WO2011158167A2

WO2011158167A2 - Fluidic gear machine with flow rate regulation

Info

Publication number: WO2011158167A2
Application number: PCT/IB2011/052555
Authority: WO
Inventors: Armando Codeca'; Matteo Cortesi; Leonardo Cadeddu; Alessandro Fauda; Matteo Calderoni
Original assignee: Vhit S.P.A.
Priority date: 2010-06-15
Filing date: 2011-06-13
Publication date: 2011-12-22
Also published as: WO2011158167A3; IT1401005B1; ITTO20100516A1; EP2582981A2

Abstract

An internal gear fluidic machine (1), in particular a pump for the lubrication circuit of a motor vehicle engine, comprises a member (13) for regulating the flow rate depending on the fluid pressure conditions in a fluidic circuit in which the machine (1) is connected. The regulating member (13) is axially slidable, without rotating, in a seat (12) formed in the body (10) of the machine (1) and has a first surface (18) for pressure application, which is permanently exposed to said pressure conditions and is arranged, when a threshold is exceeded, to cause a sliding of the regulating member (13) in order to create a fluid recirculation path through the machine (1). A method of regulating the flow rate of a fluidic machine and a combined pump (1, 100) for the automotive field, using the machine (1) as a pump for the lubrication circuit, are also provided.

Description

FLUIDIC GEAR MACHINE WITH FLOW RATE REGULATION

The present invention relates to fluidic machines, and more particularly it concerns an internal gear fluidic machine, in particular a positive displacement pump, with flow rate regulation.

Preferably, but not exclusively, the present invention is applied in a pump for the lubrication oil of an internal combustion engine, typically for a motor vehicle engine.

In several technical applications, for example in order to have lubrication oil circulate under pressure in motor vehicle engines, pumps with internal epicyclic gears are often used. These pumps generally comprise: a stationary body; an external gear rotating in said body about a first axis and having an internal toothing; an internal gear rotating inside the external gear about a second axis, different from the first one, and having an external toothing, with a number of teeth different from that of the external gear (generally, with one tooth less), meshing with the internal toothing of the external gear with only partial hydraulic seal; and a transmission member, generally driven by the vehicle engine, in order to impart the rotation to one of the two gears, which in turn drives the other because of the meshing of the respective toothings. The teeth define a succession of variable volume chambers between them, and oil is conveyed from an intake port to a discharge port through said chambers.

In such pumps, the oil flow rate at the outlet depends on the rotation speed of the engine, and therefore the pumps are designed so as to provide a sufficient flow rate at low speed, in order to ensure lubrication also in such conditions. If the pump has a fixed geometry, at high rotation speed the flow rate (and hence the pressure in the engine lubrication circuit) is higher than that required, resulting in an unnecessary energy consumption and, eventually, in an increase in fuel consumption and hence in a higher environment pollution.

Similar problems are encountered in pneumatic pumps or when the above structure is used as a motor, either hydraulic or pneumatic.

A solution for such problems is providing the pump with flow rate regulating means, which operate depending on the pressure at the delivery side of the pump. For instance, EP 1 091 126 A discloses a pump in which a flow rate regulation is obtained by varying the intake and delivery phases depending on the rotation speed of the engine. This is obtained through the rotation of a plate that separates the intake and delivery chambers and that is made to rotate when a pressure threshold is exceeded. Such rotation causes a reduction in the duration of the delivery phases, with a consequent choking effect on the fluid, and gives rise to oil recirculation.

A drawback of this prior art pump is the possibility of occurrence of strong cavitation phenomena especially at high rotation speed. Another drawback, also depending on the presence of rotating members, is the relative complexity. Moreover, the plate drive is an indirect drive and requires the provision of a pressure-responsive member that, when displacing, in turn drives the plate through a rack and pinion mechanism. This makes the pump construction still more complex and the reaction slower.

It is an object of the present invention, in a first aspect, to provide a fluidic machine with flow rate regulation, which obviates the drawbacks of the prior art.

According to the invention, this is obtained in that the machine includes a regulating member that is mounted so as to be axially slidable, without rotating, in a seat formed in the body of the machine itself and that has a first surface for pressure application, which is permanently exposed to the pressure of the fluid circulating in a fluidic circuit in which the machine is connected and which is arranged, when a pressure threshold is exceeded, to cause a sliding of the regulating member in order to move it away from a rest position, where no flow rate regulation occurs, and to create a fluid recirculation path between two chambers at different pressures in the machine.

According to a preferred feature of the invention, the regulating member further has at least one second surface for pressure application, which is exposed to the fluid pressure upon an external command, in order to make the regulating member slide and to create a fluid recirculation path independently of whether the threshold is exceeded.

