Method for detecting an emerging torque for a hybrid drive

Abstract

Method for detecting a resulting torque for a hybrid drive, wherein the hybrid drive has a first drive unit, in particular an electric motor, and a second drive unit, in particular an internal combustion engine, wherein the drive units can be coupled by means of a separating clutch (K0), characterized in that• the separating clutch (K0), when it is open, is brought into a predetermined closed position at a time (301);• the torque of the first drive unit is initially changed immediately by a predetermined torque; and• the torque subsequently occurring at the predetermined closed position is detected as a function of the change in the torque of the first drive unit,• the first drive unit is operated at a predetermined speed before the separating clutch (K0) is brought into the predetermined closed position;and• the torque of the first drive unit is changed after the separating clutch (K0) has been brought into the predetermined closed position so that a constant speed of the first drive unit is established.;

Description

Technical FieldThe present invention relates to the field of disconnect clutches in hybrid vehicles.Prior ArtFIG. 1 shows, by way of example, a hybrid drive which has an internal combustion engine ICE, a separating clutch K0, an electric motor EM, a further separating clutch K2 and a transmission module TR. The separating clutch K 0 is provided to disconnect the internal combustion engine ICE from the drive train or to connect it again to the latter. For example, when driving purely by electric motor using electric motor EM as the drive source, separating clutch K 0 is opened and internal combustion engine ICE is shut down. In the event of a transition from an electromotive drive to a hybrid drive, in which both the electric motor EM and the internal combustion engine ICE are used as drive sources, the internal combustion engine ICE can first be mechanically driven by means of the separating clutch K 0, in order to achieve a predefined rotational speed, for example. Here, the disconnect clutch K 0 is operated in a slip state in which it is not fully closed. At the same time, the separating clutch K 0 is connected to the drive train on the side of the electric motor. Therefore, it is of decisive importance, in particular for the driving comfort, to precisely control the slip of the separating clutch K 0 in the hybrid mode. DE 195 40 921 A1 discloses in this context a system for controlling a servo clutch in which the clutch control is optimized.The torque that is produced when the separating clutch K 0 illustrated in FIG. 1 is closed can be detected, for example, by means of the method illustrated in FIG. 2. FIG. 2A shows a time profile of a torque M of an electric motor, FIG. 2B shows a time profile of a rotational speed of the electric motor, and FIG. 2C shows a state profile P of the separating clutch K 0, which can assume all states between an open and a fully closed state. The state profile P of the separating clutch K 0 is determined by a profile of the locking positions of the separating clutch K 0. For example, disconnect clutch K 0 is in a slip state when it is only partially closed and an open state when it is fully open.As shown in FIG. 2A, the torque of the electric motor is increased linearly up to a resulting torque 201 and subsequently reduced again in a ramp-like manner. When the torque increases, the rotational speed of the electric motor depicted in FIG. 2B decreases due to an increasing clutch transmission torque, but with decreasing torque it increases again. As shown in FIG. 2C, the disconnect clutch K 0 is slowly closed starting from an open state 203 and is therefore in continuous slip. The separating clutch K 0 is closed until a position 205 has been reached in which the resulting torque 201 that is being set is established.To detect the torque that is being set, the internal combustion engine ICE is firstly switched off and the separating clutch K 0 is opened, the electromotive torque on the main drive axle being kept as constant as possible. The speed of the electric motor is kept constant at 500 rpm, for example, by a speed regulator. At time 207, disconnect clutch K 0 is slowly engaged. The speed regulator attempts to keep the speed of the electric motor constant, for example, by generating an additional torque. In order to detect the torque that is being set, a position of the separating clutch K 0 is detected at the time 205, at which the electromotive torque has increased by 10 Nm, for example. In this way, it is also possible to detect the so-called touch point of the separating clutch K0 at which the transmitted torque is 0 Nm.However, the disadvantage of the method described above is that it can take about 3 to 10 s until the torque that is established has been detected when the separating clutch K 0 is closed. This is because the speed of the closing separating clutch K 0 must be lower than the reaction speed of the speed regulator controlling the electric motor. As a result, the lock-up position of disconnect clutch K 0 at time 205 may be detected only as a function of the torque increased by the speed regulator. A further disadvantage is that the separating clutch K0 which is in the slip state over a longer period of time must withstand higher torques, as a result of which it can be damaged. For this reason, the learning range to be considered for detecting the torque that is being set should have lower torques than these higher