Method for operating an actuation device for actuating a switch element of a transmission for a drivetrain of a motor vehicle, and actuation device

Abstract

The invention relates to a method for operating an actuation device (12) for actuating a switch element of a transmission (10) for a drivetrain of a motor vehicle in which the actuation device (12) has an actuation piston (18) which can be displaced, relative to a housing (14) of the actuation device (12), in a first direction (22) and in a second direction (24), opposite the first direction (22), in order to actuate the switch element. A first pressure chamber (16) is provided, into which an actuation fluid can be introduced, as a result of which the actuation piston (18) can be acted on by actuation fluid and as a result can be displaced relative to the housing (18) in the first direction (22) from a first position (ST1) into a second position of the actuation piston (18). A second pressure chamber (20) is provided which is opposite the first pressure chamber (16) along the first direction (22), into which second pressure chamber the actuation fluid can be introduced, as a result of which the actuation piston (18) can be acted on by the actuation fluid and as a result can be displaced relative to the housing (14) in the second direction (24) from the second position into the first position (ST1) of the actuation piston (18).

Description

[0001] Method for operating an actuating device for actuating a shift element of a transmission for a drive train of a motor vehicle and actuating device

[0002] The invention relates to a method for operating an actuating device for actuating a shift element of a transmission for a drive train of a motor vehicle, in particular a motor vehicle. The invention also relates to such an actuating device.

[0003] Motor vehicles with drive trains are well known from the general state of the art and in particular from series vehicle construction, wherein the respective motor vehicle is drivable by means of the respective drive train. The respective drive train has, for example, a respective transmission which has at least one or more shifting elements. The respective shifting element is used, for example, to connect a transmission element of the transmission, which can generally be rotated about an axis of rotation relative to an element, to the element in a rotationally fixed manner. The element is, for example, a housing of the transmission or another transmission element. In order to selectively connect the transmission element to the element in a rotationally fixed manner by means of the shifting element or to decouple it from the element so that the transmission element can be rotated relative to the element, an actuating device is usually used by means of which the shifting element can be switched.Thus, the switching element can be switched, for example, between a coupling state in which the transmission element is connected to the element in a rotationally fixed manner by means of the switching element, and a decoupling state in which the transmission element is rotatable relative to the element.

[0004] The object of the present invention is to provide a method for operating an actuating device for actuating a shifting element of a transmission for a drive train of a motor vehicle, as well as such an actuating device, so that the shifting element can be actuated particularly advantageously. This object is achieved by a method having the features of patent claim 1 and by an actuating device having the features of patent claim 10. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

[0005] A first aspect of the invention relates to a method for operating an actuating device for actuating a shifting element of a transmission for a drive train of a motor vehicle, also referred to as a motor vehicle drive unit. This means that the motor vehicle, also referred to simply as a vehicle and designed, for example, as a motor vehicle, in particular as a passenger car, in its fully manufactured state has the drive train and thus the transmission and the actuating device and the shifting element. In particular, the motor vehicle can be driven by means of the drive train. The drive train has, for example, at least or exactly one engine, by means of which the motor vehicle can be driven via the transmission. The engine can be an internal combustion engine or an electric machine, thus an electric motor.For example, the shifting element is arranged in a transmission region of the transmission and thus of the drive train. For example, the transmission has a first transmission element and a second transmission element. For example, the shifting element can be used to selectively connect the first transmission element in a rotationally fixed manner to the second transmission element or to decouple it from the second transmission element, wherein, when the first transmission element is decoupled from the second transmission element, the first transmission element is rotatable relative to the second transmission element. In particular, for example, the shifting element can be switched between a coupled state and an uncoupled state. In the coupled state, for example, the first transmission element is connected in a rotationally fixed manner to the second transmission element by means of the shifting element, whereby relative rotations between the transmission elements about a rotational axis are prevented.In the uncoupled state, the first transmission element is rotatable about the axis of rotation relative to the second transmission element. In other words, for example, the switching element in the uncoupled state releases the transmission elements for a relative rotation between the transmission elements about the axis of rotation. For example, the first transmission element is a gearwheel. For example, the second transmission element is a transmission housing of the transmission. For example, the first transmission element is arranged in the transmission housing. By actuating the switching element, for example, the switching element can be switched between the coupled state and the uncoupled state. Thus, for example, by means of the actuating device by actuating the switching element, the switching element can be switched optionally into the coupled state or into the uncoupled state.

[0006] In the method, the actuating device has an actuating piston which, in order to actuate the switching element, can be displaced relative to a housing of the actuating device in a first direction and in a second direction opposite to the first direction. For example, the housing is the aforementioned transmission housing. For example, the actuating piston is arranged in the housing. The actuating piston, also simply referred to as the piston, can thus be displaced, i.e. moved translationally, selectively in the first direction or in the second direction relative to the housing. In particular, the switching element can be actuated by displacing the actuating piston in the first direction, and for example, the switching element can be actuated by displacing the piston in the second direction.For example, the switching element can be engaged or closed by moving the actuating piston in the first direction, i.e. in particular brought or transferred from the uncoupled state into the coupled state. For example, the switching element can be disengaged or deactivated by moving the piston in the second direction, i.e. in particular brought or transferred from the coupled state into the uncoupled state or switched. The reverse is of course conceivable. It is conceivable for the second transmission element to be rotatable about the axis of rotation relative to the transmission housing, so that in the coupled state the first transmission element and the second transmission element can be rotated together or simultaneously about the axis of rotation relative to the transmission housing. In the uncoupled state, for example, the first transmission element and the second transmission element can be rotatable about the axis of rotation relative to one another and relative to the housing.Furthermore, it is conceivable for the second transmission element to be the transmission housing, so that, for example, in the coupled state, in particular by means of the switching element, the first transmission element is rotationally fixed to the housing. In the uncoupled state, the first transmission element is rotatable about the rotational axis relative to the housing.

[0007] The actuating device has a first pressure chamber, arranged in particular in the housing, into which an actuating fluid can be introduced, i.e., introduced. Preferably, the actuating fluid is a component of the actuating device in the method. Most preferably, the actuating fluid is a liquid, thus a hydraulic fluid. For example, the actuating device has a first line element, also referred to as a first line, through which the actuating fluid can flow. The actuating fluid flowing through the first line element can be introduced into the first pressure chamber via the first line element.

