EP1521913B1 - Device and process for controlling the flow rate of a direct injection fuel pump - Google Patents

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

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

The injection system, known as I.D.E. (Gasoline Direct Injection), includes a high-pressure pump that supplies gasoline under high pressure to a common chamber, usually referred to as the "common rail", to which the injectors are directly connected.

Various means have been proposed to obtain a control of the fuel flow, whether it is gasoline or diesel for engines powered by injectors: or the flow rate of the pump which supplies the injectors with fuel at high pressure is controlled. pressure, or one acts downstream of the pump on the high-pressure circuit by recycling the excess fuel; it is also acts upstream of the pump on the fuel intake circuit to the pump to let the pump arrive at the high pressure than the desired amount of this fuel.

Generally speaking, in the 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 unconsumed fuel then being returned to the tank.

Devices of this kind are described in French patents 2,744,765 ; 2,767,932 ; 2769,954 and in patents EP 0 974 008 and DE 196 12 413A .

• il y a un gaspillage d'énergie puisque la pompe monte en haute pression du carburant en quantité excédentaire ;
• le retour du carburant non consommé à haute température est un risque supplémentaire ;
• le coût de réalisation est plus élevé.

These devices have three disadvantages:

• there is a waste of energy since the pump rises in high pressure of the fuel in excess quantity;
• the return of fuel not consumed at high temperatures is an additional risk;
• the cost of realization is higher.

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

But from the moment when the high-pressure pump only produces the quantity that is very precisely necessary, there will be problems for the following three cases of operation: engine brake operation, that is to say when there must no longer be fuel arriving at the injectors while the high pressure pump is still mechanically driven; stopping the engine, because it is then necessary to evacuate the gasoline at high pressure in the common room; and idle for which a very high accuracy of the flow rate is needed.

The subject of the invention is a method according to claim 1 and a device according to claim 3.

The method according to the present invention consists in arranging, within the solenoid valve controlling the arrival of low pressure gasoline at the intake of the high pressure pump, one or more internal leaks or low pressure upstream of the the solenoid valve to the low downstream pressure, ie from the high pressure to the low pressure, which makes it possible to solve the particular problems that arise for the three following operating modes: engine brake, engine stop and idle.

• Figure 1 une vue schématique d'un circuit d'alimentation I.D.E.
• Figure 2 une vue, également schématique, d'une pompe fournissant de l'essence à haute pression munie d'un dispositif de contrôle selon l'invention.
• Figure 3 une vue d'une deuxième variante de réalisation.
• Figure 4 une vue d'une troisième variante de réalisation.
• Figure 5 une vue partielle de la figure 4, à échelle agrandie illustrant une quatrième variante de réalisation.
• Figure 6 un diagramme illustrant le fonctionnement de l'installation.
• Figure 7 un diagramme illustrant le fonctionnement avec une fuite additionnelle.
• Figure 8 un exemple de mise en oeuvre de l'invention.

By way of non-limiting example and to facilitate the understanding of the invention, there is shown in the accompanying drawings:

• Figure 1 a schematic view of an IDE power circuit
• Figure 2 a view, also schematic, of a pump supplying high pressure gasoline provided with a control device according to the invention.
• Figure 3 a view of a second variant embodiment.
• Figure 4 a view of a third variant embodiment.
• Figure 5 a partial view of the figure 4 , on an enlarged scale illustrating a fourth variant 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 the Figure 1 it can be seen that the high-pressure fuel supply circuit comprises a fuel tank R; 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 a common rail) to which injectors I are connected.

Pump P may be any pump capable of supplying chamber C with 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 gasoline which are separated from each other in a sealed manner. The oil, subjected by the pump to a reciprocating back and forth movement, acts on a deformable element which exerts a pumping action on the gasoline.

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

The following brief description is intended to facilitate the understanding of Figures 2 to 4 .

The oil is reciprocated back and forth by hollow pistons 1. These pistons are reciprocated because they are supported by their head 2 on a swash plate. This swash plate is not shown because it is a known means. When a piston 1 moves (upwards on the Figure 2 ) in its cylinder 4, the oil raises the valve 5. A deformable member 9, bellows-shaped is sealingly attached 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 is lowered. As a result, the reciprocating movements of the oil cause a movement back and forth of said valve 5 and therefore of elongations and contractions of the bellows 9.

