EP0270720A1 - Variable-delivery pump - Google Patents

Abstract

Variable flow pump comprising at least one piston (1) associated with a chamber (2), said piston (1) cooperating with a surface (3) driven by a reciprocating movement with constant movement, characterized in that the piston (1 ) is free from any continuous mechanical connection with said surface (3); and that said chamber (2) is associated with a flow control system (9) disposed upstream, and that it is provided with a valve (7) on the supply and with a valve (8) on the repression; said adjustment system (9) being supplied by a booster pump (10).

Description

The present invention relates to a flow generation system of the variable flow pump type, which applies in particular to the fuel supply of the engines.

High pressure variable flow generation devices generally use piston pumps. In these types of pump, the piston stroke is varied mechanically.

Due to the pressures involved, and the precision required in the mechanical assembly, these known devices have the disadvantage of being very complex. On the other hand, the efforts implemented in this assembly require very high precision machining of all the components. On the other hand, these devices are difficult to adapt to an electrical control, because there are always interface problems. Most of the time, therefore, electro-hydraulic systems are used which consume a lot of energy, which gives very poor efficiency.

The object of the present invention is to provide a flow generation system, of the high-efficiency variable flow pump type, which is free from any continuous mechanical connection with the power take-off.

To this end, the invention relates to a variable flow pump which comprises at least one piston associated with a chamber; said piston cooperating with a surface driven by a reciprocating movement with constant displacement. The piston is free from any continuous mechanical connection with said surface. The chamber is associated with a flow control system, which is arranged upstream of this chamber. In addition, the chamber is provided with a valve on its supply, and it is provided with a valve on its outlet. The adjustment system is supplied by a booster pump.

It is arranged so that the chamber is formed directly by the piston, which slides in the body of the pump. The chamber is limited by the bottom of the pump body, and by the upper face of the piston.

According to one embodiment of the invention, the surface consists of the upper part of a pusher, which cooperates via its lower face with a cam linked to the power take-off.

According to one embodiment of the invention, the pusher slides in a guide, and said pusher is kept in contact with the cam by a spring.

According to one embodiment of the invention, the flow control system consists of a fixed throttle, which is associated with an adjustable pressure relief valve provided with a control.

According to one embodiment of the invention, the flow control system consists of a variable throttle provided with a control and associated with a pressure limiter.

According to one embodiment of the invention, the flow control system consists of a proportional distributor provided with a control and associated with a pressure limiter.

According to one embodiment of the invention, the adjustment system consists of a distributor provided with a control, and associated with a pressure limiter.

The variable flow pump according to the invention thus has the advantage of not requiring a mechanical connection between the piston and the power take-off. Therefore it can be easily adapted to an electrical control, because it avoids interface problems. In addition, the assembly has a very good yield, and the simplicity of the device results in a low cost price.

• - la figure 1 est une vue schématique avec une coupe partielle de la pompe à débit variable selon l'invention ;
• - la figure 2 est une coupe d'un mode de réalisation de la pompe de la figure 1 ;
• - la figure 3 est une vue schématique des éléments de règlage et de commande de la pompe de la figure 1 ;
• - la figure 4 est une vue schématique analogue à la figure 3 d'un autre mode de réalisation de l'invention ;
• - la figure 5 est une vue schématique analogue à la figure 3 d'un autre mode de réalisation de l'invention ;
• - la figure 6 est une vue schématique analogue à la figure 3 d'un autre mode de réalisation de l'invention.

Other characteristics and advantages of the present invention will emerge from the following description of the embodiments given by way of example with reference to the appended drawings in which:

• - Figure 1 is a schematic view with a partial section of the variable flow pump according to the invention;
• - Figure 2 is a section of an embodiment of the pump of Figure 1;
• - Figure 3 is a schematic view of the adjustment and control elements of the pump of Figure 1;
• - Figure 4 is a schematic view similar to Figure 3 of another embodiment of the invention;
• - Figure 5 is a schematic view similar to Figure 3 of another embodiment of the invention;
• - Figure 6 is a schematic view similar to Figure 3 of another embodiment of the invention.

