ITMI20132214A1 - HIGH PRESSURE PRESSURE VALVE FOR A HIGH PRESSURE COMMON RAIL PUMP AND HIGH PRESSURE COMMON RAIL PUMP - Google Patents

Description

DESCRIPTION

of the patent for industrial invention entitled:

"OVERPRESSURE VALVE FOR A HIGH PRESSURE COMMON RAIL PUMP AND HIGH PRESSURE COMMON RAIL PUMP"

The present invention relates to an overpressure valve for a high pressure common rail pump and to a high pressure common rail pump.

As is known, high pressure common rail pumps are used to feed pressurized fuel in internal combustion engines, in particular with compression ignition. The following discussion will explicitly refer to this case without therefore losing generality.

Fuel systems for a compression ignition internal combustion engine usually include a low pressure or pre-fuel pump and a high pressure pump.

The low-pressure pump, for example an electric pump, draws fuel from a low-pressure tank and transfers it to the high-pressure pump.

The high pressure pump, normally of the piston type, feeds fuel at a working pressure to a distribution manifold, traditionally called "common rail", from which injectors branch off and can be activated by a control unit that atomise the fuel in respective cylinders of the internal combustion engine.

The low-pressure pump and the high-pressure pump can be integrated into a single pump housing.

The fluidic connections between the low pressure tank, the low pressure pump, the high pressure pump and the distribution manifold are made by means of a hydraulic circuit, which is also equipped with regulation devices to maintain controlled pressure levels in the different sections of the fuel system.

In particular, an overpressure valve (or pressure limiter or "overflow") is used to limit the pressure inside the high pressure pump casing. The overpressure valve has an inlet and an outlet respectively communicating with the high pressure pump casing and with a return branch towards the tank. When the pressure difference between the inlet and the outlet of the valve exceeds an adjustment threshold, the overpressure valve opens and allows the disposal of a fuel flow, through the return branch.

An overpressure valve generally comprises a tubular body, having an inlet at one end and one or more outlet openings in the side wall, and a shutter, sliding axially along the tubular body between a closed position and a maximum opening position. In the closed position, the shutter closes both the valve inlet and the outlet openings, preventing the access of fuel inside the tubular body. On the other hand, when the shutter is in the maximum opening position, the inlet is free and the fuel can flow inside the tubular body up to the outlet openings.

A contrast spring keeps the shutter in the closed position. When the pressure at the inlet of the overpressure valve overcomes the resistance of the contrast spring, the shutter moves towards the maximum opening position and allows the fuel to be vented.

Known overpressure valves, while satisfactory in many respects, nevertheless suffer from some limitations. Meanwhile, the axial dimensions are not negligible, in consideration of the limited space available in the pump body. Secondly, it would generally be desirable to improve the response time of the valve, in particular to achieve greater effectiveness in the event of pressure fluctuations.

The object of the present invention is to provide an overpressure valve for a high pressure common rail pump and a high pressure common rail pump which allow to overcome the drawbacks described.

According to the present invention, an overpressure valve is made for a high pressure common rail pump comprising:

a valve body, which longitudinally delimits a chamber having a first open end, defining a fluidic inlet of the chamber, a second closed end and at least one outlet passage through a side wall of the valve body; And

a shutter sliding axially in the chamber between a first position and a second position and having a radial sealing portion cooperating with the side wall of the valve body;

in which the shutter is shaped so that the radial sealing portion is axially comprised between the first end and the outlet passage of the chamber when the shutter is in the first position and axially comprised between the outlet passage and the second end of the chamber when the shutter is in the second position. In this way, a twofold advantage is obtained. In an initial phase of the shutter travel from the first position to the second position, the outlet passage is free and allows the fuel to flow from the portion of the chamber between the shutter and the second closed end. Initially, therefore, the shutter encounters a modest hydraulic resistance, which gradually increases as the outlet passage is obstructed by the radial seal portion. The response of the overpressure valve is therefore faster and allows to effectively counteract any pressure fluctuations.