The bellows 9 is placed in a chamber filled with gasoline. This room is not represented because such an arrangement is known. The extensions and contractions of the bellows 9 cause a pumping effect.

Each chamber in which a bellows 9 is deflected comprises a pipe 10 which communicates firstly with the low-pressure circuit 20 by a non-return valve 21 and secondly with the high-pressure circuit 32 by a non-return valve 31 .

When the bellows 9 unfolds under the effect of the high pressure of the oil, it drives the gasoline at the same pressure through the valve 31; when it retracts the gasoline supplied by the pump B passes through the check valve 21 and enters the chamber in which the bellows 9 is struggling.

An upstream control of the gasoline flow is used by regulating the flow of gasoline arriving at the pump P by means of a solenoid valve 40 disposed on the pipe 23 coming from the low pressure pump B and distributing the gasoline to the circuit. supply 20 of said pump P by a pipe 22a.

It is known to specialists that in practice it is very difficult to make a slide solenoid valve with no internal leak, which is a drawback.

The present invention is to use this disadvantage by using internal leakage of solenoid valve 40 to solve the problems discussed above.

For this we go, according to a first embodiment, have on the pipe 32, which collects the high pressure from the pump P, a bypass 32a leading to the solenoid valve 40 for regulating the low pressure flow to the pump, in order to continuously recycle a gasoline leakage flow under high pressure to the low pressure circuit through said solenoid valve 40.

As we see on the Figure 2 , high-pressure gasoline from the check valves 31 is collected by the pipe 32, which feeds 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 slide valve 43 which is subjected on one side to a spring 44 and the other to an electromagnet or motor 45. drawer 43 has two peripheral grooves 47 and 46 which are placed in front of one of the inlet 32a of the high-pressure manifold 32, the other of the outlet 22a from the low-pressure to the low-pressure manifold 22.

In normal operation, the groove 46 is uncovered so that the low-pressure gasoline arriving via the pipe 25 communicates with the pipe 22a through the passage formed between the upper end of the jacket 42 and the groove 46. this passage varies according to the position of the slide 43 and thus the flow of low pressure gasoline arriving at the pump is regulated according to the needs of the engine.

When the electromagnet 45 is no longer excited, the spring 44 pushes the drawer 43 and the groove 46 enters the sleeve 42; the only low pressure gasoline flow that arrives at the pipe 22a is a leakage flow, at low pressure, which is the consequence of a necessary operating clearance between the jacket 42 and the slide 43.

It also provides a leakage flow, but at high pressure from the groove 47 to 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 apart from the drawer 43.

The internal architecture of the solenoid valve 40 is determined so that the leakage rate of the high-pressure gasoline to low pressure (at 47a) is greater than the leakage rate of the low-pressure gasoline upstream of the solenoid valve to low downstream pressure (at 46a).

When the motor works in motor braking electromagnet 45 is no longer excited, but the engine rotates and pump P is driven by the engine to which it is mechanically linked, the supply of low-pressure gasoline to line 22 is cut off; but there is a flow of gasoline arriving at said pipe 22 which is the leakage flow going through 46a from the low upstream pressure to the low downstream pressure.

When the engine is stopped there is high pressure gasoline (about 200 bar) in the pipe 32 and the chamber C. This high-pressure gasoline will, gradually, be discharged by the leak 47a to the tank R.

The respective dimensions of the spaces 46a and 47a must be determined so that the leakage flow through the space 47a is always greater (and at the equal limit) to the leakage flow through the space 46a.

• Q = le débit haute pression arrivant au collecteur 32
• Q1 = le débit basse pression arrivant au collecteur 22
• Q2 = le débit de fuite basse pression en 46a
• Q3 = le débit de fuite haute pression en 47a

on a les équations suivantes :

• Q = Q1 + Q2 - Q3 avec la condition suivante : Q2 négligeable
• Q = Q1 + Q2 - Q3 avec la condition suivante : Q3 ≥ Q2 et Q1 négligeable lorsque l'on souhaite annuler le débit Q.

Et lorsque le moteur est arrêté :

• Q = Q1 + Q2 - Q3 avec Q1 et Q2 négligeables c'est-à-dire un débit négatif et donc une décroissance de la pression dans le rail.

