METHOD AND CONTROL DEVICE FOR OPERATING A DEVICE WITH A HYDRAULIC PRESSURE SOURCE

Description

[0001] The invention relates to a method for operating a device with a hydraulic pressure source and a controllable flow control valve according to the type defined in more detail in the preamble of claim 1. The invention further relates to a control unit for carrying out the method and a corresponding computer program.

[0002] Due to space constraints and increasing cost pressures, components of hydraulic systems, particularly those of automatic transmissions in vehicles, which include proportionally controlled flow control valves or pressure control valves, are being miniaturized. These proportionally controlled flow control valves are actuated via upstream valves. To reduce the required installation space, the proportionally controlled flow control valves and the upstream valves are being replaced by so-called directly actuated flow control valves. In these valves, an actuator, for example via an electromagnetically actuated plunger, interacts directly with a valve spool.

[0003] Due to miniaturization and the direct connection of the actuators to the flow control valves, the actuating forces required to operate the flow control valves are smaller than for valves with larger dimensions. This reduction in actuator actuating forces means that disturbances can have an undesirably large impact on the control of the flow control valves, resulting in so-called pressure imbalances within the system. One such disturbance is the flow forces that occur at the control edges of valves when large volumes of hydraulic fluid are passed through the flow control valves.

[0004] The flow forces counteract the actuating forces provided by the actuators. Therefore, the hydraulic supply to downstream systems of the flow control valves, such as switching elements and cooling systems of automatic transmissions, is either too high or too low. The set pressures deviate from the specified target pressure values ​​to such an extent that the required operating state is not reached within the desired operating times. These pressure imbalances or pressure shifts result in the systems not being controlled as intended by the set actuator force.

[0005] The magnitude of pressure shifts also depends on a multitude of operating parameters of a hydraulic system. This dependency means that the timing of a downstream system must either be adjusted according to the pressure shifts, or force changes in the actuators within the hydraulic system must be set to compensate for the pressure shifts resulting from the flow forces.

[0006] However, for complete compensation of the pressure shifts, knowledge of all external influencing factors, such as the current system pressure of a pressure source and an operating temperature, the internal influencing factors, such as the flow rate through the flow control valve, and the back pressure of the downstream system is required.

[0007] Currently, hydraulically actuated friction-based switching elements, such as friction clutches or brakes in automatic transmissions, are primarily integrated into the power flow of a vehicle's drivetrain via two-phase control routines. In the first phase, or pre-filling phase, the piston chamber of such a switching element is filled with oil. During this filling process, a high volume of hydraulic fluid is directed through a flow control valve toward the piston chamber. Only a slight back pressure exists between the flow control valve and the piston chamber. The friction-based switching element does not yet transmit any significant torque in this first phase. The filling of the piston chamber of the respective switching element is carried out with varying flow rates depending on the type of switching operation.

[0008] During the second phase, also known as the pressure control phase, the pressure in the piston chamber is precisely regulated to adjust the transmissible torque of a friction-fit switching element to the required level. The torque is intended to be proportional to the applied pressure. During this second phase, only minimal flow rates pass through the flow control valve, which is located upstream of the piston chamber of the switching element relative to the pressure source.

[0009] Due to the high flow rate through the flow control valve during the initial phase, the pressure drop in the flow control valve and in the line between the valve and the piston chamber must be compensated to fill the piston chamber of the switching element within the required timeframe. This is achieved by adjusting the pressure setpoint offset values ​​to compensate for the pressure drop in the flow control valve and the line, ensuring the piston chamber reaches its desired fill point at the required time. If lower flow rates or longer filling times are required, smaller offset values ​​are used.

[0010] Once the piston chamber is filled, the pressure control is initiated, assuming the switching element has reached its desired operating state. During pressure control, it is ideally assumed that no flow is directed towards the piston chamber through the flow control valve.

[0011] The control of switching elements always occurs via the temporal sequence of different pressures or actuator forces. Therefore, it is necessary to consider all changes in the operating state of the flow control valve, the switching element, and the supply pressure of the pressure source using comprehensive characteristic maps. The application of these characteristic maps must be specifically adapted for each switching element and each size.

