WO2014067516A1

WO2014067516A1 - Method for operating a friction clutch

Info

Publication number: WO2014067516A1
Application number: PCT/DE2013/200208
Authority: WO
Inventors: Christian Vollbrecht; Lukas Holzer
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2012-10-31
Filing date: 2013-10-09
Publication date: 2014-05-08
Also published as: DE102013220324A1; JP6335911B2; CN104755782A; DE112013005229B4; DE112013005229A5; JP2015537169A; CN104755782B

Abstract

The invention relates to a method for automatic operation of a friction clutch in a drive train of a motor vehicle by means of a hydrostatic system having a pressure chamber formed by an electrically driven master cylinder of a hydrostatic clutch actuator, a slave cylinder operating the friction clutch, and a pressure line arranged between the master and slave cylinders, wherein a breathing process is initiated by displacing the master cylinder in a non-pressurised state of the friction clutch by connecting the pressure volume to a pressureless supply tank and providing a pressure compensation. In order to achieve a good ride comfort and rapid shift times of an automatic gear of the motor vehicle, a breathing process is carried out dependent on a multi-stage scale, which is continuously formed from a plurality of operating parameters of the motor vehicle and forms a measure of confidence for a reliable operation of the friction clutch.

Description

Method for actuating a friction clutch

The invention relates to a method for the automated actuation of a friction clutch in a drive train of a motor vehicle by means of a hydrostatic system with one of an electrically driven master cylinder of a hydrostatic clutch actuator, a friction clutch operating slave cylinder and a pressure line arranged between these pressure chamber, wherein a snooping operation by displacing the Donor cylinder is introduced in a non-pressurized state of the friction clutch by the pressure volume connected to a non-pressurized reservoir and a pressure compensation is provided.

In a known for example from DE 10 201 1 103 750 A1 hydrostatic

Clutch actuator for actuating a friction clutch of a drive train of a motor vehicle is moved by means of an electric motor, a master cylinder, which is connected via a hydrostatic pressure line with a slave cylinder. By moving the master cylinder, a force is transmitted to the slave cylinder via the hydrostatic pressure line. About the slave cylinder is the disengagement and engagement of the friction clutch. The liquid contained in a pressure volume formed by the slave cylinder, the master cylinder and the hydrostatic pressure line is subjected to volume changes due to external influences, for example temperature influences. With the same master cylinder position, these volume changes lead to a displacement of the slave cylinder. In order to transmit the requested clutch torque, the position of the slave cylinder must be known with sufficient accuracy. In order to compensate occurring volume changes in the hydrostatic pressure volume, the master cylinder is moved in a so-called sniffing process so that a connection is made between the pressure volume and a non-pressurized reservoir via an existing opening in the master cylinder. This allows a volume balance between the reservoir and the pressure volume done. Thereafter, there is again a known relationship between the position of the master cylinder and the position of the slave cylinder. Depending on the configuration of the friction clutch, a snooping process is carried out as a forcibly compressed (normally open) or as a force-forcibly pushed (normally closed) friction clutch when the clutch is disengaged or engaged. Due to its duration, a snooping process has a not insignificant influence on the driving behavior. On the one hand frequent snooping operations can reduce the ride comfort, on the other hand, requested shift operations of a automated transmission of the powertrain are delayed by a snooping operation. To reduce the period between snooping, it makes sense to sniff only when needed. The need to perform a sniffing must be determined using existing signals.

From DE 10 2001 102 906 A1, a method for controlling a dual clutch with two friction clutches by means of a respective one friction clutch actuated hydrostatic clutch actuator is known, wherein changes of a friction clutch for controlling the other friction clutch are used.

The object of the invention is the development of a method for controlling a

Friction clutch by means of a hydrostatic system, in which Schnuffelvorgänge to produce a high ride comfort and to reduce avoidable delays of shifts are performed in an efficient frequency.

The object is solved by the features of the method according to claim 1. The

Subclaims give advantageous embodiments of the method again.

In the proposed method for automated actuation of a friction clutch in a drive train of a motor vehicle by means of a hydrostatic system with one of an electrically driven master cylinder of a hydrostatic clutch actuator, the friction clutch operating slave cylinder and a pressure line arranged between these pressure chamber, wherein a snooping operation by displacing the master cylinder is initiated in a non-pressurized state of the friction clutch by the pressure volume connected to a non-pressurized reservoir and a pressure compensation is provided, a sniffer is dependent on a multi-level, continuously formed from several operating variables of the motor vehicle, a confidence measure for a safe operation of the friction clutch forming scale performed.

