GB2399145A

GB2399145A - Gear pump with electromagnetic drive

Info

Publication number: GB2399145A
Application number: GB0302157A
Authority: GB
Inventors: Andrew Stevenson
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2003-01-30
Filing date: 2003-01-30
Publication date: 2004-09-08
Also published as: GB0302157D0

Abstract

The gears 4,5 of a positive-displacement gear pump 1 are located within a cavity 3 and are moved by electromagnetic elements 8 incorporated in the cavity 3 and sequentially switched into and out of activation. The electromagnetic elements 8 are sequentially actuated by controller 10 to interact through magnetic induction with the teeth of the gears in order to create the necessary movement for pumping action. Gear momentum is also used to maintain movement. The whole of each tooth may be formed from magnetically inducable material or, alternatively, the gears may be formed from a base material, eg plastics or ceramic, with magnetically inducable teeth or tips, eg of cobalt iron alloy or silicon steel. The invention allows the cavity 3 to be essentially closed and thus reduces risk of leakage.

Description

PUMP

The present Invention relates to pumps and more particularly to gear pumps.

Gear pumps are known and generally comprise inter engaging gears operating in a cavity whereby rotation of the gears creates a positive pressure in order to pump a fluid through the gears and therefore the pump. Generally. one of the gears is driven by an electric motor or a drive shaft from an engine. Thus, although gear pumps can be scaled in terms of pumping capacity or particular requirements such prior gear pumps still have a relatively high component count and require a drive shaft from a prime mover such as an electric motor or combustion engine to drive one of the gears. Such a drive shaft requires an aperture with a seal through a cavity wall in order to ensure the cavity is appropriately sealed. Furthermc e with one gear acting as a drive gear there are potential abrasive problems between that driving gear and the driven or idling gear. A gear pump essentially comprises two gears in mesh mounted within a close fitting casing such that any wear of the gear teeth or driving shaft location may alter the performance of the gear pump.

In accordance of the present invention there Is provided a pump comprising inter engaging gears v, thin a cavity. movement of the gears creating a positive pressure to drive a fluid In use hrough the pump in a pumping act an, the cavity incorpcratng suitable magnetic elements to cause movement of the gears men sequentially switched between magnetic states.

Preferably, the gears are wholly formed from a magnetically inducible metal.

Alternatively, the gears are formed from a base material with magnetically inducible material teeth or bps at least. The gears may all have teeth or tips made from a number of materials including cobalt iron alloy and silicon steels. The base material may be a plastics material or a ceramic. The gears or other parts of the pump may be made up from laminations to reduce eddy current losses. - 2

Possibly, the gears may be weighted for inertia momentum smoothing of gear rotation. Such weighting will generally be at the tips of the gear teeth.

Normally, all gears will be driven by the magnetic elements when sequentially switched between magnetic states.

Possibly, each gear will be respectively driven alternately in accc--ance with the switching sequence to achieve the desired pumping action.

Possibly, the magnetic elements may be arranged to provide drac to allow more rapid stopping of the pumping action.

Possibly, two or more magnetic elements operate simultaneous, to progress movement of the gears. Normally, the two or more magnetic element will act upon different gears or gear teeth.

Possibly, the cavity is substantially closed except for an input port ad output port such that the gears are driven inductively by the magnetic elements. Pcsbly, the gear tics are drawn into touching contact..ith an internal surface of the cavity is. the magnetic e ements when sequentially switched -a driving gear movement.

Typically, the magnetic elements will be controlled by a controlle to provide the necessary sequential switching of the magnetic elements In order to caulk movement of the gears or pumping action. Normally, the switching sequence will vary dependent upon the speed of rotation of the gears within the pump. The magnetic elements about the cavity will be substantially isolated from each other.

Generally, through the magnetic elements the controller will be at e to determine the relative position of the gears within the cavity. Possibly, one tooth o' a gear may be individually marked or discernable by the controller in order to initiate an appropriate switching sequence to begin movement of the gears for pumping action.