If we designate by:

• Q = the high-pressure flow arriving at the collector 32
• Q1 = the low pressure flow arriving at the collector 22
• Q2 = low pressure leakage flow in 46a
• Q3 = the high-pressure leakage flow in 47a

we have the following equations:

• Q = Q1 + Q2 - Q3 with the following condition: Q2 negligible
• Q = Q1 + Q2 - Q3 with the following condition: Q3 ≥ Q2 and Q1 negligible when it is desired to cancel the Q rate.

And when the engine is stopped:

• Q = Q1 + Q2 - Q3 with Q1 and Q2 negligible ie a negative flow and therefore a decrease of the pressure in the rail.

The figures 3 and 4 represent two other embodiments implementing this method.

According to a first variant ( figure 3 ) a controlled check valve is added to the gate solenoid valve (40-43), which is interposed between the low pressure (BP) upstream and the low pressure (BP) downstream of the solenoid valve.

According to a second variant ( figure 4 ) a leak control device is added to the high pressure (HP) output of the solenoid valve.

As previously, on the pipe 32, which collects the high pressure coming from the pump is disposed, a bypass 32a resulting in the solenoid valve 40 for regulating the low pressure flow to the pump, so as to recycle permanently by the pump. space 47a a gasoline leakage flow under high pressure to 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 pipe 23, located upstream of the solenoid valve 40 and the pipeline BP 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 valve 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 Q1 + Q2.

In operation, that is to say when the solenoid valve 40 fulfills its control function, the electromagnet 45 is excited; the rod 51 raises the ball 50 and, through the support 53, pushes the drawer 43, which more or less discovers the light 42a supplied with BP gasoline. This BP gasoline passes through the orifices 54 of the support 53 and, the ball 50 being lifted, arrives at the pipe 22a, which feeds the supply pipe 22 BP.

The flow of gasoline BP arriving at the pump HP 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: $$\left(\mathrm{BP}\times \mathrm{Ball\; section}\right)+\mathrm{<figure-callout\; id="52"\; label="Spring\; force"\; filenames="imgf0003.png"\; state="\{\{state\}\}">Spring\; force</figure-callout>}52=\mathrm{<figure-callout\; id="44"\; label="F\; ressor\; reminder"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">F\; ressor\; reminder</figure-callout>}44.$$

At the engine stop, the electromagnet 45 is de-energized, the drawer 43 closes the light 42a and the ball 50 returns to its seat.

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

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

On the other hand, as there is no more leak on the BP circuit, it is no longer necessary to have a small leak on the HP, a small leak that has no adverse effect on the operation of the high pressure pump.

The figure 4 represents another variant embodiment, in which the same elements bear the same references.

The purpose of this variant is to provide a function called "bypass function", which allows, among other things, to bypass the HP pump for a start at BP.

Under certain starting conditions, the engine starter does not rotate fast enough that the high pressure pump can provide sufficient flow to the injectors.

It is then interesting to short-circuit, at least partially, the pump P to directly feed the common rail C in gasoline at low pressure to ensure a low pressure start.

Referring to this figure 4 we see that the return spring 44 of the drawer 43 is enclosed in a cage of variable length, consisting of two elements 60/61 which can be closer to one another.

The gasoline at low pressure coming from the booster pump B via the pipe 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 via a pipe 63 with the rail C and therefore the HP therein.

At rest the pieces are in the position shown in the figure 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 by-pass function exposed above; on the other hand it also ensures the discharge function of the common rail C in case of stop.

From the beginning of the regulation, the electromagnet 45 pushes the spool 43 and the cage 60/61 closes the orifice 62 and thus the communication between the arrival BP and the rail C. If the flow provided by the pump HP is greater than the rate consumed by the engine (valve leakage for example) the pressure in the HP circuit increases, and an HP rail leak to BP is regulated through the orifice 62. The excess flow is recycled to the BP.

In normal control phase the electromagnet 45 pushes the slide 43 which compresses the spring 44 which applies the portion 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 flow of gasoline BP arriving at the pump HP is thus regulated.

Of course 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 such that the maximum pressure of the HP multiplied by said section is less than the load in place of the spring 44.

On the figure 6 four curves (I), (II), (III) and (IV) are given by way of example.

The abscissa is graduated in percentage of PWM (Pulses Width Modulation) which is the usual control means of a solenoid valve by modifying the width of the pulses arriving at the motor 45.

