WO2011160744A1

WO2011160744A1 - Method and arrangement for starting an internal combustion engine

Info

Publication number: WO2011160744A1
Application number: PCT/EP2011/002336
Authority: WO
Inventors: Dieter Anshelm
Original assignee: Daimler Ag
Priority date: 2010-06-26
Filing date: 2011-05-11
Publication date: 2011-12-29
Also published as: DE102010025183A1

Abstract

The invention relates to a method for starting an internal combustion engine of a motor vehicle by means of an electric machine, wherein the method comprises the following steps in order to increase the service life of a hydrodynamic plain bearing: a first step (12), in which a rotational speed increase of a crank shaft of the internal combustion engine up to a plateau rotational speed (13) of the crankshaft by means of the electric machine occurs, a second step (14), in which the rotational speed of the crankshaft is maintained within a range around the plateau speed (13) for a first duration (15) or a rotational speed increase by the electric machine that is significantly slowed compared to the first step (12) and a third step (16) occurs for the first duration (15), and the third step (16), in which the rotational speed of the crankshaft is further increased after the first duration (15) has expired.

Description

Daimler AG

Method and device for starting an internal combustion engine

The invention relates to a method for starting an internal combustion engine according to the preamble of claim 1 and an apparatus for starting a

Internal combustion engine according to the preamble of claim 8.

It is known that electric motors and generators, or generally electrical machines, can be operated with speed control by means of power electronics. It has also been known for some time that

Internal combustion engines can be started speed-controlled by means of power electronics and an electric machine.

In the lecture "hybrid drive for city buses" (Martin Koellner: "hybrid drive for city buses", VDI conference gearboxes in commercial vehicles, Friedrichshafen, 22 and 23 June 2010, slide 15) discloses a method for starting an internal combustion engine by means of a generator, in which in a first start phase a

Speed control of the generator is carried out in a second start phase, a current control of a stator. From the second start phase results in an irregular

Speed curve, which is heavily affected by operating conditions such as one

Motor temperature depends. After completion of the start by the generator, fuel injection into the engine begins. The aim was to check whether the presented method compared to a conventional engine start with the help of a 24 V starter no major speed irregularities occur. A comparison of speed curves at the start with a 24 V starter on the one hand and in the process start on the other hand showed about the same degree

Speed fluctuations, so that the start of the procedure was judged as not rickier than the start with the 24 V starter. An influence of the starting process on a wear of the internal combustion engine was not examined. DE 10 2007 005 240 A1 discloses a method for starting an internal combustion engine of a motor vehicle by which method a starting comfort is to be significantly increased. It is by means of an electric machine

Speed actual value of a crankshaft of the internal combustion engine brought to a speed setpoint and the actual speed value by means of the electric machine on the

Speed setpoint controlled. This temporarily approximately constant speed is carried out during the onset of injection and ignition of the internal combustion engine until the internal combustion engine has started and has reached a stationary operating point, in which he regulates the speed value itself. The speed setpoint is an idle speed or higher than the idle speed lying high speed. In this way, comfort-impairing speed irregularities,

in particular speed overshoot, as they occur in an incipient combustion in the engine, are greatly reduced by a targeted application of positive or negative moments on the crankshaft by the electric machine. As a result of this procedure, disturbing vibrations or starting comfort are increased compared to a starting procedure with a conventional 24 V starter.

DE 10 2005 027 728 A1 discloses a method for starting a

Internal combustion engine, in which the internal combustion engine is started by means of an electric machine with a predetermined torque of the electric machine.

US 2005/0252474 A1 discloses a method for starting a

Internal combustion engine in cold conditions. In this case, the internal combustion engine is started by means of an electric machine so that a minimum speed of the internal combustion engine is ensured by the electric machine for a certain period of time. A speed up of the engine is thereby facilitated.