In a second aspect, the invention also concerns a method of regulating the flow rate of an internal gear fluidic machine, comprising:

- arranging, within the machine body, a moving member for flow rate regulation, the movement of which is controlled by the fluid pressure conditions in a fluidic circuit in which the machine is connected, and which can be made to axially slide, without rotating;

- permanently exposing a first surface for pressure application, formed on the regulating member, to said fluid pressure conditions in said circuit; and

- making the regulating member slide when a threshold is exceeded, thereby creating a fluid recirculation path between two chambers at different pressures in the machine.

Preferably, the method also comprises exposing also at least one second surface for pressure application to said fluid pressure conditions, upon an external command, to make the regulating member slide and to create the fluid recirculation path independently of whether said threshold is exceeded.

In a third aspect, the invention concerns a pumping system, preferably for use in motor vehicles, comprising a plurality of mutually coupled pumping subsystems, wherein one of the subsystems is a pump for the lubrication oil of an engine made in accordance with the invention.

The invention will now be described in further detail with reference to the accompanying drawings, which show a preferred embodiment given by way of non- limiting example and relating to the use of the invention as a pump for the lubrication oil of an internal combustion engine, typically for a motor vehicle engine, and in which:

- Fig. 1 is a partial view in axial section of a pump according to the invention, taken along plane I-I of Fig. 2 and showing the pump when no flow rate regulation takes place;

- Fig. 2 is a cross-sectional view of the pump shown in Fig. 1 , taken along plane II-II of Fig. 1;

- Fig. 3 is an enlarged view in axial section of the moving cover and the pump body parts cooperating therewith;

- Fig. 4 is a view similar to Fig. 1, showing the pump in conditions of maximum flow rate reduction;

- Fig. 5 is a diagram of an engine lubrication circuit in which the pump according to the invention is connected;

- Figs. 6 is a view similar to Fig. 1, showing a variant embodiment of the invention;

- Fig. 7 is a view in axial section of a combined pump using the present invention.

Referring to Figs. 1 to 4, the pump according to the invention, generally denoted 1, is a positive displacement pump with internal epicyclic gears. The pump comprises, in conventional manner, an external gear 2 having an internal toothing 2A, and an internal gear 4, which is housed in the axial cavity of external gear 2 and has an external toothing 4A, with a different number of teeth, meshing with the toothing of external gear 2 with only partial hydraulic seal. In this case, the relative axial position of the gears is fixed, so that the pump has fixed capacity. Internal gear 4 is mounted on a pump shaft 6, it is made to rotate by said shaft about a first axis 3 coinciding with the axis of shaft 6, and it makes external gear 2 rotate about a second axis 5, parallel to the first one. The teeth of the two gears define chambers 7 of which the volumes change during rotation and through which oil coming from an axial intake duct 8, formed in a rear base 9 of pump body 10, is compressed before being sent to an axial delivery duct 1 1 , also formed in rear base 9. Arrows Fl and F2 denote the intake and delivery oil flows, and arrow F3 denotes the rotation direction of shaft 6.

On its forward side, body 10 has an axial cavity or regulation chamber 12 in which a moving cover 13, for instance circular, is inserted so as to be axially slidable without rotating, the cover forming the member for regulating the flow rate as the pressure conditions in the lubrication circuit change. Cover 13 may be made of metal, e.g. aluminium, or plastics.

Cover 13 has an eccentric through-hole 13 A (fig. 3) through which shaft 6 extends, the shaft penetrating into an axial recess 21 of the front surface of cover 13 and freely rotating in said hole. The axial sliding stroke of cover 13 in chamber 12 is limited backwards by a plane surface of a radial flange 14 of body 10, against which cover 13 abuts in normal operation conditions of pump 1, when no regulation is required, and is limited on the other side by a front base 15 closing chamber 12. The sliding is opposed by a spring 20 eccentrically mounted around the forward end of shaft 6 and abutting at its rear end against the bottom of recess 21 and at its front end against the bottom of an axial recess 22 of front base 15. The depth of recess 22 determines the preload of spring 20.

On its rear face, cover 13 has a pair of projections or pins 16, advantageously with cylindrical (as shown in the drawing) or conical shape, penetrating into through openings 17 of corresponding shape formed in flange 14. Openings 17 are closed by cover 13 and pins 16 when no flow rate regulation is required, as shown in Fig. 1, whereas they set up a connection for oil recirculation between a delivery chamber 28 and an intake chamber 29 through chamber 12, as shown by arrow F5 in Fig. 4, when the flow rate is to be regulated. Since the flange is part of body 10, and hence is stationary, the engagement of pins 16 into openings 17 prevents cover 13 from rotating. As clearly shown in Fig. 3, pin 16 and opening 17 on the delivery side have smaller diameters than pin 16 and opening 17 on the intake side. The sizes on the delivery side depend on the maximum flow rate to be regulated, whereas the sizes on the intake side are determined so as to ensure a complete pressure release under cover 13.

