DE112017003620B4 - Method for maintaining a pressure level of a hydraulic fluid in a hydraulic actuator arrangement - Google Patents

Abstract

Method for maintaining a pressure level of a hydraulic fluid in a hydraulic actuator arrangement (100), in particular for maintaining a pressure level above a target pressure value assigned to an operating point, wherein in the hydraulic actuator arrangement (100) a volume flow source (104) via a pressure line (106) filled with the hydraulic fluid is connected to a hydraulic cylinder (108), and the operating point corresponds to a position of the actuator arrangement (100), the method comprising a control hysteresis (166, 168), characterized in that a volume of hydraulic fluid required to adjust the pressure level is in a low load range (128) is adjusted via a rotation angle control and in a higher load range (130) via a pressure control.

Description

The invention relates to a method for maintaining a pressure level of a hydraulic fluid in a hydraulic actuator arrangement, in particular for maintaining a pressure level above a target pressure value assigned to an operating point, wherein in the hydraulic actuator arrangement a volume flow source is connected to a hydraulic cylinder via a pressure line filled with the hydraulic fluid, and the Operating point corresponds to a position of the actuator arrangement.

DE 10 2004 003 931 A1 discloses a method for controlling a pressure and/or a volume flow of a hydraulic medium in a hydraulic circuit, in particular for a dual clutch transmission of a motor vehicle.

US 4,430,859 A discloses a hydraulic circuit and a charging valve assembly.

• - Einregeln der Pumpe auf den Betriebspunkt-Drehzahlwert, so dass die Pumpe einen dem Betriebspunkt-Drehzahlwert entsprechenden Fluidvolumenstrom fördert; und
• - Integrieren des Fluidvolumenstromes über die Zeit, bis zu einem Abschluss-Betriebszustand der Aktuatoranordnung, bei dem der Ansteuerwert der Pumpe kleiner gleich dem Betriebspunkt-Ansteuerwert ist. Der Betriebspunkt ist vorzugsweise der Einrückpunkt einer Reibkupplung, die mittels der hydraulischen Aktuatoranordnung betätigt wird.

From the DE 10 2012 021 211 A1 a method for determining a setting parameter in a hydraulic actuator arrangement for a motor vehicle drive train is known, the actuator arrangement having a pump and a hydraulic cylinder, a pressure connection of the pump being connected to a connection of the hydraulic cylinder, the setting parameter being a function of the volume of the fluid, which is to be promoted by the pump to set up a predetermined operating point of the actuator arrangement, the operating point being defined by a pair of values of an operating point speed value of the pump and an operating point control value of the pump, in particular an electrical current of an electric motor of the pump. The procedure has the following steps:

• - Adjusting the pump to the operating point speed value, so that the pump delivers a fluid volume flow corresponding to the operating point speed value; and
• - Integrating the fluid volume flow over time until a final operating state of the actuator arrangement is reached, in which the control value of the pump is less than or equal to the operating point control value. The operating point is preferably the engagement point of a friction clutch that is actuated by means of the hydraulic actuator arrangement.

From the WO 2015/154767 A2 a clutch module for a drive train of a motor vehicle is known, with a clutch device that can be driven by an output shaft of an internal combustion engine and has an adjustable pressure plate, and with an actuating device that has an actuating piston and a pump that is hydraulically connected to the actuating piston by means of a line system, the pump being so is accommodated in a pump receiving housing, which pump receiving housing is connected in a rotationally fixed manner to a counter-pressure plate of the coupling device, that the pump is driven in at least one operating state of the internal combustion engine by interaction with the output shaft, and the actuating piston is connected to the pump with at least one high-pressure line in such a way that the Pressure plate can be moved between a disengaged position and an engaged position depending on a pressure level generated by the pump in the high-pressure line, with a cross-sectional limiting device which influences the pressure level in the high-pressure line and reduces the line cross-section being arranged in the line system.