An embodiment of the present invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 is a schematic cross section of a pump In accordance with the present invention; and, Fig. 2 is a schematic diagram illustrating operation of a pump in accordance with the present invention.

Fig. 1 illustrates a schematic cross section of a pump in accordance with the present invention. The pump 1 comprises a casing 2 within which a cavity 3 Is defined.

Within this cavity 3, two gears 4, 5 are located in an intermeshed or engaging relationship such that rotation in the direction shown by respective arrowheads A, B causes a pressure differential pumping a fluid from an inlet 6 to an outlet 7.

Within the casing 2 a number of magnetic elements 8 are located. These magnetic elements 8 are essentially electromagnE s in which wire coils are located such that an electromagnetic force can be createc within these elements 8. The theory of electromagnetism is well known thus it wit rue appreciated Nat when an electrical current is passed through the coils in the elements 8 in order to generate the electromac,etic force.

In accordance with the present invention this electromagnetic force is used In order to cause the rotation in the direction of arrowheads A, B by switched sequencing to draw gear teeth to a respective element 8 to progress and sustain rotary movement. The specific electrical current, coil size and other factors will be determined by the necessary performance of the pump 1, its size, and fluid to be pumped from the inlet 6 to the outlet 7.

As can be seen the gears 4, 5 are essentially of a spur type in which the teeth intermesh or engage. Thus, movement of one gear 4, in accordance with the present invention creates reciprocal movement in the other gear 5. In such circumstances and in accordance with the present invention both gears 4, 5 are driving as well as driven gears within a gear pump 1 arrangement.

In order to create the necessary n,. cement In the direction of arrowhea s A, B there is normally an attractive force created by the elements 8 with at least tip portions of the teeth of the gears 4, 5. Alternatively, it may be possible to provide movement by a repulsive reaction or such repulsive action by one element 8 used in association with a positive pull action applied to other tip portions by other magnetic elements 8. In these circumstances, the gears 4, 5 must be rendered or have an inherent capability for magnetic attraction or repulsion. Normally, the gears 4, 5 will be made from a metal such as a cobalt iron alloy.

It is mostly the teeth and in particular the tip part of these teeth which will interact with the magnetic elements 8. In such circumstances, the gears 4, 5 may be made from a base material upon which the teeth or os of the teeth are formed from a magnetically inducible material. The base material rr^.y be a plastic or ceramic whilst the teeth or tips may be made from a metal alloy (cobalt On alloy) or other rr,atenal. It will isunderstood by use of a base material for the bulk of He gears 4, 5 relatively more expens e materials used In the teeth which are magnetically educible can be more economically sed.

The electromagnetic elements 8 provide individual stimulus to movements of the gears 4, 5 in the direction of arrowheads A, B. The more elements A provided the smaller the incremental steps of motion and therefore jerkiness of the motion of the gears 4, 5 in the direction of arrows A, B. In order to further smooth any Jerkiness of Such motion the gears 4, 5 and in particular the teeth or tips may be disproportionally weighted such that there is additional inertia and momentum within the respective gears 4, 5 smoothing the motion in the directions A, B between each individual electromagnetic element 8 step movement. Nevertheless, the more electromagnetic elements 8 provided generally the better the pump 1 Will perform. However, the number of electromagnetic elements 8 provided will generally be limited by the availability of casing 2 space to accommodate the elements 8 while maintaining isolation of each electromagnetic element 8 in order to provide the necessary interactive engagement with the gears ', 5 for desired motion in the direction of arrowheads A. B. It will also be understood that sequential firing or activation switching of the electromagnetic elements 8 in an appropriate sequence must be closely controlled by a controller device (described later) and the more electromagnetic elements 8 provided the more difficult such control will be.

