KR102816318B1 - Method for controlling the superimposed shifting of a hydraulically operated dual clutch - Google Patents

Abstract

The present invention relates to a method for controlling the superimposed shifting of a hydraulically actuated dual clutch having two friction clutches (2, 3) which are actuated and disengaged pressurelessly by respective slave cylinders (17, 18), in which the system pressure (p(s)) is set by means of an electrically actuated pump unit (4) and a first pressure control valve (14) arranged downstream of said pump unit, and in which a respective second pressure control valve (19, 20) having a pressure sensor (24, 25) arranged downstream is arranged between said first pressure control valve (14) and said slave cylinders (17, 18), and in which the superimposed shifting of said friction clutches (2, 3) is controlled by the superimposed pressure relief of the first slave cylinder (17, 18) assigned to the engaged first friction clutch (2, 3) and the pressure of the second slave cylinder (18, 17) assigned to the disengaged second friction clutch (3, 2). It is performed by load. In order to form a superimposed shift without pressure surge in the friction clutches (2, 3), in the first stage (A) of the superimposed shift, the system pressure (p(s)) is increased, and in the second stage (B) of the superimposed shift, the system pressure (p(s)) is specified within a specified, basically constant, negative or positive pressure gradient.

Description

Method for controlling the superimposed shifting of a hydraulically operated dual clutch

The present invention relates to a method according to the preamble of claim 1.

Dual clutch transmissions and drive trains having dual clutches with friction clutches connecting two sub-drive trains of a dual clutch transmission with a hybrid drive unit or an internal combustion engine are well known. Shifting of a dual clutch transmission between two gears arranged on two sub-transmissions can be effected by means of so-called superimposed shifting, whereby the engaged friction clutch of the active sub-transmission is disengaged and the friction clutch of the sub-transmission is engaged in a superimposed manner with a new gear.

From documents WO2015/086009 A1 and DE 10 2015 210 877 A1, hydraulic units and methods for controlling them are known for operating the friction clutches of a dual clutch, whereby a system pressure is generated by a pump unit, and by means of pressure control valves, depending on the switching state of the pressure control valves, each slave cylinder is pressure-supplied by the system pressure, and during the overlap shifting, the other slave cylinders are pressure-relieved, so that the friction clutches are shifted in an overlapped manner.

The object of the present invention is to improve a method for controlling the overlapped shifting of the friction clutches of a dual clutch controlled by a hydraulic unit. In particular, the object of the present invention is to perform the overlapped shifting without occurrence of torque peaks on the friction clutches.

The above task is solved by the subject matter of claim 1. The dependent claims of claim 1 reproduce preferred embodiments of the subject matter of claim 1.

The proposed method is used for controlling the superimposed shifting of a hydraulically actuated dual clutch of a dual clutch transmission of a drive train of a vehicle with a purely electric drive, a hybrid drive unit or an internal combustion engine. For this purpose, a routine is stored in the software for controlling the hydraulic unit for actuating the dual clutch and, if necessary, for controlling and/or cooling additional components of the drive train from the control unit.

The above hydraulic unit controls and operates two friction clutches of a dual clutch, formed as a forcibly disengaged friction clutch or preferably as a forcibly engaged friction clutch. A forcibly engaged friction clutch is to be understood as meaning a clutch which is disengaged in the non-operating state and which is engaged under the action of a slave cylinder supplied with pressure by a hydraulic unit, preferably a pump unit.

According to a preferred embodiment of the hydraulic unit, each of the two forcibly engaged friction clutches is actuated by a slave cylinder, for example against the action of a rebound spring, in which case the required pressure, such as the system pressure, is provided by an electrically actuated pump unit. The friction clutches can be formed as dry single-disk or multi-disk clutches or as wet-acting disc clutches having disc packs in which friction plates and counter plates are arranged alternately. In the case of dry-acting friction clutches, the slave cylinders can therefore be formed from a slave cylinder housing and a slave cylinder piston which can be displaced in this slave housing depending on the pressure, which, under the clamping of the friction linings of the clutch discs, exerts an initial stress on the pressure plate against the counter-pressure plate in a pressure-dependent manner and thus forms the frictional engagement of the friction clutch. In the case of wet-acting friction clutches, a pressure port provided as a slave cylinder may be integrated into the clutch housing, said pressure port being axially displaceable by contacting a pressure chamber, thereby applying an initial stress to the disc pack of the friction clutch in a pressure-dependent manner, thereby forming a frictional engagement of the friction clutch.