The assembly of the variable flow pump device according to the invention is shown diagrammatically in FIG. 1. This assembly comprises the variable flow pump proper which consists of a piston 1, which slides in a bore 20 arranged in the pump body 17. The piston 1 cooperates with a surface 3 which is driven by an alternating movement with constant displacement. This surface 3 is linked to the power take-off. The piston 1 is free from any continuous connection with this surface 3.

The chamber 2 is formed directly by the movement of the piston 1 in the bore 20. The chamber 2 is limited by the bottom 18 of the pump body 17 and by the upper face 22 of the piston 1.

The underside 21 of the piston 1 cooperates with the surface 3, which belongs to a pusher 4. This pusher 4 slides freely in a guide 23. The underside 19 of the pusher 4 is associated with a cam 5 which is linked to the grip of movement materialized by a tree 6.

Chamber 2 is provided on the supply of a valve 7 and on the discharge of a valve 8; the chamber 2 being associated with a flow control system 9 arranged upstream of the valve 7.

The supply circuit includes a reservoir 11 into which a booster pump 10 is drawn via a channel 12. This booster pump 10 delivers into a channel 13, which feeds the flow control system 9. We call the pressure prevailing in the channel 13 supply pressure P₁₃. The flow control system 9 directly feeds a booster channel 14 in which the booster pressure P₁₄ prevails. The booster channel 14 thus connects the flow control system 9 with the supply valve 7. The discharge valve 8 is connected directly to a discharge channel 15 connected to the use.

We agree to call P₂ the pressure prevailing in the chamber 2 of the pump, while the different flow rates are marked: Q₁₃ for the supply flow prevailing in the channel 13, Q₁₄ for the booster flow prevailing in the channel 14, and Q₁₅ the discharge flow prevailing in channel 15.

It should be noted in the case of FIG. 1 that the displacement of the cam 5 depends on the offset between this cam 5 and the axis of the shaft 6, which passes through the axis 16 of the piston 1 of the pump.

The variable flow pump according to the invention thus comprises a surface 3, which is driven by an alternating movement provided by a cam 5. It should be noted that this alternating movement can be provided by any other means, and that the displacement of the surface 3 is constant whatever the cubic capacity desired for the pump. The maximum amplitude of this displacement of the surface 3 defines a stroke C₃.

When the surface 3, during the operating cycle, moves away from the bore 20, the piston 1 is pushed back by the liquid arriving from the booster pump 10 through the supply valve 7. The supply flow Q₁₃ is fixed by the flow control system 9, which will be described below. The quantity of liquid introduced by means of the flow control system 9 allows the piston 1 to perform a stroke C₁ between 0 and the stroke C₃ of the surface 3. In the continuation of the operating cycle, the displacement of the surface 3 reverses, and this surface 3 thus comes into contact with the underside 21 of the piston 1. It should be noted that at the place of contact, a special arrangement may possibly be provided intended to limit the impact. This arrangement is not described because it uses means known to those skilled in the art. The surface 3 before coming into contact with the lower face 21 of the piston 1, performs a dead stroke C _m which is equal to the difference between C₃ and C₁, that is to say that the dead stroke C _m is between 0 and C₃. The stroke of the piston 1 is then equal to the difference between C₃ and C _m, that is to say the value C₁. The product of the stroke C₁ of the piston 1 by the surface of the said piston 1 defines the quantity of liquid discharged by the piston 1 through the discharge valve 8. This product is the displacement of the pump at this given moment, and it is a function of the value set by the flow control system 9.

FIG. 2 shows an embodiment of the variable flow pump according to the invention. In this embodiment the shaft 6 which carries the cam 5 is directly supported by two bearings 35 mounted in the guide 23 of the pusher 4. A spring 24 is mounted between the surface 3 of the pusher 4 and the lower part of the body 17 of the pump .