[0008] By introducing the actuating fluid into the first pressure chamber, the first actuating piston can be at least indirectly, in particular directly, subjected to the actuating fluid and can thereby be displaced in the first direction and thus from a first position to a second position of the actuating piston relative to the housing. For example, by introducing the actuating fluid into the first pressure chamber, the actuating piston can be at least indirectly, in particular directly, subjected to the actuating fluid in that the first pressure chamber is partially and directly delimited by the actuating piston, so that the actuating fluid contained in the first pressure chamber can directly contact the actuating piston.

[0009] In the method, the actuating device also has a second pressure chamber, which is arranged in particular in the housing and is opposite the first pressure chamber along the first direction. The actuating fluid can be introduced, i.e., introduced, into the second pressure chamber, whereby the actuating piston can be at least indirectly, in particular directly, exposed to the actuating fluid and can thereby be displaced in the second direction opposite the first direction, and thus from the second position to the first position of the actuating piston relative to the housing.For example, by moving the actuating piston from the first position to the second position, the switching element can be engaged, i.e. in particular, transferred, brought or switched from the uncoupled position to the coupled position, and / or, for example, by moving the actuating piston from the second position to the first position, the switching element can be disengaged or deactivated, i.e. in particular, transferred, brought or switched from the coupled state to the uncoupled state. The reverse is of course easily possible. For example, by introducing the actuating fluid into the second pressure chamber, the actuating piston can be at least indirectly, in particular directly, pressurised with the actuating fluid in such a way that the second pressure chamber is partially and directly delimited by the actuating piston.As a result, the actuating fluid introduced into the second pressure chamber and thus received in the second chamber can directly contact the actuating piston. In particular, it is conceivable for the first direction and the second direction to coincide with a common straight line, which, for example, runs parallel to the aforementioned axis of rotation or coincides with the axis of rotation. Thus, for example, the piston is displaceable relative to the housing in the axial direction of the switching element and the actuating device. For example, the respective pressure chamber is delimited, in particular directly, by the piston in a delimiting direction running perpendicular to the respective direction and thus, for example, perpendicular to the axis of rotation.The limiting direction runs, for example, in the radial direction of the actuating device, the radial direction of which runs perpendicular to the axial direction of the actuating device and thus perpendicular to the axis of rotation and in particular perpendicular to the respective direction. In particular, it is conceivable for the actuating piston to have a jacket surface on the outer circumference, by means of which the respective pressure chamber is delimited, in particular directly, in the limiting direction. In this case, it is conceivable for the jacket surface on the outer circumference of the piston to be cylindrical at least in its length region running along the respective direction, and thus has the shape of a right circular cylinder, wherein it is preferably provided that the jacket surface on the outer circumference is completely cylindrical at least in the length region in the circumferential direction of the piston running around the respective direction.

[0010] In order to be able to move the piston particularly advantageously and thereby actuate and thus switch the switching element particularly advantageously and in particular quickly, the method according to the invention provides that after a first displacement of the actuating piston in the second direction and thereby into the first position and before a second displacement of the actuating piston in the first direction and thus into the second position immediately following the first displacement and while the actuating piston is in the first position as a result of the first displacement, a first pressure increase is brought about in the second pressure chamber by means of the actuating fluid, during which or by which the actuating piston is at least indirectly, in particular directly, acted upon with the actuating fluid, whereupon the second displacement, which immediately follows the first displacement, is brought about,by causing a second pressure increase in the first pressure chamber by means of the actuating fluid, during which or through which the actuating piston is at least indirectly, in particular directly, actuated with the actuating fluid. The feature that the second displacement immediately follows the first displacement is to be understood as meaning that no other displacement of the piston in the first direction occurs between the first displacement and the second displacement. It should be explicitly noted at this point that the ordinals relating to the displacement of the actuating piston, also referred to as ordinal numbers, such as "first" and "second", are not to be understood in such a way that the wording "first displacement" means that the first displacement is the total displacement occurring after manufacture of the actuating device.This is the very first displacement of the piston, and that the phrase "second displacement" is not to be understood as meaning that the second displacement is the second displacement occurring after the manufacture of the actuating device and following the first displacement. Rather, with regard to the displacements, the ordinal numbers are used to conceptually distinguish the displacements and thus to be able to clearly refer to the displacements of the actuating piston. In particular, with regard to the displacements of the actuating piston, the ordinal numbers are used to clearly describe a temporal sequence of the displacements, in this case in particular such that the second displacement immediately follows the first displacement, thus the first displacement immediately precedes the second displacement. The same applies to the pressure increases.

[0011] The first pressure increase is to be understood in particular as meaning that after the first displacement and before the first pressure increase, a pressure prevailing in the second pressure chamber has a first value, wherein during or as a result of the first pressure increase, the pressure prevailing in the second pressure chamber is increased from the first value to a second value that is higher than the first value. It is conceivable that after the first displacement and before the first pressure increase, the actuating fluid is absorbed into the second pressure chamber, or the second pressure chamber is at least partially or completely filled with the actuating fluid, or no actuating fluid is absorbed in the second pressure chamber.Accordingly, the second pressure increase is understood to mean that, through or during the second pressure increase, the pressure prevailing in the first pressure chamber is increased from a third value to a fourth value that is greater than the third value, in order to thereby displace the actuating piston in the first direction and thus from the first position to the second position. In this case, before the second pressure increase, the first pressure chamber can be at least partially or completely filled with the actuating fluid, or before the second pressure increase, no actuating fluid is contained in the first pressure chamber.

[0012] Since the actuating piston can be moved either in the first direction or in the second direction, the piston is a double-acting piston, also known as a double-acting hydraulic piston. The method enables advantageous alignment of the actuating piston, particularly relative to the housing after the first displacement and before the second displacement, which is or causes an actuation of the switching element, also known as a switching operation. The switching element is actuated by both the first displacement and the second displacement, for example in such a way that the switching element is disengaged by the first displacement and engaged by the second displacement, or vice versa. The switching element is thus actuated by the second pressure increase, in particular in such a way that the switching element is engaged or disengaged.However, during the first pressure increase occurring before the second pressure increase, the switching element is not actuated because the first pressure increase occurs, and is therefore carried out, while the actuating piston is already in the first position. The first pressure increase can, however, cause a movement, particularly relative to the housing, and thus an alignment of the actuating piston, whereby an unfavorable alignment or position of the piston, for example a misalignment of the actuating piston, relative to the housing is corrected or canceled before the second displacement and after the first displacement, so that the actuating piston is in the first position after the first pressure increase and before the second pressure increase and is therefore in an advantageous position, particularly relative to the housing.As a result, the second displacement can take place without problems, for example without excessive friction or tilting of the piston. In particular, the method according to the invention enables advantageous alignment of the piston after the first displacement and before the second displacement, without the need for complex, costly and space-intensive mounting of the piston. For example, the first pressure increase taking place after the first displacement and before the second displacement and before the second pressure increase can cause a pivoting movement of the actuating piston relative to the housing such that an unfavorable position of the actuating piston relative to the housing, such as a misalignment of the piston, is canceled out, so that the second displacement can be advantageously carried out. The invention is based in particular on the following findings and considerations:

