ITTO20100945A1 - PUMP FOR VACUUM, IN PARTICULAR FOR VEHICLES - Google Patents

Description

VACUUM PUMP, ESPECIALLY FOR MOTOR VEHICLES

Technical sector

The present invention refers to vacuum pumps, in particular for the automotive sector.

Known technique

Several organs in an automobile require a vacuum to operate. An example is the brake booster, which is a pneumatic servo motor that uses vacuum as an energy source. In petrol-powered engines, depression can be generated in the intake manifold thanks to the choking of the inlet created by the throttle valve when the accelerator is released. In diesel engines, since there is no partialization of the air intake, the depression is instead obtained through a vacuum pump. Currently, however, to improve combustion and reduce harmful emissions, many petrol-fueled engines have a reduced vacuum level at the manifold, no longer sufficient to power the brake booster, and therefore a vacuum pump is used on these engines as well.

After the vacuum has been generated, the activation of the vacuum pump serves to compensate for the vacuum consumption by the user parts and the losses. Since these organs are not permanently active and the losses are limited, there are periods of time, even of considerable duration, during which the operation of the pump is not necessary. However, normally, vacuum pumps in motor vehicles are permanently driven by the engine. This results in unnecessary power absorption and a certain increase in fuel consumption, as well as unnecessary wear of the pump components.

Activating the vacuum pump only when its operation is necessary would reduce the total power required from the engine and therefore fuel consumption and exhaust gas emissions, as well as reduce wear on the pump components. and therefore to increase its useful life. Furthermore, to make the pump components, alternative, less expensive materials could be chosen, given the lower stresses to which they are subjected.

For this purpose, devices have been proposed to mechanically connect / disconnect the pump to / from the motor. Examples are described in DE 198 54 243 and WO 2006/010528. These devices have some drawbacks, such as: high costs in relation to benefits; high axial dimensions; considerable reduction of the usable vacuum difference, due to the intervention range of the pressure sensor; it is necessary to use a sensor of the absolute pressure type, which is considerably expensive, in order not to be affected by the influence of the altitude at which the vehicle operates.

US 4,428,195 discloses a vacuum pump for a vacuum brake booster, permanently connected to the vehicle engine and activated and deactivated according to the engine operating speed. The pump has a vane rotor which rotates eccentrically in a chamber of the pump body. The blades are coupled to a respective counterweight which, when the engine speed is below a certain threshold, keeps the blade in contact with the chamber wall thanks to the thrust exerted by a spring; when the number of revolutions exceeds the threshold, the centrifugal force overcomes the force exerted by the spring and the counterweight retracts the vane by removing it from engagement with the wall and deactivating the pump.

This solution obviates the drawbacks of pumps with mechanical coupling / decoupling devices to / from the motor, but does not take into account the fact that the need to create a certain level of vacuum can arise even when the number of revolutions is still quite high: in these conditions, failure to activate the pump could create risky situations or damage to the organ that uses the vacuum. Furthermore, the presence of the counterweight and the contrast spring makes the structure somewhat complicated and therefore expensive and more subject to failures (for example, breakage of the spring).

Description of the invention

The present invention has the purpose of providing a vacuum pump which overcomes the above problems.

According to the invention, this is achieved with a rotary vacuum pump as claimed in claims 1 - 9.

More precisely, the invention provides a pump in which the rotor comprises at least one pumping element which is able to move in a first direction to activate the pump in the event of deceleration of a motor driving it, or in a second direction to deactivate the pump in case of acceleration.

In particular, the pump allows to generate depression in conjunction with deceleration and to recover kinetic energy during the deceleration phase of the motor.

The invention also provides a control method for the aforementioned pump, as claimed in claim 10.

Brief description of the drawings

In the following, some preferred embodiments will be described, with reference to the attached drawings in which:

- fig. 1 is a schematic radial section of a first embodiment of the invention;

- figures 2A - 2D are illustrative diagrams of the operation of the pump of fig.1; and - fig. 3 is a schematic radial section of a second embodiment of the invention.

