WO2013174610A1

WO2013174610A1 - Pressure limiting valve and fuel injecion plant for an internal combustion engine comprising said pressure limiting valve

Info

Publication number: WO2013174610A1
Application number: PCT/EP2013/058659
Authority: WO
Inventors: Discar RUDINAL
Original assignee: Robert Bosch Gmbh
Priority date: 2012-05-23
Filing date: 2013-04-25
Publication date: 2013-11-28
Also published as: IN2014DN07262A; CN104321573A; ITMI20120892A1

Abstract

A pressure limiting valve (18; 68) arranged between a first conduit (6) and a second conduit comprises: a seat (41), provided with an opening (48), communicating with the first conduit (6), and with a first shoulder (43); a shutter (51), which is mobile inside the seat (41) and is provided with an inner channel (63), having an inlet (64) communicating with the second conduit (12) and at least one outlet (65), and a head (57) adapted, in use, to be arranged against the first shoulder (43); the outlet (65) being arranged on the head (57); the seat (41) and the head (57) being shaped so as to provide a sealed coupling when the difference between the pressure in the first conduit (6) and the pressure in the second conduit is lower than a threshold value and so as to provide a non-sealed coupling when said difference is greater than said threshold value.

Description

Title

PRESSU RE LIMITING VALVE AND FU EL INJECION PLANT FOR AN INTERNAL COMBUSTION ENGINE COMPRISING SAID PRESSU RE LIMITING VALVE

The present invention relates to a pressure limiting valve and to a fuel injection plant for an internal combustion engine.

As is known, the injection plants of the aforementioned type comprise a high pressure pump provided with a pump body which has, arranged inside it, the pumping elements actuated by a mechanism enclosed in a cavity of the pump body. This mechanism is lubricated with part of the fuel sent to the high pressure pump.

Normally these plants also comprise a low pressure pre-feed pump and a common rail.

The low pressure pump is designed to send the fuel to the high pressure pump via a supply conduit, while the common rail is supplied with pressurized fuel from the high pressure pump.

During the last few years, in the motor vehicle industry there has been an increasingly urgent need to reduce the dimensions and the production costs of the components of internal combustion engines.

The components taken into consideration for a reduction in the production costs include the pressure limiting valve. The pressure limiting valve is associated with the low pressure pump and is configured to discharge along the suction conduit of the low pressure pump the excess fuel pumped by the low pressure pump.

It is therefore the object of the present invention to reduce the production cost of a pressure limiting valve for an internal combustion engine.

In accordance with these objects, the present invention relates to a pressure limiting valve arranged between a first conduit and a second conduit; the valve comprising: a seat, provided with an opening communicating with the first conduit, and with a first shoulder; a shutter, which is mobile inside the seat and is provided with an inner channel, having an inlet communicating with the second conduit and at least one outlet, and with a head adapted, during use, to be arranged against the first shoulder; the outlet being arranged on the head; the seat and the head being shaped so as to provide a sealed coupling when the difference between the pressure in the second conduit and the pressure in the first conduit is lower than a threshold value and so as to provide a non-sealed coupling when said difference is greater than said threshold value.

In this way the pressure limiting valve can be produced easily and at a low cost. Owing to the arrangement of the opening in the head of the shutter it is possible to provide a shutter with smaller dimensions and achieve savings in the amount of material used. Moreover, the shape of the head and the seat ensure closing of the valve, being shaped so as to provide a sealed coupling.

It is also an object of the present invention to provide a fuel injection plant for an internal combustion engine which has lower production costs compared to the production costs of the plants of the prior art.

In accordance with these objects the present invention relates to a fuel injection plant for an internal combustion engine. Further characteristic features and advantages of the present invention will become clear from the following description of a non-limiting example of embodiment, provided with reference to the accompanying drawings in which:

- Figure 1 is a diagram of a fuel injection plant according to the present invention;

- Figure 2 is a cross-sectional view of a detail of the plant according to Figure 1 in a first operating position; and

- Figure 3 is a cross-sectional view of the detail of Figure 2 in accordance with a variant of the present invention.

In Figure 1, 1 denotes in its entirety a fuel injection plant for an internal combustion engine, which comprises essentially a fuel tank 2, a pump unit 3 (denoted schematically in Figure 1 by a broken-line polygon) and a manifold, commonly called common rail 4.

