DE102013225851A1 - Method and device for operating an internal combustion engine of a motor vehicle having a start-stop function - Google Patents

Abstract

The present invention relates to a method and a device for operating an internal combustion engine of a motor vehicle having a start-stop function, wherein it is provided in particular that during a stop phase of said start-stop function, a reduction of the rotational speed of the internal combustion engine to a level , which allows a renewed starting operation (235) of the internal combustion engine as soon as possible, by accelerating a short-term counter-torque by means arranged in the motor vehicle, connected to the internal combustion engine accelerated (245, 250).

Description

The invention relates to a method for operating an internal combustion engine of a motor vehicle having a start-stop function according to the preambles of the respective independent claims. Furthermore, the invention relates to a computer program, an electronic data carrier for storing the computer program and an electronic control unit, by means of which the method according to the invention can be carried out.

State of the art

In a start-stop function of a motor vehicle, an internal combustion engine (gasoline or diesel engine) arranged in the motor vehicle is automatically switched off in a manner known per se as soon as the vehicle stops, whereby the fuel consumption is reduced. The switching off of the engine takes place at low speed moving or rolling or already stationary vehicle usually only when the driver switches in the case of a gearbox in the idle or actuates the brake in the case of an automatic transmission. In addition, the shutdown of the internal combustion engine may also be subject to further conditions, e.g. the operating condition of an air conditioner, the battery condition and / or the current steering angle are made dependent.

The switching off of the internal combustion engine takes place electronically in most motor vehicles by means of an engine control unit, namely in a diesel engine by stopping the injection and in a gasoline engine by switching off the injection or ignition. However, it comes after switching off to a discharge operation of the internal combustion engine, in which the speed is reduced until the final standstill of the internal combustion engine. This spout is caused in particular by the flywheel of the crank mechanism and the friction of the mechanics of the internal combustion engine.

Due to the continuing in the cylinders or combustion chambers of the internal combustion engine during the phase-out compression, the speed does not fall evenly from linear, but decreases depending on the number of cylinders very unevenly. In the 1 are measured on different internal combustion engines in the phase-out phase speeds n [rpm] over the time t in [s]. The local internal combustion engines include diesel and gasoline engines, each with very different displacement (in the range of 1.3 l to 5.5 l) and different numbers of cylinders (from 2 to 8 cylinders). For most of the phasing curves shown, the time taken to decrease the speed from 600 rpm to 0 is about 0.5-0.8 s.

In particular, in internal combustion engines with a few cylinders, such as a 2-cylinder gasoline engine 100 or a 3-cylinder diesel engine 105 In particular, in engines with low internal friction, it also leads to a pronounced back swinging of one or more pistons in the cylinders and thus in the result of the crankshaft of the internal combustion engine, when the compressed residual gas mixture in the cylinder pushes the piston in the opposite direction. Therefore, for example, in friction-optimized engines with few cylinders, the discharge process can last up to 1.5 s.

After the shutdown (stop) of the internal combustion engine, a restart process is known to be initiated or initiated by the driver actuating the clutch in a manual transmission or disengaging the brake pedal in an automatic transmission. If the speed at the time of starting is above the so-called ZMS resonance frequency (ZMS stands for dual-mass flywheel), i. In the range of about 300 to 400 U / min, the internal combustion engine can be started by restarting the injection or ignition. However, due to technical reasons, the internal combustion engine can only be restarted via a modern pinion starter when the engine speed drops below a certain value. Below 300 rpm, this is not possible in the above-mentioned manner, but the internal combustion engine must be equipped with the starter motor, which is usually used as the engine Ritzelstarter is executed to be started. However, even a conventional pinion starter can track only below a speed of 75 rev / min to start the engine. However, if the meshing in of the starter occurs during a said backward oscillation of one or more pistons and thereby drives the piston or pistons in the opposite direction, undesired or even inadmissibly high mechanical loads on the internal combustion engine and the starter occur.

For the reasons mentioned, it takes about 1 s between the switching off of the internal combustion engine and the actual standstill of the crankshaft, even longer in the mentioned 2- and 3-cylinder engines. Only then can the starter engage and effect the restart of the internal combustion engine. In addition to this delay comes the time for the actual boot process, about 0.4 s, which adds up to a total delay of about 1.4 s.

In many traffic situations, however, the shortest possible restart time is required immediately after the stop function has already been activated, with the driver indicating a new start request, for example by actuating the drive or accelerator pedal. This so-called "change-of-mind" (CoM) case can be caused, for example, by a green traffic light be. In another, in 2a illustrated driving situation drives a motor vehicle with automatic transmission with stepped brake on a stop sign or a roundabout, the vehicle is briefly brought to a standstill to detect possible cross traffic.

