WO2012164466A1

WO2012164466A1 - Rotary vacuum pump, in particular for motor vehicles, and related control method

Info

Publication number: WO2012164466A1
Application number: PCT/IB2012/052636
Authority: WO
Inventors: Antonio Crotti; Luca Stagnoli; Leonardo Cadeddu
Original assignee: Vhit S.P.A.
Priority date: 2011-05-30
Filing date: 2012-05-25
Publication date: 2012-12-06
Also published as: ITTO20110467A1

Abstract

A rotary vacuum pump has a control unit including coupling elements (16), located between the rotor (12) of the pump and a driving member (13) rotating with the motor operating the pump, and preloading elements (17) for the coupling elements, associated with a common actuating member (21). The common actuating member (21) is arranged, in periods in which the motor rotates in a working direction of the pump, to cause or to allow the sliding of the preloading elements (17) relative to the coupling elements (16), so as to couple or decouple the driving member and the rotor, and hence to turn on or off the pump. A method of controlling the pump is also provided.

Description

ROTARY VACUUM PUMP, IN PARTICULAR FOR MOTOR VEHICLES, AND

RELATED CONTROL METHOD

Field of the invention

The present invention relates to pumps, and more particularly it concerns a rotary vacuum pump equipped with a control unit arranged to disconnect the pump from a driving member in the periods in which the operation of the pump itself is not required or desired.

Preferably, but not exclusively, the present invention is applied in vacuum pumps driven by the motor of a motor vehicle.

State of the art

In the automotive field, vacuum pumps are used in order to generate and maintain, within a tank or booster of a servo brake, a depression mainly serving to actuate brakes and other devices requiring a depression for operating. After depression has been generated, the operation of such pumps serves to compensate vacuum consumption by the devices connected to the vacuum source and losses. Since such devices are not permanently operating and losses are limited, time periods, even of considerable duration, exist during which pump operation is not necessary. Turning the pump off in such periods 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.

DE 102007056316 and WO 2010106505 disclose rotary vacuum pumps in which coupling elements are provided between a driving member connected to the motor and the pump rotor, which elements can take a first or a second position in order to make the driving member and the rotor integral for rotation or mutually independent, respectively, depending on the pump operating conditions.

Such known solution are not satisfactory due to the construction complexity, the need to have very narrow constructive tolerances, the high oil pressure required for changing the configuration and the difficulty of avoiding peaks of absorbed torque, in particular when the driving shaft and the rotor are being coupled again.

Summary of the invention

It is an object of the present invention to provide a pump and a control method for the same pump, which obviate the drawbacks mentioned above.

This object is achieved by means of a pump according to claim 1 and a control method for the same pump according to claim 9.

The pump comprises a control unit including coupling elements, which are located between a pump rotor and a driving member rotating with the motor, and preloading elements for the coupling elements, which are associated with a common actuating member. According to an advantageous feature of the invention, the common actuating member is arranged, in periods in which the motor rotates in a working direction of the pump, to cause or to allow the sliding of the preloading elements relative to the coupling elements, in order to achieve the coupling or the decoupling between the driving member and the rotor and hence to turn the pump on or off.

According to another advantageous feature of the invention, the preloading elements are arranged to allow decoupling the driving member from the rotor also when the motor rotates in a direction opposite to the working direction of the pump.

According to a further advantageous feature of the invention, the preloading elements are tied together by a circular spring arranged to oppose the sliding of the preloading elements towards the rotor periphery.

According to yet another advantageous feature of the invention, the preloading elements slide along a path forming a first angle with a radial direction and/or have a contact surface with the coupling elements forming a second angle, opposite to the first one, with the radial direction.

Brief description of the drawings

Other features and advantages of the invention will become apparent from the following description of preferred embodiments, given by way of non limiting examples with reference to the accompanying drawings, in which:

- Fig. 1 shows an axial sectional view of a vacuum pump according to a first embodiment and the valve controlling the coupling assembly, in a first operating condition;

Fig. 2 is an axial sectional view taken according to a plane orthogonal to that of the sectional view of Fig. 1;

Fig. 3 is a cross sectional view of the coupling assembly, according to a plane passing through line III - III in Fig. 2;

Fig. 4 is an exploded view of the rotor with the coupling mechanism;

Fig. 5 is a perspective view of a detail of Fig. 4, in assembled condition; - Fig. 6 is a schematic view of the control valve, in a second operating condition;

- Figs. 7 and 8 are views similar to Figs. 2 and 3, showing the pump in the second operating condition;

- Figs. 9 and 10 are views similar to Figs. 2 and 3, illustrating a second embodiment; - Figs. 11 and 12 are enlarged views showing a variant the preloading elements in the first and the second embodiment, respectively;

- Figs. 13 and 14 are partial views, in axial and cross section, respectively, of a variant of the second embodiment.

