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

[0001] The invention relates to a method for controlling a vehicle with a hydraulic system having an electrically operated pump that adjusts a system pressure, wherein the system pressure is controlled between a maximum pressure and a minimum pressure by means of a slave cylinder to actuate a clutch.

[0002] DE 10 2016 211 759 B3 discloses a method for determining a leak in a hydraulic clutch actuation system of a hybrid vehicle.

[0003] WO 2013 / 075 687 A2 discloses a method for checking the correct filling of a hydraulic clutch actuation system.

[0004] DE 199 37 053 A1 discloses a method for adjusting a control current for a pressure control valve.

[0005] Hydraulic systems and their control methods for vehicles, for example, purely electrically powered vehicles or hybrid vehicles, are known from the publications DE 10 2018 130700 A1, DE 10 2019 101468 A1, DE 10 2020 012611 A1, and DE 10 2021 115515 A1. 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 using a slave cylinder. The required system pressure is generated by an electrically operated pump. A relief valve is provided in a pressure line between the slave cylinder and the pump so that the system pressure can be regulated between a minimum and maximum pressure, with the system pressure being detected by a pressure sensor. Due to the nature of the system, the pressure signals detected by the pressure sensor are overlaid by interference and are filtered.

[0006] The object of the invention is to further develop a method for controlling a hydraulic system for a vehicle. In particular, the object of the invention is to propose a method for controlling a hydraulic system with improved filtering of the pressure signals from the pressure sensor.

[0007] The object is solved by the subject matter of claim 1. The claims dependent on claim 1 represent advantageous embodiments of the subject matter of claim 1.

[0008] The proposed method is used to control a hydraulic system for a vehicle, in particular a purely electrically powered vehicle or a hybrid vehicle. To actuate a clutch, for example a friction clutch, form-lock clutch and / or the like, an electrically operated pump is provided in the hydraulic system, which pump sets 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 is displaced and held between a maximum and a minimum pressure under system pressure, thereby actuating the clutch by means of an actuating mechanism. Depending on the design of the clutch, it can preferably be closed upon actuation and, in special cases, opened from the closed state when system pressure is applied.

[0009] An additional slave cylinder for actuating a parking lock can be supplied with system pressure in the pressure line via at least one switching valve.

[0010] To ensure fast and robust clutch control, a system pressure signal is filtered using different filter types depending on at least one operating parameter of the hydraulic system. At least one filter with a short time constant is used for pressure determination that is required for a short time, for example, during clutch actuation, and a filter with higher damping is used for less time-critical operation, for example, when the clutch is actuated while the vehicle is in motion. This allows, for example, a highly noisy pressure signal to be robustly differentiated from the minimum and maximum pressures.

[0011] According to an advantageous embodiment of the method, the pump speed is used as at least one operating parameter for this purpose. For example, re-pumping to raise a system pressure that has fallen below the minimum pressure when the pump is otherwise not required to maintain the system pressure can be considered driving operation of the vehicle with the proposed hydraulic system, and filtering with high damping can be applied to the pressure signal. At a high pump speed, for example, it can be assumed that the clutch is being actuated with increasing system pressure, so that filtering with a short time constant is performed to enable high-resolution detection of the pressure signal.The speed of the pump is determined, for example, from the electric motor driving it, by evaluating, for example, any speed sensor that may be present and used for its commutation and / or electrical variables such as its current consumption over time or its operating voltage over time.

[0012] To reduce the system pressure, for example when the maximum pressure is exceeded or to disengage the clutch, a shut-off valve is arranged between the pump and the slave cylinder, for example in the pressure line. When appropriately wired, this shut-off valve releases pressure medium into a depressurized sump. Alternatively or additionally, an operating position of this shut-off valve can be provided as at least one operating parameter for assessing the required filter type. For example, with the shut-off valve open, a first type of filter can be used for a specified time after a pressure increase after the shut-off valve is closed. This first type of filter provides precise time resolution of the pressure signal with low damping, since the clutch is usually closed during this period due to the rising system pressure.However, after a specified time has elapsed after the shut-off valve has closed, it can be assumed that the coupling is closed and a second type of filter with greater damping of the pressure signal can be activated.

