DE102011075216A1 - Method for starting internal combustion engine of hybrid drive train of e.g. motor vehicle, involves connecting crankshaft of internal combustion engine with electrical machine through clutch - Google Patents

Abstract

The method involves providing driving power to internal combustion engine (16) using electric machine (14). The fuel is injected into cylinder of piston-cylinder arrangement of internal combustion engine. The fuel-oxygen mixture in the cylinder is ignited. A crankshaft (20) of internal combustion engine is connected with electrical machine through clutch (26). The internal combustion engine is started directly by engaging the clutch with electric machine. Independent claims are included for the following: (1) control unit for starting internal combustion engine; and (2) motor vehicle drive train.

Description

The invention relates to a method for starting an internal combustion engine of a hybrid drive, in particular a direct injection internal combustion engine, wherein the hybrid drive, the internal combustion engine and an electric machine for providing drive power, wherein the internal combustion engine by means of a direct start by injecting fuel into at least one cylinder of a piston-cylinder arrangement Internal combustion engine and ignition of a resultant in the cylinder fuel-oxygen mixture is started, wherein a crankshaft of the internal combustion engine by means of a coupling with the electric machine is connectable.

Further, the present invention relates to a control unit for starting an internal combustion engine of a hybrid drive, wherein the hybrid drive comprises the internal combustion engine and an electric machine for providing drive power, wherein the control unit is adapted to carry out the above-mentioned method.

Finally, the present invention relates to a motor vehicle drive train with an internal combustion engine and an electric machine, which form a hybrid drive, wherein a crankshaft of the internal combustion engine is connectable by means of a coupling with the electric machine, and with a control unit of the type mentioned above.

State of the art

In the field of automotive drive technology, it is well known to use an electric machine together with an internal combustion engine as a hybrid drive. The electric machine serves to provide drive power and to convert kinetic energy into electrical energy in recuperation to store them in a battery of the motor vehicle. If the electric power stored in the battery for driving the motor vehicle is no longer sufficient or falls below a predefined value, the internal combustion engine is started to provide additional drive power and to charge the battery by the electric machine.

In hybrid vehicles, it is necessary during electric driving to start the engine without any noticeable effect on the drive torque required by the vehicle. For this purpose, for example, offers a so-called direct start.

For starting an internal combustion engine, in particular a direct injection internal combustion engine, it is for example from the DE 103 51 891 A1 It is known to carry out a direct start, in which fuel is injected into the cylinder in a certain standstill position of a piston of a cylinder and the resulting fuel-air mixture is ignited to drive the piston in the cylinder. In this case, just before the direct start of the corresponding piston / cylinder can be moved in a reverse direction in order to achieve an optimal position shortly before an ignition or dead center, so that the restart can be done safely by the appropriate ignition.

For example, it is conceivable to start an internal combustion engine by means of a direct start, wherein first fuel is injected into a cylinder and this is driven by ignition against the drive direction to achieve compression of a fuel-air mixture in another cylinder and the crankshaft after ignition to drive the second cylinder in a drive direction.

The disadvantage here is that the cylinder in which the first ignition was completed, can not be ignited in the forward movement, since there are only combustion gases of the first ignition in the combustion chamber. Since the piston must be moved beyond this ignition point without the corresponding ignition, in this way the internal combustion engine can not be started reliably.

Disclosure of the invention

According to the method mentioned above is improved by the fact that the direct start is supported by closing the clutch by the electric machine. In this case, a motor shaft of the electric machine 14 rotated during closing to transmit torque to the crankshaft.

Further, according to the present invention, there is provided a control unit for starting an internal combustion engine of a hybrid drive, wherein the hybrid drive comprises the internal combustion engine and an electric machine for providing driving power, and wherein the control unit is adapted to carry out the above-mentioned method.

Finally, the present invention provides a motor vehicle drive train with an internal combustion engine and an electric machine, which together form a hybrid drive, wherein a crankshaft of the internal combustion engine by means of a clutch with the electric Machine is connectable, and the drive train has a control unit of the type mentioned above.

By the present invention, a direct start during the electric drive by closing the clutch can be supported without noticeable influence on the drive torque.

The inventive method for starting the internal combustion engine of a hybrid drive is used to start an internal combustion engine during the purely electric drive to use the internal combustion engine as an additional prime mover or to switch to the pure combustion engine operation. It is driven by injecting fuel into at least one cylinder and igniting this fuel-air mixture and can be supported by short-term closing of the clutch or by short-term operation of the clutch in the slip individually and demand-oriented, such a short-term and / or minor discharge of drive power does not cause a significant reduction in the drive torque provided by the electric machine.

