Geared volumetric machine

A geared volumetric machine including:

TECHNICAL FIELD

The present invention relates to a geared volumetric machine. It is typically a pump but could also be a motor.

PRIOR ART

Geared pumps are known comprising cogged wheels with helical teeth. Two types of axial forces are generated on helical teeth: a mechanical one due to the interaction between the teeth and a hydrostatic one generated by the pressure acting in the compartments between the teeth. The axial force on the drive wheel is given by the sum of these two components, while on the driven wheel such two components are subtracted. Such axial force, considering the prolonged and pulsating stress, can reduce the efficiency, determine reliability problems or however generate premature wear on one of the two shims placed to the side of the cogged wheels, in particular at the cogged drive wheel. In order to completely or partially contrast such thrust (and reduce wear) a piston is known which exerts a balancing force on the cogged wheel, acting in a second direction opposite to the first.

In an alternative solution, there is a groove having a width of 2 millimetres on the shims and which extends according to an arc of a circle remaining at a constant distance from a rotation axis of one of the cogged wheels.

A fluid at high pressure is conveyed inside such groove, which exerts a counter-force in part the axial thrust induced by the helical teeth.

OBJECT OF THE INVENTION

The object of the present invention is to provide a volumetric machine that allows the manufacturing costs to be reduced, optimising the components. A further object of the present invention is that of minimising wear and therefore maximising the efficiency and reliability of a volumetric machine.

The stated technical task and specified objects are substantially achieved by a volumetric machine comprising the technical features disclosed in one or more of the appended claims.

In the accompanying figures reference number1denotes a volumetric gear machine. Typically it is a pump, but it could also be a motor or a reversible pump-motor machine. Such machine1comprises a first cogged wheel11. The first cogged wheel11in turn comprises a first and a second lateral flank111,112. The first and the second flank111,112are oriented transversally, preferably orthogonally, to a rotation axis of the first wheel11.

The machine1comprises a second cogged wheel12enmeshing with the first cogged wheel11. The first cogged wheel11comprises a plurality of teeth between which a plurality of compartments9are interposed. Such compartments9are destined to house the teeth of the second wheel12(during operation). A rotation axis of the first cogged wheel11and a rotation axis of the second cogged wheel12are parallel. The first and the second wheel11,12may be externally alongside each other. Appropriately the first cogged wheel11is the drive wheel and the second cogged wheel12is the driven wheel. The machine1comprises a casing in which the first and the second cogged wheels11,12are housed.

The machine1further comprises a first and a second abutment3,4between which the first cogged wheel11is interposed. The first and the second abutment3,4enable the abutment of the first cogged wheel11and the axial positioning thereof. The first abutment3may be a single monolithic body or an assembly of more parts. This is repeatable for the second abutment4. The first and the second abutment3,4are respectively a first and a second shim. The first and the second abutment3,4respectively face the first and the second lateral flank111,112of the first cogged wheel11. Appropriately, also the second cogged wheel12is interposed between the first and the second abutment3,4.

Advantageously the first abutment3defines a seat301in which a first stretch311of a support shaft of the first cogged wheel11is inserted. Appropriately the second abutment4defines a housing seat302of a second stretch312of the support shaft of the first cogged wheel11(the first and the second stretch311,312lie on opposite sides with respect to the first cogged wheel11). Appropriately the first and the second abutment3,4also define two seats303,304into which a first stretch313of a support shaft of the second cogged wheel12and a second stretch314of the support shaft of the second wheel12are inserted, respectively.

The machine1comprises a first and a second door91,92. The second door92operates at a higher pressure than the first door91; one from between the first and the second door91,92being an inlet door into the volumetric machine1of a fluid (incompressible, typically oil) and the other being an outlet door of the fluid from the volumetric machine1; in particular in the case in which the volumetric machine1is a pump the inlet door will be the first door91and the outlet door will be the second door92. In the event in which the volumetric machine1is a motor the inlet door will be the second door92and the outlet door will be the first door91. In that case the rotation direction of the first and the second wheel11,12is inverted with respect to the solution in which the machine is a pump (the forces diagram ofFIG. 1still remaining unaltered). The first and the second door91,92allow the inlet and outlet of fluid from a compartment housing the first and the second wheel11,12.

