Vacuum pump for a motor vehicle engine

Abstract

A vacuum pump for a motor vehicle engine which has a stator and a chamber, has a side wall, and the side wall has a transversal section with a predetermined shape. The rotor mounted in the chamber is capable of rotating around a rotation axis parallel to the side wall. The vane mounted on the rotor is free to slide in a direction at right angles with respect to the rotation axis of the rotor, and the vane has a predetermined length and two opposite end portions that substantially slide along the side wall of the chamber. At least one of the end portions of the vane has at least one part that has a bend radius substantially equal to that of a part of the side wall, when the one vane is at a reference operating position.

Claims

1. A vacuum pump for a motor vehicle engine, comprising: a stator; a vacuum chamber defined inside said stator, said vacuum chamber having a side wall whose transversal section has a predetermined substantially elliptical shape; a rotor mounted in said vacuum chamber and capable of rotating around a rotation axis parallel to said side wall; a single vane mounted on said rotor and free to slide in a direction at right angles with respect to the rotation axis of said rotor, said single vane comprising a central body having a predetermined length and two opposite end portions that are integrally formed with said central body; wherein relative movements between the central body and the two opposite end portions are prevented, and wherein the single vane is one piece, is smoothly continuous in form and all portions making up the whole of the vane are inseparable; said end portions substantially sliding along the side wall of said vacuum chamber; each of said end portions of said single vane comprising two opposite surfaces, said two opposite surfaces symmetrical with respect to a longitudinal axis of said single vane, each surface of said two opposite surfaces is shaped to have a bend radius substantially equal to that of a part of said side wall, when said single vane is in at least one reference operating position, wherein said part is shaped as a circumferential arc having a predetermined radius and is located on the same side of said surface with respect to said longitudinal axis; wherein said single vane is free to slide in a direction passing through the rotation axis of said rotor, the external circumference of said rotor is tangential to the side wall of the chamber along a tangential line parallel to the rotation axis of the rotor, wherein one of said two opposite surfaces of each end portion has a respective curvature centre that is different from the curvature centre of the other of said two opposite surfaces.

2. The vacuum pump according to claim 1, wherein said at least one reference operating position is defined at a configuration of maximum stress of the end portions of said single vane against the side wall of the chamber.

3. The vacuum pump according to claim 1, wherein said two opposite surfaces of each of said end portions of said single vane are radiused, at a longitudinal axis of said single vane, by an arc of circumference.

4. The vacuum pump according to claim 3, wherein the diameter of the ideal circumference that defines said arc of circumference is smaller than the thickness of said single vane.

5. The vacuum pump according to claim 4, wherein the ratio between the diameter of the ideal circumference that defines said arc of circumference and the thickness of said single vane ranges between about and about .

6. A vacuum pump for a motor vehicle engine, comprising: a stator; a vacuum chamber defined inside said stator, said vacuum chamber having a side wall whose transversal section has a predetermined substantially elliptical shape; a rotor mounted in said vacuum chamber and capable of rotating around a rotation axis parallel to said side wall; a single vane mounted on said rotor and free to slide in a direction at right angles with respect to the rotation axis of said rotor, said single vane comprising a central body having a predetermined length and two opposite end portions that are integrally formed with said central body; wherein relative movements between the central body and the two opposite end portions are prevented, and wherein the single vane is one piece, is smoothly continuous in form and all portions making up the whole of the vane are inseparable; said end portions substantially sliding along the side wall of said vacuum chamber; each of said end portions of said single vane comprises two opposite surfaces symmetrical with respect to a longitudinal axis of said single vane and shaped to have a bend radius substantially equal to that of a part of said side wall, when said single vane is in at least one reference operating position, wherein said part is shaped as a circumferential arc having a predetermined radius; wherein said single vane is free to slide in a direction passing through the rotation axis of said rotor, the external circumference of said rotor is tangential to the side wall of the chamber along a tangential line parallel to the rotation axis of the rotor, wherein one of said two opposite surfaces has a respective curvature centre that is different from the curvature centre of the other of said two opposite surfaces; wherein said two opposite surfaces of each of said end portions of said single vane are radiused, at a longitudinal axis of said single vane, by an arc of circumference, wherein the diameter of the ideal circumference that defines said arc of circumference is smaller than the thickness of said single vane, wherein the ratio between the diameter of the ideal circumference that defines said arc of circumference and the thickness of said single vane ranges between and .

