Method for operating a drive train

Abstract

Method for operating a drive train of a motor vehicle comprising a drive unit designed as a hybrid drive (3) comprising at least one electric machine (2) and an internal combustion engine (1), with a transmission (5), with an output (4) and with a braking system comprising at least one wear-free permanent brake (6), where, when a braking torque is requested (M B ) for the output (4) the braking torque (M B ) between the electric machine (2) of the hybrid drive (3) and the wear-free continuous brake (6) in such a way, that at the beginning of a braking torque request the braking torque (M B ) is requested exclusively by at least one electric machine (2) of the hybrid drive (3) and is provided at the output (4), and that subsequently, depending on the parameters of the wear-free continuous brake (6), the braking torque requirement is at least partially transferred from the electric machine (2) to the at least one wear-free continuous brake (6) in a controlled manner, so that the braking torque provided at the output (4) by the electric machine (2) and the continuous brake (6) in total corresponds to the requested braking torque (M). B ) corresponds, characterized in that the braking torque request from the or each electric machine (2) of the hybrid drive (3) is controlled and transmitted to the at least one wear-free permanent brake (6) in such a way that the braking torque request from the or each electric machine (2) of the hybrid drive (3) is continuously reduced and the braking torque request from the or each wear-free permanent brake (6) is continuously increased, wherein this continuous transfer of the brake torque request is determined in advance depending on the parameters of the or each wear-free continuous brake (6) and is thus carried out in the sense of a pre-controlled transfer of the brake torque request.

Description

[0001] The invention relates to a method for operating a drive train of a motor vehicle according to the preamble of claim 1.

[0002] The present invention relates to a method for operating a powertrain with a hybrid drive. Such a hybrid drive comprises at least one electric machine and an internal combustion engine. In addition to the hybrid drive, a powertrain of a hybrid vehicle comprises a transmission, wherein the transmission converts speeds and torques and thus provides tractive force from the hybrid drive to a drive shaft of the hybrid vehicle. Furthermore, a powertrain of a hybrid vehicle comprises a braking system, wherein it is already known from the prior art that a braking system can comprise several partial braking systems, namely a so-called service brake, which acts on the wheels of the drive shaft via friction, and at least one wear-free continuous brake. The wear-free continuous brake can be a so-called engine brake or a retarder of the powertrain.

[0003] From DE 198 43 580 A1, a braking system for a motor vehicle is known in which a requested braking force or braking torque is distributed between the friction brake and the continuous brake of the braking system. According to this prior art, it is proposed that when the continuous brake is applied, the friction brake is subjected to a pressure that initially corresponds to a signal from a brake force sensor and is reduced with increasing braking force of the continuous brake until the total braking force corresponds to the signal from the brake force sensor. This allows the friction brake to become fully effective with a short response time, while during prolonged braking, the continuous brake assumes full braking power and protects the friction brake from overload.

[0004] German patent DE 10 2008 023 731 A1 describes a control system for the negative drivetrain torque in a hybrid vehicle. This system uses two electric motors capable of recuperating the kinetic energy of the hybrid vehicle. To prevent thermal overload of one of the electric motors, the ratio of the recuperation torques between the motors is adjusted depending on the thermal state of one of the electric motors.

[0005] DE 44 46 485 A1 describes a method for braking a motor vehicle with a hybrid drive. Engine braking is activated when the traction battery is fully charged, its temperature is outside a charging temperature range, or the charging current exceeds a limit value.

[0006] DE 199 13 618 A1 describes an auxiliary braking device for a hybrid-powered automobile with an electrically operated brake. An auxiliary brake electric motor is activated when the electrically operated brake fails.

[0007] DE 10 2008 041 760 A1 describes a braking device for a motor vehicle with two brake circuit groups.

[0008] WO 2010 / 046 733 A1 describes a method for determining a driver's suitability for recuperating the kinetic energy of a hybrid vehicle. This involves determining the braking power of the electric motor and the braking power of the other braking systems, including a retarder, during vehicle deceleration. The braking powers determined in this way are summed and compared to each other.

