ITUB20152628A1 - METHOD FOR COLD START-UP OF AN INTERNAL COMBUSTION ENGINE POWERED BY A FUEL MIXTURE CONTAINING ETHANOL - Google Patents

Description

DESCRIPTION

"METHOD FOR COLD STARTING AN INTERNAL COMBUSTION ENGINE POWERED WITH A FUEL MIXTURE CONTAINING ETHANOL"

TECHNIQUE SECTOR

The present invention relates to a method for cold starting an internal combustion engine fed with a fuel mixture containing ethanol,

ANTERIOR ART

Typically, the internal combustion engines of a motor vehicle such as, for example, single-cylinder four-stroke engines comprise an injector which injects the fuel directly into the respective cylinder. The cylinder in turn houses a piston mechanically connected to a crankshaft to transmit the force generated by combustion inside the cylinder to the crankshaft itself.

The cylinder is connected by means of a respective intake valve to an adduction duct inside which a combustive fluid flows which passes through an intake manifold and to an exhaust duct via a respective exhaust valve. The supply duct receives a flow of fresh air coming from the external environment regulated by a control member which varies the passage section of the supply duct.

The injector is connected to a fuel supply circuit which provides a feed pump which draws the fuel from a tank and feeds it under pressure to the injector through a feed channel.

It is important to point out that the fuel in use can be any mixture with a high content of ethanol. In the event that the fuel used in the internal combustion engine is a mixture commonly referred to as E85 (mixture containing 85% ethanol and gasoline) or E10Q (pure ethanol), cold starting of the internal combustion engine is problematic because Unlike gasoline, ethanol has a very steep vaporization curve. In other words, the vapor fraction of ethanol varies rapidly from a very low value to a very high value at a defined vaporization temperature, a function of the pressure of the oxidizing fluid. Petrol, on the other hand, has a much less steep vaporization curve. For a given value of the pressure of the combustion fluid, the range of temperature values at which ethanol vaporizes is rather small and usually these temperature values are high (and in any case higher than the temperature values at which the gasoline vaporizes, with the same pressure value of the combustion fluid).

In the event that the temperature of the mixture with a high content of ethanol is very low (so-called cold start), it may therefore occur that this mixture with a high content of ethanol does not vaporize in the combustive fluid, remaining in the liquid state and preventing combustion. inside the cylinder.

To remedy this technical problem, internal combustion engines have been proposed equipped with a dedicated petrol supply circuit to be used only for cold starts. The injector is connected to the dedicated petrol supply circuit which provides a feed pump that draws the fuel from a small tank and feeds it under pressure to the injector through a respective feed channel. While allowing combustion inside the cylinder even if the temperature of the mixture with a high ethanol content is very low, these solutions are however economically disadvantageous and bulky,

DESCRIPTION OF THE INVENTION

The object of the present invention is therefore to provide a method for cold starting an internal combustion engine fed with a fuel mixture containing ethanol which is free from the drawbacks of the state of the art and which is, at the same time, easy and economical implementation.

In accordance with the present invention there is provided a method for cold starting an internal combustion engine fed with a fuel mixture containing ethanol according to what is claimed by the attached claims,

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the attached drawings, which illustrate a non-limiting example of embodiment, in which:

Figure 1 is a schematic view of an internal combustion engine fueled with a fuel mixture containing ethanol; And

Figure 2 illustrates the trend of the ethanol vaporization temperature as a function of the pressure of a comburent fluid.

PREFERRED EMBODIMENTS OF THE INVENTION

In figure 1, the number 1 indicates as a whole an internal combustion engine of a motor vehicle such as, for example, a single-cylinder four-stroke engine.

The internal combustion engine 1 comprises an injector 2, preferably electromagnetic (of a known type and not described in detail), which injects the fuel into a supply duct 6 upstream of a cylinder 3.

The cylinder 3 houses a piston 4 mechanically connected by means of a connecting rod to a driving shaft 5 to transmit the force generated by combustion inside the cylinder 3 to the driving shaft 5 itself,

The cylinder 3 is connected to the adduction duct 6 inside which a combustive fluid flows which passes through an intake manifold 6 * of the internal combustion engine 1 through a respective intake valve 7 and to an exhaust duct 8 through a respective drain valve 9.

