DE102010036132A1 - Method for retarding motor vehicle with parallel-hybrid power train, involves controlling rotation speed of electric machine based on brake pedal position, before closing separation clutch during drive of vehicle - Google Patents

Abstract

The method involves obtaining target delay of motor vehicle, and calculating delay threshold value. The driving of motor vehicle is continued with separation clutch (22) in open/close state, when target delay is smaller/greater than delay threshold value, respectively. The rotation speed of electric machine (14) is controlled based on position of brake pedal (30), before closing the separation clutch.

Description

Field of the invention

• – Vorgabe einer am Abtrieb zu realisierenden Soll-Verzögerung,
• – Berechnen eines Verzögerungsgrenzwertes
• – Vergleichen des Verzögerungsgrenzwertes mit der Soll-Verzögerung
• – Fortsetzen des Fahrbetriebs mit geöffneter Trennkupplung, falls die Soll-Verzögerung kleiner oder gleich dem Verzögerungsgrenzwert ist, und Fortsetzen des Fahrbetriebs mit geschlossener Trennkupplung, falls die Soll-Verzögerung größer als der Verzögerungsgrenzwert ist.

The invention relates to a method for decelerating a vehicle while driving with a parallel hybrid drive train, which has an output side coupled to an output electric machine, an electric machine upstream and coupled by means of a switchable clutch internal combustion engine and a control device for controlling and / or regulating the electric machine and the internal combustion engine,
comprising the following steps:

• Specification of a target deceleration to be realized at the output,
• - Calculate a delay limit value
• - Compare the delay limit with the target delay
• - Continuing the driving operation with the disconnect clutch open, if the target deceleration is less than or equal to the deceleration limit value, and continuing the traction clutch closed operation, if the target deceleration is greater than the deceleration limit value.

State of the art

Such a method is known from the DE 10 2007 008 477 A1 ,

Parallel hybrid powertrains for motor vehicles are well known. They regularly comprise an electric machine, which is coupled in particular via a transmission with an output of the motor vehicle. Before the electric machine, an internal combustion engine is arranged, which can be connected by means of a switchable separating clutch, if necessary, with the rotor of the electric machine or separated from it. This allows coupled driving modes in which both the internal combustion engine and the electric machine provide a drive torque, as well as at least a purely electric driving mode in which the internal combustion engine is disconnected from the rest of the drive train due to the open disconnect clutch and only the electric machine provides a drive torque.

To brake, d. H. For decelerating a motor vehicle from driving several basic methods are known. Classically, the deceleration takes place via the driving brake, whereby kinetic energy is converted by friction to brake discs into heat energy. Energetically cheaper is the recuperative braking in which the electric machine is operated as a generator and exerts a negative braking torque on the drive train. Finally, the deceleration by means of engine brake is known, d. H. the drag torque of the non-fueled internal combustion engine is used for deceleration.

From the above, generic document a combined braking method for decelerating the motor vehicle is known. If the driver lets go of the accelerator pedal and thus indicates his desire for deceleration, the control device calculates a set braking torque from current driving parameters and calculates further as limit braking torque that braking torque which can be applied solely by generator operation of the electric machine. If the setpoint braking torque is less than or equal to the calculated limit braking torque, which means that the setpoint braking torque can be applied solely by the electric machine, then the driving operation is continued with the separating clutch open, i. H. that the clutch remains open, if it was previously opened, or opened, if it was previously closed. In contrast, if the target braking torque is greater than the calculated limit braking torque, which means that the desired delay can not be applied solely by the electric machine, then the driving operation is continued with the clutch disconnected, d. H. the disconnect clutch remains closed if it was previously closed or closed if it was previously open. In other words, this means that in the case of a strong deceleration, the desired braking torque is generated as the sum of the negative torque contributions of the electric machine and the internal combustion engine, while small delays are accomplished solely by the electric machine. As a result, the Rekuperationsleistung is maximized.

A problem of the sudden coupling of the internal combustion engine is the associated torque jump on the drive train. This can be unpleasantly perceived by the vehicle occupants as a jerk. To remedy this problem, the cited document proposes a speed adjustment by turning up the internal combustion engine before closing the separating clutch. The required fuel consumption must be considered disadvantageous.

task

It is the object of the present invention to develop a generic method such that a lower fuel consumption is achieved.

Presentation of the invention

This object is achieved in conjunction with the features of the preamble of claim 1, characterized in that the control device switches before closing the clutch from a torque control of the electric machine on the speed control, so that an actual speed of the electric machine follows a curve of a target speed which is calculated by the controller based on a measured brake pedal position.