[0013] Alternatively or additionally, the vehicle's driving speed can be used 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 that when a predetermined speed is reached, the clutch is closed and engaged. Subsequently, the system switches from the first filter type to the second filter type when the vehicle is traveling at low speed or is stationary. Rolling of the vehicle with the clutch disengaged is taken into account, for example, by evaluating corresponding operating data of the drive unit, load data of the drive train, and / or the like.

[0014] For example, the drive unit can contain an electric motor that operates in a hybrid mode or that drives the vehicle exclusively electrically. In this case, the driving speed can be determined based on the rotational speed of this electric motor and / or, if applicable, at least one other electric motor driving the vehicle.

[0015] The pump for providing the system pressure can advantageously be designed as a reversing pump, wherein a first direction of rotation of the pump generates a pressure medium flow, for example for cooling and / or lubricating components of the vehicle, for example the clutch, transmission parts such as components of a CVT (continuously variable transmission), and / or the like, and the second direction of rotation of the pump actuates the clutch. The direction of rotation of the pump can be provided as at least one parameter, wherein the second filter type with high damping is activated in the first direction of rotation of the pump, and the first filter type is activated in the second direction of rotation, for example to engage the clutch.

[0016] Generally speaking, for example, a first type of filter is applied when the clutch is disengaged, and a second type of filter is applied when the clutch is engaged and the vehicle speed is greater than a specified threshold. The second type of filter exhibits greater signal attenuation than the first type.

[0017] In an advantageous embodiment, in combination of the operating parameters, the second filter type is set after a predetermined time of the actuated clutch, when the shut-off valve between the pump and a depressurized sump is closed, when the pump is operated in a direction of rotation opposite to the direction of rotation setting the system pressure and / or when a vehicle speed exceeds a predetermined threshold value.

[0018] In other words, the ever-increasing complexity of vehicles requires the flawless function and interaction of all components. The functioning of electrical components, in particular, is extremely important for enabling purely electric driving and increasing efficiency. Failure or defects of certain electronic components can have serious consequences for the vehicle.

[0019] Clutch actuation in such vehicles is advantageously pressure-controlled by means of a hydraulic system. If, in an advantageous embodiment, for example, a target state of "clutch engagement" is specified, a shut-off valve closes a pressure line between a pump and a slave cylinder to actuate the clutch relative to a depressurized sump, and the pump begins to deliver pressure medium towards the slave cylinder, building up system pressure. When the system pressure, such as a target pressure between a minimum and maximum pressure, is reached, the pump stops pumping and changes direction of rotation to lubricate and / or cool components of the vehicle / drivetrain. If the system pressure drops too much over time, for example because of a slight leak, and falls below the minimum pressure, the pump pumps pressure medium into the slave cylinder by changing direction of rotation.The system pressure is again checked to see if the required system pressure has been reached. This process is repeated continuously if necessary. If the system pressure rises above the maximum pressure during a pressure-holding phase with the clutch closed, the shut-off valve is opened until the system pressure returns to within the pressure limits between the minimum and maximum pressures. The pressure signals recorded during this process may contain a high level of noise and are filtered accordingly.

[0020] With appropriate filtering, it is important to represent the pressure signals as precisely as possible, for example with as much time accuracy as possible. For this reason, the filtering parameters are set as unrestrictively as possible. It was found that, depending on the vehicle speed and, for example, a system-related clutch misalignment, very strong pressure fluctuations can arise in the hydraulic path between the pump and the slave cylinder. Despite the filtering applied, a very large scatter of the pressure signals is therefore detected in the corresponding software of a control unit that controls the clutch. These pressure fluctuations can, for example, lead to the minimum and maximum pressure being exceeded very quickly one after the other. To prevent these rapid changes in the direction of rotation of the pump and activation of the shut-off valve from leading to system crashes, an improved method for adapting the filtering of the pressure signals is proposed.

