Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C29/00—Component parts, details or accessories of pumps or pumping installations, not provided for in groups F04C18/00 - F04C28/00
  • F04C29/0042—Driving elements, brakes, couplings, transmissions specially adapted for pumps
  • F04C29/005—Means for transmitting movement from the prime mover to driven parts of the pump, e.g. clutches, couplings, transmissions
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C2/00—Rotary-piston machines or pumps
  • F04C2/30—Rotary-piston machines or pumps having the characteristics covered by two or more groups F04C2/02, F04C2/08, F04C2/22, F04C2/24 or having the characteristics covered by one of these groups together with some other type of movement between co-operating members
  • F04C2/34—Rotary-piston machines or pumps having the characteristics covered by two or more groups F04C2/02, F04C2/08, F04C2/22, F04C2/24 or having the characteristics covered by one of these groups together with some other type of movement between co-operating members having the movement defined in groups F04C2/08 or F04C2/22 and relative reciprocation between the co-operating members
  • F04C2/344—Rotary-piston machines or pumps having the characteristics covered by two or more groups F04C2/02, F04C2/08, F04C2/22, F04C2/24 or having the characteristics covered by one of these groups together with some other type of movement between co-operating members having the movement defined in groups F04C2/08 or F04C2/22 and relative reciprocation between the co-operating members with vanes reciprocating with respect to the inner member
  • F04C2/3441—Rotary-piston machines or pumps having the characteristics covered by two or more groups F04C2/02, F04C2/08, F04C2/22, F04C2/24 or having the characteristics covered by one of these groups together with some other type of movement between co-operating members having the movement defined in groups F04C2/08 or F04C2/22 and relative reciprocation between the co-operating members with vanes reciprocating with respect to the inner member the inner and outer member being in contact along one line or continuous surface substantially parallel to the axis of rotation
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C29/00—Component parts, details or accessories of pumps or pumping installations, not provided for in groups F04C18/00 - F04C28/00
  • F04C29/0042—Driving elements, brakes, couplings, transmissions specially adapted for pumps
  • F04C29/005—Means for transmitting movement from the prime mover to driven parts of the pump, e.g. clutches, couplings, transmissions
  • F04C29/0057—Means for transmitting movement from the prime mover to driven parts of the pump, e.g. clutches, couplings, transmissions for eccentric movement
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C29/00—Component parts, details or accessories of pumps or pumping installations, not provided for in groups F04C18/00 - F04C28/00
  • F04C29/0042—Driving elements, brakes, couplings, transmissions specially adapted for pumps
  • F04C29/005—Means for transmitting movement from the prime mover to driven parts of the pump, e.g. clutches, couplings, transmissions
  • F04C29/0071—Couplings between rotors and input or output shafts acting by interengaging or mating parts, i.e. positive coupling of rotor and shaft

