FR2890694A1 - Fuel injection device for e.g. diesel engine of motor vehicle, has electronic control unit adapted to control transfer unit for forming target fuel mixture with characteristics defined based on engine operation conditions - Google Patents

Abstract

The device (1) has an electronic control unit (8) adapted to control a transfer unit for forming in a mixture tank (51) a target fuel mixture having characteristics defined based on engine operation conditions i.e. engine speed and engine charge level. The control unit determines the composition of return fuel mixture (C3) present in a recovery tank (34) in order to determine the quantity of return fuel mixture to be transferred in the tank (51) with a main fuel (C1) and an auxiliary fluid (C2).

Description

FUEL INJECTION DEVICE WITH CHARACTERISTICS

VARIABLE

  The present invention relates to an injection device for an internal combustion engine, in particular for a motor vehicle diesel engine. The invention more particularly relates to an injection device for an internal combustion engine comprising a fuel system with variable characteristics.

  Injection devices for an internal combustion engine typically comprise at least one fuel injector adapted to inject fuel into an associated combustion chamber, a fuel supply system comprising a storage tank for containing a fuel, connected to a feed pump ensuring the transfer under pressure of a fuel flow to said injector. In automotive applications, the injector devices comprise for the most part injectors, for example of the common rail type, having return fuel flows, not injected, also called leakage rates, which leave the injectors to be sent back to the storage tank.

  Depending on the operating conditions of the engine, including the speed and the load level, the fuel requirements are different. A high cetane number is suitable for cold start and low loads to reduce noise and HC and CO emissions, while lower cetane numbers are desirable at high loads to optimize NOx emissions and particles.

  In order to adapt the characteristics of the fuel to the operating range of the engine, it is known to multi-fuel injection devices, generally two-fuel, which differ in their cetane number. The two fuels are stored in separate tanks and are injected separately via two injectors, one of the injectors being disposed in the air intake pipe, or via a common injector, in which case the injections associated with the different fuels take place. at different times of the diesel cycle. Such injection devices only allow the injection of two different fuels and also requires an injector technology that can manage two fuel supply lines. Furthermore, these injection devices are not suitable for injectors generally used in automotive applications, with leak rates that can be important, such as common rail injectors.

  It has also been proposed in patent document JP 9068061 to pre-mix the two different fuels in order to have variable fuel properties according to the proportions of the mixture. The fuel resulting from this premix with the new associated characteristics is then fed to the injectors. This solution does not require a new dual feed line injector technology and allows for an infinite number of fuels as needed. However, the injection device described in this document is not suitable for injectors with leak rates.

  The object of the present invention is to provide a fuel injection device equipped with injectors having leak rates to adapt the characteristics of the fuel to the operating conditions of the engine.

  For this purpose, the subject of the present invention is a fuel injection device for an internal combustion engine, in particular for a motor vehicle diesel engine, comprising at least one fuel injector capable of injecting fuel into an associated combustion chamber. a fuel supply system comprising a main storage tank for containing a main fuel, connected to a feed pump for transferring a fuel flow under pressure to said injector, and a recycling circuit ensuring the transfer of fuel return fuel flow, not injected, from the fuel injector to the feed system upstream of the feed pump, characterized in that said feed system comprises - at least one auxiliary storage tank intended to contain an auxiliary fluid of the combustion additive or auxiliary fuel type having properties different from those of the fuel main, - a recovery tank connected to the recycling circuit to recover the return fuel flows from the injector, formed of mixtures of main fuel and auxiliary fluid, and - a mixing system comprising a mixing tank and means of transfer able to transfer to the mixing tank quantities of main fuel, auxiliary fluid and return fuel mixture respectively present in the main storage tank, the auxiliary tank and the recovery tank, said supply pump ensuring the transfer under pressure of a fuel flow from said mixing tank to said fuel injector, the injection device comprising a control unit adapted to control said transfer means to form in the mixing tank a target fuel mixture having characteristics defined according to engine operating conditions, in particular as a function of the engine speed and engine load level.