[0021] For this purpose, the pressure signals are filtered depending on operating parameters of the vehicle or the hydraulic system for the vehicle, for example a vehicle speed, for example based on a speed of an electric machine driving the vehicle, based on the speed and / or direction of rotation of the pump, based on an operating state of the drain valve and / or the like.

[0022] During clutch actuation, the pressure signal should be as precise as possible so that the clutch can be closed correctly. According to a first advantageous variant, if the speed of the electric motor driving the vehicle is above a speed threshold for closing the clutch, the clutch is closed. During the clutch closing process, the filtering of the pressure signal in a first filter type is as precise as possible. As soon as the clutch is closed, a decision is made depending on the speed of the electric motor whether the clutch remains closed or opens again. If the clutch is to remain closed, a check is carried out to determine whether the speed of the electric motor is greater than or equal to a speed threshold for changing the pressure filter. This threshold can, for example, be just below the maximum speed such as the rated speed of the electric motor. If this is not the case, the first filter type remains unchanged.However, if the speed of the electric motor exceeds the speed threshold and the pump is rotating in the same direction as cooling the components, the pressure signal filtering in a second filter type switches to more stringent filtering of the pressure signal. A distinction is made as to whether the clutch is already closed and is currently in the pressure holding phase, in which the system pressure is maintained by re-pumping or draining, or whether the clutch is open and needs to be completely re-closed. If the clutch is already closed and the pump is only re-pumping, the second filter type is retained because the speed of the electric motor remains above the speed limit for changing the filter type. However, if the clutch is completely re-closed, the system switches to the first filter type.

[0023] A second advantageous variant allows for filter types to be adjusted independently of the electric motor's speed. Only the pump speed and the operating position of the drain valve are evaluated. When the clutch is actuated and the pump is operating in the second direction of rotation, the first filter type is selected. As soon as the pump's rotation direction changes and the shut-off valve is closed, the second filter type is selected.

[0024] Both variants enable sufficiently precise actuation of the clutch as well as trouble-free operation at high speed of the electric motor.

[0025] The invention is based on the Fig. 1 to 4 are explained in more detail. These show: Fig. 1 a schematic representation of a hydraulic system, Fig. 2 a state diagram of the hydraulic system of the Fig. 1 to show the improved filtering method of the pressure signal of the pressure sensor, Fig. 3 a flow chart for setting different filter types of the pressure signal and Fig. 4 a compared to the flow chart of the Fig. 3 modified flowchart.

[0026] The Fig. 1 shows a schematic diagram of the hydraulic system 1 for carrying out the method according to the invention. The hydraulic system 1 contains the pump 2, designed, for example, as a gear pump, which is connected on one side to the coolant line 3 to provide a speed-controlled volume flow of pressure medium. The coolant line 3 supplies pressure medium, such as oil, to at least one first component 4, designed, for example, as a heat exchanger, the separating clutch 17 for its cooling and / or the like. The pressure medium 7 is supplied to this component 4 for the purpose of cooling or lubrication. On the other side, the pump 2 is connected to the pressure line 5. The pressure line 5 serves to pressurize the slave cylinders 6, 8 of the parking lock 9 and the clutch 17. The switching valve 10, such as a two-way switching valve, is provided for the selective actuation of the slave cylinders 6, 8.

[0027] The pump 2 is designed as an electrically driven reversing pump to supply the pressure medium 7 in a first direction of rotation to the coolant line 3 and in a second direction of rotation to the pressure line 5. The pump 2 is driven by the electric motor 11, which is 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 and is connected to the control unit 15 and, via the latter, to a higher-level control unit that controls the entire actuation system.

[0028] The shut-off valve 23, such as a two-way switching valve, serves to reduce the pressure in the pressure line 5 and thus to open the clutch 17 and for this purpose connects the slave cylinder 6 with the sump 13.

[0029] The system pressure present in the pressure line is detected by means of the pressure signals from the pressure sensor 14. Furthermore, the rotational speeds n1, n2 of the input part 18 and the output part 19 of the clutch 17 arranged around the rotational axis d can be detected and evaluated.

