Method and control device for determining a contact point of a friction clutch

Abstract

Method for determining a control-side relevant contact point of a friction clutch of a motor vehicle, wherein a current contact point of the friction clutch is determined adaptively, characterized in that the current contact point is calculated with a correction value dependent on the elasticity of the friction clutch in order to determine the control-side relevant contact point of the friction clutch, wherein the correction value is determined adaptively depending on the adaptively determined current contact point of the friction clutch and depending on an adaptively determined kink point of the friction clutch.

Description

[0001] The invention relates to a method for determining a control-relevant contact point of a friction clutch. Furthermore, the invention relates to a control device of a motor vehicle for determining a control-relevant contact point of a friction clutch.

[0002] Automatic or automated transmissions are increasingly used in motor vehicles. Such transmissions employ automated friction clutches and, optionally, automated positive-locking clutches, with the present invention relating to automated friction clutches, also referred to as automated friction clutches.

[0003] To ensure smooth and low-wear operation of an automated friction clutch, a precise understanding of the relationship between a control parameter and the torque transmitted by the clutch is essential. The control parameter could be, for example, a clutch pressure, which is used to engage or disengage the clutch. The relationship between a control parameter and the torque is typically stored in a vehicle control unit, such as a transmission control unit, as a characteristic torque curve. This torque curve is used to control the friction clutch during operation.

[0004] A key parameter or reference point of the torque characteristic curve of an automated friction clutch is the so-called contact point. The contact point is also referred to as the touchpoint, contact point, engagement point, or probing point of the friction clutch.

[0005] The contact point of the torque characteristic of an automated friction clutch is understood to be a reference point at which, when the clutch is actuated in the engaging or closing direction, the friction elements of the friction clutch just come into contact, so that the friction clutch just begins to transmit a minimum torque, and at which, when the clutch is actuated in the disengaging or opening direction, the friction elements of the friction clutch just separate, so that the frictional transmission of a torque by the friction clutch just stops.

[0006] The contact point of the friction clutch can shift during operation due to wear. Furthermore, in mass-produced, identical friction clutches, manufacturing tolerances can result in differences in the contact point between individual clutches.

[0007] To nevertheless ensure comfortable and low-wear operation of an automated friction clutch, it is already known from the prior art to adaptively determine the contact point of a friction clutch. Such a method for adaptively determining a current contact point of a friction clutch is known, for example, from DE 10 2008 043 384 A1.

[0008] The adaptively determined current contact point is used as the control-relevant contact point according to the state of the art. Furthermore, it is known in practice to determine a control-relevant contact point from an adaptively determined current contact point by applying a constant offset value to the adaptively determined current contact point of the automated friction clutch. This constant offset value is also referred to as the post-adaptation value.

[0009] WO 98 / 54483 A2 describes a method for zeroing a displacement measurement in the motion transmission from an actuator to a coupling, wherein a gripping point of the coupling is detected and forms the reference point for zeroing the displacement measurement.

[0010] US 2010 / 0268428 A1 teaches a method for calibrating a contact point for a motor vehicle, wherein the method includes steps to determine whether the contact point can be calibrated.

[0011] Based on this, the present invention aims to create a novel method for determining a control-side relevant contact point of an automated friction clutch and a novel control device for a motor vehicle for determining a control-side relevant contact point of an automated friction clutch.

[0012] This problem is solved by a method according to claim 1. According to the invention, the current contact point is calculated with a correction value dependent on the elasticity of the friction clutch in order to determine the control-side relevant contact point of the friction clutch.

[0013] The present invention proposes, for the first time, to calculate the adaptively determined, current contact point of an automated friction clutch using a correction value dependent on the elasticity of the friction clutch, in order to determine the control-side relevant contact point of the friction clutch. This makes it possible, for the first time, to take into account deviations in the stiffness or elasticity of the automated friction clutch caused by tolerances when determining the control-side relevant contact point. This enables significantly more comfortable and less wear-prone operation of an automated friction clutch.