[0012] Flow forces also significantly influence the operation of directly controlled systems. Therefore, attempts are made to compensate for these influences for each switching element using characteristic maps. Any changes in the geometries of the switching elements and flow control valves over their operating life must also be taken into account through subsequent applications to ensure the continued reliable operation of hydraulic systems.

[0013] Particularly in the transition zone between the pre-filling phase and the pressure control phase, and when large pressure gradients are present, significant deviations occur between the requested target operating states and the actual operating states during the actuation of hydraulic systems. Furthermore, downstream systems, especially those located downstream of flow control valves, may exhibit significant component elasticity or flexibility, which can make pressure control of switching elements particularly difficult.

[0014] DE 10 2019 210 248 A1 discloses a method for operating a powertrain unit.

[0015] From DE 10 2011 121 880 A1, a method considered to be the most obvious for actuating a hydraulically actuated clutch is known, in which environmental conditions are taken into account when controlling control elements.

[0016] A preferred object of the present invention is to reduce or eliminate at least one disadvantage of a previously known solution or to propose an alternative solution. In particular, a preferred object of the invention disclosed herein is to provide a method and a control unit for operating a device with a hydraulic pressure source and a controllable flow control valve, which are improved with respect to at least one of the following factors: feasibility, manufacturing time, manufacturing costs, manufacturing complexity, installation space utilization, operational reliability, sustainability, and / or component reliability. Further preferred objects may arise from the advantageous effects of the technology disclosed herein.

[0017] A particularly preferred object of the present invention is to provide a control logic for a device with a hydraulic pressure source and with a controllable flow control valve, by means of which situationally determinable compensation of all influencing factors from physical conditions can be carried out in a simple manner.

[0018] From a process engineering perspective, this problem(s) is solved starting from the preamble of claim 1 in conjunction with its characterizing features. A control unit and a computer program product are also the subject of further independent claims 9 and 10. Advantageous embodiments are the subject of the dependent claims and the following description. A method for operating a device with a hydraulic

[0019] A pressure source and a controllable flow control valve are proposed, at which a hydraulic pressure from the pressure source is applied and within whose area an actuating pressure for a hydraulically actuated switching element is set. The actuating pressure is applied downstream of the flow control valve in the area of ​​a piston chamber of the switching element, in which a piston is arranged to be longitudinally displaceable between two end positions.

[0020] In this context, the term "switching element" encompasses both positive-locking and friction-locking switching elements, each transmitting torque via a positive-locking or friction-locking connection. Such switching elements can be, for example, clutches or brakes, each transmitting torque via a friction-locking connection. The torque transmittable via such a friction-locking switching element varies depending on the closing force applied to the switching element and is preferably continuously adjustable. The closing force corresponds, for example, to a hydraulic pressure applied to the switching element. In contrast, the torque transmittable via a positive-locking switching element is not continuously adjustable.

[0021] The invention now comprises the technical teaching that a pre-control of the flow control valve is carried out depending on a hydraulic fluid volume flow that is to be guided through the flow control valve in order to generate a predetermined time profile of the actuating pressure in the piston chamber of the switching element.

[0022] In the method according to the invention, the determination of the transmission capacity of the flow control valve is thus carried out, in contrast to the prior art, as a function of the currently set operating state of the switching element. Pilot control of the flow control valve is performed in the hydraulic actuation of the switching element according to the invention, taking into account all known influencing factors. This is the case because the flow control valve is actuated as a function of the desired pressure in the piston chamber of the switching element, which must be set according to the operating state. In other words, the actuation of the switching element always takes place with pilot control of all known influencing factors and from the desired pressure in the piston chamber of the switching element.

[0023] The inventive method is based on the knowledge that the transmission capability of a switching element, such as a friction clutch or brake, is generally subject to a precisely defined sequence. The transmission capability is uniquely linked to the position of a clutch piston, which corresponds uniquely to a pressure in the piston chamber of a switching element. Thus, by controlling the pressure in the piston chamber, the transmission capability of a switching element can be determined, and the flow control valve can be actuated precisely and in the required manner without complex adaptation routines or extensive characteristic curves.