Description of preferred embodiments

With reference to Figure 1, a rotary vacuum pump 1 according to a first embodiment of the invention comprises a hollow cylindrical body 2, inside which rotor 3 rotates eccentrically, also cylindrical in shape, whose wall external 3A is tangent to the internal surface 2A of the hollow body 2 along a line of fixed tangency 4. In this example, rotor 3 rotates clockwise (arrow R1) and A indicates the axis of rotation. On the two sides of the tangency line 4 the intake and exhaust ports 6 and 7 open, respectively to the left and to the right of this line, with the indicated direction of rotation.

Advantageously, the rotor 3 is hollow and has a central bulkhead 5 connected to the inner wall 3B of the rotor 3 by radial baffles 9, e.g. ex. two baffles arranged in a diametrical plane of the rotor 3, which divide the internal cavity of the rotor 3 into a plurality of compartments 8. The baffles 9 can have an axial extension less than that of the rotor 3 and of the bulkhead 5 to allow communication between compartments 8 adjacent.

Advantageously, the rotor 3 can be made of plastic, with molding technology, for example by injection.

In the central bulkhead 5 a pair of radial cavities or slits 10 is formed which extend axially along the rotor and are symmetrical with respect to a plane S passing through the axis A. The cavities 10 open at one end on the external surface 3A of the rotor and are closed at the opposite end. A vane 11 is housed in each cavity 10 which can slide radially between a first position, which it assumes when the pump 1 is in operation and in which its front end (with reference to the direction of rotation) is in contact with the internal surface 2A of the body 2, and a second position, which it assumes when the pump 1 is not in operation and in which it is retracted into the cavity 10, so that its front end is not in contact with the surface 2A . This second position is indicated with dashed lines for the left flipper. The two positions will also be called "active position" and respectively "inactive position". The vanes are housed in the cavities 11 with sufficient clearance to allow them to slide, taking into account manufacturing tolerances. The sliding of the vanes will be facilitated by lubricating oil, eg. ex. powered directly by the engine.

Advantageously, in the inactive position, the center of gravity B of the blade is located between the central point of the cavity 10 and the bottom of the same.

In the active position, the vanes 11 will define in the cavity of the body 2 the intake and exhaust chambers communicating with the ports 6, 7.

The vanes 11 pass into the inactive position during the acceleration phases of the engine and pass into the active position in the event of deceleration. In case of engine rotation at constant speed, the vanes can be in active or inactive position, depending on whether the constant speed regime is reached after deceleration or acceleration.

The cavities 10 are connected to each other by a passage 12 which opens at or near the bottom of the cavities themselves. Always in correspondence with or near the bottom, the cavities 10 communicate with the adjacent compartments 8 through passages 13. The communication of the cavities 10 with each other and with the compartments 8 allows you to completely discharge any air present in the cavities and therefore not obstruct the retraction of the vanes 11, and, together with the communication between the compartments 8, allows the passage of the lubricating oil.

The cavities 10 and the vanes 11 can have an arched shape in section as shown in the figure, with the concavity facing forward with reference to the direction of rotation, or be rectilinear.

The operation of the pump will now be explained with reference to the schematic figures 2A - 2D, where for simplicity only one cavity 10 is represented, with the blade 11 indicated simply by a line, continuous for the active position and in pieces for the inactive one. Figures 2A - 2C show the forces acting on the vane 11 respectively in conditions of constant speed, acceleration and deceleration, and illustrate a situation in which the open end of the cavity 10 is at the top, so that in the active position the vane 11 protrudes into the cavity of body 2. FIG. 2D shows the forces acting on the vane 11 under acceleration conditions when the opening of the cavity 10 is substantially in correspondence with the tangency line 4, so that the vane 11 has re-entered the cavity 10 even in the active condition. The figures are intended to show only the direction of the forces, and the length of the vectors is not to be considered representative of the actual intensity of the forces themselves.

