EP1521913A2

EP1521913A2 - Device for controlling flow rate of a direct injection fuel pump

Info

Publication number: EP1521913A2
Application number: EP03755583A
Authority: EP
Inventors: Christian Hervault; Dominique Veret; Philippe Bauer
Original assignee: Siemens Automotive Hydraulics SA
Current assignee: Continental Automotive France SAS
Priority date: 2002-07-11
Filing date: 2003-07-08
Publication date: 2005-04-13
Anticipated expiration: 2023-07-08
Also published as: JP4441608B2; US20050252492A1; WO2004007950A2; AU2003273426A1; US7270113B2; AU2003273426A8; EP1521913B1; DE60329182D1; ATE442524T1; WO2004007950A3; JP2005538285A

Abstract

The invention concerns a method for controlling high pressure fuel supply of a set of injectors connected to a common high pressure chamber, called common rail C in a direct injection fuel circuit, through a high pressure pump (P), by acting on the low pressure supply of said pump (P) through an electromagnetic slide valve (E), controlled by the computer managing the operating conditions of the engine which consists in providing, inside the electromagnetic valve (E) one or more internal leakage flows, either from high pressure to low pressure, or from low pressure upstream of the electromagnetic valve (E) to the low pressure downstream thereby solving the specific problems related to the three operating modes of the engine: engine brake, engine shutdown, idle speed.

Description

Flow control device for a direct fuel injection pump

The present invention relates to a device for controlling the flow rate of a direct petrol injection pump.

The injection system, known by the acronym I.D.E. (Direct Fuel Injection), includes a high pressure pump which supplies gasoline under high pressure to a common chamber, usually designated by the expression "common rail", to which the injectors are directly connected.

Various means have been proposed for obtaining control of the flow of fuel, whether it be petrol or diesel for engines supplied by injectors: either the flow of the pump which supplies the injectors with high fuel is controlled. pressure, either acting downstream of the pump on the high-pressure circuit by recycling the excess fuel; or else one acts upstream of the pump on the circuit for admitting fuel to the pump in order to allow the high pressure pump to arrive only at the desired quantity of this fuel. In general, in known systems for supplying injectors for diesel engines, the high pressure pump supplies the common chamber supplying the injectors with an excess of fuel, the unused fuel then being returned to the tank.

Devices of this kind are described in French patents 2,744,765; 2,767,932; 2,769,954 and in patent EP 0 974 008.

These devices have three drawbacks:

- there is a waste of energy since the pump rises in high pressure of the fuel in excess quantity; . ._

- the return of unused fuel at high temperature is an additional risk;

- the cost of production is higher.

The present invention relates to a device for controlling the gasoline intake flow rate in the high pressure pump in an I.D.E. system. by means of which the high-pressure pump will deliver to the common chamber, or "common rail", only very precisely the volume of petrol necessary for the operation of the engine.

But from the moment when the high pressure pump produces only the quantity very precisely necessary, problems will arise for the following three cases of operation: engine brake operation, that is to say when there should no longer be gasoline arriving at the injectors while the high pressure pump is still mechanically driven; stopping the engine, since it is then necessary to evacuate the high-pressure petrol located in the common room; and idling for which a very high precision of the supplied flow is necessary. The method according to the present invention consists in fitting, inside the solenoid valve controlling the arrival of low-pressure petrol at the intake of the high-pressure pump, one or more internal leaks, ie low pressure upstream of the solenoid valve to the downstream low pressure, ie from high pressure to low pressure, which makes it possible to resolve the specific problems which arise for the following three operating modes: engine brake, engine stop and idling.

By way of nonlimiting example and to facilitate understanding of the invention, the accompanying drawings show:

Figure 1 a schematic view of an I.D.E.

Figure 2 a view, also schematic, of a pump supplying gasoline at high pressure provided with a control device according to the invention.

Figure 3 a view of a second alternative embodiment.

Figure 4 a view of a third alternative embodiment.

Figure 5 a partial view of Figure 4, on an enlarged scale illustrating a fourth embodiment. Figure 6 a diagram illustrating the operation of the installation.

Figure 7 a diagram illustrating the operation with an additional leak.

Figure 8 an example of implementation of the invention.