Preferred embodiments of the invention are the subject of the dependent claims.

The basic idea of the invention is to switch over the control of the electric machine from a torque control to a speed control before coupling the internal combustion engine. A well-designed speed control is able to correct even large torque jumps, which act as disturbances on the drive train, and adjust the actual speed curve well to a predetermined target speed curve. The relevant interference here is the taking place when closing the separating clutch acting on the drive train with the drag torque of the internal combustion engine. The basis for the calculation of the desired deceleration in the present invention is a brake pedal position measured by means of suitable sensors.

To improve the speed control can be provided in a preferred embodiment of the invention that the control device during a switching position change of the separating clutch, d. H. during the opening or closing of the separating clutch, the clutch torque curve can be included as a pilot control variable in the calculation of the course of the target speed. Thus, the measured brake pedal position and the clutch torque serve as pilot control quantities for the desired deceleration calculated as the desired speed curve.

If the closing of the separating clutch is completed, as provided in a favorable development of the invention, the drag torque of the internal combustion engine can be included as a pilot control variable in the calculation of the course of the target rotational speed. This means in other words that when the clutch is closed, the drag torque of the internal combustion engine, namely its course over a crankshaft revolution and its change with the rotational speed, together with the measured brake pedal position is used as a pilot control variable for the speed control of the electric machine.

The inventive method is particularly suitable for realizing a deceleration of the motor vehicle from a purely electric driving mode, d. H. from a driving mode with opened disconnect clutch. In modern hybrid vehicles not only low but also medium speeds can be covered in this driving mode. Correspondingly large are the delay requests of the driver occurring in this driving mode. In contrast to the generic state of the art, which had to maximize the recuperation performance in the eye, it is an important concern of the present invention to use as often as possible the drag torque of the internal combustion engine to decelerate. The deceleration limit is therefore preferably calculated as the deceleration on the basis of currently applied driving parameters, which would supply the non-fueled internal combustion engine with these driving parameters if the separating clutch were closed. In other words, the currently realizable drag torque of the internal combustion engine is preferably calculated. For target delays below this limit closing the disconnect clutch is out of the question, since the delay realized with it would then be above the requested. In all other cases, however, the deceleration contribution by the drag torque of the internal combustion engine is utilized by closing the disconnect clutch, even if the requested deceleration, i. H. the target delay, even alone by the regenerative electric machine could be achieved. Although this design reduces the achievable recuperation performance; On the other hand, however, the rotation of the internal combustion engine provides advantages that would not be available without the present invention.

Thus, the co-rotation of the coupled internal combustion engine leads to their heating by friction. This has advantages when the vehicle is to be operated at a later time in the coupled driving mode, that is, when the internal combustion engine is started to provide positive torque to the drive train. The same applies if the internal combustion engine off and the vehicle is operated in the purely electric driving mode, with a cooling of the internal combustion engine is prevented. A preheated or kept warm internal combustion engine works namely in terms of fuel consumption and emissions significantly cheaper than a cold machine. In other words, according to the invention, the desired "killing" kinetic energy of the motor vehicle for preheating the internal combustion engine is used. In an overall assessment of fuel consumption and emissions, this is more favorable than the unilateral maximization of recuperation performance. It can even acceptable, the internal combustion engine, while being entrained with the clutch disconnected, to supply slightly with fuel to accelerate their warming. Alternatively, the heating during deceleration may be facilitated by keeping the valves closed, assuming appropriate valve control, so that no heat is lost through gas exchange in the cylinder. A combination is also conceivable, with heat being emitted only specifically to the exhaust gas tract, so that the exhaust gases receive a more favorable in terms of emission protection temperature.

Further features and advantages of the invention will become apparent from the following, specific description and the drawings.

Short description of the drawing

It shows

1 : a schematic representation of a parallel hybrid powertrain.

Detailed description of preferred embodiments

1 shows a parallel hybrid powertrain 10 with an internal combustion engine 12 an electric machine 14 and a downforce not shown in detail 16 , The electric machine 14 is over its output shaft 18 with the downforce 16 connected. The input shaft 20 the electric machine 14 is with the output of a disconnect clutch 22 connected. The input side is the separating clutch 22 with the crankshaft 24 the internal combustion engine 12 connected.