The supply duct 6 receives the combustion fluid, ie fresh air coming from the external environment, at the reference external pressure and at the reference external temperature. Furthermore, the flow of the combustion fluid entering the internal combustion engine 1 is regulated by a control member 11 located downstream of a filter 10 and which varies the passage section of the supply duct 6. The intake manifold 6 * is substantially defined along the supply duct 6 between the intake valve 7 and the control member 11.

The control member 11 comprises an obturator element 12 which is housed at least partially inside the adduction duct 6 and is able to choke the flow rate of the comburent fluid according to its position inside the adduction duct 6 itself; and an actuation device 13 adapted to move the shutter element 12 to control the flow rate of the comburent fluid.

The handle (not shown) of the motor vehicle accelerator is connected to the control of the internal combustion engine by at least one metal cable 14 of the Bowden type, which is inserted inside one end of the shutter element 12 opposite the partially arranged end. inside the adduction duct 6 and is pushed by a return spring 15 towards a rest position which corresponds to a substantially null section for the passage of the comburent fluid (air) to the internal combustion engine 1 through the adduction duct 6. The throttle grip can rotate from the rest position corresponding to a driving torque which maintains the minimum speed to a maximum opening position corresponding to a maximum driving torque; and viceversa. The return spring 15 pushes the throttle grip towards the rest position and therefore the driver must apply a torque to the throttle grip to move the throttle grip from the rest position.

In other words, the section of the adduction duct 6 for controlling the flow of air supplied to the internal combustion engine 1 can be varied between the minimum SMIN value (which corresponds to said rest position) and the maximum SMAX value. ; and viceversa.

The injector 2 is connected to a fuel supply circuit which provides a feed pump 16 which draws the fuel from a tank 17 and feeds it under pressure to the injector 2 through a feed channel 18.

The exhaust duct 8 feeds the exhaust gases produced by combustion to an exhaust system, which emits the gases produced by combustion into the atmosphere and normally comprises at least one catalyst 19 (possibly provided with an anti-particulate filter).

Finally, the internal combustion engine 1 comprises a starter motor (not illustrated, of a known type and not described in detail) which allows the transformation of the electrical energy generated by a battery into the mechanical energy necessary to start the combustion engine 1 internal and that allows during the starting phase to reach a minimum number of revolutions (rpm). The starter motor consists of an electric motor, electrically activated by the ignition key and an electromagnet that connects the starter motor to the battery. The starter motor has the characteristic of having a lot of torque in the starting phase at the expense of a very high amount of absorbed current.

The internal combustion engine 1 comprises a control unit 20, which supervises the operation of the internal combustion engine 1 and is designed to control, in particular, the injector 2 and the actuation device 13.

It is important to underline that the fuel in use can be any mixture with a high content of ethanol, or pure ethanol can be used as fuel. In particular, for example, a mixture commonly indicated with E85 (mixture containing 85% of ethanol and gasoline) or E100 (pure ethanol) can be used. Figure 2 illustrates in detail the ethanol vaporization curve as a function of the reference external pressure Patm, ie the pressure Patm of the comburent fluid, expressed in bar.

Figure 2 illustrates in detail the ethanol vaporization curve as a function of the pressure Patm of the combustion fluid entering the cylinder 3 and allows to verify how the vaporization temperature of the ethanol is extremely sensitive to variations in the pressure Patm of the combustion fluid. For a given pressure value Patm of the comburent fluid, the range of temperature values at which the ethanol vaporizes is very small. There is substantially a defined temperature below which ethanol occurs in the liquid phase and above which, on the other hand, it occurs only in the vapor state for a determined value of the pressure Patm of the comburent fluid.

The strategy implemented by the control unit 20 for cold starting of the internal combustion engine 1 fed with a fuel mixture containing ethanol is described below. The lack of vaporization of the fuel mixture containing ethanol, in the event of a cold start, depends both on the temperature T of the said fuel mixture containing ethanol (lower than the range of values of the vaporization temperature for a given pressure value Patm of the combustion fluid) and by the pressure Patm of the combustion fluid.