There are two scales on the y-axis, one on the left-hand side, is a flow scale in cc / min; the other on the right side is a bar pressure scale.

Curve (I) represents idling engine consumption: it is therefore constant.

Curve (II) represents the leakage flow through the solenoid valve: it increases with the PWM (reduction of the drawer / liner cover).

Curve (III) represents the increase in flow as a function of PWM.

Curve (IV) represents the pressure required to open valve 60/62 to common rail C as a function of PWM.

It can be seen that curve (IV) is not represented from 40% of PWM. This means that, beyond this value, the force exerted by spring 44, because of crushing caused by the movement of the drawer (upwards on the figure 4 ) controlled by the motor 45, is such that the valve 60/62 can no longer open, the portion 60 of the cage 60/61 remaining applied against the orifice 62.

Examination of the curves (I) and (II) shows that, at idle, the flow rate of the internal leakage of the solenoid valve is greater than the engine consumption. As a result, 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 LP.

In this case, as the valve 60/62 is open, the HP which is sent to the common rail C through the pipe 32, flows through the pipe 63 to 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.

This has a reversal of the flow of gasoline when stopping the engine.

This possibility of reversing the flow of gasoline can be very interesting.

Indeed it allows to lower the high pressure in the common rail C for very specific operating modes of the engine.

In the systems currently in use, when one wants to lower the high pressure one enriches the mixture which increases the consumption and thus lowers the pressure; but that translates into waste.

With the device according to the invention can be cut off the supply and have a negative flow that returns to the tank and drops the pressure in the common rail C.

This provision, while satisfactory, needs to be improved.

Indeed it turns out that it is very difficult to obtain sufficient accuracy by such a regulation which involves springs and valves: it can therefore occur, at idle, injector feed irregularities that make that the engine will not have a stable regime but will "hiccup".

To eliminate this disadvantage there is, according to the invention, a permanent additional leakage flow at the valve towards the common rail C that is to say the valve 60/62.

Referring to the figure 5 it can be seen that the portion 60 of the cage 60/61 does not rest directly against the orifice 62, but on a seat 65 in which one or more precisely calibrated ducts have been arranged so as to ensure through the seat 65 a permanent leakage calibrated.

Then referring to the figure 7 it is seen that the curve (I) has been replaced by the curve (V) which represents the consumption of the engine at idle + the leakage flow through the calibrated orifice of leakage through the seat 65.

It can be seen that the curve (V) is always above the curve (II), that is to say that the consumption of the idling engine plus the permanent leakage flow rate is greater than the internal leakage of the solenoid valve .

As a result, there is a deficit in the flow of gasoline BP arriving at the pump; so that the common rail C will not be sufficiently powered; which will lower the pressure in the common rail C; this decrease in pressure will be detected and transmitted to the computer which will increase the PWM that is to say move the slide 43 of the solenoid valve 40, to increase the flow of BP by moving towards the foot of the curve III.

The flow control is much more accurate than the pressure control thus obtaining excellent control of the idle.

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

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

The solenoid valve comprises a drawer 100 (corresponding to the drawer 43) which is actuated by a motor 101 (corresponding to 45). The upstream LP, coming from the tank through the booster pump, arrives via the pipe 102 (corresponding to 23), in a chamber 103 (corresponding to 64). The downstream LP from the internal leak is collected in the groove 104 (corresponding to 46) and is directed to the inlet of the HP pump via the line 105 (corresponding to 22a). The internal leakage of the upstream BP to the downstream LP occurs in the area 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 in the chamber 103 .

The spring 107 is disposed between the slide 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 liner 114 (corresponding to 42) in which the drawer 100 slides.

The piece 112 is attached to the end of the sleeve 114 by providing a calibrated passage 113 permitting permanent leakage.

The pipe 111 and the calibrated leak 113 open into a chamber 115 which, via a pipe 116 (corresponding to 63), communicates with the 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 the leak 65 of the figure 6 .

The solenoid valve shown in figure 8 exactly matches that of figures 4 and 5 and its operation is identical.