[0014] According to the invention, the correction value is determined adaptively depending on the adaptively determined current contact point of the automated friction clutch and depending on an adaptively determined inflection point of the automated friction clutch. When the correction value is determined depending on the adaptively determined current contact point of the friction clutch and depending on the adaptively determined inflection point of the automated friction clutch, the correction value can be determined adaptively particularly advantageously.

[0015] The so-called "knee point" of the automated friction clutch, in addition to the contact point, is another reference point of the torque characteristic curve. The knee point is a reference point of the torque characteristic curve where a defined change in the actuating torque, such as the clutch pressure, results in a defined change in the torque transmitted by the friction clutch. At the knee point, the torque characteristic curve therefore has a defined gradient.

[0016] With a relatively elastic coupling behavior of an automated friction clutch, the inflection point has a relatively large distance from the contact point in the torque characteristic curve, whereas with a relatively stiff coupling behavior, the inflection point has a relatively small distance from the contact point in the torque characteristic curve of the friction clutch.

[0017] According to a first advantageous embodiment of the invention, the correction value is determined based on the difference between the adaptively determined current contact point of the automated friction clutch and the adaptively determined inflection point of the automated friction clutch. The adaptively determined current contact point, calculated using the adaptive correction value, is used as the relevant contact point for the control system. If the difference between the adaptively determined current contact point of the friction clutch and the adaptively determined inflection point of the friction clutch is negative, a positive correction value is determined, the larger the negative difference. Conversely, if the difference between the adaptively determined current contact point of the friction clutch and the adaptively determined inflection point of the friction clutch is positive, a negative correction value is determined, the magnitude of which increases with the positive difference.

[0018] According to a second, alternative, advantageous embodiment of the invention, the correction value is determined as a function of the difference between the adaptively determined current contact point of the automated friction clutch (calculated with a constant offset value) and the adaptively determined inflection point of the automated friction clutch. The control-side relevant contact point is the adaptively determined current contact point calculated with the adaptive correction value and the constant offset value. If the difference between the adaptively determined current contact point of the friction clutch (calculated with the constant offset value) and the adaptively determined inflection point of the friction clutch is negative and relatively large in magnitude, a positive correction value is determined, which is larger the greater the negative difference.If the difference between the adaptively determined current contact point of the friction clutch (calculated with the constant offset value) and the adaptively determined inflection point of the friction clutch is positive and relatively large, a negative correction value is determined. The magnitude of this negative correction value increases with the size of the positive difference. Conversely, if the absolute difference between the adaptively determined current contact point of the friction clutch (calculated with the constant offset value) and the adaptively determined inflection point of the friction clutch is relatively small, no correction value or a correction value of zero is determined.

[0019] According to the first, advantageous embodiment of the invention, the adaptive correction value serves to adjust or correct the adaptively determined, current contact point, wherein the adaptively determined contact point calculated with the adaptive correction value is used as the control-relevant contact point. According to the second, advantageous embodiment of the invention, the adaptive correction value serves to adjust or correct the constant offset value, wherein the adaptively determined contact point calculated with the adaptive correction value and the constant offset value is then used as the control-relevant contact point.

[0020] The control device according to the invention is defined in claim 8.

[0021] Preferred embodiments of the invention are described in the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawing, without being limited thereto. The drawing shows: Fig. 1 an exemplary diagram of a motor vehicle drive train; Fig. 2 another exemplary diagram of a motor vehicle drive train; Fig. 3. A diagram illustrating the state of the art; and Fig. 4 a diagram to illustrate the invention.

[0022] Fig. 1 and Fig. Figure 2 shows powertrain diagrams of a motor vehicle known from the prior art. The powertrain of the Fig. 1 via a drive unit 1 and a transmission 3 connected between the drive unit 1 and an output 2, wherein the transmission 3 can be designed as an automatic or automated transmission. The automated transmission 3 comprises at least one automated friction clutch 4, which can be used as a shifting element and, if necessary, as a starting element. Fig. Figure 2 shows another diagram of a motor vehicle's powertrain, where the powertrain diagram of Fig. 2. A transmission 3, designed as a dual-clutch transmission, is connected between the drive unit 1 and the output 2. This transmission comprises two sub-transmissions 5 and 6 with friction clutches 7 and 8 assigned to the sub-transmissions. The drive train diagrams of the Fig. 1 and Fig. Figure 2 is merely exemplary and illustrates possible applications of automated friction clutches using two exemplary drivetrain diagrams. The operation of the respective transmission 3, and thus of each friction clutch 4, 7, 8, is controlled by a control unit 15, namely the transmission control unit.