7. A vacuum pump for a motor vehicle engine, comprising: a stator; a vacuum chamber defined inside said stator, said vacuum chamber having a side wall whose transversal section has a predetermined substantially elliptical shape; a rotor mounted in said vacuum chamber and capable of rotating around a rotation axis parallel to said side wall; a single vane mounted on said rotor and free to slide in a direction at right angles with respect to the rotation axis of said rotor, said single vane comprising a central body having a predetermined length and two opposite end portions that are integrally formed with said central body; wherein relative movements between the central body and the two opposite end portions are prevented, and wherein the single vane is one piece, is smoothly continuous in form and all portions making up the whole of the vane are inseparable; said end portions substantially sliding along the side wall of said vacuum chamber; each of said end portions of said single vane comprises two opposite surfaces symmetrical with respect to a longitudinal axis of said single vane and shaped to have a bend radius substantially equal to that of a part of said side wall, when said single vane is in at least one reference operating position, wherein said part is shaped as a circumferential arc having a predetermined radius; wherein said single vane is free to slide in a direction passing through the rotation axis of said rotor, the external circumference of said rotor is tangential to the side wall of the chamber along a tangential line parallel to the rotation axis of the rotor, wherein one of said two opposite surfaces has a respective curvature centre that is different from the curvature centre of the other of said two opposite surfaces; wherein said at least one reference operating position is defined at a configuration of maximum stress of the end portions of said single vane against the side wall of the chamber, said configuration of maximum stress being defined at zones of the chamber which are around the position wherein the longitudinal axis of the vane is at right angles with respect to the plane formed by the rotor rotation axis and a tangential line of the external circumference of the rotor with the side wall of the chamber, said tangential line being parallel to the rotor rotation axis.

Description

(1) Further characteristics and advantages of the present invention will be made more apparent from the following detailed description of some preferred embodiments thereof, with reference to the attached drawings, provided without any limiting purpose and only by way of illustration. In these drawings:

(2) FIG. 1 is a schematic plane view seen from above of a single-vane vacuum pump according to prior art, without the upper cover to show the chamber of the stator;

(3) FIG. 2 is a schematic plane view seen from above, and in enlarged scale, of the vane included in the vacuum pump shown in FIG. 1;

(4) FIG. 3 is a schematic plane view seen from above of a single-vane vacuum pump according to the present invention, without the upper cover to show the chamber of the stator;

(5) FIG. 4 is a schematic plane view seen from above, and in enlarged scale, of the vane included in the vacuum pump shown in FIG. 3;

(6) FIG. 5 is a schematic plane view seen from above of a further embodiment of a single-vane vacuum pump according to the present invention, without the upper cover to show the chamber of the stator;

(7) FIG. 6 is a schematic plane view seen from above, and in enlarged scale, of the vane included in the vacuum pump shown in FIG. 5.

(8) With initial reference to FIG. 1, a vacuum pump is shown, in particular a single-vane vacuum pump for a motor vehicle engine, according to the prior art and identified by the reference numeral 10.

(9) The vacuum pump 10 comprises a stator 12 inside which a chamber 14 is defined. The chamber 14 has a side wall 16 whose transversal section has a predetermined shape.

(10) A rotor 18 is mounted inside the chamber 14. The rotor 18 is capable to rotate around a rotation axis (in FIG. 1, this is illustrated by the point O) parallel to the side wall 16.

