A fuel-supply system for an internal-combustion engine

Abstract

 A fuel-supply system (1) for an internal-combustion engine has a high-pressure pump (7) that receives fuel from a low-pressure pump (7) through a pipe (10) provided with a solenoid valve (27) of an on-off type; the solenoid valve has an open/close element (40) that translates along an axis (33) between an opening position and a closing position under the opposite actions of an electric actuator (43) and a spring (42); in the closing position, under the thrust of the spring (42), the open/close element (40) closes an axial inlet (32) and inhibits passage of fuel towards an outlet (38), which is provided in a radial direction and communicates with at least one intake valve (25) of the high-pressure pump (7).

Description

[0001] The present invention relates to a fuel-supply system for an internal-combustion engine.

[0002] As is known, fuel-supply systems of the diesel-cycle type comprise a high-pressure pump that supplies fuel to a common rail, which has a predetermined volume for accumulating fuel under pressure and supplies, in turn, a plurality of injectors associated to the engine cylinders.

[0003] To obtain a good nebulization of the fuel, the latter must be brought up to a very high pressure, in the region of 1600 bar, in the conditions of maximum power of the engine. The pressure of the fuel required in the common rail is in general defined by an electronic control unit as a function of the operating conditions of the engine.

[0004] Known to the art are injection systems in which a by-pass solenoid valve, set on the delivery pipe of the high-pressure pump, is controlled by the control unit for causing recirculation of the fuel that is in excess with respect to the fuel injected by the injectors, towards the usual fuel tank, before said excess fuel enters the common rail.

[0005] Normally, the capacity of the high-pressure pumps is directly proportional to the engine r.p.m. and is calibrated so as to meet the maximum requirements in every operating condition of the engine. However, in certain operating conditions (for example, at the maximum r.p.m., but with a reduced power supplied by the engine), the flow of excess fuel, which is discharged into the tank by the by-pass solenoid valve, is very high. Consequently, this embodiment presents the drawback of involving a waste of part of the compression work of the high-pressure pump.

[0006] Variable-capacity high-pressure pumps have been proposed in such a way as to reduce the amount of fuel pumped when the engine functions at reduced power. In one of these pumps, the intake pipe of the high-pressure pump is provided with a restriction having a passage cross-section the area of which is continuously variable. Said passage cross-section is defined by a solenoid valve controlled by the electronic control unit as a function of the pressure required in the common rail and/or of the operating conditions of the engine.

[0007] In particular, the restriction in the intake pipe is supplied with a constant pressure difference, equal to approximately 5 bar, determined by an auxiliary pump, or low-pressure pump, set in the tank. By varying continuously the area of the restriction, the amount of fuel drawn in by the pumping elements of the high-pressure pump is modulated.

[0008] According to an alternative solution, described, for example, in the European patent No. EP1612402, a solenoid valve of an on-off type is set between the high-pressure pump and the low-pressure pump. Said solenoid valve is controlled by the electronic control unit, once again as a function of the pressure required in the common rail and/or of the operating conditions of the engine, in synchronism with the intake strokes of two pumping elements of the high-pressure pump and in a chopped way so as to establish the effective amount of fuel taken in during said intake stroke.

[0009] Known solenoid valves of an on-off type mounted between the high-pressure pump and the low-pressure pump have an open/close element that is able to slide along an axis under the opposite actions of an electromagnet and a spring. The axial thrust of the spring tends to bring the open/close element against a valve seat for closing axially an opening from which the fuel exits towards the high-pressure pump. Experimentally, fuel-supply systems of the type just described have revealed an excessive noise coming from the on-off solenoid valve mounted between the high-pressure pump and the low-pressure pump. Said drawback arises above all in systems in which the solenoid valve is not controlled in synchronism with the high-pressure pump.

[0010] The noise is due to phenomena of fluid hammer that arise during closing of the on-off solenoid valve. Said phenomena are due to the fact that the open/close element intercepts a flow with a value of instantaneous flowrate that is high also on account of the difference of pressure to which the solenoid valve is subjected (approximately 3 bar). In particular, the intensity of the fluid hammer is due above all to the constructional layout of the solenoid valve, where the supply pressure of the fuel coming from the low-pressure pump tends to close the open/close element of the solenoid valve.

[0011] The aim of the invention is to provide a fuel-supply system for an internal-combustion engine, which will enable limitation or elimination of the drawback set forth above in a simple and inexpensive way.

