DE102019123111B4 - Method for leak detection in a hydrostatic clutch actuation system - Google Patents

Abstract

Method for leakage detection of a hydrostatic path between a master cylinder and a slave cylinder of a hydrostatic clutch actuation system for actuating a pressure-dependent displacement of the slave cylinder of a disconnecting clutch that is open along an actuation path (x), with a closed disconnecting clutch at a sniffing position of the master cylinder a sniffing process (DA) with pressure equalization with a Pressure medium container is provided, after a sniffing process (DA) at least one reference pair is recorded from an actuation path (x) that occurs at at least one predetermined pressure (p (M)) when the separating clutch is at least partially disengaged, continuously after the determination of the at least one reference pair detected measurement pairs from the at least one predetermined pressure (p (M)) and the respectively resulting actuation travel (x), the at least one reference pair is compared with the associated measurement pairs and if there is a deviation from a predetermined threshold (Δx (max)) is detected on a leak in the hydrostatic path, a reference characteristic curve (K (R)) being formed from a large number of reference pairs and stored in a non-volatile memory, a measurement characteristic curve (K (K ( M)) is formed and the reference characteristic curve and measurement characteristic curve are compared with one another, characterized in that the reference characteristic curve (K (R)) is recorded at a predetermined reference temperature (T (R)) immediately after a sniffing process (DA) and a measurement temperature (T ( M)) a measurement characteristic (K (M)) to be compared with the reference characteristic (K (R)) is recorded and the measurement characteristic (K (M)) is determined by means of a difference between the reference temperature (T (R)) and the measurement temperature (T ( M)) is temperature compensated.

Description

The invention relates to a method for leakage detection of a hydrostatic path between a master cylinder and a slave cylinder of a hydrostatic clutch actuation system for actuating a pressure-dependent displacement of the slave cylinder of a disconnecting clutch that is open along an actuation path, with a sniffing process with pressure equalization with a pressure medium container provided when the disconnecting clutch is closed at a sniffing position of the master cylinder is.

the DE 10 2009 055 161 A1 discloses a method for leak testing in an automated electrohydraulic clutch system in a motor vehicle.

WO 2017/206 980 A1 discloses a method for determining a leak in a hydraulic clutch system of a vehicle.

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

Hydrostatic clutch actuation systems for the automated actuation of a friction clutch, which is closed in the unloaded state, with a hydrostatic path consisting of a master cylinder, a pressure line and a slave cylinder and a pressure medium container connected without pressure to a sniffing position of the master cylinder are well known. The master cylinder piston is actuated by an electric motor that is controlled by a control unit. During the actuation of the master cylinder piston, characteristic curves of the pressure over the actuation path are formed in the hydrostatic path.

The generic method provides for leakage detection in the hydrostatic path by checking a minimum pressure threshold for a predetermined actuation path. If this minimum pressure threshold is not reached when the friction clutch is opened, or if the pressure of the hydrostatic path falls below a predetermined pressure when the friction clutch is open, a leak is assumed.

A method for determining a leak in a generic clutch system of a hybrid vehicle is known from the publication WO 2018/001 408 A1, in which the master cylinder is acted upon with small stroke movements that have no influence on the friction clutch and a pressure response in the hydrostatic path with regard to a leak is evaluated.

The object of the invention is to develop a generic method for detecting leaks in a hydrostatic clutch actuation system.

The object is achieved by the subject matter of claim 1. The claims dependent on claim 1 reproduce advantageous embodiments of the subject matter of claim 1.