In all these figures the same elements bear the same references. Referring to FIG. 1, it can be seen that the high-pressure petrol supply circuit includes a petrol tank; a low pressure pump or booster pump B; a flow control solenoid valve E, located upstream of a high pressure pump P; a pressure relief valve D; a high pressure chamber C (usually called common rail) to which the injectors I are connected. The pump P can be any pump capable of supplying the chamber

C gasoline under pressure.

In the example described below (and which is not limiting), this pump P is a pump of the type called transfer pump which comprises an oil part and a petrol part which are separated from each other in a leaktight manner. The oil, subjected by the reciprocating movement back and forth, acts on a deformable element which exerts a pumping action on the petrol.

The transfer pump is illustrated schematically in Figures 2, 3, and 4 and is not shown in detail because it is known and is not the subject of the present invention.

The purpose of the brief description which follows is to facilitate the understanding of FIGS. 2 to 4.

The oil is subjected to reciprocating movements back and forth by hollow pistons 1. These pistons are driven in an alternating movement because they are supported by their head 2 on an oscillating plate. This swash plate is not shown because it is a known means. When a piston 1 moves (upwards in FIG. 2) in its cylinder 4, the oil lifts the valve 5. A deformable member 9, in the form of a bellows is tightly fixed at one end 6 to the support of the cylinder 4 and at its other end 8 to the valve 5. When the piston 1 moves in the opposite direction, the valve 5 lowers. As a result, the back and forth movements of the oil cause a back and forth movement of said valve 5 and therefore of elongations and contractions of the bellows 9.

The bellows 9 is placed in a chamber filled with petrol. This room is not shown because such a provision is known. The extensions and contractions of the bellows 9 cause a pumping effect.

Each chamber in which a bellows 9 struggles has a pipe 10 which communicates on the one hand with the low pressure circuit 20 by a non-return valve 21 and on the other hand with the high pressure circuit 32 by a non-return valve 31. When the bellows 9 is deployed under the effect of the high pressure of the oil, it drives out the petrol at the same pressure through the valve 31; when it retracts the gasoline supplied by the pump B passes through the non-return valve 21 and enters the chamber in which the bellows 9 struggles.

Upstream regulation of the petrol flow is used by regulating the petrol flow arriving at the pump P by means of a solenoid valve 40 disposed on the line 23 arriving from the low pressure pump B and distributing the petrol to the circuit d supply 20 of said pump P via a line 22a. It is known to specialists that, in practice, it is very difficult to produce a solenoid valve having no internal leakage, which is a drawback.

The present invention consists in using this drawback by using internal leaks from the solenoid valve 40 to solve the problems described above.

For this, we will, according to a first embodiment, have on the line 32, which collects the high pressure coming from the pump P, a bypass 32a leading to the solenoid valve 40 for regulating the low pressure flow going to the pump, so as to continuously recycle a high pressure gasoline leakage flow to the low pressure circuit through said solenoid valve 40.

As seen in Figure 2, the high pressure gasoline from the non-return valves 31 is collected by the line 32, which supplies the chamber C

(or common rail). This pipe 32 has a first bypass 32a which leads to the solenoid valve 40 and a second bypass which leads to a pressure relief valve D.

The solenoid valve 40 consists of a body 41 in which is placed a jacket 42 in which slides a drawer 43 which is subjected on one side to a spring 44 and on the other to an electromagnet or motor 45. The drawer 43 has two peripheral grooves 47 and 46 which are placed opposite one of the inlet 32a of the high pressure manifold 32, the other of the outlet 22a of the low pressure towards the low pressure manifold 22.

In normal operation, the groove 46 is uncovered so that the low pressure gasoline arriving through the line 25 communicates with the line 22a through the passage formed between the upper end of the jacket 42 and the throat 46. The dimension of this passage varies as a function of the position of the spool 43 and this is how the flow of gasoline at low pressure arriving at the pump is regulated according to the needs of the engine.

When the electromagnet 45 is no longer energized, the spring 44 pushes the drawer

43 and the groove 46 enters the shirt 42; the only low pressure gasoline flow which arrives at the line 22a is a low pressure leakage flow, which is the consequence of a necessary operating clearance between the jacket 42 and the drawer A leakage flow is also provided, but at high pressure from the groove 47 towards the chamber 49 which is located at the lower end of the body 41 of the solenoid valve and which communicates with the low pressure by the central bore 48 which passes through side by side the drawer 43. The internal architecture of the solenoid valve 40 is determined so that the leakage rate of the high pressure gasoline towards low pressure (at 47a) is greater than the leakage rate of the low pressure gasoline upstream of the solenoid valve towards downstream low pressure (at 46a).

