GB2501709A

GB2501709A - Control of an Auto-Stop Phase of an Internal Combustion Engine

Info

Publication number: GB2501709A
Application number: GB1207588.3A
Authority: GB
Inventors: Giuseppe Mazzara Bologna; Vincenzo Alfieri; Alessandro Catanese
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-04-30
Filing date: 2012-04-30
Publication date: 2013-11-06
Also published as: GB201207588D0

Abstract

A method of operating an internal combustion engine 110 of a motor vehicle 10 comprising: monitoring a speed of the motor vehicle 10; monitoring an operating configuration of a clutch 16; monitoring a speed of the internal combustion engine 110; performing an auto-stop phase of the inÂternal combustion engine 110 if the monitored speed of the motor vehicle 10) is below a predetermined threshold value, the monitored engine speed is below a predetermined threshold value, and the clutch 16 is disengaged; wherein the auto-stop phase comÂprises the steps of: decreasing the engine speed from a first predetermined value (V1, fig.5) to a second predetermined value (V2, fig.5) that is greater than or equal to a minimum allowable threshold value (Vth, fig.5) for an auto-start phase of the internal combustion engine to be perÂformed, keeping the engine speed at the second predetermined value (V2) for a predeÂtermined period of time by operating a motor-generator unit 20, and then decreasing the engine speed from the second predetermined value (V2) to zero.

Description

S METHOD OF OPERATING AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method of operating an internal combustion engine of a motor vehicle.

BACKGROUND

It is known that a motor vehide is generally equipped with an internal combustion engine (ICE), such as for example a compression-ignition engine (Diesel engine) or a spark-ignition engine, and at least one wheel drive, typically a front wheel drive and/or a rear wheel drive, which receives mechanical power form the ICE and delivers it to the road surface.

The ICE usually comprises an engine block defining at least one cylinder which accom-modates a reciprocating piston coupled to rotate a crankshaft. The top of the cylinder is closed by a cylinder head, which cooperates with the piston to define a combustion chamber. A fuel-and-air mixture is cyclically supplied into the combustion chamber and ignited, thereby producing hot exhaust gasses whose expansion causes the movement of the piston and thus the rotation of the crankshaft.

The fuel is usually supplied into the combustion chamber by means of at least one fuel injector. The injected fuel quantity is determined by an electronic control unit (ECU), which is connected to the fuel injector and to a position sensor coupled to an accelerator pedal. The ECU is configured to receive input signals from the accelerator-pedal position sensor and to operate the fuel injector on the basis of these signals.

The crankshaft of the ICE is coupled to the wheel drive by means of several intermediate components, globally referred as driveline, which generally include a transmission and a clutch connecting the transmission to the crankshaft.

The transmission, also referred as gearbox is a mechanical device that include several gears provided for transferring torque from the crankshaft to the wheel drive, each of which defines a different gear ratio. These gears are selectively and alternatively en-gaged by means of a gear lever, which may be moved directly by the driver of the motor vehicle. The gear lever may also be moved in a neutral position, where no gear is en-gaged and no torque is transferred to the wheel drive.

The clutch is a mechanical device provided for selectively disengage the crankshaft from the transmission, in order to allow a gear shifting. The clutch is controlled by the driver of the motor vehicle by means of a clutch pedal, which is movable between a pressed posi-tion and a released position. When the clutch pedal is pressed, the clutch moves in a configuration where the crankshaft and the transmission are mutually disengaged. When the clutch pedal is released, the clutch returns in a configuration where the crankshaft and the transmission are engaged.

In order to reduce the polluting emissions and to increase the fuel economy, modern mo- tor vehicle can be equipped with a hybrid powertrain that, in addition to the above men-tioned ICE, includes also a motor-generator electric unit (MGU) and an electrical battery suitable to supply the MGU. The MGU can operate as an electric motor for assisting or replacing the ICE in propelling the motor vehicle and can also operate as an electric generator, especially when the motor vehicle is braking, for charging the battery.

