U.S. patent application number 13/901812 was filed with the patent office on 2014-06-12 for pump.
The applicant listed for this patent is Richard Weatherley. Invention is credited to Richard Weatherley.
Application Number | 20140161643 13/901812 |
Document ID | / |
Family ID | 46546666 |
Filed Date | 2014-06-12 |
United States Patent
Application |
20140161643 |
Kind Code |
A1 |
Weatherley; Richard |
June 12, 2014 |
Pump
Abstract
A gear pump includes a pump body 22 which defines a cavity hole
72 which holds a separate cavity body. The cavity body defines
channels and a pump cavity holding a pair of gears. An inlet and
outlet are connected to the channels. The separate cavity body may
be manufactured separately and only this component needs to be
manufactured to very accurate tolerances.
Inventors: |
Weatherley; Richard; (Kent,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Weatherley; Richard |
Kent |
|
GB |
|
|
Family ID: |
46546666 |
Appl. No.: |
13/901812 |
Filed: |
May 24, 2013 |
Current U.S.
Class: |
417/360 ;
417/410.4 |
Current CPC
Class: |
F04C 2230/601 20130101;
F04C 11/008 20130101; F04C 18/16 20130101; F04C 2/18 20130101; F04C
2/086 20130101; F01C 21/10 20130101 |
Class at
Publication: |
417/360 ;
417/410.4 |
International
Class: |
F04C 18/16 20060101
F04C018/16 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2012 |
GB |
1209242.5 |
Claims
1. A pump system comprising: a pump body having a pair of gears
located in a pump cavity and defining channels; an inlet and an
outlet connected to the channels of the pump cavity; and a motor
connected to a longitudinal shaft for driving the gears; wherein
one of the gears is a free gear located in the pump cavity by the
walls of the cavity, and the pump body defines a cavity hole and
the pump cavity and channels are defined in a cavity block mounted
in the cavity hole, the cavity block being free to move laterally
in the cavity hole.
2. A pump system according to claim 1, further comprising channels
through the cavity block connecting the inlet and the outlet to the
pump cavity, further comprising a shallow channel of thickness no
greater than 30% of the thickness of the cavity block between the
channels and the pump cavity to introduce fluid into the pump
cavity and to extract fluid from the pump cavity.
3. A pump system according to claim 1 wherein the pump cavity and
channels extend through the cavity block with constant cross
section.
4. A pump system according claim 1, further comprising a pad having
the same cross section as the cavity block, the pad being mounted
adjacent the cavity block within the cavity hole.
5. A pump system according claim 1 comprising: a drive unit
enclosing the motor; a pump unit including the pump body, the
cavity block in the pump body, the inlet, the outlet and the gears;
wherein the pump unit is a removable pump unit which may be
separated from the drive unit.
6. A pump system according to claim 1, wherein the pump unit
further comprises a driven disk, the driven disk being connected to
the longitudinal shaft and facing the drive unit, the longitudinal
shaft passing through the pump body, further comprising a drive
disk arranged on motor in the drive unit and meshed with the driven
disk.
7. A pump system according to claim 1 further comprising a detent
in the pump unit arranged to engage with a flange on the drive unit
to hold the pump unit on the drive unit.
8. A pump system according to claim 1, wherein the motor comprises
a motor housing defining a motor cavity therein cooperating with a
drive unit on a shaft, the drive unit being located in the motor
cavity.
9. A pump system according to claim 1 further comprising a PTFE
shim between the gears in the pump cavity and the cover, the PTFE
shim sealing the top of the pump cavity.
10. A pump system according to claim 1, wherein the pair of gears
are helical gears.
11. A pump system according to claim 1, wherein the motor is free
to move laterally within a motor housing by at least 0.1 mm.
12. A pump system according to claim 1 wherein the cavity block is
of plastics containing filler.
13. A pump system according to claim 12 wherein the cavity block is
of bronze-loaded PTFE.
Description
[0001] The invention relates to a gear pump and method of
manufacture.
[0002] An important application for pumps is in the medical field.
Where the fluid being processed is a bodily fluid such as blood or
peritoneal fluid, pumps need to avoid cross-contamination from one
patient to another. For this reason, medical equipment frequently
uses pumps in which fluid flows through a flexible tube and is
urged forwards by rollers outside the tube. The flexible tube can
then be replaced for each patient.
