How to Recognize Leaks in a Hydrostatic Clutch Actuation System

Abstract

To provide a method for recognizing abrupt leakage of a hydrostatic clutch operation system.SOLUTION: A method for recognizing abrupt leakage of a hydrostatic clutch operation system adjusts a clutch moment to be transmitted via a friction clutch depending on a flow path pressure / stroke characteristic curve of a flow path that has a master cylinder and a slave cylinder and, after pressure of the flow path is beyond prescribed minimum pressure, calibrates a relative position of the pressure / stroke characteristic curve along an operation stroke at a prescribed first time interval by using a reference amount (R(p, s)) capable of adapting the pressure / stroke value. In the pressure at the time when going beyond the minimum pressure, the method continuously determines a measured quantity (M(pn,sn)) of the pressure / stroke characteristic curve at a second time interval shorter than the first time interval, compares it with a reference amount (R(p, s)), and recognizes that leakage occurs when difference between the reference amount (R(p,s)) and the measured quantity (M(pn,sn)) is over a prescribed threshold (s(max)).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The invention relates to a method for recognizing a sudden leak in a hydrostatic clutch actuation system, comprising adjusting a clutch moment to be transmitted via a hydrostatic flow path having a master cylinder operated by an electric motor and a slave cylinder which actuates a pressed-closed friction clutch along an actuation stroke in an axial direction, and calibrating the relative position of a pressure-stroke characteristic curve along the actuation stroke at a first predetermined time interval using an adaptable reference quantity of pressure-stroke values ​​after the pressure in the hydrostatic flow path exceeds a predetermined minimum pressure. [Background technology]

[0002] Clutch actuation systems from the state of the art and corresponding methods for detecting leakage in their hydrostatic flow paths are known from DE 10 2016 219 336 A1 and DE 10 2016 222 648 A1. In these methods, leakage detection is carried out by comparing reference and measured quantities of the pressure-stroke characteristic curve of the hydrostatic flow path with each other over a relatively long time period. These methods are not intended for detecting sudden leakage. Summary of the Invention [Problem to be solved by the invention]

[0003] The object of the invention is to develop a method for detecting a leak in a hydrostatic clutch actuation system. In particular, the object of the invention is to propose a method for detecting a sudden leak in a hydrostatic clutch actuation system. [Means for solving the problem]

[0004] This problem is solved by the subject matter of claim 1. Each claim dependent on claim 1 reflects preferred embodiments of the subject matter of claim 1.

[0005] The proposed method serves to recognize a sudden leak in a hydrostatic clutch actuation system, which comprises a hydrostatic flow path with a master cylinder actuated by an electric motor and a slave cylinder actuated thereby in a pressure-dependent manner, and optionally a compensation container which is pressurelessly connected with the hydrostatic flow path when the friction clutch is in an unactuated state, allowing pressure compensation and compensation of the hydraulic medium. When the master cylinder is actuated, pressure is generated in the hydrostatic flow path, and a slave cylinder piston of the slave cylinder displaces an actuating member, for example a lever spring of the friction clutch, in the axial direction along an actuating stroke from an open state through a slipping state to a closed state. A friction clutch is a friction clutch which is open when in an unactuated state and which is forced closed under pressure, for example pushed closed or pulled closed.

[0006] The actuation of the friction clutch and the clutch moment transmitted via it are controlled by means of a pressure-stroke characteristic curve, so that at a given pressure in the hydrostatic flow path a given actuation stroke can be adjusted and a corresponding clutch moment can be assigned to the actuation stroke. The pressure in the hydrostatic flow path is preferably detected by a pressure sensor. Depending on the system parameters of the clutch actuation system, such as, for example, the operating temperature, the long-term trend, the pressure-stroke characteristic curve exhibits a relative behavior not only with respect to its position along the actuation stroke, but also with respect to its shape, which therefore requires calibration. Besides the calibration of the shape, such as, for example, the gradient, the assignment of the position of the pressure-stroke characteristic curve is also based on the calibration, by which a given stroke point of the actuation stroke is adjusted as a reference quantity at a given pressure. For example, as a reference quantity, the contact point of the friction clutch can be selected, at which the friction clutch starts to transmit the clutch moment.