From the WO 2015/149778 A1 a transmission control is known for fluidly actuating a transmission, which comprises a plurality of gears that can be selected and shifted using a transmission actuator device, and for fluidly actuating two partial clutches of a double clutch, the transmission control comprising two reversing pump actuators, each of which is assigned one of the partial clutches and which each have two connections to which a fluidic AND valve is connected, which has a tank connection as the third connection, the transmission actuator device being connected to the two reversing pump actuators via a fluidic OR valve.

The DE 10 2015 204 383 A1 describes a method for setting and adapting an operating point of a hydraulic actuator arrangement, in which a volume flow source is connected to a hydraulic cylinder via a pressure line filled with a hydraulic fluid, a volume of the hydraulic fluid being controlled via the volume flow source and the operating point of a position of the actuator arrangement at a predetermined Parameters of a device to be actuated by the actuator arrangement corresponds, the volume of hydraulic fluid required to set the operating point being derived from a rotational position of a volume flow source motor and / or the volume flow source. The volume of hydraulic fluid required to set the operating point is set below a predetermined operating point via the rotation angle control and above the predetermined operating point via a pressure control carried out by a pressure/angle regulator. This means that in areas where the pressure values cannot be measured adequately Pressure control replaced by rotation angle control.

The DE 10 2016 201 049 A1 describes a method for precisely setting an operating point of a hydraulic actuator arrangement, in which a volume flow source is connected to at least one hydraulic cylinder via a pressure line filled with a hydraulic fluid, a volume of the hydraulic fluid being controlled via the volume flow source and the operating point of a position of the hydraulic actuator arrangement at a predetermined parameters of a device to be actuated by the actuator arrangement, wherein angular increments and / or revolutions covered by the volume flow source are counted to determine the operating point from the start of actuation of the hydraulic actuator arrangement.

The invention is based on the object of improving a method mentioned at the outset.

The object is achieved with a method for maintaining a pressure level of a hydraulic fluid in a hydraulic actuator arrangement, in particular for maintaining a pressure level above a target pressure value assigned to an operating point, wherein in the hydraulic actuator arrangement a volume flow source is connected to a hydraulic cylinder via a pressure line filled with the hydraulic fluid, and the operating point corresponds to a position of the actuator arrangement, the method comprising control hysteresis.

Because the method includes control hysteresis, power consumption of the actuator arrangement is reduced in higher load ranges, that is to say higher pressure ranges.

The control hysteresis can be a pressure control hysteresis. The control hysteresis is preferably asymmetrical, so that, for example, a clutch that can be actuated by the actuator arrangement can be kept slip-free. The control hysteresis can be parameterized. The method can include a hysteresis map. This allows the method to be adapted, for example, to a torque to be transmitted by the clutch.

The volume flow source can have a pump driven by an electric motor. Preferably, the volume flow source is switched on as soon as a pressure in a hydraulic cylinder reaches or falls below a lower switching point, and the volume flow source is switched off as soon as a pressure in the hydraulic cylinder reaches or exceeds an upper switching point.

According to the invention, the volume of hydraulic fluid required to adjust the pressure level is adjusted in low load ranges via a rotation angle control and in higher load ranges via a pressure control. This can ensure that an exact characteristic curve can be determined in the most diverse positions of the hydraulic actuator arrangement, since in the areas where the pressure values are only insufficiently measurable, the pressure control is replaced by the rotation angle control.

A volume of hydraulic fluid required to set an operating point can be derived from a rotational position of a volume flow source motor and/or the volume flow source. This has the advantage that the proportionality between the volume delivered by the volume flow source, for example a pump or a hydrostatic master piston, and the angular position of the volume flow source is utilized, since a predetermined volume stroke occurs per revolution of the volume flow source. By using the angle of rotation of the volume flow source or the motor and the fixed relationship between the angle of rotation and the volume that is conveyed, a characteristic curve of the hydraulic actuator arrangement can be reliably created, preferably in low pressure ranges. Since the angle of rotation of the volume flow source can be measured directly, there is no need to integrate the volume flow of the hydraulic fluid.