The common rail 4 receives from the pump unit 3 the pressurized fuel so as to supply a series of injectors 5 for the cylinders of the internal combustion engine, not shown in the figures. In particular, the pump unit 3 communicates with the tank 2 via a low pressure suction conduit 6 and with the common rail 4 via one or more delivery conduits 7.

In the non-limiting example described and illustrated here, a cooling element 9, a piston 10 and a separator filter 11 are arranged along the suction conduit 6.

The cooling element 9 comprises a cooling plate configured to lower the temperature of the diesel fuel.

The piston 10 is configured for manual filling of the low pressure pump, an operation which is necessary before initial start-up. The separator filter 11 is configured to separate the water from the sucked-in fuel.

The pump unit 3 comprises a low pressure pump 12, for example of the gear type, which is designed to compress the sucked-in fuel so as to raise its pressure to a predetermined value, for example of about 5 bar. The low pressure pump 12 is designed to send the fuel thus compressed to a high-pressure pump 13, via a supply conduit 14, along which another filter 15 is preferably arranged.

The high pressure pump 13 is designed to compress the fuel received to a very high pressure, for example of about 2500 bar, so as to send it via the delivery conduit 7 to the common rail 4.

In greater detail, the low pressure pump 12 sucks in the fuel of the suction conduit 6 which is provided with a constriction 16 calibrated so as to ensure a predetermined flowrate of sucked-in fuel.

Moreover, the low pressure pump 12 is preferably provided with a bypass valve 17 and an overpressure valve 18.

The bypass valve 17 is designed to allow the fuel to bypass the low pressure pump 12 until the pressure upstream of the construction 16 reaches a minimum value, for example of about 0.1 bar above atmospheric pressure.

The overpressure valve 18, as we shall see in detail further below, is designed to discharge into the suction conduit 6 the excess fuel pumped by the low pressure pump 12.

The high pressure pump 13 comprises at least one pumping element 20 formed by a cylinder 21 along which a piston 22 slides with a reciprocating movement. The cylinder 21 communicates with the supply conduit 14 via a suction valve 23 and communicates with the respective delivery duct 7 via a delivery valve 24. The pistons 22 are actuated by an actuating mechanism (not shown in the attached figures). The high pressure pump 13 also comprises an internal cavity 27 inside which the actuating mechanism is housed.

In order to control the fuel which must be supplied to the high pressure pump 13, along the supply conduit 14, between the filter 15 and the first suction valve 23 there is arranged an electric metering valve 29 which is designed to control the quantity of fuel which is supplied to the high pressure pump 13. In particular, the electric metering valve 29 is opened and closed under the control of an electronic unit (not shown in the accompanying figures) depending on the operating conditions of the engine, namely depending on the fuel which the injectors 5 must inject in each case, so as to reduce to a minimum the variations in pressure in the common rail 4.

Preferably, the electric metering valve 29 is controlled by the electronic unit by means of the pulse width modulation (PWM) system.

The common rail 4 is provided with an electric discharge valve 30 which discharges the excess fuel via a discharge conduit 31 in communication with the tank 2. The diesel fuel discharged by the injectors 5 also flows into the discharge conduit 31.

The electronic unit also controls the electric discharge valve 30 depending on the operating conditions of the engine.

The low pressure pump 12 is operated in synchronism with the high pressure pump 13.

In order to lubricate the actuating mechanism during operation, the cavity 27 is provided with two inlet openings 35 communicating with the supply conduit 14 via a lubricating circuit 36. The lubricating circuit 36 is connected to the supply conduit at a point situated between the filter 15 and the electric metering valve 29, or between the low pressure pump 12 and the electric metering pump 29 in the case where the fuel filter 15 is not present. The lubricating circuit 36 comprises a delivery line 37 configured to meter the quantity of fuel to be sent directly to the cavity 27, and a return line 38 configured to discharge the fuel into the discharge conduit 31.

The delivery line 37 preferably comprises a variable flowrate valve 40 and two constrictions 41 and 42. The constriction 42 ensures supply of a minimum flowrate when the valve 40 is closed. The constriction 41 is necessary for damping the valve 40. Preferably, the variable flowrate valve 40 is provided with a discharge circuit 43 connected to the return line 38.

The connection to the return circuit 39 is arranged downstream of the electric metering valve 29 and is configured to discharge the fuel upstream of the low pressure pump 12 along the suction conduit 6 when the high pressure pump 13 must not supply diesel fuel. The return circuit 39 is required since the valve 29 does not generally have a perfect seal and supplies, in the closed position also, an excess flowrate which cannot be supplied to the suction valves 23, otherwise the high pressure pump 13 would produce a flowrate which is not that required.