Detailed description of preferred embodiments

Referring to Figs. 1 to 5, vacuum pump 1 is a rotary pump, for instance a vane pump, which, in the preferred embodiment, is driven by the motor (internal combustion engine, electric motor, hybrid motor) of a motor vehicle through a driving shaft (not shown). For the sake of clarity of the description, it is assumed that the pump is operated from below and that its normal rotation direction, when the pump is operating, is the counterclockwise direction (arrow Fl in Fig. 3).

Pump 1 comprises two main parts: a part 10 (hereinafter referred to as "coupling assembly") for coupling the driving shaft with rotor 12, and a valve 11, intended to control coupling assembly 10 so as to enable or stop power transmission to pump 1.

In particular, coupling assembly 10 is intended to:

- enable power transmission to pump 1 until the desired vacuum level has been attained, provided the motor rotates in the normal rotation direction;

- stop such power transmission in case of counter-rotation of the motor, thereby avoiding possible damages to the pump itself, or when vacuum supply is not required, for instance if the servo brake has already a sufficient depression, whereby power absorption by the pump itself occurs in the only periods in which pump use is actually necessary; coupling assembly 10 is to ensure that the stop and resumption of the power transmission take place in gradual manner, by avoiding anomalous pulses;

- limit the torque transmitted to pump 1 to a predetermined value, thereby avoiding biasing the pump with torque pulses which may occur in different operating conditions, such as at the motor start at particularly low temperature.

Coupling assembly 10 comprises an outer portion, consisting of driving joint 13 integral for rotation with the driving shaft, and an inner portion, consisting of rotor 12. The latter is a cup-like element, having an upper portion 12a of greater diameter, housed within a pump chamber 30 and equipped with a slot 39 through which the vane (not shown) passes, and a lower or guiding portion 12b, of smaller diameter, received within joint 13. The rotor base has downward extending projections 14 defining, together with the internal cylindrical surface 13a of joint 13 and the front face of radial vanes 17, chambers 15 with radially variable depth, each housing a roller 16.

Rollers 16 form the coupling elements between joint 13 and rotor 12, and vanes 14 form preloading elements for rollers 16 and act on such rollers through a respective contact surface 17a when power transmission to rotor 12 is required.

Vanes 17 are mounted so as to be slidable on lateral guiding surfaces 14a of adjacent projections 14. In this embodiment, surfaces 14a and 17a form, with the radial direction, respective angles α, β such that surfaces 17a move towards rollers 16 when vanes 17 move towards the rotation axis. More particularly, in the example shown in Fig. 3, surfaces 17a are inclined in the pump rotation direction by an angle β, which advantageously is in the range from about 5° to about 35°, and surfaces 14a are parallel to radial direction, i.e. a = 0°. Therefore, angle a is not indicated in Fig. 3.

A circular spring 18, received in axial recesses 19 of vanes 17, is so preloaded as to bring the vanes close to the rotation axis, as shown by arrows F2 in Fig. 3. Thanks to the resilience of spring 18, all vanes 17 are equally preloaded and thus they act on rollers 16 with the same force, so that torque transmission is better balanced. Moreover, such an arrangement makes the structure self-centring and scarcely sensitive to the tolerances among the parts.

Radially internal surfaces 20 of vanes 17 are inclined, at least over a certain length, with respect to the rotation axis and they define a seat for a tapered bottom portion 22 (e.g. a conical portion) of a piston 21 axially slidable within portion 12b of rotor 12. A widened head 23 of piston 21 closes the bottom of a chamber 24, which is closed at its top by a plug 25. Head 23 has such a diameter that it allows an actuating fluid to make piston 21 slide. The sliding is opposed by a possible return spring 26, arranged between the lower face of head 13 and the bottom of rotor 12.

A retaining disc 27, rigidly connected to projections 14, allows, during the periods in which power transmission to pump 1 is stopped, avoiding unwanted contacts between the bottom of joint 13, permanently rotating with the motor, and the bottom surfaces of rollers 16 and vanes 17 that, during such periods, are stationary and are pushed downwards by conical surface 22 of piston 21.

As far as valve 11 is concerned, it is for instance a slide valve, connected to lubrication circuit l ib of the vehicle and controlled by the depression level in vacuum circuit 11a by means of a pneumatic actuator or a solenoid (not shown). The valve can take a first and a second operating condition, shown in Figs. 1 and 6, respectively, depending on whether or not the pump has generated the predetermined vacuum level.