[0013] During operation of the motor vehicle, the piston, also referred to as a hydraulic piston or designed as a hydraulic piston, is intended to actuate the switching element highly dynamically. It is therefore desirable to be able to move the piston quickly and reproducibly relative to the housing in order to actuate the switching element quickly and, above all, reproducibly. The respective displacement of the actuating piston which causes a respective actuation of the switching element is also referred to as the switching process of the actuating piston. Thus, the first displacement and the second displacement are switching processes of the piston. When reference is made to a switching process in the following, this refers to a switching process of the actuating piston, unless otherwise stated. Since the second increase in pressure causes the second displacement, the second increase in pressure causes a switching process of the actuating piston.The first pressure increase does not cause a switching operation of the actuating piston, but can ensure such a movement, in particular pivoting, of the piston, in particular relative to the housing, that the piston is advantageously aligned relative to the housing after the first displacement and before the second displacement in order to displace the actuating piston quickly, with low friction and without jamming during or as a result of the second displacement of the actuating piston. This is particularly advantageous when the switching element is designed as a positive-locking switching element, in particular as a claw clutch. The method according to the invention makes it possible to advantageously align the piston before each switching operation of the piston without having to use a space-consuming and cost-intensive piston bearing.It has been found that, for example, if the actuating piston is not advantageously aligned, particularly relative to the housing, before a switching operation of the actuating piston, so that, for example, the actuating piston is tilted before a switching operation of the actuating piston, this can lead to an uneven pressure buildup in the respective pressure chamber and possibly to a canting of the actuating piston. This can lead to an excessively long time required for the respective switching operation of the actuating piston and thus for the respective actuation of the switching element, also referred to as the switching time or switching duration, which can lead to a loss of comfort. The aforementioned disadvantages and problems can now be avoided by the method according to the invention.Any misalignment of the actuating piston before the second displacement and after the first displacement can be caused, for example, by vibrations that occur, for example, during the first displacement and / or after the first displacement and before the second displacement. Furthermore, any misalignment of the actuating piston after the first displacement and before the second displacement can be caused, for example, by the first displacement itself, i.e., by previous switching operations of the actuating piston prior to the second displacement.Such misalignments, as well as other unfavorable positions of the actuating piston in the first position, can be corrected, i.e., eliminated, by the first pressure increase, so that after the first pressure increase and before the second pressure increase, and thus in particular before the second displacement, the piston is in the first position and in an advantageous position or orientation, in particular the desired position and / or desired orientation, so that the second displacement can be carried out quickly. In summary, the actuating piston is aligned by the first pressure increase immediately before the second displacement so that the actuating piston can be actuated quickly and reproducibly and thus carry out the second displacement.The alignment of the actuating piston occurs through or via the first pressure increase in the second pressure chamber, which is opposite the first pressure chamber and by means of which the second displacement to be carried out is brought about, namely by carrying out the second pressure increase in the first pressure chamber. The respective pressure increase in the respective pressure chamber is also referred to as pressurising the respective pressure chamber. Pressurising the respective pressure chamber means that the pressure prevailing in the respective pressure chamber is increased, for example by a quantity of actuating fluid initially arranged outside the respective pressure chamber being introduced into the respective pressure chamber, i.e. being introduced, in particular being pumped in, and / or by increasing the pressure of the actuating fluid already held in the respective pressure chamber.

[0014] If the actuating device is designed, for example, in such a way that the switching element can be engaged, i.e. transferred from the uncoupled state to the coupled state, by moving the actuating piston in the first direction, and if the actuating device is designed or constructed, for example, in such a way that the switching element can be disengaged, i.e. transferred from the coupled state to the uncoupled state, by moving the actuating piston in the second direction, then the first pressure chamber is also referred to, for example, as the “pressure chamber engaged” and the second pressure chamber is also referred to as the “pressure chamber disengaged”. The respective pressure chamber is also referred to as the respective piston chamber. Thus, for example, the switching element is disengaged by the first displacement, and thus, for example, the switching element is engaged by the second displacement.Thus, for example, the method according to the invention provides that after the switching element has been disengaged by the first displacement and before the switching element has been inserted by the second displacement, the second pressure chamber actually designed for disengagement is pressurized in order to advantageously align the actuating piston in the first position and subsequently to displace it in the first direction by pressing on the first pressure chamber, thus inserting the switching element. In other words, if the switching element is to be inserted, specifically by pressing on the first pressure chamber, the opposite "pressure chamber disengaged" is printed before the switching element is inserted, i.e. before the "pressure chamber inserted" is printed, and only then is the "pressure chamber inserted" printed to effect the second displacement. The reverse can occur accordingly.If, for example, the actuating piston is initially in the second position and the switching element is to be disengaged, the "pressure chamber engaged" is printed before the "pressure chamber disengaged" is printed in order to advantageously align the actuating piston in the second position, whereupon the "pressure chamber disengaged" is printed and thus the actuating piston is moved from the second position to the first position and in the second direction, and the switching element is disengaged. Since, for example, a respective switching process of the actuating piston and thus a respective actuation of the switching element is always triggered, in particular, by an electronic computing device, also referred to as a control unit, the respective printing of the respective pressure chamber intended to align the actuating piston can be carried out without any problems before the respective switching process of the piston.The respective pressure chamber opposite the respective pressure chamber that is to be or is being pressurized to trigger a switching operation of the actuating piston is also referred to as the counter chamber or opposite side, so that by pressing the respective opposite side, the actuating piston is aligned before a switching operation of the actuating piston is triggered. The method according to the invention thus enables the following advantages in particular:

[0015] - reproducible switching times and starting times

[0016] - Risk of jamming of the piston is avoided

[0017] - an uneven start, i.e. loose movement of the piston, is avoided.

[0018] Overall, it can be seen that the second pressure increase causes the second displacement of the actuating piston and thus the second actuating piston is moved from the first position to the second position and thus in the first direction relative to the housing. The first pressure increase does not cause a switching operation of the actuating piston because the actuating piston is already in the first position when the pressure is first increased. The first pressure increase therefore prevents the switching element from being actuated. The first pressure increase therefore does not serve to actuate the switching element but, as previously described, to align the actuating piston after the first displacement and before the second displacement, in particular relative to the housing, and thus to bring it into an advantageous position or orientation while the actuating piston remains in the first position.