Depending on the configuration of the friction clutch as a forced or forced forced friction clutch, a snooping operation is carried out in the closed and normally forcibly opened (normally closed) in a closed state, since in this case the slave cylinder essentially and up to to be eliminated by the sniffing, faulty pressures or Underpressures is depressurized. In this case, the proposed method is particularly advantageous, in particular in the case of a forced friction clutch, since the operating times of an opened friction clutch during driving of the motor vehicle are less frequent or less long even with double clutches compared to the closed states.

The need to perform a snooping operation is determined by a multi-level scale that provides a measure of confidence in the position of the slave cylinder and thus the current clutch torque transmitted through the friction clutch. The scale may be formed, for example, from "high" confidence that no snooping is requested and executed to "no" confidence that the activation of the friction clutch is restricted or disabled. The intervening stages indicate a prioritized need for snooping, and depending on the level determined, a high priority snooping operation occurs immediately, resetting other operations, such as shifts, or at a lower priority level, after such operations.

Confidence in a related to the degree of actuation of the friction clutch position of the piston of the slave cylinder as slave cylinder position and thus the need for a snooping be described with reference to below described, preferably in sum scale defining criteria such as operating variables of the motor vehicle, its drive train and in particular the friction clutch and determines their actuation system.

The formation of the scale preferably takes place by means of a first operating variable in the form of a temperature or a temperature change compared to a last-performed snooping operation of the printing volume. In this case, the first operating variable is formed on the basis of a temperature model from a single or a plurality of temperature sensors weighted depending on their influence on the temperature of the pressure volume. In detail, for example, such a temperature quantity is related to a temperature change of the pressure line since the last sniffing. A change in temperature causes due to the temperature-dependent expansion coefficient of the pressure medium, a pressure change, which leads to an undesirable, possibly due to the fixed position of the master cylinder piston not negligible loading of the slave cylinder, which optionally low actuation of the friction clutch has the consequence. In this way, the predetermined characteristic of the clutch torque to be transmitted based on a path of the slave cylinder piston and thus an associated path of the master cylinder piston whose path is again used to control the clutch actuator by the encoder cylinder piston driving electric motor is controlled accordingly. For the purposes of the invention, the hydraulic path of the pressure volume is thus detuned. As a measure of the displacement of the characteristic in this case, in particular, the evaluation of the touch point, in which the friction clutch begins to transmit moment. A threshold value may be, for example, about 5 Nm.

To form the first operating variable, a temperature sensor may be provided in the pressure line. However, it has proven to be advantageous to save such a temperature sensor when using a temperature model, which determines the temperature of the pressure line as a weighted average of temperatures that are in contact with the hydrostatic system. This can be, for example, an engine compartment, engine cooling water and / or transmission temperature of an internal combustion engine or transmission of the drive train of the motor vehicle. The weighting of the individual temperatures for determining the temperature modeled in this way depends on the respective influence and thus on the respective application and is adjusted accordingly to this. A determination of the temperature T of the pressure line or the pressure volume can be determined by the following equation (1):

where Ti are the individual temperatures and Wi are the associated weighting factors for temperature sensors in the engine "Eng", in the air "Air" and / or in a gearbox "Gearbox".

For example, the modeled temperature of the pressure line or the pressure volume of the pressure medium is stored at this time after each successful sniffing and determined from this currently calculated temperature a temperature difference since the last snooping. If this temperature difference exceeds a defined threshold len, it is concluded that a sufficiently large change in volume of the pressure medium in the pressure line, that due to the temperature criterion, a higher need to perform a snooping is given. Accordingly, if necessary, a higher level of the scale is set.

An alternative or preferably additionally forming the scale second operating variable may be formed from a pressure or a pressure change compared to a last performed snooping. A direct detection of the pressure can be determined directly, for example, on the basis of a pressure sensor provided in the pressure volume.