The pump unit is controlled by a control unit and can be designed as a tandem pump, which on the one hand supplies the system pressure over a common system pressure line (common rail) and on the other hand supplies one or more volume flows for operating or cooling components of the drive train. For example, wet-acting friction clutches can be cooled by the volume flow of the pump unit. In addition to controlling the rotational speed of the pump unit, the system pressure is controlled and the pump unit is operated for economical operation at low pressure with high volume flow demand or at high pressure with low volume flow demand, depending on the application.

A first pressure control valve for setting the system pressure is arranged downstream of the pump unit for controlling the system pressure in the system pressure line. For this purpose, the first pressure control valve can be connected to the pressure medium flow. Preferably, the system pressure in the system pressure line is set to a dynamic pressure, and the first pressure control valve is connected to a drain or discharge line of the system pressure line so that by means of the wiring of the first pressure control valve the pressure medium is discharged into the discharge line, for example into a line section for cooling. In this case, closing the pressure control valve increases the system pressure.

Between the slave cylinders and the pressure line for operating the friction clutches, a second pressure control valve is arranged in each case. In order to monitor the pressure on the slave cylinders, a pressure sensor is arranged in each case between the slave cylinders and the second pressure control valves. A check valve is arranged in front of each of the second pressure control valves, so that the pressure set on each slave cylinder can be maintained for at least a short time, independently of the system pressure. In particular, a pressure drop that may occur on the slave cylinders due to a leak occurring on the second pressure control valves is readjusted by the second pressure control valves when the system pressure is sufficiently set.

In this case, the torque that can be transmitted through the friction clutches is set by the first pressure control valve and by the system pressure, which depends on the target moment.

The torque transmitted through each engaged friction clutch is provided by the pressure supply of the associated slave cylinder. The corresponding pressure, such as the clutch pressure, is detected by a pressure sensor. The assignment of the detected pressure values to the corresponding torque values that can be transmitted through the friction clutch is carried out in the control unit with reference to the corresponding characteristic curve or characteristic diagram.

The superimposed shifting from an active gear of a sub-transmission with an engaged friction clutch to another already engaged gear of another sub-transmission with a disengaged friction clutch is in each case effected by a superimposed operation of the friction clutches by means of a superimposed pressure relief of the slave cylinder assigned to the engaged friction clutch and a pressure load of the other slave cylinder assigned to the disengaged friction clutch.

In order to be able to control the moment curve very precisely during the overlap shifting and to avoid structure-related pressure peaks of the pressure control valves, in the first stage of the overlap shifting the system pressure is increased, while in the second stage of the overlap shifting the system pressure is set within a preset, essentially constant, negative or positive pressure gradient. An essentially constant negative or positive pressure gradient is to be understood as meaning that a sudden increase in system pressure is prevented in order to prevent the friction clutch to be engaged from engaging too quickly due to the pressure build-up in the system pressure. In this case, in particular when fast shifting is required, a negative pressure gradient can be set in the second stage, whereas in the case of shifting that is not time-dependent, a constant or slightly positive pressure gradient can be provided.

For example, at the start of the first stage, the system pressure can be significantly increased, for example by operating the first pressure control valve, for example by completely closing the passage from the system pressure line to the discharge line and by reducing the pump rotational speed of the pump unit. At the start of the first stage, by means of the increased system pressure by means of the second pressure control valve and the check valve assigned to the engaged first friction clutch, the first friction clutch can be temporarily kept engaged, if necessary even in the presence of a leak. At the same time, the first friction clutch is overpressured at least for a short time. In this case, the second pressure control valve assigned to the disengaged second friction clutch is closed. At the same time, the check valve maintains the pressure applied to the slave cylinder.

In the first stage, the system pressure is lowered by the reduced pump rotation speed. When the system pressure drops, the second pressure control valve assigned to the second friction clutch opens and the second slave cylinder is charged with the pressure medium. Due to the reduced system pressure, the engagement of the second friction clutch does not occur immediately and the second stage of the superimposed shifting is switched.

When the second stage starts after the second slave cylinder is charged, the second pressure control valve assigned to the second friction clutch is closed and the system pressure increases. In the second stage, the second pressure control valve assigned to the first friction clutch is preferably closed in two stages while forming a negative pressure gradient.

In this case, the second pressure control valve assigned to the second friction clutch can be opened gradually together with the second stage of the second pressure control valve closing of the first friction clutch.