Due to the vehicle standstill and the brake actuated, the start-stop system generates a motor stop signal 200 , If the driver at this moment releases the brake again and presses the accelerator pedal and thereby a start command 205 In order to accelerate and quickly cross the priority road or enter the ancestor road or the roundabout, it is necessary to wait for about 0.7 seconds 215 until the speed of the internal combustion engine has dropped so far that it can be restarted 210 , wherein the internal combustion engine is ready for operation only about 1 s after the start command and the starting process additionally requires the mentioned 0.4 s. This delay significantly affects the operating comfort of an automatic start-stop system.

Disclosure of the invention

The invention is based on the idea to stop an engine equipped with a start-stop function as quickly as possible, i. to delay to a low speed in order to shorten the stop phase of a said function as possible. At the same time, at the same time, an oscillation of the pistons (cylinders) mentioned at the beginning should be minimized or even prevented.

The invention proposes in particular to shorten the stop phase of said start-stop function, and thus also the possible beginning of the stop phase subsequent restart of the internal combustion engine by generating a short-term mechanical counter-torque on the crankshaft, wherein the counter-torque means a arranged in the motor vehicle or on the internal combustion engine electric generator or power generator (also called "alternator") is generated. This counter-torque can also be generated with other units that are mechanically connected to the crankshaft or the belt drive. This includes, for example, an air conditioning compressor or one or more pumps (servo, oil or water pumps).

The said counter-torque is preferably generated by briefly increased electrical power consumption or power output of the power generator. The increase in power output can be generated by short-term increase of the charging current of an energy storage device (car battery or accumulator) and / or by short-term addition or short-term increase in power of existing in the motor vehicle electrical consumers and / or electrical or mechanical units or loads. By increasing the power consumption of an already activated unit, the internal combustion engine can be stopped even faster. In order to enable the power output of the power generator required for the method according to the invention, the magnitude of an exciter current of the current generator can be timed in advance. In addition, the power generator can be operated with a modified control characteristic, by means of which the necessary for the generation of the counter-torque excitation current structure is accelerated.

The method according to the invention is based on the technical effect that the said consumers during the run of the internal combustion engine on the with the internal combustion engine by means of e.g. a V-belt co-operating the current generator to build up a high counter-torque which is sufficient to retard the internal combustion engine quickly and back-free or Rückpendelarm. In addition, a possible return oscillation of the crankshaft of the internal combustion engine can be minimized or even prevented by switching off the exciter current of the current generator at a suitable time during the stop phase.

In the aforementioned consumers are such aggregates whose short-term addition or short-term increase in power have no disturbing effect on the operation of the motor vehicle. Particular consideration is given to electrical consumers or mechanically or electromechanically operated units which, in the required, very short time window in the range of about 0.1-1 s after a successful stop command, have no interfering influence on the operation of the motor vehicle or its operation short-term activation by the driver is perceived only slightly or not at all. Possible consumers are heaters installed in the motor vehicle, such as seat heaters or a rear window heater, circulating air or cooling fan or an air conditioning compressor. The latter can either be operated electrically via the generator or directly mechanically by the internal combustion engine.

Due to the shortened stop phase, a named, conventional pinion starter can engage significantly earlier, thus restarting the internal combustion engine essentially without delay, or at least with a relatively low time delay, which is very little affecting the operating comfort.

By the present invention enabled timely engagement of a starter in the only relatively slowly rotating internal combustion engine, there are no additional mechanical loads for the starter. As a result, the life of the starter is extended or achieved a nominal starter life without any additional measures required. At the same time in comparison to the prior art, according to which a timely meshing in the still relatively fast rotating internal combustion engine with loud additional noise ("ratchets") would be connected, reduced by means of the invention, the starter noise, which additionally improves the operating comfort and ride comfort of the motor vehicle.

Due to the reduced flow time of the internal combustion engine in said change-of-mind case, the internal combustion engine can be restarted much earlier. As a result, the motor vehicle can better follow a driver's request for spontaneous torque build-up, as a result of which the acceptance of a start-stop system operated in accordance with the invention and in particular also the traffic safety of the motor vehicle increases.

The inventive method can be realized by means of a control program and thus cost, in particular, no costly additional components are required.

The invention also relates to an electronic control unit for carrying out said method, which preferably has a power management module for controlling a said electric power generator and a power management module for controlling said load.

The invention can be used in particular in any internal combustion engine, in particular of motor vehicles with a named start-stop function. In addition, an application is also in future motor vehicles, in which the internal combustion engine is already switched off by means of a stop function while the vehicle is still rolling (so-called. "Sailing with engine off").

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

Brief description of the drawings

1 shows speed of rotation curves measured on internal combustion engines of different types, according to the prior art.