[0009] DE 10 2008 023 305 A1 describes a method for controlling the recuperation torque of a hybrid drive unit. If a charge level limit of the energy storage device is exceeded during recuperation operation, the electric machine is first operated to apply the braking torque, and subsequently the braking torque of the electric machine is controlled.

[0010] EP 2 127 987 A1 describes a braking method with energy recovery for a hybrid traction vehicle, which, depending on the requested braking target, controls the intervention of a motor-generator and the switching on or off of an endothermic motor from the drive train.

[0011] Based on this, the present invention addresses the problem of creating a novel method for operating a drive train.

[0012] This problem is solved by a method according to claim 1. According to the invention, when a braking torque is requested for the output of a hybrid vehicle, the braking torque is distributed between the electric machine(s) of the hybrid drive and the wear-free continuous brake(s) such that, at the beginning of a braking torque request, the braking torque is requested exclusively by at least one electric machine of the hybrid drive and provided at the output, and that subsequently, depending on the parameters of the wear-free continuous brake(s), the braking torque request is at least partially transferred from the electric machine(s) to at least one wear-free continuous brake in a controlled manner, so that the total braking torque provided at the output by the electric machine(s) and the continuous brake(s) corresponds to the requested braking torque.

[0013] In this system, the braking torque requirement is transferred from the electric machine(s) of the hybrid drive to the at least one wear-free continuous brake in such a way that the braking torque requirement from the electric machine(s) of the hybrid drive is continuously reduced and the braking torque requirement from the wear-free continuous brake is continuously increased, whereby this continuous transfer of the braking torque requirement is determined in advance depending on the parameters of the wear-free continuous brake and is thus executed in the sense of a pre-controlled transfer of the braking torque requirement.

[0014] The present invention proposes to distribute a braking torque request in a braking system of a hybrid vehicle between the electric motor(s) of the hybrid drive and the wear-free continuous brake(s) of the braking system, such that at the beginning of a braking request, the braking torque is requested exclusively by at least one electric motor of the hybrid drive and provided at the output. Only subsequently, depending on the parameters of the wear-free continuous brake(s), is the braking torque request at least partially transferred from the electric motor(s) to at least one wear-free continuous brake of the braking system. This is done in such a way that the total braking torque provided at the output by the electric motor(s) and the continuous brake(s) corresponds to the requested braking torque.

[0015] At the beginning of a braking torque request, the method according to the invention makes it possible to provide a braking torque directly at the output with high dynamics and within a short time via at least one electric machine of the hybrid drive, thus reacting immediately to a braking torque request. Subsequently, the braking torque request is reduced in a controlled manner at the respective electric machine of the hybrid drive and simultaneously increased at at least one wear-free continuous brake of the braking system in order to build up a braking torque that can be provided by the respective wear-free continuous brake at the output in a controlled manner.

[0016] The braking torque provided by the electric machine or machines at the output is reduced by the amount by which the braking torque is built up by the respective wear-free continuous brake at the output.

[0017] This ultimately makes it possible, at the beginning of a braking torque request, to provide a desired braking torque at the output with high dynamics and within a short reaction time, and, at the same time, to use the respective wear-free continuous brake in a controlled and regulated manner to build up the braking torque.

[0018] Subsequently, with a progressively decreasing output speed, the braking torque requirement is transferred from the wear-free continuous brake or brakes back to at least one electric machine of the hybrid drive, again in a controlled manner, so that the total braking torque provided at the output by the electric machine or brakes and the wear-free continuous brakes corresponds to the desired or requested braking torque.

[0019] This makes it possible, when the respective wear-free continuous brake can no longer provide sufficient braking torque at the output as a result of an increasingly decreasing output speed, to remove the respective wear-free continuous brake from the braking torque requirement in a controlled manner, in order to compensate for the braking torque that can no longer be provided by the respective wear-free continuous brake, supported by at least one electric machine of the hybrid drive.

[0020] 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 a block diagram of an exemplary drive train to illustrate the method according to the invention; Fig. 2 a first diagram to further illustrate the method according to the invention; Fig. 3 a second diagram to further illustrate the method according to the invention; and Fig. 4 a third diagram to further illustrate the method according to the invention.