Secondly, the shutter has small dimensions and therefore the overall dimensions of the entire valve body are reduced.

According to a further aspect of the invention, a high pressure common rail pump is provided, equipped with an overpressure valve for a high pressure common rail pump comprising:

a valve body, which longitudinally delimits a chamber having a first open end, defining a fluidic inlet of the chamber, a second closed end and at least one outlet passage through a side wall of the valve body; And

a shutter sliding axially in the chamber between a first position and a second position and having a radial sealing portion cooperating with the side wall of the valve body;

in which the shutter is shaped so that the radial sealing portion is axially comprised between the first end and the outlet passage of the chamber when the shutter is in the first position and axially comprised between the outlet passage and the second end of the chamber when the shutter is in the second position.

Further characteristics and advantages of the present invention will become clear from the following description of some non-limiting examples of embodiment, with reference to the figures of the annexed drawings, in which:

Figure 1 schematically shows a portion of a fuel system of an internal combustion engine, incorporating a high pressure common rail pump;

Figure 2 is a longitudinal section of an overpressure valve, in a first operating configuration, made according to an embodiment of the present invention and incorporated in the high pressure common rail pump;

Figures 3 and 4 show the overpressure valve of Figure 2 respectively in a second operating configuration and in a third operating configuration;

Figure 5 is a longitudinal section of an overpressure valve, in a first operating configuration, made according to a different embodiment of the present invention and usable in the high pressure common rail pump;

figure 6 shows the overpressure valve of figure 5 in a second operating configuration;

- Figure 7 is a longitudinal section of an overpressure valve, in a first operating configuration, made according to a further embodiment of the present invention and usable in the high pressure common rail pump;

Figure 8 shows the overpressure valve of Figure 7 in a second operating configuration.

In Figure 1, the reference number 1 indicates a fuel supply system for an internal combustion engine with compression ignition (not shown). The fuel system 1 comprises a fuel tank 2, a high pressure common rail pump 3, a low pressure supply circuit 5, which includes a low pressure pump 6 and connects the fuel tank 2 with the common rail pump of high pressure 3, and a high pressure delivery circuit 7, which connects the high pressure pump 3 with a distribution manifold or common rail 8.

The high pressure common rail pump 3 comprises a pump body 10, schematically indicated in figure 1 with a dotted line, one or more pumping elements 11 housed in the pump body 10 (two in the example illustrated), and an actuator mechanism 12 , also housed in a chamber in the pump body 10.

The two pumping elements 11 are arranged radially at 120 ° around the actuator mechanism 12 and each comprise a piston 13 axially sliding in a respective seat 14. The portion of each seat 14 not occupied by the piston 10 defines a pumping chamber ("driving chamber" ) with variable volume and is coupled to the low pressure supply circuit 5 through a supply valve 15 and to the delivery circuit 7 through a delivery valve 16.

In one embodiment, the low pressure pump 6 is an electric pump housed in the tank 2. In a different embodiment, not shown, the low pressure pump can be integrated into the pump body 10 with the high pressure common rail pump 3. The low pressure pump 6 draws fuel from the fuel tank 2 and supplies it to the high pressure pump 3 through a supply branch 18 of the supply circuit 5. The fuel drawn from the fuel tank 2 is introduced into the pump body 10, where it acts as a lubricant for moving parts. Here and in the following, reference will be made to the inside of the pump body 10 to indicate any cavity, chamber, opening, duct or other type of fluid passage defined in the pump body 10 and intended in use to be occupied by low pressure fuel, to then upstream of the supply valves 15.

The low pressure supply circuit 5 further comprises an overpressure valve (or pressure relief valve or "overflow" valve) 20, which has a fluidically coupled inlet inside the pump body 10 and an outlet connected to a branch return 19 which communicates directly with the tank 2 or, alternatively, with the supply branch 18.

