WO2022033796A1 - Method for actuating a frictionally engaging shift element - Google Patents

Abstract

The invention relates to a method for actuating a frictionally engaging shift element, wherein the actuation is effected by charging a hydraulic actuating device of the shift element, and in the process a present charging time (Δt) of the hydraulic actuating device is detected. In order now realize a simple and at the same time reliable possibility for ascertaining a present state of wear of the frictionally engaging shift element, the charging time (Δt) is subsequently used to ascertain a parameter of the actuating device, which parameter is dependent on the present state of wear of the shift element. The present state of wear of the frictionally engaging shift element is then inferred on the basis of the parameter.

Description

Method for actuating a non-positive switching element

The invention relates to a method for actuating a non-positive shifting element, the actuation being brought about by filling a hydraulic actuating device of the shifting element and a current filling time of the hydraulic actuating device required for the actuation being recorded. Furthermore, the invention relates to a control device, a computer program product and a data carrier.

Shifting elements are usually used in transmissions in order to connect components of the respective transmission that are directly connected thereto in a rotationally fixed manner when the individual shifting element is actuated, thereby representing a corresponding power flow guidance in the transmission. In this case, the shifting elements are designed as non-positive shifting elements which, when actuated, transmit torque by frictional engagement between the clutch halves of the respective shifting element. In the case of automatic transmissions in particular, the individual shifting element is often also actuated automatically, with the shifting element being assigned an actuating device for this purpose, which is usually designed as a hydraulic device. However, with an increasing number of shifts of a non-positive shifting element, its wear increases, which affects the actuation characteristics of the associated actuating device and, once a certain level of wear has been reached, can also result in failure of the shifting element.

DE 10 2005 042 933 A1 discloses a method for actuating a non-positive shifting element, with this method varying an actuating characteristic of the shifting element by changing the duration of a filling of a hydraulic actuating device of the shifting element. For this purpose, a pressure is changed with which the hydraulic actuating device is supplied, with the filling of the hydraulic actuating device also being able to determine a current filling time from knowledge of the current position of a piston of the actuating device. Furthermore, DE 10 2005 042 933 A1 proposes an adaptation of the Pressure to use it to compensate for tolerances and wear of the components of the switching element.

Proceeding from the prior art described above, it is now the object of the present invention to provide a simple and at the same time reliable possibility of determining the current state of wear of a non-positive shifting element.

This object is achieved from a procedural point of view starting from the preamble of claim 1 in conjunction with its characterizing features. The dependent claims that follow each specify advantageous developments of the invention. A control unit, by means of which a method according to the invention can be carried out, is also the subject of claims 7 and 8. Claim 9 also relates to a computer program product and claim 10 to a data carrier with a computer program product.

According to the invention, in a method for actuating a non-positive shifting element, the actuation is brought about by filling a hydraulic actuating device of the shifting element, and a current filling time of the hydraulic actuating device is recorded in the process. In the context of the method according to the invention, an actuation of a frictional shifting element, i.e. a transfer of the frictional shifting element from an open state to a closed state, is thus brought about by a hydraulic actuating device assigned to the shifting element being supplied with hydraulic fluid. A time necessary for filling the hydraulic actuating device is determined.

When actuated, the non-positive shifting element transmits torque between the clutch halves of the shifting element by frictional engagement in order to transfer torque between components that are directly connected to the clutch halves when the shifting element is in the installed state. Depending on the specific arrangement of the non-positive shifting element, this can be present as a clutch or as a brake. This is particularly preferred non-positive switching element installed in a transmission, in which case it can be provided for shifting a gear of the transmission and designing a corresponding power flow in the transmission or as a converter lock-up clutch of a hydrodynamic torque converter.