The proposed method is used to detect leakage of a hydrostatic path between a master cylinder and a slave cylinder of a hydrostatic clutch actuation system by means of a pressure-dependent displacement of the slave cylinder of a disconnect clutch that is open along an actuation path. The separating clutch is preferably designed as a friction clutch, with a slave cylinder piston acting axially on the diaphragm spring tips of a diaphragm spring producing frictional engagement of the friction clutch with the interposition of a release bearing in order to open the friction clutch. The separating clutch is preferably arranged between an internal combustion engine and a transmission, for example a dual clutch transmission with an electric machine of a hybrid drive train. With the proposed method with improved leakage detection, for example, permanent or long-term operation of the hybrid drive train can take place purely electrically by means of the electric machine with the separating clutch open, in that the open state of the friction clutch can be reliably set as a result of the improved leakage detection.

The master cylinder piston is actuated electrically by means of an electric motor. Between the rotor of the electric motor and the master cylinder piston, a transmission gear, for example a planetary roller gear, can be provided, which is preferably self-locking so that the electric motor is at least relieved when the separating clutch is in the open state, i.e. it can be operated with reduced power or preferably switched off.

For pressure equalization, removal of trapped air and / or follow-up of pressure medium into the hydrostatic path, the master cylinder has an unpressurized connection to a pressure medium container at a sniffing position when the separating clutch is closed, so that pressure equalization can take place and pressure medium can flow in during a so-called sniffing process.

The proposed method is characterized in that, after a sniffing process, at least one reference pair is obtained from a respective resultant at at least one predetermined pressure Actuating travel detected with at least partially disengaged clutch, continuously detected measuring pairs from the at least one predetermined pressure and the respective resulting actuating travel after determining the at least one reference pair, comparing the at least one reference pair with the associated measuring pairs and if they deviate from a predetermined threshold a leak in the hydrostatic path is detected.

This means that in a relative comparison between reference pairs and measurement pairs, a shift in the pressure at a given actuation path and / or a shift in the actuation path at a given pressure is determined and a leak is detected when the displacement (s) exceed a given threshold. The advantage of the relative evaluation is the determination of the at least one reference pair at a close point in time of the subsequent acquisition of the measurement pairs, so that the current state of the hydrostatic path is essentially comparable, the at least one reference pair is virtually tracked to the state of the hydrostatic path. In the simplest case, it is sufficient to acquire a single reference pair after a sniffing process at a predetermined pressure and / or a predetermined actuation travel with the actuation travel or pressure values that are established. If the disconnect clutch is operated in the open state for a longer period of time, the associated actuation or pressure values are then recorded when the disconnect clutch is closed or the disconnect clutch is opened again under the same conditions of pressure or actuation travel. A measurement pair is formed from this, which is compared with the reference pair. In the same way, several reference pairs can be recorded at different pressures or actuation travel values and corresponding measurement pairs recorded under these conditions can be formed and compared with the reference pairs.

In an advantageous embodiment of the method, a complete reference characteristic curve of the pressure of the hydrostatic path over the actuation path can be recorded and stored after a sniffing process. Subsequently, during an opening or closing process of the separating clutch, a measurement characteristic curve can be recorded and compared with the stored reference characteristic curve and, in the event of corresponding deviations, a leak can be detected.

To take into account values of the reference and measurement pairs that change at different temperatures, or reference and measurement characteristics, the comparison can be carried out at temperatures of the hydrostatic path within a predetermined temperature interval. Here, the temperature of the hydrostatic path is recorded directly by means of a temperature sensor or is calculated by means of a temperature model from the values of one or more temperature sensors available in the hybrid drive train and / or in the motor vehicle. If the temperatures of the reference pair or the reference characteristic curve and the associated measurement pair or the measurement characteristic curve lie within a predetermined temperature interval, temperature compensation can be dispensed with. If these are outside the specified temperature interval, the comparison is carried out with temperature compensation. This means that a temperature dependency of the clutch actuation system is determined empirically or computationally, for example, and preferably the reference pairs or the reference characteristic curve determined at a certain reference temperature serve as the basis and the measurement pairs or the measurement characteristic curve by means of the temperature dependency, for example by means of a temperature-dependent variable the reference temperature can be adjusted, i.e. determined in a temperature-compensated manner.

