FR2659393A1 - Vane pump - Google Patents

Abstract

The vane pump (1) includes a shaft equipped with an essentially quadrangular slider (19). The single vane (4) of the vane pump is equipped with a straight guide groove (5) which fits onto the slider (19); an additional discharge opening (11) is provided in order to avoid hammering in the oil.

Description

VANE PUMP
The invention relates to a vane pump provided with a rotationally driven shaft which is cantilevered and eccentrically in a housing cover, and the free end of which projects into the housing, and on which a vane is guided in a rectilinear manner, radially with respect to the shaft.

 This type of vane pump is known from European Patent Application NO 87114934.0 (EP-1548). This known pump has a high flow rate and has the advantage of being made up of a very small number of elements and therefore of being largely free from wear.

 The objective of the invention is to further increase the flow rate of the pump and to reduce the number of constituent elements as well as to simplify them on the technical level.

 The problem is solved according to the invention by the fact that the part of the shaft projecting from the casing is produced in the form of a sliding guide, and in that the pallet has on its front face turned towards the shaft a groove rectilinear guide, adapted to the slide guide and which engages on the slide guide.

According to the invention, the rotor mounted in cantilever on the shaft, essential in the known pump is eliminated and replaced by a slide guide mounted on the cantilevered end of the shaft. This sliding guide is an element which poses no problem as regards its manufacture, its resistance characteristics and its resistance over time. With the removal of the rotor, the volume of the housing usable for the flow is increased. On the other hand, the pallet has a slightly more complicated structure due to the arrangement of the guide groove. The arrangement and machining of the guide groove in a pallet of this type which, as a quadrangular plate, can be easily clamped, however presents no difficulty.

 The slide guide is, in the spirit of the invention, a stud arranged on the shaft. This stud has two mutually parallel side surfaces, which are adjusted in the groove of the pallet so that the pallet is perfectly guided in a rectilinear manner on the side surfaces, but can also slide. The slide guide can also be slightly curved, in the sense that the essentially parallel side surfaces are formed by portions of a cylinder envelope with a very large radius. The pallet can thus slightly modify its angular position relative to the shaft and adapt its position inside the casing so that it does not get stuck. The slide guide protrudes sufficiently axially inside the housing to ensure good straight guidance, and the paddle should not be trapped inside the housing. This is why provision is preferably made for the slide guide to extend beyond the axial center of the casing.

 The groove in the pallet can be obtained by the fact that a continuous slot is provided in the median plane of the pallet, which extends parallel to its two lateral faces. It is necessary, for proper guidance of the pallet, that the lateral faces of this slot are perfectly parallel to one another.

 The vane can also have a U shape. The vane is then guided on the slide guide by the sides extending perpendicular to the transverse wing of the U. The transverse wing slides on the front wall of the pump located opposite of the tree. Thus, the pallet is provided with a continuous unclosed groove at its ends, which is therefore easy to machine. The groove can also be used for guiding pallet segments, which are guided inside the groove by means of guide tabs and slide by their external face on the peripheral wall of the casing, and seal between the pallet and housing. In this case, the groove formed between the sides of the U-shaped section serves simultaneously to guide guide segments or sealing segments. It is imperative that the transverse wing is set back from the ends of the pallet of at least the value of the height of the guide tabs.

 In all cases, it may be advantageous to provide the ends of the pallet with guide segments or sealing segments, which have a low degree of freedom relative to the pallet. Such guide segments or sealing segments are intended to compensate for the tolerances of the casing with respect to the pallet resulting from machining and / or wear.

 The vane pump according to the invention is preferably produced in the form of a "mono-vane pump", that is to say a pump provided with a single vane, said vane being rigid, with the exception of the guide segments or possibly fitted sealing rings, which have a low degree of freedom. The outer ends of the pallet, which are formed if necessary by the guide segments or the sealing segments, have a radius of curvature. The shape of the housing is determined by the fact that it describes a closed curve. The characteristic of this curve is that all the secants, which pass through the axis of the pump shaft, have the same length, independently of the angle of inclination of these secants. The length of the secants corresponds to the distance from the centers of the radii of curvature of the ends of the pallet - seen in radial section of the casing. A closed curve of this type is for example a conchoid. German patent application 39 33 618.2 (1-1743) presents suitable curve shapes. The shape of the casing, in radial section, is then the equidistant curve with respect to this closed curve with the distance the radius of curvature of the ends of the pallet, the guide segments or the sealing segments.

