FR2699967A1 - Vane pump. - Google Patents

Abstract

Vane pump comprising a shaft driven in rotation, which is mounted cantilever and eccentrically in a housing cover and whose free end projects into the housing and is designed as a slide guide (3 ) on which the pallet (4) is engaged by a rectilinear guide groove and is guided in a rectilinear manner radially with respect to the axis of the shaft. The pallet rests elastically in both directions of movement (springs 17, 18) on the slide guide (3), at least in the area of the lower dead center.

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 straight line,

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 d 'be

largely free of 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 a groove on its front face turned towards the shaft. straight guide, suitable for

  slide guide and which engages the slide guide.

  According to the invention, the rotor mounted in cantilever on the shaft, essential in the known pump is removed and replaced by a slide guide mounted on the cantilever end of the shaft This slide guide is a element which poses no problem with regard to its manufacture, its resistance characteristics and its resistance over time With the elimination of the rotor, the volume of the casing usable for the flow rate 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, does not have

however no difficulty.

  The sliding 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 rectilinear on the side surfaces, but can also slide The sliding 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 housing so that it does not get stuck The sliding guide protrudes sufficiently axially inside the housing to ensure good guidance It is also necessary to prevent the pallet from getting stuck inside the casing. This is why it is preferably provided that the slide guide extends

beyond the axial center of the housing.

  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 good guidance of the pallet, that the side faces of this slot be

  perfectly parallel to each other.

  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 the shaft 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 the casing In this case, the groove formed between the sides of the U-shaped section serves simultaneously for guiding guide segments or sealing segments It is imperative that the transverse wing is set back from the ends of the pallet by 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 housing with respect to the resulting pallet

machining and / or wear.

  The vane pump according to the invention is produced

  preferably in the form of a "single-pallet pump", that is to say

  say a pump provided with a single pallet, said pallet being rigid, with the exception of the guide segments or sealing segments which may be fitted, which have a low degree of freedom The outer ends of the pallet, which are formed where appropriate by the guide segments or the sealing segments, have a radius of curvature The shape of the casing is determined by the fact that it describes a closed curve. This curve has the characteristic 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 vane seen in radial section of the casing A closed curve of this type is for example a concoide German patent application 39 33 618 2 (1-1743) has suitable curve shapes The shape of the casing, in radial section, is then the court be equidistant from this closed curve with the distance the radius of curvature of the ends of the pallet, guide segments or sealing segments. In order to obtain as high a volumetric efficiency as possible, the suction and the discharge are preferably provided with non-return valves. In this embodiment, the vane pump is mainly used as a vacuum pump, driven by the motor of 'a

  vehicle and used for servo operation

  users, for example of force amplifiers

braking.

  The fact of placing the suction and the discharge symmetrically with respect to the lower dead center also makes it possible to improve the volumetric efficiency. The lower dead center is the generator of the casing which is the least distant from the axis of the shaft. and the discharge are located immediately below the

  lower neutral position of the pallet, i.e.

  say below the secant axial plane perpendicular to the axial plane passing through the bottom dead center (plane of symmetry). The outer faces of the vane are, in the simplest embodiment, mutually parallel planar surfaces. This embodiment has the advantage, when using the pump as an oil-lubricated vacuum pump, to avoid the oil discharge at the bottom dead center However, the volumetric efficiency is increased when the external faces are in the form of portions of cylinder casing with relatively large radius of curvature The essential characteristic of these cylinder casings is that '' they adapt to the shape of the housing at bottom dead center, so that the pallet almost completely fills, at its bottom dead center, the portion of the housing containing the bottom dead center In the present application, the neutral position lower 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

by the bottom 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 the intermediary of

  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 Adaptation the length of the springs and their elastic characteristic

  provides the desired effects.

  Examples of embodiments are described below.

of the invention.

  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 shapes of

different palette.

  The following description concerns all

  embodiments The different forms of pallet

  will be discussed following the description.

