EP2434137B1

EP2434137B1 - Fuel pump for a direct injection system

Info

Publication number: EP2434137B1
Application number: EP20110182648
Authority: EP
Inventors: Marcello Cristiani; Daniele De Vita; Massimo Mattioli; Paolo Pasquali
Original assignee: Magneti Marelli SpA
Current assignee: Marelli Europe SpA
Priority date: 2010-09-23
Filing date: 2011-09-23
Publication date: 2013-07-03
Anticipated expiration: 2031-09-23
Also published as: IT1401819B1; EP2434137A1; CN102434347A; CN102434347B; ITBO20100569A1

Description

TECHNICAL FIELD

The present invention relates to a fuel pump for a direct injection system.

PRIOR ART

A currently marketed direct injection system (e.g. of the type described in patent application IT2009BO00197 ) comprises a plurality of injectors, a common rail which feeds pressurized fuel to the injectors and is provided with a pressure sensor, a high-pressure pump which feeds fuel to the common rail by means of a high-pressure fuel duct and is provided with an electronically controlled flow setting device, and a control unit which pilots the flow setting device by means of feedback control according to the reading provided by the pressure sensor in the common rail to keep fuel pressure in the common rail equal to a required value generally varying over time according to the operating conditions of the engine.
The high-pressure pump comprises at least one pumping chamber, within which a piston slides with reciprocating motion, a suction channel regulated by an inlet valve for feeding low-pressure fuel into the pumping chamber, and an outlet duct regulated by an outlet valve for feeding high-pressure fuel out of the pumping chamber and to the common rail through the inlet duct. The flow setting device generally acts on the suction valve keeping the suction valve itself open also during the pumping phase, so that a variable part of the fuel present in the pumping chamber and exceeding the actual feeding need of the common rail returns to the suction duct and is not pumped towards the common rail through the feeding duct.
In order to reduce the overall costs of the direct injection system it was suggested to eliminate the high-pressure pump flow electronic control, thus eliminating the common rail pressure sensor, the electronic control flow setting device, the control unit and the respective wiring harnesses. In this configuration, the common rail works at a fuel pressure which is always constant, the high-pressure pump always pumps (compresses) the maximum amount of fuel possible and the fuel exceeding the actual feeding need of the common rail is discharged by a pressure relief valve, which is integrated in the high-pressure pump and arranged immediately downstream of the outlet valve. This configuration allows to considerably limit the overall costs of the direct injection system but, on the other hand, has low energy efficiency because the energy used by the high-pressure pump to pump (compress) the fuel in excess which is discharged by the pressure relief valve is wasted. When the nominal fuel pressure in the common rail is low (of the order of 40-50 bars), the power wasted by the high-pressure pump for pumping (compressing) the fuel in excess discharged by the pressure relief valve is relatively low and thus acceptable (of the order of about 200 Watts); instead, when the nominal fuel pressure in the common rail is high (of the order of 200 bars), the power wasted by the high-pressure pump for pumping (compressing) the fuel in excess which is discharged by the pressure relief valve is no longer negligible (of the order of about 1000 Watts).
It is worth noting that the energy which is dissipated by the high-pressure pump for pumping (compressing) the fuel in excess which is discharged by the pressure relief valve is not only a worsening of the energy efficiency but also poses problems of heat disposal, because such energy is entirely converted into heat which must be adequate disposed of to avoid an overheating of the high-pressure pump.
Patent application US2006159555A1 describes a fuel pump for a direct injection system as described in the pre-characterizing part of independent claim 1.