A first embodiment of the flow control system 9 is shown in FIG. 3. The flow control system 9 comprises a fixed throttle 25 mounted on the channel 13 and supplying the channel 14. An adjustable pressure relief valve 36 is mounted in bypass upstream of the fixed choke 25, and it is controlled by a control 31. This first embodiment makes it possible to adjust the displacement of the chamber 2 by adjusting the supply pressure P₁₃ which is established in channel 13.

avec α = coefficient de striction
S₂₅ = section de l'étrangleur 25
ρ = masse volumique du fluide.When the surface 3 begins its downward travel, the flow rate passing through the fixed choke 25 is given by the relation:

with α = necking coefficient
S₂₅ = choke section 25
ρ = density of the fluid.

La pompe à débit variable ne refoulant que pendant la moitié de la rotation de l'arbre 6, le débit de refoulement Q₁₅ sera :

avec comme valeur maximale pour Q₁₅ :
Q₁₅ = cylindrée géométrique · N · η
avec : cylindrée = volume maximal de la chambre 2
N = vitesse de l'arbre 6
η = rendement volumétrique de la pompe
La cylindré apparente a pour valeur
Q₁₅/N
et la cylindrée apparente efficace que l'on appelera dans la suite de la description cylindrée efficace C_e vaut :

avec comme valeur maximale pour la cylindrée efficace
C_e = cylindrée · ηIf we call k the coefficient which is equal to:

The variable flow pump only discharging during half the rotation of the shaft 6, the discharge flow Q₁₅ will be:

with the maximum value for Q₁₅:
Q₁₅ = geometric displacement · N · η
with: displacement = maximum volume of chamber 2
N = shaft speed 6
η = volumetric efficiency of the pump
The apparent displacement has the value
Q₁₅ / N
and the effective apparent displacement which will be called in the following description of the effective displacement C _{e is} worth:

with the maximum value for the effective displacement
C _e = displacement · η

The control 31, by acting on the pressure limiter 26, makes it possible to adjust the supply pressure P₁₃, and as we have just seen, thus to regulate the displacement of the pump for a given speed.

Another embodiment of the flow control system 9 is shown in FIG. 4. The flow control system 9 comprises a variable restrictor 28 mounted on the channel 13 and supplying the channel 14; this variable choke 28 is controlled by a control 32. A pressure limiter 27 is mounted in bypass in front of the variable choke 28.

This embodiment makes it possible to adjust the displacement of the chamber 2 by adjusting the feed rate Q₁₃ with a constant feed pressure P₁₃.

avec S₂₈ = section de l'étrangleur variable 28. La commande 32, en agissant sur l'étrangleur variable 28, permet de règler la cylindrée de la pompe pour un régime donné.In this case the effective displacement C _e is given by the relation:

with S₂₈ = section of the variable choke 28. The control 32, by acting on the variable choke 28, makes it possible to adjust the displacement of the pump for a given speed.

Another embodiment of the flow control system 9 is shown in FIG. 5. The flow control system 9 comprises a proportional distributor 29 mounted on the channel 13 and supplying the channel 14; this proportional distributor 29 is controlled by a command 33. A pressure limiter 27 is mounted in bypass upstream of the proportional distributor 29. This embodiment makes it possible to adjust the displacement of the chamber 2 by dividing the feed rate Q₁₃.

The flow rate Q₁₃ of the garage pump 10 is divided between the need for boosting Q₁₄ and the excess flow rate or leakage flow rate Q _f . The proportion between the leakage rate Q _f is produced by the proportional distributor 29, which is controlled by the control 33. The supply pressure P₁₃ adjusts itself, however a pressure limiter 27 is provided for safety and to limit the pressure at the start or during regime changes.