In the simplest case, the non-positive shifting element is a friction clutch with a first clutch side and a second clutch side, which can be brought into contact with one another on friction linings in order to produce the frictional connection between the clutch sides. However, the non-positive shifting element is particularly preferably in the form of a lamellar shifting element, in which the frictional connection can be established via a lamellar set. In a manner known in principle to those skilled in the art, the multi-disk shifting element comprises in particular an inner disc carrier with inner discs and an outer disc carrier with outer discs, the inner discs and the outer discs being arranged alternating axially and each being held in the inner disc carrier or the outer disc carrier in a rotationally fixed and axially displaceable manner. To actuate the multi-disc switching element, the inner disks and the outer disks are pressed against one another against an end disk in order to form the frictional connection between the disks and thus a torque transmission between the inner disk carrier and the outer disk carrier.

The hydraulic actuating device preferably comprises a piston which is guided in a displaceable manner, with the piston being moved from a basic position to an actuating position when pressure is supplied to the hydraulic actuating device in the course of an associated pressurization of an actuating space, and the non-positive switching element being moved from its open state to a closed state transferred. In the course of its displacement, the piston particularly preferably acts directly on the disk pack of the shifting element designed as a disk shifting element, in that the piston presses the disks together against the end disk in the course of the shift into its operating position. In the context of the invention, the “filling time” is to be understood as the time during which the hydraulic actuating device is to be supplied with hydraulic fluid, ie to be filled, in order to implement torque transmission via the associated shifting element. In particular, the filling time represents the time difference between the beginning of the pressure supply to the hydraulic actuating device and the beginning of a torque transmission via the shifting element. The latter is recognized in particular by the fact that the speed of one of the clutch halves of the shifting element begins to approach the speed of the respective other clutch half.

The invention now includes the technical teaching that the filling time is then used to determine a parameter of the actuating device that is dependent on a current state of wear of the shifting element, and that the current state of wear of the non-positive shifting element is inferred from the parameter. In other words, the ascertained, current filling time is used to determine a parameter that changes with the wear of the shifting element. This parameter is then used in the following to determine how great the current wear of the switching element is.

Such a procedure when actuating a non-positive shifting element has the advantage that by detecting the filling time of the hydraulic actuating device and using the filling time to determine a parameter dependent on wear of the shifting element, the current state of wear of the shifting element can also be reliably determined can be closed. With increasing wear of the shifting element, friction partners of the shifting element wear down in the area of the surfaces on which the frictional connection is formed in the course of the transition of the shifting element into the closed state. This wear increases the path that has to be traversed for the transfer of the shifting element from the open state to the closed state, so that the hydraulic actuating device of the shifting element also has to represent a larger adjustment path. This also means that the volume increases, which on the part of the hydraulic Actuating device is to be filled, which also extends the filling time accordingly. Thus, by using the ascertained filling time, it is also possible to draw conclusions about a wear-dependent parameter and thus also about the state of wear itself. This is possible in real time and without the use of separate sensors, which correspondingly reduces the effort required to record the state of wear.

DE 10 2005 042 933 A1 speaks of being able to record the filling time at any time and using a remaining filling time from an adaptation to compensate for the influence of wear. However, no way is shown here of inferring a state of wear of the switching element.

According to one embodiment of the invention, the current filling time itself is used as a parameter dependent on the state of wear. In this case, the state of wear of the shifting element is immediately inferred from the determined, current filling time, since the filling time itself lengthens with increasing wear under otherwise constant conditions and is therefore directly dependent on the wear. This procedure correspondingly reduces the number of process steps, since the current filling time recorded can be used to directly determine the state of wear.

As an alternative to this, a current piston travel is used as a parameter dependent on the state of wear, which is covered by a piston of the hydraulic actuating device for actuating the switching element, the current piston travel being calculated from the current filling time via a filling function of the hydraulic actuating device. In this case, a piston travel of a piston of the actuating device is calculated from the recorded, current filling time, which is subsequently used to infer the current state of wear of the shifting element. Advantageously, the piston travel can be determined in a simple manner using measurement technology, so that an initial value can be determined here with a high degree of reliability. This has the advantage that, based on the piston travel, it can be easily determined in advance by measurement which piston travel causes which wear of the Assign switching element and from which piston travel the switching element is completely closed.