The ECU of many hybrid powertrains may implement a Start and Stop strategy for the ICE. The Start and Stop strategy generally provides for automatically stopping the ICE, each time the motor vehicle stops, for example in proximity of a traffic light or a stop sign.

and then for automatically starting the ICE, when the driver wants to move again, thereby reducing the amount of time the ICE spends idling.

These Start and Stop strategies are based on the fact that, when the driver wants to stop the motor vehicle, he generally releases the accelerator pedal, so as to cut the fuel injec-tions off, and decelerates the motor vehicle, for example by pressing a brake pedal.

When the motor vehicle is almost still, the driver presses the clutch pedal to disengage the ICE from the transmission, then he moves the gear lever in the neutral position and finally releases the clutch pedal.

On the other hand, when the driver wants to drive away, he presses the clutch pedal to disengage the ICE from the transmission, then moves the gear lever so as to engage a gear, typically the first gear, and finally releases the clutch pedal.

In view of this considerations, the Start and Stop strategies are essentially based on the following parameters: the position of the accelerator pedal, the rotational speed of the engine crankshaft (engine speed), the speed of the motor vehicle, the position of the gear lever of the transmission, and the position of the clutch pedal.

More particularly, a known Start and Stop strategy, which is conventionally referred as Bottom Of Travel (BOT) strategy, provides for performing an auto-stop of the ICE, as soon as the following conditions are met: -the speed of the motor vehicle is below a predetermined threshold value, -the engine speed is below a predetermined threshold value, and -the clutch pedal is pressed.

In this way, the ICE is automatically stopped before that the driver moves the gear lever in neutral position.

According to the BOT strategy, the ICE is then automatically restarted when the driver releases the clutch pedal, after having engaged the first gear.

During the normal use of the motor vehicle, it may happen that the driver suddenly de-cides to move away when the motor vehicle is still moving. This event is usually referred as driver's "change of mind", and it may happen for example when the motor vehicle is approaching a red traffic light that suddenly turns green. In such case, after having slowed down the motor vehicle and pressed the clutch pedal, the driver rapidly releases the clutch pedal and presses the accelerator pedal.

If the ECU is configured to perform the 001 Start and Stop strategy explained above, the driver's change of mind" may imply that an auto-start phase of the ICE is triggered when the auto-stop phase has not been completed.

In fact, once the clutch pedal is pressed, the auto-stop phase provides for the ECU to perform a first stage. during which the engine speed is maintained at a predetermined value usually referred as idle speed, and a second stage, usually referred as spin-down stage, during which the engine speed is decreased from the idle speed to zero. The speed of the engine during these first and second stages of the auto-stop is generally de-termined by the activation of the MGU coupled to the engine crankshaft or by properly regulating the fuel injections in the engine cylinders.

Besides, the BOT Start and Stop strategy implies that the auto-start phase of the engine is always triggered when the first gear of the transmission has been already engaged and while the clutch is actually engaging the ICE to the wheel drive, so that a high resis-tive torque is generally applied to the crankshaft during the auto-start phase.

As a consequence, if the clutch pedal is released very fast while the auto-stop phase is still running, as it generally happens when the driver "changes his mind", the automatic performing of the auto-start phase could cause the ICE to stall.

In particular, it has been found that the ICE could stall if the auto-start phase is triggered during the spin-down stage when the engine speed is already too low.

Moreover, if the engine speed is already too low, an auto-start phase of the ICE may produce loud noises and even damage some components of the driveline, such as for example the dual mass flywheel of the clutch.

For these reasons, when the engine speed falls below a predetermined minimum allow-able threshold value (about 400-450 rpm), the BOT Start and Stop strategy generally provides for preventing the auto-start phase even if the driver releases the clutch pedal and presses the accelerator pedal.

A drawback of this solution is that, during the spin-down stage of the ICE, there is only a short period of time in which the driver can "change his mind" and actually restart the ICE.