DESCRIPTION OF THE INVENTION

It is the object of the present invention to provide a fuel pump for a direct injection system, which fuel pump is free from the above-described drawbacks while being easy and cost-effective to be provided.
According to the present invention, a fuel pump for a direct injection system is provided as claimed in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the accompanying drawings, which illustrate some non-limitative embodiments thereof, in which:

figure 1 is a diagrammatic view, with parts removed for clarity, of a direct fuel injection system of the common rail type;
figure 2 is a diagrammatic, longitudinal section view, with parts removed for clarity, of a high-pressure fuel pump of the direct injection system in figure 1 provided according to the present invention;
figure 3 is a diagrammatic, cross sectional view, with parts removed for clarity, of the high-pressure fuel pump in figure 2;
figure 4 is an enlarged scale view of a detail of the suction valve in figure 3;
figure 5 is a diagrammatic, cross sectional view, with parts removed for clarity, of an alternative embodiment of the high-pressure fuel pump in figure 2; and
figure 6 is an enlarged scale view of a detail of the suction valve in figure 5.

PREFERRED EMBODIMENTS OF THE INVENTION

In figure 1, numeral 1 indicates as a whole a direct fuel injection system of the common rail type for an internal combustion thermal engine.
Direct injection system 1 comprises a plurality of injectors 2, a common rail 3 which feeds the pressurized fuel to the injectors 2 and works at a constant nominal fuel pressure, a high-pressure pump 4 which feeds the fuel to the common rail 3 by means of a feeding duct 5, and a low-pressure pump 6 which feeds the fuel from a tank 7 to the high-pressure pump 4 by means of a feeding pipe 8.
As shown in figure 2, the high-pressure pump 4 comprises a main body 9, which has a longitudinal axis 10 and defines a cylindrical shape pumping chamber 11 therein. A piston 12 is mounted sliding in the pumping chamber 11, which piston determines a cyclical variation of the volume of the pumping chamber 11 by moving with reciprocating motion along the longitudinal axis 10. A lower portion of piston 12 is coupled on one side to a spring 13, which tends to push piston 12 towards a maximum volume position of the pumping chamber 11, and on the other side is coupled to a cam (not shown), which is rotated by a driving shaft of the engine to cyclically move piston 12 upwards, thus compressing spring 13.
A suction channel 11, which is connected to the low-pressure pump 6 by means of the suction duct 6 and is regulated by a suction valve 8 arranged at the pumping chamber 11, originates from a side wall of the pumping chamber 11. As shown in greater detail in figures 3 and 4, the suction valve 15 comprises a disc 16 having a series of passing-through holes 17 through which the fuel can flow and a deformable plate 18 of circular shape which rests on a base of the disk 16 closing the passage through the holes 17. The suction valve 15 is normally pressure-controlled and, in the absence of external interventions, the suction valve 15 is closed when the fuel pressure in the pumping chamber 11 is higher than the fuel pressure in the suction channel 14, and is opened when the fuel pressure in the pumping chamber 11 is lower than the fuel pressure in the suction channel 14. In particular, when the fuel flows to the pumping chamber 11, plate 18 is deformed moving away from the plate 16 under the bias of the fuel, thus allowing the fuel to pass through the holes 17; instead, when the fuel flows from the pumping chamber 11, plate 18 is pressed against plate 16 thus sealing the holes 17 and preventing the fuel from passing through the holes 17.
The suction valve 15 is coupled to a hydraulic control setting device 19 which acts on the suction valve 15 itself for keeping, when required and according to the methods described below, the suction valve 15 open during a pumping phase of piston 12 and thus allowing a flow of fuel from the pumping chamber 11 towards the suction channel 14. The setting device 19 comprises a control rod 20, which is coupled to the suction valve 15 (in particular to plate 18 of the suction valve 15) and is movable between a passive position, in which it allows the suction valve 15 to close without pushing on plate 18 and thus leaving plate 18 free to adhere to disk 16 thus sealing the holes 17, and an active position in which it does not allow the suction valve 15 to close by pushing plate 18 for preventing plate 18 from adhering to disk 16. The setting device 19 further comprises an electromagnetic actuator 21, which is coupled to the control rod 20 to move the control rod 20 between the active position and the passive position.