During operation of the injection plant 1, the fuel is sent to the supply conduit 14 by the low pressure pump 12. From the supply conduit 14 the fuel passes through the electric metering valve 29 and supplies the suction valves 23 until it reaches the cylinders 21 of the high pressure pump 13. Part of the fuel of the supply conduit 14 enters into the cavity 27 via the lubricating circuit 36 so as to lubricate and cool the actuating mechanism. From the cavity 27 the fuel flows out through the return line 38.

Figure 2 shows the pressure limiting valve 18 which comprises a valve body 40 in which there is formed a seat 41 which extends along a longitudinal axis A and is substantially cylindrical. The seat 41 is provided with a narrowed zone defined by a shoulder 42 which is preferably annular and a second narrowed zone defined by a shoulder 43 which is preferably annular. The shoulder 42 produces a reduction in the diameter from a first value Dl to a second value D2, while the second shoulder 43 produces a reduction in the diameter from the second value D2 to a third value D3. Basically, the seat 41 is divided into three portions: a first portion 44 with a diameter Dl, a second portion 45 with a diameter D2 and a third portion 46 with a diameter D3.

The seat 41 communicates with the conduit 6 by means of an opening 48 formed along the lateral wall 46 of the first portion 44 of the seat 41. In particular, the opening 48 is arranged near the first shoulder 42. The seat 41 houses a bearing element 50, a mobile shutter 51 and a spring 52 arranged between the bearing element 50 and the shutter 51.

The bearing element 50 has the same diameter Dl as the first portion 44 of the seat 41 and is fixed by means of interference inside the first portion 44.

The spring 52 is arranged against the bearing element 50 and the shutter 51.

The shutter 51 is defined by a main body 54 which is substantially cylindrical and provided with a projecting edge 55 which projects substantially radially with respect to the main body 54. Preferably the projecting edge 55 is arranged close to one end 56 of the main body 54 and defines, together with the end 56, a head 57 of the shutter 51.

The projecting edge 55 defines an upper annular surface 59 and a bottom annular surface 60. During use, the upper annular surface 59 is arranged against one end of the spring 52, while the bottom annular surface 60 is designed to be arranged against the shoulder 43, as we shall see in detail further below.

The diameter of the shutter 51 in the region of the projecting edge 55 is substantially identical to the diameter D2 of the second portion 45 of the seat 41, while the diameter of the remainder of the main body 54 is substantially identical to the diameter D3 of the third portion 46 of the seat 41. The shutter 51 is also provided with an inner channel 63 having an inlet 64 and at least one outlet 65.

In the non-limiting example described and illustrated here, the inner channel 63 is arranged substantially in the centre of the main body 54 and is provided with two outlets 65.

Preferably, the inlet 64 is formed in a bottom side of the shutter 51 arranged close to an end 66 arranged opposite to the end 56. The inlet 64 communicates with the outlet of the low pressure pump 12.

The outlets 65 are formed in the main body 54 along the projecting edge 55 and are preferably diametrically opposed.

During use, the shutter 51 is movable along the axis A and may assume a plurality of open positions, where the outlets 65 are in fluid communication with the opening 48 and a plurality of closed positions, where the outlets 65 are not in communication with the opening 48 (one of which is shown in Figure 2).

In particular, the shutter 51 is actuated by the difference in pressure existing between the outlet of the low pressure pump 12 and the suction channel 6.

When the difference in pressure between the fuel pressure at the outlet of the low pressure pump 12 and the fuel pressure in the suction channel 6 is greater than a predetermined threshold value, the shutter 51 receives a thrust upwards until it reaches at least an open position in which the outlets 65 are in

communication with the opening 48 of the seat 41. In this way, the fuel output from the low pressure pump 12 is sent to the suction conduit 6. The threshold value depends on the type of spring used and the force which it exerts on the shutter 51.

In order to reach the open position from the fully closed position shown in Figure 2, the shutter 51 must slide along at least one section substantially equal to the distance present between the shoulder 42 and the shoulder 43. The distance present between the shoulder 42 and the shoulder 43 is therefore dependent on the difference in pressure which causes activation of the recirculating flow generated by the pressure limiting valve 18.