The present invention is described in more detail with reference to the embodiments illustrated in FIGS. 1 and 3.

In the drawing section:
FIG. 1 is a hydraulic circuit diagram schematically illustrating a hydraulic unit for operating a dual clutch, FIG. 2 is a schematic diagram illustrating a pressure control valve of the hydraulic unit of FIG. 1, and FIG. 3 is a diagram illustrating overlapping shifting over time.

Figure 1 schematically illustrates a hydraulic unit (1) for operating two friction clutches (2, 3) of a dual clutch transmission of a dual clutch transmission. The hydraulic unit (1) can operate and/or cool components (not shown to scale) of a drive train with a dual clutch transmission. The functions of such a hydraulic unit (1) are not illustrated.

The hydraulic unit (1) has an electrically actuated control pump unit (4), which is formed herein as a tandem pump (5). The pump unit (4) transports pressure medium from a sump (6) through a filter unit (7). A relatively large pump section (8) transports a large amount of pressure medium at low pressure into a cooling line (9) and through a heat exchanger (10) to components (11) to be cooled, for example wet-acting friction clutches (2, 3), brakes, transmission components and/or others.

A relatively small pump unit (12) generates a system pressure (p(s)) in the system pressure line (13). The applied system pressure (p(s)) is set on the one hand by the rotational speed of the pump unit (4) and on the other hand by the pressure control valve (14). In order to set the system pressure (p(s)), the pressure control valve (14) connects the system pressure line (13) with the cooling line (9).

Two pressure lines (15, 16) can be connected to the system pressure line (13), which provide the clutch pressures (p(K1) and p(K2)) to the slave cylinders (17, 18) via the pressure control valves (19, 20) and the check valves (21, 22) to operate the friction clutches (2, 3). Additional components (23) connected to the system pressure line (13), such as a parking lock, are not essential for the operating function of the friction clutches (2, 3). The clutch pressures (p(K1) and p(K2)) supplied to the slave cylinders (17, 18), which control the pressing force of the friction clutches (2, 3) and thus the torque that can be transmitted to these friction clutches, are detected by pressure sensors (24, 25) and evaluated by a control unit which also controls the pump unit (4) and the pressure control valves (14, 19, 20).

In normal driving outside the gears of a dual clutch transmission, one of the friction clutches (2, 3) is engaged and the other is disengaged. For this purpose, the corresponding pressure control valve (19, 20) of the engaged friction clutch (2, 3) is connected to the system pressure line (13), the other pressure control valve (20, 19) is connected to the sump (6). The check valves (21, 22) maintain the clutch pressure (p(K1), p(K2)) of the engaged friction clutch (2, 3) in this case by opening the pressure control valve (14) under the corresponding clutch pressure (p(K1), p(K2)) and/or by correspondingly controlling the pump unit (4), independently of a decrease in the system pressure (p(s)). If the clutch pressure (p(K1), p(K2)) of the engaged friction clutch (2, 3) falls below a clutch pressure (p(K1), p(K2)) value corresponding to the preset desired moment, the system pressure (p(s)) is reduced, for example, by closing the pressure control valve (14) until the required clutch pressure (p(K1), p(K2)) and, if applicable, an overpressure are reached.

When shifting between the currently active gear of the sub-transmission with the engaged friction clutch (2, 3) and the newly active gear of the sub-transmission with the disengaged friction clutch (3, 2), the engaged friction clutch (2, 3) is disengaged and the disengaged friction clutch (3, 2) is temporarily engaged in an overlapped manner. In order to perform the overlapped shifting, both the wiring of the pressure control valves (19, 20) on the friction clutches (2, 3) and the wiring of the pressure control valve (14) must be changed while taking into account and preventing the pressure peaks acting on the friction clutches (2, 3) during the shifting process of the pressure control valves (14, 19, 20). For this purpose, the overlapped shifting is performed in two steps as illustrated in the diagram (100) of Fig. 3.

With reference to FIG. 1, FIG. 2 schematically illustrates one of the pressure control valves (14, 19, 20) having a pressure inlet along the arrow (26) and a pressure outlet along the arrow (27). The pressure control valve (14, 19, 20) is actuated by a control piston (29) which is axially displaceable along the double arrow (28), which controls the pressure medium flow through the pressure inlet and outlet by means of control edges (30, 31). The control piston (29) is actuated by a magnetic force (F(M)) of an electronically controlled solenoid valve along the double arrow (28) against the action of a spring element (not shown) and a return force (F(C)). In particular at the start of the connection of the control edges (30, 31) and the corresponding pressure inlet or pressure outlet, pressure peaks occur on the pressure control valves (14, 19, 20), which can either negatively affect the system pressure (p(s)) in the system pressure line (13) or on the torque that can be transmitted via the pressure lines (15, 16) and thereby via the slave cylinders (17, 18) via the friction clutches (2, 3). For example, a friction clutch that is to be engaged can suddenly transmit torque and a friction clutch that is to be disengaged can engage again in the slip phase. Both processes result in uncomfortable overlapping shifting.

