Method for controlling a vehicle with a hydraulic system for actuating a clutch

Abstract

The invention relates to a method for controlling a hydraulic system (1) for a vehicle having an electrically operated pump (2) that adjusts a system pressure, wherein, for actuating a clutch, the system pressure is controlled between a maximum pressure (p(max)) and a minimum pressure (p(min)) by means of a slave cylinder (6). In order to enable both precise and robust control of the hydraulic system (1), a pressure signal of the system pressure is filtered using different types of filters as a function of at least one operating parameter of the hydraulic system (1).

Description

The invention relates to a method for controlling a vehicle having a hydraulic system with an electrically operated pump setting a system pressure, wherein, for the actuation of a clutch by means of a slave cylinder, the system pressure is controlled between a pressure maximum and a pressure minimum.The documents DE 10 2018 130700 A1, DE 10 2019 101468 A1, DE 10 2020 012611 A1 and DE 10 2021 115515 A1 each disclose hydraulic systems and their methods for controlling vehicles, for example purely electrically operated vehicles or hybrid vehicles. In addition to a parking lock, the hydraulic system controls a clutch such as a friction clutch by actuating it in a pressure-controlled manner by means of a slave cylinder. The system pressure required for this is generated by an electrically operated pump. A discharge valve is provided in a pressure line between slave cylinder and pump, so that the system pressure can be regulated between a pressure minimum and a pressure maximum, wherein the system pressure is detected by means of a pressure sensor. Due to the system, the detected pressure signals of the pressure sensor are overlaid by disturbances and are filtered.The object of the invention is the development of a method for controlling a hydraulic system for a vehicle. In particular, it is an object of the invention to propose a method for controlling a hydraulic system with improved filtering of the pressure signals of the pressure sensor.The object is achieved by the subject matter of claim 1. The claims dependent on claim 1 represent advantageous embodiments of the subject matter of claim 1.The proposed method serves for controlling a hydraulic system for a vehicle, in particular a purely electrically operated vehicle or a hybrid vehicle. For the actuation of a clutch, for example a friction clutch, positive-locking clutch and / or the like, an electrically operated pump is provided in the hydraulic system, which pump adjusts a system pressure, for example, in a pressure line. To actuate the clutch, a slave cylinder is operatively connected to the pump, for example via the pressure line, the slave cylinder piston of which slave cylinder is displaced and held under system pressure between a pressure maximum and a pressure minimum and in the process actuates the clutch by means of an actuating mechanism. Depending on the design of the clutch, it can be closed in a preferred manner upon actuation and, in special cases, opened from the closed state upon application of the system pressure.Via at least one switching valve, an additional slave cylinder can be supplied with system pressure into the pressure line for actuating a parking lock.In order to configure the control of the clutch in a quick and robust manner, a pressure signal of the system pressure is filtered by means of different filter types depending on at least one operating parameter of the hydraulic system. It is provided here that at least one filtering with a short time constant is provided with a briefly necessary pressure determination, for example during the actuation of the clutch, and a filtering with higher damping is used with a less time-critical operation, for example with an actuated clutch during the driving operation of the vehicle, in order to, for example, vigorously distinguish a very noisy pressure signal from the pressure minimum and the pressure maximum.According to an advantageous embodiment of the method, the rotational speed of the pump is used for this purpose as at least one operating parameter. In this case, for example, a pumping-up for raising a system pressure falling below the pressure minimum during otherwise unnecessary operation of the pump for maintaining the system pressure can be evaluated as driving operation of the vehicle using the proposed hydraulic system, and a filtering with high damping can be applied to the pressure signal. At a high rotational speed of the pump, for example, an actuation process of the clutch with increasing system pressure can be assumed, so that filtering takes place with a short time constant in order to enable a detection of the pressure signal with a high temporal resolution. The rotational speed of the pump is obtained, for example, on the basis of the electric motor driving it, for example, by evaluating any rotational speed sensor system that may be present and serves for its commutation and / or electrical variables such as, for example, its current consumption over time or its operating voltage over time.To reduce the system pressure, for example when the pressure maximum is exceeded or to open the clutch, a shut-off valve is arranged between the pump and the slave cylinder, for example in the pressure line, which shut-off valve discharges pressure medium into a pressureless sump when the circuit is appropriate. Alternatively or additionally, an operating position of this shut-off valve can be provided as at least one operating parameter for assessing the necessary filter type. For example, when the shut-off valve is open, a first type of filter can be used for a provided time after a pressure rise after the shut-off valve is closed, which filter type provides a timely resolution of the pressure signal with low damping, since the clutch is usually closed in this time period because of the rising system pressure. On the other hand, after a predetermined time has elapsed