While the shutter 51 passes from the fully closed position (shown in Figure 2) to the first open position (where the outlets 65 pass beyond the first shoulder 42), the lateral wall 67 of the second portion 45 of the seat 41 keeps the outlets 65 closed and ensures sealing, preventing fuel from flowing out. The projecting edge 55 has in fact the same diameter D2 as the second portion 45 of the seat 41.

Figure 3 shows a pressure limiting valve 68 in accordance with a second embodiment of the present invention in which the same reference numbers have been used to indicate parts which are the same or similar.

Basically, the pressure limiting valve 68 differs from the pressure limiting valve 18 in that the first shoulder 42 is arranged substantially so as to define a first portion 44 and a second portion 45 having substantially the same height

(understood as being the length in the axial direction).

Moreover in the pressure limiting valve 68 the opening 48 is arranged along the lateral wall 67 of the second portion 45 near to the shoulder 43.

In the region of the opening 48 the lateral wall is provided with an annular groove 69. In particular, the annular groove 69 is provided with a bottom wall 70 along which the opening 48 is formed.

In order to reach the first open position from the fully closed position shown in Figure 3, the shutter 51 must travel at least along a section substantially equal to the distance present between the shoulder 43 and the bottom edge of the annular groove 69.

The distance present between the second shoulder 43 and the bottom edge of the annular groove 69 is therefore dependent on the difference in pressure which causes activation of the recirculating flow generated by the pressure limiting valve 68.

While the shutter 51 passes from the fully closed position (shown in Figure 3) into the first open position (where the outlets 65 pass beyond the bottom edge of the annular groove 69), the lateral wall 67 of the second portion of the 45 of the seat 41 keeps the outlets 65 closed and ensures sealing, preventing the fuel from flowing out. The projecting edge 55 has, in fact, the same diameter D2 as the second portion 45 of the seat 41.

Finally it is clear that the fuel injection plant described here may be subject to modifications and variations without departing from the scope of the

accompanying claims.

Claims

1. Pressure limiting valve (18; 68) arranged between a first conduit (6) and a second conduit; the valve comprising:

- a seat (41), provided with an opening (48), communicating with the first conduit (6), and with a first shoulder (43);

- a shutter (51), which is mobile inside the seat (41) and is provided with an inner channel (63), having an inlet (64) communicating with the second conduit (12) and at least one outlet (65), and with a head (57) adapted, in use, to be arranged against the first shoulder (43); the outlet (65) being arranged on the head (57); the seat (41) and the head (57) being shaped so as to provide a sealed coupling when the difference between the pressure in the first conduit (6) and the pressure in the second conduit is lower than a threshold value and so as to provide a non- sealed coupling when said difference is greater than said threshold value.

2. Valve according to Claim 1, wherein the head (57) comprises two outlets (65) diametrically opposed.

3. Valve according to Claim 1 or 2, wherein the head (57) comprises at least one portion (55) arranged against the inner lateral wall (67) of the seat (41) in order to provide the sealed coupling when said difference is lower than the threshold value; the portion (55) of the head (57) being provided with the outlet (65).

4. Valve according to Claim 3, wherein the portion (55) is defined by a projecting edge, which projects radially with respect to the main body (54) of the shutter (51).

5. Valve according to any one of the foregoing claims, comprising a second shoulder (42); the opening (48) being arranged near the second shoulder (42).

6. Valve according to any one of Claims 1 to 4, wherein the seat (41) is provided with an annular groove (69) at the opening (48).

7. Valve according to Claim 6, wherein the annular groove (69) is provided with a bottom wall (70) along which the opening (48) is obtained.

8. Valve according to any one of Claims 2 to 7, wherein the projecting edge (55) defines an annular upper surface (59) and an annular bottom surface (60); the annular bottom surface (60) being adapted to be arranged, in use, against the first shoulder (43).

9. Valve according to Claim 7, comprising a bearing element (50) and a spring (52), both housed in the seat (41); the spring (52) being arranged between the bearing element (50) and the shutter (51) and having one end arranged against the annular upper surface (59).

10. Fuel injection plant for an internal combustion engine comprising a high pressure pump (13) and a low pressure pump (12); the low pressure pump (12) being configured to take fuel from a tank (2) by means of a suction conduit (6) and supply the drawn fuel to the high pressure pump (13); the low pressure pump (12) being associated with a pressure limiting valve (18; 68) arranged between the outlet of the low pressure pump (12) and the suction conduit (6); the pressure limiting valve (18; 68) being a valve of the type claimed in any one of the foregoing claims.