[0012] According to the invention, the above aim is achieved by a fuel-supply system for an internal-combustion engine as defined by Claim 1.

[0013] For a better understanding of the invention described herein is a preferred embodiment, provided by way of example with the aid of the annexed drawings, wherein:

• Figure 1 is a diagram of a fuel-supply system in an internal-combustion engine, according to the present invention;
• Figure 2 illustrates, partially and in cross section, a solenoid valve that forms part of the system of Figure 1; and
• Figure 3 is similar to Figure 2 and shows part of a variant of the solenoid valve of Figure 2.

[0014] With reference to Figure 1, designated as a whole by 1 is a fuel-supply system for an internal-combustion engine 2, for example a four-stroke diesel engine. The engine 2 comprises a plurality of cylinders 3, for example four cylinders, which co-operate with corresponding pistons (not shown), which can be actuated to turn a drive shaft 4.

[0015] The supply system 1 comprises a plurality of electrically controlled injectors 5, associated to the cylinders 3 and designed to inject the high-pressure fuel therein. The injectors 5 are connected to an accumulation volume, which has a predetermined value for one or more injectors 5. In the embodiment illustrated, the accumulation volume is formed by the usual common rail 6, connected to which are all the injectors 5.

[0016] The common rail 6 is supplied with fuel under high pressure by a high-pressure pump, designated as a whole by 7, via a delivery pipe 8. In turn, the high-pressure pump 7 is supplied by a low-pressure pump, for example, an electric pump 9, via an intake pipe 10 of the high-pressure pump 7. The electric pump 9 is in general set in the usual fuel tank 11. A discharge pipe 12 gives out into the tank 11 for causing recirculation of the excess fuel of the supply system 1.

[0017] Preferably, the common rail 6 is provided with a discharge solenoid valve 15, which is in communication with the discharge pipe 12 and performs a safety function in the case where there were to be an overpressure in the common rail 6.

[0018] Each injector 5 is designed to inject, into the corresponding cylinder 3, an amount of fuel that ranges between a minimum value and a maximum value, under the control of an electronic control unit 16, which can be formed by the usual microprocessor control unit for control of the engine 2. The control unit 16 is designed to receive signals indicating the operating conditions of the engine 2, such as the position of the accelerator pedal and the r.p.m. of the drive shaft 4, which are generated by corresponding sensors (not shown), as well as the pressure of the fuel in the common rail 6, detected by a pressure sensor 17. By processing said received signals by a purposely provided program, the control unit 16 controls the instant and duration of actuation of the individual injectors 5. In addition, the control unit 16 controls opening and closing of the discharge solenoid valve 15. Consequently, the discharge pipe 12 conveys towards the tank 11 both the discharge fuel of the injectors 5 and the possible excess fuel in the common rail 6, discharged for safety reasons by the solenoid valve 15.

[0019] The high-pressure pump 7 comprises a pair of pumping elements 18, each formed by a cylinder 19 having a compression chamber 20, in which a mobile piston 21 slides with reciprocating motion, constituted by an intake stroke and a delivery stroke. Each compression chamber 20 is provided with a corresponding intake valve 25 and a corresponding delivery valve 30. The valves 25 and 30 can be of the ball type and can be equipped with respective return springs. The two intake valves 25 are in communication with the intake pipe 10 common to said intake valves 25, whilst the two delivery valves 30 are in communication with the delivery pipe 8 common to said delivery valves 30.

[0020] In particular, the piston 21 is actuated by an eccentric 22 carried by an actuation shaft 23 of the high-pressure pump 7. In the embodiment described here, the two pumping elements 18 are coaxial and opposite to one another, and are actuated by a single eccentric 22. The shaft 23 is connected to the drive shaft 4, via a motion-transmission device 26, such that the eccentric 22 controls a compression stroke of a piston 21 for each injection of the injectors 5 into the respective cylinders 3 of the engine 2.

[0021] In the tank 11, the fuel is at atmospheric pressure. In use, the electric pump 9 compresses the fuel to a low pressure, for example in the region of just 2-3 bar. In turn, the high-pressure pump 7 compresses the fuel received from the intake pipe 10 so as to send the fuel at high pressure, for example in the region of 1600 bar, to the common rail 6, via the delivery pipe 8.

[0022] The capacity of the high-pressure pump 7 is controlled exclusively by a solenoid valve 27 arranged on the intake pipe 10.

