WO2012073165A2

WO2012073165A2 - Vacuum pump, in particular for motor vehicles

Info

Publication number: WO2012073165A2
Application number: PCT/IB2011/055301
Authority: WO
Inventors: Leonardo Cadeddu
Original assignee: VHIT SpA
Current assignee: VHIT SpA
Priority date: 2010-11-29
Filing date: 2011-11-25
Publication date: 2012-06-07
Anticipated expiration: 2013-05-29
Also published as: EP2646655A2; WO2012073165A3; ITTO20100945A1; IT1403001B1

Abstract

A rotary vacuum pump comprises a rotor (3) arranged to eccentrically rotate in the cavity of a pump body (2) and comprising at least one vane (11), received in a respective slot (10) and arranged to radially slide in a first or a second direction in order to bring a forward end thereof into engagement with the internal surface of the body (2) in an operating condition of the pump (1), or to move the forward end away from such a surface in an idle condition of the pump (1). The sliding of the vane(s) (11) in the first or the second direction is caused by an angular deceleration or acceleration, respectively, of the rotor. A method of controlling the pump is also provided.

Description

VACUUM PUMP, IN PARTICULAR FOR MOTOR VEHICLES

Technical field

The present invention relates to vacuum pumps, in particular for the automotive field.

Prior art

Several devices in a motor vehicle demand a depression for operating. An example is the servo braking system, which is a pneumatic servomotor using depression as a source of energy. In petrol-fuelled engines, the depression can be generated in the intake manifold thanks to the inlet choking created by the butterfly valve when the accelerator is released. In diesel engines, since the air inlet chocking does not exist, depression is on the contrary obtained by means of a vacuum pump. At present, however, in order to improve combustion and to reduce noxious emissions, many petrol-fuelled engines have a reduced depression level at the manifold, which level is no longer sufficient to supply the servo braking system. Hence a vacuum pump is used also in these engines.

After depression has been generated, the operation of the vacuum pump serves for compensating vacuum consumption by the utilising devices and losses. Since such devices are not permanently operating and losses are limited, time periods, even of considerable duration, exist in which pump operation is not necessary. Yet, usually, vacuum pumps in motor vehicles are permanently operated by the engine. This results in an unnecessary power absorption and in a certain increase in fuel consumption, as well as in a useless wear of the pump components.

Turning the vacuum pump on only when its operation is necessary would allow reducing the overall power required of the motor and hence fuel consumption and exhaust gas emission, as well as reducing the wear of the pump components and hence increasing their operating life. Moreover, alternative and less expensive materials could be used for manufacturing the pump components, taking into account the lower stresses they are subjected to.

Devices arranged to mechanically connect/disconnect the pump to/from the engine have been proposed to this aim. Examples are disclosed in DE 198 54 243 and WO 2006/010528. Such devices have some drawbacks, such as: high costs if compared to the benefits; great axial sizes; considerable reduction of the depression difference that can be exploited, due to the range of intervention of the pressure sensor; need to employ a sensor for absolute pressure, which is considerably expensive, in order the operation is not affected by the elevation at which the vehicle is operating. US 4,428,195 discloses a vacuum pump for a vacuum servo braking system, which pump is permanently connected to the engine and is turned on and off depending on the engine operating conditions. The pump has a vane rotor eccentrically rotating in a chamber in the pump body. The vanes are associated with a respective counterweight that, when the rotational speed of the motor is below a given threshold, keeps the vane in contact with the chamber wall due to the thrust exerted by a spring. When the rotational speed exceeds the threshold, the centrifugal force overcomes the force applied by the spring and the counterweight retracts the vane, thereby disengaging it from the wall and turning the pump off.

This solution obviates the drawbacks of the pumps with mechanical devices for coup ling/decoup ling to/from the engine, but it does not take into account that the need to create a certain vacuum level may occur even when the rotational speed is still quite high: under such conditions, failure to turn the pump on could create conditions of risk or damages to the device exploiting vacuum. Moreover, the provision of the counterweight and the contrast spring makes the structure rather complex and hence expensive and more prone to failures (e.g. break of the spring).

Description of the invention

It is an object of the present invention to provide a vacuum pump obviating the problems mentioned above.

