GB2504473A - Method of controlling a fuel injection of an idle stop-start diesel internal combustion engine - Google Patents

Abstract

Disclosed is a method of controlling a fuel injection of an internal combustion diesel engine of an automotive system during cranking the engine. The method comprises the steps of comparing a reference idle engine speed with a current engine speed and defining the difference between them as an engine speed error, multiplying said engine speed error by a proportional gain Kprop of a proportional regulator, thus obtaining a fuel quantity Uprop. The fuel quantity Uprop calculated is added to an offset fuel quantity to provide a fuel quantity Utot to be injected in to the engine. The method is for use with idle stop-start engines connected to an automatic gearbox.

Description

METHOD OF CONTROLLING A CRANK STRATEGY

IN AN INTERNAL COMBUSTION DIESEL ENGINE

TECHNICAL FIELD

-The present disclosure relates to a method of controlling a crank strategy in an internal combustion engine, particularly for diesel engines equipped with "Start & stop" system and coupled.to an automatic transmission.

BACKGROUND

As known, for automobiles, a "start & stop" system automatically shuts down and restarts the internal combustion engine to reduce the amount of time the engine spends idling, thereby reducing fuel consumption and emissions. This is most advantageous for vehicles which spend significant amounts of time waiting at traffic lights or frequently come to a stop in traffic jams. This feature is present in hybrid electric vehicles, but has also appeared in vehicles which lack a hybrid electric powertrain. For non-electric vehicles, fuel economy gains from this technology are typically in the range of 5 to 10 percent.

It is also well known that an automatic transmission is one type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the -driver from having to shift gears manually. Most automatic transmissions have a defined set of gear ranges, often with a parking pawl feature that locks the output shaft of the transmission.

Finally, it is well known that during cranking, the engine management system, by means of an engine control unit (ECU) and its actuators, provides a fuel injection strategy (also called key-crank map) which should bring the engine as fast as possible to its idle speed, even accepting an initial speed overshoot.

A problem arises in modern engines, which are electronically controlled, provided with a "start & stop system" and coupled to an automatic transmission. In fact, due to the start & stop" system, they are forced to frequent restarts and starting the engine in drive gear, could result in unwanted jerk and vibrations compromising the perceived comfort.

Therefore, to avoid this issue1 a need exists for a method that utilizes a different fuel control strategy, during auto-start crank phase, with different map and different input variables.

An object of this invention is to provide a method which defines and controls a smooth crank strategy in an internal combustion diesel engine, particularly for (but not limited to) engines equipped with Start & stop" system and coupled to an automatic transmission.

Another object is to provide an apparatus which allows to perform the above method.

These objects are achieved by a method, by an apparatus, by an engine, by a computer program and computer program product, and by an electromagnetic signal having the features recited in the independent claims.

The dependent claims delineate preferred andlor especially advantageous aspects.

SUMMARY

An embodiment of the disclosure provides a method of controlling a fuel injection of an internal combustion diesel engine of an automotive system, during cranking the engine, the method comprising: -comparing a reference idle engine speed with a current engine speed and defining the difference between them as an engine speed error, -multiplying said engine speed error per a proportional gain of a proportional regulator, thus obtaining a fuel quantity, -adding said fuel quantity and an offset fuel quantity, thus obtaining a total fuel quantity.

Consequently, an apparatus is disclosed for controlling a fuel injection of an internal combustion diesel engine of an automotive system, during cranking the engine, the apparatus comprising: -means for comparing a reference idle engine speed with a current engine speed and defining the difference between them as an engine speed error, -means for multiplying said engine speed error per a proportional gain of a proportional regulator, thus obtaining a fuel quantity, -means for adding said fuel quantity and an offset fuel quantity, thus obtaining a total fuel quantity.

An advantage of this embodiment is that it provides a method of controlling a smooth crank strategy, avoiding vibrations and jerks, through a smooth rise-up of the engine speed during crank and avoiding a speed overshoot. The method is based on the consideration that to avoid speed overshoots the fuel quantity cannot be derived from a map but should be regulated; this is realized by means of a proportional regulator which determines the fuel quantity to be injected, based on the difference between a reference idle speed to be reached and the current engine speed.

According to another embodiment of the invention, said current engine speed is acquired during time interval lower than 25 ms, preferably 12.5 ms.

An advantage of this embodiment is that with a high resolution speed acquisition the smooth crank strategy becomes very accurate.

According to a further embodiment of the invention, for the method to be applied, said current engine speed is higher than a calibratablethreshold.

An advantage of this embodiment is that the new strategy, avoiding speed overshoots, becomes effective when the engine speed comes closer to the reference engine speed for idle, which normally ranges around 700-800 rpm.

According to a still further embodiment, said proportional gain is function of said reference idle engine speed.

An advantage of this embodiment is that the proportional control of the fuel quantity becomes more effective when targeted to the reference speed to be reached without overshoot.

The method according to one of its aspects can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of computer program product comprising the computer program.

The computer program product can be embodied as a control apparatus for an intemal combustion engine, comprising an Electronic Control Unit (ECU), a data carrier associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case, when the control apparatus executes the computer program all the steps of the method described above are carried out.

The method according to a further aspect can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represents a computer program to carry out all steps of the method.

A stifl further aspect of the disclosure provides an internal combustion engine specially arranged for carrying out the method claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an automotive system.

Figure 2 is a section of an internal combustion engine belonging to the automotive system of figure 1.