In fact, the spin-down stage currently provides that the engine speed is decreased from the idle speed to zero linearly, namely that the variation of the engine speed over the time follows a linear profile, so that the auto-start phase can only be triggered within the period of time used by the engine speed to decrease from the idle speed to the minimum allowable threshold value.

An object of an embodiment of the present invention is that of solving or at least of posi-tively reducing this drawback.

Another object is to attain these goal with a simple, rational and rather inexpensive solu-tion.

SUMMARY

These and/or other objects are attained by the features of the embodiments of the inven-tion as reported in the independent claims. The dependent claims recite preferred and/or especially advantageous features of the embodiments of the invention.

In particular, an embodiment of the invention provides a method of operating an internal combustion engine of a motor vehicle comprising the steps of: -monitoring a speed of the motor vehicle, -monitoring an operating configuration of a clutch of the motor vehicle (for example by monitoring a position of a clutch pedal), -monitoring a speed of the internal combustion engine, -performing an auto-stop phase of the internal combustion engine if the monitored speed of the motor vehicle is below a predetermined threshold value, the monitored engine speed is below a predetermined threshold value, and the clutch is disengaged, wherein the auto-stop phase comprises the steps of: -decreasing the engine speed from a first predetermined value (e.g. the idle speed) to a second predetermined value that is greater or equal to a minimum allowable threshold value for an auto-start phase of the internal combustion engine to be performed, -keeping the engine speed at the second predetermined value for a predetermined pen-od of time, and then -decreasing the engine speed from the second predetermined value to zero.

In this way, the engine speed is not decreased according to a linear profile as in the prior art, but it is decreased according to a stepped profile, thereby advantageously increasing the overall period of time in which the auto-start phase can be performed in case of a driver's change of mind". In fact, the auto-start phase may be advantageously performed either during the period of time in which the engine speed decreases from the first prede-termined value to the second predetermined value, or during the period of time in which the engine speed remains at the second predetermined value.

From a theoretical point of view, the engine speed could be kept at the second prede- termined value by properly regulating the fuel injections in the internal combustion en- gine. However, this solution would increase the fuel consumption and the polluting emis-sions of the motor vehicle.

For this reason, an aspect of the invention provides that the engine speed is kept at the second predetermined value by operating a motor-generator electric unit.

This solution has the advantage of avoiding any direct or indirect consumption of fuel. In fact, the motor-generator electric unit is conventionally powered by a battery which is charged when the motor vehicle is braking.

According to another aspect of the invention, the engine speed is decreased from the first predetermined value to the second predetermined value and from the second prede-termined value to zero by still operating the above mentioned motor-generator electric unit.

This embodiment of the invention has the advantage of allowing a precise control of the engine speed. In particular, it allows to decrease the engine speed from the second pre-determined threshold value to zero as fast as possible, in order to further increase the overall period of time in which the auto-start phase can be triggered in case of a driver's "change of mind", while avoiding too loud noises due to the dual mass flywheel of the clutch.

According to another aspect of the invention, the motor-generator electric unit is operat-ed performing a feedback control loop of a parameter indicative of the torque supplied by the motor-generator electric unit.

This aspect of the invention has the advantage of ensuring that the variation of the en-gine speed during the auto-stop phase follows the desired profile.

According to still another aspect of the invention, the first predetermined value and the second predetermined value are calibration values.

S

In this way, the method can be performed with low computational effort.

In particular, the first predetermined value may be lower than 1000 rpm, for example it may be about 750 rpm, and the second predetermined value may be higher than 450 rpm, for example it may be about 500 rpm.

These first and second predetermined values advantageously allows to increase the overall period of time in which the auto-start phase can be triggered in case of a driver's "change of mind" without consuming too much energy.

According to another aspect of the invention, the predetermined period of time, during which the engine speed is kept at the second predetermined value, is a calibration period of time.