[0003] However, such pumps are not suitable in all
circumstances.
[0004] A gear pump includes two interlocked gears each mounted on a
separate shaft in a cavity that is sized to be slightly larger than
the gears. One of the gear shafts is driven to rotate the gears and
liquid is entrained on the outside of the gears and driven from an
inlet to an outlet. However, conventional gear pumps are relatively
difficult to manufacture since the tolerances for the gap between
the gears and the cavity are very tight. If the gears touch the
cavity, then the motion of the gear is impeded, and if the gap is
too large little fluid pressure is achieved. The shafts therefore
need to be rigid.
[0005] Such manufacturing difficulties are particularly difficult
when manufacturing small pumps since the tight tolerances required
are very difficult to achieve.
[0006] There is accordingly a need for pumps which can be
manufactured at relatively low cost.
[0007] According to the invention there is provided a pump system
comprising a pump body having a pair of gears located in a pump
cavity and defining channels, an inlet and an outlet connected to
the channels of the pump cavity; and a motor connected to a
longitudinal shaft for driving the gears; wherein one of the gears
is a free gear located in the pump cavity by the walls of the
cavity, and the pump body defines a cavity hole and the pump cavity
and channels are defined in a cavity block mounted in the cavity,
the cavity block being free to move laterally in the cavity
hole.
[0008] By providing a pump system as described manufacture is
eased. In particular, by providing the pump cavity in a separate
cavity block that fits within the pump body, the cavity block can
be manufactured to fine tolerances and if necessary with expensive
materials without needing to increase the expense of manufacturing
the pump body and the cover.
[0009] In a preferred embodiment, the cavity block is free to move
laterally within the pump body. This avoids the need for accurate
alignment and hence avoids the need to machine the pump body to
fine tolerances. Also, it ensures that the components are not
forced into an incorrect position by small inconsistencies in the
manufacture of the pump body.
[0010] Further, the gears may be located within the cavity block,
including one idle gear without a shaft and one drive gear with a
shaft. Preferably, the drive gear is located within the cavity
block by the gear within the cavity, the accurate alignment of the
drive gear and drive shaft with the motor being possible by virtue
of the freedom of the cavity block to move in the pump body.
[0011] The cavity block may have channels extending through the
complete block and the cavity shaped for the two gears may likewise
extend through the complete block, both having a constant cross
section. In this way, manufacture of the cavity is eased since it
is generally easier to manufacture through holes of constant
shape.
[0012] Sealing of the cavity may be provided by a top pad over the
cavity block and a bottom pad under the cavity block. In a
preferred embodiment, the top and bottom pad have a relatively low
elasticity (i.e. are made from rigid plastics).
[0013] Holes may be provided in the top pad to align with the
channels to pass fluid and hose connectors may be provided
extending through the cover and the holes in the top pad into the
channels.
[0014] A shallow groove may be provided in the cavity block between
each channel and the cavity. The groove may be shallow enough to
pass fluid without interfering significantly with the location of
the gears in the cavity.
[0015] The pump system may include a separate drive unit,
comprising a housing, at least one motor and at least one drive
disk connected to a respective motor to be rotated by the motor;
and at least one removable pump unit, having the body, the cavity
block, the gears in the cavity in the cavity block, and the cover
over the cavity block.
[0016] The pump system may further include a driven disk connected
to the pair of gears arranged to mesh with a drive disk connected
to the motor to pick up power from the drive unit to drive the
gears to pump fluid from the inlet to the outlet.
[0017] By providing a pump system as described a reliable system is
achieved that minimises the risk of contamination by providing
removable units.
[0018] For a better understanding of the invention, embodiments
will now be described, purely by way of example, with reference to
the accompanying drawings, in which:
[0019] FIG. 1 shows an exploded view of a first embodiment of the
invention;
[0020] FIG. 2 shows a detail of the cavity block of FIG. 1;
[0021] FIG. 3 shows FIG. 2 with the gears mounted;
[0022] FIG. 4 shows a side view of the removable part of the
arrangement of FIG. 1;
[0023] FIG. 5 shows an exploded view of a second embodiment of the
invention; and
[0024] FIG. 6 shows an exploded view of a third embodiment of the
invention.