In order to avoid pressure peaks on the friction clutches (2, 3), Fig. 3 shows a diagram (100) of a typical superimposed gear change by disengaging the friction clutch (2) and engaging the friction clutch (3) with reference to Fig. 1. For this purpose, the diagram (100) shows seven partial diagrams (I, II, III, IV, V, VI, VII) according to time (t).

In a partial diagram with rotational speed (n) as a function of time (t), the rotational speed curve (101) represents the rotational speed (n(GE1)) of the transmission input shaft of the sub-transmission with the friction clutch (2) engaged at the start of the overlap shifting, the rotational speed curve (102) represents the rotational speed (n(GE2)) of the transmission input shaft of the sub-transmission with the friction clutch (3) disengaged at the start of the overlap shifting and, together with this, the output rotational speeds of the friction clutches (2, 3) as a function of time (t). The rotational speed curve (103) represents the rotational speed (n(M)) of the crankshaft of the internal combustion engine and, together with this, the input rotational speeds of the friction clutches (2, 3) as a function of time (t).

Partial diagram II shows the moments (M) of the friction clutches (2, 3) as a function of time (t). The moment curve (104) represents a target moment (M(K1, soll)) to be transmitted through the friction clutch (2) such as a desired moment, the moment curve (105) represents a target moment (M(K2, soll)) of the friction clutch (3), the moment curve (106) represents an actual moment (M(K1, ist)) transmitted through the friction clutch (2), and the moment curve (107) represents an actual moment (M(K2, ist)) transmitted through the friction clutch (3).

Partial diagrams III and IV represent the unfiltered valve flow and the filtered valve flow (i, i(F)) for operating the pressure control valve (14, 19, 20) over time (t). The flow curve (108) represents the unfiltered valve flow (i(14)) of the pressure control valve (14), the flow curve (109) represents the unfiltered valve flow (i(19)) for operating the friction clutch (2), and the flow curve (110) represents the unfiltered valve flow (i(20)) of the pressure control valve (20) for operating the friction clutch (3).

The flow curve (111) represents the filtered valve flow (i(14, F)) of the pressure control valve (14), the flow curve (112) represents the filtered valve flow (i(19, F)) for operating the friction clutch (2), and the flow curve (113) represents the filtered valve current (i(20, F)) of the pressure control valve (20) for operating the friction clutch (3).

Partial diagram V shows the pump rotational speed (n(P)) versus time (t) in the rotational speed curve (114).

In the partial diagram VI of pressure (p) versus time (t), the system pressure (p(s)) is shown in the pressure curve 115, the clutch pressure (p(K1)) of the pressure line (15) is shown in the pressure curve 116, and the clutch pressure (p(K2)) of the pressure line (16) versus time (t) is shown in the pressure curve 116. The pressure curve 117 shows the system pressure (p(s)) versus time (t).

Finally, partial diagram VII with path (s) over time t shows the path curve 118 of the control piston position (s(19)) of the pressure control valve (19) over time (t) and the path curve 119 of the control piston position (s(20)) of the pressure control valve (20).

Up to a point in time (t), torque is transmitted from the internal combustion engine of the sub drive train to the drive wheels with the friction clutch (2) engaged, and the rotational speed (n(M)) and the rotational speed (n(GE1)) of the internal combustion engine are equal except for a micro-slip in the friction clutch (2). Current is supplied to the pressure control valve (19), the pressure control valve (14) is open, and is closed for a short time only when the clutch pressure (p(K1)) drops due to a leak, otherwise the check valve (21) maintains the clutch pressure (p(K1)).