Alternatively or preferably, in addition, a third variable can be formed from a currently determined touch point or one compared to a last-determined touch point or sniffing process of the friction clutch. Such a touch point information can be determined from a clutch model, which is spanned on the basis of torque, speed and / or pressure variables and receives corresponding information for updating from continuously determined sensor data. In the case of a detuned hydrostatic path, the torque actually transmitted differs from the torque calculated in the clutch model at the current master cylinder position. Thus, the change in the pressure volume in the hydrostatic path can be read directly from the touch point shift. In order to determine the need for a snooping process, for example, the touch point of the friction clutch is stored after sniffing and determined with the current touch point, the Tastpunktdifferenz since the last sniffing. If the touch point change exceeds a defined threshold value, a detuned hydrostatic path is closed. Accordingly, based on the Tastpunktkriteriums a level of the scale is set, which prioritizes a snooping higher.

The application of a scale for prioritizing a sniffing operation can be used in particular in so-called dual-clutch transmissions with a two actuated by a respective hydrostatic clutch actuator friction clutch, wherein for each friction clutch a separate multi-level scale for assessing a confidence measure of the friction clutches with an optionally be performed snooping is provided. In such a constellation, it may be advantageous if, alternatively or additionally, a fourth operating variable of a first friction clutch by means of a currently determined touch point or a touch point change since a last touch probe point determination or a last snooping operation of the other friction clutch is formed. In this case, a snooping operation on an open friction clutch can be carried out by using as the fourth operating variable a currently determined value of the touch point of the other momentum transferring friction clutch.

In this case, the two clutch actuators adjacent to each other, so that the environmental influences that lead to a detuning of the hydrostatic path of a friction clutch, also act on the hydrostatic path of the other friction clutch in at least a similar manner, from Tastpunktverschiebungen of a friction clutch on the moods in the hydrostatic section of the other friction clutch are closed. Since typically a model-based Tastpunktadaption takes place only in certain clutch actuators, for example in a not by the slave cylinder intentionally actuated friction clutch, which are often mutually present by the operation of a dual clutch transmission to the two friction clutches, the Tastpunktverschiebung a currently adapted friction clutch also provides clues to the Schnüffelnötwendigkeit on not adapted, that is currently sniffed friction clutch. In order to use such information as a fourth operating variable, for example, the touch point of a first friction clutch can be stored during a snooping operation and based on a change in the touch point of the first friction clutch can be used as an estimate for the Tastpunktänderung the second friction clutch. If the thresholds estimated from the touch point change of the other friction clutch exceed defined thresholds, a higher need for a snooping operation is detected and the level of the scale for the corresponding friction clutch is correspondingly changed.

For a reliable control of the friction clutch in each case necessary confidence in the slave cylinder position and the consequent need to perform a snooping process in the absence of confidence, the lowest required confidence and thus the highest required Schnüffelnötwendigkeit is selected by an appropriate design of the scale.

The invention will be explained in more detail with reference to the embodiment shown in Figures 1 and 2. Showing:

FIG. 1 shows a diagram for depicting the dependency of the transmitted clutch moments of a friction clutch from one way of the master cylinder piston and

Figure 2 is a diagram illustrating a dependence of the clutch torque of

Changes in the hydraulic distance between master cylinder and slave cylinder.

1 shows the two-part diagram 1 of the pressure p in a hydraulic path of a hydrostatic system for actuating a friction clutch with a hydrostatic clutch actuator whose controlled electric motor displaces a piston of a master cylinder to the pressure p in a filled with pressure medium with a predetermined pressure volume hydrostatic Range to which a slave cylinder is connected to vary. Here, the slave cylinder piston is displaced depending on the built-up of the master cylinder pressure p and from this the friction clutch along an actuation path depending on the design - here along a Einrückwegs a depressed friction clutch - on or disengaged. Accordingly, each waypoint s _{Gx of} the curve 2 of the pressure p via the master cylinder _{piston stroke} s _{G in} accordance with the curve 3 of the pressure p via the clutch _torque M _{RK of} the friction clutch, a predetermined clutch _torque M _RKx transferable. If, however, the pressure p changes in the hydrostatic path because, for example, temperature changes occur, this assignment is disturbed. If such a detuning of the hydraulic path is detected, the displacement range As _{s is} set on the master cylinder, in which a connection between the hydrostatic line and a non-pressurized reservoir produced and a pressure equalization is established, so that the original assignment of the master cylinder piston stroke s _G to the Clutch torque MRK over the pressure p is restored. This process is called a snooping process. Performing a snooping operation requires the state of an open friction clutch and takes time. Optionally, required circuits of a downstream transmission, which require an actuation of the friction clutch, delayed and disturbed in frequent snooping the ride comfort. Therefore, a method is used in which the number of sniffing operations is reduced without neglecting the quality of the illustrated mapping of the clutch torque M _RK to the master cylinder piston travel s _G ZU. For this purpose, a multi-level scale is provided which indicates a measure of confidence for the operation of the friction clutch. The levels of the scale are formed by the temperatures prevailing at the hydrostatic path, the pressure which is being set and information about a change in the touch point, and they give confidence. according to which it is judged how urgent a snooping process is. Depending on the urgency, a snooping process is carried out immediately and delayed.