According to the invention, this is achieved by means of the rotary vacuum pump as claimed in claims 1 to 9.

More precisely, the invention provides a pump where the rotor comprises at least one pumping element arranged to move in a first direction to turn the pump on in case of deceleration of a motor driving the pump, and in a second direction to turn the pump off in case of acceleration.

More particularly, the pump allows generating vacuum during deceleration and recovering kinetic energy during engine deceleration.

The invention also provides a method of controlling said pump, as claimed in claim

10.

Brief description of the drawings

Some preferred embodiments will be described hereinafter with reference to the accompanying drawings, in which:

Fig. 1 is a schematic radial cross-sectional view of a first embodiment of the invention; Figs. 2A to 2D are diagrams illustrating the operation of the pump shown in Fig. 1; and

Fig. 3 is a schematic radial cross-sectional view of a second embodiment of the invention.

Description of preferred embodiments

Referring to Fig. 1, a rotary vacuum pump 1 according to a first embodiment of the invention comprises a cylindrical hollow body 2 inside which rotor 3 eccentrically rotates. The rotor too is cylindrical and its external wall 3 A is tangent to internal surface 2 A of hollow body 2 along a stationary tangency line 4. In this example, rotor 3 rotates clockwise (arrow Rl) and its rotation axis is denoted by A. The suction and exhaust ports 6 and 7 are located at both sides of tangency line 4, at the left and the right of said line, respectively, with the rotation direction indicated.

Advantageously, rotor 3 is hollow and has a central bulkhead 5 connected to internal wall 3B of rotor 3 by means of radial partitions 9, for instance two partitions arranged in a diametric plane of rotor 3, dividing the internal cavity of rotor 3 into a plurality of chambers 8. Partitions 9 may have a shorter axial extension than rotor 3 and bulkhead 5 in order to allow communication between adjacent chambers 8.

Advantageously, rotor 3 can be made of plastics, by moulding techniques, for instance injection moulding.

A pair of radial cavities or slots 10, axially extending along the rotor and symmetrical with respect to a plane S passing through axis A, are formed in central bulkhead 5. Cavities 10 are open at one end in correspondence of external surface 3 A of the rotor and are closed at the opposite end. Each cavity 10 houses a vane 11 that is radially slidable between a first position, which is taken by the vane when pump 1 is operating and in which the vane forward end (with reference to the rotation direction) is in contact with internal surface 2A of body 2, and a second position, which is taken by the vane when pump 1 is not operating and in which the vane is retracted within cavity 10, so that its forward end is not in contact with surface 2A. This second position is shown in dashed line for the left vane. The two positions will also be referred to as "operating position" and "idle position", respectively. The vanes are received in cavities 10 with a sufficient clearance to allow their sliding, taking into account the manufacture tolerances. The vane sliding will be made easier by lubricating oil, e.g. directly supplied by the engine.

Advantageously, in the idle position, barycentre B of the vane is located between the middle point of cavity 10 and the bottom of the same cavity.

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

Vanes 11 move to the idle position during the acceleration phases of the engine, and move to the operating position in case of deceleration. When the engine is rotating at constant speed, the vanes will be in the operating or the idle position, depending on whether the constant speed condition has been attained after a deceleration or an acceleration.

Cavities 10 are mutually connected by a passageway 12 opening at or near the bottom of the cavities themselves. Still at or near their bottom, cavities 10 communicate with adjacent chambers 8 through passageways 13. Communication of cavities 10 with each other and with chambers 8 allows wholly discharging air possibly present in the cavities, whereby the retraction of vanes 11 is not hindered, and, together with communication between chambers 8, it allows passage of the lubricant oil.

The profile of cavities 10 and vanes 11 may be arc-shaped, as shown in the Figure, with the concavity directed forward with reference to the rotation direction, or it may be rectilinear.

