DE102011089678A1 - Parallel hybrid powertrain of a vehicle and method of controlling the same - Google Patents

Abstract

The invention relates to a parallel hybrid powertrain having an internal combustion engine, an electric machine, a separating clutch between the internal combustion engine and the electric machine, an output clutch behind the electric machine, and a control unit. Starting from a state in which the internal combustion engine is off and the electric machine outputs a propulsion torque via the output clutch, the control unit controls in the presence of a trigger signal, in particular the separating clutch such that in a shortened time the engine emits a propulsion torque instead of the electric machine.

Description

State of the art

In parallel hybrid systems, e.g. in the VW Touareg Hybrid, Porsche Cayenne S Hybrid, Nissan Fuga Hybrid, the combustion engine (VM) and the electric machine (EM) are on a drive shaft. To be able to drive purely electrically, the internal combustion engine is separated from the rest of the drive by a separating clutch (K0). As a result, propulsion can be generated only with the aid of the electric machine. In order to be able to reconnect the internal combustion engine as needed during the electric drive without using an additional starting unit (for example, a pinion starter), it is started by means of the separating clutch. The energy for tearing the internal combustion engine is generated by the electric machine or is present as kinetic energy in the drive train. To restart, an element (K1) between electric machine and wheel is usually brought into a slipping state. This element can e.g. be a starting element in the transmission unit. The starting element may e.g. a torque converter with converter lock-up clutch (WK), a separate start-up clutch or a clutch as part of a dual-clutch transmission (DKG). The slip is generally necessary to prevent a strong variation of the propulsion torque and thus an uncomfortable jerk safely in the highly dynamic phases of engine start.

Disclosure of the invention

By the method according to the invention it is on the one hand possible to drastically reduce the starting time of the engine and thus to increase the sportiness or to let the start time similar to the previously known start types and to reduce the required torque reserve, so that increases the electric driving range. In any case, the usual comfort of the previous start types is not deteriorated.

Since the internal combustion engine is usually only started when the driver's desired torque has increased so much that it can no longer be completely provided by the electric machine, "waiting times" of the driver on the torque of the engine to displeasure, as the driver delayed Momentum delivery, especially in sporty driving This effect is referred to as "Hesitation" or "Bad Response".

The torque compensation of the separating clutch according to the invention is carried out in real time, i. The electric machine is simultaneously driven to the disconnect clutch to compensate for much of the torque.

In general, a parallel hybrid powertrain according to the invention includes an internal combustion engine, an electric machine, a disconnect clutch disposed between an output side of the internal combustion engine and a drive side of the electric machine, an output clutch disposed on an output side of the electric machine, and a control unit for control of the drive train.

When the engine is off, the clutch is open, the electric machine outputs a propulsion torque (M _EM ) and thus at the output clutch of the moment M _is applied and a trigger signal is present, the control unit controls the clutch such that this first the internal combustion engine with the electric machine connects until the internal combustion engine reaches a self-running speed. That is, the electric machine initially rotates the crankshaft of the internal combustion engine. Subsequently, the separating clutch is controlled such that it at least partially disconnects the internal combustion engine from the electric machine until the engine reaches a desired speed. That is, the internal combustion engine generates its own acceleration torque from the first ignition, which increases the speed of the internal combustion engine. Finally, when the engine has reached a desired speed, the disconnect clutch is controlled to reconnect the engine to the electric machine, such that the engine outputs propulsive torque in place of, or in combination with, the electric machine.

According to an embodiment of the invention, during the entire process it is ensured that there is a slip in the output coupling, which is dimensioned such that no thrust reversal takes place at the output clutch. The propulsion torque is based on the driver's request and is determined by the output clutch.

According to a further embodiment, the control unit controls the output torque (M _EM ) of the electric machine to a value less than or equal to a maximum (M _EMmax ), before the _separating clutch connects the internal combustion engine for the first time with the electric machine.

