Patent Description:
Scroll pumps are a known type of pump used in various different industries to pump fluid. Scroll pumps operate by using the relative motion of two intermeshed scrolls (known as a fixed scroll and an orbiting scroll) to pump fluid.

<CIT> discloses a scroll compressor with a back pressure chamber and a back-pressure reduction mechanism.

<CIT> discloses a scroll compressor with a biasing chamber protected from overpressure by a check valve.

One particular type of scroll pump makes use of loaded axial seals between the two scrolls. The loading is typically provided by springs which bias the two scrolls against each other via the axial seals. It is generally desirable to improve the design of this type of scroll pump.

In a first aspect there is provided a scroll pump comprising an inlet and an outlet, a fixed scroll and an orbiting scroll intermeshed with each other, wherein the fixed scroll and orbiting scroll define a space therebetween for pumping fluid through the scroll pump from the inlet to the outlet. The scroll pump further comprises a biasing apparatus configured to bias the orbiting scroll against the fixed scroll, a fluid recirculation channel separate to the biasing apparatus wherein the fluid recirculation channel extends from the space to the inlet through either the fixed scroll or the orbiting scroll, and a fluid recirculation valve disposed in the fluid recirculation channel. When in an open state, the fluid recirculation valve is configured to permit flow of fluid from the space to the inlet through the fluid recirculation channel. When in a closed state, the fluid recirculation valve is configured to block flow of fluid through the fluid recirculation channel. The fluid recirculation valve is configured to switch from the closed state to the open state when a pressure differential across the fluid recirculation valve is equal to or exceeds a certain threshold value.

The fixed scroll may comprise a first base and a first spiral wall extending from the first base. The orbiting scroll may comprise a second base and a second spiral wall extending from the second base. The scroll pump may further comprise a first seal disposed between the first base and the second spiral wall. The scroll pump may further comprise a second seal disposed between the second base and the first spiral wall. The biasing apparatus may be configured to bias the orbiting scroll against the fixed scroll via the first seal and the second seal.

The first seal and/or the second seal may be formed at least partially from a polymer material. The first seal and/or the second seal may be formed at least partially from Polytetrafluoroethylene.

The first seal and/or second seal may be a channel seal.

The biasing apparatus may comprise one or more springs.

The scroll pump may comprise a drive shaft configured to drive rotation of the orbiting scroll. The biasing apparatus may be configured to exert a force on the orbiting scroll via the draft shaft. The biasing apparatus may be configured to exert a force directly on a bearing coupling the orbiting scroll to the drive shaft.

The fluid recirculation valve may be a check valve.

The scroll pump may further comprise a check valve located at the outlet of the scroll pump.

The certain threshold value may be between 100mbar and 400mbar. The certain threshold may be between 200mbar and 300mbar. The certain threshold may be 200mbar.

The scroll pump may comprise an actuator and a drive shaft, the drive shaft being coupled to the orbiting scroll, wherein the actuator is configured to actuate the drive shaft to rotate the drive shaft to drive the orbiting of the orbiting scroll, wherein the fixed scroll is located between the actuator and the orbiting scroll.

The scroll pump may comprise an actuator and a drive shaft, the drive shaft being coupled to the orbiting scroll, wherein the actuator is configured to actuate the drive shaft to rotate the drive shaft to drive the orbiting of the orbiting scroll, wherein the orbiting scroll is located between the actuator and the fixed scroll.

In a second aspect, there is provided the use of the scroll pump of the first aspect to pump fluid.

<FIG> is a schematic illustration (not to scale) showing a cross-sectional view of scroll pump <NUM> according to an embodiment.

The scroll pump <NUM> comprises a shell <NUM>, a fixed scroll <NUM>, an orbiting scroll <NUM>, a drive shaft <NUM>, an actuator <NUM>, a plurality of bearings <NUM>, a biasing apparatus <NUM>, a first axial seal 180a, a second axial seal 180b, and a fluid recirculation mechanism <NUM>.

In this embodiment, the shell <NUM> and the fixed scroll <NUM> together form an overall housing of the scroll pump <NUM> within which the rest of the components of the scroll pump <NUM> are located. However, it will be appreciated that, in other embodiments, the fixed scroll <NUM> may not form part of the overall housing of the scroll pump <NUM> and instead may be located entirely within the overall housing.