torques, so that the torque transmitted by means of the separating clutch K 0 is usually less than 10 Nm. It is therefore not possible to detect the arising torque of the separating clutch K 0 by detecting higher rotational speeds and larger torque ranges at, for example, 50 Nm. In addition, in the region in which the torque transmitted by the separating clutch K 0 is low, a higher mechanical tolerance and thus a lower closing accuracy of the separating clutch K 0 are to be expected. For this reason, the method is carried out in a mechanically unstable region, so that the torque that occurs when the separating clutch K 0 is closed cannot be detected exactly.From DE 102 28 709 A1, a method is known, similar to that described with reference to FIG. 2, to operate an electric machine with limited maximum torque under speed control and to slowly close the clutch until the speed of the electric machine drops and the position of the clutch is assigned the maximum torque minus idle torque.Further methods for determining torques are known from DE 10 2006 048 358 A1, DE 10 2008 030 473 A1 and DE 10 2006 005 470 A1.Disclosure of the InventionThe invention is based on the finding that the torque that is set in a closing position of the separating clutch can be detected efficiently if the latter is not slowly closed, but rather is moved in a dedicated manner into a predefined closing position, in which the separating clutch is in particular in a slipping state and is only partially closed. The torque that is established can be, for example, the torque that is established at the separating clutch or the clutch transmission torque that is established. The torque that is established can also include mechanical lost work, for example wear of the clutch disks, temperature rise and / or mass inertias, among others. The torque that is established can furthermore be the torque with which the separating clutch loads a drive unit in the predefined closing position.Depending on the previously adjusted closing position, the electromotive torque can be increased by a predefined torque, whereby the torque that is established can be detected in a targeted and punctiform manner. In addition, it is possible to open the separating clutch again during the detection process after each closing of the separating clutch, so that the time in which the separating clutch is in a slip state is shortened. In contrast to this, the separating clutch is, according to the known methods, for example, linearly closed for the entire detection duration and is thereby exposed to more severe loads.It is also advantageous that a shorter time period is required for the renewed determination of the torque that is being set. In addition, the separating clutch is subject to less thermal and mechanical load, so that the clutch wear is reduced overall. Furthermore, a determination of the torque that is set is possible even at higher torques of the separating clutch, whereby a higher detection accuracy is achieved. Furthermore, a characteristic curve can also be recorded at torques of different levels, whereby the disadvantage is avoided that the characteristic curve calculation is possible only on the basis of measurements in the low torque range. According to the invention, the torque that is established can also be detected at comparatively low rotational speeds, because the electric motor, in contrast to an internal combustion engine, also applies a high torque at lower rotational speeds. Due to the lower mechanical clutch load, therefore, lower clutch wear and a lower clutch temperature are also to be expected. In addition, the concept according to the invention is accurate because system influences such as noise do not enter into the calculation.The torque that is set up at the separating clutch is advantageously detected, in particular when the internal combustion engine is at a standstill and in particular when the speed-controlled electric motor rotates constantly, for example.In order to detect the torque that is being set in a closed position of the separating clutch, the latter is preferably transferred into a slip state, wherein a regulated torque of the electric motor is observed. According to the invention, a predefined torque for the speed regulator is selected and changed on the basis of the expected or setting torque, for example the setting torque at the separating clutch or the setting clutch transmission torque, for example from a look-up table, if the current torque at the separating clutch differs from the torque expected at the respective closing position at the separating clutch.According to one aspect, the invention relates to a method for detecting a torque that is being set for or in a hybrid drive, wherein the hybrid drive has a first drive unit, in particular an electric motor, and a second drive unit, in particular an internal combustion engine, wherein the drive units can be coupled by means of a separating clutch. According to the method, the separating clutch is transferred into a predefined locking position, the torque of the first drive unit is changed, and the torque that is established at the predefined locking position is detected as a function of the change in the torque of the first drive unit.In this case, the first drive unit is operated at a predefined rotational speed before the separating clutch is moved into the predefined locking position, and the torque of the first drive unit is changed after the separating clutch is moved into the predefined locking position in such