[0023] An automated friction clutch is characterized by a so-called torque characteristic curve, whereby Fig. 3. An exemplary torque characteristic curve 9 of a friction clutch is shown, in which, over a manipulated variable, in Fig. 3. A torque M transmitted by the friction clutch is plotted against a clutch pressure p. Fig. 3 Two characteristic reference points are shown in the torque characteristic curve 9, namely an adaptively determined current contact point 10 of the automated friction clutch and an adaptively determined kink point 11 of the same.

[0024] The contact point 10 is also referred to as the contact point or touchpoint or engagement point or touch point, wherein at the contact point 10 of the automated friction clutch of a clutch actuated in an engaging or closing direction, the friction elements of the same just come into contact and transmit a minimal torque, whereas in a friction clutch actuated in a disengaging or opening direction, the friction elements of the same are just separated, so that the frictional transmission of the torque through the friction clutch just ends or is interrupted.

[0025] The inflection point 11 of the friction clutch is a reference point of the torque characteristic curve 9, in which a defined change in the clutch pressure results in a defined change in the torque M transmitted by the clutch, from which it follows that the torque characteristic curve 9 has a defined gradient at the inflection point 11.

[0026] The inflection point 11 of the friction clutch, or of the torque characteristic curve 9, requires a larger control variable compared to the contact point 10, such that the inflection point 11 occurs when the friction clutch is more fully closed than the contact point 10. The inflection point 11 of the friction clutch defines, so to speak, a transition from an elastic to a rigid clutch behavior of the friction clutch, or of the torque characteristic curve 9. With an elastic clutch behavior, a relatively small increase in the transmitted clutch torque M requires a relatively large increase in the control variable, in particular the clutch pressure p, whereas with a rigid clutch behavior, a relatively small change in the control variable, in particular the clutch pressure p, results in a relatively large change in the transmitted torque M.

[0027] The adaptive determination of the contact point 10 of an automated friction clutch or of a torque characteristic 9 of an automated friction clutch is already known from DE 10 2008 043 384 A1. Likewise, the adaptive determination of the inflection point 11 is familiar to those skilled in the art.

[0028] An adaptively determined, current contact point 10 can be used in a control device, such as a transmission control device, of the motor vehicle as a control-side relevant contact point. Fig. Figure 3 further clarifies that it is already known in practice to calculate a control-relevant contact point 13 by subtracting the adaptively determined, current contact point 10 from a constant offset value 12. This constant offset value can also be referred to as a post-adaptation value.

[0029] According to the invention, the current contact point 10, determined by adaptation, is calculated using a correction value dependent on the elasticity of the friction clutch in order to determine the control-side relevant contact point of the friction clutch. The control-side relevant contact point is the reference point of the friction clutch that the control device uses to control the friction clutch.

[0030] According to the invention, the correction value is determined depending on the adaptively determined current contact point of the friction clutch and depending on an adaptively determined kink point of the friction clutch.

[0031] Details regarding this will be provided below with reference to Fig. 4 described in detail, whereby in Fig. 4 Two exemplary torque characteristics 9a, 9b of friction clutches are shown, whose adaptively determined, current contact point 10 is the same.

[0032] Furthermore, it shows Fig. 4, that this adaptively determined, current point of contact 10 is offset with a constant offset value 12, identical for both torque characteristics 9a, 9b, which then leads to an adapted point of contact 13, which in turn is identical for both torque characteristics 9a, 9b.