[0030] The pressure signals of the pressure sensor 14 are noisy, so that appropriate filter applications are used in the control unit 15 to improve the pressure signals. According to the proposed method, depending on the operating parameters of the hydraulic system 1 or the drive train containing it or the vehicle receiving it, different filter types are applied, adapted to the accuracy, intensity of the noise and / or the like. For example, according to the flow diagrams of the Fig. 3 and Fig. 4 illustrates the application of different filter types, both when the clutch 17 is engaged while the vehicle is in motion and when the clutch is actuated. For example, the speed and / or direction of rotation of the pump 2, the speeds n1, n2, the operating state of the shut-off valve 23, and / or the like can be used to detect these operating states.

[0031] The Fig. 2 shows a schematic diagram of the state diagram 24 with reference to the hydraulic system 1 of the Fig. 1 over time t for an advantageous method for applying different filter types F(1), F(2). Partial diagram I shows the state of the shut-off valve 23 with the states CLOSED and OPEN. Partial diagram II shows the speed n(e) of an electric motor driving the vehicle with the hydraulic system 1, partial diagram III shows the speed n(p) of the bidirectionally operating pump 2, partial diagram IV shows the filtered pressure signal p of the pressure sensor 14, and partial diagram V shows the activation of the different filter types F(1), F(2).

[0032] When the clutch 17 is actuated, for example from the speed limit n(e,k) of the electric motor for driving the vehicle, the shut-off valve 23 is closed at an accelerated speed n(e) and the pump 2 sets the system pressure in a positive direction of rotation, for example the second direction of rotation, using a predetermined speed n(p). Once the system pressure is between the pressure minimum p(min) and the pressure maximum p(max), the pump 2 switches to the negative speed, for example the first 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 while the clutch 17 is engaged and continues pumping to increase the system pressure again.Until time t1, filter type F(1) with less intensive filtering is retained because, for example, due to the speed n(e) or the duration of the actuated clutch 17 or due to other operating parameters, a permanently actuated clutch 17 is not assumed. By operating pump 2 in the first direction or its standstill and opening the shut-off valve 23, the clutch 17 is opened again. From time t1, for example, due to the speed n(e) being above the speed threshold n(e,g) which is just below the speed limit n(e,max), it is assumed that the clutch 17 is permanently actuated and the second filter type F(2), which is capable of filtering even strong disturbances 25, is activated in order to ensure robust evaluation of the pressure signal p and to avoid unwanted re-pumping processes or pressure reductions by means of the shut-off valve 23.

[0033] The Fig. 3 shows with reference to the Fig. 1 and Fig. 2 shows the flowchart 26 with a routine 27, implemented, for example, in the control unit 15 of the hydraulic system, for example, for implementing the proposed method. The routine 27 is started in block 28.

[0034] In branch 29, a check is made to determine whether the speed n(e) of the driving electric motor is less than or equal to the 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 process continues in branch 30.

[0035] Branch 30 checks 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 shut-off valve 23 is open, the system branches to branch 31.

[0036] At branch 31, a check is made to determine whether pump 2 is operating in the first direction of rotation, i.e., pumping pressure medium toward component 4. If pump 2 is pumping toward slave cylinder 6, a check is made at branch 32 to determine 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 maintained in block 36. If this is the case, a branch is made at node 33. If pump 2 is operating in the first direction of rotation at branch 31, i.e., pumping toward component 4, a branch is made at node 33.

[0037] From node 33, the system branches to branch 34, where it is checked whether the speed n(e) of the driving electric machine is greater than or equal to the speed threshold n(e,g). If this is the case, filter type F(2) is set in block 35. If this is not the case, filter type F(1) is set or retained in block 36.

[0038] The Fig.Figure 4 shows the flowchart 37 with the routine 38, simplified compared to routine 27, for implementing the proposed method. Routine 38 is started in block 39.