Although methods such as those described in DE 10 2007 005 240 A1 are suitable for effecting a steady speed curve when an internal combustion engine is started and thus suppressing jerky rotational courses which are transmitted comfort-reducing to the entire motor vehicle. However, these methods are disadvantageous in terms of material wear problems associated with today

Motor vehicles which are equipped with so-called stop-start automatic systems result. In such motor vehicles, the internal combustion engine for the purpose of fuel economy under certain operating conditions, where no Torque delivery of the internal combustion engine is required, automatically switched off and then, in a propulsion request by a driver, turned on again. The associated with an engine start from the engine standstill material load of

Combustion engine and start components is significantly higher in such a motor vehicle due to the higher number of starts than in a motor vehicle without stop-start automatic system. Such, life-reducing loads affect in particular hydrodynamic bearings of internal combustion engines.

As far as the wear of hydrodynamic plain bearings is concerned, it is known, for example from the so-called Stribeck curve, that the friction in such bearings increases with increasing relative speed in a lubrication gap of the bearing.

However, in an initial phase of the relative movements, a lubricating fluid is not evenly distributed in the lubricating gap, so that initially stiction or mixed friction between the moving parts of the sliding bearing occurs.

In view of these aspects, it is an object of the present invention, the

Life of a hydrodynamic sliding bearing of an internal combustion engine of a motor vehicle with a stop-start automatic system to increase.

The object is achieved by a method for starting an internal combustion engine of a motor vehicle having the features of patent claim 1 and by a device for starting an internal combustion engine of a motor vehicle having the features of patent claim 8.

The method for starting the internal combustion engine of the motor vehicle is characterized in that the internal combustion engine is set in a rotational movement by an action of an electrical machine, which is coupled to a crankshaft of the internal combustion engine or, namely via an actuatable clutch, coupled.

According to the invention, the starting of the internal combustion engine takes place with a very specific time profile of a rotational speed of the crankshaft of the internal combustion engine.

A desired time profile of the rotational speed of the crankshaft can be brought about by a scalable torque build-up of the electric machine in conjunction with a determination of the rotational speed of the crankshaft. The scalable

Torque can be connected by means of a connected to the electric machine Power electronics done, which has means for determining the speed of the crankshaft.

The method for starting the internal combustion engine with the desired time profile of the rotational speed of the crankshaft has at least 3 steps.

- A first step in which the crankshaft of the engine is rotated by the electric machine from its standstill and is turned up to a certain speed. The specific speed is referred to below as plateau speed, since the progression graphic of the speed substantially has a plateau over the time after reaching this speed. The rotation of the rotational movement of the crankshaft to the plateau speed has a substantially strictly monotonically increasing course.

A second method step in which, for a first time after reaching the plateau speed by means of a speed control by the power electronics of the electric machine, the speed of the crankshaft is kept substantially constant within a range around the plateau speed. Alternatively, during the second method step, the speed can be further increased, but in comparison to the speed increase in the first and in a third process section with a significantly reduced slope of

Speed increase over time.

The third method step, in which a further increase in the rotational speed takes place, wherein the further increase in the rotational speed occurs after the first time period has elapsed. In the course of further increase the speed is increased up to a target speed, the target speed usually an idle speed of

Internal combustion engine corresponds. In this case, the target rotational speed is expediently dependent on an engine or coolant temperature and / or on an ambient temperature and / or on further parameters. Of course, in the course of the further increase in the rotational speed, at least one further method step may take place, in which the rotational speed is kept constant again for a certain period of time at a higher value than the plateau rotational speed, before it is increased up to the target rotational speed.

It has been shown that by means of said sequence, the service life of a hydrodynamic sliding bearing can be increased many times relative to a fixed number of starting processes of the internal combustion engine. This may be due to the fact that, especially during the second process step, a perfect distribution of a lubricating oil takes place on the rubbing surfaces of the plain bearing, so that at the higher speeds, which are reached only in the third process step, only sliding friction and no mixed or static friction occurs more. Mixed friction is all the more destructive, the higher the speed. Without that by the

Speed control of the power electronics of the electric machine forced keeping the speed of the internal combustion engine, especially at a warm start, the speed of the engine would rise sharply immediately after fuel injection without a speed plateau forms because a warm start of

Internal combustion engine is very fast. On the other hand, during a cold start of the internal combustion engine, its speed would remain at low values for a very long time if the first time duration were not limited by the power electronics of the electric machine, which forces a further speed increase after the first time period. The speed control of the power electronics of the electric machine ensures that the first period of time is sufficiently long for a formation of a lubricating film on the plain bearings of the internal combustion engine and at the same time that the first time period is as short as possible, so that a starting time of

Internal combustion engine not unnecessarily extended.