Figure 3 shows the algorithm for controlling the smooth crank strategy according to an embodiment of the invention.

Figure 4 is a flowchart of the crank strategy, comprising the standard strategy, the strategy according to an embodiment of the present invention and the enabling conditions for the new strategy to be actuated.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system 100, as shown in Figures land 2, that includes an internal combustion engine (ICE) 110, particularly a Diesel engine, having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled 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 160 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 pod 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 manifold 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 turbocharger 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 pods 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 NOx traps, hydrocarbon adsorbers, selective catalytic reduction (5CR) systems, particulate filters (DPF) or a combination of the last two devices, i.e. selective catalytic reduction system comprising a particulate filter (SCRF). Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature 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 automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110 and equipped with a data carrier 40. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold 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 position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices 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.

Tuming now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system 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 may include various 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 andlor 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.

The method according to the invention, has its own goal in defining a control strategy capable to perform a smooth engine speed rise up, during the cranking phase of internal combustion engines. In this way, it would be completely avoided the initial overshoot of the engine speed, with standard key-crank map. As mentioned above, the need for this new strategy arises from the fact that modern automobiles are provided with a start-stop system, which forces the engine to restart several times, and with automatic transmissions, which cause the engine starting in drive gear, thus creating unwanted jerk and vibrations and compromising the perceived comfort.

To illustrate the new method, some background information must be provided. According to a known crank strategy (see Figure 4, left side), each crank has the same fuel 2 0 injection control strategy. The fuel quantity is calculated every predetermined time interval, for example every 12.5 ms, based on a map 27, function of the engine coolant temperature and the engine speed. The coolant temperature is updated every time interval around 25 ms. Instead, the engine speed is updated in a so called low resolution (Lores) way, that means the update is done every 180° of the crankshaft 145. It appears clear the meaning of low resolution. Being the engine in a cranking phase, the engine speed is very low and therefore the update of the speed is very rough: for example at 300 rpm, the update will be performed every 100 ms. This low resolution is not an issue for powertrains without automatic transmissions, since during cranking the gear is not engaged. As output of the standard strategy, the final actuated fuel quantity is 3 determined (injected fuel for cranking), and, consequently, from another map, the initializing torque of the idle control.

The method according to the invention (as a whole, 28 in Figure 4) starts from the consideration that to avoid speed overshoots the fuel quantity cannot be derived from a map but should be regulated. One embodiment of the invention uses a proportional regulator, whose proportional gain 22 could be function of the reference idle engine speed. Such reference idle speed is to be understood as the speed the engine has to reach to run in idle condition. Normally this value is a constant (e.g. 800 rpm or 900 rpm), but in some condition, for example in case of battery low charge, it could be changed and a map in the electronic control unit would provide the right reference value. The new smooth strategy (see Fig. 3) starts acquiring said reference idle engine speed and the current engine speed.

Advantageously, the current engine speed is updated in a so called high resolution mode (Hires), within a time interval lower than 25 ms, preferably 12.5 ms. In fact, it is very difficult to realize a smooth engine crank calibrating the fuel quantity, based on an engine speed older more than 50 ms, as happens with the standard strategy. The reference idle engine speed is preferably updated every 12.5 ms, as well.

Once acquired the engine speed, the difference from the reference idle engine speed is defined as engine speed error, which is multiplied 21 per the proportional gain Kpmp 22 of the proportional regulator. The dimension of the proportional gain are suitable to obtain such product as a fuel quantity, called As already mentioned, the proportional gain of the regulator is determined as function of the reference idle speed: the higher is the reference idle speed, the higher will be the proportional gain. This would allow the engine to reach the idle speed in a shorter time and at the same to avoid overshoots. Finally, adding 23 said fuel quantity Uprep and an offset fuel quantity 24, thus obtaining a fuel quantity Ut, to be injected during cranking. The offset fuel quantity is required to compensate the constant error of a proportional regulator and is determined by knowing the characteristics of the proportional regulator. The fuel quantity utot is the effective injected fuel quantity for cranking, Figure 4 shows the logic of the new strategy and the condition for it to be applied.

Starting from an auto-start request 25, first of all is checked 26 the need of a smooth crank strategy and secondly 29 the engine speed precondition. In fact, to be the strategy more effective, the engine speed must be higher than a calibratable threshold, preferably 450 rpm, because with low engine speed this strategy would require a too long time for reaching the idle conditions. According to this condition, a standard strategy 27 or the new smooth strategy 28 will be chosen and then the respective output will be used 30 as fuel quantity and initializing torque per idle control.

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.

REFERENCE NUMBERS block

21 block 22 block 23 block 24 block block 26 block 27 block 28 block 29 block block data carder automotive system 110 internal combustion diesel engine engine block cylinder cylinder head camshaft 140 piston crankshaft combustion chamber cam phaser fuel injector l7ofuelrail fuel pump fuel source intake manifold 205 air intake pipe 210 intake port 215 valves 220 port 225 exhaust manifold 230 turbocharger 240 compressor 245 turbocharger shaft 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 281 lean NOx trap 283 LNT upstream airlfuel ratio sensor 284 LNT downstream air/fuel ratio sensor 285 LNT upstream temperature sensor 286 LNT downstream temperature sensor 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 temperature and level sensors 385 lubricating oil temperature and level sensor 390 metal temperature sensor 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 position sensor 446 accelerator pedal 450 ECU u proportional fuel quantity u totalfuel quantity Kprop proportional gain of the regulator