This aspect as the advantage of limiting the computational effort required to perform the method.

In particular, the above mentioned predetermined period of time may be comprised be-tween 500 ms and 1000 ms, for example it may be about 700 ms.

This predetermined period of time has the advantage of limiting the energy spent for per-forming the method.

The method according to the invention can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method de-scribed above, and in the form of a computer program product on which the computer program is stored. The method can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represent a computer pro-gram to carry out all steps of the method.

Another embodiment of the invention provides an apparatus for operating an internal combustion engine of a motor vehicle, wherein the apparatus comprises: -means for monitoring a speed of the motor vehicle, -means for monitoring an operating configuration of a clutch of the motor vehicle (for ex-ample by monitoring a position of a clutch pedal), -means for monitoring a speed of the internal combustion engine, -means for performing an auto-stop phase of the internal combustion engine if the moni- tored speed of the motor vehicle is below a predetermined threshold value, the moni- tored engine speed is below a predetermined threshold value, and the clutch is disen-gaged, wherein the means for performing the auto-stop phase comprise: -means for decreasing the engine speed from a first predetermined value (e.g. the idle speed) to a second predetermined value that is greater or equal to a minimum allowable threshold value for an auto-start phase of the internal combustion engine to be per-formed, -means for keeping the engine speed at the second predetermined value for a prede-termined period of time, and -means for decreasing the engine speed from the second predetermined value to zero.

In this way, the overall period of time in which the auto-start phase can be performed in case of a driver's "change of mind" is advantageously increased.

An aspect of the invention provides that the means for keeping the engine speed at the second predetermined value may comprise means for operating a motor-generator elec-tric unit.

This solution has the advantage of avoiding any direct or indirect consumption of fuel.

According to another aspect of the invention, the means for decreasing the engine speed from the first predetermined value to the second predetermined value and the means for decreasing the engine speed from the second predetermined value to zero may still comprise means for operating the above mentioned motor-generator.

This embodiment of the invention has the advantage of allowing a precise control of the engine speed.

According to another aspect of the invention, the means for operating the motor-generator electric unit may comprise means for performing a feedback control loop of a 23 parameter indicative of the torque supplied by the motor-generator electric unit.

In this way, the method can be performed with low computational effort.

In particular, the first predetermined value may be lower than 1000 rpm. for example it may be about 750 rpm, and the second predetermined value may be higher than 450 rpm, for example it may be about 500 rpm.

In particular, the above mentioned predetermined period of time may be comprised be-tween 500 ms and 1000 ms, for example it may be about 700 ma This predetermined period of time has the advantage of limiting the energy spent for per-forming the method.

Another embodiment of the invention provides a motor-vehicle comprising an internal combustion engine, and an electronic control unit configured to: -monitor a speed of the motor vehicle, -monitor an operating configuration of a clutch of the motor vehicle (for example by mon-itoring a position of a clutch pedal), -monitor a speed of the internal combustion engine, -perform an auto-stop phase of the internal combustion engine if the monitored speed of the motor vehicle is below a predetermined threshold value, the monitored engine speed is below a predetermined threshold value, and the clutch is disengaged, 1 5 wherein the electronic control unit is configure to perform the auto-stop phase by the steps of: -decreasing the engine speed from a first predetermined value (e.g. the idle speed) to a second predetermined value that is greater or equal to a minimum allowable threshold value for an auto-start phase of the internal combustion engine to be performed, -keeping the engine speed at the second predetermined value for a predetermined peri-od of time, and then -decreasing the engine speed from the second predetermined value to zero.

In this way, the overall period of time in which the auto-start phase can be performed in case of a driver's change of mind" is advantageously increased.

An aspect of the invention provides that the electronic control unit may be configured to keep the engine speed at the second predetermined value by operating a motor-generator electric unit.