Cover 13 further has, on its side surface, a first step 18 projecting radially outwards and defining a first annular surface exposed to the oil pressure in the lubrication circuit thanks to a first radial passage 24, formed in body 10, which permanently communicates with the main duct for the engine oil and ends into a first chamber 25 defined by step 18 and by a corresponding annular surface on the internal surface of chamber 12. The width of step 18 and the preload of spring 20 determine a first pressure threshold whose attainment starts the sliding of cover 13.

In the preferred embodiment, cover 13 also has, on its side surface, at least one second step 19 projecting radially outwards and formed between the first step 18 and the front face of cover 13. This second step 19 defines a second annular surface exposed to the oil pressure in the lubrication circuit thanks to a second radial passage 26, also formed in body 10 and ending into a second chamber 27 defined by step 19 and by a corresponding annular surface on the internal surface of chamber 12. The second passage 26 can be put in communication with the main duct for the engine oil by means of a specific command supplied by the control units of the engine itself, as it will be explained later on.

In order to make the understanding of the invention easier, the lubrication circuit of a motor vehicle engine 50, where pump 1 is connected, has been schematically shown in Fig. 5. The pump is connected, at the intake side, to oil sump 51 through a pre-filter 52, and, at the delivery side, to main oil duct 53 through main filter 54. An oil pressure detector 55, connected to electronic control unit 56 of the engine, is arranged between filter 54 and main duct 53. Motor 50 uses such oil for lubricating the various moving parts, through dedicated channels branching from main duct 53. According to the invention, two of these channels are connected to radial passages 24, 26 in pump 1. The connection between main duct 53 and the second passage 26 is set up by a valve 57, in particular an electric valve, controlled by control unit 56. An overpressure valve 58 may be connected in parallel to pump 1 in order to recirculate oil directly into sump 51 in case of excessive pressure at the delivery side of the pump.

The operation of the pump according to the invention will now be described, mainly referring to Figs. 1, 3, 4 and 5.

In conventional manner, the torque transmitted to shaft 6 is applied to internal gear 4 that, by rotating, makes external gear 2 rotate, thereby allowing the pump to convey from intake chamber 29 to delivery chamber 28 oil sucked from sump 51 and compressed because of the passage through the different chambers 7 and to send such oil to main duct 53.

At low rotation speed of the engine (Fig. 1), the oil pressure in the engine, which is permanently applied to the first annular surface 18 in moving cover 13 through passage 24 (arrow F4) is not sufficient to overcome the preload of spring 20, which therefore keeps cover 13 pressed against flange 14, so as to close openings 7. The whole of the oil pumped by pump 1 is therefore transferred to the engine and the pump acts as a conventional pump without flow rate regulation.

As the rotation speed of the engine increases, oil pressure in the lubrication circuit correspondingly increases. When the pressure threshold determined by the area of step 18 and by the preload of spring 20 is attained, cover 13 starts raising from flange 14 and moving towards front base 15. The displacement causes the opening of holes 17, so that a communication between the pump delivery and intake sides is set up, whereby a recirculation of part of the compressed oil takes place through seat 12 (arrow F5), as shown in Fig. 4. The recirculation clearly entails a reduction in the oil flow rate being transferred to the engine and, consequently, a pressure reduction in the lubrication circuit. It is to be appreciated that Fig. 4 shows cover 13 in abutment against base 15, that is at the end of its regulation stroke, but obviously the cover may take any intermediate position between the positions shown in Figs. 1 and 4, depending on the pressure applied against surface 18.

If, as preferred, the second step 19 and the second passage 26 are provided, there is a second possibility of flow rate regulation, and consequently of pressure regulation. This second regulation is not automatic, but it is controlled by valve 57. The latter, upon receiving a suitable control signal from control unit 56, puts main duct 53 in communication with passage 26, thereby providing a pressure signal (arrow F6) that, when applied to step 19, may cause cover 13 to slide and to create the oil recirculation path even if the pressure threshold necessary to overcome the resistance of spring 20 by acting on step 18 has not been attained. In other words, the second step 19 allows having a different pressure regulation threshold, independent of the rotation speed of the motor. In this case, the spring preload is overcome by the sum of the forces applied onto both areas 18, 19.