In this case the effective displacement C _e is given by the relation:
C _e = (Q₁₃-Q _f ) · η / N
where the value (Q₁₃-Q _f ) depends on the command 33 and C _e = Q₁₄ · η / N.

If the speed N is identical for the booster pump 10 and for the variable flow pump, we have the relation:
Q₁₃ = C _g · N
with C _g = displacement of the booster pump 10.

The proportional distributor 29 having a flow division ratio R, we have:
Q₁₄ = Q₁₃ · R
therefore C _e = Q₁₃ · R · ηN
or C _e = C _g · R · η

The adjustment of the division ratio R of the proportional distributor 29, by control 33, then makes it possible to fix the displacement independently of the speed.

Another embodiment of the flow control system 9 is shown in FIG. 6. The flow control system 9 comprises a distributor 30 mounted on the channel 13 and supplying the channel 14; this distributor 30 is controlled by a control 34. A pressure limiter 27 is mounted in bypass upstream of the distributor 30.

This embodiment makes it possible to adjust the displacement of the chamber 2 by a sequential control.

avec S₃₀ = section de passage du distributeur 30
t = temps de commande du distributeur 30,
T = période du signal de commande de 34.The two-position distributor 30 is placed on the booster channel 14. This distributor 30 is controlled by the control 34 synchronously with the rotation of the variable flow pump. Therefore it is the opening time of the distributor 30 which determines the feeding rate Q₁₄. We have the relation:

with S₃₀ = distributor passage section 30
t = distributor control time 30,
T = period of the control signal of 34.

ou la cylindrée efficace :

Comme la période T en seconde est bien la vitesse N en tours par seconde par la relation :

On a la cylindrée efficace qui est donnée par la relation

Le règlage du temps t pour la commande 34 permet donc de fixer la cylindrée de manière indépendante du régime.The variable flow pump only discharging during half of its rotation, the discharge flow Q₁₅ will be:

or the effective displacement:

As the period T in seconds is indeed the speed N in revolutions per second by the relation:

We have the effective displacement which is given by the relation

The adjustment of the time t for the command 34 therefore makes it possible to fix the displacement independently of the speed.

The various commands 31, 32, 33 and 34 make it possible to develop a control signal by mechanical or electrical fluid. This signal maintains the displacement at the desired value according to external parameters, such as pressure, flow, power or any other.

Claims (8)

1. Variable flow pump comprising at least one piston (1) associated with a chamber (2), said piston (1) cooperating with a surface (3) driven by a reciprocating movement with constant movement, characterized in that the piston (1) is free from any continuous mechanical connection with said surface (3); and that said chamber (2) is associated with a flow control system (9) disposed upstream, and that it is provided with a valve (7) on the supply and with a valve (8) on the repression; said adjustment system (9) being supplied by a booster pump (10). 2. Variable flow pump according to claim 1, characterized directly by the piston (1) which slides in a pump body (17), said chamber (2) is limited by the bottom (18) of the pump body (17) and by the upper face (22) of the piston (1). 3. Variable flow pump according to claim 1, characterized in that the surface (3) is the upper part of a pusher (4) which cooperates via its lower face (19) with the cam (5) . 4. Variable flow pump according to claim 3, characterized in that the pusher (4) slides in a guide (23), and which is kept in contact with the cam (5) by a spring (24). 5. Variable flow pump according to claim 1, characterized in that the flow control system (9) consists of a fixed throttle (25) associated with an adjustable pressure limiter (26) provided with a control (31) . 6. Variable flow pump according to claim 1, characterized in that the flow control system (9) consists of a variable throttle (28) provided with a control (32) associated with a pressure limiter (27). 7. Variable flow pump according to claim 1, characterized in that the flow control system (9) consists of a proportional distributor (29) provided with a control (33) associated with a pressure limiter (27). 8. Variable flow pump according to claim 1, characterized in that the flow control system (9) consists of a distributor (30) provided with a control (34), and associated with a pressure limiter (27) .

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