Definitions

• the present invention generally relates to a positive displacement pump and to a method of operating same.
• the present invention relates to a rotary positive displacement vacuum pump equipped with devices arranged to modify the gear ratio between the drive members and the pump.
• the present invention is applied in vacuum pumps operated by an internal combustion engine of a motor vehicle.
• positive displacement pumps e. g. vacuum pumps arranged to generate and maintain, in a tank or booster, e. g. of a power brake, a vacuum or depression mainly serving for operating brakes and other devices requiring a vacuum in order to work.
• document WO 2013054263 in the name of the Applicant, discloses a vacuum pump connected to a shaft of the engine and rotating at a speed equal to the speed of the shaft driving it.
• Document WO 2004092588 discloses an oil pump and a vacuum pump integrated with each other and structurally independent from the engine.
• the pump is to be located at a predetermined position, in correspondence of a driving wheel fixedly connected with the driving shaft.
• the prior art pump has a rotor made of metal with gear wheels made of metal.
• Document DE 102004016237 discloses a vacuum pump having two rotors and two corresponding shafts externally equipped with two gear wheels; one of the gear wheels is driven by an internally toothed driving wheel.
• a problem with the first prior art is that the rotation speed of the vacuum pump is the same as the speed of the driving shaft.
• a problem with the second prior art is that the vacuum pump is constrained to occupy a predetermined space, inside or outside the engine, corresponding to a predetermined angle defined between the engine and the oil pump. Moreover such a prior art, having a rotor and a gear wheel made of metal, has a high moment of inertia.
• the present invention also concerns a method of operating a positive displacement pump.
• the positive displacement pump includes a driven gear wheel and a driving gear wheel, coupled so as to form a gear train in which the gear wheels are placed one inside the other.
• the driven and driving wheels have parallel axes and are cylindrical wheels with helical or straight teeth or bevel wheels.
• the driven and driving wheels are bevel wheels with crossed axes (skew bevel wheels).
• one of the driven and driving wheels has teeth formed on an outer surface and one of the driven and driving wheels has teeth formed on an inner surface, respectively.
• this allows making gear trains with a reducing or multiplying gear ratio.
• the pump can be arbitrarily located along a circumference centred on the rotation axis of the driving wheel.
• Fig. 1 is an isometric axonometric view of a rotary vacuum pump, as seen from the drive side;
• Fig. 2 is a front view, from the drive side, of the vacuum pump shown in Fig. 1;
• - Fig. 3 is an axial cross sectional view of the pump, taken according to a plane passing through line AA in Fig. 2;
• Fig. 4 is an isometric axonometric view of the vacuum pump, as seen from the side opposite to the drive side, without the cover;
• FIG. 5 is a front view of the vacuum pump, from the side opposite to the drive side, without the cover;
• - Fig. 6 shows a detail of the drive side of the pump.
• a positive displacement pump 13 is, for instance, a rotary vacuum pump.
• Positive displacement pump 13 in the exemplary embodiment, has a body 15 defining a chamber 16 with substantially elliptical cross-section, of known type, which in the example is a vacuum chamber, and a drive side 18 (Figs. 1 and 2).
• Vacuum chamber 16 in use is closed by a cover 17 (Fig. 3).
• a rotor 12 for instance a single-vane rotor, is housed within vacuum chamber 16.
• the rotor could be a multi-vane rotor, a so-called
• pendulum rotor or a rotor of any other kind envisaged in the art.
• Rotor 12 employed herein is preferably made of a lightweight material, for instance a plastic or thermoplastic material.
• the movement of rotor 12 is preferably constrained by a guide 14 formed in pump body 15.
• At least one outlet for a discharge duct 20 and at least one inlet for a suction duct 19 are formed in pump body 15 and communicate with chamber 16.
• the rotor has, on drive side 18, teeth 11a arranged to form a gear wheel 11 that in the example is a driven wheel.
• Wheel 11 referred to herein as driven wheel, is for instance a cylindrical wheel with helical teeth.
• a shaft 10 forms a control (or drive) member for the pump.
• drive member 10 is for instance a shaft of the engine, a cam shaft, a shaft of the alternator, an output shaft of an oil pump, and so on.
• a gear wheel 10a for instance a cylindrical wheel with helical teeth, can be preferably formed at or connected to one end of shaft 10.
• said wheel is made of metal and its teeth are designed for meshing with the teeth of driven wheel 11 thereby forming a gear train.
• Wheel 10a may be for instance integrally formed with shaft 10 or it may be interference-keyed on shaft 10. Wheel 10a is therefore fixedly connected with shaft 10 and is defined herein as driving wheel.
• driving wheel 10a fixedly connected with shaft 10
• driven wheel 11 fixedly connected with rotor 12
• gear train with parallel axes in which the driving wheel is placed inside the driven wheel (Figs. 1 to 3).
• the wheels could also be bevel wheels arranged to form a gear train with skew axes (in this case the whole of the two wheels is referred to as a bevel gear pair).
• driven wheel 11 has greater size than driving wheel 10a, that is, driven wheel 11 has a radius r 2 greater than radius ri of driving wheel 10a.
• driven wheel 11 has a number of teeth z 2 greater than the number of teeth zi of driving wheel 10a.
• gear ratio R can also be defined as the mathematical ratio between the numbers of teeth of the gear wheels, i.e.
• gear ratio R is therefore a reducing ratio (R > 1). This means that rotor 12 of positive displacement pump 13 rotates at a speed co 2 lower than speed coi of shaft 10, this allowing a reduction of the power dissipated by pump 13.
• the driving wheel could be external to driven wheel 11 associated with the pump rotor.
• the driven wheel will have external teeth in place of internal teeth.
• gear ratio R is a multiplying ratio (R ⁇ 1) and allows the pump rotor to rotate at higher speed than the drive shaft.
• driving wheel 10a and driven wheel 11 are cylindrical gear wheels with parallel axes (Fig. 6)
• rotation axis 0 2 of driven wheel 11 (and hence of rotor 12) can be arbitrarily located along a circumference C with radius r centred on rotation axis Oi of driving wheel 10a.
