EP0802327B1 - Gear pump - Google Patents

Abstract

The pump has a casing (3) in which are mounted two gears (4,5) which are opposed and engaged and one of which is attached to a drive shaft (20). a hollow cylinder (9) is fixed to one of the lateral walls (7) of the pump and positioned in front of an opening (8) in the lateral wall. The cylinder receives a piston (10) which moves in the axial direction of the gears. The head of the piston, at rest, engages against the front face of the gear teeth under the force of a spring . The head of the piston completely covers the face of one of the gears and the central points of the piston and gear tooth ring are on the same axis. the rear face of the piston is subjected to the hydraulic pressure within the pressure chamber (6) via a passage (13).

Description

The present invention relates to a pump gears, preferably a gear pump exterior, comprising a pump body in which rest at least two opposite toothed wheels, meshing, one of which is connected to a drive, a hollow cylinder, fixed to one of the side walls of the pump with gears and arranged in front of an opening in this wall lateral, hollow cylinder in which a piston rests movable in the axial direction of the gear wheels, the head of which piston, at rest, comes against the front face of the wheels toothed under the effect of an elastic element. For convenience of language, we will call in the rest of this text by "front face of the gears" the face of the gear, perpendicular to the axis of the gear, facing the aforementioned piston.

Because of their fairly simple structure accompanied with sufficient delivery accuracy, the pumps gears are suitable for many drives hydraulic. In particular, they are often used as lubricating oil pumps in engines with internal combustion. The oil pressure produced by the gear pump cools piston heads, lubricates and cools the piston sliding track, the bearings main and connecting rod bearings as well as rocker arms and supplies the camshaft bearings. The entrainment and the delivery of the liquid results from the fact let it penetrate into the gaps freed from the wheels toothed meshing with each other, moves, in the direction of rotation, outside, along the body wall of pump, to enter the pressure zone and is expelled from the entredents in the direction of the pressure by mutual meshing of teeth. Given that each entry is, before the complete emptying, closed by a tooth of the opposite toothed wheel, this results which is called a crushing liquid which, to avoid energy loss and a smooth running of the pump gears, must be diverted in the pressure chamber to through bores or grooves.

To reduce significant overpressures, producing within the crushing liquid, certain pumps have in the side wall of the pump body facing the front faces of the two gears, and placed next to the area where the two wheels mesh, a small movable piston, which a rear spring pushes against front faces of the meshing wheels, and which, under the effect of the overpressure of the crushing liquid may recede and let this liquid flow towards the chamber suction. This device reduces the local overpressures which can reach or even exceed 8 to 15 bars. However, the force of the spring must be high, so that when it pushes the piston against front faces of the two gears, friction is created from which results a significant energy loss.

Document US-A-2437791, on which the preamble of claim 1 is based, describes a gear pump of a similar construction, in which the axial loads of the toothed wheels are relieved by axial displacement of a side wall of sealing.

Gear pumps operating according to the volumetric principle have the property according to which the liquid discharge and pressure increase proportionally when the speed of rotation increases. Therefore, in the absence of regulation, the permissible permanent operating pressure - for a economical use and sufficient service life - is exceeded. To be able to keep the delivery constant when the speed of rotation of the gear pump increases and to be able to keep constant the permanent running pressure, we also know how to predict, in the pressure line connected to the pressure chamber of the gear pump, an expansion valve which opens when a running pressure is exceeded permanent predetermined; the pressure is lowered and the backflow of excess liquid is returned to the liquid tank from the pressure line in passing through a return line. But this technique of regulation is disadvantageously accompanied by a significant power dissipation of the pump gears, which can reach for example around 1300 W for a delivery of 10 liters / minute; when the flow increases, power dissipation only decreases relatively little.

Added to this is the fact that the flow of liquid which backflow causes foaming in the tank liquid and therefore foam may be sucked.