It is worth noting that the setting device 19 can keep the suction valve 15 open at the end of the suction phase and thus keep the suction valve 15 open during the subsequent compression phase, but cannot open the suction valve 15 closed during the compression phase because the high pressure which is developed in the pumping chamber 11 during the compression phase with the suction valve 15 closed prevents the opening of the suction valve 15 itself.
The hydraulic actuator 21 comprises a cylindrical control chamber 22 which leads into the suction channel 14, a piston 23, which is slidingly arranged in the control chamber 22, separates the control chamber 22 from the suction chamber 14, and is integral with the control rod 20, and a spring 24 which is arranged about the control rod 20 and is compressed between disk 16 and piston 23 for elastically pushing piston 23 towards the passive position (i.e. the position in which the control rod 20 does not interfere with the closing of the suction valve 15). The elastic force generated by the spring 24 and the hydraulic force determined by the pressure difference existing between the two faces of the piston 23, i.e. the pressure difference existing between the control chamber 22 and the suction chamber 14, acts on piston 23: spring 24 normally keeps piston 23 in the passive position (i.e. in the position in which the control rod 20 does not interfere with the closing of the suction valve 15) and the piston moves towards the active position (i.e. to the position in which the control rod 20 prevents the suction valve 15 from closing) only when the pressure of the fuel in the control chamber 22 is sufficiently higher than the pressure of the fuel in the suction chamber 14 (i.e. higher than a predetermined threshold) to overcome the elastic force generated by spring 24. As previously mentioned, such a displacement of the control rod 20 from the passive position to the active position may occur only during the suction phase because, during the compression phase with the suction valve 15 closed, the high-pressure which is developed within the pumping chamber 11 prevents the suction valve 15 itself from opening.
In order to allow the flow of fuel from the control chamber 22 to the suction channel 14, the outer diameter of piston 23 is slightly smaller than the inner diameter of the control chamber 22 so as to define an annular passing meatus through which the fuel may flow between piston 23 and control chamber 22. Such a solution requires a high dimensional accuracy in making the control chamber 22 and piston 23 to avoid an excessively small or excessively large passing meatus (the setting device 19 is slow when the passing meatus is too small, i.e. it takes too long to react, so the pressure of the fuel in the control chamber 22 is released through the meatus, thus considerably raising the pressure threshold required to take piston 23 to the active position). In order to avoid this problem, i.e. to avoid the construction of a control chamber 22 and piston 23 with a high dimensional accuracy, it is possible to resort to the alternative embodiment illustrated in figures 5 and 6, in which a portion of the control chamber 22 has a truncated-cone shape and is essentially fluid-tightly coupled to piston 23 (having semi-spherical shape in the terminal part). When piston 23 is in contact with the truncated-cone shaped inner wall of the control chamber 22, the passage of fuel from the control chamber 22 to the suction duct 14 is practically zero (thereby, there is no drop of pressure in the control chamber 22 due to the fuel passage towards the suction duct 14), while when piston 23 is slightly detached from the truncated-cone shaped inner wall of the control chamber 22, it opens a passing section which allows the fuel to abundantly flow towards the suction duct 14 (thereby, the response of the setting device 19 is particularly rapid). In other words, the coupling between the piston 23 and the truncated-cone shaped control chamber 22 is self-setting and allows to recover all constructional tolerances without problems.
In other words, in the embodiment shown in figures 5 and 6, the hydraulic actuator 21 of the setting device 19 is essentially shaped as a valve which opens when the fuel pressure in the control chamber 22 exceeds a predetermined value (according to the force of the spring 24 and of the fuel pressure in the suction duct 14); in this configuration, piston 23 acts as plug of the valve.
An outlet duct 25, which is connected to the common rail 3 by means of the feeding duct 5 and is regulated by a one-way outlet valve 26, which is arranged at the pumping chamber 14 and exclusively allows a fuel flow outgoing from the pumping chamber 11, originates from a side wall of the pumping chamber 11 and from the side opposite to the suction duct 17. The outlet valve 26 is pressure-controlled, and it is opened when the fuel pressure in the pumping chamber 11 is higher than the fuel pressure in the outlet duct 25 and is closed when the fuel pressure in the pumping chamber 11 is lower than the fuel pressure in the outlet duct 25.
