METHOD FOR CORRECTING A DRAG TORQUE CURVE OF AT LEAST ONE ROTATABLY MOUNTED MACHINE ELEMENT

Abstract

The present invention relates to a method for correcting a drag torque curve of at least one rotatable machine element of which the drag torque is dependent on the rotational speed of the machine element, wherein the drag torque curve has a plurality of rotational speed ranges which are different from one another, in which the drag torque curve in each rotational speed range is corrected between a measured rotational speed of the machine element and a calculated rotational speed of the machine element on the basis of a rotational speed deviation in the respective rotational speed range.

Claims

1. A method for correcting a drag torque curve of at least one rotatable machine element, in particular of a torque transmission section of a vehicle drive train, which can preferably be coupled effectively in terms of drive to a drive by means of a first clutch and to an output of the vehicle by means of a second clutch, and the drag torque thereof, and therefore the drag torque curve, are dependent on the rotational speed of the machine element, wherein the drag torque curve has a plurality of rotational speed ranges which are different from one another, and wherein the drag torque curve in each rotational speed range is corrected between a measured rotational speed of the machine element and a calculated rotational speed of the machine element on the basis of a rotational speed deviation in the respective rotational speed range.

2. The method according to claim 1, wherein the drag torque curve in each rotational speed range is corrected in that a correction factor (K.sub.x) which is assigned to the respective rotational speed range is determined on the basis of the rotational speed deviation of the respective rotational speed range, on the basis of which correction factor the drag torque curve in the respective rotational speed range is modified, in particular multiplied.

3. The method according to claim 1, wherein the rotational speed deviation of the respective rotational speed range is determined in that the rotational speed differences which are determined at different times between the measured rotational speed of the machine element and the calculated rotational speed of the machine element in the respective rotational speed range are summed.

4. The method according to claim 1, wherein each rotational speed range of a rotational speed which has been measured at first is used as a starting value for calculating the rotational speed.

5. The method according to claim 1, wherein in a predefined rotational speed band about a limiting rotational speed which separates a first rotational speed range from an adjacent second rotational speed range, the drag torque curve is corrected on the basis of two correction factors which are assigned to the two adjacent rotational speed ranges.

6. The method according to claim 5, wherein the correction of the drag torque curve in the predefined rotational speed band about the limiting rotational speed takes place between two adjacent rotational speed ranges in that in the first rotational speed range the correction factor which is assigned to the first rotational speed range is increasingly reduced and the correction factor which is assigned to the second rotational speed range is increasingly enlarged as the rotational speed increasingly approaches the limiting rotational speed, wherein, in particular in the second rotational speed range, the correction factor which is assigned to the first rotational speed range is increasingly reduced further, preferably as far as zero, and the correction factor which is assigned to the second rotational speed range is increasingly enlarged further, as the rotational speed becomes increasingly distant from the limiting rotational speed.

7. The method according to claim 5, wherein the reduction or increase in the correction factors of adjacent rotational speed ranges in the predefined rotational speed band about the limiting rotational speed between the adjacent rotational speed ranges takes place on the basis of initial functions in that, in particular, each rotational speed range is assigned an initial function which is dependent on the rotational speed and by which the correction factor of the respective rotational speed range is multiplied, wherein each initial function in the rotational speed range to which the initial function is assigned preferably has a maximum function value from which it decreases continuously, in the direction of an adjacent rotational speed range, to a function value of zero in the adjacent rotational speed range.

8. The method according to claim 7, wherein the initial functions are selected such that the sum of the function values of initial functions of adjacent rotational speed ranges has a value of one at each rotational speed.

9. The method according to at claim 1, wherein after correction of the drag torque curve has taken place, correction factors which are assigned to the individual rotational speed ranges are updated on the basis of the rotational speed deviation of the respective rotational speed range, for which purpose the rotational speed deviation of the respective rotational speed range is determined in that the rotational speed differences which are determined at different times between the measured rotational speed of the machine element and the rotational speed, calculated taking into account the corrected drag torque curve, of the machine element in the respective rotational speed range are summed.

10. The method according to claim 1, wherein the rotational speed deviation in the respective rotational speed range is determined while rotational energy of the machine element is consumed as a result of the drag torque of the machine element.