With the at the second step substantially constant around the

Plateau speed held speed of the internal combustion engine is meant that the speed of the crankshaft does not deviate more than 50 rev / min from the plateau speed, in particular not more than 10 U / min. The higher tolerance of 50 U / min has the advantage that a simplified control can be used, but the achievable wear reduction is not so great. With the smaller tolerance of 10 rpm, a large reduction in wear and a good sense of comfort can be achieved.

With the significantly reduced slope of the speed increase over time mentioned in the second method step, one is compared to the first and second

Process step meant in each case by at least 50% reduced slope. With such a reduced pitch already occurs an improvement in the wear behavior of the sliding bearing, although not to the extent as in an approximate

Constant maintenance of the speed during the second process step. However, this alternative with the only reduced slope has the advantage that a

Speed of the starting process is increased comparatively, so that the start is experienced by the driver comfortable. A start of an injection or a combustion of a fuel in the internal combustion engine can, in principle, take place during the first or the second or the third method step.

A first development of the method provides that the first, the second and the third method step take place during a normal start or warm start of the internal combustion engine, with a normal or warm start occurring in particular when a coolant temperature of the internal combustion engine is greater than -15.degree. At temperatures greater than -15 ° C takes place in a, according to the prior art, unrestrained start of the engine, a very fast speed increase, which rapid speed increase wear-increasing effect on the bearings of the engine. In addition, normal or warm starts are much more common in automobiles with stop-start automatic systems than in conventional vehicles, whereas a number of cold starts with coolant temperatures of less than -15 ° C are approximately equal in conventional vehicles and in vehicles with stop-start automatic systems , In particular, by carrying out the method steps according to the invention during normal or warm starts of the internal combustion engine, a high reduction in wear can thus be achieved in comparison to conventional starting methods.

Particularly advantageous, a further development of the method has proven, in which the beginning of the fuel injection and fuel combustion in the internal combustion engine during the second process step takes place and in which the further increase in speed solely by the force of the internal combustion engine, that is without an effect of electric machine, done. In this way, a total consumption of electrical energy can be limited to what is necessary.

A further advantageous development of the method is that the first time period and / or the respective slope of the speed increase and / or a time of commencement of fuel injection and combustion of a

Ambient temperature and / or a temperature of the internal combustion engine and / or a coolant temperature and / or a temperature of a battery for powering the electrical machine and / or a voltage of the battery depends. In this way, the fact that the mixed friction can be overcome faster in the case of a warm engine with warm engine oil, can be advantageously exploited. In the case of a warm engine, a shorter first time period or even a less slowed-down high-speed turning, that is to say a less reduced pitch of the high-speed turning, is ideally selected in this development. On the other hand, is more advantageous Way at a low battery temperature or a low battery voltage as possible battery-saving variant of the method performed, namely with a shortened operation of the electric machine and a preferred injection and combustion in the internal combustion engine.

Another development of the method is that the revving up of the internal combustion engine in the first method step and also the further increase of the speed in the third method step respectively according to a respective predetermined substantially linearly increasing time course of the speed. In this way, a uniform speed curve can be ensured, which has a gentle effect on the components of the internal combustion engine.

Another development of the method is that the further increase in the speed in the third process step takes place under the action of the electric machine on the crankshaft. By a controlled action of the electric machine, the movement of the crankshaft can be made uniform, which also has a lifetime-increasing effect on the internal combustion engine.