An object of the present invention is to configure the gear pump described at the beginning so to obtain a significant reduction in the dissipation of power and to prevent foaming.

Another object of the invention is to reduce the friction forces between the meshing wheels and the overpressure reducing device.

It is also an object of the invention to reduce the operating noise of the pump.

These goals are achieved with a pump of the type defined above in which the piston head covers completely the front face of one of the gear wheels, that the central points of the piston head and the head circle teeth of said gear wheel are located on the same axis, and in which the rear face of the piston is subjected to the hydraulic pressure prevailing in the pressure through a supply line between the pressure chamber and said rear face.

Thanks to the co-axial arrangement between the piston and a gear wheel, it is possible to increase the clearance between the piston head and the front face of the gears and therefore to reduce the friction forces.

Preferably, the elastic element can be consisting of a helical spring inserted between the face back of the piston head and the inner side of the cover of the hollow cylinder.

According to a preferred embodiment, the face of the piston head which faces the gear wheel has a hollowed-out central part, the diameter of which is slightly less than the diameter of the bottom of the brackets while the total diameter of the piston head is slightly greater than the diameter of the gear wheel head circle. In this way, only the surface of the front face of the wheel corresponding to the crown of teeth can be found in contact with the piston head. Friction forces are considerably reduced. In addition, the piston is lightened and its inertia decreases.

Thanks to the connection between pressure chamber and back side of the piston, which generates on the back of the piston a back pressure of several bars, the force of the spring support can be considerably reduced, which does not only decreases the friction forces between the head piston and front face of toothed wheel but still allows a much quieter operation of the pump.

According to a first embodiment of the present invention, the rear face of the piston on which is exerted the effect of the spring and which constitutes a back-pressure chamber is simply connected to the pressure chamber of the pump by a supply duct which can, in particular, pass through the piston head or pass through the pump body wall.

According to a second preferred embodiment of invention, the back pressure chamber is also with a second return pipe to the room suction. This conduit back to the bedroom suction valve is fitted with a calibrated valve.

According to a third preferred embodiment of the present invention, the back pressure chamber is fitted with a pipe leading to the outside of the pump, in particular a conduit allowing the return to a tank of the fluid transported by the pump.

In both cases, a diameter of the return duct greater than the diameter of the duct back pressure chamber supply.

La figure 1 est une représentation générale dans l'espace des éléments constitutifs de la pompe à engrenages ;

La figure 2 est une représentation dans l'espace de la pompe à engrenages avec une coupe partielle ;

La figure 3 montre une vue schématique, en coupe verticale dans le plan de l'axe du cylindre creux, du premier mode de réalisation de l'invention.

La figure 4 montre une vue schématique, en coupe verticale dans le plan de l'axe du cylindre creux, d'un deuxième mode de réalisation préféré de l'invention.

La figure 5 montre une vue schématique, en coupe verticale dans le plan de l'axe de cylindre creux, d'un troisième mode de réalisation préféré de l'invention.

The gear pump according to the invention is shown by way of illustration in the drawing and is described below. On the drawing :

Figure 1 is a general representation in space of the components of the gear pump;

Figure 2 is a spatial representation of the gear pump with a partial section;

FIG. 3 shows a schematic view, in vertical section in the plane of the axis of the hollow cylinder, of the first embodiment of the invention.

Figure 4 shows a schematic view, in vertical section in the plane of the axis of the hollow cylinder, of a second preferred embodiment of the invention.

Figure 5 shows a schematic view, in vertical section in the plane of the hollow cylinder axis, of a third preferred embodiment of the invention.

Identical or equivalent parts bear the same reference numbers in all of the figures.