a way that a constant rotational speed of the first drive unit is established. In this way, the torque to be additionally applied for ensuring constant rotational speed of the first drive unit can be advantageously detected.According to a further development of the invention, before the change of the torque of the first drive unit in such a way that a constant rotational speed of the first drive unit is again established, the torque of the first drive unit is increased by a torque predefined as a function of the predefined closing position. Advantageously, the method step of changing the torque of the first drive unit in such a way that a constant rotational speed of the first drive unit is established again is accelerated as only a small remaining torque deviation has to be compensated. Advantageously, it is thus also detected whether the predefined torque has to be adapted on the basis of the clutch wear.According to one specific embodiment, the value of the predefined torque is increased if the rotational speed of the first drive unit decreases after the separating clutch has been moved into the predefined closing position. The value of the predefined torque is reduced if the rotational speed of the first drive unit increases after the separating clutch has been moved into the predefined closing position. A simple detection of the predefined torque is thus advantageously carried out.According to one specific embodiment, the torque that is set is a torque that is set at the separating clutch or a clutch transmission torque that is set or a torque that is set at the first drive unit or the second drive unit or a torque with which the first or the second drive unit is loaded by the separating clutch.According to one specific embodiment, the torque of the first drive unit is increased or decreased by a predefined torque. This advantageously also counteracts a lowering of the rotational speed of the first drive unit.According to one specific embodiment, the separating clutch is not fully closed in the predefined closing position and is operated in a slip state, in particular.According to one aspect, the invention relates to a method for determining a locking position of a separating clutch at which a predefined torque is set, wherein the locking position of the separating clutch is determined as a function of a torque that is detected according to the invention and is set, for example a torque that is set at the separating clutch or a clutch transmission torque that is set. The method according to the invention for detecting the torque that is set up is preferably repeated at another closing position of the separating clutch until the detected torque that is set up at this closing position corresponds to the predefined torque at the separating clutch. In particular, a closing position is selected as the other closing position in which a lower torque is set at the separating clutch, in which the clutch is thus opened further if the torque that is set is greater than the predefined torque at the separating clutch, and / or a closing position is selected as the other closing position in which a greater torque is set at the separating clutch, in which the clutch is thus closed further if the torque that is set is less than the predefined torque at the separating clutch. In this way, the closing position can also be determined iteratively.The invention further relates to a device configured by programming, in particular a control device, which is designed to execute a computer program for executing at least one of the methods according to the invention for detection.DRAWINGSFurther exemplary embodiments are explained with reference to the attached drawings. The following are shown: FIG. 1 shows a hybrid drive; FIG. 2 is a time diagram of a method for detecting a torque that is set; FIG. 3 is a time diagram of a method for detecting a torque that is set; FIG. 4 is a time diagram of a method for detecting a torque that is set; and FIG. 5 shows a time diagram of a method for detecting a torque that is set.DESCRIPTION OF THE EMBODIMENTSFIG. 3 shows a time diagram of a method for detecting a torque that is being set in a closed position of a separating clutch K 0 shown in FIG. 1, for example. In this case, FIG. 3 ashows a time profile of a torque generated by an electric motor, FIG. 3 bshows a time profile of a rotational speed of the electric motor, and FIG. 3 cshows a time profile of a state P of the separating clutch K 0, which can have an open state, a closed state and a slip state.To carry out the method, the internal combustion engine ICE is shut down and the separating clutch K 0 is opened. Disconnect clutch K 0 remains open until time 301 while the electric motor torque is maintained constant. In this case, the transmission of the hybrid vehicle can be locked, for example, in the park position. Furthermore, the rotational speed of the electric motor is kept constant at 500 rpm, for example, by a speed regulator. At the time 301, the separating clutch K 0 is at least partially closed and is thereby transferred into a predefined state 303, for example into a predefined closing position, in which it is slipping. In this case, the torque of the electric motor is increased by a predefined torque 305, i.e. by a pilot control torque. This pilot torque, which is assigned to predefined position 303 of separating clutch K 0, achieves an electromotive torque which, as shown in FIG. 3 b, can lead to a reduction in the rotational speed of the electric motor on account of