The actuator arrangement can be a clutch actuator arrangement. The clutch actuator arrangement can be kept slip-free by means of the control hysteresis. The clutch actuator arrangement can have at least one clutch with at least one clutch disk. The clutch disc can be for a friction clutch device. The friction clutch device can be for a drive train of an internal combustion engine-driven motor vehicle. The drive train can have an internal combustion engine. The drive train can have a torsional vibration damper. The drive train can have a transmission. The drive train can have at least one drivable wheel. The friction clutch device can be arranged in the drive train. The friction clutch device can be arranged between the internal combustion engine and a transmission. The friction clutch device can be arranged between a torsional vibration damper and a transmission.

The powertrain may be a hybrid powertrain for a motor vehicle. The powertrain may be a parallel hybrid powertrain. The powertrain may be a full hybrid powertrain be. The drive train may have a first energy converter and a second energy converter. The first energy converter can be used to convert chemical energy into kinetic energy. An internal combustion engine can be the first energy converter. The internal combustion engine can be operated with a hydrocarbon, such as gasoline, diesel, liquefied petroleum gas (LPG, GPL), compressed natural gas (CNG) or liquid natural gas (Liquefied Natural Gas, LNG). The internal combustion engine can be operated with hydrogen. A first energy storage device can be provided to supply energy to the first energy converter. The first energy storage can be a fluid tank. The second energy converter can be used to convert electrical energy into kinetic energy. The electric machine can be the second energy converter. The electric machine can be operated as a motor. The electrical machine can be operated as a generator. The electric machine can structurally combine a motor and a generator. A second energy storage device can be provided to supply energy to the second energy converter. The second energy storage can be an electrical energy storage. The second energy storage can be an accumulator. The first energy converter and/or the second energy converter can be used to drive the motor vehicle selectively or in parallel.

The friction clutch device can have an input part. The friction clutch device may have an output part. The input part can be driven using the internal combustion engine. The gearbox can be driven using the output part. The friction clutch device can enable starting and changing a gear ratio.

The friction clutch device can have a single clutch. The friction clutch device can have a double clutch. The friction clutch device can have a dry clutch. The friction clutch device may have a wet clutch. The friction clutch device can have a single-disc clutch. The friction clutch device can have a multi-disc clutch. The friction clutch device can have an automatically opening clutch. The friction clutch device can have an automatically closing clutch. The friction clutch device may have a pressed clutch. The friction clutch device can have a pulled clutch. The friction clutch device can be actuated using a clutch pedal. The friction clutch device can be operated automatically.

The friction clutch device can start from a completely disengaged operating position, in which essentially no power transmission takes place between an input part and an output part, up to a completely engaged operating position, in which essentially complete power transmission takes place between the input part and the output part, depending on the actuation enable mechanical power transmission, with power transmission between the input part and the output part taking place frictionally. Conversely, starting from a fully engaged actuation position, in which essentially complete power transmission takes place between the input part and the output part, up to a completely disengaged actuation position, in which essentially no power transfer takes place between the input part and the output part, a decreasing mechanical depending on the actuation Power transmission may be possible. A fully engaged operating position may be a closed operating position. A fully disengaged operating position may be an open operating position.

In summary and in other words, the invention results in, among other things, a solution to the problem that pumps of all types are subject to leakage, in particular pressure-dependent leakage, which means that a technically completely tight system structure is not possible. The result of this is that systems known from the prior art experience a pressure drop due to leaks, which always has to be compensated for by a control system. Continuous readjustment of the system can, under certain circumstances, mean a high power consumption of the actuator, as the leakage volume flows are only very small. This results in a low speed for the pump and results in poor pump motor efficiency, as a high load torque (pressure + friction) requires a permanently high motor current, which leads to high ohmic losses. Due to the Stribeck friction, the losses increase at low speeds and thus ensure an increased power requirement.

The ones from the DE 10 2015 204 383 A1 Known pressure control can be supplemented by the method according to the invention with a targeted controller hysteresis, which can be parameterized depending on the operating point and/or the need for torque accuracy. The controller hysteresis helps to minimize the speed-dependent friction when holding the pump, so that only a small motor current, if any, is required during these periods. This is due to the fact that the hysteresis causes larger Set the required volume flows to bring the clutch back to overpressure. The higher volume flows can be carried out with high dynamics and speed, which leads to less friction in the pump. The motor current during these periods decreases due to the lower friction in the pump as opposed to constant pumping.