[0025] Like components in different embodiments are given the same
reference numbers and the corresponding description may be
omitted.
[0026] Referring to FIG. 1, a pump system includes a drive unit 2
having housing 4. An electric drive motor 6 is provided, which
drives a drive disk 8. A top piece 12 sits above the motor 6.
[0027] The pump system also includes a removable and replaceable
pump unit 20. A pump body 22 is provided, which contains a separate
cavity block 70 defining pump cavity 24 (see FIG. 2). The cavity
block 70 may also be referred to as a volute.
[0028] The pumping action is provided by a pair of gears 30, 32 in
the pump cavity 24 (see FIG. 3). One of the gears is a driven gear
30 which is connected to a shaft 34 and to a driven disk 36. The
driven disk 36 engages with the drive disk 8 as will be explained
in more detail below. The driven gear 30 meshes with a free gear 32
which is rotated by the driven gear 30. A shaft O-ring 38 seals the
shaft 34 adjacent to the driven disk.
[0029] In the embodiment, the gears 30,32 are helical gears rather
than conventional cross-cut gears to reduce noise and to reduce
power needed to drive them.
[0030] The pump unit 20 has a cover 40 which extends over the
cavity block and hence seals the upper face of pump cavity 24. A
spring detent 42 is provided which engages with flange 16 in the
drive unit to clip the pump unit 20 onto the drive unit 2. The pump
unit 20 can be removed by compressing the spring detent 42. This
enables the pump unit 20 to be replaced.
[0031] Fluid passes between inlet 26 and pump cavity 24 and between
the pump cavity 24 and outlet 28 along channels 44 in cavity block
body 22. Fluid is introduced into the channels 44 not through the
pump body 22 but through the cover 40. Fluid passes from the
channels 44 in the cavity block 70 into the pump cavity 24 through
shallow channels 52 on the underside of cavity block 70. (FIG.
2).
[0032] The cover 40 is fixed to the body 22 using screws 54.
[0033] The cavity block 70 is located in a corresponding cavity
hole 72 in pump body 22. The pump cavity 24 is provided in cavity
block 72. This saves manufacturing costs since only the cavity
block 72 needs high precision machining, and the same cavity block
72 can be used in embodiments with different numbers of pump units
as illustrated in FIGS. 1 and 3.
[0034] The cavity block 70 is sized to have a lateral clearance 71
(FIG. 4), for example 0.1 mm to 1 mm, within the cavity hole 72 in
pump body 22 so the cavity block is free to move laterally
(perpendicular to the axis). Bearing 80 is provided on shaft 34
adjacent to O-ring 38 and this bearing, which is mounted in pump
body 22 in a recess which locates shaft 34 and hence gear 30 and
thus the cavity block 70 itself. This structure means that accurate
fitting of the cavity block 70 in pump body 22 is not required.
[0035] The cavity block 70 is manufactured of material that is
specially chosen. The base material, PTFE, has a number of suitable
properties, namely chemical resistance, heat resistance and low
friction. PTFE is able to creep, which has both advantages and
disadvantages. The advantage is that the PTFE can creep to
accurately fit round a shaft and hence provide a good seal. The
disadvantage is that the creep can cause the accurate shape to
deform.
[0036] The inventors have found that by filling PTFE with a filler,
including glass or bronze, the bulk of the body of the material is
prevented from creeping but there still remains the possibility of
creep at the surface to enable the surface to deform and seal.
[0037] Thus, the material preferred is filled chemically resistant
plastic. In the embodiment, bronze-loaded PTFE is used which the
inventors have found to have excellent wear properties.
[0038] The cavity block 70 is held and sealed by an upper shim 74
with holes 76 corresponding to channels 44 and lower shim 78. These
shims 74, 78 are in this embodiment made of PTFE and not softer
elastomer to accurately define the upper and lower ends of cavity
24 since the height of the cavity is important for good pumping
action--if the height of cavity 24 is too small the shims will rub
against the gears 30,32 causing excessive wear and excessive power
consumption but if there is too large a gap between the gears 30,32
and the shims 74, 78 the gear pump will be unable to achieve
suitable pressures.