The aforementioned strategy provides, in the first instance, to intervene on the pressure value Patm of the comburent fluid which is introduced into the intake manifold 6 * by reducing the pressure inside said intake manifold 6 * to pressure values that require lower vaporization temperatures. to allow vaporization of the ethanol contained in the fuel mixture containing ethanol (as illustrated in Figure 2). Secondly, it is also possible to intervene on the temperature T of the said fuel mixture containing ethanol, in particular by increasing the temperature T of the fuel mixture containing ethanol and, consequently, increasing the pressure value Patm of the comburent fluid necessary to allow the vaporization of the ethanol contained in the fuel mixture containing ethanol (as shown in Figure 2).

The strategy implemented by the control unit 20 provides first of all to recognize when the ignition key is inserted which electrically activates the starter motor.

According to a preferred variant, the strategy which is implemented by the control unit 20 is preferably implemented following the recognition of a refueling of fuel containing ethanol.

When the start of a start-up phase is recognized, the control unit 20 is set up to determine (through measurements or estimates) by means of suitable sensors the temperature value T of the fuel mixture containing ethanol collected in the tank 17 and , at least partially, in the injector 2 and to detect the pressure value Patm of the comburent fluid. According to a preferred variant, the temperature of the coolant which is correlated to the temperature T of the fuel mixture containing ethanol collected in the tank 17 is detected. Maps are stored inside the control unit 20 which make it possible to recognize, as a function of the temperature value T of the fuel mixture containing ethanol collected in the tank 17 and the pressure value Patm of the combustion fluid, in the case of a cold start of the internal combustion engine. In other words, these maps make it possible to determine whether the temperature T of the fuel mixture containing ethanol is sufficient or not to allow the vaporization of the ethanol as a function of the pressure Patm of the comburent fluid.

If the temperature T of the fuel mixture containing ethanol collected in the tank 17 and, at least partially, in the injector 2 is sufficient to allow the vaporization of the ethanol as a function of the pressure value Patm of the comburent fluid, it is not necessary to implement any strategy designed to allow critical cold starting of the internal combustion engine 1.

If the temperature T of the fuel mixture containing ethanol collected in the tank 17 and, at least partially, in the injector 2 is not sufficient to allow the vaporization of the ethanol as a function of the pressure value Patm of the combustion fluid, the unit Control 20 is configured to implement a strategy suitable for allowing the critical cold start of the internal combustion engine 1.

According to a first variant, the internal combustion engine 1 is provided with a depressor element which is controlled by the control unit 20. When the control unit 20 recognizes that the temperature T of the fuel mixture containing ethanol is not sufficient to allow the vaporization of the ethanol as a function of the pressure value Patm of the comburent fluid, the control unit 20 drives the depressor element which creates a depression in the intake manifold 6 *; the pressure value Patm of the comburent fluid inside the intake manifold 6 * is reduced to a value which allows the ethanol contained in the fuel mixture containing ethanol to be vaporized. In other words, the control unit 20 drives the depressor element to reduce the pressure inside the intake manifold 6 * to a value which is a function of the temperature T of the fuel mixture containing ethanol and which allows vaporization of the ethanol-containing fuel mixture. ethanol contained in such ethanol-containing fuel mixture. The action of the depressor element is added to the action of the starter motor which, during the dragging of the internal combustion engine 1 and in the absence of injection of fuel containing ethanol inside the cylinder 3, contributes to creating a vacuum in the manifold 6 * suction.

According to a possible variant, in the absence of the depressor element, the starter motor alone, while driving the internal combustion engine 1 and in the absence of injection of fuel containing ethanol inside the cylinder 3, creates a depression in the manifold 6 * suction.

Alternatively or in combination with the first variant described so far, when the control unit 20 recognizes that the temperature T of the fuel mixture containing ethanol is not sufficient to allow the vaporization of the ethanol as a function of the value of the Patm pressure of the combustion fluid, the control unit 20 is configured to signal to the motor vehicle rider by means of the lighting of a warning light on the dashboard that a specific strategy has been implemented to manage the critical cold start of the combustion engine 1 internal.

For as long as the warning light on the dashboard, which signals the implementation of the strategy to manage the critical cold start of the internal combustion engine 1, remains on, the driver must avoid intervening on the throttle grip by turning it from the rest position. corresponding to a driving torque which maintains the minimum speed (and which corresponds to a decidedly reduced section of passage of the combustion fluid to the internal combustion engine through the adduction duct 6) to the position of maximum opening corresponding to a maximum driving torque. In this way, the section of the adduction duct 6 for controlling the comburent fluid supplied to the internal combustion engine 1 is kept at the minimum value SMIN to favor the creation of the vacuum inside the intake manifold 6 *.