The method is preferably designed so that the volume control is active in areas of low load ranges, since the slope of the clutch characteristic curve is very flat in this area. In areas of higher load ranges, i.e. in the area of the desired torque transfer, the pressure control is active. This can be supplemented by a hysteresis in order to bring the clutch into excess pressure. The hysteresis width is preferably designed asymmetrically so that at least the target torque is always met. In an example case, the pump pressure control would regulate the target pressure from 35bar to 40bar, switch off and wait until the pressure drops to 35bar due to a leak. The control activates again and increases the pressure again to 40bar. In real applications, this pressure delta depends in particular on the nominal torque of the clutch. The hysteresis can be deactivated if necessary, for example if a high torque accuracy is required in the event of a torque overlap between two clutches or during a start-up and therefore over-pressure must be avoided.

The implementation of the hysteresis is preferably designed so that its width can be adjusted or calibrated according to the system requirements. This makes it possible to approximate the optimal hysteresis width to the requirements of a higher-level control structure. For example, if high dynamics and/or high availability are required, the hysteresis width is used to set a compromise between the requirement and the power consumption. However, if reduced dynamics are required and availability is not the focus, the optimum for low power consumption can be set using the hysteresis width. On average over time, this results in a significantly lower power consumption of the clutch actuator system.

Furthermore, the hysteresis can be defined in the form of a switch-on and switch-off hysteresis, so that the pressure cannot fall below a target pressure. If friction-related pressure hysteresis of a clutch characteristic curve is taken into account, the switch-off hysteresis must be selected accordingly above the pressure hysteresis that drops. The switch-on hysteresis is selected by a smaller band than the switch-off band around the setpoint (increasing pressure hysteresis). For example, if the switch-off hysteresis is calibrated to +5% of the target pressure and the switch-on hysteresis to +1% of the target pressure, a target pressure deviation of between +1% and +5% of the target pressure is achieved.

The method according to the invention can include pressure control. However, the inventive teaching can also be applied to other control procedures. If the target system (pump actuator + central releaser) is supplemented with a central releaser with position measurement, a position control of the central releaser would be possible. The method according to the invention can therefore also be used for path control.

The invention provides a pressure control hysteresis which ensures a reduction in power consumption in a hydraulic actuator arrangement in higher load ranges. In particular, this hysteresis can only be used in slip-free operating states. In particular, a clutch can be kept slip-free by means of asymmetrical hysteresis. In particular, a pump actuator can be operated in a targeted manner in higher efficiency ranges. In particular, the hysteresis can be parameterized using a hysteresis map, depending on the operating point of the clutch. In particular, a hysteresis parameterization can be adapted depending on the need for torque accuracy.

An exemplary embodiment of the invention is described in more detail below with reference to figures. Further features and advantages arise from this description. Specific features of this exemplary embodiment may represent general features of the invention. Features of this exemplary embodiment associated with other features can also represent individual features of the invention.

• 1 eine hydraulische Kupplungsaktoranordnung,
• 2 eine Kupplungskennlinie der hydraulischen Kupplungsaktoranordnung aus 1,
• 3 ein Zustandsübergangsdiagramm eines Verfahrens zur Einstellung und Adaption eines Betriebspunktes der Kupplungsaktoranordnung aus 1, mit einer Regelung zur Aufrechterhaltung eines Druckniveaus, und
• 4 ausschnittsweise die Kupplungskennlinie der hydraulischen Kupplungsaktoranordnung, ergänzt um eine Darstellung einer Druckregelungshysterese.

It shows schematically and by way of example:

• 1 a hydraulic clutch actuator arrangement,
• 2 a clutch characteristic curve of the hydraulic clutch actuator arrangement 1 ,
• 3 a state transition diagram of a method for setting and adapting an operating point of the clutch actuator arrangement 1 , with a control for maintaining a pressure level, and
• 4 a section of the clutch characteristic curve of the hydraulic clutch actuator arrangement, supplemented by a representation of a pressure control hysteresis.