[0007] The pressure-stroke characteristic curve can be stored in a non-volatile memory of the control device for controlling the clutch actuation system, for example as an empirically determined model characteristic curve, and can be continuously adapted. The model characteristic curve can be visualized, for example, by an observer, and the current pressure-stroke characteristic curve can be continuously corrected. Using the pressure-stroke characteristic curve, the relative position of the pressure-stroke characteristic curve along the actuation stroke can be calibrated in a predefined first time interval with the aid of an adaptable reference quantity of pressure-stroke values ​​after exceeding a predefined minimum pressure in the hydrostatic flow path. The determination of the reference quantity can be performed, for example, with a partially or fully closed friction clutch, by converting the determined pressure-stroke values ​​into the pressure-stroke values ​​of the reference quantity, for example, with the aid of a pressure-stroke characteristic curve that is stored as a mathematical formula or table. Such a type of calibration can be performed, for example, at long time intervals, for example of several hours, for example when starting up the clutch actuation system after a relatively long stop, or daily, or at similar first time intervals, in order to take into account and compensate for wear of the clutch actuation system and / or the friction clutch, the setting process of the friction clutch, and / or the like.

[0008] Furthermore, for example, medium-term corrections can be made, in which case reference quantities are compared with current measured quantities during operation of the clutch actuation system in order to adapt the pressure-stroke characteristic curve to the temperature dependence of the clutch actuation system, for example of the hydrostatic flow path and / or of the friction clutch, and such calibrations or compensations can be made in cycles of, for example, seconds or minutes.

[0009] Furthermore, according to the concept of the invention, when the minimum pressure is exceeded, the measured quantity of the pressure-stroke characteristic curve can be determined continuously at second time intervals, which are shorter than the first time interval, and compared to a reference quantity, so that a particularly sudden leak is recognized if the difference between the reference quantity and the measured quantity is exceeded compared to a predefined threshold value. On the basis of the determination of the measured quantity, which takes place at rapid intervals, and its comparison with the reference quantity, on the one hand, leaks caused, for example, by a melted piston in a master cylinder, a broken pipe, etc. can be recognized quickly, for example within a few seconds, and on the other hand, by the correlation to the reference quantity, leaks can be recognized reliably and robustly by exceeding a predefined threshold value.

[0010] In this case, the measured quantity can be determined at essentially any pressure value having a corresponding stroke point after exceeding a certain pressure, for example after exceeding the pressure required for adjusting the contact point, and related to the reference quantity, so that the comparison or determination of the difference between the reference quantity and the measured quantity can always be related to a certain stroke point, for example the contact point of a friction clutch.

[0011] In a preferred embodiment of the proposed method, the reference quantity is determined at a first time interval for the detection of long-term changes of the clutch actuation system and / or the friction clutch, and the measurement quantity is determined at a second time interval for the detection of sudden leakage, the second time interval corresponding to the clock rate or a one-digit multiple thereof, the second time interval being dependent on the clock rate of the control device controlling the clutch actuation system.

[0012] The predetermined or settable threshold value is formed, for example, from the difference between a system-specific maximum reference quantity operating stroke, which depends on the long-term changes, and a temporarily, in particular temperature-dependently determined maximum measured quantity operating stroke, for example of the respective long-term and medium-term determined contact point of the friction clutch.

[0013] In addition to the recognition of sudden leaks by the proposed method, a method for detecting leaks with a slow pressure loss over at least several minutes can be carried out in parallel, for example according to the prior art described above. Naturally, the combination of a long-term method for the highly accurate recognition of slow leaks, for example non-tightness of hydrostatic channels, with the short-term detection of sudden leaks is also included in the concept according to the invention.

[0014] According to the proposed method, after a leak has been detected, a warning is issued and / or an error mode of the clutch actuation system or an emergency drive mode is switched on for vehicles equipped with this. [Brief description of the drawings]

[0015] [Figure 1] 1 shows a flow chart of the proposed method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The invention will now be explained in more detail with reference to an embodiment shown in just one drawing, which shows a flow chart of the proposed method.

[0017] The figure shows a flow chart 1 of a method for recognizing a sudden leak in a hydrostatic clutch actuation system having a slave cylinder pressure-actuated by a master cylinder, a corresponding routine being stored in the software of a control device of the clutch actuation system and being processed continuously, for example within the cycle rate of the control device within a time cycle in the range of microseconds to milliseconds.

[0018] In block 2, a reference quantity R(p,s) of the pressure-stroke value along the operating path s of the master cylinder piston or the slave cylinder piston at a given pressure p in the hydrostatic flow path is retrieved, for example stored in a non-volatile memory of the control device. The reference quantity R(p,s) is realized as a long-term contact point of a pressure-stroke characteristic curve that is adapted over a long period of time, for example to compensate for wear and long-term phenomena of the clutch actuation system and the friction clutch actuated thereby. Instead of the actuation stroke s, the stroke of the master cylinder piston or the slave cylinder piston and / or the rotation characteristic value of the electric motor that acts on the master cylinder can also be determined and can be determined taking into account the possibly intervening adjusted transmission ratio.