According to a preferred variant, when the control unit 20 recognizes that the temperature T of the fuel mixture containing ethanol is not sufficient to allow the vaporization of the ethanol as a function of the pressure value Patm of the comburent fluid, the unit 20 control unit is configured to control the injector 2 so as to effect the injection of fuel containing ethanol inside the cylinder 3 at an instant of the combustion cycle which allows to maximize the depression created in the intake manifold 6 * by exploiting the resonance of the pressure waves in said intake manifold 6.

According to a further variant, the internal combustion engine 1 is provided with a device 21 for heating the fuel containing ethanol placed along the supply circuit for the fuel containing ethanol, in particular along the supply channel 18, downstream of the supply pump 16 and at immediately upstream of injector 2,

When the control unit 20 recognizes that the temperature T of the fuel mixture containing ethanol is not sufficient to allow the vaporization of the ethanol as a function of the pressure value Patm of the comburent fluid, the control unit 20 is configured for control the heater device 21 so as to increase the temperature T of the fuel mixture containing ethanol. In this case, the action of the heater device 21 is added to the action of the depressor element and the starter motor which, during the cold (or critical) starting phase of the internal combustion engine 1 and in the absence of fuel injection containing ethanol inside the cylinder 3 create a depression in the intake manifold 6 *. In particular, the control unit 20 drives the heater device 21 to increase the temperature T of the fuel mixture containing ethanol to a value which is a function of the ambient pressure of the combustion fluid and of the depression inside the intake manifold 6 * and which allows the ethanol contained in such ethanol-containing fuel mixture to be vaporized. In this case, the control unit 20 is arranged to optimize the compromise between increasing the temperature T of the fuel mixture containing ethanol and reducing the pressure Patm of the comburent fluid.

According to a preferred variant, when the control unit 20 recognizes that the temperature T of the fuel mixture containing ethanol is not sufficient to allow the vaporization of the ethanol as a function of the pressure value Patm of the comburent fluid, the unit 20 is configured to control injector 2 with current pulses of shorter duration than the minimum injection time in order to increase the temperature T of the fuel mixture containing ethanol which is contained in the injector 2 in the absence of fuel injection containing ethanol. The minimum injection time corresponds to the maximum duration time interval in which an injector 2 shutter is moved from a closed position to an open position of an injector 2 valve and then back to the closed position of said injector valve 2 in the absence of injection of fuel containing ethanol.

By supplying the injector 2 with pulses having a duration shorter than the minimum injection time, the feeding of fuel containing ethanol into the cylinder 3 is prevented but a thermal power is generated due to the Joule effect sufficient to increase the temperature of the injector 2 and the temperature T of the fuel mixture containing ethanol of the injector 2. Also in this case, the driving of the injector 2 to increase the temperature T of the fuel mixture containing ethanol is added to the action of the depressor element and the starter motor which, during the cold (or critical) starting phase of the internal combustion engine 1 and in the absence of injection of fuel containing ethanol inside the cylinder 3, create a vacuum in the intake manifold 6 *. In this case, the control unit 20 is arranged to optimize the compromise between increasing the temperature T of the fuel mixture containing ethanol and reducing the ambient pressure of the combustion fluid.

The above described method for cold starting the internal combustion engine 1 fed with a fuel mixture containing ethanol can find advantageous application in any internal combustion engine 1, for example also for applications on motor vehicles.

The method described above for cold starting the internal combustion engine 1 fed with a fuel mixture containing ethanol has numerous advantages.

In particular, the strategy described in the preceding discussion is simple and economical to implement in a control unit 20 of an internal combustion engine 1 since it requires a reduced physical modification (i.e., at most, the insertion of the element depressor), has a reduced size and requires a modest calculation capacity of the control unit 20.

Furthermore, the method described above for cold starting an internal combustion engine 1 fed with a fuel mixture containing ethanol does not require the insertion of elements that require a lot of power for their operation (such as a dedicated electrical system heating of fuel containing ethanol).