after closing the shut-off valve, it can be assumed that the clutch is closed and a second type of filter with greater attenuation of the pressure signal can be activated.Alternatively or additionally, a travel speed of the vehicle can be used as the basis as at least one operating parameter if, in this case, the clutch disconnects a drive unit of the vehicle from its drive wheels. It is assumed here that when a predefined speed is reached, the clutch is closed and actuated. The system then switches from the first type of filter at low speed of the vehicle or stationary vehicle to the second type of filter. Rolling of the vehicle when the clutch is open is taken into account in that, for example, corresponding operating data of the drive unit, load data of the drive train and / or the like are evaluated.For example, the drive unit may contain a hybrid-acting electric machine or an electric machine exclusively driving the vehicle. In this case, the travel speed can be determined on the basis of the rotational speed of this electric machine and / or, if appropriate, of at least one further electric machine driving the vehicle.The pump for providing the system pressure can advantageously be designed as a reversible pump, wherein a first rotational direction of the pump generates a flow of pressurized medium, for example for cooling and / or lubricating components of the vehicle, for example the clutch, transmission parts such as components of a CVT (continuous variable transmission) and / or the like, and the second rotational direction of the pump actuates the clutch. In this case, the direction of rotation of the pump can be provided as at least one parameter, wherein the second type of filter is activated with high damping in the first direction of rotation of the pump and the first type of filter is activated in the second direction of rotation, for example, for closing the clutch.Generally speaking, for example, a first type of filter is used when the clutch is open and a second type of filter is used when the clutch is closed and the vehicle speed is greater than a predefined threshold value. In this case, the second filter type has a higher signal attenuation than the first filter type.In an advantageous embodiment, in combination of the operating parameters, the second filter type is set after a predetermined time of the actuated clutch has elapsed, when the shut-off valve between the pump and a non-pressurized sump is closed, when the pump is operated in a rotational direction opposite to the rotational direction setting the system pressure and / or when a vehicle speed is exceeded above a predetermined threshold value.In other words, ever-increasing complexity of the vehicles requires a proper function and interaction of all components. The function of the electrical components is especially important in order to enable purely electric driving and to increase the efficiency. Failure or defect of certain electronic components can lead to severe effects on the vehicle.Clutch actuation in such vehicles is advantageously effected under pressure control by means of a hydraulic system. If, in an advantageous embodiment, for example, a target state "clutch closing" is predefined, a shut-off valve closes a pressure line between a pump and a slave cylinder for actuating the clutch with respect to a non-pressurized sump, and the pump starts to convey pressure medium in the direction of the slave cylinder, with a system pressure being built up. When system pressure, such as a target pressure between a pressure minimum and a pressure maximum, is reached, the pump ceases pumping and changes direction of rotation to lubricate and / or cool components of the vehicle / powertrain. If the system pressure drops too much over time, because, for example, there is a slight leakage, and in the process drops below the pressure minimum, the pump pumps pressure medium into the slave cylinder by changing the direction of rotation. Again, it is checked whether the system pressure is reached. If necessary, this process is repeated continuously. If during a pressure holding phase, with the clutch closed, the system pressure rises above the pressure maximum, the shut-off valve is opened until the system pressure is again within the pressure limits between pressure minimum and pressure maximum. The pressure signals detected in this case can have high noise and are filtered accordingly.In this case, with appropriate filtering, it is true to represent the pressure signals as accurately as possible, for example with precision in time. Therefore, the filtering is parameterized as little restrictively as possible. It has been found that, depending on the vehicle speed of the vehicle and a clutch shift position, for example, due to the system, very strong pressure oscillations can occur in the hydraulic path between pump and slave cylinder. Despite filtering being used, therefore, a very large dispersion of the pressure signals is detected in the corresponding software of a control unit controlling the clutch. These pressure fluctuations can lead, for example, to the pressure minimum and pressure maximum being exceeded very quickly one after the other. In order to avoid that these rapid changes of the direction of rotation of the pump and activation of the shut-off valve lead to system interruptions, an improved method for adapting the filtering of the pressure signal is proposed.For this purpose, the pressure signals are filtered as a function of operating parameters of the vehicle or of the hydraulic system for the vehicle, for example a vehicle speed, for example on the basis of a rotational speed of an electric machine driving the vehicle, on the basis of the rotational speed and / or the direction of rotation of the pump, on the basis of an operating state of the discharge valve and / or the like.During the operation of the clutch, the pressure signal should be as accurate as possible so that the clutch can be properly engaged. If, according to a first advantageous variant, a rotational speed