 In order to obtain as high a volumetric efficiency as possible, the suction and discharge are preferably fitted with non-return valves. In this embodiment, the vane pump is mainly used as a vacuum pump, driven by the engine of a vehicle and used for the operation of servo-motors, for example braking force amplifiers.

 Having the suction and discharge symmetrically with respect to the lower dead center also improves the volumetric efficiency. The bottom dead center is the generator of the casing which is the least distant from the axis of the shaft. The suction and discharge are located immediately below the lower dead center position of the pallet, i.e. below the secant axial plane perpendicular to the axial plane passing through the lower dead center (plane of symmetry).

 The outer faces of the pallet are, in the simplest embodiment, mutually parallel planar surfaces. This embodiment has the advantage, when using the pump as an oil-lubricated vacuum pump, of avoiding the discharge of the oil at the bottom dead center. However, the volumetric efficiency is increased when the outer faces are in the form of cylinder envelope portions with a relatively large radius of curvature. The essential characteristic of these cylinder envelopes is that they adapt to the shape of the casing at bottom dead center, so that the pallet almost completely fills, at its bottom dead center, the portion of the casing containing the bottom dead center . In the present application, the position of lower dead center corresponds to the position of the pallet in the axial plane which forms an angle of 900 with the axial plane (plane of symmetry) passing through the lower dead center.

 In this exemplary embodiment, an additional discharge opening has been provided which is situated substantially at the bottom dead center, in order to avoid water hammer.

 Another possibility to avoid water hammer at the bottom dead center of the pallet consists, when the pallet reaches the bottom dead center, to allow the oil to pass from the front end of the pallet towards the rear end, by through grooves between the ends of the pallet.

 The pallet according to the invention is subjected to a centrifugal force when passing through the bottom dead center. In order to compensate for this centrifugal force and its harmful effects, the pallet is supported by means of springs on the slide guide. The adaptation of the length of the springs and their elastic characteristic makes it possible to obtain the desired effects.

 Examples of embodiments of the invention are described below.

 Figure 1 shows a simplified radial section of a vacuum vane pump.

 Figure 2A shows a simplified axial section of a vacuum vane pump.

 Figures 2B, 3, 4, 5, 6 show axial sections of a vacuum vane pump with different vane shapes.

 The description which follows relates to all the embodiments. The different forms of pallet will be examined after the description.

 The casing 1 of the pump has a cover 13 provided with an eccentric bearing boss. The shaft 2 is mounted movable in rotation in the bearing boss. The shaft is driven by means of a coupling 15, for example by the diesel engine, not shown, of a motor vehicle, in order to produce a vacuum for the operation of servo-users. The other front end of the casing 1 is closed by means of a cover 25 provided with a seal 14.

The shaft has a shoulder which is flush with the inner front wall of the cover 13, and which constitutes the slide guide 3. This slide guide is a plate-shaped slide mounted on the shaft, having two mutually planar guide surfaces parallel. The radial length of this slide corresponds approximately to the diameter of the shaft. Its dimension depends essentially on the eccentricity of the axis of the shaft 19 inside the cover or the casing 1. The lower this eccentricity, the greater the radial length of the slide. The guide surfaces can be slightly curved in the radial direction, however a very large radius of curvature is necessary.

Thanks to this bulging, the pallet can follow the shaft with a very slight angular offset towards the front or towards the rear, as described below.

 The pallet 4 is provided with a guide groove 5.

This guide groove is arranged in the pallet from one side. The axial depth of the guide groove corresponds approximately to the axial length of the slide guide 3. The slide guide 3 preferably extends beyond the axial center of the pump housing 1 so as not only to guarantee good guidance rectilinear of the pallet, but also to prevent it from tipping over and jamming. The pallet is provided at its ends with guide segments 6, which are mounted in grooves of the pallet, and have little freedom of movement in the radial direction. As a variant, it is possible to use sealing segments which are engaged from the outside on the ends of the pallet. The guide segments or the sealing segments are applied by their curved section to the casing. They therefore have, seen in a radial plane, a radius of curvature r. The distance from the centers of these radii of curvature is called the length of the secants S in what follows. The casing describes a closed curve, the characteristic of which is that all the secants - seen in a radial plane - which pass through the axis of the shaft have the same length. The shape of the casing - considered in the same radial plane - is therefore defined by the equidistant curve relative to this closed curve, distant from the value of the radii of curvature r. The closed curve is in the ideal case a conchoid or a Pascal spiral.

