DE102015218691A1 - Method for determining a coefficient of friction of a clutch of a dual-clutch transmission system - Google Patents

Abstract

The invention relates to a method for determining a coefficient of friction of a clutch of a dual-clutch transmission system during initial and / or recommissioning of the dual-clutch transmission system, wherein the clutch (9) is actuated by a hydrostatic clutch actuator (3) and the clutch (9) is opened and / or closed is detected, wherein a pressure (p) above the respective position of the clutch (9) detected and a pressure characteristic is created. In a method in which an increased ride comfort is present from the already first driving torque, a clutch torque (Trqmeasured) is measured over the respective position of the clutch (9) during the opening and / or closing of the clutch (9) to produce a clutch torque characteristic curve. wherein the coefficient of friction (μ_learned) is determined from the measured clutch torque (Trqmeasured) and an estimated clutch torque (Trqestimated).

Description

The invention relates to a method for determining a coefficient of friction of a clutch of a dual-clutch transmission system during initial and / or recommissioning of the dual-clutch transmission system, wherein the clutch is actuated by a hydrostatic clutch actuator and the clutch is opened and / or closed, wherein a pressure above the respective position the clutch detected and a pressure curve is created.

In the production of new vehicles, the dual clutch with the engagement system is installed together in a bell housing. The entire system will then be measured. According to the DE 10 2010 012 756 A1 This is done at the end of the tape on a transmission tester. In this case, a torque characteristic, which represents a clutch torque over a position of the clutch, measured. From the survey, the coupling parameters touch point, coefficient of friction, shape factors and hysteresis parameters are determined and stored in a non-volatile memory of the control unit for later use.

From the DE 10 2012 204 940 A1 a method for the adaptation of parameters of a clutch of a dual-clutch transmission system is known, which has a hydrostatic clutch actuator with a pressure sensor. The adaptation of the parameters takes place during initial startup and / or recommissioning of the dual-clutch transmission system by opening and / or closing the clutch, and during the closing and / or opening of the clutch by means of the pressure sensor, a pressure profile is determined as a function of the position of the clutch , From this pressure curve, parameters for the coupling are subsequently adapted. These parameters include the touch point, clamping force stiffness, shape factors and hysteresis parameters stored in non-volatile memory.

Other parameters such as the coefficient of friction are not determined during initial or recommissioning, but certain default values are assumed as substitute values, which are used as the basis for commissioning. After the first start-up and switching in the vehicle, these parameters are then adapted.

The disadvantage here is that the previously assumed default values for the coefficient of friction parameters deviate greatly from the parameters actually prevailing in the dual-clutch transmission system. This has the consequence that in the control of a single clutch with an inaccurate coefficient of friction, a false clutch torque is set or required. This can lead to heavy losses in ride comfort, especially in the case of circuits and starting operations with relatively high torques in the form of full loads. However, since exactly this area depends strongly on a coefficient of friction, this effect can have an effect of varying degrees on each individual dual-clutch transmission system as a result of series production.

The invention is therefore based on the object of specifying a method for determining a coefficient of friction of a clutch, which is determined during commissioning and / or recommissioning of the dual-clutch transmission system.

According to the invention, the object is achieved in that a clutch torque is measured over the respective position of the clutch during opening and / or closing of the clutch to create a torque characteristic, the coefficient of friction is determined from the measured clutch torque and an estimated clutch torque. By estimating the coefficient of friction from a clutch torque characteristic which is determined at the same time and in addition to the pressure characteristic in the initialization process, it is prevented that the initial friction value deviates greatly from the actual friction value of the new clutch. This leads to a significantly improved ride comfort right from the beginning of the use of the vehicle by the vehicle user.

Advantageously, a clamping force characteristic curve for deriving a nominal clutch torque is determined from the pressure characteristic, the estimated clutch torque being determined from the nominal clutch torque. The determination of the clamping force characteristic from the pressure characteristic is possible at any time, since pressure and force are proportional to each other. The estimated clutch torque is thus derived from the directly measured pressure characteristic and is therefore based on a measurement of the current clutch conditions.