  According to the invention, the return fuel flows are recovered in a recovery tank, the control unit being able to determine a target mixing ratio between the main fuel quantity and the auxiliary fluid quantity as a function of the operating conditions. of the engine and then controlling the transfer means to form in the mixing tank the corresponding mixture from the main fuel of the main storage tank, the auxiliary fluid of the auxiliary storage tank, and the return fuel mixture of the recovery tank .

  The injection device according to the invention can advantageously be used to obtain mixtures between two different fuels, whatever their type, especially fuels which differ in their cetane number. The injection device can also be used to form mixtures in the mixing tank between the main fuel stored in the main storage tank, and a fluid, other than a fuel, stored in the auxiliary storage tank, such as water or a liquid combustion additive, in particular a procetane (ethylhexyl nitrate) or an additive for reducing the soot oxidation temperature, for example.

  According to one feature, the control unit is able to determine the composition of the return fuel mixture present in the recovery tank over time in order to dose the amount of return fuel mixture to be transferred into the mixing tank with the fuel. main present in the main storage tank and / or the auxiliary fluid present in the auxiliary storage tank. Determining the composition of the return fuel mixture by the control unit can be performed from the knowledge of at least one mixing law of the main fuel and the auxiliary fluid and the history of the engine operation. This determination of the composition of the return fuel mixture present in the recovery tank by the control unit can also be deduced from at least one characteristic of the return fuel mixture, such as density, measured by appropriate sensor implanted. in the recovery tank.

  According to one embodiment, said transfer means comprise individual supply lines individually connecting the main storage tank, the auxiliary storage tank and the recovery tank to the mixing tank, each supply line being equipped with a low pressure pump and a valve interposed between the mixing tank and the low pressure pump, said valves being controlled by the control unit to regulate the flow of the supply lines.

  Advantageously, the main storage tank, the auxiliary storage tank and the recovery tank are each equipped with a level sensor connected to the control unit, the control unit controlling the transfer means according to the quantity of main fuel and auxiliary fluid remaining in the main storage tank and the auxiliary storage tank, and the return fuel mixture remaining in the recovery tank.

  According to one embodiment, the fuel injection device comprises a common fuel distribution rail, connected on the one hand to the high pressure type feed pump and on the other hand to a set of fuel injectors. .

  The invention will be better understood, and other objects, details, features and advantages will become more clearly apparent from the following detailed explanatory description of a presently preferred particular embodiment of the invention, with reference to FIG. single annexed, which represents a schematic view of an injection device of an internal combustion engine of a motor vehicle.

  In the present embodiment illustrated in the figure, the injection device 1 comprises, in a manner known per se, a common fuel distribution rail 2, this ramp being connected on the one hand to a high pressure pump 31 of a fuel supply system 3 and, on the other hand, a set of fuel injectors 6, for example four in number, each of them cooperating with an associated combustion chamber. The fuel injectors 6, only one of which is shown in the figure for purposes of simplification, comprise an injection nose 61 through which the pressurized fuel is injected into the associated combustion chamber, and an outlet 62 through which are evacuated uninjected fuel flows, also referred to as back flow or leakage rates.

  The injection device includes a variable-characteristic fuel delivery system that operates in the present embodiment, with two fuels differentiating from one another by their cetane number. The feed system comprises a first storage reservoir, said main 32, which contains a first fuel C1 having a low cetane number, a second storage tank, said auxiliary 33, which contains a second fuel C2 having high cetane number , and a recovery tank 34 connected via a recycling circuit 7 to the outlets 62 of the injectors for recovering low pressure return fuel streams from the injectors. Each injector is for example connected by an individual recycling line 71 to the recovery tank, as shown in the figure. This recovery tank makes it possible to create a buffer zone for managing these leak rates.

  The feed system further comprises a mixing system 5 comprising a mixing tank 51 provided with three flow control valves (not shown), to which the main tank 32, the auxiliary tank 33 and the recovery tank 34 are connected by individual supply lines, respectively 52, 53, 54, each equipped with a low pressure pump, respectively 55, 56, 57, for transferring the corresponding fuel into the mixing tank.