 The vane pump has a suction port 7, controlled by a non-return valve 8, and a discharge port 9 controlled by a non-return valve 10.

The discharge opening 9 opens, for example, into the motor casing. Remains of air and oil are discharged through the discharge port in the crankcase. The suction is connected to a servo user, for example to the braking force amplifier of a motor vehicle.

 The suction and discharge are located on either side of the lower dead center. The lower dead center corresponds to the generator of the casing which is closest to the axis of the shaft 19. In FIG. 1, the pallet is shown in an angular position which corresponds to the axial plane passing through the lower dead center. This axial plane divides the casing into two essentially symmetrical halves, and is therefore called the plane of symmetry.

The inlet and outlet are located below the axial plane which intersects the plane of symmetry at right angles, that is to say on the side facing towards the bottom dead center.

This perpendicular axial plane is called, in the context of this patent application, neutral position of the pallet. The neutral position of the pallet is shown for example in Figure 3.

 When it rotates in the direction of rotation 22, the pallet defines two chambers inside the casing. One of these chambers communicates with the discharge orifice 9, while the other chamber communicates with the suction orifice 7. During rotation, the suction chamber enlarges while the discharge chamber narrows between two consecutive neutral positions on the pallet.

 Pallet shapes are described in the following. The shape of the pallet according to FIGS. 1, 2A essentially corresponds to the shape according to FIGS. 3 and 4. In these cases, the external surfaces 23 and 24 of the pallet are portions of cylinder with a relatively large radius or even relatively small curvature. As shown in FIG. 3, the curvature is chosen in such a way that the pallet adapts to the casing with its lateral surface concerned in these lower dead center positions. This results in complete emptying of the delivery chamber when the pallet reaches its lower dead center position. However, when the pump is used as a vacuum pump lubricated with oil, it is necessary to expel the excess oil. An additional discharge orifice 11, also controlled by a non-return valve 12 in the flow direction, is provided for this purpose. The additional discharge orifice 11 also opens, for example, into the motor casing.

This additional delivery port avoids the appearance of high pressures in the oil remaining inside the casing, which can cause bending or rupture of the pallet, the slide guide or the shaft. The particularity of the pallet according to Figure 1 also lies in the fact that the pallet is provided with axial conduits 26. These conduits 26 are arranged in such a way that, on the one hand, they reduce the mass and the weight of the pallet, and on the other hand do not affect its resistance.

 The particularity of the pallet according to FIG. 4 lies in the fact that the pallet rests on the slide guide 3 when it passes through the bottom dead center. For this purpose the slide guide 3 is provided with radial holes, in which are housed compression springs 17, 18. These compression springs are fixed in the region of the axis. When one end of the pallet reaches the bottom dead center, this rests on one of the compression springs 17, 18. Thus, the force of the springs opposes the centrifugal force. The effects of centrifugal force are thus compensated.

 The pallets according to FIGS. 1 to 4 can be split over their entire width, which corresponds to the axial length of the casing, so that the rectilinear guide groove 5 is open at the two front ends of the pallet on the front face side. of the housing. The groove can also be closed at one of its front ends by a transverse wing 21. The pallet has, in this case, a U-shaped section, with a transverse wing 21 and lateral wings 20 which are attached to it . The transverse wing 21 is applied to a front face, that is to say on the cover 25, of the pump housing. In FIGS. 1 and 2A, the groove is closed at the ends of the pallet facing the periphery of the casing.

 The pallet according to FIG. 2B also has a U shape. It comprises a transverse wing 21 extending in the radial direction, which is applied to one of the covers 25. The pallet also comprises lateral wings 20, perpendicular which join the two ends of the transverse wing and form two parallel flat surfaces. The lateral wings 20 form the groove, by means of which the pallet is guided in a rectilinear manner on the slide guide 3.