When the engine operates as an engine brake, the electromagnet 45 is no longer energized, but the engine is running and the pump P is therefore driven by the engine to which it is mechanically linked, the supply of low-pressure petrol to the line 22 is cut; but there is a fuel flow arriving at said

^{• line} 22 which is the leakage flow going through 46a from the low upstream pressure to the low downstream pressure. When the engine is stopped, high pressure gasoline (approximately 200 bar) remains in the line 32 and the chamber C. This high pressure gasoline will gradually be discharged by the leak at 47a towards the tank R.

The respective dimensions of the spaces 46a and 47a must be determined so that the leakage rate passing through the space 47a is always greater (and at the same limit) than the leakage rate passing through the space 46a. If we designate by:

Q = the high pressure flow arriving at the manifold 32 Ql = the low pressure flow arriving at the manifold 22 Q2 = the low pressure leak flow at 46a Q3 = the high pressure leak flow at 47a we have the following equations:

Q = Ql + Q2 - Q3 with the following condition: Q2 negligible Q = Ql + Q2 - Q3 with the following condition: Q3 ^ Q2 and Ql negligible when we want to cancel the flow rate Q. And when the engine is stopped:

Q = Ql + Q2 - Q3 with negligible Ql and Q2, that is to say a negative flow and therefore a decrease in the pressure in the rail. Figures 3 and 4 show two other alternative embodiments implementing this method.

According to a first variant (FIG. 3), a piloted check valve is added to the solenoid valve with slide valve (40-43), which is interposed between the low pressure (BP) upstream and the low pressure (BP) downstream from the solenoid valve.

According to a second variant (FIG. 4), a leakage control device is added to the high pressure (HP) outlet of the solenoid valve.

As before, on the pipe 32, which collects the high pressure coming from the pump, is disposed, a bypass 32a leading to the solenoid valve 40 for regulating the low pressure flow going to the pump, so as to recycle constantly by the space 47 has a leakage rate of gasoline under high pressure towards the low pressure circuit through said solenoid valve 40.

In the case of the variant shown in Figure 3 there is a check valve 50 between the BP line 23, located upstream of the solenoid valve 40 and the BP line 22a, located downstream.

The non-return valve 50 is controlled by the electromagnet 45 by means of a push rod 51. The valve is counter-held in the closed position by a spring 52 bearing on a support 53, provided with orifices 54; this support 53 being in abutment against the slide 43 of the solenoid valve 40. In the rest position, the solenoid valve 40 is closed. The ball 50 rests on its seat in a sealed manner and the drawer 43 covers the supply light 42a. The internal leakage of the solenoid valve 40 is contained in the envelope 41 of the drawer 43. This is the "zero flow" position, that is to say the suppression of the flow Ql + Q2.

In operation, that is to say when the solenoid valve 40 fulfills its regulatory function, the electromagnet 45 is excited; the rod 51 lifts the ball 50 and, via the support 53, pushes the drawer 43, which more or less discovers the light 42a supplied with LP gasoline. This BP gasoline crosses the orifices 54 of the support 53 and, the ball 50 being raised, arrives at the pipe 22a, which feeds the BP supply line 22. The BP fuel flow arriving at the HP pump is thus regulated.

In order to guarantee a substantially constant steering effort, a functional clearance is provided between the ball 50 and the support 53, with the following equation: (BP x Ball section) + Spring force 52 = F return spring 44. When the engine stops, the electromagnet 45 is de-energized, the drawer 43 closes the light 42a and the ball 50 returns to its seat.

The high pressure which remains in the pipes 32 / 32a will leak, due to the internal leak, at 47a, from the solenoid valve 40 towards the pipe 23 so that the residual pressure HP is gradually discharged.

This variant has the advantage of ensuring a real zero flow rate without leakage of the booster pressure (BP) as is the case in the examples of FIG. 2.

On the other hand, as there is no longer any leak on the LP circuit, it is only necessary to have a small leak on the HP, a small leak which has no penalizing effect on the operation of the high pressure pump.

Figure 4 shows another alternative embodiment, in which the same elements have the same references.