Description

DRAWINGS

[0025] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. There now follows a description of the invention, purely by way of example, with reference to the drawing, in which:

[0026] FIG. 1 shows a schematic representation of a drive train of a vehicle with a switched-off all-wheel drive, in which the rear axle or secondary axle can be switched on and switched off;

[0027] FIG. 2 explains the decrease in rotational speed of the torque transmission section after uncoupling over time and also the ascertainment of the rotational speed deviation in individual rotational speed ranges;

[0028] FIG. 3 shows on the one hand a given drag torque curve, dependent on the rotational speed, and on the other hand initial functions assigned to three rotational speed ranges;

[0029] FIG. 4 shows a schematic representation of a function for ascertaining the correction increments; and

[0030] FIG. 5 shows correction factors modified by means of the initial functions and also the effect of these correction factors on the drag torque curve.

[0031] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION

[0032] Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0033] FIG. 1 illustrates the drive train of a motor vehicle, in the front region of which a drive unit 12 is arranged, which in the case of the embodiment represented is an internal combustion engine oriented transversely in relation to the longitudinal axis of the vehicle. The drive unit is permanently connected by means of a variable-speed gearbox 14 to a front axle 16 of the vehicle comprising a front axle differential 22, so that front wheels 18 that are connected effectively in terms of drive to the front axle 16 can be permanently driven by the drive unit 12 during the driving of the vehicle. The front axle 16 consequently forms a primary axle 20.

[0034] In a rear region of the vehicle, the motor vehicle has a rear axle 24 with a rear axle differential 26 and rear wheels 28. The rear axle 24 forms a secondary axle 30, since in all-wheel operation it is driven by the drive unit 12. Arranged for this purpose on the primary axle 20 is a controllable torque branching device 32, by which an adjustable proportion of the drive torque provided by the drive unit 12 can be branched off to the secondary axle 30. The torque branching device 32 comprises for this purpose an all-wheel clutch 33, which is designed as a multidisc clutch and is controlled by a control unit 34.

[0035] The output of the multidisc clutch 33 is connected to one end of a torque transmission section 36, which comprises, inter alia, a cardan shaft. At its other end, the torque transmission section 36 is connected to a bevel gear 38, which is in engagement with a ring gear 40, which is connected to a differential cage 42 of the rear axle differential 26.

[0036] In order to prevent the torque transmission section 36, including the differential cage 42, from unnecessarily also being able to rotate and consume energy when driving with the multidisc clutch 33 open, i.e. in the case of purely front-wheel drive, a device for shutting down the torque transmission section 36 is provided. In the case of this exemplary embodiment, the shutting-down device is formed by a dog clutch 46, which is arranged on a half axle 44 of the rear axle 24 in the vicinity of the rear axle differential 26, and likewise can be controlled by the control unit 34.

[0037] If the torque transmission section 36 has been shut down by means of the dog clutch 46 for driving purely with front-wheel drive, the torque transmission section 36 must first be synchronized with the secondary axle 30 before the dog clutch 46 can be engaged again for torque transmission for all-wheel drive. For this purpose, the multidisc clutch 33 is engaged in a controlled manner, in order in this way to bring the torque transmission section 36 up to speed again. The acceleration of the torque transmission section 36 should take place here as uniformly as possible, in order on the one hand to be able to determine precisely in advance the time at which the dog clutch 46 can/is to be engaged, and in order on the other hand not to adversely influence driving comfort, as could otherwise be the case with nonuniform acceleration of the torque transmission section. In order therefore to be able to bring the torque transmission section 36 up to speed as uniformly as possible, the most exact possible knowledge of the drag torque of the torque transmission section 36 is needed, which is dependent on the rotational speed of the same, as can be seen from the solid line in FIG. 3.

[0038] The drag torque curve M(n) represented in FIG. 3 may be for example a drag torque curve that is predefined or ascertained on a vehicle test bench, which however can change over time owing to friction and wear. To be able to record the changing of the drag torque curve, and correct the drag torque curve correspondingly, according to the invention the entire rotational speed range which the torque transmission section 36 can run through is divided into a number of rotational speed ranges X.sub.i that are different from one another. In the case of the exemplary embodiment represented here, it is divided into three rotational speed ranges, to be specific a rotational speed range of low rotational speeds from 0 to 2000 rpm, a mid rotational speed range from 2000 to 5000 rpm and a speed range of high rotational speeds above 5000 rpm. In FIG. 3, these rotational speed ranges are identified by X.sub.1, X.sub.2 and X.sub.3. The division of the drag torque curve M(n) into a number of rotational speed ranges takes place here in order to be able to correct the drag torque curve section by section, or in each rotational speed range X.sub.i on its own. For this purpose, in each rotational speed range X.sub.i a rotational speed deviation N.sub.i is ascertained, obtained in the respective rotational speed range X.sub.i between a measured rotational speed of the torque transmission section 36 and a calculated rotational speed, so that the drag torque curve M(n) can be corrected on the basis of this rotational speed deviation N.sub.i in the respective rotational speed range X.sub.i.