[0024] In the inventive method, which requires minimal control and regulation effort, the current filling volume of the piston chamber and the current component elasticity of the switching element are determined as a function of the actuating pressure over time. The component elasticity of the switching element varies depending on the position of the piston of the switching element.

[0025] The component elasticity is a determining factor for the pressure in the piston chamber of the switching element. The relationship between the current component elasticity and the pressure in the piston chamber of the switching element is such that the pressure increase in the piston chamber is comparatively low with high component elasticity despite a high hydraulic fluid flow rate, while the pressure increase is high with low component elasticity and a low hydraulic fluid flow rate.

[0026] Each pressure level in the piston chamber can be assigned a unique position of the piston. Using this relationship, the current volume of the piston chamber of the switching element can be determined. Additionally, the component elasticity, or elasticity characteristic, of the switching element can be easily determined via a functional relationship between the filling volume of the piston chamber and the pressure within the piston chamber. The change or derivative of this functional relationship between the volume of the piston chamber and the pressure within the piston chamber describes the elasticity characteristic.

[0027] The hydraulic fluid volume flow rate to be passed through the pressure regulating valve can be easily determined depending on the product, the specified pressure change over time in the piston chamber, and the position-dependent component elasticity of the switching element.

[0028] In simple variants of the inventive method, the current filling volume of the piston chamber and the associated component elasticity can be determined with minimal effort using characteristic curves.

[0029] Furthermore, it is possible to determine the flow resistance of a line connecting the flow control valve to the piston chamber of the switching element with minimal effort and high accuracy, depending on the measured hydraulic fluid flow rate. Additionally, it can be provided that the flow resistance of the line is determined as a function of the temperature of the hydraulic fluid flowing through the line.

[0030] Depending on the flow resistance of the pipe, a pressure loss in the pipe between the flow control valve and the piston chamber of the switching element can be determined. Additionally, it is possible to calculate the pressure directly after the flow control valve from the sum of the pressure loss in the pipe and the pressure in the piston chamber, which can be measured, estimated, or determined via a setpoint.

[0031] The pressure in the piston chamber of the switching element can be measured using a suitably positioned sensor. Alternatively, the pressure in the piston chamber can be determined or estimated using a model that accurately represents the device. The target pressure value in the piston chamber can be determined from the predefined time profile of the actuation pressure in the piston chamber.

[0032] In other words, the pressure loss in the hydraulic fluid supply line (the line between the flow control valve and the piston chamber) is determined based on the desired hydraulic fluid flow rate and the known resistance of the coupling line. The sum of the pressure in the piston chamber of the switching element and the pressure loss in the line results in a total pressure that must be present at the branch point of the line at the flow control valve, or directly after the flow control valve, to achieve the required pressure in the piston chamber.

[0033] In a further advantageous variant of the method according to the invention, the flow resistance of the flow control valve during an operating state of the switching element, during which the pressure in the piston chamber is increased, is determined from the pressure difference between the pressure applied to the flow control valve on the inlet side by the pressure source and the pressure directly after the flow control valve and the hydraulic fluid volume flow rate to be passed through the flow control valve.

[0034] This means that the pressure differential at the flow control valve is determined by measuring the pressure directly after the valve and the known supply pressure applied to the valve inlet from the pressure source. Additionally, in conjunction with the known flow rate through the flow control valve, the pressure loss across the valve is also calculated, based on the flow force acting on the valve.

[0035] In contrast, the flow resistance of the flow control valve during an operating phase of the switching element, during which the pressure in the piston chamber is reduced, is determined by the pressure difference between the pressure exerted by the piston chamber of the switching element on the flow control valve and the pressure downstream of the flow control valve, as well as the hydraulic fluid flow rate that must pass through the flow control valve. The pressure downstream of the flow control valve essentially corresponds to the pressure in a so-called tank line, in which the pressure is preferably equal to the ambient pressure or atmospheric pressure of the device, and through which the pressure in the piston chamber of the switching element is reduced or lowered.

[0036] In a further advantageous embodiment of the method according to the invention, the flow control valve is actuated by pilot control depending on the sum of the flow resistance of the flow control valve, the pressure loss in the line, and the pressure currently to be set in the piston chamber of the switching element. In addition to pilot control, the flow control valve can also be actuated by controlled operation.