(11) A vane 20 is mounted on the rotor 18 so that it is free to slide in a direction at right angles with respect to the rotation axis (O) of rotor 18. The vane 20 has a predetermined length L and two opposite end portions 22a and 22b which, during the operation of the vacuum pump 10, substantially slide on the side wall 16 of the chamber 14.

(12) As shown in FIG. 2, in the prior art the opposite end portions 22a and 22b of the vane have a semicircumferential shape or profile in the longitudinal section, with a radius R1 substantially equal to the thickness S of the vane 20, the thickness S being measured at the point of the central body 22c of vane 20.

(13) In the example shown in FIG. 1, the vane 20 is free to slide in a direction passing through the rotation axis (O) of said rotor 18, the external circumference CE of the rotor 18 is tangential to the side wall 16 of the chamber 14 along a tangential line (in FIG. 1, this is illustrated by the point T), parallel to the rotation axis (O) of the rotor 18, and the transversal section of the side wall 16 comprises a part shaped as an arc of circumference with a predetermined radius R2.

(14) In particular, an operational configuration of the vacuum pump 10 is illustrated wherein the vane 20 is positioned with the longitudinal axis X at right angles with respect to the plane defined by the rotation axis (O) of the rotor 18 and by said tangential line (T).

(15) In this position, the longitudinal axis X intersects the side wall 16 at the points A and B: the distance between the points A and B defines a theoretical length LT of the vane 20.

(16) Points A and B are the end points of the aforesaid arc of circumference of radius R2, and this arc of circumference passes through the tangential line (T). Furthermore, the centre point O1 of the arc of circumference of radius R2 is set on the plane defined by the rotation axis (O) of the rotor 18 and said tangential line (T).

(17) The remaining part of the transversal section of the side wall 16 is the geometrical locus of the points generated by point B when rotor 18 is rotated in a clockwise direction, thus moving point A along the aforesaid arc of circumference of radius R2, the distance between the points A and B being kept constant.

(18) Thus, the transversal section of the side wall 16 has a substantially elliptical shape. The end portions 22a and 22b intersect the longitudinal axis X of the vane 20 at the points A1 and B1, the distance between points A1 and B1 being the actual length L of the vane 20, said length L being less than the theoretical length LT of the vane 20, as illustrated in FIG. 1. In particular, in the prior art, quite a considerable difference exists between the theoretical length LT and the length L, approximately 0.5-07 mm, for example.

(19) FIG. 3 shows a single-vane vacuum pump according to the present invention, that is identified by the reference numeral 110.

(20) All structural elements identical or equivalent from a functional point of view to those of the vacuum pump 10 of the prior art described above with reference to FIG. 1 will be assigned the same reference numerals and will not be described any further.

(21) In particular, the vacuum pump 110 differs from the vacuum pump 10 in that a different vane is provided, identified by reference numeral 120, that replaces the vane 20 of the prior art. FIG. 4 shows said vane 120 in more detail.

(22) The vane 120 is mounted on the rotor 18 and is free to slide in a direction at right angles with respect to the rotation axis (O) of the rotor 18, said vane 120 having a predetermined length L2, a predetermined thickness S (measured at the central body 122c of the vane 120 and in the example illustrated, equal to the thickness S of the vane 20) and two opposite end portions 122a and 122b that in operation substantially slide wall 16 of the chamber 14. Like vane 20, vane 120 is comprised of a central body 122c and two end portions 122a and 122b that are integrally formed with each other. As for vane 120 being integrally formed, which is seen in FIGS. 3 and 4, the vane 120 is one piece that is smoothly continuous in form and that all (i.e., 122a, 122b, and 122c) making up the whole of the vane are inseparable.

(23) In accordance with the present invention, the longitudinal section of at least one of said end portions 122a and 122b (in FIGS. 3 and 4, both said end portions) of the vane 120 comprise at least one part 124 having a bend radius R3 substantially equal to a part 126 of the transversal section of the side wall 16 of the chamber 14 when the vane 120 is in one reference operating position, such as that shown in FIG. 3.

