Method for managing the amount of fuel injected into an engine

Abstract

A method for managing the mass of fuel injected into the cylinder of an internal combustion engine fed by direct injection. The pressure and the pressure drop per unit of time are monitored (13) during the starting phase. If the pressure becomes too low (7), or if it drops too quickly (9), the mass of fuel injected on each cycle is adjusted (15) in order to maintain a high fuel pressure in the injector (37). The method can be applied, for example, in the event of low-temperature starting using any type of fuel, for example pure or mixed ethanol.

Claims

1. A method for feeding an internal combustion engine by a direct injection of a mixture of fuel and combustion air into each cylinder of the engine, the supply of fuel being performed at high pressure by a pump providing an output flow situated in a higher interval of its operating range, the method comprising: in a preliminary fuel injection phase which precedes starting of the engine at low temperature, regulating an injection mass of fuel delivered per cycle of operation of the engine such that, when the pressure of the fuel that is injected into a cylinder decreases during the preliminary injection phase, the pressure remains above a predetermined threshold value.

2. The method as claimed in claim 1, wherein the injection phase is the preliminary phase which precedes the starting of the engine, and the injection mass is regulated by an adjusted decrease.

3. The method as claimed in claim 2, wherein the pressure of the injected fuel is controlled in real time and is corrected by an adjustment of the injection mass in order to define a pressure gradient such that the pressure of the injected fuel remains greater than the threshold value of the pressure.

4. The method as claimed in claim 1, wherein the pressure of the injected fuel is controlled in real time and is corrected by an adjustment of the injection mass in order to define a pressure gradient such that the pressure of the injected fuel remains greater than the threshold value of the pressure.

5. The method as claimed in claim 4, wherein the pressure gradient remains greater than a determined threshold value.

6. The method as claimed in claim 5, wherein the progression of the pressure gradient is controlled in real time and is corrected by a continuous adjustment of the injection mass such that the pressure gradient remains greater than the determined threshold value.

7. The method as claimed in claim 5, wherein four parameters are measured in the course of the injection period: the pressure, the pressure gradient, the speed of the engine and the temperature of the coolant, three of the parameters being compared with thresholds as follows: the pressure of the injected fuel is compared with the predetermined threshold value for the pressure, when the pressure of the injected fuel is greater than the predetermined threshold value for the pressure, the pressure gradient is compared with the predetermined threshold value for the pressure gradient, when the pressure gradient is greater than the determined threshold value for the pressure gradient, the speed of the engine is compared with a determined speed threshold for the engine, such that when the pressure of the injected fuel decreases towards the predetermined threshold value for the pressure, or when the pressure gradient is lower than the determined threshold value for the pressure gradient, the quantity of fuel is calculated according to the four parameters in order to decrease or arrest the drop in pressure, the comparing the speed of the engine with a determined speed threshold for the engine being activated when the pressure gradient is greater than the threshold value for the pressure gradient such that, when the speed of the engine remains lower than or equal to the threshold value for the speed of the engine, the iteration of the steps of comparison is resumed, and, when the speed of the engine becomes greater than the value of the speed threshold, the engine then adopts a steady speed operating condition and the feeding in the preliminary phase preceding starting of the engine is stopped.

8. The method as claimed in claim 4, wherein the progression of the pressure gradient is controlled in real time is corrected by a continuous adjustment of the injection mass such that the pressure gradient remains greater than the determined threshold value.

9. The method as claimed in claim 8, wherein four parameters are measured in the course of the injection period: the pressure, the pressure gradient, the speed of the engine and the temperature of the coolant, three of the parameters being compared with thresholds as follows: the pressure of the injected fuel is compared with the predetermined threshold value for the pressure, when the pressure of the injected fuel is greater than the predetermined threshold value for the pressure, the pressure gradient is compared with the predetermined threshold value for the pressure gradient, when the pressure gradient is greater than the determined threshold value for the pressure gradient, the speed of the engine is compared with a determined speed threshold for the engine, such that when the pressure of the injected fuel decreases towards the predetermined threshold value for the pressure, or when the pressure gradient is lower than the determined threshold value for the pressure gradient, the quantity of fuel is calculated according to the four parameters in order to decrease or arrest the drop in pressure, the comparing the speed of the engine with a determined speed threshold for the engine being activated when the pressure gradient is greater than the threshold value for the pressure gradient such that, when the speed of the engine remains lower than or equal to the threshold value for the speed of the engine, the iteration of the steps of comparison is resumed, and, when the speed of the engine becomes greater than the value of the speed threshold, the engine then adopts a steady speed operating condition and the feeding in the preliminary phase preceding starting of the engine is stopped.