In the gear pump (1), the discharge of the liquid takes place in such a way that the liquid penetrates, suction side, in the suction chamber (2) of the pump, in the free spaces of the gear wheels (4, 5) meshing, arranged in the pump body (3); he moves, from the outside, along the body wall pump, in the direction of rotation of the wheels, in the direction on the discharge side of the pump and is expelled from between the mutual meshing of the teeth. Given that each entry, before complete emptying, is closed by the corresponding tooth of the opposite toothed wheel, it here results what is called a crushing liquid which is diverted into the pressure chamber (6) through bores not shown to avoid energy losses and a knocked gears step. Cogwheels, one of which, for example the wheel (4) is connected to a drive element (20), not shown in the figures 1 and 2, rotate with a very small backlash in the direction radial and axial between them and the pump body. In the side wall (7) of the pump body, opposite the side gear pump drive, there is a hole passage (8) arranged coaxially with respect to the wheel toothed, hole whose surface is similar to the surface of the head circle of the teeth of the gear wheel. On the side outside of the wall (7) of the pump body, in front of the hole passage, a hollow cylinder is arranged coaxially (9) integral with the wall (7) of the pump body. The cylinder (9) and the wall (7) may consist of two separate integral parts. As shown on Figures 3, 4, 5, the cylinder body and the wall (7) are come from one piece and the bottom of the cylinder is closed by a lid. The inside diameter of the hollow cylinder coincides with the diameter of the through hole. In the bore of hollow cylinder movably rests a piston (10) which, in the embodiment illustrated in FIGS. 1 and 2, presents the shape of a hollow cylinder whose piston head (11) flat, at rest, comes against the front face of the wheel toothed. Since the surface of the piston head is similar to the surface of the head circle of the teeth of the gear wheel, the front side of it is fully covered by the piston head. Between the inner side of the piston and the bottom wall of the hollow cylinder, or the cylinder cover, a pressure spring is inserted helical cylindrical (12) whose spring force press, in the axial direction and against the front face of the toothed wheel, the piston head which completely covers this front face of the toothed wheel.

When, in operation, it exceeds one determined delivery, the piston is, despite the force of the helical pressure spring, pushed inside the hollow cylinder, so that a slit opens between the head piston and the front face of the toothed wheel, that the excess backflow can flow, through this bypass, directly to the suction side, to the suction chamber of the gear pump, and that it produces a drop in pressure. Therefore, dissipation of power decreases significantly and an amount lower liquid must be entrained in the circuit. Only the quantity of liquid which is actually useful. For example, in the case of a conventional gears, without movable piston, and for a rotation speed of 3000 rpm, if dissipation power is 1240 W for a discharge of 20 liters / minute, the use of the gear pump produced with a movable piston according to the invention reduced to 960 W power dissipation. In addition, it prevents the foaming liquid.

As can be seen in Figure 2, or again in Figures 3, 4, 5, the diameter of the piston (11) is slightly greater than the bore of the pump body (3) in which rests the gear (4) facing it. In this embodiment, the cylinder abuts against the edge of this bore. If the gear is not flush, but very slight shrinkage, this results in very little play which advantageously reduces the friction forces.

This advantageous arrangement is not possible in pumps where a small back pressure piston is arranged opposite the meshing zone, between the axes on two wheels.

In the embodiments shown in the Figures 3, 4, 5, the piston head has an area hollowed-out central unit E, the diameter of which is slightly less than the diameter of the wheel, at the bottom of the crossbeams. There is therefore no contact or friction between the part center of the piston and the central part of the gears or gables.

As we can see for example in Figure 3, through the suction pipe (13), when the pressure increases in the pressure chamber (6), the pressure concomitantly increases in the part of the cylinder (9) at the rear of the piston (10), which forms a back pressure 14. The essential function of the spring 12 in this configuration is then to maintain the piston 10 when starting the pump against the toothed wheel 4 in order to guarantee a good seal.

For example, for a pump in which the pressure in the pressure chamber must be regulated at 5 bars, and fitted with a 34 mm diameter wheel, in the absence of the conduit (13) allowing the pressure rise in the chamber (14), the spring should provide an effort of around 30 daN. However, thanks to the back pressure established in chamber 14), the spring only has to provide an effort of the order of 5 daN. Spring size and therefore its price is significantly reduced and its mounting is also greatly facilitated.