[0039] In branch 40, a check is made to determine whether the shut-off valve 23 is closed, i.e., in the CLOSED state. If this is not the case and the shut-off valve 23 is open while the clutch 17 is disengaged, the filter type F(1) with a low filter level 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 branch 42 to determine whether the direction of rotation of pump 2 is transporting pressure medium in the direction of component 4, which corresponds to the speed -n(p) in the first direction of rotation. If this is the case, the second filter type F(2) with a stronger filter level is set via node 43 in block 44.

[0040] If branch 42 determines that pump 2 is delivering toward slave cylinder 6, i.e., pump 2 has a positive direction of rotation with speed n(p) in the second direction of rotation, branch 45 checks whether clutch 17 is engaged. To do this, it checks whether the system pressure is greater than or equal to the minimum pressure p(min). If this is the case, filter type F(2) is set via node 43 in block 44. If the system pressure is less than the minimum pressure p(min), filter type F(1) is set in block 41. List of reference symbols 1 hydraulic system 2 pumps 3 coolant line 4 Component 5 Pressure line 6 slave cylinders 7 Pressure Means 8 slave cylinders 9 Parking lock 10 switching valve 11 Electric motor 12 Power electronics 13 Swamp 14 Pressure sensor 15 Control unit 17 Clutch 18 Entrance part 19 Output part 20 slave cylinder pistons 21 Actuator 23 Shut-off valve 24 State diagram 25 Disturbance 26 Flowchart 27 Routine 28 blocks 29 Branching 30 branching 31 branching 32 branching 33 knots 34 Branching 35 blocks 36 blocks 37 Flowchart 38 Routine 39 Block 40 branching 41 Block 42 branching 43 knots 44 Block 45 Branching d axis of rotation F(1) Filter type F(2) Filter type n(e) speed n(e,g) speed threshold n(e,k) speed limit n(e,max) speed limit n(p) speed n1 speed n2 speed p pressure signal p(max) pressure maximum p(min) pressure minimum t time t1 time point

Claims

[1] Method for controlling a hydraulic system (1) for a vehicle with an electrically operated pump (2) which sets a system pressure, wherein the system pressure is controlled between a maximum pressure (p(max)) and a minimum pressure (p(min)) for actuating a clutch (17) by means of a slave cylinder (6), characterized by that a pressure signal (p) of the system pressure is filtered by means of different filter types (F(1), F(2)) depending on at least one operating parameter of the hydraulic system (1). [2] Method according to claim 1, characterized by that the at least one operating parameter is a speed (n(p)) of the pump (2). [3] Method according to claim 1 or 2, characterized by that the at least one operating parameter is an operating position of a shut-off valve (23) arranged between the pump (2) and a pressureless sump (13). [4] Method according to one of claims 1 to 3, characterized bythat at least one operating parameter is a driving speed of the vehicle. [5] Method according to claim 4, characterized by that the driving speed of the vehicle is determined by means of at least one electric machine based on the rotational speed (n(e)) of the at least one electric machine. [6] Method according to one of claims 1 to 5, characterized by that the pump (2) is designed as a reversing pump, wherein a first direction of rotation of the pump (2) generates a pressure medium flow and the second direction of rotation of the pump (2) actuates the clutch (17) and the at least one operating parameter is a direction of rotation of the pump (2). [7] Method according to one of claims 1 to 6, characterized by that a first type of filter (F(1)) is applied when the clutch (17) is open. [8] Method according to one of claims 1 to 7, characterized bythat when the clutch is closed and the driving speed is greater than a predetermined threshold, a second type of filter (F(2)) is applied. [9] Method according to one of claims 1 to 8, characterized by that the second filter type (F(2)) has a higher signal attenuation than the first filter type (F(1)). [10] Method according to one of claims 1 to 9, characterized by that the second type of filter (F(2)) is set after a predetermined time of the actuated clutch (17), with the shut-off valve (23) between the pump (2) and a pressureless sump (13) closed, when the pump (2) is operated in a direction of rotation opposite to that which sets the system pressure and / or when a vehicle speed exceeds a predetermined threshold value.

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