2a shows a speed curve of an internal combustion engine in a said CoM case according to the prior art

2 B shows one of the 2a corresponding speed curve at inventively optimized start of such an internal combustion engine.

3 schematically shows an inventive device for operating an internal combustion engine of a start-stop function having motor vehicle.

4 shows an embodiment of the inventive method for operating an internal combustion engine of a start-stop function having motor vehicle with reference to a flowchart.

5a and 5b show a comparison with the prior art ( 5a ) ( 5b ) Control characteristic of a current generator affected here.

Description of exemplary embodiments

The 1 and 2a have already been described above.

In 2 B is a time course of the speed of an internal combustion engine resulting in execution of the method according to the invention, in comparison with a resulting according to the prior art speed curve shown.

According to the prior art would be at an already generated engine stop signal 220 in the mentioned CoM case, in which the driver again releases the brake and actuates the gas pedal and thereby a start command 225 triggers, the internal combustion engine again at the time 230 ie with a delay shown 240 be started by about 0.7 s, which would result in a total delay of about 1.4 s until the completion of the restart of the internal combustion engine.

When using the method according to the invention, the internal combustion engine according to the generated start-stop signal 220 already at the time 235 be restarted, with a shortened in the present embodiment reaction time 245 and thus a total time advantage 250 of about 0.3 s.

The 2 B illustrates the speed reduction made possible by the method according to the invention during a stop operation of an internal combustion engine having a start-stop function to a time level 245 , which promptly reboots 235 the internal combustion engine allows. In addition, the speed is reduced in such a way that a swinging of the crankshaft is avoided or at least the extent of a back swing is reduced. As a result, the time window for a renewed, timely restart of the internal combustion engine can be reduced.

The in the 3 The control arrangement or device shown allows a modified as described above operation of a start-stop function providing internal combustion engine 300 which is from a control unit (ECU) 305 is controlled. The electrical supply is known to be via an energy store (or car battery or accumulator) 310 in the operation of the internal combustion engine 300 from a standard power generator (or alternator) 315 is charged.

The coordination or control of the start-stop function according to the invention and the load management required for this purpose is an energy management module or unit 320 arranged, which in particular the control of the power generator 315 and via a consumer management module or unit 325 (BCU = body control unit) additional loads or consumers 330 . 335 if necessary, it activates or activates or deactivates it. Alternatively or additionally, the power or power loss of already activated consumers can be briefly increased.

With these additional consumers 330 . 335 In the present exemplary embodiment, this is a rear window heater, a heater for the interior of the motor vehicle and / or a cooling fan. Furthermore, the energy management module controls 320 in this embodiment, directly an air compressor 340 ,

The power generator 315 is also operated in the embodiment by means of a (not shown) generator control with a comparison with the prior art control characteristic to ensure that the short-term power increase described herein can be implemented. An exemplary adjusted control characteristic is in the 5a and 5b shown, where 5a a corresponding control characteristic according to the prior art and 5b shows a modified according to the invention control characteristic.

The in 5a excitation current represented in relative units [%] over time t in [s] (I ^excitation _rel. ) 500 of the generator is deactivated according to the prior art simultaneously with the stopping of the engine, wherein no counter-torque is generated. Turning off the engine also drops the engine speed (s) indicated in [rpm] 505 to the value zero.

Like from the 5b can be seen, by suitable feedforward control, for example, depending on the control characteristic, the excitation current (I ^Erreg. _Rel. ) shown again in relative units 510 even before stopping the engine and up to the desired speed point of the engine speed 515 (currently up to the time of about 1.7 s) maintained.

The energy management module 320 is also with the control unit 305 the internal combustion engine 300 connected to allow communication required for start-stop management. An in 3 also not shown energy or battery management system is used to communicate the maximum allowable battery power.

In the 3 shown control device allows the generation of a short-term (in the range of 0.1-1 s) engine counter or braking torque to increase the engine drag load. For this purpose, already existing units are used in the motor vehicle or on the internal combustion engine. Due to the very short time required change, the power of the power generator 315 be increased to a maximum allowable rated power, or even above this rated power, since because of the short duration no thermally excessive or undue load on the power generator 315 entry.

An additional power peak (or peak) of the current generator, which increases the said drag torque 315 can by briefly increased charging of the energy storage 310 by means of the power generator 315 are generated, to the extent that the power generator 315 can absorb such additional power. In order to maximize this additional power consumption, the generator voltage can be temporarily increased to a voltage level which is higher than the usual DC electrical system voltage of approximately 12 V of the motor vehicle, namely in the range of up to 16 V.

By means of a named, adapted or additional generator control characteristic, the fastest possible structure of the necessary exciter current can be achieved. In this case, the said energy management module 320 , possibly including a suitable communication concept, the generator torque are pre-controlled accordingly before the internal combustion engine stops.

