Method for determining a torque characteristic of an automated friction clutch

This application is a national stage completion of PCT/EP20071054011 filed Apr. 25, 2007, which claims priority from German Application Serial No. 10 2006 019 824.7 filed Apr. 28, 2006.

The invention concerns a method for determining a torque characteristic of an automated friction clutch arranged in a drive train of a motor vehicle in the force flow between a drive engine and a drive transmission and which is engaged in the rest position, such that at least two marker points M_K 1 (x_K 1 ), M_K 2 (x_K 2 ) of a regulating-path-dependent torque characteristic M_K=f(x_K) are determined, of which at least one marker point is determined at a slippage limit of the friction clutch.

The invention relates to all possible friction clutch structures that are engaged in the rest position. A generally known structural form with which the method, according to the invention, can preferably be applied, is a dry clutch that can be engaged passively by the action of a contact pressure spring and disengaged and engaged by way of a pressure-medium-actuated or electric-motor- or electromagnetically operated clutch control element. Another possible structural form is a dry clutch that can be actively engaged by the contact pressure of a controllable contact pressure element which, in the rest condition, i.e., when the motor vehicle is parked with its drive engine switched off, is held engaged by a contact pressure element acted upon by energy, for example by compressed air from a pneumatic pressure reservoir. Likewise, the method can be used with a wet clutch that can be actively or passively engaged, in particular a disk clutch.

With such friction clutches, the fundamental problem arises of determining a torque characteristic M_K=f(x_K) which represents the transferable torque M_K of the friction clutch as a function of the regulating path x_K of an associated clutch control element, such as a hydraulic or pneumatic control cylinder or a transfer element connected thereto, such as a disengagement lever or release bearing, by way of which the desired transferable torque of the friction clutch is controlled.

Without any limitation of the invention to this type of structure, an example of a path-controlled dry clutch with spring contact pressure will be considered below, which can be disengaged and engaged by way of an associated clutch control element. In this case, the torque characteristic M_K=f(x_K) concerned describes the clutch torque M_K as a function of a regulating path x_K of the clutch control element that corresponds to the disengagement path. Since, as is known, the respective regulating positions x_K, associated with particular values of the clutch torque M_K, can vary depending on the operating temperature and the wear condition, in particular of the friction linings of the friction clutch. For exact actuation control of the friction clutch it is necessary to precisely determine a torque characteristic M_K=f(x_K) that corresponds to the situation at the time, i.e., to the momentary operating conditions.

For this purpose, it is known to determine at least two marker points M_K 1 (x_K 1 ) and M_K 2 (x_K 2 ) of the torque characteristic M_K=f(x_K), of which at least one marker point is determined at a slippage limit of the friction clutch. The entire torque characteristic M_K=f(x_K) can then be obtained by adapting an existing torque characteristic M_K′=f(x_K) to the currently determined marker points M_K 1 (x_K 1 ) and M_K 2 (x_K 2 ) by projection of the torque values M_K 1 (x_K 1 ′) and M_K 2 (x_K 2 ′) concerned.

In this case, until now at least one of the marker points has been determined at a slippage limit in that with the friction clutch engaged, the transmission shifted to neutral and the drive engine running, the friction clutch is first completely disengaged; one then waits until the speed of the transmission input shaft has fallen far enough compared with the speed of the drive engine and, finally, the friction clutch is slowly engaged until an increase in the speed of the input shaft is sensed.

The pair of values M_K 1 , x_K 1 determined at this point in time with the known braking torque M_B of the input shaft (M_K 1 =M_B) and the set position x_K(M_B) is then stored as the value pair of the fixed point M_K 1 (x_K 1 ) and used for the adaptation of an existing characteristic M_K′=f(x_K).

In this case, the braking torque M_B and, hence too the torque value M_K 1 concerned, is relatively small and corresponds to the drag torque of the input shaft, which is caused by bearing wear, rolling losses of meshing gear wheels and oil splash losses of the input shaft and of components connected to it. In addition, the drag torque is strongly temperature-dependent and increases as the operating temperature falls, in particular the oil temperature of the transmission. The disadvantage of this known method for determining a torque characteristic are the large number of process steps needed, the relatively long duration of the process sequence, which can lead to delays during normal driving operation of the motor vehicle, and the relatively poor precision of the fixed point determinations.

The purpose of the present invention is to indicate a method for determining a torque characteristic of an automated friction clutch of the type mentioned to begin with, by way of which at least one of the marker points M_K 1 (x_K 1 ), M_K 2 (x_K 2 ) of the torque characteristic M_K=f(x_K) can be determined more simply, more rapidly and with greater precision.

Accordingly, the invention concerns a method for determining a torque characteristic of an automated friction clutch arranged in a drive train of a motor vehicle in the force flow between a drive engine and a drive transmission, and which is engaged in its rest position, such that at least two marker points M_K 1 (x_K 1 ) and M_K 2 (x_K 2 ) of a regulating-path-dependent torque characteristic M_K=f(x_K) are determined, of which at least one marker point is determined at a slippage limit of the friction clutch.