During the rotation of the rotor, the vane 11 is obviously subjected to the centrifugal force, which is directed according to the joining the center of rotation A of the rotor 3 with the center of gravity of the vane 11. With B1, B2 the center of gravity is indicated in the position active and inactive respectively of the vane, and with F1, F2 the centrifugal force in the two conditions. The force F1, F2 has a component normal to the vane 11 in the center of gravity, indicated by F1N, F2N, and a tangential component F1T, F2T. The normal component, which in the position illustrated in Fig. 2D is the only component since the centrifugal force is normal to the blade, tends to push the blade 11 against the wall of the cavity 10 and gives rise to a friction force F1N <.> Î1⁄4, F2N <.> Î1⁄4 (where Î1⁄4 is the friction coefficient), tangentially directed. The frictional force is not indicated for simplicity and clarity of representation. The tangential component, purified by the frictional force F1N <.> Î1⁄4, F2N <.> Î1⁄4, can cause the displacement of the blade 11.

If the rotor 3 rotates at a constant speed, the blade 11 is subjected to the action of the centrifugal force alone. If the vane 11 is in the active position (i.e. the constant speed has been reached after a deceleration), the tangential component F1T of the centrifugal force tends to cause it to slide outwards and therefore the vane remains in the active position. This happens whatever the position of the rotor in the cycle (compare figures 2A and 2D). Similarly, if the vane 11 is in the inactive position (i.e. the constant speed has been reached after an acceleration), the tangential component F2T will tend to push the vane 11 towards the bottom of the cavity 10, as long as the center of gravity B2 is between the center of the cavity and the bottom.

If an acceleration occurs (Figures 2B, 2D), a tangential force indicated with F3 (in active condition) and F4 (in inactive condition) is also applied to the vane 11, normal respectively to F1, F2. Also F3, F4 have a "normal" component F3N, F4N, which gives rise to a frictional force F3N <.> Î1⁄4, F4N <.> Î1⁄4 (also not represented) which is added to the force F1N < .> Î1⁄4, F2N <.> Î1⁄4, and a "tangential" component F3T, F4T. As for the centrifugal force, only the "tangential" component (which in the position illustrated in Fig.2D is the only component) can cause the displacement of the blade against the forces of friction. If the vane is in active condition, the F3T component is directed in the opposite direction to F1T and the vane will reenter its seat if F3T> F1T + (F1N + F3N) <.> Î1⁄4. The skilled in the art has no problem choosing materials, surface treatments, etc. so that the condition is always satisfied. If the vane is already in an inactive condition, F2T and F4T both tend to push the vane towards the bottom of the seat 10, thus maintaining the existing condition.

If a deceleration occurs (fig.2C), the tangential force F5, F6 is directed in the opposite direction to F3, F4, and therefore clearly its tangential component F5T, F6T will tend to make the blade 11 come out of its seat (always against the frictional forces) by activating the pump.

In fig. 3 illustrates a second embodiment of the pump according to the invention, indicated with 101. Elements corresponding to those of fig.1 have been indicated with corresponding references, increased by 100.

In this embodiment, the central bulkhead 105 is constituted by a hollow cylindrical element, coaxial to the rotor 103, and has a diametrical partition 120, for example substantially perpendicular to the septa 109. With the illustrated arrangement, two pairs of compartments 108 are formed. , an "external" pair between the external surface of the bulkhead 105 and the internal surface 103B of the rotor, and an "internal" pair in the cavity of the bulkhead 105. Also in this embodiment, the baffles 109 can have axial extension less than that of the rotor 103 and bulkhead 105 to allow communication between the external compartments 108.

The vanes 111, which in this embodiment are flat, are arranged on the two sides of the partition 120 and slide in slits 110 which cross the walls of both the element 105 and the rotor 103 at least at one end of the partition 120, and preferably at both ends. The through slits 110 have similar functions to the passages 12, 13 of fig. 1. As in the previous embodiment, the vanes 111 are designed to move to the inactive position in the event of acceleration of the engine and to the active position in the event of deceleration.