[0039] For calculating these rotational speed deviations N.sub.i, therefore, after the uncoupling of the torque transmission section 36, i.e. after the release of the two clutches 33, 46, the running down of the torque transmission section 36 is monitored, as can be seen in the upper representation of the diagram in FIG. 2, which illustrates the profile over time of the measured rotational speed n.sub.measured. As can be seen from this representation, the rotational speed of the torque transmission section 36 decreases continuously after the uncoupling from the remaining drive train, to approach the value of zero. When doing so, the torque transmission section 36 over time runs through the three rotational speed ranges X.sub.3, X.sub.2 and X.sub.i, which are separated from one another by the limiting rotational speeds 5000 rpm and 2000 rpm. In each of these rotational speed ranges X.sub.i, a rotational speed deviation between the measured rotational speed n.sub.measured and a calculated rotational speed n.sub.model is thus calculated for the correction of the drag torque curve. For this purpose, at the beginning of each rotational speed range X.sub.i the calculated rotational speed n.sub.model is made equal to the measured rotational speed n.sub.measured, as can be seen from the upper representation of the diagram in FIG. 2 from the mid rotational speed range X.sub.2, where, on entering the mid rotational speed range, the calculated rotational speed n.sub.model is equal to the measured rotational speed n.sub.measured equal to 5000 rpm, so that, starting from this initialization value, the rotational speed can be calculated, inter alia, while taking into account the drag torque curve curve M(n).

[0040] The rotational speed deviation N.sub.i of each rotational speed range X.sub.i is thus calculated in that rotational speed differences that are obtained at different times between the measured rotational speed n.sub.measured and the calculated rotational speed n.sub.model in the respective rotational speed range X.sub.i are summed, as represented in the middle representation of the diagram in FIG. 2. The greater the ascertained rotational speed deviation N.sub.i is here in the respective rotational speed range X.sub.i, the greater the actual profile of the drag torque curve deviates from the predefined profile in the respective rotational speed range X.sub.i; the greater therefore the torque deviation N.sub.i is in the respective rotational speed range X.sub.i, the more the predefined drag torque curve M(n) in the respective rotational speed range X.sub.i must be corrected, the drag torque curve having to be increased or decreased according to whether the rotational speed deviation N.sub.i is positive or negative.

[0041] If the associated rotational speed deviation N.sub.i has been ascertained in the way described above for each rotational speed range X.sub.i, a correction factor K.sub.x can subsequently be ascertained in dependence on the respective rotational speed deviation N.sub.i for the respective rotational speed range X.sub.i according to the following equation:

K.sub.x(t+1)=K.sub.x(t)+k.sub.x,(1)

where K.sub.x(t) is the correction factor from a previous pass through the loop for the correction of the drag torque curve, this value having been initialized to one. The component k.sub.x represents a correction increment, which is added to the correction factor from the previous pass through the loop in order to obtain the correction factor K.sub.x(t+1) for the current correction of the drag torque curve M(n). The correction increment k.sub.x in tis case establishes how strongly an ascertained rotational speed deviation N.sub.i is to have an effect on the correction of the drag torque curve M(n). The correction increment k.sub.x is consequently a function of the rotational speed deviation N.sub.i.

[0042] A function, given by way of example, for determining the correction increment k.sub.x on the basis of the rotational speed deviation N.sub.i is represented for example in FIG. 4, from which it can be seen that the correction increment k.sub.x behaves substantially proportionally to the rotational speed deviation N.sub.i. It can likewise be seen from FIG. 4 that negative rotational speed deviations N.sub.i result in a positive correction increment k.sub.x and positive rotational speed deviations N.sub.i result in a negative correction increment k.sub.x, in order to be able to increase or decrease the drag torque curve according to the operational sign of the rotational speed deviation N.sub.i.