In order to drive rrotion in the direction of arrowheads A. B it will be understood that at least one electromagnetic element 8 will be activated or energised in order to bring a gear tooth or tip into alignment with it. Clearly, it is necessan. that the alignment be drawn in the direction required for motion in the direction of arrowheads A, B. Thus, in order to cause the necessary motion the attracted gear tooth or gear t should be relatively near to the specific electromagnetic element 8 energised in order that it is that tooth which is attracted rather than a gear tip or tooth which has already passed the electromagnetic element 8 In the moverrent cycle in the direction of arrowheads A, B for the gears 4, 5 in the pump 1. In such c-^umstances, careful consideration must be made with respect to the switching sequence of electromagnetic i- ement 8 acts con. It Will be noted in the embodiment depicted fir Fig. 1 there are twelve electromagnetic elements 8 and twenty gear teeth or gear tips tooth gears 4, 5 combined. Thus. -he choice with respect to the appropriate electromagnetic element 8 and gear tooth o tip combination to achieve desired continued motion in the direction of arrowheads A, B Is relatively complex.

An open loop control approach may be provided where there is a substantially fixed switching sequence for the electromagnetic elements 8. In this approach the order of switching or energising the electromagnetic elements 8 is fixed for initial start up followed by a steady state operation at a desired gear rotation speed between the gears 4, 5 for pumping action. Thus, this open loop control depends upon predictability with respect to - 6 the position of the gear teeth or tips within the cavity relative to known positions of the electromagnetic elements 8. In such circumstances, continuing movement of the gears 4, in the direction of arrowheads A, B is achieved by repeating that sequence of switched energising of the electromagnetic elements 8 whereby each element 8 in its sequence provides the necessary nudge (pull attraction or push repulsion) for further movement in the direction of arrowheads A. B in the knowledge that its respective gear tooth Or tip will be in the approximate desired position for that sequence of electromagnetic elements 8 activations. Unfortunately, although possibly acceptable during steady state conditions it will be appreciated that the gears 4, 5 will pass through a number of rotational speeds from a standstill condition to that of the relatively stable rotation. Furthermore, there may be a degree of slippage between the gears 4, 5 in relation to their position such that over time the fixed sequential energising program of the elements 8 may not adequately continue the desired rotation of the gears 4, 5 in orcer to create a necessary pumpir 3 action.

Nevertheless, if periodically gear position is determined it may be possible to zero" the pump and so begin again the switching sequence at the correct stage.

In view of the above when possible a closed control approach will be taken with respect to the sequence of electromagnetic e ement 8 activation. It will be unders cod that the gear teeth or tips themse!,es will influer e any current passnc. through the c- Is in the electromagnetic elements 8. in such circumstances, the relative,costion of tr.e Gears 4, 5 may be determined within the cavity 3 of the pump 1. Through such knowledge f relative gear position it is possible to determine the most appropriate electromagnetic element 8 to be activated to continue further movement of the gears 4, 5 in the direction of ar owheads A, B. In any event, with a closed loop control system the necessary switching sequence of electromagnetic element 8 activation may vary and is dependent upon the temporal consideration as to the best electromagnetic element 8 activation to create onward movement in the direction of arrowheads A, B in the gears 4, 5 which in tum may be dependent upon slippage, viscosity of the fluid pumped and other factors. - 7

As can be seen in Fig. 1, the tips of the gears 4, 5 essentially sweep an internal surface of the cavity 3 in order to create the positive pressure driving fluid flow from the inlet 6 to the outlet 7. In such circumstances there will generally be a small film of fluid between the gear tip and the internal surface of the cavity 3. Some consideration may be necessary with respect to the fluid pumped in terms of its effect upon the electromagnetic attractiveness of the elements 8 in moving the gears 4, 5 in the directions A, B. Where desirable it may be possible to draw the gear teeth into a slight extension in order to provide at least during transit past the attracting electromagnetic element 8 that tooth into even closer engagement with the inner surface of the cavity 3.

Although there will be an induced magnetism in the gear 4 5 teeth by the sequential switching of the elements 8 into activation normally that induced magnetism will be short lived and generally will not create any interaction between the centrally meshing teeth between the gears 4, 5.

Fig. 2 illustrates a schematic diagram of a pump in accordance with the present invention coupled to a controller and switch arrangement. Thus. the pump 1 as described previously has a casing 2 defining a cavity 3 within which gears 4, 5 are located in order to pump a fluid from an inlet 6 to an outlet 7. Movement of the gears 4. 5 is through sequenced switched actv:;;ion of electromagnetic elements 8 n ounted within the cas rig 2.