Another development of the method is that the plateau speed is between 200 and 900 U / min, more preferably between 350 and 700 U / min and that the first time period is between 100 and 700 ms, preferably between 200 and 500 ms. The plateau speed and thus an injection speed is advantageously below a normal idle speed of the engine because thereby the highest reduction in wear is achieved in the internal combustion engine.

On the other hand, the plateau speed should not be too low for acoustic or vibration reasons. It has been shown in experiments that plateau speeds between 350 and 700 rpm as well as first time durations between 100 and 700 ms can achieve improvements in terms of the service life of the slide bearing by a factor of approximately 10 compared to a start procedure without a controlled plateau phase. Plateau speeds between 350 and 700 rev / min and time periods between 200 and 500 ms have also proven to be a particularly effective compromise between a very significant life improvement and at the same time a slight deterioration of the starting times of the internal combustion engine.

The target speed is preferably an idling speed of the internal combustion engine, for example in the range of about 700 U / min, or a speed of a first load point, which is approached directly from the starting process of the internal combustion engine. If the internal combustion engine is part of a serial hybrid system, it usually eliminates one Idle control, and the target speed is in this case or similar cases advantageously at the speed of the lowest load point, which corresponds to a speed of about 1200 U / min.

The device for starting an internal combustion engine of a motor vehicle is characterized by an electrical machine, which with a crankshaft of the

Internal combustion engine is coupled or coupled and power electronics for controlling and regulating the electric machine, which is connected to a device for determining a rotational speed of the crankshaft, from. According to the invention, the power electronics have means for carrying out a method according to claim 1. These are, in particular, means for cranking the internal combustion engine up to a plateau speed of the crankshaft and means for maintaining the speed of the crankshaft within a range around the plateau speed for a first period of time or for slowing down the crankshaft of the crankshaft

Internal combustion engine for the first period.

In a further development of this device, this further comprises a motor control for controlling and regulating the internal combustion engine and communication means for exchanging information between the power electronics and the engine control, wherein the engine control

a start of fuel injection and fuel combustion in the internal combustion engine during or after expiration of the first period of time, and - a further increase in the rotational speed of the crankshaft by a speed control of the internal combustion engine after the first period has elapsed

can cause.

Further advantages and features will become apparent from the following description of exemplary embodiments and with reference to the drawings, in which like elements are provided with identical reference numerals.

Showing:

Fig. 1 is a schematic representation of a device according to the invention for

Starting an internal combustion engine of a motor vehicle,

Fig. 2 is a diagram with the plot of the time-dependent speed curve of a

Crankshaft of the internal combustion engine according to the invention

Procedure as well Fig. 3 is a diagram showing the plot of the time-dependent speed curve of a crankshaft of the internal combustion engine according to an alternative

Embodiment of the method according to the invention.

A device 1 according to the invention schematically illustrated in FIG. 1 for starting an internal combustion engine 2 of a motor vehicle, not shown, has an electric machine 3, which is connected to a crankshaft 4 of the internal combustion engine 2. The electric machine 3 can drive the crankshaft 4, that is, exert positive or negative torques on it. A speed n of the crankshaft 4 is detected by a speed sensor 5 and as actual speed n, to a

Motor control 7 transmitted. The engine controller 7 is connected to power electronics 6 via a CAN bus 8, so that information between the engine controller 7 and the power electronics 6 can be exchanged. The power electronics 6 receives the actual speed value n, via the CAN bus 8. The power electronics 6 controls and regulates the electric machine 3 and in turn provides a speed setpoint n _s for the electric machine 3, wherein the specification of the speed setpoint n _s in accordance with a software program as a function of time and different parameters, in particular the parameters of Ambient temperature and / or a temperature of the internal combustion engine and / or a coolant temperature and / or a temperature of a battery for powering the electric machine and / or a voltage of the battery is carried out. Differs the actual speed n, from the

Speed setpoint n _s from, the power electronics 6 controls the electric machine 3 so that the crankshaft 4 of the speed setpoint n _{s is} impressed.

The internal combustion engine 2 is controlled and / or regulated by a motor controller 7. A regulation of the idle speed of the internal combustion engine 2 is carried out in a known manner, for example by processing suitable measured values, such as the actual speed n, the crankshaft and by setting appropriate sizes on

Internal combustion engine 2, such as an injected amount of fuel M.