The operation of the pump will now be explained with reference to schematic Figures 2A to 2D, where, for the sake of simplicity, only one cavity 10 has been shown, with vane 11 being simply shown as a line, namely a solid line for the operating position and a dashed line for the idle position. Figs. 2A to 2C show the forces acting on vane 11 in conditions of constant speed, acceleration and deceleration, respectively, and show a situation in which the open end of cavity 10 is up, so that in the operating position vane 11 projects into the cavity of body 2. Fig. 2D shows the forces acting on vane 11 in conditions of acceleration, when the open end of cavity 10 is substantially located in correspondence of the line of tangency 4, so that vane 11 is retracted within cavity 10 also in the operating position. The Figures are intended to show only the direction of the forces, and the lengths of the vectors are not be intended as being representative of the actual intensities of the forces themselves.

During rotation of the rotor, vane 11 is obviously subjected to the centrifugal force, which is directed along a line joining the centre of rotation A of rotor 3 with the barycentre of vane 11. Reference symbols Bl and B2 denote the barycentre in the operating and idle position of the vane, respectively, and reference symbols Fl and F2 denote the centrifugal force in the two conditions. Force Fl, F2 has a component, denoted FI_N, F2_N, normal to vane 11 in the barycentre, and a tangential component F1_T, F2_T. The normal component, which is the only component in the position depicted in fig. 2D since the centrifugal force is directed normally to the vane, tends to push vane 11 against the wall of cavity 10 and generates a tangentially directed frictional force Fl -μ, F2_N where μ is the coefficient of friction. The frictional force is not shown for the sake of simplicity and clarity of representation. The tangential component, diminished by the frictional force

FlN-μ, F2_N can cause displacement of vane 11.

If rotor 3 is rotating at constant speed, vane 11 is subjected to the action of the centrifugal force only. If vane 11 is in the operating position (i.e. the constant speed condition has been attained after a deceleration), tangential component F1_T of the centrifugal force tends to make the vane slide towards the outside, and hence the vane remains in operating position. This occurs whatever the position of the rotor in the cycle may be. Similarly, if vane 11 is in the idle position (i.e. the constant speed condition has been attained after an acceleration), tangential component F2_T will tend to push vane 11 towards the bottom of cavity 10, provided barycentre B2 is located between the middle point and the bottom of the cavity.

If an acceleration occurs (Figs. 2B and 2D), an inertial force denoted F3 (in the operating position) and F4 (in the idle position), normal to Fl, F2, respectively, is also applied to vane 11 due to the effect of inertia. Also F3 and F4 have a "normal" component F3_N, F4_n originating a frictional force F3_N F3_N^ (it too not shown), which adds to force

Fl -μ, F2_N and a "tangential" component F3_T, F4_T. Like in the case of the centrifugal force, only the tangential component (which is the only component in the position depicted in fig. 2D) can cause displacement of the vane against the action of the frictional forces. If vane 11 is in the operating position, component F3_T is directed in opposite direction with respect to FI_T and the vane will retreat into its seat if

The skilled in the art has no problem in choosing the materials, the surface workings etc. so that the above condition is always met. If the vane is already in the idle position, both F2_T and F4_T tend to push the vane towards the bottom of cavity 10, thus maintaining the existing condition.

If a deceleration occurs (Fig. 2C), an inertial force F5, F6 is applied to vane 11 due to inertia, which force is directed in opposite direction with respect to F3, F4. Hence, clearly, the tangential component F5_T, F6_T of this inertial force will tend to make vane 11 move out of its seat (always against the action of the frictional forces), thereby turning the pump on.

Fig. 3 shows a second embodiment of the pump according to the invention, denoted 101. Elements corresponding to those shown in Fig. 1 are denoted by corresponding reference numerals, increased by 100.

In this embodiment, central bulkhead 105 is formed by a hollow cylindrical member, coaxial with rotor 103, and has diametric partition 120, for instance substantially normal to partitions 109. With the depicted arrangement, two pairs of chambers 108 are formed, an "outer" pair between the external surface of bulkhead 105 and the internal surface 103B of rotor 103, and an "inner" pair inside the cavity of bulkhead 105. In this embodiment too, partitions 109 may have a shorter axial extension than rotor 103 and bulkhead 105 in order to allow communication between outer chambers 108.

Vanes 111, which in this embodiment are flat, are arranged at both sides of partition 120 and are slidable within slots 110 extending through the walls of both bulkhead 105 and rotor 103 at least at one end of partition 120 and, preferably, at both ends thereof. The through slots have similar functions to passageways 12, 13 in Fig. 1. Like in the previous embodiment, because of inertia and the relevant inertia force (inertial force), vanes 111 will move to the idle position in case of engine acceleration and to the operating position in case of deceleration.

