DE102014219031A1 - Method for determining a coefficient of friction of a separating clutch of a hybrid vehicle - Google Patents

Abstract

The invention relates to a method for determining a coefficient of friction of a disconnect clutch of a hybrid vehicle in which a friction value change of the disconnect clutch (4) closed in the unactuated state is determined by an electric motor (3) during a restart of an internal combustion engine (2) and an actual rotational speed of the internal combustion engine ( 2) is measured. In a method in which a particularly accurate determination of the coefficient of friction is possible, an estimated speed of the internal combustion engine (2) is calculated from a model, comparing the actual speed and the estimated speed of the internal combustion engine (2) at the end of the restart a correction factor of the coefficient of friction is determined.

Description

The invention relates to a method for determining a coefficient of friction of a disconnect clutch of a hybrid vehicle, in which a friction value change of the disconnect clutch closed in the unactuated state is determined at a restart of an internal combustion engine by an electric motor and an actual speed of the internal combustion engine is measured.

In hybrid vehicles, which allow different combinations of types of drive, such as electric motor, elektrozeratorisch, internal combustion engine in push or pull operation, engine or electric motor-off, a mechanical decoupling of the moments of the internal combustion engine and electric motor is necessary. The decoupling of internal combustion engine and electric motor is carried out by a separating clutch, which is automatically actuated. This automatic actuation of the separating clutch via an actuator, consisting of a control unit with appropriate software for controlling the separating clutch and an electromechanical or electro-hydraulic actuator for actuating the clutch.

To control the separating clutch, it is important that the real clutch torque is known at the separating clutch. Since this can not be measured in the hybrid vehicle, it is estimated based on other parameters of the separating clutch and stored in a clutch torque characteristic. However, it may be that the nominal clutch torque characteristic stored in the software of the control unit changes during operation. An important parameter to consider when changing the clutch characteristic is the coefficient of friction.

Various strategies are known which allow the coefficient of friction to be learned. So revealed the EP 2 008 899 A1 a method for adapting the coefficient of friction of a separating clutch, where from the speed change of the internal combustion engine and its moment of inertia, an accelerating clutch torque is continuously calculated at the separating clutch. The coefficient of friction is adjusted by comparing the currently estimated clutch torque with the calculated clutch torque. A disadvantage is that in this method, a large number of characteristics of the hybrid vehicle must be made available, but which are not known exactly in practice. Thus, an engine torque can be made available only after firing the engine. The speed signal is only accurate enough from a threshold value to be used for calculating the current torque. A running adjustment thus leads to a falsification of the learned parameters. In addition, the calculation of the clutch torque by derivation of the speed by a differentiation to an enormous amplification of signal noise and thus to increase the errors occurring.

The invention has for its object to provide a method for determining a coefficient of friction of a separating clutch of a hybrid vehicle, in which a high accuracy in the calculation of the coefficient of friction is achieved.

According to the invention the object is achieved in that an estimated speed of the internal combustion engine is calculated from a model, wherein the actual speed and the estimated speed of the internal combustion engine are compared at the end of the restart, from which a correction factor of the friction coefficient is determined. This has the advantage that the coefficient of friction over the entire period of the restart, i. from closing to re-opening the separating clutch, is determined and only at the end of this period is determined once. The determination of the coefficient of friction is bound to real, transmitted from the clutch torque, which prevents inaccuracies in the determination of the coefficient of friction or its change.

Advantageously, to determine the speed estimated from the model, a clutch torque is determined from a clutch torque characteristic of the disconnect clutch, from which reference is made to the estimated rotational speed after an acceleration process of the restart torque. Since the clutch torque results from an already existing and the operation of the clutch release underlying clutch torque curve, it can be assumed that deviations from the actual clutch torque curve are manageable and this existing clutch torque curve sufficiently expresses the current operating state of the clutch.