The measurement pairs or measurement characteristic can be recorded during a pressure increase or when the pressure decreases, that is to say when the separating clutch is closing or opening. In a preferred manner, the comparison of these can be evaluated as a function of a time interval lying between the acquisition of the at least one reference pair or the reference characteristic curve and the associated measurement pairs or the measurement characteristic curve. In this way, for example, leakage rates and leaks defined as leakages in the hydrostatic sections can be determined empirically and independently of time intervals between the reference values and the measured values. If a leak is detected, a corresponding entry in a fault memory of a control unit for controlling the clutch actuation system, an acoustic, optical and / or haptic warning to the driver of the motor vehicle with the hybrid drive train and / or the like can be provided.

According to the invention, a reference characteristic is formed from a large number of reference pairs, which is stored in a non-volatile memory of a control unit for controlling the clutch actuation system, a measurement characteristic being formed from the measurement pairs and the reference characteristic and measurement characteristic being compared with one another. The reference characteristic is recorded at a predetermined reference temperature immediately after a sniffing process and a measurement temperature of a measurement characteristic to be compared with the reference characteristic is recorded, and the measurement characteristic is temperature-compensated by means of a variable determined from the difference between the reference temperature and the measurement temperature.

By means of the proposed method, even smaller leaks can be detected in a robust manner by evaluating the pressure in the hydrostatic path. In motor vehicles with a hybrid drive train, this enables high proportions without interference from the disconnect clutch, in which driving is purely electrically with the disconnect clutch disengaged. For example, in a so-called plug-in hybrid, a traction battery is continuously charged on the power grid and purely electric driving is then possible for a very long time, with the disconnect clutch remaining permanently open in this phase. The method makes it possible to safely meet the higher demands placed on the hydrostatic section of the separating clutch in terms of thermal load and pressure load.

In order to reliably detect even small leaks, according to a preferred exemplary embodiment, the shift of the current measurement characteristic curve relative to a reference characteristic curve is determined. If the shift is too great compared to a comparison threshold, it can be concluded that there is a leak.

The relative displacement is determined after a sniffing process in that the reference characteristic is determined and the current pressure-travel characteristic is compared as a measurement characteristic with this reference characteristic in the further course of the operation of the clutch actuation system. This measurement characteristic used for comparison is advantageously temperature-compensated. For this purpose, for example, the temperature of the pressure medium such as hydraulic fluid at the time of the sniffing process is determined as a reference temperature. A variable such as a path compensation value can be determined from the difference with the current temperature and the measured current measurement characteristic can be shifted by this path compensation value.

The pressure-travel characteristics of the hydrostatic path are shown shifted to higher positions such as actuation travel due to a leak and a drop in temperature. When the temperature rises, the pressure-displacement curves are shifted to smaller positions. If a preferably temperature-compensated overall shift towards larger positions is greater than a limit value, which is determined empirically, for example, it can be concluded that there is a leak.

mit dem Kompensationswert x(T) aus der Temperaturdifferenz zwischen dem aktuellen Betätigungsweg x(M) und dem Referenzbetätigungsweg x(R) nach dem Schnüffelvorgang. Die Verschiebung Δx kann neben Temperaturunterschieden zwischen dem aktuellen Betätigungsweg x(M) und dem Referenzbetätigungsweg x(R) abhängig von der Zeitdauer zwischen dem aktuellen Betätigungsweg x(M) und dem Referenzbetätigungsweg x(R) sein. Es kann daher vorteilhaft sein, eine Entscheidung einer ermittelten Leckage abhängig von der Zeitdauer, beispielsweise von einem vorgegebenen Zeitintervall zu machen.As an alternative to determining a leak using reference and measurement characteristics, a leak can be determined using position values such as actuation travel when a certain pressure value is reached, for example 3 bar when the pressure rises or falls. The postponement Δx at a pressure of 3 bar, for example, the following is calculated for the rising pressure from the current actuation travel x (M): $$\Delta \text{x}=\text{x}\left(\text{M.}\right)-\text{x}\left(\text{T}\right)-\text{x}\left(\text{R.}\right)$$

