DESCRIPTION

A VACUUM PUMP HAVING A SINGLE VANE

BACKGROUND OF THE INVENTION

This invention concerns a vacuum pump having a single vane [in Ital- ian: monopaletta]. The object of the invention is to improve the performances of a vacuum pump. The invention is mainly intended for use in the automotive field, but it could also find applications in other fields.

In the automotive field, in general the vacuum pump is particularly intended to generate a depression in a front chamber of a servomotor for the braking assistance. The depression present in said servomotor allows generating a force that is needed for assisting the actuation of a braking system and producing a deceleration or stopping a vehicle. The vacuum pumps are mainly used on vehicles driven by a diesel engine, wherein no intake depression is available and a pump is needed for generating a depression, however they are also used on vehicles driven by a gasoline engine wherein an intake depression is available, when it is required not to depend from the intake depression for assisting the braking system.

There are known vacuum pumps that generate a depression by means of a single vane rotating inside a pump body. The vane pumps have the ad- vantage of producing an important flow and generating a noticeable depression, of the order of 0,133 Pa. Such a vacuum pump comprises a hollow cylindrical container forming a body, a cover, a single vane and a rotor. The cover closes the body and allows delimiting the inner space of the pump. Inside this vacuum pump, the single vane is arranged between the pump body and the pump cover and along a diameter of the pump body, in such a way that the single vane is allowed to circulate inside the body, and that it slides with its two end portions resting against a peripheral wall of the body. In this way, on the two sides of the single vane a first compartment and a second compartment are defined within the pump body. The single vane has a bottom face contacting the pump body and a top face contacting the pump cover.

Inside the pump body, a rotor is arranged for rotating around a rotation axis. The rotor is provided with a slit traversing the rotor along its diame-

ter. The single vane is housed within this slit, and the slit is so realized that the single vane can slide inside this slit along its longitudinal direction. Thus the single vane can be made to revolve around a rotation axis, by means of the rotor. This latter is driven by a rotary shaft. The rotary shaft (which is driven, for example, by an electric motor) is mounted through the cover that closes the pump body. The rotary shaft has teeth or protrusions which, when the cover is mounted onto the pump body, are inserted into recesses of the rotor in order to connect in rotation the rotary shaft to the rotor. When this connection has been made, the rotary shaft drives the rotor and drags the single vane in a revolution around the rotation axis of the rotor and of the single vane.

In order to generate the depression, a certain volume of fluid, in the practice air, can be sucked into the first pump compartment through a first duct made in the body, whereas the fluid volume present in the second com- partment can be expelled from the pump through a second duct also present in the body. The depression is generated in the following manner. When the pump is operating, due to the rotation of the rotor and the single vane an air volume is sucked into the first pump compartment through the first duct. Then the air volume is dragged within the first compartment by the rotating single vane, the first compartment takes the place formerly occupied by the second compartment, and the air contained in the first compartment is expelled from the pump through the second duct. Simultaneously the second compartment has taken the place of the first compartment and it is been filled with air through the first duct. Thus, in the volume from which air is sucked by the pump, a depression is established.

The conformations of the body and the cover are so chosen that the single vane is theoretically situated about contacting the body and the cover. However, in order to allow a free rotation of the single vane with respect to the body and the cover of the pump, it is needed that, on one side, some space is left free between the bottom face of the single vane and the pump body and, on the other side, some space is left free between the top face of the single vane and the pump cover. These spaces also allow preventing vibrations during the rotation of the component parts of the pump. Vibrations are produced by the cyclic rubbings between the vane and the body and cover of the pump.

However, some additional spaces are due to the different thermal expansion of the various parts, which often are manufactured of different materials. Some spaces also result from the working tolerances allowed in manufacturing the vanes and the pumps. If the resulting spaces are too important, the air volume present in one of the pump compartments can be dragged by the vane only in incomplete manner, and in part it can escape through the spaces towards the other compartment. The result is a reduction in the pump performance. These spaces can therefore be responsible for bad performances of the vacuum pump, that can then affect the vehicle braking, which will be carried out as much less effectively.