[0019] In block 3, the measured quantity M(pn,sn) is detected, whereby a pressure-stroke value with a pressure pn and a corresponding actuating stroke sn, which differ from the pressure p and the corresponding actuating stroke s of the reference quantity R(p,s), is detected so that the pressure-stroke value corresponding to the pressure p of the reference quantity R(p,s) can be determined using a corresponding pressure-stroke characteristic curve, calculated, for example, from a model characteristic curve.

[0020] In block 4, the reference quantity R(p,s) and the measured quantity M(p,s) corrected for the same pressure p are compared with each other, and from this, for example, a difference Δs between the long-term contact point and the latest temporarily determined contact point is determined.

[0021] In branch 5, it is checked whether this difference Δs is greater than a predefined threshold value s(max). The threshold value s(max) is determined, for example, for one embodiment, from the maximum difference of the contact points, i.e. from the long-term difference, and from the medium-term, e.g. temperature-dependent, difference, using the contact points as reference quantity R(p,s) minus the maximum long-term difference. In this way, the long-term changing contact points can be taken into account in the reference quantity R(p,s). The medium-term temperature-dependent changes in the contact points are taken into account when setting the threshold value s(max). In order to exclude erroneous assumptions of sudden leakage due to changing medium-term contact points, the threshold value s(max) is set greater than the maximum medium-term difference of the contact points.

[0022] If the difference Δs is greater than, less than or equal to the threshold value s(max), a new measurement quantity M(pm,sm) is detected in the next time cycle, for example of 10 microseconds, and one continues with blocks 3, 4 and branch 5. If a new reference quantity R(p1,s1) is determined, for example a new long-term contact point is determined, and one continues with block 2.

[0023] If the difference Δs exceeds the threshold value s(max), then in block 6 a sudden leak, e.g. a melted slave cylinder piston or master brake piston, is recognized and an error memory entry is made, which can then for example be followed by the output of a warning W and / or a switch to emergency operation N of the clutch actuation system or the vehicle. [Explanation of symbols]

[0024] 1 Flowchart 2 Blocks 3 Blocks 4 Blocks 5. Branch 6 Blocks M(pn,sn) measurements N Emergency operation p Pressure R(p,s) reference amount s Operation stroke s(max) threshold W Warning Δs difference

Claims

1. a master cylinder operated by an electric motor and a slave cylinder for operating a friction clutch pressed closed along an operating stroke (s) in the axial direction, said master cylinder controlling said friction clutch in a hydrostatic flow path, said clutch moment being adjusted as a function of the pressure-stroke characteristic curve of said hydrostatic flow path; 1. A method for recognizing a sudden leak in a hydrostatic clutch actuation system, comprising calibrating a relative position of the pressure-stroke characteristic curve along the actuation stroke (s) at a first predetermined time interval after the pressure in the hydrostatic flow path exceeds a predetermined minimum pressure using a reference quantity (R(p,s)) which is a pressure and stroke value at a contact point of the friction clutch where the friction clutch starts to transmit the clutch moment, 2. A method for detecting a leak, comprising: determining a measured quantity (M(pn,sn)) of the pressure-stroke characteristic curve continuously at a second time interval shorter than the first time interval at which the minimum pressure is exceeded, comparing the measured quantity (M(pn,sn)) with the reference quantity (R(p,s)); and recognizing the presence of a leak if a difference (Δs) between the reference quantity (R(p,s)) and the measured quantity (M(pn,sn)) is exceeded compared to a predefined threshold value (s(max)).

2. A method according to claim 1, characterized in that the reference quantity (R(p,s)) and the measured quantity (M(pn,sn)) are compared with each other at the contact point of the friction clutch after the pressure required for its adjustment has been exceeded.

3. 3. The method according to claim 1, wherein the reference quantity (R(p,s)) is determined at a first time interval for the detection of long-term changes in the clutch actuation system and / or the friction clutch.

4. 4. The method according to claim 1, wherein the measured quantity (M(pn,sn)) is determined at second time intervals depending on a clock rate of a control device controlling the clutch actuation system.

5. 5. The method of claim 4, wherein the second time interval corresponds to a clock rate or a single digit multiple thereof.

6. 6. The method according to claim 1, wherein the predetermined threshold value (s(max)) is formed from the difference between a system-specific maximum reference quantity actuation stroke and a temporary, temperature-dependently determined maximum measured quantity actuation stroke.

7. 7. The method according to claim 1, wherein the method is applied to detect pressure loss in the hydrostatic flow path within a few seconds.

8. 8. The method according to claim 1, further comprising the step of: after the detection of a leak, an error memory entry is made and, possibly, a warning (W) is output and / or an emergency operation (N) of the clutch actuation system is switched on.

Images