1 shows an exemplary embodiment of an actuator arrangement according to the invention, designed as a hydraulic clutch actuator arrangement 100, as used, for example, in a drive train of a motor vehicle, the hydraulic clutch actuator arrangement 100 being used to actuate a clutch 102. A volume flow source designed, for example, as a pump 104 is connected via a high-pressure hydraulic line 106 to a hydraulic cylinder 108, which acts on the clutch 102 via an engagement bearing 110. Via the pump 104, hydraulic fluid is sucked in from a hydraulic reservoir 112 via a low-pressure hydraulic line 114 by the pump 104 and fed to the hydraulic cylinder 108 via the high-pressure hydraulic line 106. The hydraulic fluid displaces a piston of the hydraulic cylinder 108, thereby moving the engagement bearing 110 and also displacing the clutch 102.

The pump 104 is driven by an electric motor 116, on which an angle sensor 118 is positioned, which determines the rotational position of the electric motor 116 in the form of an angle of rotation. A pressure sensor 120 is positioned in the hydraulic cylinder 108 for measuring the pressure p of the hydraulic fluid that occurs in the high-pressure hydraulic line 106. The angle sensor 118 can preferably be designed as a multiturn sensor, which also detects the angle of rotation over 360°.

If the pump 104 is rotated sufficiently quickly, a leakage can be neglected or represented reproducibly, so that a clutch characteristic curve 122 can be created, which represents a pressure p in the high-pressure hydraulic line 106 or in the hydraulic cylinder 108 over a path s of the piston of the hydraulic cylinder 108. Such a clutch characteristic curve 122 is shown in a diagram in 2 shown. Due to friction, the clutch characteristic curve 122 has a pressure hysteresis. As a result, the clutch characteristic curve 122 has two branches. An ascending branch 124 of the clutch characteristic curve 122 corresponds to the pressure p during a pressure build-up to increase the distance s. A falling branch 126 of the clutch characteristic curve 122 corresponds to the pressure p during a pressure drop to reduce the distance s.

A method for setting and adapting an operating point of the clutch actuator arrangement 100 is designed so that in a low load range 128, a volume control 138 is active, since the slope of the clutch characteristic curve 122 is very flat in this range. In a higher load range 130, particularly in areas of torque transmission via the clutch 102, a pressure control is active. As a result, in the areas in which the pressure values can only be measured insufficiently, the pressure control is replaced by a volume control 138, in particular a rotation angle control of a rotation angle of the electric motor 116 or the pump 104. Such a procedure is in the DE 10 2015 204 383 A1 described, the relevant disclosure content of which is expressly included.

In order to maintain a pressure level of the hydraulic fluid in the hydraulic cylinder 108 above a target pressure value assigned to an operating point, the method for setting and adapting an operating point of the clutch actuator arrangement 100 is supplemented by a pressure control hysteresis. Due to the pressure control hysteresis, the clutch 102 can be brought into overpressure. For this purpose, the method includes a switch-on limit 132 and a switch-off limit 134 in the higher load range 130.

In the present case, the switch-on limit 132 is a pressure-displacement line that runs approximately parallel to the descending branch 126 of the clutch characteristic curve 122. The switch-on limit 132 assigns a predetermined path s a pressure p which is slightly higher, for example 1% higher, than a pressure p of the descending branch 126 of the clutch characteristic curve 122 assigned to this path s.

In the present case, the switch-off limit 134 is a pressure-displacement line that runs approximately parallel to the ascending branch 124 of the clutch characteristic curve 122. The switch-off limit 134 assigns a predetermined path s a pressure p that is slightly higher, for example 1% higher, than a pressure p of the ascending branch 124 of the clutch characteristic curve 122 assigned to this path s. Alternatively, the switch-off limit 134 assigns a predetermined path s Pressure p which is higher, for example 5% higher, than a pressure p of the descending branch 126 of the clutch characteristic curve 122 assigned to this path s.

The switch-on limit 132 and the switch-off limit 134 are essential components for a pressure control hysteresis, which is described in more detail below.