Furthermore, as shown in the figures 3 and 5, an exhaust channel 27 originates from the outlet channel 25 and close to the outlet valve 26, which communicates with the outlet channel 25 with the control chamber 22 of the hydraulic actuator 21 of the setting device 19 and is adjusted by a one-way pressure relief valve 28 (i.e. maximum pressure valve) which allows only a flow of fuel out from the outlet channel 25. The pressure relief valve 28 is calibrated so as to open when the fuel pressure exceeds the nominal value required for the common rail 3. According to a preferred embodiment, the exhaust cannel 27 is developed partially inside the main body 9 (i.e. it consists of a hole obtained through the main body 9) and in part outside the main body 9 (i.e. it consists of a tube connected to the main body 9).
The fuel fed inside the pumping chamber 11 is extremely discontinuous, i.e. it has moments in which the fuel enters into the pumping chamber 11 (during the suction phase with the suction valve 15 open), it has moments in which the fuel does not enter or exit to/from the pumping chamber 11 (during the pumping phase with the inlet valve 15 closed), and it has moments in which the fuel exits from the pumping chamber 11 (during the pumping phase with the inlet valve 15 open due to the action of the regulating device 19).
According to a preferred embodiment, a compensation chamber 29, within which elastically deformable (or better elastically compressible) compensator bodies are arranged having the function of attenuating the fluctuations (pulsations) of the fuel rate along the suction duct 8, is arranged along the suction channel 14 (thus upstream of the suction valve 14).
According to a preferred embodiment, a collection duct 30 is obtained in the main body 9, which collection duct is arranged underneath the pumping chamber 11 and is crossed by an intermediate portion of piston 12, which is shaped so as to cyclically vary the volume of the collection duct 30 due to the reciprocating movement thereof. In particular, the intermediate portion of piston 12 which is in the collection duct 30 is shaped as the upper portion of piston 12 which is in the pumping chamber 11, so that when piston 12 moves, the volume variation in the collection chamber 30 due to the movement of piston 12 is equal and opposed to the volume variation which occurs in the pumping chamber 11 due to the displacement of piston 12. The collection chamber 30 is connected to the suction channel 14 by means of a connection duct 26 which flows into the inlet valve 15. In use, a further function of the collection chamber 30 is to contribute to compensating the fuel flow rate pulsations: when piston 12 moves up thus reducing the volume of the pumping chamber 11, the fuel ejected by the pumping chamber 11 through the inlet valve 15, which is kept open by the regulating device 19, may flow towards the collection chamber 30 because the moving up of piston 12 increases the volume of the collection chamber 30 by an amount equal to the corresponding volume reduction of the pumping chamber 11. When piston 12 moves up thus reducing the volume of the pumping chamber 11 and the suction valve 15 is closed, the increase of volume of the collection chamber 30 determines a fuel suction within the collection chamber 30 of the suction chamber 14. When piston 12 moves down, the volume of the pumping chamber 11 is increased and the volume of the collection chamber 30 is reduced by the same amount; in this situation, the fuel is ejected from the collection chamber 30 due to the decrease of volume of the collection chamber 30 itself due to the increase of volume of the pumping chamber 11 itself. In other words, a fuel exchange cyclically occurs between the collection chamber 30 (which is filled when piston 12 moves up during the pumping phase and is emptied when piston 12 moves down during the suction phase) and the pumping chamber 11 (which is emptied when piston 12 moves up during the pumping phase and is filled when piston 12 moves down during the suction phase).
According to a preferred embodiment shown in figure 1, an overpressure valve 32, which is used to discharge the fuel from the feeding duct 8 to the tank 7 when the pressure in the feeding duct 8 exceeds a predetermined threshold value due to the fuel return from the pumping chamber 11, is inserted along the feeding duct 8 downstream of the low-pressure pump 6. The function of the overpressure valve 47 is to prevent the pressure in the feeding duct 8 from reaching relatively high values which could cause the breakage of the low-pressure pump 6 over time.
The operation of the high-pressure pump 4 is described below with particular reference to the operation of the setting device 19 hydraulically controlled by means of the hydraulic actuator 21.