 The transverse wing 21 extends in the radial direction over only part of the length of the pallet. There is thus obtained at the ends of the pallet facing the periphery of the housing, a groove in which the guide segments 6 are guided by means of a guide tongue. The center M of the radius of curvature r of the pallet segment 6, as well as the secant length S, which, as indicated above, determine the shape of the casing, are also indicated in FIG. 2. The groove therefore serves simultaneously for rectilinear guidance on the slide guide 3 and the rectilinear guide of the guide segments in the pallet 4.

 The radial length of the transverse wing 21 is determined by the length of the guide tabs 27. It is indeed necessary for the guide tabs 27 to extend continuously over the entire axial width of the casing to ensure the sealing, suction side and discharge side.

 This embodiment of the pallet has the advantage that the rectilinear guide groove 5 as well as the guide groove of the guide tongues 27 can be machined continuously in a single operation with the same tool, for example by grinding or by milling .

 In the embodiment of the pallet according to FIG. 6, the external surfaces 23 and 24 essentially correspond to the shape according to the preceding figures.

We will therefore refer to the corresponding description.

Each of the outer surfaces 23 is further provided with a discharge groove 26. The discharge groove 26 extends essentially from one end of the pallet to the other.

One or more grooves can be provided. There is shown a groove provided with a straight throat bottom.

The bottom of the groove can also be arranged at a substantially constant distance from the side walls 23, 24. The function of the discharge grooves 26 is to avoid pressure peaks in the lubricating oil. When the pallet reaches its neutral position, the oil can pass from the discharge side to the other end of the pallet on the suction side. Thanks to this arrangement, the additional delivery orifice 11 of FIGS. 1, 3, 4 is no longer necessary.

 In the form of a pallet according to FIG. 5, the lateral surfaces 23, 24 of the pallet are planar. The pallet therefore has, with the exception of its end zones, an essentially quadrangular section profile. The lubricating oil can also pass from the discharge side to the suction side with this form when the pallet reaches its lower dead center position. Pressure peaks are thus avoided and the additional discharge orifice 11 in FIGS. 1, 3, 4 is no longer necessary.

Claims (12)

 1. Vane pump comprising a shaft driven in rotation, which is cantilevered and eccentrically in a housing cover, and whose free end protrudes in the housing (1), and on which a pallet is guided in a rectilinear manner radially with respect to the axis, characterized in that the part of the shaft (2) projecting into the casing (1) is produced in the form of a sliding guide (3), and in that the pallet (4) has on its front face turned towards the shaft a rectilinear guide groove (5), adapted to the slide guide and which engages on the slide guide.  2. Vane pump according to claim 1, characterized in that the vane (4) is made in one piece and in that the casing (1) describes a closed curve, which is defined by the fact that all of its intersections passing through the axis (19) of the shaft have substantially the same length.  3. Vane pump according to claim 1 or 2, characterized in that the suction (7) and the discharge (9) are located in or near the axial plane of symmetry of the shaft (2) at the bottom dead center , and preferably on the side of the axial plane facing the bottom dead center.  4. Vane pump according to any one of claims 1 to 3, characterized in that the vane is composed in section of two cylinder portions, which largely follow the shape of the casing on either side of the lower dead center.  5. Vane pump according to claims 3 and 4, characterized in that an additional discharge orifice (11) controlled by a non-return valve (12) is provided in the area of lower dead center.  6. Vane pump according to claim 4 or 5, characterized in that the vane has on its outer face, between its ends, a groove (16).  7. Vane pump according to any one of claims 1 to 3, characterized in that the vane (4) has two parallel side faces.  8. Vane pump according to any one of the preceding claims, characterized in that the vane (4) is applied against the pump housing via guide segments (6) or radially movable sealing segments.  9. Vane pump according to any one of the preceding claims, characterized in that the vane (4) bears in both directions of movement, elastically (compression spring (17, 18)) on the slide guide, at least in the lower dead center area.  10. Vane pump according to any one of the preceding claims, characterized in that the vane has a U-shaped section such that the slide guide engages between the two parallel wings (high wings 20).  11. Vane pump according to any one of the preceding claims, characterized in that the guide surfaces of the slide guide (3) are produced in the form of cylindrical surfaces with low curvature.  12. Vane pump according to any one of the preceding claims, characterized in that the slide guide protrudes beyond the axial center of the housing.