Claims (1)

CLAIMS 1.- Method for cold starting an aspirated internal combustion engine (1), in particular for a motor vehicle, fed with a fuel mixture containing ethanol comprising at least one cylinder (3) which receives a combustive fluid, i.e. air fresh coming from the external environment, from a supply duct (6) through a respective suction valve (7); a control member (11) comprising an obturator element (12) which is at least partially disposed inside the supply duct (6) and is made movable inside the supply duct (6) so as to partialize the flow rate of combustive fluid entering the cylinder (3) as a function of its position inside the adduction duct (5) itself; a respective injector (2) of said ethanol-containing fuel mixture; and an intake manifold (6 *) formed along the supply duct (6) and defined between the intake valve (7) and the control member (11); the method involves: detecting the temperature (T) of the fuel mixture containing ethanol and the pressure (Patm) of the comburent fluid entering the cylinder (3); And - if the temperature (T) of the fuel mixture containing ethanol is not sufficient to allow the vaporization of the ethanol as a function of the pressure (Patm) of the combustion fluid entering the cylinder (3), create a depression inside of the intake manifold (6 *) in order to reduce the pressure inside the intake manifold (6 *) to a value that is a function of the temperature (T) of the fuel mixture containing ethanol and which allows the ethanol to be vaporized contained in this mixture. 2, - A method according to claim 1 wherein the internal combustion engine (1) comprises a depressor connected to the intake manifold (6 *); the method involves the further step of driving the depressor if the temperature (T) of the fuel mixture containing ethanol is not sufficient to allow the vaporization of the ethanol as a function of pressure (Patm) of the combustion fluid entering the cylinder (3) in order to reduce the pressure inside the intake manifold (6 *) to a value which is a function of the temperature (T) of the fuel mixture containing ethanol and which allows to vaporize the ethanol contained in this mixture. 3.- Method according to Claim 1 or 2 and comprising the further step of signaling to the driver the case in which the temperature (T) of the fuel mixture containing ethanol is not sufficient to allow the vaporization of the ethanol as a function of pressure ( Patm) of the combustion fluid entering the cylinder (3); and driving the control member (11) so that the flow of comburent fluid entering the cylinder (3) through the adduction duct (6) is substantially zero. 4.- Method according to one of the preceding claims and comprising the further step of controlling the injector (2) so as to carry out the injection of fuel containing ethanol into the respective cylinder (3) in an instant of the combustion cycle which allows to maximize the depression created in the intake manifold (6 *) by exploiting the resonance of the pressure waves in said intake manifold (6 *). 5.- Method according to one of the preceding claims and comprising the further step of increasing the temperature (T) of the fuel mixture containing ethanol if the temperature (T) of the fuel mixture containing ethanol is not sufficient to allow vaporization of ethanol as a function of the pressure (Patm) of the combustion fluid entering the cylinder (3). 6.- Method according to Claim 5 and comprising the further step of controlling the injector (2) with current pulses having a duration shorter than the minimum injection time so as to prevent the injection of the fuel containing ethanol inside the cylinder (3) and in such a way as to generate a Joule effect thermal power sufficient to increase the temperature of the injector (2) and the temperature (T) of the fuel mixture containing ethanol contained in the injector (2). 7. A method according to claim 5 or 6, wherein the internal combustion engine (1) comprises an ethanol-containing fuel heater device (21) placed along an ethanol-containing fuel supply circuit upstream of the injector (2) ; in which the method involves the further step of driving the heater device (21) in the event that the temperature (T) of the fuel mixture containing ethanol is not sufficient to allow the vaporization of the ethanol as a function of the pressure (Patm) of the combustion fluid entering the cylinder (3) so as to increase the temperature (T) of the fuel mixture containing ethanol fed to the injector (2). 8.- Method according to one of claims 5 to 7, in which the temperature (T) of the fuel mixture containing ethanol is increased up to a value such as to allow the ethanol contained in said mixture to be vaporized and variable according to the pressure (Patm) of the combustion fluid entering the cylinder (3) and of the depression inside the intake manifold (6 *). 9.- Method according to one of the preceding claims and comprising the further step of detecting the temperature (T) of the fuel mixture containing ethanol and the pressure (Patm) of the comburent fluid entering the cylinder (3) only after the recognition of a refueling of a fuel mixture containing ethanol.