In the embodiment described above, the sliding of cover 13 is opposed by spring 20. As known, the rigidity of a spring is variable within a relatively broad range (± 10%) and, therefore, the preload and the compression of the spring are also variable within a broad range. Consequently, the point of intervention of the spring may exhibit an imprecision with respect to the pressure threshold demanded by the motor. In order to avoid the use of high load springs and the resulting bulk, the oil pressure at the delivery side can be used to improve the pump structure and the intervention precision. As shown in Fig. 6, this may be obtained by setting up a connection 30 between the pump delivery side and the interior of recess 22, so as to apply the oil pressure against the front face of cover 13. The oil action could not only supplement, but also replace the action of spring 20. It is also to be appreciated that pin 16 on the delivery side is in turn exposed to the pressure existing in delivery chamber 28, as shown by arrows F7 in Fig. 6. The free surface of that pin forms therefore a further surface for pressure application, and the pressure in delivery chamber 28 can cause the cover displacement, and the consequent creation of the oil recirculation path, even if the pressure applied to step 18 is not sufficient to overcome the resistance of spring 20. In this manner, sliding cover 13 acts also as the conventional overpressure valve 58, which therefore can be dispensed with thereby simplifying the structure.

It is clear that the invention allows attaining the desired objects.

Thanks to the absence of members regulating the intake phase, the cavitation problems of the prior art pump are eliminated. The absence of rotating members makes the structure simpler and allows reducing the torque absorbed by the pump, and hence it further contributes to the reduction of consumption and pollution obtained thanks to the flow rate regulation.

Moreover, the regulating member is directly controlled by the oil pressure in the lubrication circuit, and not by driving members in turn responsive to such a pressure, so that the reaction is faster and the structure is further simplified, whereby costs can be reduced. A contribution to such simplification is also provided by the possibility of exploiting the pressure existing at the delivery side in order to make the regulating member perform the functions of the external overpressure valve.

The following advantages of the invention are also to be mentioned:

- the fact that the pump is self-regulating, since it keeps the delivery pressure constant depending on the engine needs, independently of the oil characteristics (viscosity, temperature, etc.); and

- the possible provision of at least one second regulation level, allowing also a regulation independent of the engine speed, so that a high flexibility is attained; in case of two or more regulation levels, regulation is continuous in the whole interval between the two or more levels.

Pump 1 according to the invention may be used as a self-standing pump or as a part of a combined pump including for instance, in the case of application in the automotive field, a pump for the lubrication oil as one of the subsystems and a vacuum pump or a fuel pump. A combined pump of this kind is shown in Fig. 7, where reference numeral 1 denotes the pump for the lubrication oil according to the invention and reference numeral 100 denotes a second pump. In this application, pumps 1 , 100 may be connected in parallel, with a suitable transmission system transmitting the motion to both shafts, or they may be connected in tandem. In this second case, shaft 6 of pump 1 can be used as a unique integrated shaft extending through both pumps, as shown in Fig. 7. As an alternative, the two shafts could be separate and be connected for instance through an Oldham joint.

A method of regulating the flow rate of a pump as described above comprises the steps of:

- arranging, within a seat 12 formed in body 10 of pump 1, a regulating member 13 which is arranged to axially slide without rotating (since, as said, it is held by pins 16 received in openings 17) and has a first surface 18 responsive to the oil pressure in the lubrication circuit;

- permanently applying the pressure existing in said circuit to the first surface 18 so as to keep regulating member 13 in a rest position as long as the pressure does not exceed a first threshold, and to make the regulating member slide and move away from the rest position when the pressure exceeds the threshold; and

- setting up, by such a sliding, a fluid recirculation path between a delivery side and an intake side in pump 1 through seat 12 of regulating member 13.

If regulating member 13 also includes the second pressure-responsive surface 19, the method also includes the step of applying the pressure existing in the lubrication circuit to surface 19, upon an external command, in order to make regulating member 13 slide independently of whether the first threshold is attained.

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.

For instance, cover 13 could have more than two annular surfaces for pressure application in order to allow a multi-level regulation. In this case, one of the levels will correspond to the regulation depending on the engine speed, whereas the other levels will be actuated by respective external commands.

Moreover, even if the invention has been disclosed with reference to its application to a pump, it can be employed also in a machine used as a motor, which receives a fluid at high pressure through duct 11 and discharges the fluid at a lower pressure through duct 8. The changes to be carried out in the description in order to adapt it to the case of use as a motor are obvious for the skilled in the art.

Of course, the pump or the motor could be pneumatic machines instead of being hydraulic machines. Also, the individual elements described here can be replaced by functionally equivalent elements.