of the electric machine driving the vehicle is above a rotational speed threshold for closing the clutch, the clutch is closed. During the clutch closing process, the filtering of the pressure signal is as accurate as possible in a first type of filter. As soon as the clutch is closed, it is decided depending on the rotational speed of the electric machine whether the clutch remains closed or opens again. If the clutch is to remain closed, a check is made as to whether the rotational speed of the electric machine is greater than or equal to a rotational speed threshold, which may be, for example, just below the rotational speed maximum, such as, for example, the nominal rotational speed of the electric machine, for changing the pressure filtering. If this is not the case, the first type of filter remains unchanged. However, if the speed of the electric machine exceeds the speed threshold and the pump is in the rotational direction of cooling the components, the filtering of the pressure signal switches to a stronger filtering of the pressure signal in a second filter type. A distinction is made here as to whether the clutch is already closed and is currently in the pressure holding phase in which the system pressure is held by pumping up or draining, or whether the clutch is open and has to be completely re-closed. If the clutch is already closed and the pump pumps up only, the second filter type is maintained since the rotational speed of the electric machine remains above the rotational speed limit for changing the filter type. If, in contrast thereto, the clutch is completely re-closed, then a switch is made to the first type of filter.In a second advantageous variant, an adaptation of the filter types is provided independently of the rotational speed of the electric machine. Only the rotational speed of the pump and the operating position of the discharge valve are evaluated. In this case, when the clutch is actuated with corresponding activity of the pump in the second direction of rotation, the first type of filter is selected. As soon as the direction of rotation of the pump changes and the shut-off valve is closed, the second filter type is changed.Both variants make possible both a sufficiently precise actuation of the clutch and also trouble-free operation at high rotational speed of the electric machine.The invention is explained in more detail with reference to the exemplary embodiment shown in FIGS. 1 to 4. These show: FIG. 1 shows a schematic illustration of a hydraulic system, FIG. 2 is a state diagram of the hydraulic system of FIG. 1 illustrating the improved filtering method of the pressure signal of the pressure sensor, FIG. 3 is a flow chart for setting various filter types of the pressure signal; and FIG. 4 is a modified flow chart compared with the flow chart of FIG. 3.FIG. 1 shows a schematic illustration of the hydraulic system 1 for carrying out the method according to the invention. The hydraulic system 1 contains the pump 2, which is designed, for example, as a gear pump and is connected on one side to the coolant line 3 for providing a speed-regulated volume flow of pressure medium. The coolant line 3 delivers pressure medium, such as oil, for example, to at least one first component 4, which is designed, for example, as a heat exchanger, the separating clutch 17 for cooling it and / or the like. On the other hand, the pump 2 is connected to the pressure line 5. The pressure line 5 serves to act upon the slave cylinders 6, 8, the parking lock 9 and the clutch 17.The pump 2 is designed as an electrically driven reversible pump in order to supply the pressure medium 7 to the coolant line 3 in a first rotational direction and to the pressure line 5 in a second rotational direction. The pump 2 is driven by the electric motor 11 controlled by the control unit 15. The pump 2, the electric motor 11 and the power electronics 12 form an electric pump actuator. The pressure sensor 14 is arranged in the pressure line 5, which is connected to the control unit 15 and via the latter to a superordinate control unit controlling the entire actuation system.The shut-off valve 23, such as a two-way switching valve, serves for reducing the pressure in the pressure line 5 and thus for opening the clutch 17 and for this purpose connects the slave cylinder 6 to the sump 13.The system pressure present in the pressure line is detected by means of the pressure signals of the pressure sensor 14. Furthermore, the rotational speeds n 1, n 2 of the input part 18 and of the output part 19 of the clutch 17 arranged about the rotational axis d can be detected and evaluated.The pressure signals of the pressure sensor 14 are noisy, so that corresponding filter applications are applied in the control unit 15 to improve the pressure signals. According to the proposed method, different filter types adapted to the accuracy, intensity of the noise and / or the like are applied depending on operating parameters of the hydraulic system 1 or of the drive train containing it or of the vehicle receiving it. For example, according to the flowcharts of FIGS. 3 and 4, different filter types are used on the one hand when the clutch 17 is closed during the driving operation of the vehicle and on the other hand when the clutch is actuated. For example, the rotational speed and / or rotational direction of the pump 2, the rotational speeds n 1, n 2, the operating state of the shut-off valve 23 and / or the like can be used to detect these operating states.FIG. 2 shows a schematic diagram of the state diagram 24 with reference to the hydraulic system 1 of FIG. 1 over time t for an advantageous method for applying different filter types F( 1), F( 2). The sub-diagram I shows the state of the shut-off valve 23 with the states ZU and OPEN. The sub-diagram II shows the rotational speed n(e) of an electric machine driving the vehicle with the hydraulic system 1, the sub-diagram III shows the rotational speed n(p) of the bidirectionally operating pump 2, the sub-diagram IV shows the filtered