Method for the approximate determination of the torque which is actually transmitted by a clutch of a drive train of a vehicle

0001Method for regulating the torque transmitted by means of a drive train of a vehicle on drive wheels of the vehicle in accordance with a target torque.

0002The present invention relates to a method for regulating the torque transmitted by means of a drive train of a vehicle to the drive wheels of the vehicle in accordance with a target torque according to the features of patent claim 1.

0003From the <patcit id="pcit0001" dnum="WO0120200A1"><text>WO 01/20200 A1</text></patcit> A method for regulating an electrohydraulically controlled clutch or brake of a transmission is known, in which the clutch or brake is regulated by means of a model-based compensation pressure regulator using an observer.

0004The technical background of the present invention includes <patcit id="pcit0002" dnum="FR2921453A"><text>FR 2 921 453 A</text></patcit> such as <nplcit id="ncit0001" npl-type="b"><text>Beck R ET AL: "Model Predictive Control of a Parallel Hybrid Vehicle Drivetrain"; DECISION AND CONTROL, 2005 AND 2005 EUROPEAN CONTROL CONFERENCE. CDC-E CC '05. 44TH IEEE CONFERENCE ON SEVILLE, SPAIN 12-15 DEC. 2005, PISCATAWAY, NJ, USA, IEEE, December 12, 2005 (2005-12-12), pages 2670-2675, XP010884098, ISBN: 978-0-7803-9567-1</text></nplcit>.

0005In parallel hybrid vehicles, the crankshaft of the internal combustion engine is usually connected via a separating clutch to a transmission input shaft on which an electrical machine is arranged. The transmission input shaft can thus be driven either by the internal combustion engine or by the electrical machine or simultaneously by the internal combustion engine and the electrical machine. The transmission is usually an automatic transmission which has an “integrated starting element”, that is to say a clutch designed for starting operations.

0006So-called "full hybrid vehicles" can also drive without an internal combustion engine, ie purely electrically. In purely electrical operation, the separating clutch arranged between the crankshaft of the internal combustion engine and the transmission input shaft is opened and the internal combustion engine is switched off. For a transition to the internal combustion engine driving mode or to a "mixed mode" in which the vehicle is driven by both the internal combustion engine and the electric machine, the internal combustion engine must be started from the purely electric driving mode.

0007In many hybrid concepts known to date, a separate start system is provided for this. The internal combustion engine is not started by the electric machine assigned to the drive train, but by a separate "starter". After synchronization of the speed of the crankshaft with the speed of the electric machine of the hybrid drive, the disconnect clutch is closed and the internal combustion engine can provide torque to drive the vehicle.

0008A separate starting system has the advantage that the electric machine of the hybrid drive is not, or is not directly influenced by, the starting of the internal combustion engine. A disadvantage of a separate start-up system, however, is the associated additional costs. In addition, the 14-volt electrical system has to be extensively expanded to limit voltage drops during the starting process of the internal combustion engine. A separate start system is usually coupled to the internal combustion engine via a belt drive. Such a belt drive requires additional space in the longitudinal direction of the vehicle.

0009It is often not possible to do without a separate start-up system due to the wide range of technical constraints. If one were to start the internal combustion engine in electric driving operation via the electric machine of the hybrid drive by closing the disconnect clutch, then a "high-quality control" of the startup process (avoidance of torque fluctuations on the drive wheels of the vehicle) would be as precise as possible of the torque transmitted by the disconnect clutch required.

0010The object of the invention is to provide a method for determining the "torque" that is actually transmitted as accurately as possible from a clutch of a drive train of a vehicle, in particular a hybrid vehicle.

0011This object is solved by the features of claim 1. Advantageous refinements and developments of the invention can be found in the subclaims.

0012Clutches, in particular separating clutches, such as those installed in drive trains of vehicles, are usually controlled hydraulically or electro-hydraulically. Even if one knows the various parameters (e.g. hydraulic control pressure, clutch temperature, etc.) with or under which the control device of the clutch is controlled, it can only be roughly related to the torque that can be transmitted by the clutch or the torque actually transmitted by the clutch can be closed. The torque actually transmitted by a clutch depends on a large number of partly unknown or only approximately known parameters (such as the state of wear of the clutch, oil temperature and the viscosity that correlates with it, etc.).

0013The starting point of the invention is the idea of ​​considering the torque that can actually be transmitted or transmitted by a clutch as the sum of a “torque controlled via the clutch control” or a “theoretically transmitted or transmissible torque” and a “disturbing torque” that of a large number can be influenced by disruptive factors.

0014The basic principle of the invention is to measure the disturbance torque (in the control engineering sense) by observing a disturbance variable using a state estimator, e.g. B. to determine via a Kalman filter.

0015In order to improve the accuracy of the determination of the torque actually transmitted by the clutch, the clutch torque is introduced as the "state of a state space model". The clutch torque calculated from the hydraulic control (theoretically transmitted or transferable torque) is additionally corrected by a disturbance variable observer. It can be provided that the correction of the Kalman filter is only active when the internal combustion engine is started. It should be based on the clutch speed error (clutch speed = speed difference between internal combustion engine and electrical machine) between model and reality.

0016The better you know the torque actually transmitted by the clutch, the better the internal combustion engine drag torque superimposed on the drive train when the internal combustion engine is started. The better the engine drag torque can be compensated for, the less the effects of starting on the drive torque of the drive wheels and the greater the driving comfort.

0017A prerequisite for an approximate determination of the torque actually transmitted by the clutch is the provision of a "state space model" representing the drive train. Under the term drivetrain z. B. the entirety of the torque transmitting components can be understood, starting from the internal combustion engine or the crankshaft of the internal combustion engine to the drive wheels of the vehicle.