The orbiting scroll <NUM> is located within the overall housing of the scroll pump <NUM> and is intermeshed with the fixed scroll <NUM>. The orbiting scroll <NUM> is configured to orbit relative to the fixed scroll <NUM> to pump fluid (e.g. a gas) from an inlet (not shown) of the scroll pump <NUM> to an outlet (not shown) of the scroll pump <NUM>. The scroll pump <NUM> may comprise a check valve located at the outlet (which may be referred to as an exhaust check valve). The exhaust check valve is configured to prevent fluid from re-entering the scroll pump <NUM> when the scroll pump <NUM> is switched off. This in turn reduces the amount of fluid that can come back out of the inlet of the scroll pump <NUM>, which would cause an undesirable pressure rise in the system being pumped by the scroll pump <NUM>. The exhaust check valve is also configured to prevent exhaust fluid and/or air/oxygen from entering the scroll pump <NUM>, which may react with the pumped fluid.

The physical mechanism by which fluid is pumped by the orbiting of the orbiting scroll <NUM> relative to the fixed scroll <NUM> is well known and will not be described herein.

The fixed scroll <NUM> comprises a first base <NUM> and a first spiral wall <NUM>. The orbiting scroll <NUM> comprises a second base <NUM> and a second spiral wall <NUM>. The first spiral wall <NUM> extends perpendicularly from the first base <NUM> towards the second base <NUM>. The second spiral wall <NUM> extends perpendicularly from the second base <NUM> towards the first base <NUM>. In this embodiment, the first base <NUM> and first spiral wall <NUM> are integrally formed with each other. Also, in this embodiment, the second base <NUM> and second spiral wall <NUM> are integrally formed with each other.

The first spiral wall <NUM> and second spiral wall <NUM> are intermeshed with each other such that an end surface of the first spiral wall <NUM> is in contact with an opposing surface of the second axial seal 180b, and an end surface of the second spiral wall <NUM> is in contact with an opposing surface of the first axial seal 180a. In this way, the first axial seal 180a, first spiral wall <NUM>, second axial seal 180b and second spiral wall <NUM> together define a space between the fixed and orbiting scrolls <NUM>, <NUM> which is used by the scroll pump <NUM> during operation to pump fluid. The first and second spiral walls <NUM>, <NUM> each define a respective spiral shaped channel between the turns or wraps of the spiral wall.

The drive shaft <NUM> is coupled to the orbiting scroll <NUM> and configured to rotate to drive the orbiting of the orbiting scroll <NUM>. The drive shaft <NUM> is located within the overall housing of the scroll pump <NUM>. In this embodiment, the drive shaft <NUM> is coupled to the orbiting scroll <NUM> and shell <NUM> via a plurality of bearings <NUM> which facilitate rotation of the drive shaft <NUM>. In this embodiment, the draft shaft <NUM> extends through the fixed scroll <NUM> and the orbiting scroll <NUM> is mounted at an end of the draft shaft <NUM>. In this embodiment, the fixed scroll <NUM> is located between the actuator <NUM> and the orbiting scroll <NUM>.

The actuator <NUM> (e.g. a motor) is coupled to the drive shaft <NUM> and configured to actuate the drive shaft <NUM> to cause the drive shaft <NUM> to rotate to drive the orbiting of the orbiting scroll <NUM>. The actuator <NUM> is located within the overall housing of the scroll pump <NUM>.

The plurality of bearings <NUM> mechanically couple the drive shaft <NUM> to the orbiting scroll <NUM> and the overall housing of the scroll pump <NUM> such that the drive shaft <NUM> is able to rotate within the scroll pump <NUM> to drive the orbiting scroll <NUM>. In this embodiment, the plurality of bearings <NUM> comprise a bearing <NUM> located between (and mechanically coupling) a first end of the drive shaft <NUM> and the overall housing of the scroll pump <NUM>, a bearing <NUM> located between (and mechanically coupling) the fixed scroll <NUM> and the drive shaft <NUM>, and a bearing <NUM> located between (and mechanically coupling) the orbiting scroll <NUM> and a second end of the drive shaft <NUM> opposite to the first end.