pressure signal p of the pressure sensor 14 and the sub-diagram V shows the activation of the different filter types F( 1), F( 2).When the clutch 17 is activated as desired, for example starting from the rotational speed limit n(e,k) of the electric machine for driving the vehicle, the shut-off valve 23 is closed at an accelerated rotational speed n(e) and the pump 2 adjusts the system pressure by means of a predefined rotational speed n(p) in a positive rotational direction, for example a second rotational direction. After the system pressure has been reached between the pressure minimum p(min) and the pressure maximum p(max), the pump 2 switches to the negative, for example first rotational speed - n(p) and supplies the component 4 with pressure medium. When the pressure minimum p(min) is reached, the pump 2 reverses its direction of rotation again while the clutch 17 is closed and pumps up again in order to increase the system pressure again. Until the time t 1, the filter type F( 1) is retained with less intensive filtering, since a permanently actuated clutch 17 is not assumed, for example, due to the rotational speed n(e) or the duration of the actuated clutch 17 or due to other operating parameters. By operating the pump 2 in the first direction or by stopping it and opening the shut-off valve 23, the clutch 17 is opened again. Starting from the time t 1, a permanent actuation of the clutch 17 is assumed, for example, on the basis of the rotational speed n(e) above the rotational speed threshold n(e,max) lying just below the rotational speed limit n(e,max), and the second filter type F( 2), which is also capable of filtering severe disturbances 25, is activated in order to ensure a robust evaluation of the pressure signal p and to avoid undesired pumping-up processes or pressure reductions by means of the shut-off valve 23.Referring to FIGS. 1 and 2, FIG. 3 shows the flow diagram 26 with a routine 27 implemented, for example, in the control unit 15 of the hydraulic system for carrying out the proposed method, for example. Routine 27 is started in block 28.In branch 29, a check is made as to whether the rotational speed n(e) of the driving electric machine is less than or equal to the rotational speed limit n(e,k). If this is not the case, the first filter type F( 1) remains or is set in block 36. If this is the case, the method continues in branch 30.In branch 30, a check is made as to whether shut-off valve 23 is closed. If the shut-off valve is open, the first filter type F( 1) is set in block 36. If the shut-off valve 23 is open, the system branches off in branch 31.In the branch 31, a check is made as to whether the pump 2 is operated in the first direction of rotation, i.e. whether it is pumping pressure medium in the direction of the component 4. If the pump 2 is conveying in the direction of the slave cylinder 6, it is checked in branch 32 whether the system pressure is greater than or equal to the pressure minimum p(min). If this is not the case, the first filter type F( 1) is set or retained in block 36. If this is the case, the system branches to the node 33. If the pump 2 is located at the branch 31 in the first rotational direction, i.e. delivers in the direction of component 4, the branch is made to the node 33.From node 33, the system branches to branch 34, in which it is checked whether the rotational speed n(e) of the driving electric machine is greater than or equal to the rotational speed threshold n(e,g), if this is the case, the filter type F( 2) is set in block 35. If this is not the case, the filter type F( 1) is set or retained in block 36.FIG. 4 shows the flow diagram 37 with the routine 38 for carrying out the proposed method, which is simplified compared to the routine 27. Routine 38 is started in block 39.In branch 40, a check is made as to whether shut-off valve 23 is closed, i.e., is in the ZU state. If this is not the case and the shut-off valve 23 is opened with the clutch 17 open, the filter type F( 1) with a low degree of filtering is set in block 41 or the filtering of the pressure signal p remains in this state. If the shut-off valve 23 is closed, a check is made in the branch 42 as to whether the direction of rotation of the pump 2 is transporting pressure medium in the direction of component 4, which corresponds to the rotational speed -n(p) in the first direction of rotation. If this is the case, the second filter type F( 2) with stronger filtering is set via the node 43 in block 44.If it is determined in branch 42 that pump 2 is pumping in the direction of slave cylinder 6, i.e., pump 2 has a positive direction of rotation at rotational speed n(p) in the second direction of rotation, it is checked in branch 45 whether actuation of clutch 17 is active. For this purpose, it is checked whether the system pressure is greater than or equal to the pressure minimum p(min). If this is the case, the filter type F(2) is set via the node 43 in block 44. If the system pressure is less than the pressure minimum p(min), the filter type F(1) is set in block 41.List of reference characters1 Hydraulic system 2 Pump 3 Coolant line 4 Component 5 Pressure line 6 Slave cylinder 7 Pressure medium 8 Slave cylinder 9 Parking lock 10 Switching valve 11 Electric motor 12 Power electronics 13 Sump 14 Pressure sensor 15 Control unit 17 Clutch 18 Input part 19 Output part 20 Slave cylinder piston 21 Actuating element 23 Shut-off valve 24 State diagram 25 Disturbance 26 Flow diagram 27 Routine 28 Block 29 Branch 30 Branch 31 Branch 32 Branch 33 Node 34 Branch 35 Block 36 Block 37 Flow diagram 38 Routine 39 Block 40 Branch 41 Block 42 Branch 43 Node 44 Block 45 Branch d Axis of rotation F( 1) Filter type F( 2) Filter type n( e) Rotational speed n( e, g) Rotational speed threshold n( e, k) Rotational speed limit n( e, max) rotational speed limit n(p) rotational speed n1 rotational speed n2 rotational speed p pressure signal p(max) pressure maximum p(min) pressure minimum t time t1 timeReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2018 130700 A1