As a result, the advantages of the hybrid drive and the direct start can be used in the connection of the internal combustion engine, whereby the ride comfort of the hybrid drive can be increased.

Furthermore, for a necessary start of the internal combustion engine no torque reserve of the electric machine must be maintained or only to a much smaller extent than would be necessary for a conventional start, or if the entire direct start would be supported by the electric machine with torque.

In the present case, a direct start is understood to mean the startup of an internal combustion engine in which a fuel-oxygen mixture in a cylinder is ignited without a complete compression stroke of the cylinder being passed through.

Preferably, the internal combustion engine is started during an electrical operation or drive of the hybrid drive, whereby the internal combustion engine can be started by simply deriving torque or speed of the electric machine.

Preferably, the electric machine drives the crankshaft in a forward rotation.

As a result, the rotation of the electric machine can be used directly and the torque of the electric machine can be superimposed on the torque of the internal combustion engine developed during the direct start.

It is further preferred if the electric machine drives the crankshaft after a first ignition for the direct start.

As a result, only a small additional torque from the electric machine is necessary because a torque is already exerted by the first ignition of the internal combustion engine to the crankshaft.

It is also of particular advantage when the electric machine drives the crankshaft after a second ignition in a second cylinder.

As a result, an even greater torque can be supplied to the crankshaft from the internal combustion engine through the direct start, as a result of which the additional torque required by the electric machine is reduced.

In this case, it is preferred if the electric machine assists the direct start during the crossing of a top dead center of a piston of a cylinder used for the direct start.

As a result, the internal combustion engine is assisted in a critical moment in which the speed of the crankshaft and the applied torque is reduced.

In this case, it is preferred if the electric machine assists the direct start during the top dead center of the piston of the cylinder in which the first ignition has taken place.

As a result, a suspension of the ignition of the cylinder in which the first ignition has occurred, be overcome.

It is further preferred if the first ignition in the first cylinder causes a reverse rotation of the crankshaft and thereby a compression in a second cylinder is effected, in which a second ignition takes place.

This can be a particularly fast and effective direct start. It is particularly preferred if the second ignition causes a forward rotation of the crankshaft and the forward rotation is supported by closing the clutch by the electric machine.

As a result, the forward-rotating crankshaft can cause a compression in another cylinder, thus ensuring a reliable start.

It is particularly advantageous if the forward rotation is supported during the crossing of the top dead center of the first cylinder.

As a result, a non-ignition of the first cylinder can be bridged and thus still a reliable direct start can be made possible.

Brief description of the drawings

1 schematically shows a motor vehicle with a hybrid powertrain having an internal combustion engine and an electric machine;

2a to 2d show in schematic form components of the internal combustion engine during different times of a direct start; and

3 shows a diagram for explaining the crankshaft position, the engine speed and the compression in two cylinders of the internal combustion engine.

Embodiments of the invention

In 1 a motor vehicle is shown schematically and generally with 10 designated. The car 10 has a drive train 12 on, in the present case an electric machine 14 and an internal combustion engine 16 for providing drive power. The electric machine 14 and the internal combustion engine 16 form in this case a parallel hybrid drive. The powertrain 12 serves to drive driven wheels 18L, 18R of the vehicle 10 ,

The internal combustion engine 16 is over a crankshaft 20 with the electric machine 14 connected or connectable, wherein the internal combustion engine 16 and the electric machine 14 on an output shaft 22 provide a torque t that rotates at an adjustable speed. The output shaft 22 is with a gear unit 24 connected to transmit the torque t to the driven wheels 18R, 18L. The crankshaft 20 and the output shaft 22 each have a coupling in the present case 26 . 28 on to the internal combustion engine 16 with the electric machine 14 or the electric machine 14 with the gear unit 24 connect to.

The crankshaft 20 is by means of the coupling 26 with a rotor of the electric machine 14 connected or connectable to a speed or torque to the electric machine 14 transferred to. The rotor of the electric machine 14 is with the output shaft 22 connected to the torque t on the gear unit 24 transferred to. The torque t is thereby the sum of that of the internal combustion engine 16 and the electric machine 14 provided individual torques.

In motor operation, the electric machine generates 14 a drive torque that drives the engine 16 , for example in an acceleration phase, supported. In regenerative or recuperation the electric machine generates 14 electrical energy, which is generally the vehicle 10 is made available.

The internal combustion engine 16 is through a fuel tank 30 fueled.