In a further development of the aforementioned variant, the filling function is formed by filling parameters including a control current, a filling pressure, a volume flow and/or a piston volume. This is because the physical relationship between the filling time of a volume at a specific pressure can be described from the various filling parameters and the piston path of the piston of the hydraulic actuating device can thus be mathematically deduced.

Within the scope of the invention, it would be conceivable to infer the current state of wear of the shifting element by comparing the parameter dependent on the current state of wear of the shifting element with an associated output value. In this case, the output value represents a wear-free state of the switching element, that is to say the state which the switching element had before it was used for the first time. This output value is particularly preferably measured, ascertained or calculated when the shifting element is put into operation for the first time, for example during an initial function test of the associated transmission. This prevents manufacturing tolerances from being mistakenly declared as wear by assuming an incorrect initial value. In principle, however, it is also conceivable within the scope of the invention for the initial value to be permanently defined.

According to a further possible embodiment of the invention, after the parameter has been determined, it is checked whether the parameter exceeds a limit value which is assigned to a wear limit of the switching element, with a signal being output if the answer is yes. As a result, from a certain level of wear on the switching element, attention can be drawn to this state at an early stage and before the switching element fails. The limit value can be selected in such a way that there is still sufficient time before the switching element needs to be replaced. An error signal or maintenance signal can be sent to the transmission error memory or a service data memory or transmitted online to a remote diagnosis device. In a further embodiment of the invention, the parameter is set in relation to a limit value representing a wear limit of the shifting element and from this a prognosis is made of the service life of the shifting element that can be achieved before the wear limit is reached. This has the advantage that the expected service life of the shifting element is continuously monitored and the need to replace the shifting element as soon as possible due to wear and tear can accordingly be recognized early on, for example during maintenance.

The subject matter of the invention is also a control unit, which is in particular a transmission control unit. This control unit is now set up to cause an actuation of a non-positive shifting element by initiating a filling of a hydraulic actuating device of the shifting element and in doing so to record a current filling time of the hydraulic actuating device required for the actuation, with the control unit also being designed to record the recorded filling time in consequently to be used to determine a parameter of the actuating device that is dependent on a current state of wear of the shifting element and to use the parameter to infer the current state of wear of the non-positive shifting element. In addition, the control unit is particularly preferably set up to implement one or more of the variants of a method described above.

The method according to the invention can also be embodied as a computer program product which, when it runs on a processor, for example a processor of an aforementioned control unit, instructs the processor via software to carry out the associated method steps that are the subject of the invention. In this context, the subject matter of the invention also includes a computer-readable medium on which a computer program product described above is stored in a retrievable manner.

The invention is not limited to the specified combination of the features of the independent claims or the claims dependent thereon. It arise in addition, possibilities for combining individual features with one another, including those that emerge from the claims, the following description of a preferred embodiment of the invention, or directly from the drawings. Reference of the claims to the drawings by the use of reference signs is not intended to limit the scope of the claims.

An advantageous embodiment of the invention, which is explained below, is shown in the drawings. It shows:

1 shows a schematic view of a drive train of a motor vehicle;

FIG. 2 shows a detailed view of the drive train from FIG. 1 , in the area of a converter lockup clutch;

3 shows a flow chart of a method according to the invention for determining a state of wear of the converter lockup clutch; and

4 shows a diagram with different courses of parameters in the course of an actuation of the converter lockup clutch.

1 shows a schematic view of a drive train 1 of a motor vehicle, which can be a passenger car or a commercial vehicle. The drive train 1 comprises a drive machine 2, which is preferably designed as an internal combustion engine and is connected on the output side to a motor vehicle transmission 4 via an intermediate starting element 3. The motor vehicle transmission 4 is preferably an automatic transmission.