According to another aspect of the invention, the electronic control unit may be config- ured to decrease the engine speed from the first predetermined value to the second pre-determined value and from the second predetermined value to zero by still operating the above mentioned motor-generator electric unit.

According to another aspect of the invention, the electronic control unit is configured to operate the motor-generator electric unit by performing a feedback control loop of a pa-rameter indicative of the torque supplied by the motor-generator electric unit.

In this way, the method can be performed with low computational effort.

These first and second predetermined values advantageously allows to increase the overall period of time in which the auto-start phase can be triggered in case of a driver's change of mind" without consuming too much energy.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings.

Figure 1 shows an internal combustion engine.

Figure 2 is a simplified section A-A of the internal combustion engine of figure 1.

Figure 3 schematically shows a hybrid motor vehicle comprising the internal combustion engine of figure 1.

Figure 4 is a flowchart of a method of operating the internal combustion engine in the au-tomotive system of figure 3.

Figure 5 is an explanatory diagram representing the engine speed during an auto-stop phase of the internal combustion engine.

DETAILED DESCRIPTION

Some embodiments may include an internal combustion engine (ICE) 110, such as a Diesel engine or a spark ignition engine. As shown in figures 1 and 2, the ICE 110 com- prises an engine block 120 defining at least one cylinder 125 having a piston 140 cou-pled to rotate a crankshaft 145. A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150. A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received a fuel source 190. Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200.

An air intake duct 205 may provide air from the ambient environment to the intake mani-fold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a tur-bocharger 230, having a compressor 240 rotationally coupled to a turbine 250. may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NO traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters. Other embodiments may include an exhaust gas recircu- lation (EGS) system 300 coupled between the exhaust manifold 225 and the intake man- ifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the tempera-ture of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The ICE 110 may further be provided with an electronic control unit (ECU) 450 in com-munication with one or more sensors and/or devices associated with the ICE 110. The ECU 450 may receive input signals from various sensors configured to generate the sig- nals in proportion to various physical parameters associated with the ICE 110. The sen- sors include, but are not limited to, a mass airflow and temperature sensor 340, a mani-fold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam posi-tion sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and a position sensor 445 for an accelerator pe- dal 446. Furthermore, the ECU 450 may generate output signals to various control de-vices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system 460 and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system. and send and receive signals to/from the interface bus. The memory system 460 may include van-ous storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices.

The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

Referring to figure 3, the ICE 110 can be mounted on a hybrid motor vehicle 10, wherein the crankshaft 145 of the ICE 110 is provided for actuating a couple of drive wheels 13 through a driveline 14.

The dniveline 14 comprises a transmission 15 (also referred as gearbox), in this example a manual transmission, which is connected to the drive wheels 13, and a clutch 16 for selectively coupling the crankshaft 145 to the transmission 15.

The clutch 16 may be disposed in an engaged configuration, in which the crankshaft 145 and the transmission 15 are mutually engaged, and in a disengaged configuration, in which the crankshaft 145 and the transmission 15 are disengaged. The clutch 16 is actu- ated by the driver of the motor vehicle through a clutch pedal 17, which is movable be-tween a pressed position and a released position. When the clutch pedal 17 is pressed, the clutch 16 is in the disengaged configuration. When the clutch pedal 17 is released, the clutch 16 returns in the engaged configuration.

The clutch pedal 17 is coupled to a wide-range position sensor 103 which is connected to the ECU 450. The position sensor 103 is provided for generating an electronic signal representative of the position of the clutch pedal 17.

The transmission 15 is generally designed to allow multiple gear ratios (or simply "gears") between the crankshaft 145 and the drive wheels 13, including a neutral or idle gear, in which the transmission 15 does not transmit any torque from the crankshaft 145 to the drive wheels 13, a first gear, which has the lowest forward gear ratio in the trans-mission 15, and several other gears, whose gear ratio progressively increases.