The volumetric machine1comprises a first grooved pathway31which at, least in a first angular position of the first cogged wheel11(advantageously in every angular position of the first wheel11) connects a first and a second zone51,52. The first zone51comprises/is at least one (preferably each) of the compartments9which is in communication with the second door92. The first zone51therefore affects at least one of the compartments9at high pressure (preferably all the compartments9at high pressure); compartment at high pressure means a compartment in which the instantaneous mean pressure is comprised between 50-100% of the instantaneous mean pressure of the second door92. Appropriately the first zone51comprises at least one (preferably all) of the compartments9in connection with the second door92through a track having a minimum cross section of greater area than that of a ball with a diameter of 2 millimetres. Appropriately, the first zone51comprises at least one (preferably all) of the compartments9in connection with the second door92through:a track that allows the passage of a ball (fictitious test element) with a diameter greater than 1 mm; ora hydraulic connection with an equivalent diameter equal to 1 millimetre.

The second zone52is the locus of the points interposed between the first abutment3and the first flank111(i.e. the part of the first abutment3covered by the first wheel11). The second zone52is called “passageway”.

The track that connects one of the compartments9to the second door92can comprise, for example, a groove93formed on an outer perimeter edge of the first or of the second abutment3,4. Such track may possibly simply be an interface defined between one of the compartments9that opens (radially) directly into a zone facing the second door92. Such track can also comprise a micro-incision being part of the first grooved pathway31.

If, with respect to a reference tooth, the left and right compartments (51aand51bofFIG. 7) are connected to the high pressure and the seats301,302,303,304of the support shafts work at low pressure (i.e. the support shafts do not have a forced sustenance with fluid under pressure), the pressure distribution in the passageway52is that ofFIG. 7: note the isobaric curves from the high pressure zone H to the low pressure zone L.

The first grooved pathway31has the objective of modifying the above pressure distribution. InFIG. 7(where the expedient according to the present invention is absent) a plurality of isobaric curves can be identified between a zone H at higher pressure and a zone L at lower pressure whereas inFIG. 6(according to the present invention) such isobaric curves have been concentrated below the arc33and the zone H at high pressure is much larger. The effect of increasing the surface wetted by oil at high pressure has the consequence of generating an extra force61that tends to separate the first abutment3and the first flank111.

The first abutment3can comprise such first grooved pathway31that faces the first flank111or, in an alternative solution not illustrated, the first flank111can comprise at least a first grooved pathway31that faces the first abutment3. The first grooved pathway31is part of the distribution means in a second zone52of an incompressible fluid (at high pressure) present in a first zone51. In this way it is possible to modify the distribution of pressure ofFIG. 7obtaining that ofFIG. 6. The first grooved pathway31therefore performs a driving channel function. In fact, it transfers pressure from the first to the second zone51,52. In this way, the pressure increases at a passageway present between the teeth of the first wheel11and the first abutment3moving it closer/equalising it with the (greater) pressure that is recorded at the compartments9between the teeth. In particular, the increase in pressure due to such expedient is particularly clear at the base of the teeth of the first wheel11.

