressure line is connected to the hydraulic reservoir without pressure, thus ensuring, for instance, that a friction clutch is reliably open. It has been observed that commercially available pressure sensors exhibit a variable offset over their lifespan, depending on temperature and / or other factors. To nevertheless achieve reliable and robust pressure measurement of the pressure present in the pressure lines using the pressure sensors, this offset is calculated and compensated for.To avoid an incorrect determination of the offset, for example in an undefined state of the dual-pressure valve with residual pressure remaining in the pressure line, the offset of each of the pressure sensors is only determined and compensated when the associated pressure line is connected to the pressure medium reservoir without pressure.

[0013] According to the invention, the reliable determination of the connection between a first pressure line and the pressure medium reservoir, i.e., with a dual-pressure valve connected to this line to determine the offset of the pressure sensor arranged on this pressure line, is achieved by determining a pressure above a predetermined threshold value in the second pressure line. This pressure in the second pressure line is advantageously determined by means of a second pressure sensor in the second pressure line. Since this second pressure sensor may also have an offset that is not yet compensated, the threshold value is preferably calculated as the sum of the maximum expected offset of the (second) pressure sensor and a minimum switching pressure of the dual-pressure valve. After determining the offset of the first pressure sensor, the offset of the second pressure sensor can then be determined accordingly with the second pressure line connected to the reservoir.Depending on the frequency of offset measurements from the two pressure sensors, the threshold value can be changed. At the very least, this threshold value can be adapted based on factors such as lifespan, temperature, and / or similar considerations.

[0014] To prevent an incorrectly determined offset due to a pressure drop in the corresponding pressure line caused by a flow rate, for example, a pressure drop, the offset of a pressure sensor can be determined when the flow rate in the pressure line falls below a predefined threshold. This threshold can also be adjustable. For example, the offset can be determined when the pump is off, thus sufficiently minimizing the flow rate if necessary. In this case, residual pressure may remain in the other pressure line and generate a further flow rate. Alternatively or additionally, the offset of a first pressure sensor in a first pressure line can only be determined if the pressure change in the second pressure line is less than a predefined, for example, adjustable, threshold.

[0015] The invention is explained in more detail with reference to the embodiment shown in the single figure. This figure shows a circuit diagram of an electro-hydraulically operated actuator.

[0016] The electro-hydraulic actuator 1 contains the pump 2, which is driven by the electric motor 3. Depending on the direction of rotation of the electric motor 3, the pump 2 delivers hydraulic fluid into one of the two pressure lines 4, 5. The pump 2 draws hydraulic fluid from the hydraulic fluid reservoir 6 via the other pressure line 4, 5. The dual-pressure valve 7 controls the hydraulic fluid flow. The pressure lines 4, 5 each supply a device configured as a consumer, for example, a slave cylinder of a friction clutch, a brake, or a shock absorber.

[0017] A pressure sensor 8, 9 is provided for each of the two pressure lines 4, 5 to monitor the pressure and to control the downstream equipment. The offset pressure sensors 8, 9 are regularly adapted, i.e., their offset is compensated. For this purpose, their offset is only measured when pressure lines 4, 5 are connected to the pressure medium reservoir 6.

[0018] For example, pressure sensor 8 is calibrated when pressure line 4 is connected to the pressure medium reservoir 6. For this to occur, the dual-pressure valve 7, shown here in an undefined position, must be in position II, meaning it must seal pressure line 5 against pressure medium reservoir 6. This ensures that the passage from pressure line 4 to pressure medium reservoir 6 is open and pressure-free. This is verified by checking whether the pressure signal at pressure sensor 9 exceeds a predefined threshold. The threshold is determined by the sum of the minimum switching pressure of dual-pressure valve 7 and the maximum offset of pressure sensor 9. The offset of pressure sensor 8 is then determined and compensated for.

[0019] The adaptation of the pressure sensor 9 then takes place when the pressure of the pressure line 4 exceeds the threshold value and thus when the dual pressure valve 7 is switched to switching position I. The exceedance of the threshold value is checked by means of the pressure sensor 8 and if the threshold value is exceeded, the offset of the pressure sensor 9 is determined and compensated.

[0020] Additionally, offsets of the pressure sensors 8, 9 influenced by existing volume flows can be eliminated by determining the pressure drop of pressure sensor 8, 9 over the time of offset determination of the other pressure sensor 9, 8 and, if a predetermined threshold value of the pressure change rate is undershot, determining and compensating the offset of the pressure-free pressure sensor 8, 9.

[0021] When determining the offset of one of the pressure sensors 8, 9, it may be advantageous to switch off the pump 2 during this time to avoid high volume flows in the pressure-free pressure line 4, 5. Reference symbol list 1 actuator 2 pumps 3 Electric motor 4 Pressure line 5 Pressure line 6 Pressure medium reservoir 7 Dual pressure valve 8 Pressure sensor 9 Pressure sensor I Switch position II Switch position

Claims

[1] Method for controlling an electro-hydraulically operated actuator (1) with two pressure lines (4, 5) supplied with pressure medium depending on a direction of rotation of an electric motor (3) operating a pump (2), wherein a pressure sensor (8, 9) is arranged in each pressure line (4, 5) and a double pressure valve (7) is connected between a pressure medium reservoir (6) and the pressure lines (4, 5), wherein an offset of each of the pressure sensors (8, 9) is determined and compensated only when the associated pressure line (4, 5) is connected to the pressure medium reservoir (6) without pressure, characterized by , that the offset of a first pressure sensor (8, 9) in a first pressure line (4, 5) is determined when a pressure above a predetermined threshold is detected at the second pressure line (5, 4). [2] Method according to claim 1, characterized by, that the pressure of the second pressure line (5, 4) is determined by means of a second pressure sensor (9, 8) in the second pressure line (5, 4). [3] Method according to claim 2, characterized by , that the offset of the second pressure sensor (9, 8) is then determined when the second pressure line (5, 4) is connected to the pressure medium reservoir (6). [4] Method according to any one of claims 1 to 3, characterized by , that the threshold value is formed from the sum of a maximum expected offset of the pressure sensor (8, 9) and a minimum switching pressure of the dual pressure valve (7). [5] Method according to any one of claims 1 to 4, characterized by , that the determination of the offset of a pressure sensor (8, 9) is provided when the volume flow of the pressure line (4, 5) falls below a predetermined threshold. [6] Method according to claim 5, characterized by , that the offset is determined with the pump (2) at rest. [7] Method according to claim 5 or 6, characterized by , that a determination of the offset of a first pressure sensor (8, 9) in a first pressure line (4, 5) is only carried out if a pressure change in the second pressure line (5, 4) is less than a specified threshold. [8] Method according to any one of claims 1 to 7 for actuating two friction clutches. [9] Method according to claim 8, characterized by , that the friction clutches are closed by means of a pressure applied to each pressure line (4, 5).

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