In the present case, the starting element 3 is designed as a hydrodynamic torque converter 5, which has a structure known in principle to a person skilled in the art. During a starting process of the motor vehicle, the drive motor 2 is coupled to the motor vehicle transmission 4 via the hydrodynamic torque converter 5. However, since an efficiency of the hydrodynamic torque converter 5 deteriorates with increasing harmonization of an output speed of the engine 2 and an input speed of the motor vehicle transmission 4, a converter lockup clutch 6 is provided parallel to the hydrodynamic torque converter 5, via which the hydrodynamic torque converter 5 can be locked and which is shown in Fig. 2 as a detail in the Section is shown.

As can be seen in FIG. 2, the converter lockup clutch 6 is designed as a non-positive shifting element 7 and here specifically as a multi-plate shifting element, which has an outer plate carrier 8 and an inner plate carrier 9 . In the outer disk carrier 8, several outer disks 10 are accommodated in a rotationally fixed and axially displaceable manner, which are present as steel disks. The outer disks 10 are arranged in an alternating manner in the axial direction with the inner disks 11 which are each provided in the inner disk carrier 9 so that they can be displaced axially and are non-rotatable. The inner discs 11 are in the form of lining discs which are each provided with friction linings on the axial end faces.

The outer disk carrier 8 also carries an end disk 12, against which the outer disks 10 and the inner disks 11 are pressed together when the switching element 7 is actuated, in order to create a non-positive connection between the outer disk carrier 8 and the inner disk carrier 9 and thus also a non-rotatable connection between the drive motor 2 and the To realize motor vehicle transmission 4 bypassing the hydrodynamic torque converter 5. The switching element 7 is actuated via a hydraulic actuating device 13, which is indicated in FIG. 1 and partially shown in FIG it is preferably a transmission control unit of motor vehicle transmission 4 .

The hydraulic actuating device 13 comprises a piston 15 which can be moved axially by pressurizing a pressure chamber 16 and thereby presses the outer disk 10 and the inner disk 11 against the end disk 12 to actuate the switching element. However, the friction linings of the inner disks 11 increasingly wear out with an increasing number of actuations of the switching element 7, since with each actuation relative speeds between the outer disks 10 and the inner disks 11 must first be reduced with slippage. This slippage of the shifting element 7 at the start of actuation results in increasing wear of the shifting element 7, with the risk of failure of the shifting element 7 above a certain level of wear.

In the present case, control unit 14 is therefore able to check the current state of wear of converter lockup clutch 6 in real time, with this check being carried out according to a method according to the invention, which is to be described below with the aid of further FIGS. 3 and 4 . A flow chart of the method is shown in FIG. 3 .

The method begins with an actuation of the converter lockup clutch 6 via the control unit 14 using the actuating device 13. In the course of the actuation, a filling time At is determined in a step S1, which is required for the filling of the pressure chamber 16 of the actuating device 13 with hydraulic fluid up to a first torque transmission via the converter lockup clutch 6 is necessary. The filling time At is determined by forming a difference between a point in time to and a point in time ti, the point in time to marking the start of pressurization of the pressure chamber 16, while the point in time ti is the start of torque transmission. This can also be seen from the diagram in FIG. 4, in which the curves of an actuating pressure 17, an input speed 18 of the motor vehicle transmission 4 and an output speed 19 of the motor vehicle transmission 4 are shown over time. As can be seen here, the point in time t o is at the point at which an increase in the pressure of the actuating pressure 17 begins, ie at the point at which the converter lock-up clutch 6 begins to be actuated. In this case, the point in time ti marks the beginning of an adjustment of the input speed 18 to the output speed 19. In a step S2 following step S1, a piston travel AS is calculated from the filling time At determined in step S1 using a filling function of the actuating device 13, the filling function reflecting the physical relationship between the filling time of a volume at a specific pressure. Based on the known parameters of the actuating device 13, such as the control current, the pressure, the volumetric flow and the volume, the filling time At determined in step S1 can be used to infer the piston travel AS that the piston 15 must have covered in the filling time At.