If the pressure inside the pump body 10 exceeds a pressure threshold, the overpressure valve 20 opens and allows the recirculation of fuel towards the fuel tank 2 and in any case upstream of the inlet to the high pressure pump 3.

A metering valve 50, fluidically arranged between the inside of the pump body 10 and the pumping chambers, regulates the flow of fuel fed to the pumping chambers themselves through the respective supply valves 15.

With reference to Figures 2 to 4, in one embodiment the overpressure valve 20 is embedded in the pump body 10 and comprises a valve body 21, longitudinally delimiting a chamber 22, a shutter 23 movable in the chamber 22 and a contrast spring 25 adapted to keep the shutter 23 in a closed position of the chamber 22.

More in detail, the valve body 21 has an essentially cylindrical shape and extends along a longitudinal axis A. The valve body 21 has a coupling portion, which can be inserted with interference or screwed into a cup seat 26 obtained in the pump body. 10 in fluid communication with the inside of the pump body 10. An annular seat 27, obtained on an external surface of the valve body 21, houses a sealing gasket 28, capable of deforming against the pump body 10.

The chamber 22 is defined by a through cavity having a preferably, but not necessarily circular section, which extends through the whole valve body 21 and has an open end 22a and an end 22b closed by a thrust body 29. The end 22a open forms a fluidic inlet of the overpressure valve 20 and of the chamber 22 and communicates with the inside of the pump body The thrust body 29 is inserted in a fluid-tight manner in the longitudinal through cavity and can comprise, for example, a spherical, oval metal insert either substantially cylindrical driven with interference or a threaded dowel screwed to the end 22b.

The chamber 22 also has a plurality of radial outlet passages 30 with a substantially circular cross section, obtained through a side wall 21a of the valve body 21 and angularly distributed around the longitudinal axis A; and, near the closed end 22b, at least one radial vent passage 31, also obtained through the side wall 21a of the valve body 21.

In a position corresponding to the outlet passages 30, the pump body 10 has an annular chamber 32, which extends around the valve body 21 in a plane substantially perpendicular to the longitudinal axis A and is connected with the supply branch 18.

The contrast spring 25 is housed in the chamber 22 against the thrust body 29 and tends to keep the shutter 23 in the first position, counteracting the movement away from the first position itself due to pressure increases inside the pump body. 10.

The shutter 23 has a radial sealing portion 23a, which cooperates with an internal surface of the side wall 21a of the valve body 21, delimiting the chamber 22. Furthermore, the shutter 23 can slide axially inside the chamber 22 between the position and a position of maximum opening of the overpressure valve 20. The radial sealing portion 23a has a length L shorter than the maximum axial distance DMAXe preferably, but not necessarily, also shorter than the minimum distance DMIN between the end 22a defining the fluidic inlet of the chamber 22 and each outlet passage 30. Furthermore, the length L of the radial sealing portion 23a is less than the maximum axial distance DMAX 'and preferably, but not necessarily, also less than the minimum distance DMIN' between each outlet passage 30 and the blind end 22b of chamber 22.

In this way, when the shutter 23 is in the first (closed) position, the radial sealing portion 23a is axially comprised between the outlet passages 30 and the end 22a defining the fluidic inlet of the chamber 22 and the outlet passages 30 , which are open at least partially and, preferably, completely. In this configuration, in practice, the shutter 23 fluidically decouples the outlet passages 30 from the fluidic inlet at the end 22a. The portion of the chamber 22 between the shutter 23 and the second end 22b is instead in fluid communication with the outside of the valve body 21 through the outlet passages 30.

In intermediate positions between the first position and the second position, the shutter 23 first progressively occludes the outlet passages 30, consequently reducing the flow of fuel from the blind portion towards the outside through the outlet passages 30 themselves. In this phase, the resistance encountered by the shutter 23 during the ascent grows progressively as the light of the exit passages 30 decreases.

