Patent Description:
A direct injection system comprises multiple injectors, a "common rail" supplying the pressurised fuel to the injectors, a high-pressure fuel pump, which supplies the fuel to the common rail via a high-pressure supply duct and is provided with a flow rate adjustment device, and a control unit driving the flow rate adjustment device to keep the pressure of the fuel within the common rail equal to a desired value that generally varies over time depending on the engine's operating conditions.

The high-pressure fuel pump described in the patent application <CIT> comprises: a main body, a pumping chamber made in the main body and inside of which a piston slides with reciprocating motion, an intake duct adjusted by an intake valve to supply the fuel at low pressure inside the pumping chamber, and a delivery duct adjusted by a delivery valve to supply the fuel at high pressure outside the pumping chamber and towards the common rail.

A modern vehicle normally implements the "Start & Stop" system that, to reduce the consumption of fuel during city use, stops and starts the internal combustion engine automatically when the vehicle is stopped, typically due to a red light (generally the internal combustion engine remains stopped for a few tens of seconds or even for some minutes). To enable a fast and regular restart of the internal combustion engine, it is preferable that, during the shutdown of the internal combustion engine (which also entails the stoppage of the high-pressure fuel pump that is driven by the engine shaft of the internal combustion engine), the pressure of the fuel in the common rail remains basically unchanged. As a result, it is necessary to minimise all the fuel leakages entailing a loss of fuel from the common rail and, thus, a decrease in the pressure of the fuel in the common rail.

The main cause of fuel leakage from the common rail is linked to the imperfect seal of the delivery valve of the high-pressure fuel pump and the imperfect seal of the pressure relief valve of the high-pressure fuel pump. To reduce the leakage of fuel through the delivery valve and the pressure relief valve, it has been suggested to improve the construction features of the valves, modifying their shape, increasing their processing precision, and using higher performing materials; in any case, these solutions entail a notable increase in the cost of the high-pressure fuel pump.

The patent applications <CIT> and <CIT> describe a high-pressure fuel pump for an internal combustion engine; when the internal combustion engine is stopped (shut off), the fuel pump is controlled so as to reduce the pressure of the fuel in a high-pressure supply system.

The purpose of this invention is to provide a control method of a fuel injection system reducing the leakage of fuel through the delivery valve of the high-pressure fuel pump and through the pressure relief valve of the high-pressure fuel pump when the internal combustion engine is stopped and, at the same time, is easy and fast to implement.

According to this invention, a method to control a fuel injection system is provided, according to what is set forth in the attached claims.

The claims describe preferred embodiments of this invention forming an integral part of this description.

This invention will now be described with reference to the attached drawings that illustrate a non-limiting embodiment thereof, in which:.

In <FIG>, reference number <NUM> denotes, as a whole, a direct fuel injection system of the common rail type for an internal combustion engine.

The direct injection system <NUM> comprises multiple injectors <NUM>, a common rail <NUM> that supplies the pressurised fuel to the injectors <NUM>, a high-pressure pump <NUM>, which supplies the fuel to the common rail <NUM> via a supply duct <NUM>, and is provided with a flow rate adjustment device <NUM>, a control unit <NUM> that maintains the pressure of the fuel inside the common rail <NUM> equal to a desired value that generally varies over time depending on the operating conditions of the internal combustion engine, and a low-pressure fuel pump <NUM> that supplies the fuel from a tank <NUM> to the high-pressure pump <NUM> via a supply duct <NUM>.

The control unit <NUM> is coupled to the flow rate adjustment device <NUM> to control the flow rate of the high-pressure pump <NUM> so as to supply, moment by moment, to the common rail <NUM> the quantity of fuel needed to have the desired pressure value inside the common rail <NUM>; in particular, the control unit <NUM> adjusts the flow rate of the high-pressure pump <NUM> via a feedback control using, as a feedback variable, the value of the fuel pressure (detected in real time by the pressure sensor <NUM>) inside the common rail <NUM>.

According to what was illustrated in <FIG>, the high-pressure pump <NUM> comprises a main body <NUM> that has a longitudinal axis <NUM> and defines, inside, a pumping chamber <NUM> with a cylindrical shape. Inside the pumping chamber <NUM>, a piston <NUM> is mounted so as to slide that, moving by reciprocating motion along the longitudinal axis <NUM>, determines a cyclical variation of the volume of the pumping chamber <NUM>. A smaller portion of the piston <NUM> is, on the one hand, coupled to a spring <NUM> that tends to push the piston <NUM> towards a maximum volume position of the pumping chamber <NUM> and, on the other hand, is coupled to a cam (not illustrated) that is rotated by an engine shaft of the internal combustion engine to cyclically move the piston <NUM> upwards, compressing the spring <NUM>.