[0023] The solenoid valve 27 is of the on-off type and has an effective passage cross-section that is relatively wide so as to supply fuel without causing any drop of pressure when it is open.

[0024] With reference to Figure 2, the solenoid valve 27 (partially illustrated) comprises a casing 28 and a plate-like portion 31, which is coupled in a fixed position to the casing 28, for example via an externally threaded ringnut 31a screwed to a side wall 36 of the casing 28. The plate-like portion 31 has a hole 32, which extends along an axis 33 and defines an inlet for the fuel that arrives from the delivery of the pump 9.

[0025] The wall 36 and the plate-like portion 31 define the perimeter and the bottom of a chamber 37, which communicates in a permanent way with a hole 38 made on the wall 36 in a radial direction with respect to the axis 33. The hole 38 defines an outlet for the fuel that flows towards the valves 25 of the high-pressure pump 7.

[0026] The chamber 37 houses an open/close element 40, which is defined by a ball or by a spherical portion, in the particular example shown. The open/close element 40 is subject to the opposite actions of a spring 42 and of an electric actuator 43. In particular, the actuator 43 is defined by an electromagnet comprising: a magnetic core 44 fixed with respect to the casing 28; and an armature 45, which impinges upon the open/close element 40 so as to keep it in a closing position when the electric actuator 43 is not energized, transferring onto the open/close element 40 the elastic force of the spring 42. Even though the open/close element 40 is spherical, the travel allowed for the armature 45 is of a small amount so that there is no possibility for the open/close element 40 to be able to displace radially.

[0027] In the particular example illustrated, the armature 45 is defined by a body comprising: a central portion 45a, which rests on the open/close element 40; and a peripheral portion 45b, which is disk-shaped and is made of ferromagnetic material. Preferably, the armature 45 is guided by one or more guide elements 36a, fixed with respect to the wall 36 so as to translate along the axis 33 between a raised position and a lowered position with respect to the magnetic core 44.

[0028] As mentioned above, the spring 42 has a pre-load and a stiffness such as to exert an action of axial thrust that tends to bring the armature 45 into a lowered position and, hence, the open/close element 40 into the closing position. In the closing position, the open/close element 40 engages in a fluid-tight way a valve seat 47 defined by a conical surface provided on the plate-like portion 31 around the hole 32 so as to close the hole 32 itself. In the particular embodiment shown, the spring 42 is housed in the magnetic core 44 and acts directly on the armature 45.

[0029] When the magnetic core 44 is electrically supplied, it causes axial translation of the armature 45 into the raised position, and hence causes displacement of the open/close element 40 into an opening position. In the opening position, the hole 38 communicates with the hole 32 through the space or volume of the chamber 37 for supplying fuel from the pump 9 to the intake valves 25 of the high-pressure pump 7.

[0030] Figure 3 is a partial illustration of a variant of the solenoid valve 27, the components of which are designated by the same reference numbers used in Figure 2, wherever possible.

[0031] Unlike what is shown in Figure 2, the open/close element 40 is defined by a cup-shaped body (partially illustrated) comprising: a bottom wall 40a orthogonal to the axis 33, axially facing the plate-like portion 31, and provided with through holes 48; and a cylindrical side wall 40b, which extends axially starting from the perimetral edge of the wall 40a in a position set facing the wall 36 and is fixed with respect to the wall 40a itself.

[0032] The guide element 36a is a casing portion that is defined by the prolongation of the wall 36 towards the actuator (not illustrated in Figure 3) and is slidably coupled directly to the wall 40b of the open/close element 40. The wall 36 is provided with at least two radial holes 38, which are set in diametrally opposite positions with respect to one another.

[0033] The plate-like portion 31 is fixed to the wall 36 underneath holes 38 for interference fit, for example via drive fit, and has a plane face that is orthogonal to the axis 33, faces the wall 40a, and defines the valve seat 47.

[0034] The spring 42 is at least partially housed in the open/close element 40, is coaxial with respect to the wall 40b, and acts directly against the wall 40a. Towards the plate-like portion 31, the wall 40a comprises an annular projection 46, which is coaxial to the hole 32, is set in a more internal position with respect to the holes 48 and has the purpose of guaranteeing fluid-dynamic sealing against the valve seat 47 so that the sealing area has the mean diameter of the projection 46. Once again towards the plate-like portion 31, the open/close element 40 comprises a projection 49, which is set along the perimetral edge of the wall 40a, i.e., in a position more external respect to the holes 48 and to the projection 46, and has radial passages not visible in Figure 3.