an increased clutch transmission torque. In order to keep the rotational speed constant, a speed regulator regulates the rotational speed of the electric motor to a constant value as a function of a rotational speed difference which is caused by a difference between the expected and the present transmission torque of the separating clutch K 0. For this purpose, a further torque 307 is generated, so that a resulting torque 309 is obtained, which is related to a constant rotational speed of the electric motor.When the resulting torque 309 is reached at the time 311, the rotational speed of the electric motor EM stabilizes, so that the current state of the separating clutch K 0, i.e. its final closing position, and / or the increased electromotive torque, can be detected. Based on this, the torque that is set can be detected.At time 313, disconnect clutch K 0 is opened again, and its state 315 may be detected. Subsequently, the rotational speed of the electric motor increases and the electromotive torque decreases to the value of the output torque. The difference 316 between the torque that is set and the output torque results in a learning torque range. For detecting the torque that is being established, in particular for detecting a clutch transmission torque, the method can be carried out at different closing positions. A characteristic curve of the torque that is established can thus be detected at a plurality of locking positions of the separating clutch.In the event that the speed regulator of the electric motor EM is not able to compensate for a rapid torque change, the speed regulator can, as mentioned above, generate a torque by increasing the electromotive torque by the predefined torque, which can also be referred to as a pilot torque (so-called feed forward torque). In the event that the torque that is set is equal to the present clutch transmission torque, the speed regulator therefore no longer has to perform any regulation.Proportional-integral feedback elements (PI) can be used to control the rotational speed of the electric motor EM. However, its response speed is too slow to compensate for a speed change due to a movement of the separating clutch K 0. Therefore, it is preferred to use exclusively proportional P elements for controlling the rotational speed of the electric motor.In order to detect a state of the separating clutch K 0, for example its closed position, at which a specific torque is set, the method can be carried out as illustrated in FIG. 4. FIG. 4 ashows a torque of the electric motor and FIG. 4 bshows a position P of the separating clutch K0, which is determined by its state or by the arrangement of the clutch plates, as a function of time T. Beginning with a predefined rotational speed and an open separating clutch K 0, this clutch is at least partially closed at time 401, and is thus transferred into a slip state. The torque of the electric motor EM is preferably increased simultaneously, it being possible to detect a torque that is established, which may be higher than an expected torque 403, for example, and differs from the expected torque 403 by a differential torque 405, for example. After a predetermined time interval has elapsed, the clutch is opened again at the time 407, as a result of which the electromotive torque falls. The separating clutch K 0 is then closed again and is thus transferred into a further slip state, in which the torque transmitted by the separating clutch K 0 is lower by the differential torque 405 than the torque transmitted at the point in time 401. The closing position of the separating clutch differs by the difference amount 409. The torque of the electric motor preferably increases simultaneously and reaches the expected torque 403, for example.The above-described sequence steps can be repeated until a predefined slip state or a predefined closing position of the separating clutch K0 in which the resulting electromotive torque corresponds to the expected torque 403 has been set. Thus, depending on a torque deviation, the position of disconnect clutch K 0 is adjusted toward open disconnect clutch K 0 if the detected torque is greater than expected torque 403. If the detected torque is less than the expected torque 403, the position of the separating clutch K 0 is adjusted in the direction of its closed state as a function of the torque deviation.In the event that the expected clutch transmission torque is greater or less than the current clutch transmission torque, the speed regulator is normally unable to maintain the speed of the electric motor EM constant because the movement of the disconnect clutch K 0 is faster than the speed regulator's reaction time. In this case, the expected torque and thus the predefined torque by which the torque is to be increased or reduced in the presence of a predefined slip state of the separating clutch K 0 can be set, as illustrated in FIG. 5. In this case, FIG. 5 ashows a time profile of the torque of the electric motor, FIG. 5 bshows a time profile of the predefined torque, FIG. 5 cshows a time profile of the rotational speed of the electric motor and FIG. 5 dshows a state, i.e. a locking position of the separating clutch K 0.Starting from a predefined electromotive torque, an open clutch state and a predefined rotational speed of the electric motor EM, the separating clutch K 0 is at least partially closed at the time 501 and is thus transferred into a slip state. As shown in FIG. 5 c, the rotational speed of the electric motor decreases by a rotational