10. The method as claimed in claim 4, wherein four parameters are measured in the course of the injection period: the pressure, the pressure gradient, the speed of the engine and the temperature of the coolant, three of the parameters being compared with thresholds as follows: the pressure of the injected fuel is compared with the predetermined threshold value for the pressure, when the pressure of the injected fuel is greater than the predetermined threshold value for the pressure, the pressure gradient is compared with the predetermined threshold value for the pressure gradient, when the pressure gradient is greater than the determined threshold value for the pressure gradient, the speed of the engine is compared with a determined speed threshold for the engine, such that when the pressure of the injected fuel decreases towards the predetermined threshold value for the pressure, or when the pressure gradient is lower than the determined threshold value for the pressure gradient, the quantity of fuel is calculated according to the four parameters in order to decrease or arrest the drop in pressure, the comparing the speed of the engine with a determined speed threshold for the engine being activated when the pressure gradient is greater than the threshold value for the pressure gradient such that, when the speed of the engine remains lower than or equal to the threshold value for the speed of the engine, the iteration of the steps of comparison is resumed, and, when the speed of the engine becomes greater than the value of the speed threshold, the engine then adopts a steady speed operating condition and the feeding in the preliminary phase preceding starting of the engine is stopped.

11. The method as claimed in claim 1, wherein the fuel is a low-volatility fuel that is a petrol/ethanol mixture.

12. The method as claimed in claim 1, wherein monitoring of the pressure of the injected fuel is performed by sensors or by modeling.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other details, characterizing features and advantages of the present invention will become evident from a perusal of the following non-restrictive description, with reference to the accompanying figures which represent, respectively:

(2) FIG. 1, an example of a flow chart showing the steps of the method according to the invention;

(3) FIG. 2, a diagram illustrating the correlation in time of the main quantities measured under the conditions of the invention, specifically the mass of fuel injected, the pressure and the rpm of the engine; and

(4) FIG. 3, a schematic example of the engine architecture concerned in order to implement the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) The flow chart in FIG. 1 illustrates an example of the sequencing of the principal steps for starting an engine according to the invention. After switching on the electrical circuits of the vehicle and, in particular, its components (starter, generator, pumps, etc.) in conjunction with the engine, step 2 for implementing the method of the invention involves the initial adjustment of the following parameters depending on the fuel utilized: P.sub.threshold: minimum pressure of the fuel accepted in the injector; P.sub.max: maximum pressure that it is possible to achieve in the injector, this parameter likewise being dependent on the characterizing features of the said components, in particular of the high-pressure pump; G.sub.threshold: minimum value of the pressure gradient defined by the ratio ΔP/Δt of variation in the pressure per unit of time of the engine operating cycle (unit of time separating two consecutive top dead centre positions of a cylinder of the engine, abbreviated to “pmh”, or “tdc” in English terminology); V.sub.threshold: speed of the engine above which the starting phase is considered to be complete, the engine then running at a steady speed; M.sub.o: mass of fuel injected initially for each engine tdc cycle (or initial injection mass) by the injector into the combustion chamber of the engine.

(6) On first switching on the high-pressure pump (step 3), the fuel pressure inside the high-pressure circuit of the engine is increased up to the maximum value P.sub.max of this pressure.

(7) Step 5 corresponds to the start of the injection of fuel into the cylinders of the engine, according to the cycle of the engine and its engine characteristics (number of cylinders, etc.).

(8) Four parameters are measured (step 13) in the course of the injection period: the pressure P, the pressure gradient G, the speed V of the engine, and the temperature T of the coolant. Three of these parameters are compared with thresholds, as follows: the pressure P of the fuel in the injector is compared with the value P.sub.threshold (step 7); if the pressure P is greater than P.sub.threshold, the gradient G is compared with the value G.sub.threshold (step 9); if the pressure gradient G is greater than G.sub.threshold, the speed V is compared with the speed threshold V.sub.threshold (step 11);

(9) in such a way that, when the pressure P of the fuel in the injector decreases towards the value P.sub.threshold or when the pressure gradient G is lower than the value G.sub.threshold, the quantity of fuel is calculated by a processor according to the parameters P, G, V and T (step 15) in order to decrease or arrest the drop in pressure to prevent it from falling below P.sub.threshold.

(10) In step 7, the pressure P is compared with the value P.sub.threshold in order to monitor whether it is approaching this value P.sub.threshold and to act on the quantity of fuel if this is the case. Step 9, involving the comparison of the gradient, is preferably implemented at a pressure P greater than P.sub.threshold in order to detect in particular a gradient for the drop in pressure and to ensure that sufficient time is available to act on the quantity of fuel to ensure that the pressure threshold P.sub.threshold is not crossed.