In one embodiment, the nominal clutch torque, which depends on a given coefficient of friction, is matched with at least one compensation factor for the correction of clutch-based errors and / or a drag torque. This will display the current measured coupling parameters Operating state-dependent errors and design-related deviations of the individual clutches adapted.

In a variant, a slip of the clutch is kept constant during the opening and / or closing of the clutch. By keeping the slip constant, the influence of slip variations on the learned friction coefficient is kept to a minimum, so that a particularly accurate determination of friction coefficient is possible.

In one development, the coefficient of friction is determined from a quotient of at least one measured and at least one estimated clutch torque.

In one embodiment, the coefficient of friction is determined on the basis of the estimated and measured clutch torques when at least one clutch torque threshold is reached. The clutch torques measured or estimated at a plurality of clutch torque thresholds are added together and used to form the ratio, resulting in a very precise friction coefficient when using a plurality of clutch torque thresholds.

Preferably, the coefficient of friction is determined at a fixed position of the clutch or a changing position of the clutch. In particular, when measuring at changing positions constructive peculiarities of the clutch are considered sufficiently in the determination of the coefficient of friction.

In an alternative, the coefficient of friction is learned in a fixed position of the clutch by the fixed position of the clutch is approached several times. Due to the multiple start of the clutch and the subsequent determination of the coefficient of friction, it is easy to determine an average value of the coefficient of friction which comes closest to the actual coefficient of friction.

Advantageously, the determination of the coefficient of friction takes place when the coupling closes. With a closing clutch, the measured and estimated clutch torques can be determined particularly well, since influences from partial loops of the hysteresis of the pressure characteristic are avoided.

In one variant, the determination of the coefficient of friction is effected by a coefficient of friction model integrated into a clutch temperature model. This friction coefficient model may include the methodology explained in the preceding paragraphs, so that the coefficient of friction can also be determined as a function of the temperature of the clutch, which has a decisive influence on the coefficient of friction.

The invention allows numerous embodiments. One of them will be explained in more detail with reference to the figures shown in the drawing.

Show it:

1 a schematic structure of a hydraulic coupling system,

2 a schematic representation of the measurement of a pressure characteristic,

3 a schematic representation of the measurement and estimation of a clutch torque characteristic,

4 a simplified model for the estimation of a clutch torque characteristic in a wet clutch system during commissioning,

5 an embodiment for the determination of the coefficient of friction on the basis of a changing position of the coupling,

6 an embodiment for the determination of the coefficient of friction on the basis of a fixed predetermined position of the clutch.

In 1 is schematically the structure of a hydraulic coupling system 1 illustrated by the example of a hydrostatic clutch actuator. This schematic diagram shows only the structure for operating one of the two double clutches of a dual-clutch transmission system. The actuation of the second clutch of the dual-clutch transmission system is analogous and will not be explained further here.

The hydrostatic coupling system 1 includes a controller 2 that has a clutch actuator 3 controls. When the position of the clutch actuator changes 3 becomes a piston 4 a master cylinder 5 along the Aktorweges moved to the right, reducing the volume in the master cylinder 5 changed and a pressure p in the master cylinder 5 is built. This pressure p is via a hydraulic fluid 6 , which serves as a pressure medium, via a hydraulic line 7 to a slave cylinder 8th transferring the clutch 9 via a preload spring 12 actuated. The pressure p of the hydraulic fluid 6 causes it in the slave cylinder 8th a change of direction, resulting in the operation of the clutch 9 reflected. The pressure p is at the master cylinder 5 by means of a pressure sensor 10 determined. The of the clutch actuator 3 traversed distance along the Aktorweges is from a displacement sensor 11 certainly. That of the clutch actuator 3 The distance traveled will be determined by the path of the clutch 9 set equal.