speed difference shown by the arrow in FIG. 5 c. In order to prevent this drop, according to FIG. 5 b, a predefined torque, which is illustrated in FIG. 5 b, is selected at a point in time which lies before the point in time 501, by which the torque of the electric motor is increased. The speed controller attempts to balance the speed. Subsequently, the separating clutch K 0 is opened again and the torque of the electric motor EM is reduced by the predefined torque. As shown in FIG. 5 c, the rotational speed of the electric motor EM thereby increases. Subsequently, in a second phase, the separating clutch K 0 is closed again, wherein a further predefined torque, which is higher than the predefined torque used previously, for example, is selected shortly beforehand in order to increase the torque of the electric motor. As shown in FIG. 5 c, the rotational speed of the electric motor likewise decreases in this case, but the decrease is lower than in the preceding cycle. In a subsequent cycle, the separating clutch K 0 is opened again and transferred again into the predefined slip state, i.e. into a predefined closing position, wherein an even greater predefined torque, for example, is selected in order to increase the torque of the electric motor. This method is repeated in further phases 3 and 4 until a predefined torque results which can be assigned to the always same predefined slip state shown in FIG. 5 d. Thus, the pilot torque can be increased depending on a speed deviation if the speed of the electric motor EM becomes lower. In the event that the rotational speed of the electric motor EM increases, the additional pilot control torque can be reduced as a function of the rotational speed deviation. These method steps can be repeated until a stable state with a constant rotational speed of the electric motor has been established.

Claims

Method for detecting a torque which is set up for a hybrid drive, wherein the hybrid drive has a first drive unit, in particular an electric motor, and a second drive unit, in particular an internal combustion engine, wherein the drive units can be coupled by means of a separating clutch (K0), characterized in that • the separating clutch (K0), when it is opened, is brought into a predefined closing position at a point in time (301); • the torque of the first drive unit is initially changed directly by a predefined torque; and • the torque which is set up thereafter is detected at the predefined closing position as a function of the change in the torque of the first drive unit, • the first drive unit is operated at a predefined rotational speed before the separating clutch (K0) is brought into the predefined closing position; • the torque of the first drive unit, after the separating clutch (K0) has been moved into the predetermined closing position, is changed in such a way that a constant rotational speed of the first drive unit is set.Method according to Claim 1da characterized in that • before the change in the torque of the first drive unit, a constant rotational speed of the first drive unit is set again; and • the torque of the first drive unit is increased by a torque which is predefined as a function of the predefined closing position.Method according to Claim 2da, characterized in that the value of the predefined torque is increased if the rotational speed of the first drive unit decreases after the separating clutch (K0) has been moved into the predefined locking position, and in that the value of the predefined torque is decreased if the rotational speed of the first drive unit increases after the separating clutch (K0) has been moved into the predefined locking position.Method according to one of the preceding claims, characterized in that the torque which is set up is a torque which is set up at the separating clutch (K0) or a clutch transmission torque or a torque which is set up at the first drive unit or the second drive unit.Method according to one of the preceding claims, characterized in that the torque of the first drive unit is increased or decreased by a predefined torque.Method according to one of the preceding claims, characterized in that the separating clutch (K0) is not fully closed in the predefined closing position, in particular is operated in a slip state.Method for determining a closing position of a separating clutch (K0) at which a predefined torque is set at the separating clutch (K0), wherein the closing position of the separating clutch (K0) is determined as a function of the set torque detected according to one of the preceding claims, characterized in that the method according to one of the preceding claims is repeated at another closing position of the separating clutch (K0) until the detected set torque at this closing position corresponds to the predefined torque at the separating clutch (K0).Method according to Claim 7, characterized in that a closing position is selected as the other closing position, in which a lower torque is set at the separating clutch (K0) if the torque which is set is greater than the predefined torque at the separating clutch (K0), and / or a closing position is selected as the other closing position, in which a greater torque is set at the separating clutch (K0) if the torque which is set is less than the predefined torque at the separating clutch (K0).Device configured in terms of programming, in particular a control device, which is designed to execute a computer program for executing one of the methods according to one of Claims 1 to 8.

Images