In contrast to the known method, in this case it is provided that a first marker point M_K 1 (x_K 1 ) is determined, in that with the friction clutch engaged, the transmission in neutral and the drive engine running, the friction clutch is slowly disengaged until a speed decrease of the transmission input shaft, compared with the speed of the engine, is sensed and the corresponding pair of values M_K 1 , x_K 1 with the known braking torque M_B of the input shaft and the set position x_K(M_B) determined are noted, stored as the value pair for the marker point M_K 1 (x_K 1 ), and then used for adapting an existing characteristic M_K′=f(x_K).

Thus, the marker point M_K 1 (x_K 1 ) is already determined during the process of disengaging the friction clutch, for example when the motor vehicle is first operated after starting the engine and before the starting gear has even been engaged and, therefore, substantially more quickly than usual until now.

Since the drag torque, acting on the input shaft as a braking torque M_B during the determination of the first marker point M_K 1 (x_K 1 ), is essentially temperature-dependent, i.e., it increases as the operating temperature of the transmission decreases, for a precise determination of the drag torque, it is expedient to sense the operating temperature of the transmission.

Moreover, the determination of the first marker point M_K 1 (x_K 1 ) can be accelerated, at the latest before the slippage limit of the friction clutch is reached, if a transmission brake that acts upon the input shaft of the transmission or a synchronization device of a transmission gear is actuated. In this case, the braking torque M_B that acts upon the transmission input shaft is formed by the sum of the drag torque and the braking torque of the transmission brake or synchronization device. Consequently, the torque value M_K 1 determined is larger in such a case, but can be determined more accurately because the operating temperature and the measurement errors have less effect.

A second marker point M_K 2 (x_K 2 ) is preferably determined in such a manner that in the partially engaged condition the friction clutch is actuated in the engaging direction until no further change of the regulating path x_K is sensed and the corresponding pair of values M_K 2 , x_K 2 with the known maximum torque M_K_max and the determined set position x_K=0 are noted, stored as the value pair of the second marker point M_K 2 (x_K 2 ) and then used for adapting the existing characteristic M_K′=f(x_K).

The position range, between the two marker points M_K 1 (x_K 1 ) and M_K 2 (x_K 2 ) determined in this manner, is appropriately defined as the working range of the friction clutch for producing torque values M_K 1 (x_K 1 ) with M_K 1 (x_K 1 )=0% and M_K 2 (x_K 2 )=100%. This then makes it possible to produce a desired, discrete torque value M_K 1 and a desired time variation of the clutch torque M_K, for example for starting, maneuvering, shifting and stopping.

The invention will now be described, by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a diagram of the clutch torque of a friction clutch as a function of regulating path, and

FIG. 2 is a clutch arrangement for implementing the method according to the invention.

FIG. 2 shows an example of a clutch arrangement 1 for implementing a method according to the invention. In the Figure, a friction clutch 2 , made as a single-disk, dry clutch, is shown arranged in the force flow between a drive engine 3 made as a piston-driven internal combustion engine and a drive transmission 4 .

The part of the friction clutch 2 on its input side is formed by a flywheel 6 attached to a crankshaft 5 of the drive engine 3 and a pressure plate 8 connected thereto via a clutch cage 7 . The part of the friction clutch 2 on its output side is formed by a carrier disk 9 arranged axially between the flywheel 6 and the pressure plate 8 , which is mounted rotationally fixed to, but able to move axially on an input shaft 10 of the transmission 4 . By virtue of a contact pressure spring 11 made as a membrane spring and arranged between the clutch cage 7 and the pressure plate 8 , the friction clutch 2 is engaged in its rest position free from any control force, but can be disengaged and engaged by way of a release bearing 13 mounted to move axially on a guide sleeve 12 fixed on the housing, which contacts radially inner spring tabs of the contact pressure spring 11 .

The release bearing 13 is actuated and a given clutch torque M_K of the friction clutch 2 is produced by a pressure-medium-actuated clutch control element 14 , in this case in the form of a simply acting control cylinder with a piston 16 , mounted to move axially and displaced by a control pressure p_K, that acts in a pressure chamber 15 and pushes the piston against the restoring force of a restoring spring. Via a piston rod and a disengagement lever 17 mounted on the housing at its end, the piston 16 is connected to the release bearing 13 in such a manner that increasing the control pressure p_K results in disengagement of the friction clutch 2 and hence in a reduction of the clutch torque M_K.

The clutch control element 14 is actuated by a control valve 18 in the present case formed as a 3/2-way proportional magnetic valve with two inlets and one outlet. The first inlet is connected to a pressure line 19 ; the second inlet to an unpressurized line 20 and the outlet, via a connection line 21 , to the pressure chamber 15 of the clutch control element 14 . To actuate the control valve 18 , the latter is connected via an electric control line 22 to a control unit 23 . Thus by way of the structure, a change of the clutch torque M_K is brought about by a continuous variation of the control pressure p_K of the clutch control element 14 .