[0033] Furthermore, it shows Fig. 4. Adaptively determined inflection points 11a, 11b for the two torque characteristics 9a and 9b, wherein in the case of a stiffer friction clutch with torque characteristic 9a the inflection point 11a is closer to the contact point 10 or adapted contact point 13 than is the case for the inflection point 11b of a relatively elastic clutch with torque characteristic 9b.

[0034] According to Fig. 4. A difference is determined between the contact point 10 calculated with the constant offset value 12, i.e., the adjusted contact point 13, and the adaptively determined buckling point of the friction clutch. In Fig. Figure 4 shows the two differences 14a and 14b to the adapted point of contact 13 for the two inflection points 11a and 11b, which is determined by calculating the adaptively determined point of contact 10 with the constant offset value 12.

[0035] Then, if the difference 14a or 14b between the adaptive touch point 10 calculated with the constant offset value 12 or the adjusted touch point 13 and the inflection point 11a or 11b is negative and relatively large in absolute value, a positive correction value is determined, which is larger the greater the absolute value of the negative difference.

[0036] This is in Fig. 4 for both characteristic curves 9a and 9b, the case in which the adapted contact point 13, which results from calculating the adaptively determined contact point 10 with the constant offset 12, lies to the left of the inflection point 11b in the torque characteristic curves 9a and 9b. In this case, Fig. 4. For torque characteristic curve 9b, the negative difference 14b is larger in magnitude than for torque characteristic curve 9a, the negative difference 14a.

[0037] Then, if the difference 14a or 14b between the adjusted contact point 13 and the inflection point 11a or 11b of the friction clutch or torque characteristic curve is positive and relatively large, a negative correction value is determined, the absolute value of which is greater the larger the positive difference.

[0038] However, if the absolute difference between the adjusted contact point 13 and the inflection point 11a or 11b of the friction clutch or torque characteristic is relatively small, no correction value or a correction value of zero is determined.

[0039] The relevant contact point for control purposes is then the current contact point calculated with the adaptive correction value and the constant offset value, from which it follows that in the preferred embodiment of the invention according to Fig. 4 the control-side relevant contact point depends on the adaptively determined, current contact point 10, on the constant offset value 12 and on the adaptive correction value, which is determined from the difference 14a or 14b between the current contact point 10 of the friction clutch calculated with the constant offset value 12 and the adaptively determined kink point 11a or 11b of the friction clutch.

[0040] Unlike the one in Fig.In the variant shown in Figure 4, in which the adaptively determined current contact point 10 is calculated using the constant offset value 12, it is also possible to determine a correction value dependent on the elasticity of the friction clutch, independent of any difference between the adaptively determined current contact point of the friction clutch and the adaptively determined buckling point of the friction clutch. In this case, if this difference is negative, a positive correction value is determined, which is larger the greater the absolute value of the negative difference. Conversely, if this difference is positive, a negative correction value is determined, which is larger the greater the absolute value of the positive difference. The adaptively determined contact point, calculated using the adaptive correction value, is then used as the control-relevant contact point.

[0041] According to the invention, it is therefore proposed to determine the control-relevant contact point of a torque characteristic curve of a friction clutch depending on a correction value that depends on the elasticity or stiffness of the clutch. This correction value is preferably determined adaptively, namely depending on the adaptively determined contact point and an adaptively determined inflection point. In contrast, it is also possible to determine the correction value based on a previously measured elasticity or stiffness of the specific friction clutch. However, since the measurement of the stiffness or elasticity of a friction clutch is complex, the adaptive determination of the correction value via the adaptively determined inflection point of the friction clutch is preferred.

[0042] The specific numerical determination of the correction value, which depends on the difference between the adaptively determined current contact point of the friction clutch and the adaptively determined inflection point, or on the difference between the adaptively determined contact point (calculated with the constant offset value) and the adaptively determined inflection point, can be carried out, for example, using a characteristic curve that has, for instance, several data points. The correction value can be determined between the individual data points of such a characteristic curve by interpolation.

[0043] The invention ensures that the control-relevant contact point maintains a defined distance from the inflection point, and thus from the transition between elastic and rigid coupling behavior. This significantly reduces the response time of the coupling and considerably improves the pressure response behavior of the friction coupling. Ultimately, this ensures smooth and low-wear operation of an automated friction coupling.