[0043] With knowledge of the correction increment k.sub.x ascertained in this way for each rotational speed range X.sub.i, the correction factor K.sub.x for the respective torque range X.sub.i can be ascertained on the basis of equation (1), so that subsequently the drag torque curve M(n) in each rotational speed range X.sub.i can be multiplied by the associated correction factor K.sub.x for correction purposes.

[0044] In order however, when doing so, to avoid discontinuities in the profile of the corrected drag torque curve, in a predefined rotational speed band about a limiting rotational speed which separates a first rotational speed range from an adjacent second rotational speed range, for example in a rotational speed band about the limiting rotational speed 2000 rpm that separates the lower rotational speed range X.sub.i from the mid rotational speed range X.sub.2, the drag torque curve M(n) can be corrected on the basis of the two correction factors K.sub.x which are assigned to the two adjacent rotational speed ranges X.sub.1 and X.sub.2. For this purpose, for example, in the first rotational speed range X.sub.1 the correction factor K.sub.x1 which is assigned to the first rotational speed range X.sub.1 is increasingly reduced and the correction factor K.sub.x2 which is assigned to the second rotational speed range X.sub.2 is increasingly enlarged as the rotational speed increasingly approaches the limiting rotational speed of 2000 rpm. Equally, in the second rotational speed range X.sub.2, the correction factor K.sub.x1 which is assigned to the first rotational speed range X.sub.1 is increasingly reduced further, as far as zero, and the correction factor K.sub.x2 which is assigned to the second rotational speed range X.sub.2 is increasingly enlarged further, as the rotational speed becomes increasingly distant from the limiting rotational speed of 2000 rpm.

[0045] This modification of the correction factors K.sub.x takes place here according to the invention by means of so-called initial functions, which are represented in FIG. 3 as dashed and dotted line profiles. Each initial function A.sub.xi is in this case dependent on the rotational speed and has a maximum function value equal to one, from which it steadily falls down to zero in the respective adjacent rotational speed range X.sub.i. The initial functions A.sub.xi are in this case selected such that the sum of the function values of the initial functions A.sub.xi of adjacent rotational speed ranges X.sub.i has a value of one at each rotational speed n.

[0046] To be able to modify the correction factors K.sub.x of the individual torque ranges X.sub.i in a rotational speed band about the respective limiting rotational speeds, the initial functions A.sub.xi are multiplied by the respectively associated correction factors K.sub.xi, which has the result that the correction factor K.sub.xi of a respective rotational speed range also has an influence on the correction of the drag torque curve in an adjacent rotational speed range, as represented in FIG. 5, which shows, inter alia, the correction factors K.sub.xi modified by means of the initial functions A.sub.xi in dashed and dotted lines. Consequently, the initial functions A.sub.xi have the effect to a certain extent of activating the correction factors K.sub.x in the respective rotational speed range, wherein this activation of the correction factor also acts on the adjacent rotational speed ranges X.sub.i, since the initial functions A.sub.xi extend into the respective adjacent rotational speed ranges.

[0047] The corrected drag torque curve M.sub.corr(n) is consequently calculated as

M.sub.corr(n)=M(n).Math.sum(K.sub.xi.Math.A.sub.xi(n)).(2)

This corrected drag torque curve M.sub.corr(n) is represented in the diagram of FIG. 5 by dash-dotted lines and is obtained from the predefined drag torque curve M(n), in that at each rotational speed n the predefined drag torque curve M(n) is multiplied by the sum of the modified correction factors.

[0048] Once the corrected drag torque curve has been ascertained in this way, in a subsequent pass through the loop of the method the rotational speed of the torque transmission section in the respective rotational speed range X can be calculated on the basis of this corrected drag torque curve, in order to be able to determine from this the respective rotational speed deviation N while taking into account the measured rotational speed.

[0049] Once the drag torque curve has been corrected in the way described above, when later switching on the all-wheel drive or the secondary axle the multidisc clutch 33 can be engaged, while taking into account the corrected drag torque curve M.sub.corr(n), in such a way that the torque transmission section 46 is uniformly accelerated and brought up to speed. Equally, the clutch characteristic of the multidisc clutch 33 may be adapted, while taking into account the corrected drag torque curve, in order to be able to make the switching on of the all-wheel drive as smooth as possible.

[0050] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.