The start mode described here is optimized for the combination of a proportional clutch (K0) with a friction clutch (K1). This topology has the advantage that the clutch acting as a clutch coupling K0 can be steplessly controlled and the propulsion of the vehicle depends solely on the moment of the output clutch K1. The amount of slippage in the clutch K1 has no effect on ride comfort (as long as the slip direction is not reversed). In any case, one is To avoid sign changes in the slip, as this effect is clearly noticeable by the driver (jerk in the drive train).

• • Es wird nur die kinetische Energie benötigt, die den Verbrennungsmotor auf „Selbstlaufdrehzahl" bringt, d.h. weniger Schlupfaufbau ist nötig als bei einem reinen Impulsstart.
• • Der Hochlauf des Verbrennungsmotor auf Synchronisationsdrehzahl wird durch das vom Verbrennungsmotor lieferbare Moment (Einspritzung + Zündung) unterstützt, wodurch die Startzeit verkürzt wird.
• • Das mögliche Moment der Elektromaschine wird zum frühst möglichen Zeitpunkt vollständig und unmittelbar ausgenutzt, d.h. es kann bei geringer Momentenreserve dennoch ein schneller und komfortabler Start erzielt werden.
• • Der Verbrennungsmotor wird immer sicher angedreht, da bis zur „Selbstlaufdrehzahl" mit hohem bzw. maximalem Trennkupplungs-Moment angesteuert wird.
• • Der positive Schlupf der Kupplung K1 wird durch intelligente Ansteuerung der Trennkupplung K0 sichergestellt, d.h. die Gefahr einer Schlupfumkehr in der K1 (Ruck) wird durch die Trennkupplung K0 vermieden.
• • Es findet keine reine Momentenkompensation statt, sondern eine drehzahlabhängige Regelung mit Vorsteuerung. Durch die stärkere Gewichtung der Regelung verliert die Momentengenauigkeit an der Trennkupplung K0 an Bedeutung.
• • Der schnelle Hochlauf des Verbrennungsmotor wird durch die optimale Kombination aus K0-Moment und Verbrennungsmotor-Selbstlauffähigkeit erzielt.

Further advantages of the starting method according to the invention:

• • Only the kinetic energy is needed, which brings the internal combustion engine to "self-running speed", ie less slip build-up is required than with a pure pulse start.
• • The acceleration of the combustion engine to synchronization speed is assisted by the torque available from the combustion engine (injection + ignition), which shortens the starting time.
• • The possible moment of the electric machine is fully and immediately utilized at the earliest possible time, ie a quick and comfortable start can still be achieved with a low torque reserve.
• • The internal combustion engine is always turned on safely, as it is driven to the "self-running speed" with high or maximum clutch torque.
• • The positive slip of the clutch K1 is ensured by intelligent control of the separating clutch K0, ie the risk of slip reversal in the K1 (jerk) is avoided by the separating clutch K0.
• • There is no pure torque compensation, but a speed-dependent control with feed forward control. Due to the greater weighting of the control, the torque accuracy at the separating clutch K0 loses significance.
• • The fast startup of the internal combustion engine is achieved by the optimum combination of K0 torque and internal combustion engine self-running capability.

According to another aspect of the invention, there is provided a computer program that performs all the steps of a method of the invention when running on a control unit of a parallel hybrid powertrain as described above. A corresponding computer program is preferably loaded into a main memory of a control unit. The control unit or a data processor is thus equipped to carry out the method according to the invention.

Furthermore, the invention also relates to a computer-readable medium, such as a CD-ROM, in which the computer program can be stored. However, the computer program may also be provided over a network such as the Internet and may be downloaded to the memory of the control unit from that network.

It is noted that embodiments of the invention will be described with reference to different items. In particular, some embodiments or aspects related to device claims and other embodiments or aspects related to method claims will be described. However, one skilled in the art from the above and following description will recognize, in addition to any combination of features associated with a type of item, any combination of features described with respect to different items. All this is part of the overall disclosure of the application.