The electric machine 14 can be single-phase or multi-phase and is by means of power electronics 32 or an inverter 32 controlled and supplied with electrical energy. The power electronics 32 is with a power supply unit 34 like a DC power supply (eg accumulator or battery) 34 of the vehicle 10 connected and serves to one from the power supply unit 34 supplied voltage in alternating current in general or in a number of phase currents for the phases of the electric machine 14 transform judge. The power supply unit 34 is with a battery control unit 36 connected, which is adapted to the power supply of the electric machine 14 via the power electronics 32 and the state of charge of the power supply unit 34 to control. The power electronics 32 is further adapted to the recuperation operation of the electric machine 14 the power supply unit 34 through by the electric machine 14 to charge generated electrical energy.

The internal combustion engine 16 is further provided with a control unit 38 connected, the injection valves and spark plugs of the internal combustion engine 16 controls and is designed to a total, a direct start of the engine 16 initiate or control. The control unit 38 is also adapted to briefly start the clutch for a direct start 26 close and thereby the crankshaft 20 of the internal combustion engine 16 drive.

In 2a to 2d are for clarity only two cylinders of the internal combustion engine 16 represented, which are relevant to the explanation of the method according to the invention. In 2a are the cylinders 40 . 42 generally shown, each having a piston 44 . 46 in a middle position. Furthermore, in 2a a rotation of the crankshaft 20 shown schematically. In the in 2a shown center position of the piston 44 . 46 is a Direct start not optimally possible. To initiate a corresponding optimal direct start, one of the pistons must 44 . 46 located near a top dead center or an upper ignition point. To the pistons 44 . 46 to move in such a position, the crankshaft 20 rotated in a forward direction, as in 48 is shown. An angular position of the crankshaft 20 is in the 2a -D each by an arrow 49 indicated.

To the piston 44 of the cylinder 40 to move to a position near top dead center and thereby enable an optimal direct start, the crankshaft 20 by briefly closing the clutch 26 be rotated.

In 2 B is the piston 44 of the cylinder 40 has been moved to a position near top dead center, wherein the piston 46 has been moved to a lower opposite position. This is the crankshaft 20 only rotated by less than 90 °, as indicated by the different angular positions of the arrow 49 in the 2a and 2 B is indicated. In this position of the cylinder 44 is a direct start over the ignition of a fuel-air mixture in the cylinder 40 possible.

The direct start is made by injecting fuel into the cylinder, not shown here 40 and subsequent ignition of the resulting fuel-air mixture or fuel-oxygen mixture.

In 2c the ignition of the fuel-oxygen mixture is shown schematically. This combustion causes the piston 44 in the cylinder 40 moved down and the crankshaft 20 driven in a direction opposite to the drive direction, as in 50 is shown. Through this rotation of the crankshaft 20 becomes the piston 46 in the cylinder 42 moved upward, causing a compression of a fuel-oxygen mixture in the cylinder 42 is effected.

When the top dead center of the piston 46 in the cylinder 42 is reached, the compressed fuel-oxygen mixture is ignited accordingly, causing the piston 46 moved down and reversing the direction of rotation of the crankshaft 20 is effected. This downward movement and the reversal of the direction of rotation of the crankshaft 20 is together with the ignition in 2d shown schematically. By the movement of the crankshaft 20 in the drive direction 48 becomes the piston 44 moved in the direction of top dead center. A compression and a corresponding ignition are in the cylinder 40 not possible in this work cycle, as in the cylinder 40 only residual gas 51 or burnt mixture 51 from the previous ignition.

In an internal combustion engine with more than two cylinders, a corresponding ignition is then initiated in another cylinder with prior compression.

So that the piston 44 can overcome the top dead center, as it is in 2d is shown, and thus the direct start can be performed reliably, must briefly overcome the top dead center, the internal combustion engine 16 with an additional torque via the crankshaft 20 are driven. This is done by momentarily closing the clutch 26 , resulting in a short time or a slight torque from the electric machine 14 on the crankshaft 20 is transmitted. As a result, a drive torque to the crankshaft without noticeable effects 20 be transmitted to allow a reliable direct start.

In 3 are a crankshaft position, a speed of the internal combustion engine 16 , ie the crankshaft speed, and a combustion chamber pressure over time during a direct start according to the invention shown schematically.

In 3 are the crankshaft position generally with 52 and the engine speed generally with 54 designated. The respective combustion chamber pressure in the cylinder 40 is by a dashed line, in the cylinder 42 represented by a dotted line and in another cylinder by a dashed line.