When the outlet passages are completely obstructed (Figure 3), the resistance to rising of the shutter 23 is maximum and the fuel can leave the portion of the chamber 22 between the shutter 23 and the closed end 22b only through the vent 31.

Subsequently, the shutter 23 continues its stroke towards the second position and, approaching the second end of the chamber 22, progressively frees the outlet passages 30, which are put in fluid communication with the end 22a of the chamber 22 and the inside of the pump body 10.

When the shutter 23 is in the second position (of maximum opening, illustrated in Figure 4), the radial sealing portion 23a is axially comprised between the outlet passages 30 and the blind end 22b of the chamber 22, so as to leave the outlet passages 30 are free. The latter are then coupled to the fluidic inlet defined by the opening 22a directly through the chamber 22.

The described overpressure valve has a double advantage. In the first place, the initial phase of the stroke from the first position towards the second position is carried out against a modest hydraulic resistance, because the fuel present in the portion of the chamber 22 between the shutter 23 and the end 22b can flow through the exit 30, which are initially open. In this way, the response of the overpressure valve is particularly rapid in an initial phase and allows to effectively compensate for any pressure fluctuations.

In addition, the shutter has modest dimensions and therefore also the valve body that must house it can have limited dimensions.

Figures 5 and 6 illustrate a different embodiment of the invention. In this case, an overpressure valve 120 comprises a body comprises a valve body 121, longitudinally delimiting a chamber 122, an obturator 123 movable in the chamber 122 and a contrast spring 125 adapted to keep the obturator 123 in a position closing of the chamber 122.

The valve body 121, substantially similar to the valve body 21 already described with reference to Figure 2, has an essentially cylindrical shape and extends along a longitudinal axis A.

The chamber 122 is defined by a through cavity of preferably, but not necessarily circular section, which extends through the whole valve body 121 and has an open end 122a and an end 122b closed by a thrust body 129. The end 122a open forms a fluidic inlet of the overpressure valve 120 and chamber 122 and communicates with the inside of the pump body 10.

Chamber 122 also has a plurality of radial outlet passages 130 with a substantially triangular cross section, obtained through a lateral wall 121a of the valve body 121 and angularly distributed around the longitudinal axis A; and, in proximity to the closed end 122b, at least one radial vent passage 131, also obtained through the side wall 121a of the valve body 121. The cross section of the outlet passages 130 has a vertex facing the end 122a defining the fluidic inlet is a base facing the end 122b of the chamber 122.

The shutter 123 slides axially inside the chamber 122 between the closed position (Figure 5) and a maximum opening position (Figure 6) of the overpressure valve 120. In the embodiment described here, the shutter 123 is shaped like a cup and has a radial sealing portion 123a and a base 123b.

The radial sealing portion 123a cooperates with an internal surface of the side wall 121a of the valve body 121, delimiting the chamber 122. The obturator 123 is shaped so that, both in the closed position and in the maximum open position, the portion radial seal 123a leaves the outlet passages 130 at least partially free and, preferably, but not necessarily, completely free. In the closed position of the shutter 123, the radial sealing portion 123a is axially comprised between the end 122a of the chamber 122 and the outlet passages 130. In the position of maximum opening of the shutter 123, the radial sealing portion 123a is axially comprised between the outlet passages 130 and the end 122a of the chamber 122.

The shutter 123 has a concavity facing the end 122a of the chamber 122 and the base 123b facing the end 122b. In addition, the base 123b of the shutter 123 centrally has a through opening 135 with a smaller cross section than each of the outlet passages 130. The opening 135 constantly allows a minimum recirculation of fuel which maintains optimal lubrication conditions.

With exit passages 130 with a triangular cross section, the progressive variation of hydraulic resistance encountered by the shutter in the ascent towards the maximum opening position is more evident.

The embodiment of figures 7 and 8 differs from the previous one due to the fact that the shutter 123 has the base 123b facing the end 122a of the chamber 122 and the concavity facing the end 122b. In this way, one end of the contrast spring 125 can be housed inside the shutter 123 and therefore the valve body, indicated here with 121 ', can have even more compact dimensions.