The purpose of this variant is to provide a function called "bypass function", which allows, among other things, to short-circuit the HP pump for starting at BP. In certain starting conditions, the engine starter does not rotate fast enough for the high pressure pump to provide sufficient flow to the injectors.

It is therefore advantageous to short-circuit, at least partially, the pump P to directly supply the common rail C with gasoline at low pressure to ensure starting at low pressure.

Referring to this FIG. 4, it can be seen that the return spring 44 of the drawer 43 is enclosed in a cage of variable length, constituted by two elements 60/61 which can approach each other.

The low-pressure petrol coming from the booster pump B via the line 23 arrives laterally in the chamber 64 in which the cage 60/61 is located, which closes the return spring 44.

This chamber 64 has at its upper end an orifice 62 which communicates by a pipe 63 with the rail C and therefore the HP which is there.

At rest, the parts are in the position shown in FIG. 4. The low booster pressure arriving via the pipe 23 enters the chamber 64 of the solenoid valve 40 and communicates through the orifice 62 and the pipe 63 with the rail C. This ensures the bypass function described above; on the other hand this also ensures the discharge function of the common rail C in the event of a stop. From the start of the regulation, the electromagnet 45 pushes the drawer 43 and the cage 60/61 closes the orifice 62 and therefore the communication between the inlet BP and the rail C. If the flow rate supplied by the pump HP is greater than the flow consumed by the motor (valve leak for example) the pressure in the HP circuit increases, and a rail HP leak to BP is regulated through orifice 62. The excess flow is therefore recycled to the BP.

In normal regulation phase the electromagnet 45 pushes the drawer 43 which compresses the spring 44 which applies the part 60 of the cage 60/61 against the orifice

62 which is thus closed; going up, the drawer 43 communicates the pipe 23 with the groove 46 connected to the pipe 22a. The BP fuel flow arriving at the HP pump is thus regulated.

Obviously, it is necessary to avoid an untimely opening of the orifice 62 and for this it is necessary to determine the section of the orifice 62 so that when the electromagnet 45 applies through the drawer 43 the part 60 of the cage against the orifice 62 the latter is dimensioned so that the maximum pressure of the HP multiplied by said section is less than the load in place of the spring 44.

FIG. 6 shows four curves (I), (II), (III) and (IV), given by way of example. The abscissa is graduated as a percentage of PWM (Puises Width Modulation) which is the usual means of controlling a solenoid valve by modifying the width of the pulses arriving at the motor 45.

There are two scales on the ordinate, one on the left side, is a flow scale in cc / min; the other on the right is a pressure scale in bar. Curve (I) represents the consumption of the engine at idle: it is therefore constant.

Curve (II) represents the leakage rate through the solenoid valve: it increases with the PWM (reduction in drawer / jacket overlap).

Curve (III) represents the increase in flow as a function of PWM. The curve (IV) represents the pressure necessary to open the valve 60/62 towards the common rail C as a function of PWM.

We see that the curve (IV) is not represented from 40% of PWM. This means that beyond this value, the force exerted by the spring 44, due to the crushing caused by the movement of the slide (upwards in FIG. 4) controlled by the motor 45, is such that the valve 60/62 can no longer open, the part 60 of the cage 60/61 remaining applied against port 62.

Examination of curves (I) and (II) shows that, at idle, the flow rate of the internal leak of the solenoid valve is greater than the consumption of the engine. Consequently, the computer controlling the engine will control the PWM so that the valve 60/62 can open and the excess fuel from the internal leak is returned to the upstream BP.

In this case, as the valve 60/62 is open, the HP which is sent to the common rail C by the pipe 32, is discharged through the pipe 63 towards the pipe 23, through the chamber 64 of the solenoid valve 40; because the pressure prevailing in the common rail C and therefore in the pipe 63 is greater than that prevailing in the pipe 23.

There is thus a reversal of the circulation of the petrol when the engine is stopped.

This possibility of reversing the circulation of petrol can be very interesting.

In fact, this makes it possible to lower the high pressure in the common rail C for very specific operating modes of the engine. In the systems currently in service, when it is desired to lower the high pressure, the mixture is enriched, which increases the consumption and therefore lowers the pressure; but that translates into waste.

Thanks to the device according to the invention, it is possible to cut off the supply and have a negative flow which returns to the tank and drops the pressure in the common rail C.