In the embodiment shown in Figure 4, the back pressure chamber (14) is connected to the chamber suction by a return suction duct (19) whose diameter is greater than the diameter of the duct suction (13). The return duct (19) is closed by a ball valve, comprising a sealing ball (15), on which pushes a valve spring (16), a stop (18) forming a plug. This execution mode allows circulation, tight vis-à-vis the outside, oil between the pressure chamber (6), the back pressure chamber (14) and the suction chamber (2): these are a sealed internal circuit. This execution mode is suitable particularly to a pump placed outside a Crankcase.

In the embodiment illustrated in FIG. 5, the back pressure chamber (14) is connected to the exterior by a return duct (17). This conduit (17) is itself closable by means of a calibrated valve comprising a ball (15), a valve spring (16) and a stop (18). This embodiment having an open circuit between pressure chamber (6) - back pressure chamber (14) and outlet of the conduit (17), particularly suitable for a pump placed in the fluid reservoir, for example at inside a crankcase.

In the two embodiments shown in the Figures 4 and 5, the use of the additional calibrated valve limits back pressure and thus facilitates movement and the release of the piston, which allows regulation more frank. The valve spring is chosen in such a way so that the valve opens at the pressure of desired regulation.

Claims (8)

1. A gear pump, comprising a pump body (3) in which at least two opposed, meshing gear wheels (4, 5) are located, one of which is connected to a drive (20), characterized in that a hollow cylinder (9), [lacuna] fixed to one of the lateral walls (7) of the gear pump (1) and arranged in front of an opening (8) in the lateral wall (7), in which hollow cylinder (9) a piston (10) movable in the axial direction of the gear wheels (4, 5) is located, the piston head (11) of which, at rest, comes against the front face of the gear wheels (4, 5) under the effect of an elastic element and in that the piston head (11) completely covers the front face of one of the gear wheels (4, 5), that the central points of the piston head (11) and of the addendum circle of the teeth of the said gear wheel are situated on one and the same axis, and in that the rear face of the piston is subjected to the hydraulic pressure prevailing in the pressure chamber (6) via a supply conduit (13) between the said pressure chamber (6) and the said rear face, so as to form a counterpressure chamber (14).
2. Gear pump according to Claim 1, characterized in that the said elastic element is a helical spring (12) inserted between the rear face of the piston head (11) and the inner face of the cover of the hollow cylinder (9).
3. Gear pump according to one of Claims 1 and 2, characterized in that the piston head has, facing the front face of the gear wheel, a recessed central part E, the diameter of which is substantially equal to or less than the diameter of the bottom of the tooth spaces of the said gear wheel and in that the outside diameter of the piston head is substantially equal to or greater than the diameter of the addendum circle of the said gear wheel.
4. Gear pump according to one of Claims 1 to 3, characterized in that the counterpressure chamber (14) is only connected to the pressure chamber (6) via a supply conduit passing through the piston head.
5. Gear pump according to one of Claims 1 to 3, characterized in that the counterpressure chamber (14) is only connected to the pressure chamber (6) via a supply conduit passing through the wall of the pump body.
6. Gear pump according to any one of Claims 1 to 3, characterized in that the counterpressure chamber (14) is provided with a return conduit (19) connecting the said counterpressure chamber and the suction chamber (2) and in that the said return conduit (19) is provided with a calibrated valve (15, 16, 18).
7. Gear pump according to any one of Claims 1 to 3, characterized in that the counterpressure chamber (14) is provided with a conduit (17) connecting the said counterpressure chamber (14) to the outside of the pump and in that the said conduit leading to the outside is provided with a calibrated valve (15, 16, 18).
8. Gear pump according to one of Claims 6 and 7, characterized in that the said return conduit (17, 19) has a diameter greater than the diameter of the supply conduit (13).

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