An intake duct <NUM>, which is adjusted by an intake valve <NUM> arranged at the pumping chamber <NUM>, starts from one side wall of the pumping chamber <NUM>. The intake valve <NUM> is normally controlled under pressure and in the absence of external interventions, the intake valve <NUM> is closed when the pressure of the fuel in the pumping chamber <NUM> is greater than the pressure of the fuel in the intake duct <NUM> and is open when the pressure of the fuel in the pumping chamber <NUM> is less than the pressure of the fuel in the intake duct <NUM>. The flow rate adjustment device <NUM> is mechanically coupled to the intake valve <NUM> to allow the control unit <NUM> to keep, when necessary, the intake valve <NUM> open during a pumping step of the piston <NUM> and, thus, to enable fuel to flow out of the pumping chamber <NUM> through the intake duct <NUM>.

A delivery duct <NUM> that is adjusted by a one-way delivery valve <NUM> (also called an "OCV - Outlet Closing Valve"), which is arranged at the pumping chamber <NUM> and only allows fuel to flow out of the pumping chamber <NUM>, starts from a side wall of the pumping chamber <NUM> and from the opposite side to the intake duct <NUM>. The delivery valve <NUM> is controlled under pressure and is open when the pressure of the fuel in the pumping chamber <NUM> is greater than the pressure of the fuel in the intake channel <NUM> and is closed when the pressure of the fuel in the pumping chamber <NUM> is less than the pressure of the fuel in the delivery channel <NUM>.

The intake duct <NUM> is adjusted by the intake valve <NUM> (arranged at the pumping chamber <NUM>) and extends partially inside the main body <NUM>. A damping device <NUM> (compensator), which is fixed to the main body <NUM> of the high-pressure pump <NUM> and has the function of reducing, in the low-pressure branch, the quantity of pulsations of the fuel flow rate and, thus, the quantity of oscillations of the fuel pressure, is arranged along the intake duct <NUM> (upstream of the intake valve <NUM>).

The flow rate adjustment device <NUM> comprises a control rod <NUM>, which is coupled to the intake valve <NUM> and is movable between a passive position, in which it allows the intake valve <NUM> to close, and an active position, in which it does not allow the intake valve <NUM> to close. The flow rate adjustment device <NUM> also comprises an electromagnetic actuator <NUM>, which is coupled to the control rod <NUM> to move the control rod <NUM> between the active position and the passive position.

According to what is illustrated in <FIG>, the electromagnetic actuator <NUM> comprises a spring <NUM>, which holds the control rod <NUM> in the active position, and an electromagnet <NUM>, which is designed to move the control rod <NUM> to the passive position magnetically attracting a ferromagnetic anchor <NUM> integral with the control rod <NUM> and, thus, overcoming the elastic force generated by the spring <NUM>. When the electromagnet <NUM> is excited, the control rod <NUM> is recalled to the passive position and the communication between the intake duct <NUM> and the pumping chamber <NUM> may be interrupted by the closure of the intake valve <NUM>. The control rod <NUM> and the anchor <NUM> together form mobile equipment of the flow rate adjustment device <NUM> that is moved axially between the active position and the passive position under the control of the electromagnetic actuator <NUM>.

According to what is illustrated in <FIG>, the intake valve <NUM> comprises a disc <NUM> that has a series of feeding holes that the fuel may flow through and a flexible sheet <NUM> with a circular shape (better illustrated in <FIG>) that rests on a base of the disc <NUM> closing the passage through the feeding holes. The intake valve <NUM> is normally controlled under pressure and in the absence of external interventions (i.e., of interventions of the flow rate adjustment device <NUM>), the intake valve <NUM> is closed when the pressure of the fuel in the pumping chamber <NUM> is greater than the pressure of the fuel in the intake duct <NUM> and is open when the pressure of the fuel in the pumping chamber <NUM> is less than the pressure of the fuel in the intake duct <NUM>. In particular, when the fuel flows towards the pumping chamber <NUM>, the sheet <NUM> is deformed moving away from the disc <NUM> under the thrust of the fuel allowing the passage of the fuel through the feeding holes; instead, when the fuel flows from the pumping chamber <NUM>, the sheet <NUM> is crushed against the disc <NUM> sealing the feeding holes and, thus, preventing the passage of the fuel through the feeding holes. In its active position, the control rod <NUM> centrally pushes on the sheet <NUM> preventing the sheet <NUM> from adhering to the disc <NUM> and, thus, preventing the sheet <NUM> from sealing the feeding holes; instead, in the passive position, the control rod <NUM> is relatively far from the sheet <NUM> allowing the sheet <NUM> to adhere to the disc <NUM> and, thus, allowing the sheet <NUM> to seal the feeding holes.