Aspects described above and other aspects, features and advantages of the invention may also be obtained from the example of an embodiment which will be described below with reference to the attached drawings. It is noted that the invention is not limited to this embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

1 is a schematic representation of a parallel hybrid powertrain according to the invention.

2 is a flowchart for schematically illustrating a method according to the invention.

3 is a flow chart illustrating the moments and speeds of the elements of a parallel hybrid powertrain according to the invention over time.

DETAILED DESCRIPTION OF THE DRAWINGS

1 shows a schematic representation of a parallel hybrid powertrain of a vehicle. In 1 a disconnect clutch K0 is arranged between an internal combustion engine VM and an electric machine EM, which can be used both as an electric motor and as a generator, wherein, following the electric machine, the drive train is continued to a driven axle of a vehicle.

The powertrain further includes a number of actuators A and sensors S that may be used to detect, on the one hand, a current operating state of one of the elements of the powertrain, such as the engine, the disconnect clutch, the electric machine or the output clutch, and the other Change operating state. The actuators and sensors are at least one Control unit ECU connected. The control unit of the powertrain in 1 has, on the one hand, an engine control unit MSG-ECU and, on the other hand, a transmission control unit TCU-ECU. Further, the control unit may include a brake controller Br-ECU and a battery controller BMS-ECU. The individual control units are interconnected via a bus system.

• – Im Schritt S1 wird in einem Anfangszustand, in dem ein Fahrzeug elektrisch fährt, d.h. der Verbrennungsmotor aus ist, die Trennkupplung offen ist, die Elektromaschine ein Vortriebsmoment leistet, wobei die Abtriebskupplung ein Vortriebsmoment ohne Schlupf überträgt, ein Signal erfasst, welches anzeigt, dass ein Fahrer Gas gibt, d.h. beschleunigen will.
• – In Schritt S2 wird das Abtriebskupplungs-Moment (M_K1) so gesteuert, dass Schlupf in der Abtriebskupplung erzeugt wird (d.h. Schlupf zwischen n_EM und n_K1). Sollte sich die Abtriebskupplung bereits im Schlupf oder Microschlupf befinden, kann direkt zu Schritt S3 gewechselt werden.
• – Sobald Schlupf in der Abtriebskupplung erkannt ist, wird in Schritt S3 das Abtriebskupplungs-Moment eingefroren, d.h. auf einem bestimmten Wert gehalten, der sich am aktuellen Fahrerwunschmoment orientiert.
• – In Schritt S4 wird die Elektromaschine mit einem hohen Moment (z.B. dem maximal möglichen Moment) angesteuert (z.B. M_EMmax), um den Schlupf in der Abtriebskupplung zu vergrößern und somit kinetische Energie aufzubauen (Ladevorgang).
• – In Schritt S5 erreicht die Drehzahl der Elektromaschine eine Schlupfschwelle, wobei diese so adaptiert (und max. begrenzt) wird, dass der Rotor der Elektromaschine genug kinetische Energie gespeichert hat, um den Verbrennungsmotor durch die Trennkupplung sicher auf „Selbstlaufdrehzahl" zu bringen (z.B. ca. > 300rpm).
• – Das Trennkupplungs-Moment (M_K0) wird in Schritt S6 idealerweise auf Maximum gesetzt (ähnlich zu einem Impulsstart) oder auf einen schlupfabhängigen Wert, bis die Drehzahl des Verbrennungsmotors die „Selbstlaufdrehzahl" erreicht.
• – In Schritt S7 kann sich der Verbrennungsmotor selbst befeuern und erzeugt ein hohes positives Moment, um sich selbst der Elektromaschine-Drehzahl anzunähern.
• – In Schritt S8 wird das Trennkupplungs-Moment abhängig vom Schlupf in der Abtriebskupplung zurückgefahren. Ab hier unterstützt das Trennkupplungs-Moment nur noch den Verbrennungsmotor-Hochlauf. Hauptaufgabe ist es, den Abtriebskupplungs-Schlupf positiv stabil zu halten.
• – In Schritt S9 kann der gewünschte Abtriebskupplungs-Schlupf von der Abtriebskupplungs-Steuerung so vorgegeben werden, dass eine spätere Synchronisierung begünstigt wird (ähnlich wie bei einer Zugrückschaltung). Der Vortrieb des Fahrzeugs wird weiterhin durch das Abtriebskupplung-Moment bestimmt.
• – Sobald die Drehzahl des Verbrennungsmotors und der Elektromaschine synchron sind, wird die Trennkupplung in Schritt S10 soweit geschlossen, dass kein Schlupf mehr zwischen Verbrennungsmotor und Elektromaschine auftritt (z.B. maximal mögliches Trennkupplungs-Moment). Der Abtriebskupplungs-Schlupf wird ab hier von den Momenten von Verbrennungsmotor und Elektromaschine bestimmt.
• – In Schritt S11 übernimmt die Abtriebskupplungs-Steuerung die Steuerung und synchronisiert die Drehzahlen des Verbrennungsmotors und der Elektromaschine mit der Ausgangsdrehzahl der Abtriebskupplung (n_K1). Das Vortriebsmoment wird weiterhin durch die Abtriebskupplung bestimmt.
• – In Schritt S12 wird der Schlupf in der Abtriebskupplung durch die Abtriebskupplungs-Steuerung abgebaut, sodass Drehzahlgleichheit herrscht. Ab hier wird der Vortrieb nicht mehr von der Abtriebskupplung bestimmt, sondern von der Antriebseinheit (Verbrennungsmotor, Elektromaschine oder beide in Kombination).