with the compensation value x (T) from the temperature difference between the current actuation path x (M) and the reference actuation path x (R) after the sniffing process. The postponement Δx can, in addition to temperature differences between the current actuation path x (M) and the reference actuation path x (R), depend on the time between the current actuation path x (M) and the reference actuation path x (R). It can therefore be advantageous to make a decision on a detected leak as a function of the duration, for example on a predetermined time interval.

In particular, if a limit value of the displacement is exceeded, interpolation measures and / or averaging measures can be taken before a decision about the presence of a leak to determine the reference actuation travel x (R) and / or the current actuation travel x (M) in order to avoid possible signal noise from the pressure - and actuation travel signal must be taken into account and compensated.

If it is recognized that the displacement has been exceeded, a signal, for example an engine warning lamp, can be activated. Alternatively, a sniffing process can be requested.

• 1 ein Ablaufdiagramm eines Verfahrens zur Ermittlung einer Leckage eines Kupplungsbetätigungssystems und
• 2 ein Diagramm mit verschiedenen Kennlinien eines Kupplungsbetätigungssystems mit dem Druck der hydrostatischen Strecke über den Betätigungsweg des Geberzylinderkolbens.

The invention is based on the in the 1 and 2 illustrated embodiment explained in more detail. These show:

• 1 a flowchart of a method for determining a leakage of a clutch actuation system and
• 2 a diagram with different characteristics of a clutch actuation system with the pressure of the hydrostatic path over the actuation path of the master cylinder piston.

the 1 shows the flow chart 1 a preferred method for leak detection of a hydrostatic section of a clutch actuation system of a disconnect clutch of a hybrid drive train. After the start of the procedure takes place in block 2 a sniffing process THERE , that is, a master cylinder piston of the clutch actuation system is moved into a sniffing position at which a pressure equalization can take place with a pressureless pressure medium tank and, if necessary, overpressure can be reduced or pressure medium can be tracked.

After the sniffing process THERE takes place during the opening of the separating clutch by moving the master cylinder in the block 3 the determination of the reference characteristic K (R) the pressure of the hydrostatic path against the actuation path of the master cylinder displacing the slave cylinder for direct actuation of the plate spring of the separating clutch and the reference temperature T (R) , which are stored in a non-volatile memory of a control unit of the clutch actuation system.

In block 4th each time the disconnect clutch is opened a further measurement curve is generated K (M) and the current measurement temperature T (M) recorded.

In block 5 becomes from the reference temperature T (R) and the measuring temperature T (M) the temperature dependency to be taken into account, for example as a compensation coefficient, actuation travel corrector or the like, and the measurement characteristic K (M) on the measuring temperature T (M) to the reference temperature T (R) convicted.

In the branch 6th is based on a comparison of individual or multiple reference pairs and measurement pairs of the reference characteristic K (R) and the measurement characteristic K (M) or evaluation of the entire characteristic curve checks whether there is a shift Δx the actuation travel greater than a predetermined threshold Δx (max) is.

Is the shift Δx smaller than the threshold Δx (max) , there is no leakage and it is in a block 4th another measurement curve K (M) determined and the check continued or, alternatively, the method in block 2 with a sniffing process THERE started again.

Is the shift Δx greater than or equal to the threshold Δx (max) , there is a leak and in block 7th a message appears AL to a fault memory of the control unit and / or to a driver of the motor vehicle with the hybrid drive train.

the 2 FIG. 4 shows with reference to the flow chart of FIG 1 the diagram 8th with the pressure p the hydrostatic path of a clutch actuation system over the actuation path x . The different characteristics show the possible behavior of the hydrostatic section under different operating conditions with characteristics that depend on the tightness and the operating temperature of the hydrostatic section. The characteristics shift depending on a leak in the direction of the arrow 9 to greater actuation paths x . With increasing temperature, the characteristics shift in the opposite direction and with decreasing temperature in the direction of the arrow 9 .