Each vane 111 has on its forward face (with reference to the rotation direction of the rotor, which in this embodiment has been supposed to be the counterclockwise direction, as shown by arrow R2), near its forward end intended to engage wall 102A of body 102, a recess 121 which can be engaged by one end of an anchoring element 122, intended to hold the vane in the retracted position. Advantageously, a similar recess is provided also on the rearward face of the vane, near the rearward end, and both ends of elements 122 are so shaped that they can engage recesses 121. This assists in an error-proof mounting.

Both anchoring elements 122, identical to each other, are slidably mounted in a respective outer chamber 108, in the region defined by the forward face of vane 111 and the closest partition 109, and are symmetrically arranged. Elements 122 have an arched shape, corresponding to the shape of the chambers, and they may have a substantially circular cross section.

In case of acceleration, due to the effect of inertia and the relevant inertia force (inertial force), anchoring elements 122 will be in contact with the surface of vanes 111 and, when the latter are retracted in rotor 103, such elements will engage recesses 121 thereby locking vanes 111. In case of deceleration, always due to the effect of inertia and the relevant inertia force (inertial force), anchoring elements 122 will disengage from recesses 121 and vanes 111 will be free to move out of the rotor, due to the effects of the centrifugal force, and into contact with internal surface 102A of body 102. As before, at constant speed, the vanes will remain in the idle position (and hence they will be locked by anchoring elements 122) or in the operating position, depending on whether the constant speed has been attained after an acceleration or a deceleration.

It is to be appreciated that in Fig. 3 one of the vanes (the upper one) has been shown in the operating position, whereas the other is shown in the idle position, in order to show an anchoring element 122 in engagement with the corresponding recess 121.

It is clear that the invention achieves the aim indicated above. Since the turning on of the pump depends on the deceleration and not on the speed, the possible risk or damage situations are eliminated. Moreover, the forces present because of rotation are directly exploited in order to bring the pump to the operating or the idle position: thus, there is no need for counterweights and springs or external devices, such as valves, so that the structure is simpler, less expensive and less prone to possible failures.

In synthesis, the pump according to the invention, in the various embodiments, comprises pumping elements directly operated by forces generate internally of the rotor because of acceleration or deceleration of the same rotor.

It is to be appreciated that an operation depending on acceleration/deceleration reproduces the conditions created by a conventional petrol engine having no pump.

The invention also implements a method of controlling a vacuum pump, in order to automatically turn the pump on or off at the occurrence of first or second operating conditions, respectively, of a motor driving the same pump. Such a method includes the following steps:

- in case of an angular acceleration of rotor 3, 103, retracting vanes 11, 111 in the respective seats 10, 110 and, if anchoring elements 122 are provided, holding the vanes in the retracted position by means of those elements;

- in case of an angular deceleration of rotor 3, 103, making anchoring elements 122, if provided, to disengage from vanes 11, 111 and making the vanes move out of seats 10,

110 to bring their forward ends into contact with the internal wall of body 2, 102.

It is clear that the above description is given only by way of non-limiting example and that changes and modifications are possible without departing from the scope of the invention as defined in the following claims. Thus, for instance, the pump may have a single vane. In that case, the pump, when it is operating, sucks and compresses, at each revolution, a volume of fluid equal to the volume comprised between the internal surface of the body and the external surface of the rotor, less the vane volume. Yet, the two-vane embodiment is preferable, in that it allows doubling the displacement, with the same size, since the two phases are separated.

Moreover, vanes 111 having a recess 121 on each face, at opposite ends, have been shown in Fig. 3. It is also possible to provide opposing recesses 121 on both faces and at both ends of each vane. In this way, vanes 111 may be mounted with any orientation. Further, anchoring elements 122 could be mounted at one end of respective arms or spokes pivotally connected, at the opposite end, in correspondence of rotation axis A of rotor 103. Elements 122, instead of having circular cross-section, could be shaped so that each of them engages an elongated recess or a plurality or recesses, for instance aligned recesses: the configuration must be such that the axial extension of elements 122 is shorter than that of vanes 111 , to allow air/oil to flow through slots 110.