Each vane 111 has on the front face (with reference to the direction of rotation of the rotor, which in this embodiment has been assumed to be the counterclockwise direction, as indicated by the arrow R2), near its front end intended to engage with the wall 102A of the body 102, a recess 121 in which an end of an anchoring element 122 can engage, designed to hold the blade in the retracted position. Advantageously, a similar recess is also provided on the rear face of the blade, near the rear end, and both ends of the elements 122 are shaped so as to be able to engage with the recesses 121: this facilitates error-proof assembly .

The two anchoring elements 122, identical to each other, are slidably mounted in a respective external compartment 108, in the area delimited by the front face of the blade 111 and by the closest partition 109, and are arranged symmetrically. The elements 122 have an arched shape, corresponding to the shape of the compartments, and can have a substantially circular section.

In the event of acceleration, due to inertia, the anchoring elements 122 will be in contact with the surface of the vanes 111 and, when these have returned to the rotor 103, they will engage with the recesses 121 blocking the vanes 111. In the event of deceleration, the anchoring elements 122, again due to inertia, will disengage from the recesses 121 and the vanes 111 will be free to exit the rotor due to the centrifugal force, coming into contact with the internal surface 102A of the body 102. As before, at constant speed, the vanes will remain in the inactive position (and therefore blocked by the anchoring elements 122), or in the active position, depending on whether the constant speed has been reached after an acceleration or a deceleration.

Note that in fig. 3 one of the vanes (the one at the top) is shown in an active condition, while the other is shown in an inactive condition, to show an anchoring element 122 engaged with the respective recess 121.

It is evident that the invention achieves the indicated aim. The fact that pump activation depends on deceleration and not on speed eliminates potential risk or damage situations. Furthermore, to bring the pump into an active or inactive condition, the forces present due to rotation are directly exploited: there is therefore no need for counterweights and springs, so that the structure is simpler, less expensive and less subject to possible failures.

Note that acceleration / deceleration dependent operation mimics the conditions created by a conventional gasoline engine without a pump.

The invention also implements a method for controlling a vacuum pump, for automatically activating or deactivating the pump in the presence of first or respectively second operating conditions of a motor for driving it. This process includes the following steps:

- in the event of angular acceleration of the rotor 3, 103, make the vanes 11, 111 retract into their respective seats 10, 110 and, if the anchoring elements 122 are provided, hold the vanes with them in the retracted position;

- in the event of angular deceleration of the rotor 3, 103, make the anchoring elements 122, if provided, disengage from the vanes 11, 111, and make them come out of the seats 10, 110 to bring the front end into contact with the internal wall of the body 2, 102. It is clear that what has been described is given only by way of non-limiting example, and that variations and modifications are possible without departing from the scope of the invention, as defined in the following claims.

Thus, for example, the pump can have only one vane. In this case, when the pump is running, it sucks and compresses, at each revolution, a volume of fluid equal to that between the internal surface of the body and the external surface of the rotor, decreased by that of the vane. The realization with two vanes is however preferable since, with the same overall dimensions, it allows to double the displacement, since the two phases are separate.

Furthermore, in fig. 3, vanes 111 are shown provided with a recess 121 on each face, at opposite ends. It is also possible to provide opposite recesses 121 on both faces and at both ends of each blade: in this way, the blades 111 can be mounted in any orientation. Furthermore, the anchoring elements 122 could be mounted at one end of respective articulated arms or spokes, at the opposite end, in correspondence with the axis of rotation A of the rotor 103. The elements 122, instead of having a circular section, can also be configured to engage each one with an elongated recess or with a plurality of recesses, eg. ex. aligned: the configuration must be such that the axial extension of the elements 122 is less than that of the vanes 111, to allow the passage of air / oil through the slits 110.

Advantageously, the pumps as illustrated in the embodiments considered to be preferable can also be used applied to electric control motors. In these embodiments it is foreseeable that, in the face of a deceleration or acceleration of the thermal or electric engine that drives the vehicle, for example a hybrid vehicle, the deceleration or acceleration is transmitted either directly or a suitable signal is sent to the electric control motor that activates a corresponding deceleration or acceleration of the pump.