[0044] An inventive control device 15 of a motor vehicle for determining a control-side relevant contact point of a friction clutch is preferably designed as a transmission control device and includes means for calculating the current contact point with the correction value dependent on the elasticity of the friction clutch to determine the control-side relevant contact point of the friction clutch.

[0045] In particular, when the correction value dependent on the elasticity of the friction clutch is determined adaptively, the control device 15 according to the invention further comprises means for adaptively determining the current contact point of the friction clutch, means for adaptively determining the inflection point of the friction clutch and furthermore means for adaptively determining the correction value depending on a difference between the adaptively determined current contact point of the friction clutch and the adaptively determined inflection point of the friction clutch or depending on the difference between the adaptively determined current contact point of the friction clutch calculated with the constant offset value stored in the control device 15 and the adaptively determined inflection point of the friction clutch.

[0046] The above means of the control device 15 are in particular a memory, a processor and interfaces of an electronic control device, wherein the electronic control device exchanges data via the interfaces with the transmission 3 or the automated friction clutch 4, 7, 8 or with actuators and sensors of the automated friction clutch 4, 7, 8. Reference sign 1 drive unit 2 Drive 3 gearboxes 4 friction clutch 5 partial gearboxes 6 partial gearboxes 7 Friction clutch 8 Friction clutch 9 Torque characteristic curve 9a Torque characteristic curve 9b Torque characteristic curve 10 adaptively determined touchpoints 11 adaptively determined inflection point 11a adaptively determined inflection point 11b adaptively determined inflection point 12 Offset value 13 adaptively determined touchpoints calculated with offset value 14a Difference 14b Difference 15 Control unit

Claims

[1] Method for determining a control-side relevant contact point of a friction clutch of a motor vehicle, wherein an actual contact point of the friction clutch is determined adaptively, characterized by , that the current contact point is calculated with a correction value dependent on the elasticity of the friction clutch in order to determine the control-side relevant contact point of the friction clutch, whereby the correction value is determined adaptively depending on the adaptively determined current contact point of the friction clutch and depending on an adaptively determined kink point of the friction clutch. [2] Method according to claim 1, characterized by , that the correction value is determined depending on a difference between the adaptively determined current contact point of the friction clutch and the adaptively determined kink point of the friction clutch. [3] Method according to claim 2, characterized by, that if the difference is negative, a positive correction value is determined, which is larger the greater the absolute value of the negative difference, and that if the difference is positive, a negative correction value is determined, which is larger the greater the absolute value of the positive difference. [4] Method according to claim 2 or 3, characterized by , that the adaptively determined, current point of contact, calculated using the adaptive correction value, is determined as the control-side relevant point of contact. [5] Method according to claim 1, characterized by , that the correction value is determined depending on a difference between the adaptively determined current contact point of the friction clutch, calculated with a constant offset value, and the adaptively determined kink point of the friction clutch. [6] Method according to claim 5, characterized by, that if the difference is negative and relatively large, a positive correction value is determined, which is larger the greater the absolute value of the negative difference; that if the difference is positive and relatively large, a negative correction value is determined, which is larger the greater the absolute value of the positive difference; and that if the absolute value of the difference is relatively small, no correction value or a correction value of zero is determined. [7] Method according to claim 5 or 6, characterized by , that the adaptively determined current contact point, calculated using the adaptive correction value and the constant offset value, is determined as the control-side relevant contact point. [8] Control device of a motor vehicle for determining a control-side relevant contact point of a friction clutch of a motor vehicle, with means for adaptively determining a current contact point of the friction clutch, characterized byMeans for calculating the current contact point with a correction value dependent on the elasticity of the friction clutch to determine the control-side relevant contact point of the friction clutch, wherein the correction value is determined adaptively depending on the adaptively determined current contact point of the friction clutch and depending on an adaptively determined kink point of the friction clutch. [9] Control device according to claim 8, characterized by Means for carrying out the method according to any one of claims 1 to 7.

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