If during a pumping cycle an amount of fuel in excess is pumped (compressed) with respect to the feeding need of the common rail 3, the fuel pressure in the outlet channel 26 (thus in the feeding duct 5 and in the common rail 3) rises over the nominal value determining an opening of the pressure relief valve 28 to relief the amount of fuel in excess through the exhaust duct 27 which leads into the control chamber 22 of the hydraulic actuator 21. Therefore, the fuel pressure in the control chamber 22 increases thus determining the displacement of piston 23 (and thus of control rod 20) from the passive position to the active position (obviously only during a suction phase as previously mentioned): thereby, at least part of the fuel which is aspirated into the pumping chamber 11 through the suction valve 15 is not compressed (because it exits through the suction valve 15 which is kept open by the action of the setting device 19) and the amount of pumped (compressed) fuel is thus reduced.
When the amount of pumped (compressed) fuel is equal to (or lower than) the actual feeding need of the common rail 3, the fuel pressure in the outlet channel 26 (and thus in the feeding channel 5 and in the common rail 3) does not exceed the nominal value and thus the pressure relief valve 28 closes (or remains closed). Therefore, the fuel pressure in the control chamber 22 remains constant (or decreases due to the passage of fuel towards the suction duct 14); thereby, piston 23 (and thus the control rod 20 which is integral with piston 23) remains in the passive position (in which the control rod 20 does not interfere with the closing of the suction valve 15) or moves from the active position or the passive position: the amount of fuel pumped (compressed) during the subsequent cycle either remains constant or decreases.
From the above, it is apparent that the system is perfectly balanced and stable, because the setting device 19 acts promptly and in a fully autonomous manner (i.e. without the intervention of external electronic devices) to decrease the amount of pumped (compressed) fuel when an excess of pumped (compressed) fuel occurs, i.e. when the fuel pressure in the outlet channel 26 (thus in the feeding duct 5 and in the common rail 3) exceeds the nominal value and vice versa.
It is worth noting the importance of the passage of fuel from the control chamber 22 to the suction channel 14 when piston 23 moves from the active position: without such a passage of fuel, spring 24 would never succeed in returning the piston 23 to the passive position (unless taking a very long time to do so) because this would reduce the volume of fuel present in the control chamber 22 (which has no other relief because it obviously cannot return up along the exhaust channel 27 which is closed at the other end by the pressure relief valve 28, which is a one-way valve); instead, by virtue of the passage of fuel from the control chamber 22 to the suction channel 14, part of the fuel present in the control chamber 22 exits from the control chamber 22 thus allowing piston 23 to move to the passive position (thus "creating space" for the movement of piston 23 towards the passive position).
Finally, it is worth noting that the amount of fuel which is discharged by the pressure relief valve 28 through the exhaust channel 27 and is used for hydraulically actuating the hydraulic actuator 21 of the setting device 19 is modest, and thus its total impact on energy efficiency of the high-pressure pump 4 is negligible (the energy spent to pump such a fuel is wasted because the fuel is reintroduced into the suction duct 14) .
The above-described high-pressure pump 4 has many advantages.
Firstly, the hydraulically controlled setting device 19 of the high-pressure pump 4 can manage the opening and closing of the suction valve 14 in a fully autonomous manner (i.e. without any type of external intervention of the electronic control devices) so as to pump (compress), at each pumping cycle, only the amount of fuel actually needed to feed the common rail 3. Thereby, it is avoided to pump (compress) fuel in excess with respect to the need of feeding the common rail 3 thus allowing the high-pressure pump 4 to reach an energy efficiency which is substantially identical to the energy efficiency of high-pressure pumps with electronic flow control.
Furthermore, the above-described high-pressure pump 4 is simple and cost-effective to be implemented because it can be easily obtained with a few, simple changes to a similar standard high-pressure pump with electronic flow control.
As a result of the above-listed advantages, the high-pressure pump 4 is particularly suited to be used in a low cost, direct fuel injection system of the common rail type which works at constant fuel pressure (thus without the pressure sensor and without the electronic control of the high-pressure pump 4).