To detect the set position x_K of the piston 16 or the disengagement lever 17 , a path sensor 24 is arranged on the piston rod of the piston 16 . To determine the input speed of the friction clutch 2 , a first speed sensor 26 is arranged on the crankshaft 5 of the drive engine 3 while, to determine the output speed of the friction clutch 2 , a second speed sensor 28 is provided on the input shaft 10 of the drive transmission 4 . To determine the operating temperature of the transmission 4 , a temperature sensor 30 is positioned in the oil sump of the transmission 4 . The sensors 24 , 26 , 28 , 30 are connected to the control unit 23 by respective sensor leads 25 , 27 , 29 , 31 .

In the diagram of FIG. 1 , for the clutch arrangement 1 according to FIG. 2 , a regulating-path-dependent torque characteristic M_K=f(x_K), representing the variation of the clutch torque M_K as a function of the regulating path x_K, is shown (continuous line), which is obtained from an adaptation of an existing torque characteristic M_K′=f(x_K) by projecting two torque values M_K 1 (x_K 1 ′), M_K 2 (x_K 2 ′) of the existing characteristic M_K′=f(x_K) onto two determined marker points M_K 1 (x_K 1 ) and M_K 2 (x_K 2 ).

Until now, to determine a first marker point M_K 1 (x_K 1 ) of the torque characteristic M_K=f(x_K), the usual procedure has been with the friction clutch 2 engaged, the transmission 4 in neutral and the drive engine 3 running, first, to completely disengage the friction clutch 2 , then to wait until the speed of the input shaft 10 of the transmission 4 has fallen far enough, compared with the speed of the drive engine 3 , and then to slowly engage the friction clutch 2 until an increase in the speed of the input shaft 10 is sensed. The pair of values M_K 1 , x_K 1 determined at that time with a known braking torque M_B of the input shaft (M_K 1 =M_B) and the detected set position x_K(M_B) is then stored as the value pair of the marker point M_K 1 (x_K 1 ) and used for adapting or modifying the existing characteristic M_K′=f(x_K). This known method, which is illustrated in FIG. 1 by the steps S 1 ′ to S 3 ′, takes a relatively long time and demands considerable control effort.

In contrast, according to the invention, the method provides that with the friction clutch 2 engaged, the transmission 4 in neutral and the drive engine 3 running, to determine a first marker point M_K 1 (x_K 1 ) of the torque characteristic M_K=f(x_K) the friction clutch 2 is slowly disengaged until a drop in the speed of the input shaft 10 of the transmission 4 compared with the speed of the drive engine 3 is sensed, and then the corresponding pair of values M_K 1 , x_K 1 with the known braking torque M_B of the input shaft (M_K 1 =M_B) and the set position x_K(M_B) are noted, stored as the value pair for the marker point M_K 1 (x_K 1 ), and used for adapting the existing characteristics M_K′=f(x_K). The method, which is illustrated in FIG. 1 by the single step S 1 (symbolized by the arrow drawn with a continuous line), takes up much less time and demands less control effort.

Without having to adopt any further measures, the braking torque M_B of the input shaft 10 and also the torque value M_K 1 concerned, correspond to the drag torque of the input shaft 10 . This drag torque is comparatively small and also markedly temperature-dependent so it can only be determined relatively approximately. However, the drag torque of the input shaft 10 can be determined with greater precision if the operating temperature of the transmission 4 is determined by the temperature sensor 30 , if possible arranged in the oil sump of the transmission, as shown in FIG. 2 .

The measured marker point M_K 1 (x_K 1 ) can be corrected as a function of the drag torque.

A further increase of accuracy when determining the effective braking torque M_B can be achieved by increasing the latter, since measurement errors then have a smaller effect. To do this, it can be provided that at the latest before the slippage limit is reached, i.e., before the speed of the input shaft 10 decreases, an additional transmission brake or a synchronization device of a gear of the transmission 4 that acts upon the input shaft 10 is actuated.

In the present case, a second marker point M_K 2 (x_K 2 ) is determined by actuating the friction clutch 2 in its partially engaged condition in the engaging direction until no further change of the regulating path x_K is sensed, noting the corresponding pair of the values M_K 2 , x_K 2 with a known maximum torque M_K_max and the set position x_K(M_K_max) or x_K=0, then storing the marking point M_K 2 (x_K 2 ) as a value pair, and then using the point for adapting the existing characteristic M_K′=f(x_K).

The path range, between the marking points M_K 1 (x_K 1 ) and M_K 2 (x_K 2 ), can be defined as the working range of the friction clutch 2 , as illustrated in FIG. 1 in which the set position x_K 1 , x_K 2 , are marked 0% and 100% respectively, since within this range, which is relevant for practical operation the torque of the friction clutch 2 , can be adjusted with great precision.