In order to fill these spaces it is possible to introduce oil inside the pump. Thus the oil establishes a seal between a vane face and the pump body and between the other vane face and the pump cover. In this way the oil can ensure a mutual seal between the two compartments situated at the oppo- site sides of the single vane.

However it may happen that the oil quantity is insufficient for filling the spaces, particularly when one of the component parts of the pump undergoes a too important deformation, or when inside the pump there is a not sufficient oil quantity. Such oil shortage cannot be easily foreseen by the driver. Therefore there are needed a special maintenance or an expensive device for supplying oil or grease to the pump.

SUMMARY OF THE INVENTION

In order to improve the performances of such a vacuum pump and to find a remedy for a possible shortage of oil, the invention proposes to practi- cally eliminate the said spaces. More in particular, the invention proposes to eliminate or at least to reduce these spaces by means of at least one flexible seal element applied onto at least one of the faces of the single vane. This flexible element can be maintained on the single vane, for example, by side walls of the vane. According to an example, the flexible element may have two flexible arms resting against a projection formed on at least one of the vane faces.

The flexible element according to the invention comprises a face intended to be inserted into one of the vane faces and another face intended to

contact the pump body or the pump cover. In this way the flexible element fills at least one space between a vane face and the pump body, or between another vane face and the pump cover. Thanks to its flexibility, this flexible element can adapt itself to the possible deformations of the various parts forming the vacuum pump, for example when a thermal expansion of the pump body and/or the pump cover takes place. According to an example, the flexibility of this element is due to the element comprising two arms that cover a face of the flexible element. These two arms delimit a space between the arms themselves and the corresponding face of the flexible element. Said two arms can be flattened in a reversible manner against a projection formed on a vane face. They go to rest against the top surface of the flexible element when this flexible element is inserted onto a vane face. Thus, the flexible element can plunge inward the single vane or even project from the single vane, in order to adapt itself to the various surrounding stresses. When such a flexible element is installed on one side of the single vane, it is not needed that another flexible element is installed on the opposite side of the single vane in order to fill the space that there is present. In effect, due to the presence of a single flexible element, the single vane is displaced towards the opposite wall of the pump. This other wall is a part of the pump cover, if the flexible element is put to contact the pump body, or vice- versa.

Therefore, the subject of the invention is a vacuum pump of the single vane type, comprising a single vane having a top face and a bottom face and circulating inside the pump, characterized in that the single vane includes a flexible element at least partially covering at least one of said faces of the single vane.

Preferably, the flexible element of the single vane is made of rubber, and it has a top face intended to be inserted into at least one of the faces of the single vane, and a bottom face intended to face a body or a cover of the pump. The top face of the flexible element is preferably provided with two arms that are located at the same height.

Advantageously, the single vane is provided on at least one of its faces with at least one cavity intended to receive the flexible element and having a

^' projection situated in correspondence of the end portions of the arms of the flexible element, and preferably located middle the length of the single vane.

The flexible element may include along its length two beveled end portions complementary to two beveled end portions provided on at least one of the faces of the single vane. Preferably, the flexible element entirely covers one of the faces of the single vane.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood by reading the following description and considering the annexed drawings, which have only an indicative purpose and do in no way limit the invention. In the drawings:

Figure 1 shows a diagrammatic view from above of a vacuum pump with a single vane whose cover has been removed.

Figures 2a to 2c show views of a single vane according to the known art preceding the invention.