This provision, although satisfactory, must be improved. Indeed it turns out that it is very difficult to obtain sufficient precision by such regulation which involves springs and valves: it can therefore occur, at idle, irregularities of supply of the injectors which make that the engine will not have a stable speed but will “hiccup”.

To eliminate this drawback, there is, according to the invention, an additional permanent leakage rate at the valve going to the common rail C, that is to say the valve 60/62. Referring to FIG. 5, it can be seen that the part 60 of the cage 60/61 does not rest directly against the orifice 62, but on a seat 65 in which one or more conduits have been precisely calibrated so as to ensure through said seat 65 a permanent calibrated leak. Referring then to FIG. 7 we see that the curve (I) has been replaced by the curve (V) which represents the consumption of the engine at idle + the leak rate through the calibrated orifice of leak through the seat 65.

We can then see that the curve (V) is always above the curve (II), that is to say that the consumption of the engine at idle plus the permanent leak rate is greater than the internal leak of the solenoid valve. .

As a result, there is a deficit in the BP petrol flow rate arriving at the pump; therefore that the common rail C will not be supplied with sufficient power; which will lower the pressure in the common rail C; this reduction in pressure will be detected and transmitted to the computer which will increase the PWM, that is to say move the spool 43 of the solenoid valve 40, to increase the flow rate of LP by moving towards the foot of the curve III.

The flow regulation being much more precise than the pressure regulation, an excellent control of the idle speed is thus obtained.

This is achieved at the cost of a loss of overall pump performance; but this loss is very small and considered negligible compared to the result obtained.

FIG. 8 represents an exemplary embodiment of the device shown diagrammatically in FIGS. 5 and 6.

The solenoid valve includes a drawer 100 (corresponding to drawer 43) which is actuated by a motor 101 (corresponding to 45). The upstream BP, coming from the reservoir thanks to the booster pump, arrives via the pipe 102 (corresponding to 23), in a chamber 103 (corresponding to 64). The downstream BP, coming from the internal leak, is collected in the groove 104 (corresponding to 46) and is directed towards the inlet of the HP pump via the line 105 (corresponding to 22a). The internal leakage from the upstream BP to the downstream BP occurs in the zone referenced 106 between the chamber 103 and the groove 104. The drawer is counter-held by a spring 107 (corresponding to the spring 44) which is located in the chamber 103 . The spring 107 is disposed between the drawer 100 and a pusher 108 carrying a ball 109 which closes a small pipe 110 which opens into a pipe 111 which communicates with the common rail C. The pipes 110 and 111 are formed through a part 112 which is fixed to the folder 114 (corresponding to 42) in which the drawer 100 slides.

The part 112 is fixed to the end of the jacket 114 by providing a calibrated passage 113 allowing a permanent leak.

Line 111 and calibrated leak 113 emerge into a chamber 115 which, via line 116 (corresponding to 63), communicates with common rail C.

The ball 109 on its seat of the pipe 110 and the calibrated passage 113 correspond to the valve 60/62 and to the leak 65 of FIG. 6.

The solenoid valve shown in Figure 8 corresponds exactly to that of Figures 4 and 5 and its operation is identical.

Claims

1. Method for controlling the supply of high pressure (HP) petrol to a set of injectors connected to a common high pressure chamber, called a “common rail” C in a Direct Fuel Injection circuit, called IDE, by a high pressure pump (P), by acting on the low pressure supply (BP) of said pump (P) by means of a solenoid valve (E), controlled by the computer managing the engine operation consisting in fitting, inside the solenoid valve (E) one or more internal leaks, either from high pressure to low pressure, or from low pressure upstream of the solenoid valve (E) to the low pressure downstream which makes it possible to resolve the particular problems which arise for the three following modes of engine operation: engine brake, engine stop, idling.

2. Method according to claim 1 consisting in recycling towards the supply line BP of the pump (P) the internal leaks of the solenoid valve (40) coming from the low and / or the high pressure.

3. Method according to claim 2 making it possible to remove the high residual pressure in the common rail (C) in the case where the engine is stopped and to ensure zero flow in the case where it acts as an engine brake, consisting in employing means (41,42) providing a leakage flow rate from the high pressure (32) to the low pressure (23) such that when a zero flow rate of gasoline to the injectors is required, the flow rate at the pump outlet is zero and if necessary the residual high pressure may leak to the low pressure.