The first grooved pathway31comprises a stretch having a passage section with a surface area less than 1 mm2, preferably less than 0.75 mm2even more preferably less than 0.5 mm2. Such stretch can also envisage changes in direction that are more or less marked but without interruptions. Advantageously, such stretch extends for a greater length than at least 25% of the length of the pitch circle radius of the first cogged wheel11. Advantageously said stretch affects at least 90%, preferably 100%, of the first grooved pathway31. Preferably such stretch of the first grooved pathway31has a depth comprised between 0.07 and 0.7 millimetres. Such stretch of the first grooved pathway31has a width comprised between 0.03 and 0.7 millimetres. Appropriately the depth and/or the width of the first grooved pathway31are constant. It can therefore be defined as a micro-slit. A reduced width of said first grooved pathway31allows the surface that is subtracted from the contact between the first flank111and the first abutment3to be minimised. Therefore, it is possible to keep the support surface between the first abutment3and the first flank111high, consequently not reducing/penalising the hydrostatic and hydrodynamic sustenance capacity at the interface between the first abutment3and the first flank111.

The first grooved pathway31, at the second zone52, at least partly extends between a radially nearer position and a radially more distant position from a rotation axis of the first cogged wheel11.

Advantageously, for at least half of the angular pathway of the first wheel11the first grooved pathway31connects the first and the second zone51,52.

Appropriately, in each angular position of the first wheel lithe first grooved pathway31connects the first and the second zone51,52.

Even more preferably in each angular position of the first wheel lithe first grooved pathway31connects the first zone51and the passageway placed between:each tooth of the first wheel11in communication with the second door92(or at least 75% of the teeth of the first wheel11in communication with the second door92); andthe first abutment3.

Possibly the machine1can comprise a plurality of grooved pathways31,310which in combination, in each angular position of the first wheel11, connect the first zone51and the fluid passageways placed between:each tooth of the first wheel11in communication with the second door92(or at least 75% of the teeth of the first wheel11in communication with the second door92); andthe first abutment3.

Appropriately, each of said grooved pathways31,310at the second zone52, at least partly extends between a radially nearer position and a radially more distant position from a rotation axis of the first cogged wheel11.

Appropriately, the first and second cogged wheels11,12are cogged wheels having helical teeth.

The mechanical interaction between the helical teeth of the first and of the second wheel11added to the hydrostatic force generated by the pressure between the compartments9of the teeth of the first wheel11determines an axial thrust of the first wheel11towards the first abutment3. Such thrust is greater for the drive wheel with respect to the driven wheel (for this reason it was previously indicated that the first cogged wheel11is appropriately the drive wheel). The teeth of the first wheel11comprise a first tooth that extends between the first and the second abutment3,4from a first end113placed at the first flank111to a second end114placed at the second flank112. The first end113is more advanced than the second end114with respect to a rotation direction of the first wheel11.

An axial counter-force (indicated by the reference61) exerted by the pressure of a fluid interposed between the first flank111and the first abutment3is greater than the axial thrust (indicated by reference62) towards the first abutment3(induced by the mechanical interaction between the teeth and by the hydrostatic pressure between the compartments9of the first wheel11). Such fluid is the operating fluid processed by the volumetric machine1(it is typically oil). As highlighted inFIG. 2, during the rotation of the first and the second cogged wheel11,12there is an oscillation both of the axial thrust62and of the axial counter-force61exerted by the pressure of the fluid interposed between the first flank111and the first abutment3(generated for example by the first grooved pathway31). Despite such oscillation, the counter-force61indicated above still remains greater than the axial thrust62.

In fact, it occurs that the axial thrust62is oriented against the first abutment3, at the first end113. In such first end113it occurs that the tooth forms with the first abutment3a positive rake angle (A) (seeFIG. 8). In other words the acute angle formed by the tooth with the first abutment3is turned in the opposite direction to the advancement direction of the first cogged wheel11. From the theory of cutting tools it is known that a positive rake angle (with equivalent tool compression force) induces a more effective cutting and shaving removal action with respect to a negative rake angle (in the same way, with a fixed compression force between the elements, a positive rake angle can cause more wear and more quickly on the relative sliding surfaces with respect to the case in which there is a negative rake angle). In this case the fact that the axial thrust62exerts its action at the positive rake angle is worthy of attention. The use of a counter-force61with a greater modulus and opposite direction generated by the presence of pressurised fluid between the first abutment3and the first flank111ensures that the axial resultant63is turned towards the second abutment4(where the teeth have a negative rake angle and therefore the wear action on the second abutment4is lower).