[0037] The invention further relates to a control unit according to claim 10.

[0038] The control unit according to the invention can be equipped with at least one receiving interface configured to receive signals from signal transmitters. The signal transmitters can, for example, be designed as sensors that detect measured quantities and transmit them to the control unit. A signal transmitter can also be referred to as a signal sensor. Thus, the receiving interface can receive a signal from a signal transmitter indicating that the switching element of the device needs to be monitored.

[0039] The control unit according to the invention can also include a data processing unit to evaluate and / or process the received input signals or the information contained in the received input signals.

[0040] The control unit according to the invention can also be equipped with a transmission interface configured to output control signals to actuators. An actuator is understood to be an actuator that implements the commands of the control unit. The actuators can, for example, be electromagnetic actuators, via which the flow control valve is controlled.

[0041] The control unit according to the invention enables the operation of a device comprising a hydraulic pressure source and a controllable flow control valve. A hydraulic pressure from the pressure source is applied to the flow control valve. In the area of ​​the pressure control valve, the control unit sets an actuating pressure for a hydraulically actuated switching element. This actuating pressure is applied downstream of the flow control valve in the area of ​​a piston chamber of the switching element, in which a piston is arranged to be longitudinally displaceable between two end positions.

[0042] The control unit is designed in such a way that the flow control valve is pre-controlled depending on a hydraulic fluid volume flow that is to be guided through the flow control valve in order to generate a predetermined time profile of the actuating pressure in the piston chamber of the switching element.

[0043] This means that the flow control valve is actuated via the control unit in such a way that the specified time profile of the actuating pressure is always present in the piston chamber of the switching element, with the advance of all known influencing variables and the desired pressure in the piston chamber.

[0044] The aforementioned signals are merely examples and are not intended to limit the invention. The acquired input signals and the output control signals can be transmitted via a vehicle bus, for example, a CAN bus. The control unit according to the invention can, for example, be configured as a central electronic control unit of a vehicle or as an electronic transmission control unit.

[0045] The present invention is also defined by a computer program product according to claim 10.

[0046] The invention is not limited to the specified combination of features of the dependent or suffixed claims. Furthermore, it is possible to combine individual features, including those apparent from the claims, the subsequent description of embodiments, or directly from the drawings, whereby the present invention and the associated scope of protection are defined by the subsequent claims. References in the claims to the drawings by means of reference numerals are not intended to limit the scope of protection of the claims.

[0047] Preferred embodiments are described in the dependent claims and the following description. An exemplary embodiment of the invention is explained in more detail with reference to the drawing, without being limited thereto.

[0048] This shows: Fig. 1 a block diagram of a device with a hydraulic pressure source, a flow control valve and a hydraulically actuated switching element; Fig. 2 the flow control valve in an enlarged, schematic detail view; Fig. 3 an enlarged view of a Fig. 2 more precisely marked area III; Fig. 4 a schematic, enlarged detail view of the hydraulically actuated switching element of the device according to Fig. 1 ; and Fig. 5 a progression of a volume of a piston chamber of the switching element according to Fig. 4 and a curve of the component elasticity of the switching element as a function of the pressure in the piston chamber of the switching element.

[0049] Fig. 1Figure 1 shows a block diagram of a device 1 with a hydraulic pressure source 2 and a controllable flow control valve 3. The pressure source 2 is designed as a hydraulic pump whose suction side 4 is connected to an oil sump 5 of an automatic transmission and draws hydraulic fluid from the oil sump 5. A pressure side 6 of the hydraulic pump 2 is connected to a system pressure valve 7, by means of which a system pressure p_sys is set at least before the fluid enters the flow control valve 3.