For determining the coefficient of friction at the hydrostatic clutch actuator 1 actuated clutch 9 of a dual-clutch transmission system, a pressure characteristic is first measured during commissioning of the dual-clutch transmission system. Such a measured pressure characteristic is in 2 where once the pressure over time ( 2 B ) and on the other according to the pressure curve the actuator position over time ( 2a ) is measured. On the basis of the pressure characteristic parameters of the preload spring 12 that of the slave cylinder 8th for actuating the clutch 9 is actuated, determined in the form of offset and rigidity. In addition, a clamping force characteristic curve is determined, from which parameters such as the touch point, the clamping force rigidity and form factors for the clamping force are determined. The clamping force of the preload spring 12 above the position of the clutch actuator 3 is in 2c illustrates, wherein the curve A represents a nominal clamping force characteristic, which runs before the achievement of the touch point TP. Curve B shows a clamping force while curve C shows the stiffness of the preload spring 12 clarified. The actuation force of the preload spring actually occurring after the touch point TP 12 is indicated by curve D.

In a second step for determining the coefficient of friction, a clutch torque characteristic is measured by, as in FIG 3 represented, the clutch torque over time ( 3b ) and the position of the clutch actuator 3 also over time ( 3a ). In this case, the learned from the clamping force characteristic probe TP is in 3b displayed. The measurement of the clutch torque is carried out at a constant slip speed of the clutch 9 , The measured clutch torque Trq _measured leads to a cancellation of the measuring process.

From this measured pressure characteristic, an estimated clutch torque Trq _{estimated is} determined ( 3b ).

The estimation of the estimated clutch torque Trq _estimated is in 4 shown schematically, where from the pressure characteristic a clamping force F _{clampAct is} determined.

With the aid of this clamping force F _clampAct , a nominal clutch characteristic for the coefficient of friction is determined, which represents a clutch torque T _clutch above the clamping force F _clampAct . For the nominal clutch characteristic, the clutch torque is T _{clutch nominal} = f (F _clampAct , μ _initial ).

In this case, a starting friction _value is assumed to be μ _initial , which is estimated at a clutch torque of, for example, 270 Nm. Subsequently, a _{clutch torque} T _{clutch Nom} taken from the nominal clutch characteristic _{curve is} corrected with compensation factors. These compensation factors are the slip speed, the engine speed, the temperature and the friction power. To correct the offset of this clutch _torque T _{clutch Nom} , which is above a certain position of the clutch actuator 3 occurs, is also the slip speed, a flow of hydraulic fluid 6 , the temperature of the hydraulic fluid 6 and an airway. After these two corrections, one obtains the estimated clutch torque Trq _estimated .

Especially for wet clutch systems, the coefficient of friction is above all the slip speed and the temperature of the clutch 9 dependent. For an even higher accuracy of the estimated clutch torque, the other compensation factors must also be taken into account. The slip speed is _measured when measuring the clutch torque Trq _measured over the position of the clutch actuator 3 kept constant by controlling the output torque of the vehicle. To avoid influences from partial loops of the hysteresis of the pressure characteristic, the position of the clutch actuator becomes 3 only move in one direction. This is advantageously the sloping closing branch of the clutch characteristic.

The friction coefficient μ_learned is determined on the basis of the estimated clutch torques Trq _estimated and the measured clutch torques Trq _measured when various clutch torque thresholds are reached, as in FIG 5 shown.

In this case, the clutch torques Trq _{measured are measured} via the touch point TP.

The use of different approach positions of the clutch actuator 3 allows to increase the accuracy of the friction coefficient μ_learned. In particular, it is advantageous if different positions of the clutch actuator 3 and thus the clutch 9 be used in the determination of the coefficient of friction μ_learned.