2 Fig. 3 is a flow chart showing in principle the steps of a method for controlling a parallel hybrid powertrain. It is noted that the described steps are main steps, which main steps can be differentiated and subdivided. In addition, further substeps may be provided between the main steps. Therefore, a sub-step is only mentioned if this step is important for understanding the principle of the method according to the invention.

• In step S1, in an initial state in which a vehicle is electrically running, ie, the engine is off, the disconnect clutch is open, the electric machine provides propulsive torque, and the output clutch transmits propulsion torque without slip, detecting a signal indicating that a driver gives gas, ie wants to accelerate.
• In step S2, the output clutch torque (M_K1) is controlled to generate slip in the output clutch (ie, slip between n_EM and n_K1). If the output clutch is already in slip or micro-slip, you can switch directly to step S3.
• - As soon as slip is detected in the output clutch, the output clutch torque is frozen in step S3, ie held at a certain value, which is based on the current driver's desired torque.
• - In step S4, the electric machine with a high torque (eg the maximum possible torque) is controlled (eg M_EMmax) to increase the slip in the output clutch and thus build up kinetic energy (charging).
• In step S5, the rotational speed of the electric machine reaches a slip threshold, whereby it is adapted (and limited) that the rotor of the electric machine has stored enough kinetic energy to safely bring the internal combustion engine through the separating clutch to "self-running speed" (eg about> 300rpm).
• The disconnect clutch torque (M_K0) is ideally set to maximum (similar to a pulse start) in step S6 or to a slip dependent value until the engine speed reaches the "self-running speed".
• In step S7, the internal combustion engine can self-fire and generate a high positive torque to approximate even the electric machine speed.
• - In step S8, the clutch torque is reduced depending on the slip in the output clutch. From here, the disconnect torque only supports the engine run-up. The main task is to keep the output clutch slip positively stable.
• In step S9, the desired output clutch slip may be predetermined by the output clutch controller so as to favor later synchronization (similar to a train downshift). The propulsion of the vehicle is further determined by the output clutch torque.
• - Once the speed of the engine and the electric machine are synchronized, the separating clutch is closed in step S10 so far that no more slip occurs between the engine and electric machine (eg maximum possible clutch torque). The output clutch slip is determined from here by the moments of internal combustion engine and electric machine.
• In step S11, the output clutch controller accepts the control and synchronizes the rotational speeds of the internal combustion engine and the electric machine with the output speed of the output clutch (n_K1). The propulsion torque is still determined by the output clutch.
• In step S12, the slip in the output clutch is reduced by the output clutch control, so that speed equality prevails. From here, the propulsion is no longer determined by the output clutch, but by the drive unit (internal combustion engine, electric machine or both in combination).