Furthermore, the invention applies to any rotary pump in which a pumping element moves in the rotor between an active position and an inactive position.

Claims (10)

CLAIMS 1. Rotary vacuum pump, comprising: a hollow body (2; 102) with a substantially cylindrical internal cavity and a rotor (3; 103) adapted to rotate eccentrically in the cavity, fluid-tight with an internal surface (2A, 102A ) of the body (2; 102) along a line of constant tangency (4; 104) placed between an intake port (6; 106) and an exhaust port (7; 107) of the pump (1; 101), the rotor (3; 103) comprising at least one pumping element (11, 111) adapted to move in the rotor in a first or respectively a second direction to activate or deactivate the pump (1; 101); characterized in that the at least one pumping element (11, 111) is able to move in the first direction in the event of a deceleration of a pump drive motor (1; 101), and in the second direction in the event of a acceleration of that engine. 2. Pump according to rev. 1, characterized by the fact that the at least one pumping element (11; 111) is a radial vane extending axially into the rotor (3; 103), and by the fact that the rotor (3; 103) is a hollow element with a central bulkhead (5; 105) in which at least one slit is formed (10; 110) which gives seat to the blade or to a respective blade (11; 111). 3. Pump according to claim 1 or 2, characterized in that it comprises a pair of blades (11, 111) arranged in opposite and symmetrical slots (10; 110). 4. Pump according to any one of the preceding claims, characterized in that the slot or each slot (10) is open at one end at the outer surface of the rotor (3) and has a bottom at the opposite end, and by fact that in the central bulkhead (5) there is a first passage (12) which connects an area of the slit or of each slit (10) close to the bottom with an internal cavity (8) of the rotor (3). 5. Pump according to claims 3 and 4, characterized in that a second passage (13) is formed in the central bulkhead (5) which connects areas of the two slits (10) close to the respective bottom. 6. Pump according to rev. 4 or 5, characterized by the fact that the slit or each slit (10) has a depth such that, with the pump deactivated, the center of gravity of the respective vane (11) is between a central point of the slit (10) and the bottom of the same. 7. Pump according to any one of claims 1 to 3, characterized in that: - the central bulkhead (105) is a hollow cylindrical element coaxial to the rotor (103) and provided with a diametrical septum (120) along which the at least one pumping element (111) slides; - the central bulkhead (105) defines with the internal surface of the rotor (103), the at least one pumping element (111) and at least one radial septum (109) which connects the bulkhead (105) to the internal surface (103B) of the rotor (103), at least one seat (108) for an anchoring element (122) movable tangentially with respect to the rotor (103) and able to engage with the element or a respective pumping element (111) to retain it in the slot (110) a pump (101) deactivated; - the at least one pumping element (111) has, at least on one of its faces facing forward with reference to the direction of rotation of the rotor (103) and in proximity to at least one of its extremities intended to move in contact with the internal surface (102A) of the body (102) with the pump (101) activated, at least one recess (121) in which the anchoring element (122) is able to engage; And - the slot (110) consists of a radial passage that crosses the walls of the rotor (103) and the central bulkhead (105) at one or both ends of the diametrical partition (120). 8. Pump according to rev. 7, characterized in that the element or each anchoring element (122) is mounted at one end of an articulated arm, at the opposite end, in correspondence with the rotation axis (A) of the rotor (103). Pump according to any one of the preceding claims, characterized in that it is associated with a motor vehicle engine, in particular for generating and maintaining a vacuum required for controlling a brake booster. 10. Process for controlling a rotary vacuum pump, comprising the steps of automatically activating or deactivating the pump (1; 101) respectively in the presence of first or respectively second operating conditions of an actuating motor of the same, characterized by the fact that the phase of activating the pump is started by a deceleration of the motor and the phase of deactivating the pump is started by an acceleration of the motor.