[0050] The system pressure relief valve 7 can be configured either as a pressure relief valve or as a pressure reducing valve. As a pressure relief valve, it is arranged in parallel or in a branch to a section of the hydraulic system where the pressure is lower than the system pressure p_sys, thus limiting the pressure both on the pressure side 6 of the hydraulic pump 2 and in the supply line to the flow control valve 3, which is located in Figs. 2 and 3 for example, represented by a connection 31. In an alternative embodiment as a pressure reducing valve, the system pressure valve 7 would be as schematically shown in Fig. 1The valve is shown to be arranged between the hydraulic pump 2, or rather its pressure side 6, and the flow control valve 3, and would adjust the system pressure p_sys independently of the pressure generated by the hydraulic pump 2, only downstream of the system pressure valve 7. Alternatively, a more complex valve system could be designed by means of which the system pressure p_sys could be adjusted downstream of the system pressure valve 7 towards the flow control valve 3, and for a pressure range of the hydraulic system, such as a cooling and / or lubrication system, a pressure lower than the system pressure p_sys could be set.

[0051] The system pressure p_sys is located at the flow control valve 3 or in a connection 31 ( Figs. 2 and 3) and is regulated in the area of ​​the flow control valve 3 depending on an actuation of the flow control valve 3 by a transmission control unit 8 to a requested pressure level of an actuation pressure of a switching element 9 of the device 1 which is designed here as a friction-fit coupling.

[0052] The flow control valve 3 is in Fig. 2 The device is shown in a separate illustration and is designed as a directly controlled pressure control valve in which an electromagnetic actuator 10 with an anchor rod 11 interacts directly with a valve spool 12 of the flow control valve 3. When the electromagnetic actuator 10 is energized, the valve spool 12 is longitudinally displaceable within a valve housing 14 by the anchor rod 11 against the spring force of a spring 13.

[0053] The system pressure p_sys, set in the area of ​​the system pressure valve 7, is applied to a first valve port 31 of the flow control valve 3. Depending on the axial position of the valve spool 12, the first valve port 31 is in the Fig. 3 as shown in more detail, with a second valve port 32 of the flow control valve 3, which is connected to the switching element 9 via a line 15. In this way, both the flow rate through the flow control valve 3 and the pressure downstream of the flow control valve 3 vary depending on the system pressure p_sys, the axial position of the valve spool 12, and the filling volume of a Fig. 4 The piston chamber 16 of the switching element 9 is shown in more detail. In the piston chamber 16, a piston 17 of the switching element 9 is arranged to be longitudinally displaceable between two end positions.

[0054] A lamellar pack 18 of the switching element 9 is compressed by applying appropriate pressure to the piston 17 in order to transmit a desired torque via the switching element 9. In the compressed state of the lamellar pack 18, the inner lamellae 19 and outer lamellae 20 are frictionally engaged with each other, whereby, in the fully closed state of the switching element 9, an applied torque is transmitted without slippage between the inner lamellae 19 and the outer lamellae 20.

[0055] In contrast, the switching element 9 transmits no torque when fully open. In this state, the pressure p_16 in the piston chamber 16, hereinafter referred to as piston chamber pressure p_16, is such that the piston 17 is moved away from the lamellar pack 18 by a spring unit 21, thus releasing the compression of the lamellar pack 18.

[0056] The switching element 9 can, for example, be engaged to represent a gear ratio stage of an automatic transmission in the power flow of a vehicle drivetrain equipped with the automatic transmission. If the transmission control unit 8 issues a corresponding engagement request, it specifies a time profile for the piston chamber pressure p_16 in the piston chamber 16 of the switching element 9. This allows the switching element 9 to transition from its fully open operating state to its fully closed operating state within a defined operating period. The desired transmission capability of the switching element 9 is determined by the time profile of the piston chamber pressure p_16, or the actuation pressure of the switching element 9. The transmission capability of the flow control valve 3 is then determined from this desired transmission capability of the switching element 9 in the manner described in more detail below.

[0057] The transmission capability of the switching element 9 is subject to a precisely defined sequence. The transmission capability of the switching element 9 is uniquely linked to the position of the piston 17. Additionally, the position of the piston 17 is uniquely linked to the piston chamber pressure p_16 in the piston chamber 16. Therefore, the transmission capability of the switching element 9 can be easily determined by controlling the piston chamber pressure p_16 in the piston chamber 16. Furthermore, the corresponding piston chamber pressure p_16 in the piston chamber 16 can be uniquely determined from the known transmission capability of the switching element 9.