[0002] DE 10 2019,101468 A1

[0002] DE 10 2020 012611 A1

[0002] DE 10 2021 115515 A1

[0002]

Claims

Method for controlling a hydraulic system (1) for a vehicle with an electrically operated pump (2) setting a system pressure, wherein, for actuating a clutch (17) by means of a slave cylinder (6), the system pressure is controlled between a pressure maximum (p(max) and a pressure minimum (p(min)), characterized in that a pressure signal (p) of the system pressure is filtered as a function of at least one operating parameter of the hydraulic system (1) by means of different filter types (F(1), F(2)).Method according to claim 1, characterized in that said at least one operating parameter is a rotational speed (n(p)) of said pump (2).Method according to Claim 1 or 2, characterized in that the at least one operating parameter is an operating position of a shut-off valve (23) arranged between the pump (2) and a non-pressurized sump (13).Method according to one of Claims 1 to 3, characterized in that the at least one operating parameter is a travel speed of the vehicle.Method according to Claim 4, characterized in that the travel speed of the vehicle is determined by means of at least one electric machine on the basis of the rotational speed (n(e)) of the at least one electric machine.Method according to one of Claims 1 to 5, characterized in that the pump (2) is designed as a reversible pump, wherein a first rotational direction of the pump (2) generates a flow of pressure medium and the second rotational direction of the pump (2) actuates the clutch (17), and the at least one operating parameter is a rotational direction of the pump (2).Method according to one of Claims 1 to 6, characterized in that, when the clutch (17) is open, a first type of filter (F(1)) is used.Method according to one of Claims 1 to 7, characterized in that, when the clutch is closed and the vehicle speed is greater than a predefined threshold value, a second type of filter (F(2)) is used.Method according to one of Claims 1 to 8, characterized in that the second filter type (F(2)) has a higher signal attenuation than the first filter type (F(1)).Method according to one of Claims 1 to 9, characterized in that the second type of filter (F(2)) is set after a predetermined time of the actuated clutch (17) has elapsed, when the shut-off valve (23) is closed between the pump (2) and a non-pressurized sump (13), when the pump (2) is operated in a rotational direction which sets the system pressure and / or when a vehicle speed is exceeded above a predetermined threshold value.

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