4. Method according to claim 3 consisting in employing for the regulation of the low pressure supply of the pump (P), carrying the gasoline at high pressure, a solenoid valve (40) with slide (43) and in connecting the manifold high pressure outlet (32) of the pump (P) to said solenoid valve (40) so as to obtain through said solenoid valve (40) a high pressure leakage flow which is recycled to low pressure by said solenoid valve.

5. Device for regulating the supply of petrol to a direct injection engine of the type comprising: a supply of petrol at low pressure by a pump (B); a high pressure pump (P) and means (E) regulating the supply of fuel to said pump (P) upstream thereof, characterized by the fact that the regulating means is a solenoid valve (40) with slide (43) sliding in a jacket (42), this solenoid valve regulating the flow of gasoline at low pressure which passes through it towards the pump and recycling, by internal leaks , a portion of the high pressure, towards the low pressure.

6. Device according to claim 5 wherein the solenoid valve (40) is traversed right through by a central bore (48) which goes from the inlet of the solenoid valve to a chamber (49) located at its other end, this central bore communicating by an internal leak with a groove (47) connected by a bypass (32a) to the pipe (32) collecting the high pressure flows supplied by the pump (P).

7. Device according to claim 6 wherein there is between the jacket (42) and the valve (43) of solenoid valve (40) a space creating on the one hand a gasoline leakage rate at low pressure and on the other hand a high pressure leakage rate, the first being evacuated to the pump supply pipe (22) and the second being recycled to the low pressure by a central bore (48) passing through the slide (43) right through .

8. Device according to claim 1 wherein the relative dimensions of the parts are determined so that the leakage rate from high pressure to low pressure is always greater and at the limit equal to the leakage rate from low pressure.

9. Device according to claim 5 characterized in that a non-return valve (50) controlled by the electromagnet (45) of the solenoid valve (40) is interposed between the low pressure upstream and the low pressure downstream of this solenoid valve (40); so as to be able to obtain zero flow during engine brake operation.

10. Device according to claim 9 in which the non-return valve is held in its seat by a spring (52) disposed between the ball (50) and a support (53), provided with orifices (54), bearing against the end of the drawer (43).

11. Device according to claim 10 wherein in the rest position the ball (50) rests in a sealed manner on its seat and the orifice (42a) for the arrival of the low pressure at the solenoid valve (40) is closed by the drawer (43).

12. Device according to claim 11, in which the sealing section of the ball is calculated such that its opening force is equal to the force in place of the spring (44).

13. Device according to claim 1, wherein there is between the jacket (42) and the drawer (43) a space (47a) creating a leakage rate from the high pressure (32a) to the low pressure (49).

14. Device according to claim 5 characterized in that the return spring (44) of the drawer (43) is arranged in a cage (60/61) deformable, disposed in a chamber (64) in which arrives the pipe (23 ) arrival of the low pressure, the upper part (60) of this cage closing or opening an orifice (62) connected by a pipe (63) to the common rail (C) so that in the absence of high pressure coming from the pump (P) the low pressure petrol coming from the line (23) can go directly to said common rail (C) by the line (63) by short-circuiting the pump (P).

15. Device according to claim 14 wherein the dimension of the orifice (62) and the calibration of the spring (44) are determined so that the maximum pressure of the HP in the pipe (63) multiplied by the section of the orifice (62) is less than the load in place of the spring.

16. Device according to claim 15 wherein the orifice (62) comprises a seat (65) against which rests the movable part (60) of the deformable cage (60/61); said seat (65) being traversed by one or more conduits calibrated so as to ensure through said seat (65) a permanent calibrated leak.

17. Device according to claims 5 to 8 and l3 to l6 comprising, for control, the LP supply of the pump (P): a solenoid valve (40) whose slide (43-100) is actuated by a motor (45-101); the BP arriving at the solenoid valve by a pipe (23-102) opening into a chamber (64-103) where there is a spring (44-107) counter-holding the drawer (43-100) and being directed on the pump (P) by a pipe (23 a-105), the internal leak from the upstream BP to the downstream BP occurring between the chamber (64-103) and the common rail (C) being made by a valve (60/61 -110) controlled by the movements of the slide (43-108) with the addition of a calibrated and permanent leakage rate either through said valve (60/61) or next to it by a calibrated passage (113).