Claims

Patent claims

1. A fluidic gear machine with flow rate regulation, comprising a body (10) in which a low pressure chamber (29) and a high pressure chamber (28) are formed that communicate with low and high pressure sections (51 , 53), respectively, of a fluidic circuit in which the machine (1) is connected, and in which a pair of gears (2, 4) forming a gear pump are arranged, which gears rotate about respective axes and define, between the respective teeth (2A, 4A), chambers the volume of which varies during rotation and through which a fluid is conveyed between said two chambers (29, 28), a moving member (13) for flow rate regulation, the movement of which is controlled by the fluid pressure conditions in said fluidic circuit, being further arranged in said body (10), the machine being characterised in that said regulating member (13) is mounted so as to be axially slidable, without rotating, in a seat (12) formed in said body (10) and comprises:

- at least one first annular surface (18) for pressure application, which is permanently exposed to the fluid pressure in the circuit and is arranged, when a pressure threshold is exceeded, to cause a sliding of the regulating member (13) in order to move it away from a rest position, where no flow rate regulation occurs, and to create a fluid recirculation path (F5) between said two chambers (29, 28); and,

- on a base directed towards said chambers (29, 28), a pair of projections (16), which are received in through openings (17) formed in said body so as to prevent rotation of the regulating member (13).

2. The fluidic machine as claimed in claim 1, characterised in that said regulating member (13) further comprises at least one second annular surface (19) for pressure application, which is arranged to be exposed to the fluid pressure upon commands externally controlled, in order to make the regulating member (13) slide and to create a fluid recirculation path (F5) independently of whether said threshold is exceeded.

3. The fluidic machine as claimed in claim 2, characterised in that said regulating member (13) has a plurality of second surfaces (19) for pressure application, which are arranged to be exposed to the fluid pressure upon respective commands externally controlled.

4. The fluidic machine as claimed in any of claims 1 to 3, characterised in that said openings (17) open on the one side into the seat (12) of the regulating member (13) and on the other side into the low or high pressure chamber (29, 28), respectively, are kept closed by said projections (16) and said regulating member (13) in the rest position of the regulating member (13) and put said chambers (29, 28) in communication with said seat (12), thereby creating said recirculation path, when the regulating member (13) is displaced from the rest position.

5. The fluidic machine as claimed in claim 4, characterised in that a free end of the projection (16) received in the opening (17) opening into the high pressure chamber (28) defines a further surface for pressure application, permanently exposed to the fluid pressure in the high pressure chamber (28), for creating the fluid recirculation path (F5) independently of whether said threshold is exceeded.

6. The fluidic machine as claimed in any preceding claim, characterised in that it includes a duct (30) for communication between a high pressure side of the machine (1) and the seat (12) of the regulating member (13), in order to convey pressurised fluid into said seat (12) and to apply said fluid against the base of the regulating member (13) opposite the base provided with said projections (16), in order to oppose the sliding of the regulating member.

7. The fluidic machine as claimed in any preceding claim, characterised in that it is a positive displacement internal gear pump (1) connected in the lubrication circuit of an engine, in particular a motor vehicle engine (50).

8. A method of regulating the flow rate of a fluidic gear machine (1), comprising the steps of:

- arranging, within a body (10) of the machine (1), a moving member (13) for flow rate regulation, the movement of which is controlled by the fluid pressure conditions in a fluidic circuit in which the machine is connected; and

- moving the regulating member (13) in order to create a fluid recirculation path (F5) between a high pressure side and a low pressure side of the machine;

characterised in that:

- said step of arranging a regulating member (13) within the body (10) of the machine (1) provides that said regulating member (13) comprises, on a base directed towards said high pressure side and said low pressure side, a pair of projections (16), which are received in through openings (17) formed in said body (10) so that said regulating member (13) is axially slidable without rotating; and in that

- said step of moving the regulating member (13) comprises:

a) permanently exposing at least one first annular surface (18) for pressure application, formed on said regulating member (13), to said fluid pressure conditions and making the regulating member (13) slide when a pressure threshold is exceeded; b) preferably, exposing to said fluid pressure conditions, upon commands externally controlled, also at least one second annular surface (19) for pressure application, to make the regulating member slide independently of whether said threshold is exceeded.

9. The method as claimed in claim 8, characterised in that said f uidic machine (1) is a positive displacement internal gear pump (1) connected in the lubrication circuit of an engine (50), in particular a motor vehicle engine.

10. A combined pump comprising a plurality of mutually coupled pumping subsystems, characterised in that one of said subsystems is a pump as claimed in any of claims 1 to 7.