[0019] In order to be able to align and move the actuating piston particularly as needed so that the switching element can be actuated particularly advantageously, one embodiment of the invention provides that the actuating device has a first valve device which can be supplied with the actuating fluid and which can be switched, in particular moved, between a first switching position and a second switching position. In the first switching position, the actuating fluid supplied to the first valve device is supplied to the first pressure chamber via the first valve device, thus introduced into the first pressure chamber and thus introduced into the first pressure chamber. In the second switching position, the actuating fluid supplied to the first valve device is supplied to the second pressure chamber via the first valve device, thus introduced into the second pressure chamber.Also provided is a second valve device which can be supplied with the actuating fluid and which can be switched, in particular moved, between a third switching position and a fourth switching position. In the third switching position, the actuating fluid supplied to the second valve device is supplied via the second valve device to the first valve device, which can thereby be supplied with the actuating fluid and thus subsequently can selectively pass the actuating fluid supplied to the first valve device into the first pressure chamber or into the second pressure chamber. In the fourth switching position, the first valve device is not supplied with the actuating fluid via the second valve device. For example, in the fourth switching position, the actuating fluid supplied to the second valve device is supplied via the second valve device to a cooling device of the motor vehicle.For example, at least a portion of the motor can be cooled by means of the cooling device. For example, the portion of the motor, also referred to as the drive motor, is or includes a rotor and / or a stator of the drive motor, particularly when the drive motor is embodied as the aforementioned electric machine.

[0020] In order to be able to align and also displace the actuating device particularly advantageously, a further embodiment of the invention provides that, to effect the first pressure increase, the second valve device is in the third switching position and, in particular, simultaneously, the first valve device is in the second switching position. Furthermore, it is provided that, to effect the second pressure increase, the second valve device is in the third switching position and, in particular, simultaneously, the first valve device is in the first switching position.A further embodiment of the invention is characterized in that, to effect the first pressure increase, the second valve device is switched from the fourth switching position to the third switching position at a first point in time. To effect the second pressure increase and while the second valve device remains in the third switching position, the first valve device is switched from the second switching position to the first switching position at a second point in time following the first point in time. As a result, the actuating piston can be initially aligned and then displaced in a short time and thus particularly quickly.

[0021] To achieve a particularly advantageous actuation of the switching element, it has proven particularly advantageous if a time period between the first point in time and the second point in time, and thus, for example, the second point in time, is dependent on a temperature and / or is adjusted, i.e., varied, depending on the temperature. Thus, the actuating piston can be quickly aligned and, in particular, subsequently displaced, so that the switching element can be actuated particularly advantageously.

[0022] In a further embodiment of the invention, it is provided that a second time period is determined which lies between the first point in time and a determination time following the first point in time, at which determination time a movement of the switching element following the first point in time is determined. The determined second time period is compared as the actual time period with at least one reference period which characterizes the second time period determined in at least one previous, past implementation of the method. The time period between the first point in time and the second point in time, also referred to as the first time period, is increased if the comparison determines that the actual time period is longer than the reference period. As a result, the actuating piston can be aligned quickly, i.e. in a short time, and subsequently moved.

[0023] In a further, particularly advantageous embodiment of the invention, it is provided that a first time period is determined which lies between the first time and a determination time following the first time, at which determination time a movement of the switching element following the first time is determined. The determined first time period is compared as the actual time period with at least one reference period which characterizes the first time period determined in at least one previous, past implementation of the method. In this case, a second time period between the first time and the second time is set as a function of the comparison, in particular such that the second time period is increased if it is determined by the comparison that the actual time period is greater than the reference period.As a result, the actuating piston can be advantageously aligned and, in particular, subsequently displaced, so that the total time required for aligning the actuating piston and for a subsequent switching operation of the actuating piston can be advantageously kept low.

[0024] In order to be able to move the actuating piston in both the first direction and the second direction in a highly dynamic and thus particularly fast manner, a further embodiment of the invention provides that after the second movement of the actuating piston in the first direction and before a third movement of the actuating piston in the second direction immediately following the second movement, during which the actuating piston is in the second position as a result of the second movement, a third pressure increase is brought about in the first pressure chamber, which is now the opposite side, by means of the actuating fluid, during which the actuating piston is actuated by the actuating piston and a switching operation of the actuating piston, thus an actuation of the switching element, is omitted, whereupon the third movement is brought about and thus the switching element is actuated,by causing a fourth pressure increase in the second pressure chamber by means of the actuating fluid, during which the actuating piston is pressurised with the actuating fluid.

[0025] Finally, it has proven particularly advantageous if the respective pressure increase is brought about by introducing, i.e. introducing, a quantity of the actuating fluid initially arranged outside the respective pressure chamber into the respective pressure chamber.

[0026] A second aspect of the invention relates to an actuating device for actuating a shift element of a transmission for a drive train of a motor vehicle, wherein the actuating device is designed to carry out a method according to the first aspect of the invention. Advantages and advantageous embodiments of the first aspect of the invention are to be regarded as advantages and advantageous embodiments of the second aspect of the invention, and vice versa.

[0027] Further advantages, features, and details of the invention will become apparent from the following description of a preferred embodiment and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respective specified combinations, but also in other combinations or on their own, without departing from the scope of the invention.

[0028] The drawing shows:

[0029] Fig. 1 shows a partial schematic longitudinal sectional view of a transmission for a motor vehicle, with an actuating device for actuating a shift element of the transmission;

[0030] Fig. 2 shows a further schematic longitudinal sectional view of the transmission;

[0031] Fig. 3 is a schematic representation of the actuating device;

[0032] Fig. 4 is a diagram illustrating a method of operating the actuating device;

[0033] Fig. 5 is a further schematic representation of the actuating device; and

[0034] Fig. 6 shows a further schematic representation of the actuating device.

[0035] In the figures, identical or functionally identical elements are provided with the same reference symbols.