[0021] Fig. Figure 1 shows an exemplary powertrain diagram of a hybrid vehicle powertrain in which the method according to the invention can be used. The powertrain of the Fig. 1 via an internal combustion engine 1 and an electric machine 2, which together form a hybrid drive 3 of the powertrain. Between the hybrid drive 3, namely the electric machine 2 thereof, and an output 4 are connected according to Fig. 1 both a gearbox 5 and a retarder 6 are engaged, the retarder 6 being a wear-free continuous brake.

[0022] According to Fig. In one case, the retarder 6 is connected between the electric machine 2 of the hybrid drive 3 and the transmission 5. In contrast, it is also possible for the retarder 6 to be connected between the transmission 5 and the output 4 or between the combustion engine 1 and the electric machine 2.

[0023] It should be noted at this point that the method according to the invention is not limited to application to the [device / system] in [location]. Fig. The invention is limited to the drive train shown in Figure 1. Rather, the invention can be used in other drive trains of hybrid vehicles, for example, when the combustion engine and the electric machine of the hybrid drive act on different axles of the hybrid vehicle's drive system.

[0024] A hybrid drive system includes a braking system that can provide braking torque at output 4. Thus, the braking system of a hybrid vehicle includes a service brake that acts on the wheels of output 4 via friction.

[0025] In addition to such a service brake, the braking system of a hybrid vehicle includes at least one wear-free continuous brake, whereby this wear-free continuous brake is, for example, the one in Fig. The retarder 6 shown in Figure 1 can be used. A further wear-free continuous brake of a hybrid vehicle's braking system is provided by a so-called engine brake of the combustion engine 1.

[0026] In accordance with the present invention, it is proposed that when a braking torque is requested for the output 4, the requested braking torque is divided at least between the electric machine 2 of the hybrid drive 3 and the wear-free continuous brake.

[0027] The requested braking torque is distributed in such a way that at the beginning of a braking torque request, the braking torque is requested exclusively by at least one electric machine 2 of the hybrid drive 3 and provided at the output 4, and that subsequently, depending on the characteristics of the wear-free continuous brake, the braking torque request is transferred from the electric machine 2 of the hybrid drive 3 to at least one wear-free continuous brake 6 in a controlled manner, so that the total braking torque provided at the output 4 by the electric machine 2 of the hybrid drive 3 and the continuous brake corresponds to the requested braking torque.

[0028] Details regarding this will be provided below with reference to Fig. 2 described, wherein in Fig. 2. Several time-dependent curves are shown over time t, namely a time-dependent curve of a rotational speed n. ABof output 4 of the drive train, a time-dependent curve M B a braking torque requested with a braking torque request, a time-dependent curve M R a braking torque provided by the retarder 6 at the output 4, as well as a time-dependent curve M EM a braking torque provided by the electric machine 2 at the output 4.

[0029] Starting at time t1, in Fig. 2 a brake torque request M B for a braking torque to be provided at the output 4. According to the invention, at the beginning of this braking torque request, i.e., immediately following time t1, this braking torque request is made exclusively by the electric machine 2, so that at the beginning of the braking torque request, i.e., immediately following time t1, the requested braking torque M B exclusively via the braking torque M provided by the electric machine 2EM is provided at output 4.

[0030] Only subsequently, namely in Fig. Starting at time t2, the braking torque requirement M is determined based on parameters of the retarder 6. B from the electric machine 2 to the retarder 6, the braking torque M is continuously and in a controlled manner transferred at least partially, such that the braking torque M provided at the output 4 by the electric machine 2 is EM and the braking torque M provided by the retarder 6 at the output 4 R in total the requested braking torque M B corresponds.

[0031] In Fig. 2 remains the requested braking torque M B constant, so that machine 2 and retarder 6 together provide an approximately constant braking torque at output 4.

[0032] The partial transfer of the braking torque request from the electric machine 2 of the hybrid drive 3 to the retarder 6 or the wear-free continuous brake takes place in Fig. 2 between times t2 and t3, respectively, the braking torque requirement from the electric machine 2 of the hybrid drive 3 is reduced in a ramp-like manner, and the braking torque requirement from the wear-free continuous brake, namely the retarder 6, is increased in a ramp-like manner, and thus the braking torques M provided by them at the output 4 are also increased. EM or M R .