3 shows a state transition diagram of the method for setting and adapting an operating point of the clutch actuator arrangement 100 with corresponding control for maintaining the pressure level. First, a current state 136 is determined, determining whether the clutch actuator arrangement 100 is in the low load range 128 or in the higher load range 130. If the clutch actuator arrangement 100 is in the low load range 128, the method provides volume control 138. If the clutch actuator arrangement 100 is in the higher load range 130, a pressure control 140 is carried out by the method. During the process, due to a changing operation of the clutch actuator arrangement 100, a state transition 142 can take place from a volume control 138 to a pressure control 140 and/or a state transition 144 from the pressure control 140 to the volume control 138.

In the state of pressure control 140, the sub-states “pressure control hysteresis on” 146 and “pressure control hysteresis off” 148 can be present. A state transition 150 from “pressure control hysteresis on” 146 to “pressure control hysteresis off” 148 can take place, in particular if a target pressure, for example a target pressure defined by the descending branch 126 of the clutch characteristic curve 122, is undershot. The pressure control hysteresis should also be able to be deactivated as required, if, for example, in the event of a torque overlap between two clutches or during a start-up, a high torque accuracy of the clutch 102 is required and overpressure must therefore be avoided.

In addition, a state transition 152 from “pressure control hysteresis off” 148 to “pressure control hysteresis on” 146 can take place, which activates the pressure control hysteresis, whereby the clutch 102 is overpressurized.

4 shows a section of the clutch characteristic curve 122 of the clutch actuator arrangement 100 in a diagram, supplemented by a representation of the pressure control hysteresis. The ascending branch 124 and the descending branch 126 of the clutch characteristic curve 122, the switch-on limit 132 and the switch-off limit 134 are shown as pressure curves over the path s of the piston of the hydraulic cylinder 108. A transferable clutch torque M of the clutch 102 over the distance s is represented by a torque characteristic curve 154.

A target torque 156 is assigned to an operating point of the clutch actuator arrangement 100. A path s assigned to the target torque 156 and thus to the operating point can be shown in the diagram 4 can be read and is represented by a vertical line. The intersection of the vertical line through the torque characteristic curve 154 corresponds to the target torque 156. However, the target torque 156 can also be a different value, that is, further to the left or further to the right of the vertical line 4 lie on the torque characteristic curve 154. The target torque 156 is particularly dependent on the torque that the clutch 102 must be able to transmit. Based on the in 4 The target torque 156 shown below describes how the pressure control hysteresis works. An intersection of the vertical line with the descending branch 126 of the clutch characteristic curve 122 results in the target pressure at the operating point.

An intersection of the vertical line corresponding to the path s of the operating point 4 with the switch-on limit 132 is a lower switching point 158. The lower switching point 158 corresponds to the switch-on point at the operating point. An intersection of the vertical line corresponding to the path s of the operating point 4 with the switch-off limit 134 is an upper switching point 160. The upper switching point 160 corresponds to the switch-off point at the operating point. If the pressure p in the hydraulic cylinder 108 reaches or falls below the lower switching point 158 when the pump 104 is switched off, the pump 104 is switched on. If the pressure p in the hydraulic cylinder 108 reaches or exceeds the upper switching point 160 when the pump 104 is switched on, the pump 104 is switched off.

A pressure value assigned to the lower switching point 158 at the operating point is slightly higher, for example 1% higher, than a value of the descending branch 126 of the clutch characteristic curve 122 assigned to the operating point. This means that the pump 104 switches on at a pressure p that is slightly larger than the target pressure assigned to the operating point. A path s assigned to this slightly larger pressure p results in the diagram of 4 as the intersection of a horizontal switch-on line 162 with the descending branch 126 of the clutch characteristic curve 122.

A pressure value assigned to the upper switching point 160 at the operating point is higher than a value of the switch-on limit 132 assigned to the operating point and slightly higher, for example 5% higher, than a value of the switch-off limit 134 assigned to the operating point. This results in the pump 104 only at one Pressure p switches off, which is slightly larger than the pressure of the ascending branch 124 of the clutch characteristic curve 122 assigned to the operating point. A path s assigned to this slightly larger pressure p results in the diagram of 4 as the intersection of a horizontal switch-off line 164 with the ascending branch 124 of the clutch characteristic curve 122.