In the first position, valve 11 sends oil to chamber 30 via a duct 32 formed in pump body 31, in order to ensure pump lubrication and heat removal.

In the second position, valve 11 sends oil to chamber 24 of rotor 12 via a duct 33 ending into a groove 34 formed in the external surface of rotor 12 and communicating with chamber 24 via holes 35. In order to avoid any oil leakage towards the pump while the latter is turned off, a sealing gasket (not shown) can be provided between groove 34 and chamber 30.

The operation of the invention will now be described, referring also to Figs. 6 to 8.

In the periods where pump 1 is to operate, that is, when the depression level in vacuum circuit 11a is to be increased, valve 11 is in the condition shown in Fig. 1 and sends oil to chamber 30. Chamber 24 is not pressurised and piston 21 is kept lifted. Under such conditions, the preload of spring 18 applies a centripetal force to the vanes, bringing them in contact with rollers 16 (Fig. 3). Such a contact gives rise to a force applied onto rollers 16, bringing them to the minimum depth regions of chambers 15 and in contact with projections 14 and surface 13a of the joint.

If the motor rotates in the direction of arrow Fl, the frictional forces between rollers 16 and surface 13a are directed in the same direction as the force applied by vanes 17, and power transmission from joint 13 to rollers 16, and hence to rotor 12, which is thus made to rotate, is therefore obtained. The torque that can be transmitted depends on the force exchanged between vanes 17 and rollers 16, on spring 18 and on the geometries of the contacting elements.

If the motor rotates in the opposite direction, the frictional forces between rollers 16 and surface 13a are directed in opposite direction to the force applied by vanes 17, thereby reducing down to zero torque transmission from joint 13 to rollers 16, and hence to rotor 12.

Upon the attainment of the desired depression in circuit 11a, slide valve 11 is switched and passes to the position shown in Fig. 6, so that oil is sent to chamber 24. The oil pressure pushes piston 21 downwards (arrow F3, Fig. 7). Consequently, conical portion 22 of the piston, by acting on inclined surfaces 20 of vanes 17, causes a gradual, outward directed radial displacement of the same vanes (arrows F4, Figs. 7, 8) against the preload of spring 18, with a resulting decrease of the force transmitted to rollers 16, and hence of the torque transmitted to rotor 12. When vanes 17 are fully disengaged from rollers 16, the latter are freely movable in chambers 15 (see the enlarged detail shown in Fig. 8), with a consequent stop of power transmission to the rotor.

When the pump is to be turned on again, valve 11 resumes the condition shown in Fig. 1, so that the supply to chamber 24 is stopped and oil is sent again to chamber 30. As a consequence of the decrease in the pressure acting on head 23 of piston 21, spring 18 tends to apply the centripetal force on vanes 17, surfaces 20 of which push piston 21 upwards, thereby making oil flow out from chamber 24. The force exchanged between vanes 17 and rollers 16, and consequently the torque transmitted between cylindrical surface 13a and rollers 16, gradually increases. In this way, a behaviour corresponding to that of an actual clutch is obtained, since initially a relative sliding of rollers 16 and cylindrical surface 13a occurs. The speed of the relative sliding gradually decreases down to zero, thereby bringing rotor 12 to the same speed as that of the driving shaft. The pump resumes therefore its rotation, ensuring its depressor function, while however avoiding impulsive torque increases.

The gradualness of the upward displacement of piston 21, and hence of the coupling, can be ensured by means of an adjustment of the flow-out rate of oil from chamber 24. Different methods exist for adjusting such a flow rate, for instance:

- using a choke 36 (fig. 1) in channel 33;

- suitably sizing the diametric clearance between head 23 of piston 21 and rotor 12.

In order to avoid that, during the step of pump restart, in the period elapsing between the operation of valve 11 and the resumption of power transmission, oil flooding into chamber 30 takes place through channel 32, means can be provided that suitably delay oil flow in channel 32, for instance a dead volume 37 to be filled and/or a choke 38 (Fig. 1), both being suitably sized.

The described system has two advantageous force multiplication systems: a first system is due to the inclination of surfaces 17a, the other to conical surface 22 with acute angle, which substantially acts as a wedge. The first multiplication system amplifies the preload of circular spring 18, so that this preload can be kept within acceptable values. The second multiplication system amplifies the effect of the force generated by the oil pressure onto piston 21, thereby ensuring the pump disconnection even when the available pressures are very low.

Figs. 9 and 10 show a pump 101 according to another embodiment of the invention, in the condition in which the driving shaft and the rotor are coupled together. Elements present also in Figs. 1 to 8 are denoted by reference numerals increased by 100.