[0033] As already explained, this transfer of the brake torque request depends on parameters of the retarder 6, whereby this transfer is determined before the actual brake torque request and thus offline depending on the parameters of the retarder 6, so that the transfer of the brake torque request between times t2 and t3 is carried out in the sense of a pre-controlled transfer of the brake torque request or in the sense of a pre-control.

[0034] Fig. Figure 3 shows a further development of the method according to the invention for the case where the output speed n AB increasingly reduced. Thus, it can Fig. 3 can be deduced that when the output speed n AB at the output shaft 4, and thus the driving speed of the hybrid vehicle is increasingly reduced, subsequently the braking torque request is transferred from the retarder 6 to the electric machine 2 of the hybrid drive 3, namely according to Fig. 3 between times t4 and t5.

[0035] This further development of the method according to the invention is based on the understanding that the retarder 6 can no longer provide a braking torque at the output 4 once a minimum speed is undershot. According to the invention, the braking torque requirement at the retarder 6 is continuously, preferably ramp-like, and thus controlled, reduced in good time before this minimum speed is undershot, and correspondingly continuously, preferably ramp-like, and controlled, increased at the electric machine 2 of the hybrid drive 3, so that the total braking torque provided at the output 4 by the retarder 6 and the electric machine 2 again meets the requested braking torque M. B corresponds.

[0036] The time t4 from which, with increasing reduction of the output speed n ABThe braking torque request from the retarder 6 back to the electric machine 2 can be determined offline in advance, depending on the parameters of the retarder 6. Preferably, however, the current output speed n is determined during the braking torque request and thus during the execution of the braking process. AB The output 4 is monitored and, depending on this, the time t4 from which the torque transfer from the retarder 6 to the electric machine 2 begins is determined online during the execution of the brake torque request, in the sense of a control-technical observation.

[0037] From time t5, from which the retarder 6 no longer has a braking torque M at the output 4 R The electric machine 2 alone provides a corresponding braking torque M, which can provide more. EM Ready at drive point 4.

[0038] Then, when the hybrid vehicle is stationary at time t6, the braking torque M provided by the electric machine 2 of the hybrid drive is applied to protect it. EM reduced to zero and then the requested braking torque is provided by a service brake of the braking system, which acts in particular on the wheels of the output 4 via friction.

[0039] Fig. Figure 4 shows a variant of the invention in which a braking torque requirement is divided between the electric machine 2 of a hybrid drive and two wear-free partial brakes of the braking system of the hybrid vehicle, namely between an engine brake and a retarder.

[0040] This shows Fig. 4 above the rotational speed n AB of the output shaft 4 of a hybrid vehicle, torque profiles, namely the speed-dependent profile of a requested braking torque M B, the speed-dependent curve of a braking torque M provided by the electric machine 2 of the hybrid drive at the output 4 EM , the speed-dependent curve of a braking torque M provided by a motor brake at output 4 MB , as well as the speed-dependent torque curve of a braking torque M provided by the retarder at output 4 R . This way Fig. It can be deduced from Figure 4 that, on the one hand, a controlled transfer of the braking torque request takes place between the electric machine 2 and the motor brake, and on the other hand, between the electric machine 2 and the retarder 6, so that the braking torque provided in total at the output 4 by the partial braking systems corresponds to the requested braking torque M. B corresponds.

[0041] It is therefore in line with the present invention to distribute, on the control side, a braking torque requested by a braking system in a drive train of a hybrid vehicle between an electric machine 2 of the hybrid drive 3 of the hybrid vehicle and at least one wear-free continuous brake of the hybrid vehicle, namely between a retarder and / or an engine brake.

[0042] The lack of dynamics of the retarder or engine brake can be compensated for by the dynamic behavior of the electric machine 2 of the hybrid drive 3, which is operated as a generator to provide braking torque. At the beginning of a braking torque request, the requested braking torque is therefore first provided at the output 4 via at least one electric machine 2 of the hybrid drive 3. Subsequently, braking torque is built up at the output via the wear-free continuous brake, in particular via a retarder or, if applicable, an engine brake. Then, when the retarder or engine brake can no longer provide braking torque, depending on the output speed, the retarder or engine brake is deactivated.The motor brake is controlled and withdrawn from the brake engagement at output 4, while then the electric machine 2 of the hybrid drive 3 in generator mode takes over the reduced brake torque requirement at the respective wear-free continuous brake and provides the corresponding brake torque at the output.