(11) Step 11 is activated when the pressure gradient G is greater than G.sub.threshold so that if the speed V of the engine remains below V.sub.threshold at this step 11, the iteration of the comparison steps (steps 7, 9, 11) is resumed, and when the speed V of the engine becomes greater than V.sub.threshold, the engine then adopts a steady speed operating condition (step 17), and the method of feeding in a preliminary phase preceding starting of the engine is stopped.

(12) FIG. 2 illustrates more particularly an example of the correlation in time of the three principal parameters by application of the method according to the invention: the pressure P of the fuel in the high-pressure circuit (curve 20), the speed V of the engine (engine rpm curve 22), and the mass M of fuel injected into the cylinder (injection curve 24). In the example, the fuel is pure ethanol hydrated to 7%, at a temperature T of −3° C., this being the critical temperature for starting the engine with such a mixture.

(13) The high-pressure pump starts to function at the point in time t.sub.1, marking the start of the injection process intended to initiate starting. The maximum pressure P.sub.max (curve 20) is achieved at the point in time t.sub.i, and the process of injecting fuel (curve 24) into the cylinders begins. The injection mass M of fuel injected into the cylinders is increased progressively until M.sub.max is reached. The regulation involves calculating the decrease in the injection mass M from the point in time t.sub.j at which it is established, by extrapolation, that the pressure P or the pressure gradient G is moving towards a value that is lower than the required threshold value, P.sub.threshold or G.sub.threshold, ahead of the proposed point in time t.sub.2 for starting.

(14) The consequence of this decrease in the injection mass M of fuel into the cylinders is an increase in the gradient G (resulting in a recovery in the slope of the curve 20) from the point in time t.sub.j, followed by a rise in the pressure P. The pressure P thus passes through a minimum value P.sub.min, which is greater than the value P.sub.threshold that was preset initially. In the example, the value P.sub.threshold is 40 bars, the value P.sub.max is 180 bars, that of the speed of the engine is 210 r/min (at a steady speed) and that of the injection mass M varies between a maximum value M.sub.max and a stabilized value M.sub.s.

(15) Maintaining the pressure P above the threshold value accordingly entails the more effective atomization of the fuel and of the fuel/air mixture, which permits starting of the engine to be confirmed by the rise in the rpm of the engine (curve 22) on approaching the effective starting time t.sub.2. In the example, the total duration of starting, between the points in time t.sub.1 and t.sub.2, is 3.7 seconds at −3° C. for pure ethanol hydrate (7% H.sub.2O).

(16) After the effective starting time t.sub.2, the values for the pressure, the injection mass and the speed approach constant values, respectively P.sub.s, M.sub.s and V.sub.s, corresponding to steady speeds.

(17) The diagram in FIG. 3 shows in greater detail an example of engine architecture which falls within the scope of the invention. This architecture includes the following devices: a high-pressure fuel supply pump 31; an electronic fuel injector 37; fuel inlet pipes 33a and 33b between the high-pressure pump 31 and the electronic injector 37 via the common rail 35; one of the cylinders 45 of the engine, housing a piston 47 driving a crankshaft 48 via a connecting rod 49; an air inlet 43a into the cylinder 45; an outlet for the exhaust gases 43b from the cylinder 45; and a cooling water circuit 41 including inlet pipes 41a and outlet pipes 41b; sensors for the temperature of the cooling water circuit 39a, for the pressure of the fuel in the inlet pipe 39b, for the speed 39d and a controller for the injection valve 39c of the injector 37; and a processor 50 which receives the measurement signals from the sensors 39a, 39b and 39d and controls the injection valve 39c.

(18) In operation, the value of the injection mass of fuel into the cylinder 45, controlled by the processor 50 via the injection valve 39c, is adjusted by the processor 50 according to the measurements performed on the sensors 39a, 39b and 39d. These measurements are transmitted to the processor 50, the value of the pressure gradient being determined by the processor 50.

(19) The invention is not limited to the illustrative embodiments described and depicted here. It may be adapted for different fuels, for example: petrol, diesel, ethanol, or mixtures thereof, at low temperatures where the conventional method of starting results in failure, for example below −5° C. for ethanol, or below −30° C. for petrol. The invention can also be adapted in the case in which, in the course of a period running at a steady speed, the high-pressure pump does not offer a desired value for the high pressure, in spite of the fact that it is operating at its maximum output.