It is noted that the electric machine can be used by the active engine as a generator for generating power and charging a battery.

In 3 the process according to the invention is presented in another way. In this flowchart, the rotational speeds n and moments M of the electric machine EM, the internal combustion engine VM, the output clutch K1 and the separating clutch K0 over the time t are shown. Furthermore, the moment M M _Soll lying on the output _{clutch is} drawn.

In the period between the times 1 and 8, the actual start of the engine takes place. In the period between times 1 and 3, the start time can be further shortened if "micro-slip" is present. The output clutch K1 is in the period between the times 2 and 9 in the slip.

While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustrations and descriptions are to be considered illustrative or exemplary only and not restrictive. The invention is not limited to the disclosed embodiment. Other variations of the disclosed embodiment may be understood and accomplished by one of ordinary skill in the art of practicing the claimed invention, from the study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" does not exclude a plurality.

The mere fact that individual features are mentioned in different dependent claims is not intended to mean that a combination of these features can not be used to advantage. The reference numerals in the claims are not intended to limit the scope thereof.

Claims (8)

A parallel hybrid powertrain comprising: an engine (VM), an electric machine (EM), a disconnect clutch (K0) disposed between an output side of the engine and a drive side of the electric machine, an output clutch (K1) disposed on an output side of the electric machine is arranged, and a control unit (ECU) for controlling the drive train, wherein, when the engine is off, the disconnect clutch is open, the electric machine abgiebt a propulsion torque (M _EM ) and thus the output clutch, the torque M _is applied, and a trigger signal is present, the control unit (ECU) the separating clutch (K0) controls such that it connects the internal combustion engine with the electric machine until the internal combustion engine reaches a self-running speed, that then at least partially separates the internal combustion engine from the electric machine until the internal combustion engine after a self-ignition Target speed reached ht, and that this then connects the internal combustion engine with the electric machine such that the internal combustion engine outputs a propulsion torque via the output clutch. The parallel hybrid powertrain of claim 1, wherein the control unit further controls the electric machine (EM) and the output clutch (K1) to slip in the output clutch and to maintain the propulsion torque (M _soll ) constant. Parallel hybrid powertrain according to claim 1 or 2, wherein the control unit, the output torque (M _EM ) of the electric machine (EM) to a value less than or equal to a maximum (M _EMmax ) controls before the _separating clutch (K0) the internal combustion engine for the first time with the Electric machine connects. A method of controlling a parallel hybrid powertrain having an internal combustion engine (VM), an electric machine (EM), a disconnect clutch (K0) between the internal combustion engine and the electric machine, an output clutch (K1), and a control unit (ECU), the method comprising the steps Detecting a triggering signal, in a state in which the internal combustion engine (VM) is off, the disconnect clutch (K0) is open, and the electric machine (EM) a propulsion torque (M _EM ) abgiebt and thus the output clutch, the torque M _is applied at least partially closing the disconnect clutch until the engine reaches a self-running speed, partially opening the disconnect clutch in response to the speed of the engine, closing the disconnect clutch when the engine reaches a predetermined speed. The method of claim 4, further comprising the step of: Monitoring and maintaining a positive slip of the output clutch (K1). The method of claim 4 or 5, further comprising the step of: Controlling the electric machine (EM) to a maximum torque before the disconnect clutch (K0) is first closed. A computer program executing all steps of a method according to any one of claims 4-7 when executed on a parallel hybrid drive train control unit according to any one of claims 1-3. A computer program product with program code stored on a machine-readable medium for carrying out the method according to any one of claims 4-6, when the program is executed on a control unit of a parallel hybrid drive train according to any one of claims 1-3.

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