In this second embodiment, chamber 124 pressurised in order to operate piston 121 is defined between the lower face of piston head 123 and the bottom of rotor 112, whereas the upper face of head 123 and plug 125 define a seat 140 for spring 126, the preload of which keeps piston 121 in the lowered position (arrow F5), where it pushes outwards vanes 117 (arrows F6). Spring 118 acts here as a return spring for bringing vanes 117 back towards the rotation axis when piston 121 is lifted to decouple the rotor from the driving shaft. Angles α, β of surfaces 114a and 117a with the radial direction are such that surfaces 117a move towards rollers 116 when vanes 117 move away from the rotation axis. In particular, in the example illustrated in Fig. 10, surfaces 114a are inclined relative to the radial direction by an angle a (advantageously in the range from about 5° to about 35°) in the pump rotation direction, and surfaces 117a are parallel to the radial direction, i.e. β = 0°. Therefore, angle β is not indicated in Fig. 10. As a consequence of the different location of chamber 124, duct 133, groove 134 and holes 135 are displaced downwards with respect to the embodiment shown in Figs. 1 to 8. For the sake of simplicity, the valve, whose operation is unchanged, has not been shown.

The operation of such an embodiment is complementary to that disclosed above. When power is to be transmitted to the pump (valve 11 in the position shown in Fig. 1), pistonl21 is kept lowered by the preload of spring 126, so that vanes 117 are pushed outwards and transmit to rollers 116 the preload necessary to ensure the contact forces required for power transmission. When the desired depression value is attained (valve 11 in the position shown in Fig. 6), the pressure of the oil sent to chamber 124 overcomes the preload of spring 126, thereby pushing piston 121 upwards and progressively removing the preload from elements 117 and consequently from rollers 116. The progressive decrease in the transmitted torque is thus obtained, until complete pump disconnection. When the valve is brought back to the starting position, preload spring 126 brings piston 121 back to its starting position, thus ensuring the preload for elements 117 and rollers 116 and progressively increasing the torque transmitted to the pump. The gradualness of the reestablishment of the connection is obtained in the same manner as in the first embodiment.

The present invention also implements a method of controlling a vacuum pump. The method includes the steps of:

- providing, between rotor 12, 112 of the pump and driving joint 13, 113, coupling elements 16, 116 arranged to make the joint and the rotor integral for rotation only in periods where the pump operation is required or desired, and to make the joint and the rotor independent of each other in other periods;

- detecting first and second operating conditions of the pump, corresponding to the periods where the pump operation is required or desired and to the other periods, respectively; and

- bringing coupling elements 16, 116 to a first or a second position depending on whether the first or the second operating conditions are detected.

This latter step includes moving preloading elements 17, 117, individually associated with the coupling elements 16, 116, in a first or second direction in order to bring them in engagement with or to disengage them from the coupling elements, the movement being obtained through the amplification of a force applied to actuating members 21, 121 of preloading elements 17, 117.

It is clear that the above description has been 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.

For instance, in both embodiments, both angles α, β can be different from 0°, as shown in Figs. 11 and 12 for the first and the second embodiment, respectively. More particularly, in the first embodiment, surfaces 14a will be inclined by an angle a in a direction opposite to the pump rotation direction, whereas in the second embodiment, surfaces 117a will be inclined by an angle β in a direction opposite to the pump rotation direction. In both Figures, the engaged condition of vanes 17, 117 and rollers 16, 116 is shown in solid lines, whereas the disengaged condition is shown in dotted lines.

In order to obtain a self-centring effect for the preloading elements in the case of the second embodiment, means are provided arranged to load the preloading elements in uniformly distributed manner in the actuation phase.

For instance, the above effect may be achieved by using a pyramidal shape arranged to form an elastic expansion calliper.

According to an example of such kind of embodiment, i.e. of the provision of an elastic expansion calliper, the pyramidal tapered portion belongs to a component distinct from piston 121 and capable of self-centring with respect to the preloading elements. In such a variant, the tapered portion could also consist of a plurality of separate elements or "slices", each arranged to cooperate with one preloading element 117 and preferably made of a resilient material (e.g. spring steel or rubber), in order to allow a force sharing among the slices themselves. If the tapered portion is pyramidal (thus, with flat surfaces), also inclined surfaces 120 of the preloading elements will be advantageously flat surfaces.

A possible example of such a variant is shown in Figs. 13 and 14, where reference numeral 150 denotes the pyramidal tapered portion, which is separate from piston 121, is arranged to build the elastic expansion calliper and is formed, for instance of a plurality of separate elements.