  The valves are electrically driven by an electronic control unit, or ECU 8, via a control line 81, to meter the flow rate of each supply line 52, 53, 54 depending on the desired final mixture in the mixing tank. , the mixing tank being equipped with mixing means (not shown) for mixing the various fuels to obtain a homogeneous mixture.

  The high pressure pump 31 is connected by a suction pipe 40 to the mixing tank, to suck the mixture formed in the mixing tank, and discharge it under high pressure to the common supply rail 2 via a discharge pipe 38, so as to supply the injectors connected to the ramp via a set of high pressure tubes 21.

  The main tank, the auxiliary tank and the recovery tank are each equipped with a level sensor 35, 36, 37. The ECU unit 8 receives as input signals indicative of the quantity of fuel C1 and C2 remaining in the tanks. storage 32, 33 and the amount of return fuel mixture C3 remaining in the recovery tank 34, as well as signals indicative of the engine speed N and the load level PME, for example from a engine speed sensor 91 and a air flow meter 92 indicating the amount of air admitted into the cylinders.

  In operation, the ECU sets the mixing ratio between the amount of main fuel and auxiliary fuel as a function of the engine load conditions and the engine speed, and then controls the valves to form the corresponding mixture in the mixing tank. from the main fuel stored in the main tank, auxiliary fuel stored in the auxiliary tank and / or C3 mixture of return fuel contained in the recovery tank.

  The recovery tank advantageously has a limited volume for reasons of space, which implies that the return fuel mixture, the composition of which varies over time, must be reused within a relatively short time.

  The nature of the return fuel mixture in the recovery tank is monitored over time in order to know the evolution of the characteristics that can impact combustion (cetane number, density, volatility) and to determine the mixture to be mixed in the mixing tank. with one of the two fuels C1, C2 depending on the engine demand. This monitoring is performed by the ECU unit based on knowledge of mixing laws of the two initial fuels C1 and C2 and the history of the engine operation (dosing and fuel flow injected over time). The injected fuel flow is calculated via the ECU, based on the engine speed N, the load level PME and the main fuel / auxiliary fuel mixture ratio, the return fuel flow rates being deductible by the unit. ECU from injected fuel flow rates. The return fuel flow rates can also be determined by means of the recovery tank level sensor and / or a flow meter provided on the recycling circuit. By mixing law is meant a relation between the variations of the characteristics of a fuel resulting from a mixture of the two initial fuels as a function of the proportions of the mixture.

  For a more accurate follow-up over a long time base, resets may be performed using point measurements of characteristics of the return fuel mixture present in the recovery tank, such as density measurements, for example. Since the density mixing law is linear, the density measurement makes it possible to easily go back to the composition of the return fuel mixture.

  A linear mixing law f as a function of the mixing ratio x of a mixture composed of x% by volume of main fuel C1 and (1-x)% by volume of auxiliary fuel C2 is represented by the following equation A: Y3 = f (x) = x. Y1 + (1-x) .Y2 (A) wherein Y1 and Y2 denote fixed values associated with the two initial fuels, namely the main fuel C1 and the auxiliary fuel C2, and Y3 denotes a measured value.

  Knowing Y1 and Y2, the mixing ratio x is then easy to determine according to the measurement of Y3 by the following equation (B): x = (Y3-Y2) / (Y1-Y2) (B) Once the mixing rate x known, the other characteristics of the return fuel, can be deduced from charts previously established on the various possible mixtures between the two fuels and stored in the ECU unit.

  In the present embodiment, the recovery tank is equipped with a density sensor 38 and a temperature sensor 39, the ECU receiving signals representative of the density and temperature from said sensors. In operation, the control unit calculates the mixing ratio x of the return fuel mixture present in the recovery tank from the initial fuel densities Y1, Y2 and the density measurement Y3 of the fuel mixture in return, and then calculates the amount of return fuel mixture that can be transferred to the mixing tank taking into account the measured temperature, to obtain the desired target mixture in the mixing tank.