In the present example, the shifting between these gears of the transmission 15 is oper-ated through a gear lever 18, also referred as transmission lever. The gear lever 18 may be coupled to a position sensor 105, which is connected to the ECU 450. The position sensor 105 is provided for generating an electronic signal indicative of the gear that is actually engaged in the transmission 15.

The hybrid motor vehicle 10 further comprises a Motor-Generator electric Unit (MGU) 20, and an electrical battery (not shown) suitable to electrically supply the MGU 20. The MGU 20 can operate as an electric motor for assisting or replacing the ICE 110 in propel-ling the motor vehicle 10, and can also operate as an electric generator, especially when the motor vehicle 10 is braking, for charging the battery. For example, the MGU 20 may be embodied as a Belt Alternator Starter (BAS), which is generally provided for starting the ICE 110, but which is also capable of providing a certain contribution of torque direct- ly to the drive wheels 13 during acceleration, and of generating a certain quantity of elec-trical energy during deceleration, working as a regenerative brake. The MGU 20 and the ICE 110 are both controlled by the ECU 450.

According to the present embodiment of the invention, the ECU 450 is configured to im-plement a Bottom Of Travel (BOT) Start and Stop strategy, which generally provides for automatically switching the ICE 110 off, each time the motor vehicle 10 stops1 for exam-ple in proximity of a traffic light or a stop sign, and then for automatically switching it on, when the driver wants to drive the motor vehicle 10 away.

The BOT strategy is based on a series of typical manoeuvres that the drivers perform when he wants to stop the motor vehicle 10 or to drive the motor vehicle 10 away.

More specifically, in order to drive the motor vehicle 10 away, the driver generally press-es the clutch pedal 17 to disengage the clutch 16, then he moves the gear lever ISso as to engage a gear (typically the first gear) of the transmission 15, and then releases the clutch pedal 17 to reengage the clutch 16.

Considering this sequence of manoeuvres, the BOT strategy implemented in the present embodiment of the invention provides for the ECU 450 to automatically performing an auto-start phase of the ICE 110 when the gear has been already engaged and the driver release the clutch pedal 17.

On the other hand, in order to stop the motor vehicle 10, the driver generally releases the accelerator pedal 445, so that the ECU 450 cuts the fuel injections off, and then he de-celerates the motor vehicle 10, for example by pressing a brake pedal (not shown), so that the speed of the motor vehicle 10 progressively decreases as well as the rotational speed of the crankshaft 145 of the ICE 110. When the speed of the motor vehicle 10 is below a certain level, the driver presses the clutch pedal 17 in order to disengage the clutch 16. Finally, when the motor-vehicle is still, the driver usually actuates the gear lev-er 18 so as to engage the neutral gear of the transmission 15.

Considering this sequence of manoeuvres, the BOT strategy provides for the ECU 450 to automatically performing an auto-stop phase of the ICE 110, as soon as the driver presses the clutch pedal 17 during the deceleration.

In greater detail, the BOT strategy may manage the auto-stop of the motor vehicle ac-cording to the procedure illustrated in the flowchart of figure 4.

This procedure starts if the ICE 110 is actually switched-on (block 500) and provides for the ECU 450 to repeatedly monitor the following parameters: the motor vehicle speed (block 505), the engine speed (namely the rotational speed of the crankshaft 145) (block 510) and the position of the clutch pedal 17 (block 515).

The speed of the motor vehicle 10 can be monitored by means of a speed sensor 102 associated to the drive wheels 13. The engine speed can be measured by means of the position sensor 420 associated to the crankshaft 145. Finally, the movement of the clutch pedal 17 can be monitored by means of the position sensor 103.

The procedure then provides for the ECU 450 to check whether the speed of the motor vehicle is within a predetermined threshold value VS (block 520), whether the engine speed is below a predetermined threshold value ESIh (block 525), and whether the clutch pedal 17 is in the pressed position (block 530).

The threshold value VSIh for the motor vehicle speed and the threshold value ESEh for the engine speed may be calibration threshold values determined during an experimental ac-tivity on a test bench. The threshold value ESth may be for example comprised between 1000 rpm and 750 rpm.