[0039] The inlet 26 and outlet 28 are in the form of tube fixings
for fixing to flexible tubes that extend through cover 40 and the
holes 76 in upper shim 74 (FIG. 4) into the channels 44. Flexible
(plastic) tubes can be mounted to the inlet and outlet for use.
[0040] The pump is designed to be a micropump, i.e. the housing is
no bigger than 20 cm in the maximum direction and preferably no
bigger than 10 cm. The pump is designed to be portable and low
power. It is also important that the replaceable pump unit 20 can
be manufactured at low cost. Since the pump may be used in medical
applications, reliability is also important.
[0041] These desiderata are difficult to achieve together, and a
number of design features are used to address some of these
aspects.
[0042] Firstly, it is useful that the gears 30,32 are retained
within the pump cavity without the need to provide a spindle. This
is achieved using a pump cavity 24 in the form of a figure of 8 as
illustrated in FIG. 2.
[0043] However, the inventors have found that for the cavity 24 to
correctly retain the gears the central point 50 of the figure of 8
shape is particularly important.
[0044] However, fluid needs to be introduced here. Therefore, the
fluid is brought from the end of the channel 44 adjacent to the
cavity 24 to the cavity 24 along shallow channels 52. These are no
thicker than 30% of the thickness of the cavity block 70 and so
retain central point 50 (FIG. 2) to retain correctly the gears 30,
32. Preferably, these shallow channels are less than 20%, further
preferably less than 10% of the thickness of the cavity block
70.
[0045] A further design feature is the shape of the drive disk 8
and the matching shape of driven disk 36. It is important that
these reliably mesh to provide a strong drive without risking that
the pump unit 20 cannot be clipped onto the drive unit 2 if the
disks 8, 36 are misaligned.
[0046] The drive disk has a pair of opposed teeth 56, each of which
has a vertical end face and an inclined top face. The driven disk
has the same shape.
[0047] Accordingly, if the pump unit is placed onto the drive unit
with the teeth 56 of the pump unit interfering with the teeth 56 of
the drive unit, the inclined top faces engage to rotate the disks
to allow the placement of the pump unit. When the motor is switched
on, the end faces of the teeth engage to provide a reliable and
strong drive.
[0048] The O-rings 38 seals the shaft and the pump unit 20 on drive
unit 2. To provide a suitable resilience in a small O-ring, a soft
O-ring is used, typically with a Shore hardness of 30 to 60 instead
of 70 to 90 for a conventional O-ring. The embodiment uses a
material with a Shore hardness of 40 to 50.
[0049] The motor 6 is free to move laterally in the housing 4. In
other words, the rotor is in a sense floating. The design of the
drive disk 8 and driven disk 36 is such that when the motor is
operated, the motor will tend to centre. In other words, there is a
free play of about 0.1 mm to 0.3 mm, in the embodiment 0.2 mm,
which allows the motor 6 to laterally move to align the axis of the
motor with the axis of the driven gear 30. By aligning the axes
accurately in this way, the noise is reduced as is the power needed
to drive the motor thereby reducing noise and increasing battery
life.
[0050] The upper shim 74 is a polytetrafluorethylene (PTFE) shim.
This has two functions. It is very low friction allowing the gears
to rotate with minimum friction loss. It also functions as a seal.
In the embodiment shown, the shim 76 is provided in matching recess
in cover 40. Lower shim 78 fits in the cavity hole 72 in pump body
22.
[0051] If the height of cavity 24 is too small the shims will rub
against the gears 30,32 causing excessive wear and excessive power
consumption but if there is too large a gap between the gears 30,32
and the shims 74, 78 the gear pump will be unable to achieve
suitable pressures.
[0052] By using this construction, the shape of pump body 22 is
greatly simplified so this component can be manufactured with lower
precision than cavity block 70.
[0053] FIG. 1 also illustrates a separate housing bottom 102
attached to the underside of housing 4 and allowing the motor 6 to
be introduced from the underside, as well as circuit board 104 with
connectors 106 for electrical connection to motor 6.
[0054] In this way, a reliable pump system is provided with a
reusable pump unit 20 that can be manufactured relatively cheaply.