How out 3 can be seen, the speed up to a time t0 = 0, and the crankshaft position 52 stays unchanged. At time t0, fuel enters the cylinder 40 injected and ignited, leaving a combustion chamber pressure in the cylinder 40 rises, as with 56 is shown. This will cause the backward movement 50 the crankshaft 20 causes. The crankshaft position 52 decreases accordingly in this illustration, which simultaneously shows a rotation against the drive direction. Simultaneously with the backward movement 50 takes a combustion chamber pressure in the cylinder 42 too, as with 58 is shown. At time t1, the compressed fuel-oxygen mixture in the cylinder 42 ignited, causing the combustion chamber pressure in the cylinder 42 rises sharply, as is the case with 60 is shown. The rotation direction reversal of the crankshaft caused thereby 20 is apparent from the change in crankshaft position, as with 62 is shown. The speed 54 the crankshaft 20 increases with a time delay abruptly, in the drive direction 48 ,

By the rotation of the crankshaft 20 in the drive direction 48 will be a compression in the cylinder 40 causes, as with 64 is shown. This compression occurs, however, without combustion, since in the cylinder 40 only residual gas 51 located. The piston 44 passes through the top dead center at time t2, but with the lack of ignition, the speed decreases after passing through the top dead center again.

At the time t3, the clutch 26 For a period delta t closed to an excessive drop in speed 54 To prevent and cause a compression of another cylinder, as in 66 is shown. By closing the clutch 26 becomes the rotating shaft of the electric machine 14 with the crankshaft 20 connected, whereby this is rotated or driven accordingly.

By a further ignition of another cylinder at t4, the speed of the crankshaft increases 20 strong, whereby the direct start is essentially complete.

By the short-term closing of the clutch 26 can thus a strong drop in speed 54 after passing through the top dead center of the piston 42 be prevented and thus initiated a further compression of a cylinder. This is due to an imperceptible redirecting torque to the crankshaft 20 a reliable direct start of the internal combustion engine 16 possible.

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 10351891 A1 [0006]

Claims (12)

Method for starting an internal combustion engine ( 16 ) of a hybrid drive, in particular an internal combustion engine ( 16 ) with direct injection, wherein the hybrid drive the internal combustion engine ( 16 ) and an electric machine ( 14 ) for providing drive power, wherein the internal combustion engine ( 16 ) by means of a direct start by injecting fuel into at least one cylinder ( 40 . 42 ) a piston-cylinder arrangement of the internal combustion engine ( 16 ) and igniting a thereby in the cylinder ( 40 . 42 ) fuel-oxygen mixture is started, wherein a crankshaft ( 20 ) of the internal combustion engine ( 16 ) by means of a coupling ( 26 ) with the electric machine ( 14 ) is connectable, characterized in that the direct start by closing the clutch ( 26 ) by the electric machine ( 14 ) is supported. Method according to claim 1, wherein the internal combustion engine ( 16 ) is started during an electric operation of the hybrid drive. Method according to claim 1 or 2, wherein the electric machine ( 14 ) the crankshaft ( 20 ) in a forward rotation ( 48 ) drives. Method according to one of claims 1 to 3, wherein the electric machine ( 14 ) the crankshaft ( 20 ) drives after a first ignition for the direct start. Method according to one of claims 1 to 4, wherein the electric machine ( 14 ) the crankshaft ( 20 ) after a second ignition in a second cylinder ( 42 ) drives. Method according to one of claims 1 to 5, wherein the electric machine ( 14 ) the direct start during the crossing of a top dead center of a piston ( 44 . 46 ) of a cylinder used for the direct start ( 40 . 42 ) supported. Method according to claim 6, wherein the electric machine ( 14 ) the direct start during the top dead center of the piston ( 44 ) of the cylinder ( 40 ) in which the first ignition took place. Method according to one of claims 1 to 4, wherein the first ignition in the first cylinder ( 40 ) a reverse rotation ( 50 ) of the crankshaft ( 20 ) and thereby a compression in a second cylinder ( 42 ) is effected, in which a second ignition takes place. The method of claim 8, wherein the second ignition is a forward rotation ( 48 ) of the crankshaft ( 20 ) and the forward rotation ( 48 ) by closing the clutch ( 26 ) by the electric machine ( 14 ) is supported. Method according to claim 9, wherein the forward rotation ( 48 ) during the top dead center of the first cylinder ( 40 ) is supported. Control unit ( 38 ) for starting an internal combustion engine ( 16 ) of a hybrid drive, wherein the hybrid drive the internal combustion engine ( 16 ) and an electric machine ( 14 ) for providing drive power, wherein the control unit ( 38 ) is adapted to carry out the method according to one of claims 1 to 10. Motor vehicle drive train ( 12 ) with an internal combustion engine ( 16 ) and an electric machine ( 14 ), which form a hybrid drive, wherein a crankshaft ( 20 ) of the internal combustion engine ( 16 ) by means of a coupling ( 26 ) with the electric machine ( 14 ) is connectable, and with a control unit ( 38 ) according to claim 11.

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