(24) The following description will explain more clearly that said reference operating position is defined at the configuration of maximum stress of the end portions 122a and 122b of the vane 120 against the side wall 16 of the chamber 14, or in other words the configuration where the force of inertia and the centrifugal force of vane 120 have the greatest effect.

(25) In the preferred embodiment of the invention, shown in FIG. 3, the vane 120 is free to slide in a direction passing through rotation axis (O) of the rotor 18, the external circumference CE of the rotor 18 is tangential to side wall 16 of the chamber 14 along one tangential line (in FIG. 3, this is shown by point T), parallel to the rotation axis (O) of the rotor 18, and the transversal section of the side wall 16 comprises a part shaped as an arc of circumference with a predetermined radius R2.

(26) In accordance with the present invention, the longitudinal section of each of the end portions 122a and 122b of the vane 120 comprises two opposite parts 124, symmetrical with respect to the longitudinal axis X of the vane 120 and having respective bend radii R3 substantially equal to the aforesaid predetermined radius R2.

(27) In particular, parts 124 of the vane 120 are shaped so thatduring the rotor 18 rotationthey are each time substantially in contact with the side wall 16 of the chamber 14 when the longitudinal axis X of the vane 120 is at right angles with respect to the plane defined by the rotation axis (O) of the rotor 18 and by said tangential line (T): in this manner, the end portions 122a and 122b of the vane 120 slide along the side wall 16 of the chamber 14 with large contact surface areas in the operational zones wherein the vane 120 is subjected to most stress.

(28) In the example shown in FIG. 3, the operational zones wherein the vane 120 is most subjected to stress are precisely those around the position wherein the longitudinal axis X of the vane 120 is at right angles with respect to the plane defined by the rotation axis (O) of the rotor 18 and by the aforesaid tangential line (T).

(29) In particular, in the example shown in FIG. 3, the effects of the force of inertia and of the centrifugal force of the vane 120 are at a maximum at an angle 1 equal to about 30, the angle 1 being that wherein, during clockwise rotation of the rotor 18, the vane 120 precedes by about 30 the position wherein the longitudinal axis X of the vane 120 is at right angles with respect to the plane defined by the rotation axis (O) of the rotor 18 and by said tangential line (T). The operational zones wherein the vane 120 is most subjected to stress are approximately those between the aforesaid angle 1 and the angle 2 equal to about 15, the angle 2 being that wherein, during clockwise rotation of the rotor 18 the vane 120 follows by about 15 the position wherein the longitudinal axis X of the vane 120 is at right angles with respect to the plane defined by the rotation axis (O) of the rotor 18 and by said tangential line (T).

(30) As shown in FIG. 3, the two parts 124 of each of the end portions 122a and 122b have a substantially pointed shape, due to the fact that they are oriented to converge towards the end of the vane.

(31) Preferably, said opposite parts 124 of the longitudinal section of each of said end portions 122a and 122b of said vane 120 are radiused, at the longitudinal axis X of the vane 120, by a circumferential arc 128.

(32) In particular, the diameter D of the ideal circumference CI (shown by the dotted line in FIG. 4) that defines said arc of circumference 128 between said opposite parts 124, is smaller than the thickness S of the vane 120. Preferably, the ratio between the diameter D of the ideal circumference CI that defines said arc of circumference 128 and the thickness S of the vane ranges between and .

(33) Advantageously, with the aforesaid values, the Applicant observed that it is possible to obtain vanes 120 having a length L2 that varies very little from the theoretical length LT described previously with reference to FIG. 1 (it should be noted that the theoretical length LT of the vane 20 in FIG. 1 is equal to the theoretical length LT of the vane 120 in FIG. 3 and the transversal section of the side wall 16 in FIG. 1 is equal to the transversal section of the side wall 16 in FIG. 3).