[0058] Due to the fact that each pressure level of the piston chamber pressure p_16 in the piston chamber 16 can be assigned a unique position of the piston 17, an elasticity characteristic e_9 of the switching element 9 and a volume V_16 of the piston chamber 16 can be determined during the entire switching process of the switching element 9. The volume V_16 of the piston chamber 16 is a function of the piston chamber pressure p_16. The change or the derivative of the volume characteristic yields the following formulaic relationship for the elasticity characteristic e_9 of the switching element 9: e_ 9 p_ 16 = dV_ 16 / dp_ 16

[0059] If a time-dependent profile of the piston chamber pressure p_16 in the piston chamber 16 of the switching element 9, i.e., not in the area of ​​the flow control valve 13, is specified, then the volume flow rate required to achieve the desired pressure profile of the piston chamber pressure p_16 through the flow control valve 3 is obtained by multiplying the time-dependent pressure change dp_16 / dt, which is equal to the derivative of the piston chamber pressure p_16 with respect to time t, by the position-dependent elasticity characteristic e_9 (p_16). By specifying the time-dependent profile of the piston chamber pressure p_16, the aim is to transition the switching element 9 from its fully open operating state to a defined operating state, in particular to its fully closed state, within a predefined period.

[0060] Fig. 5The graph shows a curve of the volume V_16 of the piston chamber 16 and a curve e_9 of the component elasticity of the switching element 9 as a function of the piston chamber pressure p_16. The graph is shown according to... Fig. 4 It can be deduced that the component elasticity e_9 assumes high values ​​at low piston chamber pressure p_16 and small volumes V_16 of the piston chamber 16, and decreases with increasing piston chamber pressure p_16 and increasing volume or filling volume of the piston chamber 16. This results from the fact that at the beginning of the filling process of the piston chamber 16 of the switching element 9, only a low pressure p_16 is initially established in the piston chamber 16. During this phase of actuation of the switching element 9, the piston chamber pressure p_16 acting on the piston 17 essentially only has to overcome the spring force of the spring unit 21.

[0061] Only when the piston 17 has compressed the spring unit 21, which in the present embodiment is designed as a disc spring, and when the piston 17 comes into contact with the lamellar pack 18 and this begins to compress, is the elasticity e_9 of the switching element 9 determined according to the figure in Fig. 5 The depicted curve becomes progressively smaller as the piston chamber pressure p_16 simultaneously increases. The volume V_16 of the piston chamber 16 then also increases with a significantly smaller gradient. In this pressure range of the piston chamber pressure p_16, the switching element 9 exhibits high component stiffness because the lamellar assembly 18 is then in a so-called locked operating state. In this locked operating state, the lamellar assembly 18 is strongly compressed by the piston 17, and the switching element 9 is then completely closed. The piston 16 is then in its end position, which it assumes when the switching element 9 is closed.

[0062] During the entire switching process of the switching element 9, the pressure loss in the line 15 is determined using the desired volume flow rate and the known flow resistance of the coupling feed, i.e. the flow resistance in the line 15 between the flow control valve 3 and the piston chamber 16 of the switching element 9.

[0063] The currently measured pressure loss in line 15 is added to the specified time profile of the actuation pressure or the piston chamber pressure p_16. This summed pressure value corresponds to the pressure in line 15 directly after the flow control valve 3.

[0064] The pressure differential across the flow control valve 3 is determined from the pressure downstream of the flow control valve 3 and the system pressure p_sys. This involves determining the pressure differential between the area of ​​the device 1 upstream of the first valve port 31 and the area of ​​the device 1 downstream of the second valve port 32. Additionally, the flow force FS acting on the valve spool 12 is determined based on the calculated hydraulic fluid volume flow rate. Subsequently, the flow resistance of the flow control valve 3 is determined from the sum of the pressure loss across the flow control valve 3 and the pressure loss across the pressure control valve 3 caused by the flow force FS.

[0065] The flow force FS acts in the Fig. 3The force provided or pre-controlled by the electromagnetic actuator 10 is counteracted in the manner described in more detail. If the flow force FS is not taken into account when controlling downstream systems, in this case the switching element 9, the piston chamber pressure p_16 will be either too high or too low.