Fig. 2 shows a diagram with a time-dependent speed curve 11 of a

Actual speed value n _{t of} the crankshaft 4 of the internal combustion engine 2 according to the method according to the invention.

A first method step 12, in which the internal combustion engine 2 is rotated up to a plateau speed 3 of the crankshaft 4 by means of the electric machine 3, is reflected in an increase in the actual rotational speed n, of the crankshaft 4 up to the plateau speed 3 of 600 rev / min again. The speed increase is controlled by the power electronics 6 approximately linearly within about 600 ms.

Upon reaching the plateau speed 13 of 600 rev / min begins at a time t _0, a second process step 14. During the second process step 14, again controlled by the power electronics 6, the speed of the crankshaft 4 held approximately constant, so that for the second process step a straight corner portion with slope zero at a speed actual value n, the crankshaft 4 of 600 rev / min results. The second method step 14 ends at a time or after a first time duration 15, which extends from t ₀ to ti. The plateau speed 13 of 600 rpm provides an optimal compromise between the achievement of a high reduction in wear and a low vibration level in the vehicle.

Before the end of the first time period 15 takes place at a time t ₂ (which is thus before) an injection of fuel into the engine 2. The actual speed n, the crankshaft 4, however, remains after the time t ₂ first in the

Plateaudrehzahl 13 of 600 rev / min, since as the torque of the engine increases to the crankshaft 4 by an incipient combustion, the torque of the electric machine 3 is lowered by the speed control. At the latest at the time that is from the engine 2 to the

Crankshaft 4 applied torque so large that the torque exerted by the electric machine 3 on the crankshaft 4 torque has become zero.

From the time ti, at which a third process step 16 begins, the rotational speed n of the crankshaft 4 increases further up to a target rotational speed 17, which is at 1200 rpm. This speed increase takes place without the action of force of the electric machine 3 solely by a torque control of the internal combustion engine 2.

In the third method step 16, the increase in the rotational speed of the crankshaft 4 can additionally be effected by acting on the electric machine 3. In this way, a more accurate speed control can be ensured than by the

Torque control of the internal combustion engine 2 alone would be possible. As a result, material-loading non-uniformities of the rotation of the crankshaft 4 can be compensated.

The course of the speed curve 11 advantageously depends on vehicle parameters, which characterize a heating state of the internal combustion engine 2 and / or a state of a battery which serves to supply power to the electric machine 3. That is, the power electronics 6 and the motor controller 7 the Control electric machine 3 and the internal combustion engine 2 in a manner and that at least one of the following control variables

Plateau speed 13,

Time t ₀ , at which the second method step 14 begins,

- And thus the slope of the speed increase in the first

Procedural step 12,

Time t ₂ , at which the injection starts in the internal combustion engine 2,

Time ti (or the first time period 15) at which the third method step 16 starts,

- Target speed 17 and the slope of the speed increase in the third

Process step 16

depend on at least one of the following parameters:

Ambient temperature,

- temperature of the internal combustion engine,

Coolant temperature,

Temperature and / or voltage of the battery used for

Voltage supply of the electric machine 3 is used.

3 shows a diagram with the plot of the time-dependent speed curve of a crankshaft 4 of the internal combustion engine 2 according to an alternative

Embodiment of the method according to the invention. In this embodiment, in an alternative form of the second method step 314, the plateau speed 13 is not kept constant but steadily increased over the entire first time period 15, wherein the slope of the speed increase over time during the second

Method step 314 is significantly lower than the slope of the speed increase over time both in the first method step 12 and in the third method step 16.

An improvement in the life of a hydrodynamic sliding bearing of the internal combustion engine (2), even if to a lesser extent, can still be achieved in the manner according to the invention, if during the second

Process step briefly a slight negative slope of the speed curve occurs. Such a negative course can, for example, result from a less conveniently controlled incipient injection in the internal combustion engine.