[0043] With the aid of the present invention, it is possible to reliably provide the desired braking torque for the output 4 during an entire braking torque request, without the risk of overbraking and without the risk of vibrations in the drive train, both at the beginning of a braking torque request and with the increasing reduction of the output speed at the end of the braking torque request. Reference sign 1 Internal combustion engine 2 electric machine 3 Hybrid drive 4 Drive 5 gearboxes 6 Retarder

Claims

[1] Method for operating a drive train of a motor vehicle comprising a drive unit designed as a hybrid drive (3) comprising at least one electric machine (2) and an internal combustion engine (1), a transmission (5), an output (4) and a braking system comprising at least one wear-free permanent brake (6), where, when a braking torque is requested (M B ) for the output (4) the braking torque (M B ) between the electric machine (2) of the hybrid drive (3) and the wear-free continuous brake (6) in such a way, that at the beginning of a braking torque request the braking torque (M B ) is requested exclusively by at least one electric machine (2) of the hybrid drive (3) and is provided at the output (4), and that subsequently, depending on the parameters of the wear-free continuous brake (6), the braking torque requirement is at least partially transferred from the electric machine (2) to the at least one wear-free continuous brake (6) in a controlled manner, so that the braking torque provided at the output (4) by the electric machine (2) and the continuous brake (6) in total corresponds to the requested braking torque (M). B ) corresponds, characterized by , that the braking torque requirement from the or each electric machine (2) of the hybrid drive (3) is controlled and transmitted to the at least one wear-free permanent brake (6) in such a way that the braking torque requirement from the or each electric machine (2) of the hybrid drive (3) is continuously reduced and the braking torque requirement from the or each wear-free permanent brake (6) is continuously increased, wherein this continuous transfer of the brake torque request is determined in advance depending on the parameters of the or each wear-free continuous brake (6) and is thus carried out in the sense of a pre-controlled transfer of the brake torque request. [2] Method according to claim 1, characterized by , that subsequently with progressively decreasing output speed (n AB ) the braking torque request from the or each wear-free continuous brake (6) is controlled and transferred back to at least one electric machine (2) of the hybrid drive (3), so that the braking torque provided at the output (4) by the or each electric machine (2) of the hybrid drive (3) and the or each continuous brake (6) in sum corresponds to the requested braking torque (M) B ) corresponds. [3] Method according to claim 2, characterized by, that the braking torque request from the or each wear-free continuous brake (6) to at least one electric machine (2) of the hybrid drive (3) is controlled such that the braking torque request from the or each wear-free continuous brake (6) is continuously reduced and the braking torque request from the or each electric machine (2) of the hybrid drive (3) is continuously increased, wherein this continuous transfer during the braking torque request depends on the current output speed (n AB ) is determined. [4] Method according to any one of claims 1 to 3, characterized by , that then, when the output speed (n AB ) at the output (4) until the motor vehicle comes to a standstill, the braking torque (M B ) is requested exclusively by a service brake of the braking system and is provided at the output (4) of the drive train. [5] Method according to any one of claims 1 to 4, characterized by , that in this way braking torque (M B ) is requested by an electric machine (2) of the hybrid drive (3) and a wear-free continuous brake designed as a retarder (6) and is provided at the output (4). [6] Method according to any one of claims 1 to 4, characterized by , that in this way braking torque (M B ) is requested by an electric machine (2) of the hybrid drive (3) and a wear-free continuous brake designed as an engine brake and is provided at the output (4). [7] Method according to any one of claims 1 to 4, characterized by , that in this way braking torque (M B ) is requested by an electric machine (2) of the hybrid drive (3), a first wear-free continuous brake designed as an engine brake and a second wear-free continuous brake designed as a retarder (6) and is provided at the output (4).

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