The at the different positions of the clutch actuator 3 and the associated clutch torque thresholds of, for example, 20 Nm, 40 Nm, 50 Nm, 60 Nm, etc., of certain measured clutch torques Trq _measured as well as the estimated clutch torques Trq _estimated are respectively summed. The coefficients of friction μ_learned are determined from their quotients:

6 shows the determination of the coefficient of friction μ_learned from the measured and the estimated coefficient of friction at a fixed predetermined position of the clutch actuator 1 ,

This is the clutch actuator 1 advantageously repeatedly approached to increase the accuracy of the coefficient of friction μ_learned and thereby determines the measured and estimated clutch torques. The determination of the coefficient of friction μ_learned also takes place here from equation (1).

As a result of this measurement, the learned friction coefficient μ_learned is an optimum value along the entire measured clutch characteristic curve. This learning process can be used with both dry and wet clutches. Due to this determination of the coefficient of friction in an initialization process after installation of a new clutch, very good driving characteristics are achieved by the first driven meter.

LIST OF REFERENCE NUMBERS

1

hydraulic coupling system

2

 control unit

3

 hydrostatic clutch actuator

4

 piston

5

 Master cylinder

6

 hydraulic fluid

7

 hydraulic line

8th

 slave cylinder

9

 clutch

10

 pressure sensor

11

 displacement sensor

12

 preload

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102010012756 A1 [0002]
• DE 102012204940 A1 [0003]

Claims (10)

Method for determining a coefficient of friction of a clutch of a dual-clutch transmission system during initial and / or recommissioning of the dual-clutch transmission system, wherein the clutch ( 9 ) from a hydrostatic clutch actuator ( 3 ) and the clutch ( 9 ) is opened and / or closed, wherein a pressure (p) above the respective position of the clutch ( 9 ) and a pressure characteristic curve is generated, characterized in that a clutch torque (Trq _measured ) over the respective position of the clutch ( 9 ) during opening and / or closing of the coupling ( 9 ) is measured to produce a clutch torque characteristic, wherein the coefficient of friction (μ_learned) from the measured clutch torque (Trq _measured ) and an estimated clutch torque (Trq _estimated ) is determined. A method according to claim 1, characterized in that from the pressure characteristic of a clamping force characteristic for deriving a nominal clutch torque (T _{clutch Nom} ) is determined, from the nominal clutch torque (T _{clutch Nom} ), the estimated clutch torque (Trq _estimated ) is determined. Method according to Claim 2, characterized in that the nominal clutch torque (T _{clutch nom} ), which depends on a starting coefficient of friction (μ_initial), has at least one compensation factor for correcting clutch-based errors and / or a drag torque of the clutch ( 9 ) is adjusted. A method according to claim 1, 2 or 3, characterized in that during the opening and / or closing of the coupling ( 9 ) a slip of the clutch ( 9 ) is kept constant. A method according to at least one of the preceding claims, characterized in that the coefficient of friction (μ_learned) from a quotient of at least one measured and at least one estimated clutch torque (Trq _Measured; Trq _estimated) is determined. A method according to claim 5, characterized in that the coefficient of friction (μ_learned) on the basis of the estimated and measured clutch torques (Trq _{estimated; Measured} Trq) is determined in achieving at least one clutch torque threshold. A method according to claim 5 or 6, characterized in that the coefficient of friction (μ_learned) at a fixed position of the coupling ( 9 ) or a changing position of the coupling ( 9 ) is determined. A method according to claim 7, characterized in that the coefficient of friction (μ_learned) in a fixed position of the coupling ( 9 ) is learned by the fixed position of the clutch ( 9 ) is approached several times. Method according to at least one of the preceding claims, characterized in that the determination of the coefficient of friction (μ_learned) in the case of a closing clutch ( 9 ) he follows. Method according to at least one of the preceding claims, characterized in that the determination of the coefficient of friction (μ_learned) is effected by a coefficient of friction model integrated in a coupling temperature model.

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