As soon as all these checks yield affirmative (block 535), the procedure provides for the ECU 450 to perform an auto-stop phase of the ICE 110 (block 540).

As shown in figure 4, the auto-stop phase of the ICE 110 may include four main stages.

The first stage (block 542) provides for the ECU 450 to keep the engine speed constant at a first predetermined value Vi for a predetermined period of time Ti. The first prede-termined value Vi may be equal to the so called idle speed, and may be a calibration value determined during an experimental activity on a test bench and then stored in the memory system 460. For example, the first predetermined value Vi may be lower than 1000 rpm, for instance about 750 rpm. The period of time Ti may be a calibration pa-rameter too, which may be determined during a calibration activity and then stored in the memory system 460. For example, the period of time Ti may be comprised between 800 ms and 1200 ms, for instance about 1000 ms. This first stage is performed in order to other operating strategies, such as for example the Stop Position of the crank angle.

When the period of time Ti is over, the second stage of the auto-stop phase provides for the ECU 450 to reduce (block 543) the engine speed from the first predetermined value Vi to a second predetermined value V2. The decrease of the engine speed in this se- cond stage is linear, namely the variation of the engine speed over the time in this se-cond stage follows a linear profile.

The second predetermined value V2 is comprised between the first predetermined value Vi and zero. More specifically, the second predetermined value V2 is greater or equal than/to a minimum allowable threshold value Vth. The minimum allowable threshold val-ue Vth may be the minimum value of the engine speed for which the BOT Start and Stop strategy still allows the ICE 110 to be restarted in case of a driver's "change of mind". In other words, when the engine speed falls below the minimum allowable threshold values Vth, the BOT Start and Stop strategy prevents the ICE 110 to be restarted even if the driver releases the clutch pedal 17. Both the minimum allowable threshold value Vth and the second predetermined threshold value V2 may be calibration values determined duN ing an experimental activity on a test bench and then stored in the memory system 460.

For example, the minimum allowable threshold value Vth may be comprised between 400 rpm and 450 rpm, whereas the second predetermined value V2 may be higher than 450 rpm, for instance about 500 rpm.

Once the engine speed has reached the second predetermined value V2, the thirst stage of the auto-stop phase provides for the ECU 450 to keep the engine speed constant at the second predetermined value V2 for a predetermined period of time T2 (block 544).

The period of time T2 may be a calibration parameter, which may be determined during a calibration activity and then stored in the memory system 460. For example, the period of time T2 may be comprised between 500 ms and 1000 ms, for instance about 700 ms.

When the period of time T2 is over, the fourth stage of the auto-stop phase provides for the ECU 450 to reduce (block 545) the engine speed from the second predetermined value V2 to zero so as to complete the auto-stop phase. The decrease of the engine speed in this forth stage is linear, namely the variation of the engine speed over the time in this second stage follows a linear profile, and it should be as fast as possible, provided that the noises generated by the engine in this stage do not become too loud.

In order to perform the above disclosed four stages of the auto-stop phase, the ECU 450 uses the MGU 20 whose operation, being the clutch 16 disengaged and the fuel injec-tions cut off, has a direct impact on the speed of the crankshaft 145, thereby determining the engine speed. More precisely, during the first and the third stages, the ECU 450 acti-vates the MGU 20 lo generate torque at the crankshaft 145, in order to keep constant the engine speed at the first predetermined value and at the second predetermined value re-spectively. During the second and the fourth stages, the ECU 450 activates the MGU 20 to absorb and/or generate torque at the crankshaft 145, thereby progressively reducing the engine speed. In order to improve the control of the engine speed during all the above mentioned stages of the auto-stop phase, the ECU 450 may regulate the opera-tion of the MGU 20 using a closed control loop of the toque generated/absorbed by the MGU 20 itself.