These electromagnetic elements 8 as Indicated previously are electrically and magnetically Isolated from each other This may be achieved through the material from which the casing 2 is formed or alternatively by specific isolation of the elements 8 within respective insulating seats formed in the casing 2. Each electromagnetic element 8 is coupled to a switch 9 which in turn is controlled by a controller 10. The switch 9 activates the electromagnetic elements 8 in the desired switching sequence in order to generate the necessary movement of the gears 4, 5 in order to create pumping action between the inlet 6 and the outlet 7. As indicated previously, the switch arrangement 9 may operate in accordance with an open loop or a closed loop control regime. In an open loop regime the controller 10 would simply provide the sequential switching instructions to the switch - 8 arrangement 9 in order to energse the appropriate electromagnetic element 8 in order to achieve desired motion by the gears 4, 5 to create the pumping action. In a closed loop control regime the controller 10 through the switch arrangement 9 would dynamically determine the relative positions of the gears 4, 5 as indicated previously and then activate through that switch arrangement 9 the necessary electromagnetic element 8 in order to create or continue motion of the gears 4, 5 in the desired pumping action. As described previously the fixed or variable switching sequence for the electromagnetic elements 8 may vary dependent upon sensed viscosity in the liquid pumped, the rate of fluid flow required through the pump 1 and other factors. Generally, the controller 10 through an appropriate sensor pathway 11 will at least confirm that the desired flow rate of fluid through the pump is achieved.

As Indicated previously the number of electromagnetic elements 8 used will generally be maximised in order to achieve greater controllability and performance of pump 1 operation. The more electromagnetic elements 8 the greater the pump 1 efficiency. However, it will also be understood that the number of electromagnetic elements 8 may be limited by the possibility of appropriate control by the arrangement 9 and controller 10 as well as the ability to install electromagnetic elements 8 in appropriate isolation within the casing 2 without weakening that casing in terms of me--apical strength.

Generally, a statistical analysis will be made in order to determine the required positions of the electromagnetic elements 8 to achieve pump 1 efficiency. As indicated previously at least one appropriate electromagnetic element 8 to gear tip or tooth combination engagement should be available during pump 1 operation in order to continue desired operation. In such circumstances, the relative electromagnetic strength of the installed electromagnetic elements 8 and their ramped strength to full power are required in order to determine a capture angle within which it can capture a gear tooth or gear tip and bring it into alignment and then switched off such that another electromagnetic element 8 can then draw another gear tip or tooth into alignment and so progress rotation - 9 movement of the gears as required to provide the pumping action. Gear momentum Is also utilised to maintain movement. Generally, the electromagnetic elements 8 will have a shaped electromagnetic field when energised in the appropriate switch sequence in order to create attraction of a gear tooth or tip to it. As indicated previously it is drawing of the tip to the electromagnetic element 8 which is desired rather than pulling back of that tooth or tip such that the shaping of the electromagnetic element will reflect that desired objective In order to enhance positional sensing of the gears 4, 5 one of the gear teeth or tips may be individually marked in terms of its response to electromagnetic element 8 as a sensor or itself have a permanent magnet secured to it in order to create a distinct response in electromagnetic elements 8 which can be deduced by the controller 8 in order to determine the gear 4, 5 position.

When it is desirable or possible two or more electromagnetic elements 8 may be switched into and out of operation in order to maintain or initiate rotation of the gears 4. 5 and so the pumping action. Nevertheless, it will be appreciated that In such circumstances care must be taken that the electromagnetic elements 8 act in combined beneficial operation rather than opposing each other. Such multiple electromagnetic element 8 operation may be beneficial when greater torque is required to initiate rotation of the ge^-rs 4, 5 from a standstill position particularly with relatively viscous flucs.