At time t1 the overlapped shifting is initiated and within the time interval Δt(A) the first stage (A) begins. At time t1 the system pressure (p(s)) increases significantly due to the closing of the pressure control valve (14). This leads to a pressure increase of the clutch pressure (p(K1)) which is maintained on the check valve (21). The pressure peak caused by the switching of the pressure control valve (14) is of no importance, since the friction clutch (2) is engaged anyway and the pressure control valve (20) of the friction clutch (3) to be engaged is still open. After the pressure peak has decreased, in stage A the system pressure (p(s)) decreases and the pressure line (16) and the slave cylinder (18) are quickly charged at the low system pressure (p(s)) and the high volume flow. After charging has taken place, the system pressure (p(s)) rises again at the end of stage A due to the increased stiffness of the charged pressure line (16).

At the beginning of phase B at time point (t2), which takes place between time points (t2, t3) within the time interval (Δt(B)), the system pressure (p(s)) is reduced again by opening the pressure control valve (14), and the clutch pressure (p(K2)) is also reduced again, while the pressure line (16) and the slave cylinder (18) remain charged. Due to the opening of the pressure control valve (14) and the leakage of the pressure control valve (19) and due to the time-delayed opening, the friction clutch (2) is gradually lowered, while the control piston of the pressure control valve (19) is set so that the pressure medium does not approach the pressure line (15) but is discharged into the sump (6). The system pressure (p(s)) increases again towards the end of phase B, so that the torque transmission in the friction clutch (3) gradually increases, while the torque transmission in the friction clutch (2) decreases.

)) 설정에 의해 압력 매체의 배출 및 그에 따라 마찰 클러치(2)의 완만하고 제어 방식 체결 해제가 가능해짐으로써 방지될 수 있다. 그 결과 클러치 압력(p(K1))의 감소하는 압력 구배가 달성된다. 대안적으로 단계 B에서 시스템 압력(p(S))은, 압력 라인(15)으로 전파되는 시스템 압력 라인(13)의 압력 펄스를 피하기 위해 서서히 증가될 수 있다. 이러한 절차는 특히 중첩 변속이 시간에 구애 받지 않을 때 제공될 수 있다.The essential purpose of the two-stage guide of the superimposed shifting in stages A and B is to prevent undesirable torque peaks in the friction clutches (2, 3) as a result of pressure peaks occurring at the pressure control valves (14, 19, 20) during the path change. The first pressure peak at the pressure control valve (14) in stage A is prevented by keeping the friction clutch (2) pressed in the pressurized state while the slave cylinder (18) of the still disengaged friction clutch (3) and the pressure line (16) are charged. A second pressure surge for the disengaged friction clutch (3) is prevented by the inflow of pressure medium into the pressure line (15) and the corresponding position (s(19,

)) setting, this can be prevented by allowing a discharge of the pressure medium and thus a gentle and controlled disengagement of the friction clutch (2). As a result, a decreasing pressure gradient of the clutch pressure (p(K1)) is achieved. Alternatively, in step B the system pressure (p(S)) can be increased gradually in order to avoid pressure pulses in the system pressure line (13) propagating into the pressure line (15). This procedure can be provided in particular when the superimposed shifting is not time-critical.

): 위치
s(20): 위치
t: 시간
t1: 시점
t2: 시점
t3: 시점
Δt(A): 시간 간격
Δt(B): 시간 간격1: Hydraulic unit
2: Friction Clutch
3: Friction Clutch
4: Pump unit
5: Tandem pump
6: Sump
7: Filter unit
8: Pump section
9: Cooling line
10: Heat exchanger
11: Components
12: Pump section
13: System pressure line
14: Pressure control valve
15: Pressure line
16: Pressure line
17: Slave Cylinder
18: Slave Cylinder
19: Pressure control valve
20: Pressure control valve
21: Check valve
22: Check valve
23: Components
24: Pressure sensor
25: Pressure sensor
26: Arrow
27: Arrow
28: Double Arrows
29: Control piston
30: Control Edge
31: Control Edge
100: Diagram
101: Rotational speed curve
102: Rotation speed curve
103: Rotation speed curve
104: Moment Curve
105: Moment Curve
106: Moment Curve
107: Moment Curve
108: Flow curve
109: Flow curve
110: Flow curve
111: Flow curve
112: Flow curve
113: Flow curve
114: Rotation speed curve
115: Pressure curve
116: Pressure curve
117: Pressure curve
118: Path Curve
119: Path Curve
A: Step
B: Step
F(C): Rebound
F(M): Magnetic force
i: valve flow
i(F): valve flow
i(14): valve flow
i(14,F): valve flow
i(19): valve flow
i(19,F): valve flow
i(20): valve flow
i(20,F): valve flow
M: Moment
M(K1,ist): actual moments
M(K1,soll): Target moment
M(K2,ist): actual moment
M(K2,soll): Target moment
N: Rotation speed
n(GE1): Rotation speed
n(GE2): Rotation speed
n(M): rotational speed
N(p): Pump rotation speed
P: Pressure
p(K1): Clutch pressure
p(K2): Clutch pressure
p(s): system pressure
s: path
s(19): location
s(19,