Figures 3a to 3d show corresponding views of a single vane according to the invention. Figures 4 and 5 show the cross sections of two different modifications of the single vane according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the drawings, Figure 1 shows a vacuum pump 1 with a single vane, intended for example for a vehicle, which comprises a body 2, a single vane 3 and a rotor 4. Pump 1 is suitable for receiving a single vane according to the invention. The body 2 of pump 1 is a cylindrical container having, with respect to the rotor center C ₁ uniform inner diameters 5, and delimited by a wall 6. Inside this wall 6 open a first duct 7 and a second duct 8, both made in the wall 6 of body 2. The first duct 7 is intended to allow enter- ing an air volume inside the pump 1 , and the second duct 8 is intended to allows expelling from the pump 1 this air volume. The ducts 7 and 8 are situated, with respect to the position of rotor 4, in such a way that the two ducts 7 and 8 are always mutually separated by the vane 3 and by the rotor 4; in particular, they are separated when expelling the air through the second duct 8. Body 2 is closed by a cover (not represented in Figure 1 ) which supports a rotary shaft (shown in phantom at 0) intended to rotate the rotor 4 and the single vane 3. Rotor 4 has a hollow central portion provided, at both sides

with respect to the single vane 3, with some recesses 4 ¹ suitable for receiving a rotation key, which is solid with the rotary shaft 0 carried by the pump cover. Figures 2a to 2c and the description thereof refer to a single vane 3 according to the known art preceding this invention. Figure 2a shows the single vane 3 viewed in profile from a plane perpendicular to the plane of Figure 1 and to the longitudinal direction of vane 3. Figure 2b shows the single vane 3 viewed from above (as in Figure 1 ) or even from below. Figure 2c shows a longitudinal section of the single vane 3 taken along direction A-A of Figure 2b. The single vane 3, which has an elongated shape, is overall arranged according to a diameter 5 of body 2. Between the single vane 3 and body 2 there is present a space 9 emerging from the need to provide some clearance at least between these two parts, according to Figure 2c. The reason of this space or clearance has been stated in the preamble. The single vane 3 has the shape of a rectangular cylinder with semicircular end portions. It has a width 10 (Figure 2b), a length 11 and a height

12 (Figures 2c and 2b). The length 11 of the single vane 3 corresponds to the diameters 5 of body 2. The single vane 3 is so arranged that its height 12 is perpendicular to the bottom plane 17 of body 2, which is perpendicular to the wall 6. At the opposite ends of the height 12, the single vane 3 has a top face

13 and a bottom face 14. The top face 13 is intended to face the cover of the vacuum pump 1. The bottom face 14 is intended to rest against the body 2 of the vacuum pump 1.

At both ends of its length 11 (figure 2c) the single vane 3 has end por- tions 15 and 16 extending on the entire height 12 of the single vane 3. The single vane 3 has, near its end portions 15 and 16, two bores 18 and 19 traversing the entire height of the single vane 3 (figures 2b and 2c); these bores 18 and 19 allow circulating sealing oil inside the pump 1. This single vane 3 is intended to slide through rotor 4 (Figure 1 ). Rotor 4 has a circular cylindrical shape (Figure 1 ); it has a diameter 20 and a height (not visible in Figure 1 ) that corresponds at the most to the height of the single vane 3. This rotor 4 has a slit 21 diametrically traversing rotor 4. This slit 21 , which in this case has the shape of a upturned U, is carried out in such a way that the single vane 3 can slide along its entire length 11 within the slit 21 of rotor 4, by resting on the plane 17. Rotor 4, driven by means of the

rotary shaft O ₁ imparts to the single vane 3 a rotational movement. As already stated, the rotary shaft is mounted in the pump cover, and it allows driving the rotor 4 and the single vane 3.

According to the invention (Figures 3a to 3c), the single vane 3 in- eludes a flexible element 22 that is applied onto at least one of the faces 13 and 14 of the single vane 3 and covers at least in part the face of the single vane 3 to which it is applied. For example, the flexible element 22 may be applied onto the bottom face 14 of the single vane 3, which is intended to contact the pump body 2. The element 22 is preferably made of rubber, whereby the element 22 is flexible and it can adapt itself to possible deformations of the bottom 17.