Finally, it is clear that modifications and variations can be made to the pump and system described, without departing from the scope of the present invention, as defined in the attached claims.

In particular, the shutter can be shaped so that in the closed position and / or in the maximum opening position the outlet passages are partially obstructed, rather than completely free. In this case, the radial sealing portion partially overlaps the outlet passages.

The cross section of the outlet passages may differ from what is described and illustrated.

Claims (14)

CLAIMS 1. Overpressure valve for a high pressure common rail pump comprising: a valve body (21; 121; 121 '), which longitudinally delimits a chamber (22; 122) having a first open end (22a; 122a), defining a fluidic inlet of the chamber (22; 122), a second closed end (22b; 122b) and at least one outlet passage (30; 130) through a side wall (21a; 121a) of the valve body (21; 121; 121 '); And a shutter (23; 123) axially sliding in the chamber (22; 122) between a first position and a second position and having a radial sealing portion (23a; 123a) cooperating with the side wall (21a; 121a) of the valve body ( 21; 121; 121 '); wherein the shutter (23; 123) is shaped so that the radial sealing portion (23a; 123a) is axially comprised between the first end (22a; 122a) and the outlet passage (30; 130) of the chamber ( 22; 122) when the shutter (23; 123) is in the first position and axially included between the outlet passage (30; 130) and the second end (22b; 122b) of the chamber (22; 122) when the shutter (23; 123) is in the second position. 2. Valve according to claim 1, wherein the shutter (23; 123) is shaped so that a portion of the chamber (22; 122) comprised between the shutter (23; 123) and the second end (22b; 122b ) is in fluid communication with the outside of the valve body (21; 121; 121 ') through the outlet passage (30; 130) when the shutter (23; 123) is in the first position. Valve according to claim 1 or 2, wherein the shutter (23) in the first position fluidically decouples the outlet passage (30) from the first end (22a) and in the second position allows the fluidic coupling between the first end ( 22a) and the exit passage (30). 4. Valve according to any of the previous claims, in which the outlet passage (30; 130) is completely free when the shutter (23; 123) is in the first position. 5. Valve according to any of the previous claims, in which the outlet passage (30; 130) is completely free when the shutter (23; 123) is in the second position. Valve according to any one of the preceding claims, wherein the outlet passage (30) of the chamber (22) has a substantially circular cross section. Valve according to any one of the preceding claims, wherein the outlet passage (130) of the chamber (122) has a substantially triangular cross section. Valve according to claim 7, wherein the cross section of the outlet passage (130) has a vertex facing the first end (122a) and a base facing the second end (122b) of the chamber (122). Valve according to any one of the preceding claims, wherein the chamber (22; 122) has a plurality of outlet passages (30; 130) through the side wall (21a; 121a) of the valve body (21; 121; 121 ') . 10. Valve according to any one of the preceding claims, comprising an elastic contrast element (25; 125), configured so as to oppose the movement of the shutter (23; 123) from the first position to the second position. Valve according to any one of the preceding claims, wherein the chamber (22; 122) is defined by a longitudinal through cavity of the valve body (21; 121; 121 ') and the second end (22b; 122b) is closed by a thrust body (29; 129) inserted in a fluid-tight manner in the longitudinal through cavity. High pressure common rail pump, comprising an overpressure valve (20; 120) according to any one of the preceding claims. 13. Fuel supply system for an internal combustion engine comprising a high pressure common rail pump (3) according to claim 12. System according to claim 13, comprising a fuel tank (2), a low pressure pump (6) for transferring fuel from the tank (2) into a pump body (10) of the high pressure common rail pump ( 3); and in which the first end (22a; 122a) and the outlet passage (30; 130) of the overpressure valve (20; 120) are respectively connected inside a pump body (10) and to the tank (2).