Is used, for example, by the characteristic 10 as a reference characteristic K (R) and of the other characteristics as measurement characteristics K (M) assumed, for example, after temperature compensation, that is, projecting a measurement characteristic K (M) with the measuring temperature T (M) to a corrected characteristic 11 with the reference temperature T (R) the postponement Δx (1) at a given pressure p (M) be determined. If this is - as shown, for example - within the threshold Δx (max) , there is no leak. For example, is the temperature-compensated characteristic 12th there is a leak because the shift Δx (2) bigger than the threshold Δx (max) is.

List of reference symbols

1

Flowchart

2

block

3

block

4th

block

5

block

6th

branch

7th

block

8th

diagram

9

arrow

10

curve

11

curve

12th

curve

AL

report

THERE

Sniffing process

K (M)

Measurement characteristic

K (R)

Reference characteristic

T (M)

Measuring temperature

T (R)

Reference temperature

p

pressure

p (M)

pressure

x

Actuation path

Δx

shift

Δx (1)

shift

Δx (2)

shift

Δx (max)

threshold

Claims (8)

Method for leakage detection of a hydrostatic path between a master cylinder and a slave cylinder of a hydrostatic clutch actuation system for actuating a pressure-dependent displacement of the slave cylinder of a disconnecting clutch that is open along an actuation path (x), with a closed disconnecting clutch at a sniffing position of the master cylinder a sniffing process (DA) with pressure equalization with a Pressure medium container is provided, after a sniffing process (DA) at least one reference pair is recorded from an actuation path (x) resulting at at least one predetermined pressure (p (M)) with at least partially disengaged clutch, continuously after the determination of the at least one reference pair detected measurement pairs from the at least one predetermined pressure (p (M)) and the respectively resulting actuation travel (x), the at least one reference pair is compared with the associated measurement pairs and if there is a deviation from a predetermined threshold (Δx (max)) is detected for a leak in the hydrostatic path, with a reference characteristic (K (R)) being formed from a large number of reference pairs and stored in a non-volatile memory, with a measurement characteristic (K ( M)) is formed and the reference characteristic curve and measurement characteristic curve are compared with one another, characterized in that the reference characteristic curve (K (R)) is recorded at a predetermined reference temperature (T (R)) immediately after a sniffing process (DA) and a measurement temperature (T ( M)) a measurement characteristic (K (M)) to be compared with the reference characteristic (K (R)) is recorded and the measurement characteristic (K (M)) is determined by means of a difference between the reference temperature (T (R)) and the measurement temperature (T ( M)) is temperature compensated. Procedure according to Claim 1 , characterized in that the comparison is carried out at temperatures of the hydrostatic path within a predetermined temperature interval. Procedure according to Claim 2 , characterized in that if the temperature of the at least one reference pair and the associated measurement pairs lie outside the temperature interval, the comparison is carried out in a temperature-compensated manner. Method according to one of the Claims 1 until 3 , characterized in that measurement pairs are recorded during a pressure increase. Method according to one of the Claims 1 until 4th , characterized in that measuring pairs are recorded with decreasing pressure. Method according to one of the Claims 1 until 5 , characterized in that the threshold (Δx (max)) is evaluated as a function of a time interval lying between the detection of the at least one reference pair and the associated measurement pairs of a comparison. Method according to one of the Claims 1 until 6th , characterized in that when a leak in the hydrostatic path is detected, an entry is made in a fault memory of a control unit for controlling the clutch actuation system. Method according to one of the Claims 1 until 7th , characterized in that when a leakage of the hydrostatic path is detected, a warning is issued to a driver of a motor vehicle with the clutch actuation system.

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