): location
s(20): location
t: time
t1: time point
t2: point in time
t3: viewpoint
Δt(A): time interval
Δt(B): time interval

Claims (10)

A method for controlling the overlapped shifting of a hydraulically actuated dual clutch, comprising two friction clutches (2, 3) actuated by respective slave cylinders (17, 18) and disengaged without pressure, wherein a system pressure (p(s)) is set by an electrically actuated pump unit (4) and a first pressure control valve (14) arranged downstream of the pump unit, and between the first pressure control valve (14) and the slave cylinders (17, 18), a respective second pressure control valve (19, 20) having a pressure sensor (24, 25) arranged downstream is arranged, and wherein the overlapped shifting of the friction clutches (2, 3) is performed by the overlapped pressure relief of the first slave cylinder (17, 18) assigned to the engaged first friction clutch (2, 3) and the pressure load of the second slave cylinder (18, 17) assigned to the disengaged second friction clutch (3, 2). A method for controlling overlap shifting of a hydraulically operated dual clutch, characterized in that in a first stage (A) of the overlap shifting, the system pressure (p(s)) increases, and in a second stage (B) of the overlap shifting, the system pressure (p(s)) is preset within a preset, basically constant, negative or positive pressure gradient. A method for controlling the overlapped shifting of a hydraulically operated dual clutch, characterized in that in the first paragraph, at the start of the first stage (A), the first pressure control valve (14) arranged between the system pressure line (13) and the cooling line (9) is completely closed, and the pump speed (n(p)) of the pump unit (4) is lowered. A method for controlling a superimposed shift of a hydraulically operated dual clutch, characterized in that, at the start of the first stage (A), the first friction clutch (2) is kept closed by the system pressure (p(s)) increased by the second pressure control valve (19) and the check valve (21) assigned to the first friction clutch (2). A method for controlling a superimposed shift of a hydraulically operated dual clutch, characterized in that in the second or third paragraph, after the system pressure (p(s)) is reduced in the first step (A), the second pressure control valve (20) assigned to the second friction clutch (3) is opened and the second slave cylinder (18) is filled with a pressure medium. A method for controlling a superimposed shift of a hydraulically operated dual clutch, characterized in that in the fourth paragraph, at the start of the second stage (B) after the second slave cylinder (18) is charged, the second pressure control valve (20) assigned to the second friction clutch is closed, and the system pressure (p(s)) increases. A method for controlling the overlapped shifting of a hydraulically operated dual clutch, characterized in that in the second or third paragraph, the second pressure control valve (19) assigned to the first friction clutch (2) in the second step (B) is set to be closed toward the slave cylinder (17) and opened toward the sump (6). In the sixth paragraph, the position (s(19,) of the control piston of the second pressure control valve (19) in the second stage (B)

)) is characterized in that the system pressure (p(s)) is increased by the first pressure control valve (14) and the second pressure control valve (20) assigned to the second friction clutch (3) is gradually opened. A method for controlling the superimposed shifting of a hydraulically operated dual clutch, characterized in that the torque that can be transmitted through the friction clutches (2, 3) according to any one of claims 1 to 3 is set by the system pressure (p(s)) that is set by the first pressure control valve (14) and is set according to the target torque (M(K1, soll), M(K2, soll)). A method for controlling the superimposed shifting of a hydraulically actuated dual clutch, characterized in that in any one of claims 1 to 3, the torque transmitted via each engaged friction clutch (2, 3) is provided by pressurization of the associated slave cylinder (17, 18), the clutch pressure (p(K1), p(K2)) applied to the slave cylinder (17, 18) is maintained by a check valve (21, 22), and the leakage in the subsequent pressure line (15, 16) leading to the slave cylinder (17, 18) is controlled by pressure control by a respective second pressure control valve (19, 20). A method for controlling the superimposed shifting of a hydraulically operated dual clutch, characterized in that in the 9th paragraph, the clutch pressure (p(K1), p(K2)) is detected by the pressure sensor (24, 25), and torque values that can be transmitted through the friction clutches (2, 3) are assigned to the control unit using a characteristic curve based on the pressure values detected by the pressure sensor.