[0036] Fig. 1 and 2 each show a detail in a schematic longitudinal sectional view of a transmission 10 of a drive train for a motor vehicle. This means that the motor vehicle, also referred to simply as a vehicle and preferably designed as a motor vehicle, in particular as a passenger car, in its fully manufactured state has the drive train, also referred to as a motor vehicle drive train, and can be driven by means of the drive train. The drive train comprises the transmission 10, via which, for example, the motor vehicle can be driven, in particular by a drive motor of the drive train. The transmission 10 has an actuating device 12, by means of which, as will be explained in more detail below, a shifting element of the transmission 10 can be actuated.The transmission 10 has, for example, a first transmission element (not visible in the figures), which can be or comprise a gear, for example. Furthermore, the transmission 10 has a second transmission element, wherein the transmission elements can be connected to one another in a rotationally fixed manner by means of the switching element mentioned. This is to be understood in particular that the switching element can be switched between a coupled state and a decoupled state. In the coupled state, the transmission elements are connected to one another in a rotationally fixed manner, in particular by means of the switching element. In the decoupled state, the transmission elements can be rotated relative to one another, in particular about a rotational axis.The second transmission element is, for example, a transmission housing of the transmission 10, so that, for example, in the coupled state, the first transmission element is fixed to the transmission housing in a rotationally fixed manner, in particular by means of the shifting element, thereby preventing rotation of the first transmission element about the rotational axis relative to the transmission housing. In the uncoupled state, the first transmission element is rotatable about the rotational axis relative to the transmission housing. Thus, the shifting element is, for example, a brake shifting element, in particular a brake claw.

[0037] The actuating device 12 has a housing 14, which can be, for example, the transmission housing or a part of the transmission housing. Furthermore, the actuating device 12 has a first pressure chamber 16 arranged in the housing 14. An actuating fluid, preferably in the form of a liquid, in particular oil, can be introduced into the first pressure chamber 16, in particular via a first line element of the actuating device 12. The actuating device 12 also has an actuating piston 18, which is also simply referred to as a piston. The actuating device 12 also has a second pressure chamber 20, into which the actuating fluid can be introduced and thus introduced, in particular via a second line element of the actuating device 12.To actuate the switching element, the actuating piston 18 is displaceable, and thus translationally movable, relative to the housing 14 either in a first direction indicated by an arrow 22 or in a second direction opposite the first direction indicated by an arrow 24. Thus, the piston (actuating piston 18) is displaceable in the first direction and in the second direction relative to the housing 14. By introducing the actuating fluid into the first pressure chamber 16, the actuating piston 18 can be directly subjected to the actuating fluid and can thus be displaced in the first direction and from a first position ST1 into a second position of the actuating piston 18 relative to the housing 14. It can be seen that the pressure chambers 16 and 20 are opposite one another, in this case such that the second pressure chamber 20 is opposite the first pressure chamber 16 along the first direction.By introducing, i.e. introducing, the actuating fluid into the second pressure chamber 20, the actuating piston 18 can be directly actuated with the actuating fluid and can thus be displaced in the second direction and from the second position to the first position of the actuating piston 18 relative to the housing 14. The respective displacement of the actuating piston 18 from the first position ST 1 to the second position and from the second position to the first position ST 1, also referred to as displacement, is also referred to as a respective switching operation of the actuating piston 18. By one or the respective switching operation of the actuating piston 18, the switching element is or is actuated or actuated, i.e. switched, so that the respective switching operation of the actuating piston 18 is accompanied by a respective switching operation of the switching element, which is actuated during the respective switching operation of the switching element.Thus, the respective switching operation of the actuating piston 18 is to be understood as synonymous with the respective switching operation of the switching element and vice versa.

[0038] In the exemplary embodiment shown in the figures, the switching element is engaged, i.e., moved, transferred, or switched from the uncoupled state to the coupled state, by moving the actuating piston 18 in the first direction from the first position ST1 to the second position. Furthermore, the switching element is disengaged, i.e., moved, transferred, or switched from the coupled state to the uncoupled state, by moving the actuating piston 18 in the second direction from the second position to the first position ST1.

[0039] The directions illustrated by arrows 22 and 24 coincide with a straight line that, for example, runs parallel to the axis of rotation or coincides with the axis of rotation. In particular, the axis of rotation runs in the axial direction of the switching element and / or the transmission 10 and / or the actuating device 12.

[0040] For example, the switching element can be moved relative to the housing 14 between two switching element positions. A first of the switching element positions is a coupling position, which effects the coupling state, and a second of the switching element positions is a decoupling position, which effects the decoupling state. In other words, if the switching element is in the coupling position, the switching element is in the coupling state. If the switching element is in the decoupling state, the switching element is in the decoupling position. Thus, for example, the first position of the actuating piston 18 coincides with the decoupling position, so that, for example, and in particular always when the actuating piston 18 is in the first position ST1, the switching element is in the decoupling position.Furthermore, for example, the second position of the actuating piston 18 corresponds to the coupling position, so that, for example, and in particular always when the actuating piston 18 is in the second position, the switching element is in the coupling position. Thus, for example, by moving the actuating piston 18 from the first position ST1 to the second position, the switching element can be moved from the uncoupling position to the coupling position. Furthermore, for example, by moving the actuating piston 18 from the second position to the first position ST1, the switching element can be moved from the coupling position to the uncoupling position. The respective pressure chamber 16, 20 is also referred to as the piston chamber or actuating chamber.

[0041] Viewed along the respective direction, a respective seal 26, 28 is arranged on this side and on the other side of the first pressure chamber 16, wherein the seal 26 is also referred to as the first seal and the seal 28 is also referred to as the second seal. It can be seen that the first seal 26 is arranged on a first side of the pressure chamber 16, and the second seal 28 is arranged on a second side of the pressure chamber 16, wherein the sides are also referred to as axial sides and lie opposite one another along the respective direction. The seals 26 and 28, which are also referred to as sealing elements, are spaced apart from one another when viewed along the respective direction, in particular such that the first pressure chamber 16 is arranged between the seals 26 and 28 along the respective direction.By means of the seals 26 and 28, the actuating piston 18 is sealed against the housing 14, in particular such that the seal 26 bears, on the one hand, in particular directly, against the actuating piston 18, in particular against an outer peripheral surface 30 of the actuating piston 18, and on the other hand, in particular directly, against the housing 14, in particular in the radial direction of the actuating device 12, the radial direction of which runs perpendicular to the axial direction of the actuating device 12 and perpendicular to the axis of rotation and perpendicular to the respective direction. Accordingly, for example, the seal 28 bears, on the one hand, in particular directly, against the actuating piston 18, in particular against the outer peripheral surface 30, and on the other hand, in particular directly, against the housing 14, in particular in the radial direction. Furthermore, Fig.1 and 2 that the outer peripheral surface 30 faces the pressure chamber 16 in the radial direction of the actuating device 12, in particular of the transmission 10 as a whole. The pressure chamber 16 is delimited in a delimiting direction illustrated by an arrow 32, and in particular in the radial direction of the actuating device 12, directly inwardly by the outer peripheral surface 30 of the actuating piston, which is also simply referred to as the piston. This is to be understood in particular that the actuating fluid received in the first pressure chamber 16 directly contacts the outer peripheral surface 30 or the actuating piston 18. The delimiting direction illustrated by the arrow 32 runs perpendicular to the respective direction and thus perpendicular to the axis of rotation and to the axial direction of the actuating device 12.