According to the invention, the flexible element 22 has a top face 23 and a bottom face 24. The top face 23 is intended to be inserted into at least one of the faces 13 and 14 of the single vane 3. The bottom face 24 is in- tended to be kept in contact with the body 2 and/or the cover of pump 1. The flexible element 22 has a length 25, and on both sides of its length 25 the flexible element 22 has two end portions 26 and 27. On its top face 23, near each of the end portions 26 and 27, the flexible element 22 has two extensions or arms 28 and 29. These two arms 28 and 29 extend from the beginning in a direction perpendicular to the top face 23, then they are curved in such a way that these two arms 28 and 29 are disposed mutually parallel, facing the one another. The two arms 28 and 29 are situated at the same height and extend parallel to the top face 23. By curving and mutually facing, the two arms 28 and 29 delimit a space 30 among them and the face 23. This space 30 con- fers to the arms 28 and 29 the ability to be bent towards the top surface 23 of the flexible element 22. In order to be inserted in a stable manner inside the single vane 3, the two end portions 26 and 27 of the flexible element 22 are so shaped as to provide a shoulder 31 of the flexible element 22 on the side facing the top face 23. This shoulder 31 prevents any longitudinal sliding of the flexible element 22 with respect to the single vane 3.

The length 25 of the flexible element 22 is such that, according to an example, it covers only a surface portion of the single vane 3 (Figures 3b and 3c). The uncovered portion corresponds to the regions of the single vane 3 located between the end portion 26 of the flexible element and the end portion 15 of the single vane 3 and between the end portion 27 of the flexible element

and the end portion 16 of the single vane 3 (Figure 3c).

As a modification, the end portions 26 and 27 can be located in correspondence of the end portions 15 and 16 of the single vane 3 (Figures 4 and 5), and then the flexible element entirely covers one of the faces of the single vane 3.

According to the modification shown in Figure 4, the end portions 26 and 27 are beveled. Then the thus shaped end portions 26 and 27 can be entirely inserted into the two end portions 15 and 16, also beveled, formed on at least one of the faces 13 and 14 of the single vane 3. According to the invention, in order that the flexible element can be inserted into the bottom face 13 of the single vane 3, this latter is hollowed on at least one of its faces 13 and 14, thus forming a cavity 32 (Figure 3c). This cavity 32 corresponds at least to the size of a portion of the flexible element 22 that is intended to be inserted. Near the center of the cavity 32, a portion of the single vane 3 forms a projection 33, which preferably is located middle the length 11 of the single vane 3 according to the invention.

When the flexible element 22 is inserted into one of the hollowed faces (for example the face 14) of the single vane 3, the arms 28 and 29 come to rest against the projection 33 (Figure 3c). The rigidity of the arms 28 and 29 prevents the flexible element 22 to be entirely inserted into the cavity 32. Therefore the flexible element 22 projects from the surface of the face 14 of the single vane 3. In order to entirely insert the flexible element, it is sufficient to apply a pressure to the bottom face 24 of the flexible element 22. Then both arms 28 and 29 are forced to flatten against the surface 23, whereby the flexible element 22 can be entirely inserted into the cavity 32 of the single vane 3 (Figure 3d). In this manner, when the single vane 3 is applied with its flexible element 22 against the body 2 (or against the pump cover), the space 9 present between the bottom face 14 of the single vane 3 and the body 2 (or between the top face 13 of the single vane 3 and the cover) is reduced or practically suppressed because the flexible element 22 projects from the single vane 3.

Due to the force exerted by the arms 28 and 29 and to the reaction opposed by plane 17 to the flexible element 22, the single vane 3 is pushed towards the pump cover in order to ensure at the same time a better seal also on the side opposite the flexible element.

In order to prevent the flexible element to escape from its inserted position during the rotation of the single vane 3, this latter is provided with rigid shoulders 34 and 35 (Figure 3a) that guide the displacements. As a modification, the U-shaped slit of rotor 4 can be provided with shoulders for the same purpose.

The described flexible element 22 having the arms 28 and 29 is preferred due to the easy of its manufacture. However the arms 28 and 29 could also be replaced by springs resting on one side against the single vane 3 (inside the cavity 32) and on the opposite side against the surface 32 of the flexible element 22.