Claims (10)

1. Method for controlling the high-pressure supply (HP)of a set of injectors which are connected to a high-pressure common chamber, known as the "common rail" (C), in a direct petrol injection circuit, known as IDE, by a high-pressure pump (P), by acting on the low-pressure supply (BP) of the said pump (P) by means of a solenoid valve (E) with a slide, which valve is controlled by the computer which controls the functioning of the engine, the said solenoid valve (E) comprising an internal escape for the low pressure upstream, which reaches the solenoid valve (E), towards the low pressure downstream, which goes towards the pump (P), characterised in that in the said solenoid valve (E) there is provided an escape for the high-pressure petrol (HP) which is located in the common rail (C), towards the low pressure upstream.
2. Method according to claim 1, consisting of connecting the chamber (64) of the solenoid valve (E) which receives the upstream low pressure, to the common rail (C), by means which act as a non-return and calibrated passage valve, such that, in certain conditions of functioning of the engine, the petrol which is at a high pressure in the common rail can be driven back to the low-pressure intake upstream.
3. Device for regulation of the petrol supply of a direct-injection engine, for implementation of the method according to claim 2, of the type comprising: a supply of petrol at low pressure by a pump (B) which draws from a tank(R); a high-pressure pump (P) which supplies a common rail (C), and a solenoid valve (E) which regulates the low-pressure petrol supply of the said pump (P), the said solenoid valve (E) being a solenoid valve (40) with a slide (43), the latter sliding in a casing (42) such as to make the low-pressure intake upstream (23) communicate with the low-pressure duct downstream (22a) which supplies the pump (P)by means of a groove (46) which is provided in the slide (43), an escape throughput being provided between the low pressure upstream (23) and the low pressure downstream (22a) by means of play between the casing (42) and the slide (43), characterised in that the slide (43) is driven by a motor (45) and is retained by a spring (44), the latter being disposed in a deformable cage (60/61) which is disposed in a chamber (64), into which there opens the intake piping (23) of the low pressure upstream, the upper part (60) of this cage shutting or opening an aperture (62) in the chamber (64), which is connected by piping (63) to the common rail (C), this shutting means also being provided with calibrated apertures (65) such that, according to the demand of the engine, communication can be established between the tank (R) and the common rail (C) by the piping (23) and (63), through the aperture (62) and/or the calibrated apertures (65).
4. Device according to claim 3, wherein the aperture (62) comprises a seat (65) against which the mobile part (60) of the deformable cage (60/61) is supported, one or more calibrated ducts passing through the said seat (65) such as to assure a permanent calibrated escape though the said seat (65).
5. Device according to claim 3, wherein a bore (48) passes through the slide (43) of the solenoid valve (E).
6. Device according to claim 4, the device being such that, in normal functioning of the engine, the petrol which is supplied at low pressure by the low-pressure pump (B) passes through the solenoid valve by passing via the groove (46), which is uncovered to a greater or lesser extent by the displacement of the slide (43) driven by the motor (45), against the spring (44) which applies the part (60) of the cage against the aperture (62).
7. Device according to claim 3, the device being such that, when the engine is stopped, the residual high pressure which exists in the common rail (C) flows towards the tank (R) via the calibrated apertures (65), the chamber (64) and the piping (23).
8. Device according to claim 3, the device being such that, when the engine is acting as an engine brake, the injectors being stopped, but the pump (P) still being driven and pumping the escape throughput which goes from the low pressure upstream to the low pressure downstream, the high pressure increases in the common rail, and thrusts the cage (60) back, and opens the aperture (62) such as to be returned to the tank (R).
9. Device according to claim 3, the device being such that, when the engine is idling, the excess of high-pressure petrol supplied by the pump (P) is driven back to the tank (R) via the piping (63), the aperture (62) and the piping (23).
10. Device according to claims 3 to 9, comprising for the control of the low-pressure supply of the pump (P): a solenoid valve (40), the slide (43-100) of which is activated by a motor (45-101), the low pressure reaching the solenoid valve via piping (23-102) which opens into a chamber (64-103) where there is located a spring (44-107) which retains the slide (43-100), and being directed to the pump (P) by piping (23a-105), the internal escape of the upstream low pressure towards the downstream low pressure which takes place between the chamber (64-103) and the common rail (C) being provided by a valve (60/61-110) which is controlled by the movements of the slide (43-108), with the addition of a calibrated escape throughput, and permitting communication between the high pressure and the low pressure upstream, either via the said valve (60/61) or adjacent to the latter via a calibrated passage (113).

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