[0035] According to the invention, as compared to the on-off solenoid valves of a known type used for adjusting the flowrate, like the ones described in the patent No. EP1612402, the direction of the flow of the fuel that traverses the solenoid valve is reversed, i.e., the supply pressure tends to raise the open/close element 40, instead of closing it. This results in longer closing times of the open/close element 40, because the supply pressure is now opposite to the action of the spring 42, instead of being concordant therewith: given that the flow of fuel that traverses the solenoid valve is interrupted for a longer time as compared to what occurs in the known art, the intensity of the fluid hammer caused by closing of the open/close element 40 is lower, with consequent benefit in terms of noise emission.

[0036] It is clear that modifications and variations may be made to the system 1 described and illustrated herein, without thereby departing from the scope of protection of the present invention, as defined in the annexed claims.

[0037] For example, it is possible to eliminate the motion-transmission device 26, and actuate the shaft 23 of the high-pressure pump 7 at a rate independent of the r.p.m. of the drive shaft 4. Also the solenoid valve 15 for discharge of the fuel from the common rail 6 can be eliminated without jeopardizing operation of the system.

[0038] In addition, the two pumping elements 18 can be set in parallel and actuated in phase opposition by two different eccentrics, and/or the actuator 43 could be different from the one shown by way of example in Figure 2; and/or the shape of the solenoid valve 27 could be different from the ones shown in Figures 1 and 2, and/or the high-pressure pump 7 could have a different number of pumping elements, for example a single pumping element, or else three pumping elements preferably actuated by a common eccentric with a phase offset of 120°.

[0039] Finally, the invention applies both to systems where the solenoid valve 27 is controlled in a way synchronous with the rate of rotation of the pump and to systems where the control of the solenoid valve 27 is asynchronous.

Claims

1. A fuel-supply system (1) for an internal-combustion engine, comprising:

- a high-pressure pump (7);

- a low-pressure pump (9);

- a pipe (10) for supplying fuel from said low-pressure pump (9) to at least one intake valve (25) of said high-pressure pump (7);

- a solenoid valve (27) of an on-off type, set along said pipe (10) and comprising:

a) an electric actuator (43);

b) elastic means (42) exerting a closing thrust;

c) an inlet (32) for the fuel, which communicates with the delivery of said low-pressure pump (9);

d) an outlet (38) for the fuel, which communicates with said intake valve (25); and

e) an open/close element (40), which is mobile along an axis (33) under the opposite actions of said electric actuator (43) and of said elastic means (42) between an opening position, in which said inlet (32) communicates with said outlet (38), and a closing position, in which the passage of fuel from said inlet (32) to said outlet (38) is blocked;

characterized in that said inlet (32) is made axially, and said open/close element (40) closes said inlet (32) when it is set in said closing position so as to oppose, in use, the supply pressure at said inlet to the closing thrust exerted by said elastic means (42).

2. The system according to Claim 1, characterized in that said outlet (38) is provided in a radial direction with respect to said axis (33).

3. The system according to Claim 2, characterized in that said outlet (38) is defined by at least two holes set at the same angular distance apart.

4. The system according to any one of the preceding claims, characterized in that said elastic means (42) exert a thrust action to bring said open/close element (40) into said closing position, and said electric actuator (43) is defined by an electromagnet, which attracts said open/close element (40) into said opening position when it is electrically supplied.

5. The system according to any one of the preceding claims, characterized in that said solenoid valve (27) comprises:

- a side wall (36), on which said outlet (38) is made;

- a plate-like portion (31) fixed with respect to said side wall (36); said inlet (32) being provided on said plate-like portion (31);

- a valve seat (47) extending on said plate-like portion (31) around said inlet (32) and engaged in a fluid-tight way by said open/close element (40) when said open/close element (40) is set in the closing position; and

- a chamber (37) defined laterally by said side wall (36) and axially by said plate-like portion (31).

6. The system according to Claim 5, characterized in that said open/close element (40) comprises a wall (40a) orthogonal to said axis (33), facing said plate-like portion (31), and having an annular projection (46) defining the sealing area against said valve seat (47).

7. The system according to Claim 5 or Claim 6, characterized in that said solenoid valve (27) comprises guide means (36a) fixed with respect to said side wall (36) for guiding said open/close element (40) and/or an armature of said electric actuator along said axis (33) between said opening position and said closing position.

Drawing