In this way, during the auto-stop phase of the ICE 110, the engine speed may vary over the time according to a profile of the kind shown in figure 5.

The profile has a stepped shape that advantageously increases the overall period of time in which an auto-start phase of the ICE 110 can be performed in case of a driver's "change of mind". In fact, being the second threshold value V2 greater (or equal) than the minimum allowable value Vth, the auto-start phase may be advantageously performed either during the first stage, in which the engine speed is kept constant at the first prede-termined value VI, or during the second stage, in which the engine speed decreases from the first predetermined value Vi to the second predetermined value V2, or even during the third stage, in which the engine speed remains at the second predetermined valueV2.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCES

motor vehicle 13 drive wheels 14 driveline transmission 16 clutch 17 clutch pedal 18 gear lever 20 MGU 102 speed sensor 103 position sensor position sensor internal combustion engine 120 engine block cylinder cylinder head camshaft piston 145 crankshaft combustion chamber cam phaser fuel injector fuel rail 180 fuel pump fuel source intake manifold 205 air intake duct 210 intake port 215 valves 220 port 225 exhaust manifold 230 turbocharger 240 compressor 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 260 aftertreatment devices 290 VGT actuator 300 exhaust gas recirculation system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant and oil temperature and level sensors 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator pedal position sensor 446 accelerator pedal 450 ECU 460 memory system 500 block 505 block 510 block 515 block 520 block 525 block 530 block 535 block 540 block 542 block 543 block 544 block 545 block VSth vehicle speed threshold value ESIb engine speed threshold value Vi first predetermined value Ti first predetermined period of time V2 second predetermined value T2 second predetermined period of time Vth minimum allowable threshold value

Claims

CLAIMS1. A method of operating an internal combustion engine (110) of a motor vehicle (10) comprising the steps of: -monitoring a speed of the motor vehicle (10), -monitoring an operating configuration of a clutch (16) of the motor vehicle (10), -monitoring a speed of the internal combustion engine (110), -performing an auto-stop phase of the internal combustion engine (110) it the monitored speed of the motor vehicle (10) is below a predetermined threshold value, the monitored engine speed is below a predetermined threshold value, and the clutch (16) is disen-gaged, wherein the auto-stop phase comprises the steps of: -decreasing the engine speed from a first predetermined value (Vi) to a second prede-termined value (V2) that is greater or equal to a minimum allowable threshold value (Vth) for an auto-start phase of the internal combustion engine to be performed, -keeping the engine speed at the second predetermined value QJ2) for a predetermined period of time (T2), and then -decreasing the engine speed from the second predetermined value (V2) to zero.
2. A method according to claim 1, wherein the engine speed is kept at the second predetermined value N2) by operating a motor-generator electric unit (20).
3. A method according to claim 2, wherein the engine speed is decreased from the first predetermined value (Vi) to the second predetermined value (V2) and from the se-cond predetermined value (V2) to zero by operating the motor-generator electric unit (20).
4. A method according to claim 2 or 3, wherein the motor-generator electric unit (20) is operated performing a feedback control loop of a parameter indicative of the torque supplied by the motor-generator electric unit (20).
5. A method according to any of the preceding claims, wherein the first predetermined value (Vi) and the second predetermined value (12) are calibration values.
6. A method according to any of the preceding claims, wherein the first predetermined value (Vi) is lower than 1000 mm, and the second predetermined value (V2) is higher than 450 rpm.
7. A method according to any of the preceding claims, wherein the predetermined pe-nod of time (T2) is a calibration period of time.
8. A method according to any of the preceding claims, wherein the predetermined pe-riod of time is comprised between 500 ms and 1000 ms.
9. A computer program comprising a computer code suitable for performing the method according to any of the preceding claims.
10. A computer program. product on which the computer program of claim 9 is stored.
11. An electromagnetic signal modulated as a carrier for a sequence of data bits repre-senting the computer program according to claim 9.