  The injection device described in the present embodiment can also be used to form mixtures in the mixing tank between a fuel stored in the main tank and a fluid other than a fuel, stored in the auxiliary tank, such as a combustion additive. Alternatively, the supply system comprises a plurality of auxiliary storage tanks, each containing a fuel or a combustion additive.

  Although the invention has been described in connection with a particular embodiment, it is obvious that it is not limited thereto and that it comprises all the technical equivalents of the means described and their combinations if they are within the scope of the invention.

Claims (7)

  A fuel injection device for an internal combustion engine, comprising at least one fuel injector capable of injecting fuel into an associated combustion chamber; a fuel supply system comprising a main storage tank intended to contain a main fuel, connected to a feed pump for transferring a fuel flow under pressure to said injector, and - a recycling circuit ensuring the transfer of fuel flows back, not injected, from the fuel injector to the supply system upstream of the feed pump, characterized in that said feed system comprises - at least one auxiliary storage tank (33) intended to contain an auxiliary fluid (C2), of the combustion additive type or auxiliary fuel having properties different from those of the main fuel, - a recovery tank (34) connected to the recycling circuit (7) for recovery the return fuel streams from the injector (6), formed from mixtures of main fuel (C1) and auxiliary fluid (C2), and - a mixing system (5) comprising a mixing tank (51) and transfer means (52-57) capable of transferring to the mixing tank quantities of main fuel (C1), auxiliary fluid (C2) and return fuel mixture (C3) respectively present in the main storage tank (32). ), the auxiliary storage tank (33) and the recovery tank (34), said feed pump (31) ensuring the transfer of a fuel flow from said mixing tank (51) to said fuel injector fuel, the injection device comprising a control unit (8) adapted to control said transfer means to form in the mixing tank a target fuel mixture having characteristics defined according to the operating conditions of the engine, in particular according to engine speed and engine load level.   Fuel injection device (1) according to claim 1, characterized in that the control unit (8) is able to determine the composition of the return fuel mixture (C3) present in the recovery tank (34). ) over time to determine the amount of return fuel mixture (C3) to be transferred into the mixing tank (51) with the main fuel (C1) stored in the main storage tank (32) and / or the fluid auxiliary (C2) stored in the auxiliary storage tank (33).   Fuel injection device (1) according to claim 2, characterized in that the determination of the composition of the return fuel mixture (C3) by the control unit (8) is carried out from the knowledge of at least one mixing law of the main fuel and the auxiliary fluid and the history of the engine operation.   Fuel injection device (1) according to claim 2 or 3, characterized in that the determination of the composition of the return fuel mixture (C3) present in the recovery tank (34) by the control unit (8) is derived from at least one characteristic of the return fuel mixture (C3), such as density, measured by sensor (38) implanted in the recovery tank (34).   Fuel injection device (1) according to one of claims 1 to 4, characterized in that said transfer means comprise individual supply lines (52, 53, 54) connecting the storage tank individually. main (32), the auxiliary storage tank (33) and the recovery tank (34) to the mixing tank (51), each supply line being equipped with a low pressure pump (55, 56, 57) and a valve interposed between the mixing tank and the low pressure pump, said valves being controlled by the control unit (8) to regulate the flow of the supply lines.   Fuel injection device (1) according to one of claims 1 to 5, characterized in that the main storage tank (32), the auxiliary storage tank (33) and the recovery tank (34) are each equipped with a level sensor (35, 36, 37) connected to the control unit (8), the control unit controlling the transfer means as a function of the main fuel quantity (Cl) and auxiliary fluid (C2) remaining in the main storage tank and the auxiliary storage tank, and return fuel mixture (C3) remaining in the recovery tank (34).   7. fuel injection device (1) according to one of claims 1 to 6, characterized in that it comprises a common fuel distribution rail (2), connected firstly to the feed pump (31) high pressure type and secondly to a set of fuel injectors (6).