  The casing 1 of the pump has a cover 13 provided with an eccentric bearing boss The shaft 2 is mounted to rotate 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 parallel flat guide surfaces 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 more the radial length of the slide may be significant The guide surfaces may be slightly curved in the radial direction,

  however, a very large radius of curvature is required.

  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 rectilinear guide of the pallet, but also to prevent it from tilting and jamming thereof. 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 segments of are applied by their curved section on 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 length of the secants S in what follows The casing describes a closed curve, the characteristic of which is that all of 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 consequently defined by the equidistant curve compared 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 9 controlled by a non-return valve 10.

  The discharge opening 9 opens, for example, into the crankcase of the engine. The remains of air and oil are discharged via the discharge opening in the

  motor housing The suction is connected to a servo

  user, for example to the force amplifier of

braking 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 represented in an angular position which corresponds to the axial plane passing through the bottom dead center This axial plane divides the casing into two halves essentially

  symmetrical, 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 the bottom dead center.

  This perpendicular axial plane is called, in the context of the present 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 orifice of suction 7 During rotation, the suction chamber expands while the discharge chamber narrows between two neutral positions

of the palette.

  The forms of the pallet are described in the following. The form of the pallet according to FIGS. 1, 2 A it essentially corresponds to the form according to FIGS. 3 and 4 In these cases, the external surfaces 23 and 24 of the pallet are cylinder portions with a relatively large radius or a 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 discharge 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 oil in excess An additional discharge port il, also controlled by a non-return valve 12 in the flow direction, is provided for this purpose The additional discharge port

  It also opens, for example, into the engine casing.

  This additional delivery port avoids the appearance of high pressures in the oil remaining inside the crankcase, which can cause bending or breaking of the pallet, the slide guide or the shaft. of the pallet according to FIG. 1 also resides 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 hand do not affect its resistance. The particularity of the pallet according to FIG. 4 resides 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 compression springs 17, 18 are housed These compression springs are fixed in the axis area When one end of the pallet reaches the bottom dead center, it rests on one of the compression springs 17 , 18 Thus, the force of the springs is opposed to 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 side wings 20 which are there attach 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 2 A, the groove is closed at the ends of the pallet turned towards the periphery. of the housing. The pallet according to FIG. 2 B 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 are connect to 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 straight 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 turned towards 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 serves therefore simultaneously with the straight guide on the slide guide 3 and the straight 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 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 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 It is

  shown a groove provided with a straight throat bottom.

  The bottom of the groove can also be disposed at a substantially constant distance from the side walls 23, 24 The discharge grooves 26 have the function of avoiding pressure peaks in the lubricating oil Indeed, when the pallet reaches its point position dead, 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 discharge orifice 11 of the

  Figures 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 flat. The pallet therefore has, with the exception of its end zones, a profile of essentially quadrangular section. The lubricating oil can, also with this shape, switch from the discharge side to the suction side when the pallet reaches its lower dead center position. The pressure spikes are thus avoided and the additional discharge orifice il in FIGS. .

Claims (4)

  1 Vane pump comprising a shaft (2) driven in rotation, which is cantilevered and eccentrically in a housing cover and the free end of which projects into the housing (1) and is produced under form of slide guide (3) on which the pallet (4) is engaged by a straight guide groove (5) and is guided in a straight line radially with respect to the axis (19) of the shaft, characterized by causes the pallet (4) to bear elastically in both directions of movement (springs 17, 18) on the slide guide   (3), at least in the area of lower dead center.   2 Vane pump according to claim 1, characterized in that the slide guide (3) is provided with radial holes in which are housed compression springs (17,18).   3 Vane pump according to claim 1 or 2, characterized in that the vane (4) is applied against the pump housing by means of guide segments (6) or sealing segments, movable radially.   4 Vane pump according to any one of   previous claims, characterized in that   the guide surfaces of the slide guide (3) are made in the form of cylindrical surfaces with low curvature.   Vane pump according to any one of   previous claims, characterized in that   the slide guide projects beyond the axial center of the housing.