[0066] Such a pressure shift then leads to the switching element 9 not being actuated in the manner intended, for example, by the set actuator force of the actuator 10. To compensate for the pressure shift, the determined pressure loss in line 15 and the calculated flow resistance of the flow control valve 9 are first added. This pressure represents the setpoint for the actuation of the flow control valve 3. The pressure to be set in the area of ​​the flow control valve 3, or the force to be applied by the electromagnetic actuator 10, is determined in the procedure described here without the complex adaptations, characteristic curves, and the like known from the prior art.

[0067] The previously described determination is now performed for each new task depending on the current position of piston 17 until the switching element 9 no longer experiences any dynamic pressure change. At this point, the flow rate in the area of ​​the flow control valve 3, the flow force FS, and the pressure loss in line 15 are essentially zero. The pressure to be controlled in the area of ​​the flow control valve 3 then corresponds to the pressure to be set in the piston chamber 16 of the switching element 9.

[0068] This means that the switching element 9 is always controlled by pre-control of all known influencing variables and starting from the desired pressure, which is to be set in the piston chamber 16 of the switching element 9.

[0069] The procedure described above can also be carried out with minor adjustments during an operating state sequence of the switching element 9, during which the switching element 9 is to be transferred from its fully closed operating state to its fully open operating state as required.

[0070] During the shutdown process of the switching element 9, the pressure p_16 in the piston chamber 16 of the switching element 9 must be reduced. For this purpose, the valve spool 12 of the flow control valve 3 must be axially adjusted. The valve spool 12 is moved by the spring 13 such that it blocks the connection between the second valve port 32 and the first valve port 31 and opens a connection between the second valve port 32 and a third valve port 33. The third valve port 33 is connected via a line 22 to the oil sump 5, which is essentially unpressurized or whose pressure is equal to atmospheric pressure.

[0071] In principle, the pressure profiles in line 15 between piston chamber 16 and flow control valve 3, as well as the piston chamber pressure p_16, exhibit a negative pressure gradient during the switching process of the switching element 9. The pressure loss in line 15 between the switching element 9 and the flow control valve 3 must therefore be subtracted from the desired pressure in piston chamber 16. The pressure difference at the flow control valve 3 is calculated as the difference between the piston chamber pressure p_16 (reduced by the pressure loss in line 15) and the pressure in the oil sump 5 when the second valve port 32 is connected to the third valve port 33.

[0072] To prevent the device 1 from draining completely, the line 22 can also be equipped with a so-called pre-filling valve between the further valve connection 33 and the oil sump 5. Such a pre-filling valve allows the pressure in the line 22 to be set to a pre-filling pressure level above atmospheric pressure, thus preventing the device 1 from draining completely in the area between the flow control valve 3 and the switching element 9.

[0073] The flow force acting in the area of ​​the flow control valve 3 during the switching off of the switching element 9 results from the pressure difference at the flow control valve 3, the flow through the flow control valve 3 and the geometry of the flow control valve 3 through which the hydraulic fluid volume flow passes, whereby this may differ from the geometry of the flow control valve 3 during the switching on process of the switching element 9.

[0074] The procedure described above for setting a predetermined time profile of an actuation pressure can also be used in systems designed for cooling and lubrication, provided their resistance characteristics are known. The resistance characteristics are determined, among other things, by the operating temperature of the hydraulic fluid or oil, the flow rate, and other relevant operating parameters. Reference sign

[0075] 1 Device 2 Pressure source, hydraulic pump 3 Flow control valve 4 Suction side of hydraulic pump 5 Oil sump 6 Pressure side of hydraulic pump 7 System pressure valve 8 Transmission control unit 9 Switching element 10 Electromagnetic actuator 11 Anchor rod 12 Valve slide 13 Spring 14 Valve body 15 Line 16 Piston chamber 17 Piston 18 Reed pack 19 Inner reeds 20 Outer reeds 21 Spring unit 22 Line 31 to 33 Valve connection e_9 Component elasticity FS Flow force p_sys System pressure p_16 Piston chamber pressure V_16 Volume of the piston chamber