In one embodiment, the clutch torques taken from the clutch torque characteristic during re-start are integrated over the re-start time and an integrated clutch torque is divided by an inertia moment of the engine. This has the advantage that since the speed does not act on the model, the error is reduced because the corrections by means of very inaccurate signals, especially at the beginning of the restart, are omitted in each calculation step. The model inaccuracies average out by simulating the model over several sampling steps and result in a moderate and less volatile adjustment of the coefficient of friction by the one-time adjustment.

In one variant, the correction factor is determined once, from which a new clutch torque characteristic is determined on the basis of the existing clutch torque characteristic, which is based on a subsequent restart of the internal combustion engine. Thus, at each restart of the engine, the clutch torque characteristic can be adjusted by calculating a new coefficient of friction, which is used in the control of the separating clutch by a control unit on a clutch torque curve, which represents the actual state of the clutch.

In a further development, a ratio is formed from the estimated rotational speed and the actual rotational speed of the internal combustion engine, which ratio is used as the basis for balancing the new clutch torque characteristic with the existing clutch torque characteristic. This has the advantage that as few iteration steps are necessary in order to adapt the existing clutch torque characteristic to the actual clutch torque characteristic of the separating clutch.

In one embodiment, an initial threshold is defined for the speed to be estimated from the model. By initializing the estimated speed from the model to the measured speed of the engine, errors from the speed calculation are minimized. Such errors in the speed calculation decrease with increasing value of the speed.

Advantageously, a deviation direction of the rotational speed is determined from a deviation of the estimated rotational speed from the actual rotational speed, wherein the friction coefficient is increased or reduced by a fixed value in accordance with the direction of deviation, from which the new clutch torque characteristic curve is established. Thus, the new clutch torque characteristic can be adjusted regardless of the size of the speed deviation by a fixed increment of Reibwertänderung.

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 diagram of a drive train of a hybrid vehicle,

2 a schematic representation of the course of the rotational speeds of the internal combustion engine and the clutch torque with small deviations of the rotational speeds,

3 a schematic representation of the course of the rotational speeds of the engine and the clutch torque at large deviations of the speed.

In 1 is a schematic diagram of a drive train 1 represented the hybrid vehicle. This powertrain 1 includes an internal combustion engine 2 and an electric motor 3 , Between the combustion engine 2 and the electric motor 3 is right behind the combustion engine 2 a separating clutch 4 arranged. internal combustion engine 2 and separating clutch 4 are over a crankshaft 5 connected with each other. The electric motor 3 has a rotatable rotor 6 and a fixed stator 7 on. The output shaft 8th the separating clutch 4 is with a gearbox 9 connected, which contains a coupling element, not shown, for example, a second clutch or a torque converter, between the electric motor 3 and the transmission 9 is arranged. The gear 9 transmits that from the internal combustion engine 2 and / or the electric motor 3 generated torque on the drive wheels 10 of the hybrid vehicle. The separating clutch 4 and the gearbox 9 form a gear system 11 , which is a hydrostatic actuator 12 is controlled.

In addition, it is assumed that it is the disconnect clutch 4 to an unconfirmed closed clutch (normally closed) is. The method is also applicable without major changes in a "normally open" coupling. The between the internal combustion engine 2 and the electric motor 3 arranged separating clutch 4 is closed to, while driving the hybrid vehicle with the, of the electric motor 3 generated torque the internal combustion engine 2 to start or during a boost operation with driving internal combustion engine 2 and electric motor 3 to drive. The separating clutch 4 is doing by the electrostatic clutch actuator 12 actuated. To ensure that when restarting the engine 2 through the electric motor 3 sufficient torque from the electric torque 3 is provided, which is both the hybrid vehicle via the drive wheels 10 moves without loss of comfort and at the same time the internal combustion engine 2 actually starts, is an accurate knowledge of a clutch torque characteristic of the clutch 4 required, in which a clutch torque is shown above the Aktorweg.