In the preferred embodiment of the invention, the drive train 10 initially operated in the purely electric driving mode, ie the separating clutch 22 it is open. Alone the electric machine 14 delivers a positive torque to the output 16 , In this driving mode can be realized in modern hybrid vehicles low and medium speeds. In particular, vehicles are operated immediately after the cold start in city operation, for example until reaching the highway preferably in the purely electric driving mode. Typically, the electric machine 14 while torque-controlled, with the downforce 16 To be dispensed moment from a control device 26 from a measured position of an accelerator pedal 28 is calculated. A desire for delay signals the driver by pressing a brake pedal 30 whose position is measured by suitable sensors and also passed to the control device. This calculates the desired deceleration from the brake pedal position, ie typically initially a desired braking torque. In addition, the control device calculates the braking torque that the internal combustion engine 12 would deliver if it were dragged without fuel at the given driving parameters (eg temperature, speed ect.), ie when the clutch 22 would be closed.

In the case that the requested braking torque, ie the desired braking torque, smaller than the hypothetical drag torque of the internal combustion engine 12 is, it remains in the moment-controlled operation of the electric machine 14 , which is then operated according to generator to generate the requested braking torque. Otherwise, ie when the requested braking torque is greater than the hypothetical drag torque of the internal combustion engine 12 , the requested braking torque is "converted" into a desired speed curve and the control of the electric machine 14 switched to a speed control mode. Subsequently, the separating clutch 22 closed, whereby the hitherto hypothetical drag torque of the internal combustion engine 12 is realized. The resulting torque jump is compensated by the speed control, wherein the portion of the deceleration, which exceeds that of the internal combustion engine 12 delivered contribution goes through appropriate generator operation of the electric machine 14 is contributed.

As pilot control variables for this speed control of the electric machine are used during the closing operation of the separating clutch 22 the position of the brake pedal 30 as well as the current clutch torque of the separating clutch 22 , After closing the separating clutch 22 serve as Vorsteuergrößen the position of the brake pedal 30 as well as the drag torque, preferably both its actual course and its change with the speed.

This ensures that, whenever possible, the drag torque of the internal combustion engine 12 is used to support the deceleration of the motor vehicle, which indeed reduces the maximum achievable recuperation, but for preheating or keeping hot the internal combustion engine 12 ensures the purely electrical operation of the motor vehicle.

Of course, the embodiments discussed in the specific description and shown in the figure represent only illustrative embodiments of the present invention. In the light of the disclosure herein, those skilled in the art will be offered a wide range of possible variations.

LIST OF REFERENCE NUMBERS

10

powertrain

12

Internal combustion engine

14

electric machine

16

drive

18

Output shaft of 14

20

Input shaft of 14

22

separating clutch

24

Crankshaft of 12

26

control unit

28

accelerator

30

brake pedal

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007008477 A1 [0002]

Claims (6)

Method for decelerating a motor vehicle in running mode with a parallel hybrid drive train ( 10 ), which has an output side with an output ( 16 ) coupled electric machine ( 14 ), one of the electrical machine ( 14 ) upstream and by means of a switchable disconnect clutch ( 22 ) coupled internal combustion engine ( 12 ) as well as a control device ( 26 ) for controlling and / or regulating the electric machine ( 14 ) and the internal combustion engine ( 12 ), comprising the following steps: - specification of an output ( 16 ) to be realized target deceleration, - calculating a deceleration limit value, - comparing the deceleration limit value with the target deceleration, - continuing the traction operation with the decoupler clutch open ( 22 ), if the desired deceleration is less than or equal to the deceleration limit, and resuming driving with closed ( 22 ) Disconnect clutch, if the desired deceleration is greater than the deceleration limit value, characterized in that the control device ( 26 ) before closing the separating clutch ( 22 ) of a torque control of the electric machine ( 14 ) Switches to the speed control, so that an actual speed of the electric machine ( 14 ) follows a course of a target rotational speed, which is determined by the control device ( 26 ) is calculated based on a measured brake pedal position. Method according to claim 1, characterized in that the control device ( 26 ) during a switching position change of the separating clutch ( 22 ) whose clutch torque curve can be incorporated as a pilot control variable in the calculation of the course of the target speed. Method according to one of the preceding claims, characterized in that the control device ( 26 ) with the disconnect clutch ( 22 ) a course of a drag torque of the internal combustion engine ( 12 ) can be included as a pilot control variable in the calculation of the course of the target speed. Method according to one of the preceding claims, characterized in that it for deceleration of the motor vehicle from a purely electric driving mode with open disconnect clutch ( 22 ) is used. Method according to Claim 4, characterized in that the deceleration limit value calculated is that deceleration on the basis of currently applied driving parameters which the non-fueled internal combustion engine ( 12 ) at these driving parameters, when the disconnect clutch ( 22 ) would be closed. Method according to one of the preceding claims, characterized in that valves of the internal combustion engine ( 12 ) during a deceleration operation with closed disconnect clutch ( 22 ) stay closed.

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