(34) In particular, the end portions 122a and 122b intersect the longitudinal axis X of the vane 120 at the points A2 and B2, the distance between the points A2 and B2 being the length L2 of the vane 120, said length L2 being less than the theoretical length LT of the vane 20, as shown in FIG. 3. Thanks to this invention, as can be observed when comparing FIGS. 1 and 3, drawn on the same scale, the difference between the theoretical length LT and length L2 is noticeably less than the difference between the theoretical length LT and the length L in FIG. 1, for example of 0.1 mm.

(35) The aforesaid reduced difference between the theoretical length LT and the length L2 provides the great advantage of drastically limiting the aforesaid damage (undulations formed by the removal of material) on the wall 16 of the chamber 14, provoked by the play between the vane 120 and wall 16 of the chamber 14, especially in those operational positions of the vane 120 wherein the force of inertia of the vane 120 substantially counterbalances the centrifugal force of the vane 120. In particular, in the example shown in FIG. 3, the aforesaid operational positions are roughly defined in an angular sector with angle 5 defined between an angle 3 and an angle 4, said angles 3 and 4 being respectively those wherein, during clockwise rotor 18 rotation, vane 120 follows by about 25 and about 55 the position wherein the longitudinal axis X of the vane 120 is at right angles with respect to the plane defined by the rotation axis (O) of the rotor 18 and by said tangential line (T).

(36) FIG. 5 shows a further embodiment of a single-vane vacuum pump according to the present invention, identified by the reference numeral 210.

(37) In FIG. 5, all structural elements identical or equivalent from a functional point of view to those of the vacuum pump 110 in FIG. 3 will be assigned the same reference numerals and will not be described any further.

(38) In particular, the vacuum pump 210 differs from the vacuum pump 110 because a different vane is provided, identified by reference numeral 220, that replaces the vane 120 of FIG. 4. FIG. 6 shows said vane 220 in greater detail.

(39) The vane 220 is mounted on rotor 18 and is free to slide in a direction at right angles with respect to the rotation axis (O) of the rotor 18, said vane 220 having a predetermined length L2, a predetermined thickness S (measured at the central body 222c of the vane 120 and, in the illustrated example, equal to the thickness S of the vane 120) and two opposite end portions 222a and 222b that, during operation of the vacuum pump 210, substantially slide along side wall 16 of the chamber 14.

(40) In accordance with this embodiment of the present invention, the longitudinal section of at least one of said end portions 222a and 222b (in FIGS. 5 and 6, both said end portions) of the vane 220 comprises a part 224 having a bend radius R3 substantially equal to the predetermined radius R2 of the part 126 of the transversal section of the side wall 16 of the chamber 14.

(41) Preferably, the two parts 224 of said end portions 222a and 222b are positioned on opposite sides with respect to the longitudinal axis X of said vane 220, that is the two curvature centres O1 and O2 of said parts 224 are symmetrical with respect to the longitudinal axis X of said vane 220.

(42) Each of the end portions 222a and 222b has, on the opposite side with respect to the longitudinal axis X of the respective part 224, a part 230 that is substantially parallel to the longitudinal axis X of said vane 220.

(43) The part 224 and the part 230 of each end portion 222a and 222b are radiused at the longitudinal axis X of the vane 220, by an arc of circumference 228, preferably of a size similar to the arc of circumference 128 of FIGS. 3 and 4.

(44) Obviously, those skilled in the art are able to apply numerous changes and variants to the single-vane vacuum pump for a motor vehicle engine and to the vane for a single-vane vacuum pump as described above, in order to satisfy specific and related requirements, while remaining within the scope of the present invention which will be defined in the following claims.

(45) For example, the shape of the transversal section of the chamber 14 could be different from that illustrated in the attached drawings and described above. In particular, the part of the side wall 16 between points A, T and B could be different from an arc of circumference; in this case, the radius R3 described above will be the bend radius that defines this part of side wall 16.