[0042] 1 and 2, the actuating piston 18 is displaced in the first direction, illustrated by arrow 22, relative to the housing 14 when the actuating fluid is introduced into the pressure chamber 16 and, in particular, when this causes a pressure increase in the pressure chamber 16 and the actuating piston 18 is initially in the first position ST1. The actuating piston 18 is displaced in the second direction, illustrated by arrow 24, relative to the housing 14 when the actuating fluid is introduced into the second pressure chamber 20 and, in particular, when this causes a pressure increase in the pressure chamber 20 and the actuating piston 18 is initially in the second position.

[0043] The actuating piston 18 has a first actuating surface B1, which can be acted upon, in particular directly, by the actuating fluid introduced into the first pressure chamber 16. By actuating the first actuating surface B1, the actuating piston 18 can be displaced in the first direction and thus from the first position ST1 into the second position. The actuating surface B1 partially and directly delimits the first pressure chamber 16, at least in the first position ST1. The actuating piston 18 also has a second actuating surface B2, which in this case can be directly acted upon by the actuating fluid introduced into the second pressure chamber 20. By actuating the second actuating surface B2, the actuating piston 18 can be displaced from the second position into the first position ST1 and thus in the second direction relative to the housing 14. The second pressure chamber 20 is partially and directly delimited by the second actuating surface B2.

[0044] In the exemplary embodiment shown in the figures, the actuating piston 18 has, in particular, a step 34 arranged at least in the first position ST1 along the respective direction between the seals 26 and 28, with the first actuating surface B1, in particular, arranged at least in the first position ST1 along the respective direction between the seals 26 and 28, also referred to as the active surface, which extends obliquely or perpendicularly to the respective direction. The actuating surface B2 also extends obliquely or perpendicularly to the respective direction.If the actuating fluid is now introduced into the first pressure chamber 16, the actuating fluid can flow directly onto the first actuating surface B1 and thus act directly on the first actuating surface B1, which is hereby, in particular directly, subjected to the actuating fluid introduced, i.e., introduced, into the first pressure chamber 16 and can thus be acted upon. As a result, in order to actuate the switching element, the actuating piston 18 can be displaced along the first direction, i.e., in the first direction, relative to the housing 14. If the actuating fluid is introduced, i.e., introduced, into the second pressure chamber 20, the actuating fluid can flow directly onto the second actuating surface B2 and thus act directly on the second actuating surface B2, which is hereby, in particular directly, subjected to the actuating fluid introduced, i.e., introduced, into the second pressure chamber 20 and can thus be acted upon.As a result, the actuating piston 18 can be displaced in the second direction relative to the housing 14 to actuate the switching element. The first direction is referred to as the first sliding direction, and the second direction is also referred to as the second sliding direction.

[0045] In order to be able to move the actuating piston 18 highly dynamically and thus particularly quickly and subsequently switch, i.e. actuate, the switching element highly dynamically and thus particularly quickly, the actuating device 12 is operated by means of a method which is carried out, for example, by means of an electronic control unit and is explained below. In the method for operating the actuating device 12, after a first displacement of the actuating piston 18 in the second direction and thus into the first position and before a second displacement of the actuating piston 18 in the first direction and thus into the second position immediately following the first displacement and while the actuating piston is in the first position ST1 as a result of the first displacement, a first pressure increase is brought about in the second pressure chamber 20 by means of the actuating fluid, at which the actuating piston 18,in particular the actuating surface B2, is actuated with the actuating fluid and an actuation of the switching element, thus a switching operation of the actuating piston 18 and a switching operation of the actuating element, does not occur or does not occur, whereupon the second displacement is effected by a second pressure increase being effected in the first pressure chamber 6 by means of the actuating fluid, during which the actuating piston 18, in particular the first actuating surface B1, is actuated with the actuating fluid. Both the first displacement and the second displacement are thus switching operations of the actuating piston 18, so that both the first displacement and the second displacement result in a respective actuation of the switching element. Thus, the switching element is actuated by the second pressure increase, in this case in such a way,that the switching element is engaged. However, during the first pressure increase, the switching element is not actuated. This means that, as a result of the first pressure increase, both the switching of the switching element from the coupled state to the uncoupled state and the switching of the switching element from the uncoupled state to the coupled state are prevented, i.e., they do not occur. The first displacement is or was caused, for example, by a further pressure increase in the second pressure chamber 20, wherein, during the further pressure increase, the actuating piston 18, and in particular the second actuating surface B2, is or was actuated by the actuating fluid. Between the first displacement and the second displacement, there is no actuation of the switching element and thus no displacement of the actuating piston 18 from the first position ST1 to the second position. The first pressure increase therefore does not serve to effect a switching operation of the actuating piston 18.This means that the first pressure increase does not serve to actuate the switching element, but rather the actuating piston 18 located in the first position ST1 can be advantageously aligned relative to the housing 14 by means of the first pressure increase in order to then be moved quickly and with little friction from the first position ST1 to the second position and subsequently to be able to actuate the switching element.

[0046] Fig. 2 shows the actuating piston 18 in the first position ST1, wherein the actuating piston 18 is in an unfavorable alignment or position, designed as an oblique position, relative to the housing 14. Thus, after the first displacement, before the second displacement, the second pressure chamber 20 is pressurized, for example by introducing a quantity of the actuating fluid initially arranged outside the pressure chamber 20 into the pressure chamber 20 and / or by increasing the pressure of the actuating fluid held in the pressure chamber 20. As a result, the actuating piston 18 can be moved from the oblique position shown in Fig. 2 into an advantageous alignment shown in Fig. 1 relative to the housing 14, while the actuating piston 18 remains in the first position ST1, thus preventing a displacement of the actuating piston 18 from the first position ST1 to the second position.The second pressure increase is then effected, and for example, a pressure reduction in the pressure chamber 20 is permitted, for example in such a way that a discharge of the actuating fluid from the pressure chamber 20 is permitted and / or in such a way that a pressure reduction of the actuating fluid received in the pressure chamber 20 is permitted.