As previously mentioned, a plurality of grooved pathways31,310are appropriately provided, each comprising at least one portion having a passage section less than 1 mm2, preferably less than 0.5 mm2. The grooved pathways310also comprise the first grooved pathway31.

The grooved pathways310are at least in part (preferably all) formed on the first flank111and face the first abutment3or vice versa they are at least in part formed on the first abutment3and face the first flank111.

What is indicated with reference to the first grooved pathway31with reference to the extension or to the width or to the depth of said stretch can be repeated for the grooved pathways310.

As exemplified inFIGS. 3, 4, 5the first grooved pathway31comprises a plurality of grooves32which extend between a radially more internal position and a radially more external position. The grooves32are preferably formed in the first abutment3and face the teeth of the first cogged wheel11.

Advantageously the grooves32extend in spoke-fashion. Appropriately the spoke-fashion grooves32are separated from each other by an angle comprised between 10° and 40°. Preferably the spoke-fashion grooves32are separated from each other by an angle that is less than half the angular pitch. The grooves32extend from a common channel33which extends in an arc (the grooves32extend transversally to the channel33). Appropriately such arc remains at a same distance from the rotation axis of the first cogged wheel11. The arc is coaxial with the rotation axis of the first cogged wheel11. Such arc extends for at least 150°, preferably at least 180°. In the preferred solution, for each angular position of the first wheel11, at least one (preferably a plurality) of the grooves32face a zone that is uncovered by the first wheel11so as to prime oil from the pressurised compartments9and distribute it in zones in which the teeth of the first wheel11and the first abutment3are superposed. Appropriately the channel33extends in a radially more internal position with respect to the lower bottom of the tooth. This allows the pressure exerted by the fluid present therein to be increased.

In the preferred solution, the first grooved pathway31is a laser incision. Appropriately, the grooved pathways310are laser incisions. Likewise, also said common channel33is a laser incision. Such channel33has a surface passage section less than 1 mm2or preferably less than 0.5 mm2.

In a particular constructive solution the grooved pathways31,310as well as extending in a zone of the first abutment3opposing the first flank111(or in a zone of the first flank111opposing the first abutment3) could also be formed in a zone of the first abutment3opposing a flank of the second cogged wheel12(or a zone of a flank of the second wheel12opposing the first abutment3). As previously mentioned, also in that case the grooved pathways31,310each have at least one portion having a passage section (cross sectional area) less than 1 mm2, preferably less than 0.5 mm2.

Further subject matter of the present invention is an operating method of a volumetric machine having one or more of the characteristics described hereinabove.

The method comprises the steps of:generating a layer of pressurised fluid between said first abutment3and said first flank111redistributing the pressure of said layer of fluid at least through the first grooved pathway31(or better the plurality of grooved pathways310);exerting by means of said layer of fluid an axial counter-force with a greater and opposite modulus with respect to an axial thrust62induced by the sum of the mechanical interaction between the helical teeth of the first and of the second wheel11,12and the hydrostatic force of pressure on the teeth of the first wheel11.

Further subject matter of the present invention is a method for realising a volumetric machine having one or more of the characteristics described hereinabove. Such realisation method comprises the steps of:realising the first cogged wheel11, the second cogged wheel12, the first and second abutment3,4;carrying out said first grooved pathway31(or however said grooved pathways31,310), preferably by laser incision on the first cogged wheel11or the first abutment3.

The invention achieves important advantages.

Above all it allows the realisation costs of a volumetric machine to be optimised, at the same time improving the operating reliability and minimising wear. The invention as it is conceived is susceptible to numerous modifications and variations, all falling within the scope of the inventive concept characterising it. Furthermore, all the details can be replaced by other technically equivalent elements. In practice, all the materials used, as well as the dimensions, can be any according to requirements.