0018When the clutch under consideration (ie the clutch whose torque is to be determined) is closed, a theoretically transmittable or transmitted from the clutch is made on the basis of a predefined physical model of the clutch and the controlled closing parameters (e.g. controlled hydraulic pressure etc.) Moment determined.

0019The torque actually transmitted by the clutch can differ from the theoretically transmissible or transmitted torque, which is taken into account by adding the "disturbing torque" already mentioned.

0020The disturbance torque is determined on the basis of the state space model depicting the drive train and on the basis of actual speeds of individual drive train components and / or on the basis of actual torques that are currently being transmitted by individual drive train components. The disturbance torque is thus determined in terms of control technology by monitoring the state of the drive train. The actual speeds or the actual torques which are included in the state monitoring can be measured directly or derived from other measured or otherwise determined or known state parameters of the drive train.

0021An important advantage of the invention is that the torque that can actually be transmitted or transmitted by the clutch can be determined relatively precisely with the method according to the invention, which is a prerequisite for high-quality control of the starting of the internal combustion engine from purely electric driving. The invention thus makes it possible to dispense with a separate starting system.

0022If the torque actually transmitted from a clutch of the drive train is known precisely or at least relatively precisely, it can be based on this that the torque transmitted to the drive wheels of the vehicle is regulated in accordance with a target torque. As already explained above, the disturbance torque describes a possible deviation of the torque that can actually be transmitted or transmitted by the clutch from the target torque that is input via the locking parameters.

0023According to a development of the invention, the disturbance torque can be compensated for by applying a compensation torque by means of the electrical machine of the drive train to a rotary component of the drive train (e.g. on the transmission input shaft) and / or by changing the input locking parameters of the clutch. In this way, undesirable rotational irregularities in the drive train can be reduced or are eliminated, which is not only of great importance for starting the internal combustion engine from purely electric driving operation, but also for active vibration damping during normal driving operation.

0024The invention is explained in more detail below in connection with the drawing.

0025The only <figref idref="f0001">Figure 1</figref> describes a state space model of a typical parallel hybrid powertrain of a vehicle. A parallel hybrid drive train 1 of a vehicle has an internal combustion engine 2, the crankshaft of which outputs a torque T_Vm. At the in<figref idref="f0001">Figure 1</figref> The exemplary embodiment shown is a crankshaft 3 of the internal combustion engine 2 via a torsional vibration damper 4 (or via a combination of a torsional vibration damper and a "centrifugal force pendulum") with an input side 5 of a separating clutch, which is also referred to here as "K0". The separating clutch 6 or K0 transmits an actual torque T_K0 to an output element 7 of the clutch K0. The output element 7 is formed here by a transmission input shaft of an automatic transmission 8.

0026The automatic transmission 8 has an integrated starting element 9, ie a clutch, which is designed in such a way that it enables the vehicle to start. A transmission output shaft 10 of the automatic transmission 8 is e.g. B. connected via a propeller shaft not shown here with a rear axle 11. The rear axle gear 11 distributes the torque over an "axle" 12, ie Via a left and right drive shaft on drive wheels, which are shown here schematically with the reference number 13. The drive wheels 13 are in turn mounted on a vehicle body not shown here.

0027As from the in <figref idref="f0001">Figure 1</figref> The model shown can be seen, the drive train 1 can essentially be described by the following torques:<ul id="ul0001" list-style="dash" compact="compact"><li>T_Vm: torque delivered by the internal combustion engine.</li><li>T_K0: Torque that can actually be transmitted or transmitted from the disconnect clutch 6 or K0.</li><li>T_EM: Torque exerted by an electric machine 14 of the hybrid drive train on the hybrid drive train 1.</li><li>T_IAE: Torque exerted on drive train 1 by an integrated starting element of the transmission.</li><li>T_B: braking torque exerted by vehicle brakes on drive wheels of the vehicle.</li><li>T_RL: Driving resistance moments resulting e.g. B. from the slope of the road, air resistance of the vehicle etc.</li></ul>

0028The drive train of the vehicle can be mapped in terms of control technology in a manner known to those skilled in the art using a state space model. For a linear, time-invariant multivariable system of order n with r input variables and m output variables, the state space model can be represented by the following two equations:<maths id="math0001" num=""><math display="block"><mrow><mi mathvariant="normal">dx</mi><mfenced><mi mathvariant="normal">t</mi></mfenced><mo>/</mo><mi mathvariant="normal">German</mi><mo>=</mo><mi mathvariant="normal">A x</mi><mspace width="1em" /><mfenced><mi mathvariant="normal">t</mi></mfenced><mo>+</mo><mi mathvariant="normal">B u</mi><mfenced><mi mathvariant="normal">t</mi></mfenced><mo>;</mo></mrow></math><img file="EP2769112B1_D0001.tif" /></maths><maths id="math0002" num=""><math display="block"><mrow><mi mathvariant="normal">y</mi><mfenced><mi mathvariant="normal">t</mi></mfenced><mo>=</mo><mi mathvariant="normal">C x</mi><mfenced><mi mathvariant="normal">t</mi></mfenced><mo>+</mo><mi mathvariant="normal">D u</mi><mfenced><mi mathvariant="normal">t</mi></mfenced><mo>;</mo></mrow></math><img file="EP2769112B1_D0002.tif" /></maths>x (t) describes a state vector, u (t) an input vector or control vector and y (t) an output vector (observation vector). A is the system matrix describing the drive train, B the input or control matrix, C the output or observation matrix and D the so-called through matrix.

0029By means of such a state space model, which takes into account several speeds currently occurring in the drive train and / or several torques currently occurring in the drive train and the torque applied to clutch K0, an interference torque occurring at clutch K0 can be determined which corresponds to that of clutch K0 Set target torque to the torque K actually transmitted by the clutch K0_{0 is} is superimposed.