FIG. 2 shows the diagram 4 for illustrating the influence of detuning

Coupling characteristics 5, 6 with the clutch torque M _RK on the Geberzylinderkolbenweg s _G. The characteristic curve 5 shows the relationship of the clutch torque M _RK on the Geberzylinderkolbenweg s _G based on a stored in a control unit, adaptable clutch model with the currently adapted touch point TP _M. The characteristic curve 6 shows the relationship of the clutch torque M _RK on the Geberzylinderkolbenweg s _G in example detuned as a result of a change in temperature hydraulic path. In this case, as a result of the changed pressure conditions in the hydraulic section, the touch point TP _{M of} the clutch model is displaced to the real touch point TP _R by the higher pressure being applied to the slave cylinder. Accordingly, the characteristics 5, 6 are shifted from each other under otherwise identical conditions, so that when set Geberzylinderkolbenweg s _Gx a torque difference corresponding to the double arrow 7 is set. By actual determination and comparison of the tactile points TP _M , TP _R , the temperatures and pressures varying in the hydraulic path, the multi-level scale can be given a confidence measure reflecting the need for a snooping operation.

LIST OF REFERENCE NUMBERS

1 diagram

2 curve

3 curve

4 diagram

5 characteristic

6 characteristic

7 double-headed arrow

MRK clutch torque

MR X clutch torque

P pressure

So donor cylinder piston way

SGX waypoint

TP _M touch point

TPR touch point

As _s walk area

Claims

claims

1 . A method for automated actuation of a friction clutch in a drive train of a motor vehicle by means of a hydrostatic system with one of an electrically driven master cylinder of a hydrostatic clutch actuator, the friction clutch operating slave cylinder and a pressure line arranged between these pressure chamber, wherein a snooping operation by displacing the master cylinder in a non acted upon state of the friction clutch is initiated by the pressure volume connected to a non-pressurized reservoir and a pressure compensation is provided, characterized in that a sniffer operation depending on a multi-level, continuously formed from a plurality of operating variables of the motor vehicle, a trust measure for safe operation of the friction clutch forming scale is made.

2. Method according to claim 1, characterized in that a lowest value of the scale represents no need for snooping and an uppermost value of the scale represents an immediate need for snooping.

3. The method according to claim 1 or 2, characterized in that a Schnüffelbedarf is performed in a forcibly forced friction clutch in the open and in a forced open friction clutch in a closed state.

4. The method according to any one of claims 1 to 3, characterized in that a first operating variable, the temperature or a temperature change compared to a last performed snooping process of the pressure volume is formed.

5. The method according to claim 4, characterized in that the first operating variable based on a temperature model of a single or more depending on their influence on the temperature of the pressure volume weighted temperature sensors is formed.

6. The method according to any one of claims 1 to 5, characterized in that a

second operating variable is formed from a pressure or a pressure change compared to a last performed snooping.

7. The method according to any one of claims 1 to 6, characterized in that a third variable is formed from a currently determined touch point or a comparison with a last-determined touch point or sniffing the friction clutch.

8. The method according to any one of claims 1 to 7, characterized in that in a double clutch formed by two friction clutches with two hydrostatic systems, a fourth operating variable of a first friction clutch by means of a currently determined tactile point or a Tastpunktänderung since a last Tastpunktermittlung or a last snooping the other Friction clutch is formed.

9. The method according to claim 8, characterized in that a snooping operation is performed on an open friction clutch by a currently determined value of the Tastpunkts the other, a torque-transmitting friction clutch is used as the fourth operating variable.

10. The method according to any one of claims 1 to 9, characterized in that depending on a determined level of the scale, a snooping operation is preferred to a necessary switching operation of a transmission.