The hysteresis of the clutch characteristic curve 122, whereby the ascending branch 124 of the clutch characteristic curve 122 is not congruent with the descending branch 126 of the clutch characteristic curve 122, results in the pressure control hysteresis due to the previously described process sequence. The pressure control hysteresis has an ascending branch 166 and a descending branch 168.

If the pressure p in the hydraulic cylinder 108 reaches the lower switching point 158, the pump 104 is switched on and the pressure p increases in accordance with the ascending branch 166 of the pressure control hysteresis. Due to an increasing path s, the ascending branch 166 of the pressure control hysteresis leads from the descending branch 126 of the clutch characteristic curve 122 to the ascending branch 124 of the clutch characteristic curve 122. If the pressure p in the hydraulic cylinder 108 reaches the upper switching point 160, the pump 104 is switched off and the pressure p falls slowly due to leaks and in accordance with the descending branch 168 of the pressure control hysteresis. Due to a resulting decreasing path s, the descending branch 168 of the pressure control hysteresis leads from the ascending branch 124 of the clutch characteristic curve 122 to the descending branch 126 of the clutch characteristic curve 122.

The ascending branch 166 and the descending branch 168 of the pressure control hysteresis correspond to pressures that are above the operating point assigned to the target torque 156. As a result, the pressure control hysteresis is designed asymmetrically and the target torque 156 is always exceeded. This ensures slip-free operation of the clutch 102.

Reference symbol list

100

Actuator arrangement, clutch actuator arrangement

102

coupling

104

pump

106

High pressure hydraulic line

108

Hydraulic cylinder

110

Engaging bearing

112

Hydraulic reservoir

114

Low pressure hydraulic line

116

Electric motor

118

Angle sensor

120

Pressure sensor

122

Clutch characteristic curve

124

ascending branch

126

descending branch

128

low load ranges

130

higher load range

132

Switch-on limit

134

Switch-off limit

136

Condition

138

Volume control

140

Pressure control

142

State transition

144

State transition

146

Pressure control hysteresis

148

Pressure control hysteresis off

150

State transition

152

State transition

154

Torque characteristic

156

Target moment

158

lower switching point

160

upper switching point

162

Switch-on line

164

Shutdown line

166

ascending branch

168

descending branch

Claims (9)

Method for maintaining a pressure level of a hydraulic fluid in a hydraulic actuator arrangement (100), in particular for maintaining a pressure level above a target pressure value assigned to an operating point, wherein in the hydraulic actuator arrangement (100) a volume flow source (104) via a pressure line (106) filled with the hydraulic fluid is connected to a hydraulic cylinder (108), and the operating point corresponds to a position of the actuator arrangement (100), the method comprising a control hysteresis (166, 168), characterized in that a volume of hydraulic fluid required to adjust the pressure level is in a low load range (128) is adjusted via a rotation angle control and in a higher load range (130) via a pressure control. Procedure according to Claim 1 , characterized in that the control hysteresis is a pressure control hysteresis (166, 168). Method according to at least one of the preceding claims, characterized in that the control hysteresis (166, 168) is asymmetrical. Method according to at least one of the preceding claims, characterized in that the volume flow source has a pump (104) driven by an electric motor (116). Method according to at least one of the preceding claims, characterized in that the volume flow source (104) is switched on as soon as a pressure in the hydraulic cylinder (108) reaches or falls below a lower switching point (158), and that the volume flow source (104) is switched off as soon as a pressure in the hydraulic cylinder (108) reaches or exceeds an upper switching point (160). Method according to at least one of the preceding claims, characterized in that the control hysteresis (166, 168) can be parameterized. Method according to at least one of the preceding claims, characterized in that the method comprises a hysteresis map. Method according to at least one of the preceding claims, characterized in that the actuator arrangement is a clutch actuator arrangement (100). Procedure according to Claim 8 , characterized in that the clutch actuator arrangement (100) is kept slip-free by means of the control hysteresis (166, 168).

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