Claims

1. Method for operating a device (1) with a hydraulic pressure source (2), and with a controllable flow control valve (3), at which a hydraulic pressure of the pressure source (2) prevails and in the region of which an actuating pressure (p_16) for a hydraulically actuable switching element (9) is set, wherein the actuating pressure (p_16) prevails downstream of the flow control valve (3) in the region of a piston chamber (16) of the switching element (9), in which piston chamber a piston (17) is arranged longitudinally displaceably between two end positions, wherein pilot control of the flow control valve (3) takes place as a function of a hydraulic fluid volume flow which is to be guided through the flow control valve (3), in order to generate a predetermined time course of the actuating pressure (p_16) in the piston chamber (16) of the switching element (9), characterized in that a current filling volume (V_16) of the piston chamber (16) and a current component elasticity (e_9) of the switching element (9) are each determined as a function of the time course of the actuating pressure (p_16), wherein the component elasticity (e_9) of the switching element (9) varies as a function of a position of the piston (17) of the switching element (9).

2. Method according to Claim 1, characterized in that the hydraulic fluid volume flow, which is to be guided through the flow control valve (3), is determined as a function of the product from the predetermined temporal pressure change in the piston chamber (16) and the position-dependent component elasticity (e_9) of the switching element.

3. Method according to either of Claims 1 or 2, characterized in that a flow resistance of a line (15), which connects the flow control valve (3) to the piston chamber (16) of the switching element (9), is determined as a function of the determined hydraulic fluid volume flow.

4. Method according to Claim 3, characterized in that the flow resistance of the line (15) is determined as a function of the temperature of the hydraulic fluid.

5. Method according to Claim 3 or 4, characterized in that a pressure loss in the line (15) between the flow control valve (3) and the piston chamber (16) of the switching element (9) is determined as a function of the flow resistance of the line (15), wherein the pressure downstream of the flow control valve (3) is determined from the sum of the pressure loss in the line (15) and the pressure (p_16) in the piston chamber (16) of the switching element (9).

6. Method according to Claim 5, characterized in that the flow resistance of the flow control valve (3) during an operating state course of the switching element (9), during which the pressure (p_16) in the piston chamber (16) is raised, is determined from the pressure difference between the pressure, applied by the pressure source (2) to the pressure control valve (3), and the pressure downstream of the flow control valve (3) and the hydraulic fluid volume flow to be passed through the flow control valve (3).

7. Method according to Claim 5 or 6, characterized in that the flow resistance of the flow control valve (3) during an operating state course of the switching element (9), during which the pressure (p_16) in the piston chamber (16) is lowered, is determined from the pressure difference between the pressure, applied by the piston chamber (16) of the switching element to the flow control valve (3), and the pressure downstream of the flow control valve (3) and the hydraulic fluid volume flow to be passed through the flow control valve (3).

8. Method according to Claim 6 or 7, characterized in that the flow control valve (3) is actuated in a pilot-controlled manner as a function of the sum of the flow resistance of the flow control valve (3), the pressure loss in the line (15) and the pressure currently to be set in the piston chamber (p_16) of the switching element (9).

9. Control unit (8) for operating a device (1) with a hydraulic pressure source (2), and with a controllable flow control valve (3), at which a hydraulic pressure of the pressure source (2) prevails and in the region of which an actuating pressure (p_16) for a hydraulically actuable switching element (9) is set, wherein the actuating pressure (p_16) downstream of the flow control valve (3) prevails in the region of a piston chamber (16) of the switching element (9), in which piston chamber a piston (17) is arranged longitudinally displaceably between two end positions, wherein the control unit (8) is designed in such a way that pilot control of the flow control valve (3) takes place as a function of a hydraulic fluid volume flow, which is to be guided through the flow control valve (3), in order to generate a predetermined time course of the actuating pressure (p_16) in the piston chamber (16) of the switching element (9), characterized in that the control unit is still designed in such a way that a current filling volume (V_16) of the piston chamber (16) and a current component elasticity (e_9) of the switching element (9) are each determined as a function of the time course of the actuating pressure (p_16), wherein the component elasticity (e_9) of the switching element (9) varies as a function of a position of the piston (17) of the switching element (9).

10. Computer program product with program code means which are stored on a computer-readable data carrier in order to carry out all steps of a method according to one of Claims 1 to 8 when the computer program product is run on a computer or on a corresponding computing unit, in particular a control unit according to Claim 9.