Advantageously, the pumps as shown in the embodiments considered as preferable can be used also in conjunction with electric control motors. In such embodiments, it can be envisaged that, in case of deceleration or acceleration of the thermal engine or the electric motor driving the vehicle, for instance a hybrid vehicle, the electric control motor is directly supplied with the deceleration or the acceleration or is supplied with a suitable signal causing a corresponding deceleration or acceleration of the pump.

Moreover, the invention can be applied to any rotary pump in which a pumping element is displaceable in the rotor between an operating position and idle position.

Claims

Patent Claims

1. A rotary vacuum pump, comprising a hollow body (2; 102) with a substantially cylindrical internal cavity, and a rotor (3; 103) arranged to eccentrically rotate in the cavity in fluid-tight manner relative to an internal surface (2A, 102A) of the body (2; 102) along a constant tangency line (4, 104) located between a suction 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) arranged to move within the rotor in a first or a second direction, respectively, in order to bring the pump (1; 101) to an operating condition or an idle condition; the pump being characterised in that the at least one pumping element (11; 111) is arranged to move in the first direction in case of a deceleration of a motor driving the pump, and in the second direction in case of an acceleration of said motor.

2. The pump as claimed in claim 1, characterised in that the at least one pumping element (11; 111) is a radial vane axially extending in the rotor (3; 103), and in that the rotor (3; 103) is a hollow element with a central bulkhead (5; 105) in which at least one slot (10; 110) is formed housing the or a respective vane (11; 111).

3. The pump as claimed in claim 1 or 2, characterised in that it comprises a pair of vanes (11; 111) arranged in opposite and symmetric slots (10; 110).

4. The pump as claimed in any preceding claim, characterised in that the or each slot (10) is open at one end in correspondence of the external surface of the rotor (3) and has a bottom at the opposite end, and in that a first passageway (12) is provided in the central bulkhead (5), which passageway puts a zone of the or each slot (10) located near the slot bottom in communication with an internal cavity (8) of the rotor (3).

5. The pump as claimed in claims 3 and 4, characterised in that a second passageway (13) is provided in the central bulkhead (5), which passageway puts zones of both slots (10) located near the respective bottom in communication with each other.

6. The pump as claimed in claims 4 or 5, characterised in that the or each slot (10) has such a depth that, when the pump is in the idle condition, the barycentre of the respective vane (11) is located between a middle point and the bottom of the slot (10).

7. The pump as claimed in any of claims 1 to 3, characterised in that:

- the central bulkhead (105) is a cylindrical hollow element coaxial with the rotor (103) and having a diametric partition (120) along which the at least one pumping element (111) moves;

- 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 partition (109) connecting the bulkhead (105) to the internal surface (103B) of the rotor (103), at least one seat (108) for an anchoring element (122) tangentially movable relative to the rotor (103) and arranged to engage the or a respective pumping element (111) in order to hold it in the slot (110) when the pump (101) is in the idle condition;

- the at least one pumping element (111) has, at least on a face directed forward with reference to the direction of rotation of the rotor (103) and near at least one end thereof arranged to move in contact with the internal surface (102 A) of the body (102), at least one recess (121) arranged to be engaged by the anchoring element (122); and

- the slot (110) is a radial passageway extending through the walls of the rotor (103) and the central bulkhead (105) in correspondence of one or both ends of the diametric partition (120).

8. The pump as claimed in claim 7, characterised in that the or each anchoring element (122) is mounted at one end of a spoke, the opposite end of which is articulated in correspondence of the rotation axis (A) of the rotor (103).

9. The pump as claimed in any preceding claim, characterised in that it is associated with the motor of a motor vehicle, in particular for generating and maintaining a vacuum required for controlling a brake booster.

10. A method of controlling a rotary vacuum pump, comprising the steps of automatically bringing the pump (1; 101) to an operating condition or an idle condition at the occurrence of first or second operating conditions, respectively, of a motor driving the pump itself, characterised in that the step of bringing the pump to the operating condition is started by a motor deceleration and the step of bringing the pump to the idle condition is started by a motor acceleration.