Claims

Daimler AG

claims

1. A method for starting an internal combustion engine (2) of a motor vehicle by means of an electric machine (3), which with a crankshaft (4) of the

Combustion engine (2) is coupled or can be coupled, the method comprising the following method steps:

- A first method step (12), in which a revolving of the

Internal combustion engine (2) by means of the electric machine (3) up to a plateau speed (13) of the crankshaft (4),

a second method step (14, 314) in which a substantially constant speed of the crankshaft (4) is maintained within a range around the plateau speed (13) for a first time duration (15) or in comparison to the first method step (12). and a third method step (6) markedly slowed down spin-up by a speed control of a power electronics of the electric machine (3) for the first time period (15),

- The third step (16), in which there is a further increase in the rotational speed of the crankshaft (4) to a target speed (17) after the first time period (15).

2. The method according to claim 1,

characterized in that

the first method step (12), the second method step (14, 314) and the third method step (6) during a normal start or warm start of the

Internal combustion engine (2) take place, in which a temperature of the

Internal combustion engine (2) is higher than -15 ° C.

3. The method according to claim 1 or 2,

characterized in that - A start of fuel injection and fuel combustion in the internal combustion engine (2) at a predetermined time (t ₂ ) during the second method step (14, 314) takes place and

- The further increase in the speed of the crankshaft (4) by a

Speed control of the internal combustion engine (2) takes place.

Method according to one of claims 1 to 3,

characterized in that

in the second method step (14, 314) the first time duration (15) and / or a slope of the high rotation of an ambient temperature and / or a temperature of the internal combustion engine (2) and / or a coolant temperature of the internal combustion engine (2) and / or a temperature and / or a voltage of a battery for the power supply of the electric machine (3) depends.

Method according to one of claims 1 to 4,

characterized in that

the turning up of the internal combustion engine (2) to the plateau speed (13) in the first method step (12) and the further increase of the speed up to the target speed (17) in the third method step (16) according to a respective predetermined substantially linearly increasing temporal Course of the speed takes place.

Method according to one of claims 1 to 5,

characterized in that

maintaining the speed of the crankshaft (4) in the second

Process step (14, 314) in the form of a substantially constant holding the speed by the electric machine (3).

Method according to one of claims 1 to 6,

characterized in that

the further increase in the speed under a speed-controlled action of the electric machine (2) on the crankshaft (4).

Method according to one of claims 1 to 7,

characterized in that

the plateau speed (13) is between 200 and 900 rpm, preferably between 350 and 700 rpm.

9. The method according to any one of claims 1 to 8,

characterized in that

the first time duration (15) is between 100 and 700 ms, preferably between 200 and 500 ms.

10. The method according to any one of claims 1 to 9,

characterized in that

the target rotational speed (17) is 700 to 1400 rpm, preferably 1100 to 1300 rpm.

11. Device for starting an internal combustion engine (2) of a motor vehicle,

including

an electric machine (3) connected to a crankshaft (4) of the

Combustion engine (2) is coupled or can be coupled,

a power electronics (6) for controlling and regulating the electric machine (3), which are provided with a device (5) for determining a

Speed of the crankshaft (4) is connected,

characterized in that

the power electronics (6) by means of the electric machine (3)

a rotation of the internal combustion engine (2) up to a plateau speed (13) of the crankshaft (4) and

a substantially constant speed of the crankshaft (4)

within a range around the plateau speed (13) for a first time duration (15) or a slowed down speeding up of the crankshaft (4) of the internal combustion engine (2) for the first time duration (15)

can cause.

12. Device according to claim 11,

characterized in that

the device is a motor controller (7) for controlling and regulating the

Combustion engine (2) and communication means (8) for exchanging information between power electronics (6) and motor control (7), wherein the motor control (7)

a start of fuel injection and fuel combustion in the internal combustion engine during or after expiration of the first time period (15) as well as a further increase in the rotational speed of the crankshaft (4) by a rotational speed control of the internal combustion engine (2) after expiration of the first time period (15) to a target rotational speed (17)

can cause.