According to what is illustrated in <FIG> and <FIG>, in the main body <NUM> and below the pumping chamber <NUM>, a containing seat <NUM> is formed with a cylindrical shape having a greater diameter than the diameter of the pumping chamber <NUM> and houses a guide bushing <NUM> of the piston <NUM>; the guide bushing <NUM> has, essentially, the function of guiding the axial, alternative sliding of the piston <NUM>. The guide bushing <NUM> is made of a material with a suitable hardness and with a superficial finish so as to facilitate the axial sliding of the piston <NUM>.

The guide bushing <NUM> has a tubular shape and has, inside, a central through hole <NUM> that houses the piston <NUM> so as to slide; the central hole <NUM> of the guide bushing <NUM> (in which the piston <NUM> is arranged) and the piston <NUM> are processed with great precision so as to minimise the mechanical play (i.e. the distance) existing between the central hole <NUM> of the guide bushing <NUM> and the piston <NUM> (so as to limit, as much as possible, the leaking of fuel along the piston <NUM>) without, in any case, completely eliminating this mechanical play (which is, obviously, indispensable for allowing the sliding of the piston <NUM> inside the guide bushing <NUM>).

According to the embodiment illustrated in <FIG>, between the piston <NUM> and the central hole <NUM> of the guide bushing <NUM> a sealing gasket <NUM> is interposed that has the function of further limiting the leaking of fuel along the piston <NUM>. The sealing gasket <NUM> has a certain elasticity for being able to deform elastically (in particular for being radially compressed against the internal surface of the central hole <NUM> of the guide bushing <NUM>). The sealing gasket <NUM> is preferably made with a material with a low friction coefficient; for example, the sealing gasket <NUM> could be made from a material based on PTFE (polytetrafluoroethylene, also commercially known with the name Teflon®) potentially loaded with glass or graphite.

According to a preferred embodiment illustrated in the attached figures, the piston <NUM> has an annular throat that houses the sealing gasket <NUM>; in other words, the annular throat constitutes a site where the sealing gasket <NUM> is accommodated so that the sealing gasket <NUM> cannot make axial movements in relation to the piston <NUM>.

According to a preferred embodiment, there is also a one-way pressure relief valve (also called a "PRV - Pressure Relieve Valve") that only allows fuel to flow inside the pumping chamber <NUM> through the delivery duct <NUM> and may be integrated together with the delivery valve <NUM>. The function of the pressure relief valve is to allow a release of fuel in the event that the pressure of the fuel in the common rail <NUM> (i.e. downstream of the delivery valve <NUM>) exceeds a maximum value established in the design phase (for example, in the event of errors in the check performed by the control unit <NUM> or in the event of a failure of an injector <NUM> connected to the common rail <NUM>); in other words, the pressure relief valve is calibrated to automatically open when the jump in pressure at its ends is greater than a threshold value established in the design phase and, thus, to prevent the pressure of the fuel in the common rail <NUM> from exceeding the maximum value established in the design phase.

From the above, it is clear that the flow rate adjustment device <NUM> only acts on the intake valve <NUM> and does not have any effect on the delivery valve <NUM>; in other words, the intake valve <NUM> is completely separate and independent of the delivery valve <NUM>.

In use, the control unit <NUM> detects when the internal combustion engine is stopped (switched off) and controls, immediately after (i.e. without any appreciable delay) the internal combustion engine has been stopped, the flow rate adjustment device <NUM> to allow the intake valve <NUM> to close (i.e., it activates the electromagnetic actuator <NUM> to move the control rod <NUM> from the normally active position assumed due to the thrust of the spring <NUM> to the passive position that allows the intake valve <NUM> to close).

The control unit <NUM> preferably continues to control the flow rate adjustment device <NUM> to enable the intake valve <NUM> to close for a predetermined amount of time (generally lasting between <NUM> and <NUM> seconds). In other words, the control unit <NUM> keeps the electromagnetic actuator <NUM> active to keep the control rod <NUM> in the passive position that allows the intake valve <NUM> to close for the predetermined amount of time.