Additionally or alternatively to the measures described for generating a short-term peak power in the power generator 315 Further electrical consumers (eg, interior or rear window heating) or mechanical loads (units) can be activated or switched on briefly and / or the power of one or more already activated consumers can be briefly increased. Also, an existing air conditioning compressor can be briefly activated or engaged or an already coupled air conditioning compressor can be briefly set to maximum cooling capacity. These extra loads can provide additional electrical energy or power from the power generator 315 is generated, but from the energy storage 310 can no longer be included, at least in part, to maximize the overall performance peak.

4 shows an embodiment of a method implementing the inventive routine. This in 3 shown energy management (module) 320 of the motor vehicle initially recognizes in a known manner, for example, based on various technical driving conditions or operating parameters, the need for activating a motor stop, eg based on an engine stop signal 400 , In contrast to the immediate deactivation of the internal combustion engine according to the state of the art, the power generator is activated in the manner described as an additional engine load (counter-torque) 405 , This activation takes place in this embodiment by suitable feedforward control of the current generator, by temporal feedforward control of the exciter current level 410 , In addition, as described, electrical loads 415 and / or mechanical loads (aggregates) 420 activated briefly or their energy or power consumption are increased briefly.

Due to the counter-torque thus generated, the rotational speed of the internal combustion engine is braked supportive so that a return oscillation of the crankshaft or an additionally increased return oscillation is effectively avoided. Only after the construction of the required or desired counter-torque, the internal combustion engine is issued active in a conventional manner 430 (see corresponding first delay step 425 ). The structure of the counter-torque is controlled so that the speed reduction is supported as effectively as possible after actively switching off the internal combustion engine.

By means of a for the start-stop case, as described, modified regulator characteristic for operation of the current generator can be achieved that the necessary in the current generator for generating the counter-torque exciter current build-up is faster. In addition, the structure of the braking or counter-torque can be terminated by switching off the exciter current of the power generator during the switch-off or shutdown of the internal combustion engine 435 , whereby the angular acceleration of the crankshaft is limited and the swinging or an increase of the return swing is effectively prevented.

After the structure or the effect of a described counter-torque has been terminated or deactivated 435 , a second delay step occurs 440 to wait until the engine speed has dropped to a value suitable for the next engine start. If this condition is met, the internal combustion engine is restarted 445 ,

The described method can be implemented either in the form of a control program for an electronic control unit for controlling an internal combustion engine or in the form of one or more corresponding electronic control units (ECUs).

Claims (13)

Method for operating an internal combustion engine of a motor vehicle having a start-stop function, characterized in that, during a stop phase of said start-stop function, a reduction of the rotational speed of the internal combustion engine to a level which causes a restart ( 235 ) of the internal combustion engine for a short time after a successful start command permits, by generating a short-term counter-torque by means arranged in the motor vehicle, connected to the internal combustion engine electrical generator takes place ( 245 . 250 ). A method according to claim 1, characterized in that the counter-torque is generated by briefly increased electric power output of the generator. A method according to claim 2, characterized in that the increase in the electrical power output by briefly increasing the charging current of an energy storage takes place. A method according to claim 2 or 3, characterized in that the increase of the electric power output by short-term switching on and / or short-term increase in power of at least one arranged in the motor vehicle electrical and / or electromechanical load is generated. Method according to one of the preceding claims, characterized in that the Counter torque is generated in a time interval of about 0.1 to 1 s after the presence of a stop command. A method according to claim 4 or 5, characterized in that arranged as said consumer in the motor vehicle electrical and / or electromechanical units whose short-term addition or power increase have no disturbing influence on the operation of the motor vehicle and / or are perceived by the driver only slightly or not , be included. Method according to one of the preceding claims, characterized in that the height of an excitation current of the electric generator is timed in advance. Method according to one of the preceding claims, characterized in that the electric generator is operated with a modified control characteristic, by means of which the necessary for the generation of the counter-torque excitation current structure is accelerated. A method according to claim 8, characterized in that during a stop phase of the excitation current of the electric generator is turned off to minimize or prevent back swinging of a crankshaft of the internal combustion engine. Computer program for carrying out all the steps of a method according to one of claims 1 to 9, when it is stored on a computing device or an electronic control device ( 305 ) is performed. An electronic data storage medium for storing a computer program according to claim 11, wherein the computer program carries out all steps of a method according to one of claims 1 to 9 when it is stored on a computing device or an electronic control unit ( 305 ) is performed. Electronic control device for carrying out a method according to one of claims 1 to 9. Control unit according to claim 12, characterized by an energy management module ( 320 ) for controlling an electric generator connected to an internal combustion engine ( 315 ) and a consumer management module ( 325 ) for controlling at least one electrical or electromechanical consumer ( 330 . 335 ).

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