• gear trains with skew axes provides an additional degree of freedom with respect to the embodiment using gear trains with parallel axes.
• Wheels 10a and 11 described above as cylindrical wheels with helical teeth and parallel axes, may have any shape known in the art, for instance they can be two straight- toothed cylindrical wheels with parallel axes, two bevel wheels with parallel or skew axes, etc.
• helical gear trains with a suitably defined and oriented angle of the helix allows obtaining an axial thrust directed from the inside of pump 13 towards the drive side and aimed at balancing, or at least reducing, the axial thrust in the opposite direction due to the pressure difference, thereby reducing the greater friction generated by the latter.
• a further positive displacement pump for instance an oil pump
• a further positive displacement pump for instance an oil pump
• Configurations of the above type in which two pumps are arranged downstream each other, are usually referred to as tandem pumps in the present technical field.
• FIG. 1 to 6 showing an exemplary preferred embodiment.
• drive shaft 10 When drive shaft 10 (and hence wheel 10a) rotates at a given angular speed coi, it transmits the rotary motion or torque to rotor 12 of pump 13, through the pair of driving wheel 10a and driven wheel 11.
• Rotation speed co 2 depends on rotation speed coi of drive shaft 10 and on gear ratio
• Vane 12a of rotor 12 is forced against wall 16a of vacuum chamber 16 so as to ensure tightness with the same wall 16a.
• a suction step in which part of a gas present in at least one environment where vacuum is to be created is sucked into vacuum chamber 16 through at least one suction duct 19;
• a discharge step in which the gas compressed during the compression step is discharged through at least one discharge duct 20.
• the structure of the positive displacement pump and the corresponding operation method as described herein have several advantages.
• the reducing gear ratio of the pair of driving wheel 10a and driven wheel 11 allows reducing in predetermined manner the rotation speed of rotor 12 of pump 13 relative to the speed of driving shaft 10.
• pump 13 connected with a reducing gear ratio, has a pumping efficiency similar to that of a pump connected with a unit (“impartial") gear ratio - i.e. a ratio where the rotation speeds of the rotor and the driving shaft are the same - it is preferably useful to increase the displacement of pump 13.
• impartial gear ratio i.e. a ratio where the rotation speeds of the rotor and the driving shaft are the same - it is preferably useful to increase the displacement of pump 13.
• the Applicant provides hereinbelow an example of approximate calculation of dissipated powers, assuming a vacuum pump where the reducing gear ratio is 2 (i.e. where the pump rotor rotates at half the speed of the drive shaft) and the displacement is twice the displacement of a reference pump having a unit gear ratio.
• the Applicant has assumed that, in the average use of the motor vehicle, the pump operates for 10% of the operation time in order to restore a vacuum required by the braking system and for 90% of the operation time in order to maintain such a vacuum. In any case, this assumption has been confirmed by the practice.
• the Applicant has realised that, due to the greater pump displacement, the power absorbed by the vacuum pump increases, during vacuum restoration, by about 50% relative to the power absorbed by the reference pump.
• the Applicant has realised that, due to the lower rotation speed, the power absorbed by the vacuum pump during vacuum maintenance decreases by about 50% relative to the power absorbed by the reference pump, since, under such conditions, the power due to the torque, or resistant torque, associated with the pump rotor does not change as the number of revolutions of the pump changes.
• W power absorbed by the pump, in watts
• the structure and the operation method of a pump using gear trains with parallel or skew axes, like the gear trains described above, offers the advantage of making installation of pump 13 easier, depending on the available space in a motor vehicle.
• the driving wheel can for instance be exchanged with the driven wheel, i.e., the teeth of the driven wheel are formed on the external surface thereof and the teeth of the driving wheel are formed on the internal surface thereof.
• drive gear trains characterised by a multiplying gear ratio towards the driven wheel in case of a low rotation speed of the drive shaft and the driving wheel associated therewith, it is possible to use drive gear trains characterised by a multiplying gear ratio towards the driven wheel.
• a reducing or multiplying gear ratio is advantageous, for instance, in tandem configurations, in which a first positive displacement pump is arranged downstream a second positive displacement pump, while maintaining all advantages of installation simplicity and energy balance as described above.
• Another advantage of the invention is the possibility of using a rotor made of a lightweight material, for instance a plastic or thermoplastic material, with a consequent reduction in the moment of inertia of the same rotor.
• a further advantage results from the possibility of limiting, in the case of vacuum pumps, the axial thrust acting on rotor 12 because of the pressure difference between chamber 16 of pump 13 and the outside environment.
• Such a skewing force is applied to the pump rotor and consequently to the guide thereof, passes through the centre of rotation of the rotor, is directed from a compression region to a suction region in the vacuum chamber and has an orientation that is rotated by about 20*, in the direction of rotation of the rotor, relative to the straight line passing through the rotor centre and the point of tangency between the rotor and the vacuum chamber.
• a drive shaft configured in accordance with the present invention generates a radial thrust on the rotor, due to the drive of the same rotor, in such a direction as to space out the teeth of the driven wheel from the teeth of the driving wheel along a straight line passing through the respective centres of rotation.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Applications Or Details Of Rotary Compressors (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=50159450

Family Applications (1)

Country Status (3)

Citations (5)

• 2013
  • 2013-12-30 IT IT001081A patent/ITTO20131081A1/it unknown
• 2014
  • 2014-12-23 EP EP14830724.2A patent/EP3090183B1/de active Active
  • 2014-12-23 WO PCT/IB2014/067259 patent/WO2015101902A1/en active Application Filing

Patent Citations (5)

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