Claims

Patent claims

1. A rotary vacuum pump, with a control unit (10; 110) transmitting the rotary movement of a motor to a rotor (12; 112) of the pump (1; 101) and including:

- coupling elements (16; 116), which are located between the rotor (12; 112) and a driving member (13; 113) rotating with the motor and are arranged to take a first operating position in order to make the driving member (13; 113) and the rotor (12; 112) integral for rotation in periods where the pump operation is required or desired, and a second operating position in order to make the driving member (13; 113) and the rotor (12; 112) independent of each other in other periods; and

- preloading elements (17; 117) for the coupling elements (16; 116), arranged to bring the latter to the first or the second operating position;

the pump being characterised in that the preloading elements (17; 117) are associated with common actuating members (21; 121; 121, 150) arranged, in periods in which the motor rotates in a working direction of the pump (1; 101), to cause or to allow a sliding of the preloading elements (17; 117) in a first or a second direction in order to move such elements towards or away from a rotation axis of the rotor, the sliding in one direction bringing the preloading elements (17; 117) in engagement with the coupling elements (16;

116) and the sliding in the other direction disengaging the preloading elements (17; 117) from the coupling elements (16; 116), the sliding of the preloading elements (17; 117) being obtained by means of the cooperation between a tapered surface (22; 122) of the actuating members (21; 121; 121, 150) and correspondingly inclined surfaces (20; 120) of the preloading elements (17; 117).

2. The pump as claimed in claim 1, wherein the preloading elements (17; 117) are distributed along a circumference and are tied together by a circular spring (18; 118) arranged to oppose the sliding of the preloading elements (17; 117) in the direction away from the rotation axis.

3. The pump as claimed in claim 2, wherein the preloading elements (17; 117) are inserted between guiding elements (14; 114) defining, with the preloading elements (17;

117) and the driving member (13; 113), seats (15; 115) with variable radial depth for the coupling elements (16; 116).

4. The pump as claimed in claim 3, wherein a guiding surface (14a) formed in the guiding elements and a contact surface (17a) of the preloading elements (17) with the coupling elements (16) form, with a radial direction, a respective angle (α, β) such that the preloading elements (17) move into engagement with the coupling elements (16) by sliding in the direction towards the rotation axis.

5. The pump as claimed in claim 3, wherein a guiding surface (114a) formed in the guiding elements and a contact surface (117a) of the preloading elements (117) with the coupling elements (116) form, with a radial direction, a respective angle (α, β) such that the preloading elements (117) move into engagement with the coupling elements (116) by sliding in the direction away from the rotation axis.

6. The pump as claimed in any one of preceding claims, wherein the actuating members include a piston (21; 121) operated by a control fluid in order to cause the sliding of the preloading elements (17; 117) necessary to disengage them from the coupling elements (16; 116), and wherein a circuit for the control fluid includes means (36, 37, 38; 136, 138) for making the return to the engagement condition gradual.

7. The pump as claimed in claim 6, wherein the tapered surface (22; 122) is part of a lateral surface of the piston (21; 121) or is a radially external surface of an element (150) that is separate from the piston (21; 121) and is located between the piston and the preloading elements (17; 117), said element being arranged to build an elastic expansion calliper and possibly consisting of a plurality of components made of resilient material.

8. The pump as claimed in any one of preceding claims, wherein the driving motor is the motor of a motor vehicle.

9. A method of controlling a rotary vacuum pump (1; 101), comprising the steps of:

- providing, between a rotor (12; 112) of the pump and a driving member (13; 113) causing the rotation of the rotor, coupling elements (16; 116) arranged to make the driving member (13; 113) and the rotor (12; 112) integral for rotation only in periods where the pump operation is required or desired, and to make the driving member (13; 113) and the rotor (12; 112) independent of each other in other periods;

- detecting first and second operating conditions of the pump corresponding to the periods where the pump operation is required or desired and to the other periods, respectively; and

- bringing the coupling elements (16; 116) to a first or a second position depending on whether the first or the second operating conditions are detected;

characterised in that the step of bringing the coupling elements (16; 116) to a first or a second position includes

- moving preloading elements (17; 117), individually associated with the coupling elements (16; 116), in a first or a second direction in order to move them towards or away from a rotation axis of the rotor and to bring them in engagement with or to disengage them from the coupling elements (16; 116), the movement being obtained through the amplification of a force applied to actuating members (21; 121; 121, 150) of the preloading elements (17; 117) .

10. The method as claimed in claim 9, wherein the step of moving the preloading elements (17; 117) includes the movement along a trajectory forming a first angle (a) with a radial direction and the contact of the preloading elements (17; 117) with the coupling elements (16; 116) through a contact surface (17a; 117a) forming a second angle (β) with the radial direction.