In a step S3, the piston travel AS is then set in relation to a limit value of the piston travel AScrenz, which the piston 15 exhibits when a wear limit of the shifting element 7 is reached. In step S3, a query is made as to whether the ratio of the current piston travel AS to the limit value ASCrenz is greater than or equal to one. If the answer is no, in a step S4, based on the determined ratio, a prognosis is given and stored, which reflects the service life of the shifting element 7 that can be achieved before the wear limit is reached. If the result in step S3 is positive, a signal is generated directly in step S5, which is transferred to an error memory or service data memory of the vehicle transmission 4 as an error signal or maintenance signal. This indicates an impending failure of the converter lockup clutch 6 .

Using the method according to the invention, a state of wear of a non-positive shifting element can be determined in real time. In this case, what was described in advance with regard to use in a converter lockup clutch can also be used analogously in other non-positive shifting elements of a motor vehicle transmission. reference sign

1 drivetrain

2 prime mover

3 approach element

4 automotive transmissions

5 hydrodynamic torque converter

6 torque converter lockup clutch

7 switching element

8 outer disk carriers

9 inner disc carrier

10 outer slats

11 inner slats

12 end lamella

13 operating device

14 control unit

15 pistons

16 pressure room

17 Actuating pressure curve

18 Drive speed curve

19 Output speed curve to point in time ti point in time

At filling time t time

AS piston travel

ALimit limit

S1 to S5 single steps

Claims

patent claims 1. Method for actuating a non-positive shifting element (7), the actuation being brought about by filling a hydraulic actuating device (13) of the shifting element (7) and a current filling time (At) of the hydraulic actuating device (13) being recorded, characterized in that the filling time (At) is subsequently used to determine a parameter of the actuating device (13) that is dependent on a current state of wear of the shifting element (7), and that the current state of wear of the non-positive shifting element (7) is inferred from the parameter. 2. The method according to claim 1, characterized in that the current filling time (At) itself is used as a parameter dependent on the state of wear. 3. The method according to claim 1, characterized in that a current piston travel (AS) is used as a parameter dependent on the state of wear, which is covered by a piston (15) of the hydraulic actuating device (13) for actuating the switching element (7), the current piston travel (AS) being calculated from the current filling time (At) via a filling function of the hydraulic actuating device (13). 4. The method as claimed in claim 3, characterized in that the filling function is formed by filling parameters of the hydraulic actuating device (13) comprising a control current, a filling pressure, a volume flow and/or a piston volume. 5. The method according to any one of the preceding claims, characterized in that after determining the parameter, it is checked whether the parameter exceeds a limit value (ASCrenz), which is assigned to a wear limit of the switching element (7), with a signal being output if the answer is yes . 6. The method according to any one of the preceding claims, characterized in that the parameter in relation to a wear limit of the Limit value (ASCrenz) representing the switching element is set and from this a prognosis is made of the service life of the switching element (7) that can be reached before the wear limit is reached. 7. Control unit (14), in particular a transmission control unit, which is set up to cause an actuation of a non-positive shifting element (7) by initiating a filling of a hydraulic actuating device (13) of the shifting element (7) and thereby a current filling time (At) of the hydraulic actuating device (13), the control unit (14) also being designed to subsequently use the recorded filling time (At) to determine a parameter of the actuating device (13) that is dependent on a current state of wear of the switching element (7), and to use the parameter to infer the current state of wear of the non-positive shifting element (7). 8. Control unit (14) according to claim 7, which is further set up to carry out a method according to one or more of claims 2 to 6. 9. Computer program product for a control unit (14) according to claim 7 or 8, by means of which a method according to one or more of claims 1 to 6 can be carried out, with a routine for determining the current state of wear of the non-positive switching element (7) by corresponding software stored control commands is implemented. 10. Data carrier with a computer program product according to claim 9.