[0047] Fig. 3 shows a schematic representation of the actuating device 12. A reservoir in which the actuating fluid can be received or is received is designated by 36. The actuating device 12 has a first valve device 38 and a second valve device 40. The first valve device 38 can be supplied with the actuating fluid and can be switched between a first switching position S1 and a second switching position S2. In the first switching position S1, the actuating fluid supplied to the first valve device 38 is introduced into the first pressure chamber 16 via the first valve device 38. In the second switching position of the first valve device 38, the actuating fluid supplied to the first valve device 38 is introduced into the second pressure chamber 20 via the first valve device 38, so that in Fig. 3 the valve device 38 is in the second switching position S2.The valve device 40 can be switched between a third switching position S3 and a fourth switching position S4. In the third switching position, the actuating fluid supplied to the second valve device 40 is fed via the second valve device 40 to the first valve device 38, which can then optionally forward the actuating fluid supplied to the valve device 38 into the first pressure chamber 16 or into the second pressure chamber 20. In the fourth switching position S4, the first valve device 38 is not supplied with the actuating fluid via the second valve device 40. In the fourth switching position S4, the actuating fluid supplied to the valve device 40 is fed via the valve device 40 to a cooling device 42, shown particularly schematically in Fig. 3, by means of which the drive motor, designed for example as an electric motor, can be cooled using the actuating fluid. In Fig.3, the valve device 40 is in the third switching position S3. Also provided is a pump 44, preferably designed as an electric pump, by means of which the actuating fluid can be conveyed from the reservoir 36 and conveyed to the valve device 40, whereby the valve device 40 can be supplied with the actuating fluid, thus whereby the actuating fluid can be supplied to the valve device 40. In the third switching position S3, the actuating fluid conveyed by the pump 44 and thereby supplied to the valve device 40 is supplied to the valve device 38 via the valve device 40.In the fourth switching position S4, the actuating fluid conveyed by means of the pump 44 and thereby conveyed to the valve device 40 is guided by means of, i.e. via, the valve device 40 to the cooling device 42, so that the valve device 38 is not supplied with the actuating fluid conveyed by means of the pump 44 via the valve device 40.

[0048] Fig. 4 shows a diagram with time plotted on the abscissa 46. A pressure prevailing in the pressure chamber 20 is plotted on the ordinate 47, so that a curve 48 illustrates the pressure prevailing over time in the second pressure chamber 20, for example caused by the actuating fluid. In Fig. 4, a total time period is designated G, which is also referred to as the total time duration. The total time period G comprises, in this case precisely, two time periods Z1 and Z2 as partial time periods, with the time periods Z1 and Z2 also being referred to as time durations. The total time period G begins at a first time t1 and ends at a second time t2, which follows time t1 in time. The time period Z1 begins at time t1 and ends at a third time t3, which follows time t1 and lies before time t2 in time and thus lies between time t1 and t2.The second time period Z2 begins at time t3 and ends at time t2.

[0049] The respective valve device 38, 40 can be supplied with electrical energy, i.e. with electrical current, and can thereby be switched from one of the respective switching positions to the other of the switching positions. Supplying the respective valve device 38, 40 with electrical energy, i.e. with electrical current, is also referred to as energizing the respective valve device 38, 40. If the respective valve device 38, 40 is not supplied with electrical current, the respective valve device 38, 40 is in a de-energized state, and thus the respective valve device 38, 40 is de-energized. In the present case, by energizing the valve device 38, the valve device 38 can be switched from the switching position S2 to the switching position S1, so that the valve device 38 assumes the second switching position S2 when the valve device 38 is de-energized.By energizing the valve device 40, the valve device 40 can be switched from the fourth switching position S4 to the third switching position S3, so that the valve device 40 assumes the fourth switching position S4 when the valve device 40 is not energized.

[0050] Thus, to effect the first pressure increase, the second valve device 40 is in the third switching position S3, and the first valve device 38 is in the second switching position S2. To effect the second pressure increase, the second valve device 40 is in the third switching position S3, and the first valve device 38 is in the first switching position S1. As can be seen and illustrated in Fig. 3, for example, at time t1 the valve device 40 is energized and thereby switched to the third switching position S3, while the valve device 38 is and remains de-energized. For example, in the first switching position S1 the actuating fluid can flow from the valve device 38 into the first pressure chamber 16 via the first line element; for example, in the second switching position S2 the actuating fluid can flow from the valve device 38 into the second pressure chamber 20 via the second line element.

[0051] As a result, for example, during the time period Z1, the second line element and, for example, also the second pressure chamber 20 are pre-filled with the actuating fluid. Thus, during the time period Z1, the valve device 40 is energized and the valve device 38 is de-energized. Also during the time period Z2, the valve device 40 is and remains energized and the valve device 38 remains de-energized, thereby causing the first pressure increase in the second pressure chamber 20. As a result, the actuating piston 18 is aligned relative to the housing 14, in particular as a result of circumferential pressure and thus the application of force resulting from the first pressure increase. For example, the actuating piston 18 is positioned at an end stop of the housing 14.In order to effect the second pressure increase and thus the second displacement after the first pressure increase, the valve device 38 is energized, for example, at the second time t2, and thereby switched from the second switching position S2 to the first switching position S1, while the valve device 40 remains energized. This is illustrated in Fig. 5. As a result, the valve device 38 is supplied with the actuating fluid via the valve device 40, and the actuating fluid is introduced into the first pressure chamber 16 by the valve device 38, thereby effecting the second pressure increase in the first pressure chamber 16. This results in a switching operation of the actuating piston 18 and a switching operation of the switching element, which occurs, for example, during a second overall time period G2, which begins at time t2 and ends, for example, at a fourth time t4 following the time t2. Thus, the time t2 lies between the times t3 and t4.After the second displacement of the actuating piston 18, the current supply to the valve device 40 is terminated, thus the valve device 40 is switched to its de-energized state, so that the.

[0052] Valve device 40 is switched from switching position S3 to switching position S4, and, for example, the energization of valve device 38 is also terminated, which is thus switched from switching position S1 to switching position S2. This is indicated in Fig. 6. The actuating fluid delivered to valve device 40 by pump 44 is then guided via valve device 40 to cooling device 42, whereby supply of the actuating fluid to valve device 38 via valve device 40 is omitted.