The unit may be small enough, typically of order 10 cm, that it is
easily portable and may even be battery driven.
[0055] The use of separate top pieces 12 and cover 40 to cover the
drive unit 2 and body 22 allows for easy manufacture.
[0056] The skilled person will realise that all or some of these
details may be changed. For example, instead of the use of screws
54 glue may be used to fix the cover 40 on the pump unit body 22.
Alternatively, a press fit or snap fit may be used.
[0057] Other types of pump may also be used, if appropriate. The
gear pump described above is particularly suitable if the pump
needs to operate with significant back pressure but if this
requirement is relaxed other designs may be possible.
[0058] The number of teeth 56 may be varied and more than two teeth
on each disk may be used if desired.
[0059] Note that the channels 44 and cavity 24 in cavity block 70
extend through the cavity block 70 with constant cross section.
This greatly eases manufacture to high tolerance and makes it easy
to check the positions of the channels 44 and cavity 24 to ensure
reliable pump operation.
[0060] The number of motors 6 and pumps may be varied. FIG. 1 shows
a single motor and a single pump but FIG. 2 shows a variation with
two motors and pump units. Note that the same cavity block 70 may
be used for both arrangements. This allows only a single cavity
block 70 to be manufactured for different numbers of pumps. Since
the cavity block 70 is the part that needs to be manufactured most
accurately, this saves in manufacturing costs.
[0061] In the embodiments shown, all parts are manufactured in
plastics by injection moulding but it may also be possible to
manufacture individual components in different ways. In particular,
the cavity block 70 may be machined if required.
[0062] In an alternative embodiment, the top piece 12 is omitted
and the top of the motor is part of the housing. In this case, the
bottom plate of the housing may be omitted to allow introduction of
the motor 6 into the housing 4 during manufacture. The motor may
then be sealed with a flexible material such as glue or a further
O-ring at its base. In this case, even if the bottom of the motor
is held in place the top of the motor may still have enough
flexibility of movement to allow automatic centring if the seal has
sufficient flexibility to allow small angular deviations.
[0063] A further alternative embodiment uses a cavity block 70
without requiring a removable drive unit as illustrated in FIG. 4.
In this embodiment, a cheap to manufacture gear pump is provided
for applications where it is not necessary to replace part of the
pump for reasons of hygiene or otherwise. As in the embodiments
above, the gear pump is defined by pump cavity 24 in a cavity block
70 mounted in a cavity hole 72 in pump body 22. Cover 40 is screwed
on to the pump body with screws 54 and inlet 26 and outlet 28
provided on cover 40.
[0064] FIG. 4 illustrates a further feature. In this embodiment,
lower shim 78 is replaced with pad 80. A number of alternative
cavity blocks 70 and pads 81 may be provided, each with the same
total height. In this way, a number of different pumps may be
manufactured simply by replacing the gears 30,32, cavity block 70
and pad 81 without requiring a large variety of different
parts.
[0065] The motor 6 is a brushless motor with shaft 82 passing
through. Motor coils are integrated into motor housing 84 which has
a motor cavity 86 for accepting brushless drive unit 88 attached to
shaft 82. The motor housing is fixed onto pump body 22 with screws
90.
[0066] Between the pump body 22 and hence the pump cavity 24 in
cavity block 70 and the motor cavity 86 are provided O-ring 92,
rotary seal 94, bearing 96 and spacer 97 arranged in that order on
the shaft 82. A second bearing 98 and second spacer 97 is provided
to locate the opposite end of the shaft 82, the second bearing 98
locating in the motor cavity 86 so that the shaft 82 is supported
at each end. The first bearing 96 locates in the pump body 22.
[0067] In embodiments, the rotary seal 94 may be omitted. In this
case, suitable for use in pumping non-corrosive fluids such as
water, the pumped fluid may flow into and fill the motor cavity 86
to provide lubrication. Such embodiments may have extended life
since rotary seals may be the first component to wear out when a
pump of this type is used.
[0068] Of course, where there is a requirement to contain the
pumped fluid, the rotary seal 94 may prevent egress of the pumped
fluid.
[0069] Those skilled in the art will realise that there may be many
variations of the embodiments described above and that the
materials and spatial arrangements may be changed.
* * * * *