Although illustrated with conventional spur tooth gears 4, 5 it,vill be appreciated that alternative tooth or tip shapes may be provided. Thus, a square or castellated tooth cross- section may be provided in order to create better interaction with the electromagnetic elements 8 for driving of the gears 4, 5. It will also be understood that as indicated previously both gears 4, 5 can be driving or be driven dependent upon the switching sequence of the electromagnetic elements 8. In such circumstances, any potential additional abrasive effects upon the driving gear in comparison with the driven or idle gear within the present pump will be diminished. 10

As indicated above the teeth or at least the tips of the teeth must be able to sustain or present sufficient electromagnetic attraction anc repulsion to drive the pump. Thus. he gears or teeth or tip have to be made from a suitable material such as a cobalt iron alloy or silicon steel but other materials may be used. Similarly, the gears or parts of the gears or other parts of the pump may be formed from lam nated sections of material to limit eddy current losses by inhibiting conduction across inset ation between the laminations.

The present pump allows the cavity 3 to be essentially closed and therefore dangers with respect to leakage of fluids within the cavity can be reduced as a potential or failure of a driving shaft seal arrangement is remolded.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon. - 11

Claims

1. A pump comprising interengaging gears within a cavity, movement of the gears creating a positive pressure to drive a fluid in use through the pump In a pumping action, the cavity incorporating suitable magnetic elements to cause movement of the gears when sequentially switched between magnetic states.

2. A pump as claimed in claim 1 wherein the magnetic elements are electromagnetic.

3. A pump as claimed in claim 1 or claim 2 wherein the gears are wholly formed from a magnetically inducible metal.

4. A gear as claimed in claim 1 or claim 2 wherein the gears are formed from a base metal with magnetically inducible teeth or tips.

5. A pump as claimed in claim 3 or claim 4 wherein the magnetically inducible material is a cobalt iron alloy or silicon steel.

6. A pump as claimed in claim 4 wherein the base material is a Mastics material or a ceramic.

7. A pump as claimed in any preceding claim wherein the gears are weighted for inertia momentum smoothing of gear movement.

8. A pump as claimed in claim 7 wherein the weighting is provided at the tips or teeth of the gears.

9. A pump as claimed in any preceding claim wherein all gears are driven by the magnetic elements when sequentially switched between magnetic states. - 12

10. A pump as claimed in any preceding claim wherein each gear is selectively driven alternately in accordance with the switching sequence to achieve the desired pumping action.

11. A pump as claimed in any preceding claim wherein the magnetic elements are arranged to provide drag upon the pumping action.

12. A pump as claimed in any preceding claim wherein two or more magnetic elements operate simultaneously to progress movement of the gears.

13. A pump as claimed in claim 12 wherein the two or more magnetic elements act upon different gears or gear teeth.

14. A pump as claimed in any preceding claim wherein the cavity is substantially closed except for in input port and an output port such that the gears are driven solely inductively by the magnetic elements.

15. A pump as claimed in any preceding claim wherein the teeth or tips of each gear are drawn into touching contact with an internal surface of the cavity by the magnetic elements when sequentially switched to drive gear movement.

16. A pump as claimed in any preceding claim wherein the magnetic elements are controlled by a controller to provide the necessary sequential switching of the magnetic elements in order to create movement of the gears and so pumping action.

17. A pump as claimed in any preceding claim wherein the switching sequence varies dependent upon the speed of rotation movement of the gears within the pump.

18. A pump as claimed in any preceding claim wherein the magnetic elements about Me cavity are substantially isolated from each other by specific insulation means. - 13

19. A pump as claimed in claim 16 and any claim dependent thereon wherein the controller can determine the position of the respective gears within the cavity through positional response from respective magnetic elements.

20. A pump as claimed in claim 19 wherein one tooth of at least one gear is individually marked or discernable by the controller in order to initiate an appropriate switching sequence to begin movement of the gears for pumping action.

21. A pump as claimed in any preceding claim wherein the gears or other parts of the pump are formed from laminations to reduce eddy current losses and so facilitate movement within the pump.

22. A pump substantially as herenbefore described with reference to the accompanying drawings.

23. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.