[0053] The time t2 can, for example, be set, i.e., varied, in particular depending on a temperature, in particular of the actuating fluid, and / or the actuating device 12 and / or the drive motor. The time t2 can, for example, be determined by a reproducible pre-filling behavior and a pressure rise rate, in particular such that, for example, the time t2 is read from a characteristic map as a function of the pre-filling behavior and the pressure rise rate. Through regular switching operations, i.e. switching processes during operation, a pre-filling time and thus the pre-filling behavior can be continuously learned and remains precise over the service life despite any deviations.A residual pressure resulting in particular from the first pressure increase and, for example, still prevailing in the second pressure chamber 20 during the second pressure increase keeps the actuating piston 18 stable in its advantageous orientation, so that the second displacement can then be carried out quickly.

[0054] List of reference symbols

[0055] 10 gearboxes

[0056] 12 Actuating device

[0057] 14 housings

[0058] 16 first printing room

[0059] 18 actuating pistons

[0060] 20 second printing room

[0061] 22 Arrow

[0062] 24 Arrow

[0063] 26 Seal

[0064] 28 Seal

[0065] 30 outer circumferential surface

[0066] 32 Arrow

[0067] 34th level

[0068] 36 Reservoir

[0069] 38 first valve device

[0070] 40 second valve device

[0071] 42 Cooling device

[0072] 44 Pump

[0073] 46 Abscissa

[0074] 47 Ordinates

[0075] 48 History

[0076] G Total time span

[0077] G2 Total time span

[0078] B1 first actuating surface

[0079] B2 second actuating surface

[0080] S1 first switching position

[0081] S2 second switching position

[0082] S3 third switching position

[0083] S4 fourth switching position

[0084] ST1 first position t1 time (small t in the text) t2 time t3 time t4 time

[0085] Z1 time span

[0086] Z2 time span

Claims

Patent claims 1. A method for operating an actuating device (12) for actuating a shift element of a transmission (10) for a drive train of a motor vehicle, in which: - the actuating device (12) comprises: o an actuating piston (18) which, for actuating the switching element, is displaceable relative to a housing (14) of the actuating device (12) in a first direction (22) and in a second direction (24) opposite to the first direction (22); o a first pressure chamber (16) into which an actuating fluid can be introduced, whereby the actuating piston (18) can be acted upon by the actuating fluid and can thereby be displaced in the first direction (22) from a first position (ST1) into a second position of the actuating piston (18) relative to the housing (18);and o a second pressure chamber (20) opposite the first pressure chamber (16) along the first direction (22), into which second pressure chamber the actuating fluid can be introduced, whereby the actuating piston (18) can be acted upon by the actuating fluid and can thereby be displaced in the second direction (24) from the second position into the first position (ST1) of the actuating piston (18) relative to the housing (14); - after a first displacement of the actuating piston (18) in the second direction (24) and before a second displacement of the actuating piston (18) in the first direction (22) immediately following the first displacement and while the actuating piston (18) is in the first position (ST1) as a result of the first displacement, a first pressure increase is effected in the second pressure chamber (20) by means of the actuating fluid, at which the The actuating piston (18) is acted upon with the actuating fluid, whereupon the second displacement is effected by causing a second pressure increase in the first pressure chamber (16) by means of the actuating fluid, during which the actuating piston (18) is acted upon with the actuating fluid.

2. Method according to claim 1, characterized in that: - a first valve device (38) is provided which can be supplied with the actuating fluid and which can be switched between: o a first switching position (S1), in which the actuating fluid supplied to the first valve device (38) is introduced into the first pressure chamber (16) via the first valve device (28); and o a second switching position (S2), in which the actuating fluid supplied to the first valve device (38) is introduced into the second pressure chamber (20) via the first valve device (38); and - a second valve device (40) is provided which can be supplied with the actuating fluid and which can be switched between: o a third switching position (S3), in which the actuating fluid supplied to the second valve device (40) is supplied via the second valve device (40) to the first valve device (38), which is thereby supplied with the actuating fluid; and o a fourth switching position (S4), in which the first valve device (38) is not supplied with the actuating fluid supplied to the second valve device (40) via the second valve device (40).

3. Method according to claim 2, characterized in that: - to effect the first pressure increase, the second valve device (40) is in the third switching position (S3) and the first valve device (38) is in the second switching position (S2); and - to effect the second pressure increase, the second valve device (40) is in the third switching position (S3) and the first valve device (38) is in the first switching position (S1).

4. Method according to claim 3, characterized in that in order to effect the first pressure increase, the second valve device (40) is switched from the fourth switching position (S4) into the third switching position (S3) at a first time (t1), wherein in order to effect the second pressure increase and while the second valve device (40) remains in the third switching position (S3), the first valve device (38) is switched from the second switching position (S2) into the first switching position (S1) at a second time (t2) following the first time (T1).

5. Method according to claim 4, characterized in that a time period (G) between the times (t1, t2) is dependent on a temperature and / or is set depending on the temperature.

6. Method according to claim 5, characterized in that: - a second time period is determined which lies between the first time (t1) and a determination time following the first time (t1), at which determination time a movement of the switching element following the first time is determined; - the determined second time period is compared as the actual time period with at least one reference period which characterises the second time period determined in at least one previous, past execution of the method; and - the time duration (G) is increased if the comparison shows that the actual time duration is greater than the reference duration.

7. Method according to claim 4, characterized in that: - a first time period is determined which lies between the first time (t1) and a determination time following the first time (t1), at which determination time a movement of the switching element following the first time (t1) is determined; - the determined first time period is compared as the actual time period with at least one reference period which characterises the first time period determined in at least one previous, past implementation of the method; and - a second time period (G) between the first time (t1) and the second time (t2) is set as a function of the comparison.

8. Method according to one of the preceding claims, characterized in that after the second displacement of the actuating piston (18) in the first direction (22) and before a third displacement of the actuating piston (18) in the second direction (24) immediately following the second displacement, and while the actuating piston (18) is in the second position as a result of the second displacement, a third pressure increase is brought about in the first pressure chamber (16) by means of the actuating fluid, during which the actuating piston (18) is acted upon with the actuating fluid, whereupon the third displacement is brought about in that a fourth pressure increase is brought about in the second pressure chamber (20) by means of the actuating fluid, during which the actuating piston (18) is acted upon with the actuating fluid.

9. Method according to one of the preceding claims, characterized in that the respective pressure increase is effected by introducing a quantity of the actuating fluid into the respective pressure chamber (16, 20).

10. Actuating device (12) for actuating a shift element of a transmission (10) for a drive train of a motor vehicle, wherein the actuating device (12) is designed to carry out a method according to one of the preceding claims.

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