Claims

A fuel pump (4) for a direct injection system fitted with a common rail (3); the fuel pump (4) comprises:
at least one pumping chamber (11) defined in a main body (9);

a piston (12) which is mounted sliding inside the pumping chamber (11) to vary cyclically the volume of the pumping chamber (11);

a suction channel (14) connected to the pumping chamber (11) and regulated by a suction valve (15);

a setting device (19) acting on the suction valve (15) to keep the suction valve (15) open during a pumping phase of the piston (12) and therefore to allow a flow of fuel out of the pumping chamber (11) into the suction channel (14);

an outlet channel (16) connected to the pumping chamber (11) and regulated by an outlet valve (17); and

an exhaust channel (27), which originates from the outlet channel (16) and is regulated by a pressure relief valve (28) calibrated to open when the fuel pressure exceeds a predetermined nominal value;

the fuel pump (4) is characterized in that the setting device (19) comprises an hydraulic actuator (21) which is connected to the exhaust channel (27) to be driven by the pressure of fuel present in the exhaust channel (27).
A fuel pump (4) according to claim 1, wherein the hydraulic actuator (21) pilots the setting device (19) to keep the suction valve (15) open during a pumping phase of the piston (12) when the fuel pressure in the exhaust channel (27) exceeds a threshold and to allow the closure of the suction valve (15) during a pumping phase of the piston (12) when the fuel pressure in the exhaust channel (27) is below the threshold.
A fuel pump (4) according to claim 1 or 2, wherein the hydraulic actuator (21) comprises:
a control chamber (22) that is in communication with the exhaust channel (27);

a piston (23) that is mounted sliding inside the control chamber (22); and

a spring (24) which pushes the piston (23).
A fuel pump (4) according to claim 3, wherein the piston (23) is arranged between the control chamber (22) and the suction channel (14).
A fuel pump (4) according to claim 4, wherein:
the control chamber (22) and the piston (23) have a cylindrical shape; and

the outer diameter of the piston (23) is smaller than the inner diameter of the control chamber (22) to define between the piston (23) and control chamber (22) an annular passing meatus through which fuel can flow from control chamber (22) to the suction channel (14).
A fuel pump (4) according to claim 4, wherein the setting device (19) is depicted as a valve that opens when the fuel pressure in the control chamber (22) exceeds a predetermined value and the piston (23) acts as the valve's plug.
A fuel pump (4) according to claim 6, wherein a portion of the control chamber (22) that is coupled with the piston (23) has a truncated cone shape.
A fuel pump (4) according to one of the claims from 3 to 7, wherein the setting device (19) comprises a control rod (20) acting on the suction valve (15) and is integral to the piston (23).
A fuel pump (4) according to claim 8, wherein the suction valve (15) comprises a disk (16) presenting a series of passing-passing-through holes (17) through which fuel can flow and a plate (18) which is deformable and is supported by a base of the disk (16) closing the passage through the holes (17) and is mechanically coupled to the control rod (20); the control rod (20) is movable between a passive position, in which it allows the plate (18) to bind fluid-tight the disk (16) to seal the holes (17), and an active position, which does not allow the plate (18) to bind fluid-tight the disk (16) leaving the holes (17) open.
A fuel pump (4) according to one of the claims from 1 to 9 and comprising:
a collection chamber (30), which is placed below the pumping chamber (11) and is crossed by an intermediate portion of the piston (12) which is shaped in such a way as to vary cyclically the volume of the collection chamber (30) due to its alternating motion; and

a connection channel (31), which connects the collection chamber (30) to the suction channel (14).
Fuel pump (1) according to claim 10, wherein the intermediate portion of the piston (12) which is located inside the collection chamber (30) is shaped like the upper portion of the piston (12) which is located inside the pumping chamber (11) in such a way that when the piston (12) moves the variation of volume that occurs in the collection chamber (30) because of the displacement of the piston (12) is equal and opposite to the variation of volume that occurs in the pumping chamber (11) because of the displacement of the piston (12).