In the control unit 13 of the clutch actuator 12 is stored a software that the clutch torque characteristic of the clutch 4 includes. This clutch torque characteristic is intended during the restart of the internal combustion engine 2 through the electric motor 3 be adapted. For this purpose, a period of re-start of the internal combustion engine 2 considered, by which the period is to be understood, in which the separating clutch 4 from the open to the closed state. At predetermined intervals is from the per se in the control unit 13 existing clutch torque characteristic determines a current clutch torque. The clutch torques calculated during this restart period are integrated over time at the end of the restart torque, and the thus-obtained integrated and averaged clutch torque becomes an inertia torque of the internal combustion engine 2 divided, from which the estimated speed is determined from the described model, which the internal combustion engine 2 after completion of the acceleration process underlying the restart. When the speed threshold of the internal combustion engine is exceeded 2 , which the self-running of the internal combustion engine 2 represents, the estimated speed of the internal combustion engine 2 compared with a measured, actual speed of the internal combustion engine. From the deviation of the estimated and the actual speed of the internal combustion engine 2 a correction factor is determined once for the correction of the coefficient of friction, with which a new current clutch torque characteristic is calculated from the existing clutch torque characteristic and stored in the software.

Signal curves of the speed of the internal combustion engine 2 and the clutch torque of the clutch 4 are in the 2 and 3 shown. In 2 is a moderate deviation between a desired clutch torque and an actual clutch torque of the clutch 4 shown. It is in 3 a large deviation between nominal and actual torque of the separating clutch 4 shown. The deviation is characterized by the differences between speed_computed and speed_permitter_signal. A dynamic course of the clutch torque has no effect on the adaptation.

By the described method for determining the coefficient of friction during the restart of an internal combustion engine by an electric motor in a hybrid vehicle is from the comparison of the speed of the internal combustion engine 2 and a speed of the internal combustion engine calculated in the model 2 at the end of the phase of restart, the friction value change is determined.

LIST OF REFERENCE NUMBERS

1

 powertrain

2

 internal combustion engine

3

 electric motor

4

 separating clutch

5

 crankshaft

6

 rotor

7

 stator

8th

 output shaft

9

 transmission

10

 drive wheels

11

 transmission system

12

 Hydrostatic actuator

13

 control unit

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

• EP 2008899 A1 [0004]

Claims (7)

Method for determining a coefficient of friction of a separating clutch of a hybrid vehicle, in which during a restart of an internal combustion engine ( 2 ) by an electric motor ( 3 ) a coefficient of friction change in the unactuated state closed separating clutch ( 4 ) is determined and an actual speed of the internal combustion engine ( 2 ), characterized in that an estimated speed of the internal combustion engine ( 2 ) is calculated from a model, wherein the actual speed and the estimated speed of the internal combustion engine ( 2 ) are compared at the end of the restart, from which a correction factor of the friction coefficient is determined. A method according to claim 1, characterized in that for determining the speed estimated from the model, a clutch torque from a clutch torque characteristic of the separating clutch ( 4 ) is determined, from which is closed to the estimated speed after an acceleration operation of the restarting torque. A method according to claim 1 or 2, characterized in that the extracted from the clutch torque characteristic during the restart clutch torque over the time of restart are integrated and an integrated clutch torque by an inertia of the internal combustion engine ( 2 ) is divided to obtain the estimated speed. A method according to claim 1, 2 or 3, characterized in that the correction factor is determined once, from which a new clutch torque characteristic is determined on the basis of the existing clutch torque characteristic, which a subsequent restart of the internal combustion engine ( 2 ) is used. Method according to one of the preceding claims, characterized in that from the estimated speed and the actual speed, a ratio is formed, which is based on the comparison of the new clutch torque characteristic with the existing clutch torque characteristic. Method according to at least one of the preceding claims, characterized in that an initial threshold value for the speed to be estimated from the model is defined. Method according to at least one of the preceding claims, characterized in that a deviation direction of the rotational speed is determined from a deviation of the estimated rotational speed from the actual rotational speed, wherein the friction coefficient is increased or reduced by a fixed value corresponding to the direction of deviation, resulting in the new clutch torque characteristic curve.

Images