As soon as the internal combustion engine is stopped (and, as a result, the piston <NUM> stops all its alternating, sliding movements), the fuel pressure in the pumping chamber <NUM> becomes equal to the pressure of the fuel in the intake duct <NUM> and, thus, the pressure differential across the delivery valve <NUM> and the pressure relief valve becomes very high, causing the fuel to leak through the delivery valve <NUM> and the pressure relief valve (i.e. the high-pressure fuel that is found in the delivery duct <NUM> leaks through the delivery valve <NUM> and the pressure relief valve entering into the pumping chamber <NUM>). At the same time as the shutdown of the internal combustion engine (i.e. immediately after the internal combustion engine has been stopped), the control unit <NUM> controls the flow rate adjustment device <NUM> to allow the intake valve <NUM> to close: when the pressure in the pumping chamber <NUM> increases (due to the high-pressure fuel that leaks through the delivery valve <NUM> and the pressure relief valve), the intake valve <NUM> spontaneously closes since the pressure of the fuel in the pumping chamber <NUM> has become greater than the pressure of the fuel in the intake duct <NUM>. Once the intake valve <NUM> has closed (since the flow rate adjustment device <NUM> has allowed it to close), the pressure of the fuel in the pumping chamber <NUM> increases gradually (but increasingly slowly) due to the continuous (but increasingly reduced) leakage of fuel through the delivery valve <NUM> and the pressure relief valve. After a relatively short time (even less than a second or, in any case, very few seconds), the pressure of the fuel in the pumping chamber <NUM> reaches a value so as to keep the intake valve <NUM> closed irrespective of the action of the flow rate adjustment device <NUM>; in other words, the flow rate adjustment device <NUM> is able to prevent the intake valve <NUM> from closing when the pressure of the fuel in the pumping chamber <NUM> is only slightly (marginally) higher than the pressure of the fuel in the intake duct <NUM> but is not able to reopen the intake valve <NUM> when the pressure of the fuel in the pumping chamber <NUM> is basically higher than the pressure of the fuel in the intake duct <NUM>.

In other words, the control unit <NUM>, in the moment when the internal combustion engine has been stopped and without an appreciable delay, controls the flow rate adjustment device <NUM> to allow the intake valve <NUM> to close keeping, at the same time, the delivery valve <NUM> completely closed (i.e. without causing the delivery valve <NUM> to open, even partially), so as to minimise, from the moment when the internal combustion engine has been stopped and without an appreciable delay, both the fuel flowing out of the pumping chamber <NUM> through the intake valve <NUM> and the fuel flowing into the pumping chamber <NUM> through the delivery valve <NUM>. In this way, the reduction of the pressure of the fuel in the delivery duct <NUM> and downstream of the pumping chamber <NUM> is minimised.

The embodiments described herein may be combined between them without departing from the scope of protection of this invention.

The control method described above has numerous advantages.

In the first place, the control method described above is able to significantly reduce the leaking of fuel both through the delivery valve <NUM> and through the pressure relief valve when the internal combustion engine is stopped (shut off). This result is obtained thanks to the fact that allowing the intake valve <NUM> to close when the internal combustion engine is stopped (shut off), the fuel that initially flows through the delivery valve <NUM> and through the pressure relief valve remains in the pumping chamber <NUM>, increasing the pressure of the fuel inside the pumping chamber <NUM> and, thus, significantly reducing the pressure differential between the delivery valve <NUM> and the pressure relief valve. Of course, reducing (almost eliminating) the pressure differential between the delivery valve <NUM> and the pressure relief valve reduces (almost eliminates), as a consequence, the leaking of fuel through the delivery valve <NUM> and the pressure relief valve.

The control method described above is still more effective when the sealing gasket <NUM> is included that makes it possible to minimise the leaking of fuel from the pumping chamber <NUM> and through the play between the guide bushing <NUM> and the piston <NUM>.

The control method described above has an implementation cost that is basically zero since it only entails the addition of a small portion of code in the software of the control unit <NUM>.

Claim 1:
A method to control a fuel injection system (<NUM>) for an internal combustion engine and provided with a fuel pump (<NUM>); the fuel pump (<NUM>) comprises: a pumping chamber (<NUM>); a piston (<NUM>) mounted so as to slide within the pumping chamber (<NUM>); an intake duct (<NUM>), which ends in the pumping chamber (<NUM>) and is provided with an intake valve (<NUM>); a delivery duct (<NUM>), which starts from the pumping chamber (<NUM>) and is provided with a delivery valve (<NUM>); and a flow rate adjustment device (<NUM>), which is coupled to the intake valve (<NUM>) and can be controlled so as to prevent the intake valve (<NUM>) from closing or allow it to close when a fuel pressure inside the pumping chamber (<NUM>) exceeds a fuel pressure in the intake duct (<NUM>);
the control method comprises the step of detecting when the internal combustion engine is stopped;
the control method is characterized in that it comprises the further step of controlling, in the moment when the internal combustion engine has been stopped and without an appreciable delay, the flow rate adjustment device (<NUM>) to allow the intake valve (<NUM>) to close keeping, at the same time, the delivery valve (<NUM>) completely closed so as to minimise, from the moment when the internal combustion engine has been stopped and without an appreciable delay, both the fuel flowing out of the pumping chamber (<NUM>) through the intake valve (<NUM>) and the fuel flowing into the pumping chamber (<NUM>) through the delivery valve (<NUM>).