The biasing apparatus <NUM> is configured to bias the fixed and orbiting scrolls <NUM>, <NUM> against each other. More specifically, the biasing apparatus <NUM> is configured to bias the orbiting scroll <NUM> towards the fixed scroll <NUM> such that the orbiting scroll <NUM> is axially loaded against the fixed scroll <NUM> via the first axial seal 180a and the second axial seal 180b. In more detail, the biasing is such that the end surface of the first spiral wall <NUM> is pressed against the opposing surface of the second axial seal 180b, and the end surface of the second spiral wall <NUM> is pressed against the opposing surface of the first axial seal 180a. Thus, the axial load on the fixed and orbiting scrolls <NUM>, <NUM> is at least partially supported by the first and second axial seals 180a, 180b. The axial loading caused by the biasing apparatus <NUM> maintains a seal between the end surfaces of the first and second spiral walls <NUM>, <NUM> and the respective opposing surfaces of the first and second axial seals 180a, 180b. This tends to act to prevent undesired leakage of fluid between different radial portions of the space between the fixed and orbiting scrolls <NUM>, <NUM>. In this embodiment, the biasing apparatus <NUM> comprises a plurality of springs which are configured to exert a force on the orbiting scroll <NUM> via a plurality of the bearings <NUM> and the drive shaft <NUM> in order to bias the orbiting scroll <NUM> towards the fixed scroll <NUM>. Specifically, in this embodiment, the plurality of springs comprise a spring configured to exert a force on the bearing <NUM> located between the first end of the drive shaft <NUM> and the overall housing of the scroll pump <NUM>, and a spring configured to exert a force on the bearing <NUM> located between the fixed scroll <NUM> and the drive shaft <NUM>. However, in other embodiments, the biasing apparatus <NUM> comprises only one spring (e.g. either one of the springs described above).

The first and second axial seals 180a, 180b are seals located in the channels defined by the spiral walls <NUM>, <NUM> of the fixed and orbiting scrolls <NUM>, <NUM>. These seals may also be referred to as channel seals. Each of the first and second axial seals 180a, 180b is a spiral shaped piece of material which is sized to fit snugly in the channels defined by the spiral walls <NUM>, <NUM>. The first axial seal 180a is adjacent to the first base <NUM> and fully extends across the width of the channel defined by the first spiral wall <NUM>. The first axial seal 180a is located between the second spiral wall <NUM> and the first base <NUM>. The second axial seal 180b is adjacent to the second base <NUM> and fully extends across the width of channel defined by the second spiral wall <NUM>. The second axial seal 180b is located between the first spiral wall <NUM> and the second base <NUM>. In this embodiment, the first and second axial seals 180a, 180b are both formed from Polytetrafluoroethylene (PTFE). However, in general, it will be appreciated that one or both of the first and second axial seals 180a, 180b may be formed from one or more other types of material (e.g. other types of polymer which may be filled with carbon or glass to reduce wear).

The fluid recirculation mechanism <NUM> comprises a fluid recirculation channel 190a and a fluid recirculation valve 190b located in the fluid recirculation channel 190a. In this embodiment, the fluid recirculation channel 190a extends through the fixed scroll <NUM> from the space defined between the fixed and orbiting scrolls <NUM>, <NUM> to the inlet of the scroll pump <NUM>. More specifically, in this embodiment, the fluid recirculation channel 190a extends through the first axial seal 180a and first base <NUM> of the fixed scroll <NUM>. The fluid recirculation valve 190b is disposed in the fluid recirculation channel 190a and is configured to permit flow of fluid through the fluid recirculation channel 190a when open and to block flow of fluid through the fluid recirculation channel 190a when closed. The fluid recirculation valve 190b is configured to be in the closed state when the fluid pressure differential across the fluid recirculation valve 190b is below a certain threshold value. However, when the fluid pressure differential across the fluid recirculation valve 190b is equal to or exceeds the certain threshold value, the fluid recirculation valve 190b is configured to switch from the closed state into the open state in order to allow fluid flow out of the space between the scrolls, thereby reducing the pressure in the space defined between the fixed and orbiting scrolls <NUM>, <NUM>. The threshold value is a value in the range 100mbar-400mbar. In scroll pumps such as the ones illustrated in the Figures, tests have revealed that 100mbar tends to be the lowest pressure differential that will deliver a significant and effective reduction in the scroll lift-off force. Also, tests have revealed that 400mbar tends to be the highest pressure differential that will be generated by scroll pumps of the type illustrated in the Figures. Preferably, the threshold value is a value in the range 200mbar-300mbar. More preferably, the threshold value is 200mbar.

The entrance to the fluid recirculation channel 190a is fluidly connected to the space between the scrolls, the exit of the fluid recirculation channel 190a is fluidly connected to the inlet of the scroll pump <NUM>, and the fluid recirculation valve 190b is disposed in the fluid recirculation channel 190a between the entrance and exit of the fluid recirculation channel 190a. When the fluid recirculation valve 190b is in a closed state, the fluid pressure differential across the fluid recirculation valve 190b is equal to the pressure differential between the pressure at the entrance to the fluid recirculation channel 190a from the space between the scrolls and the pressure at the inlet of the scroll pump <NUM> (i.e. the pressure differential is equal to the pressure at the entrance to the fluid recirculation channel 190a minus the pressure at the inlet of the scroll pump <NUM>). Thus, the fluid recirculation valve 190b essentially acts as a blow-off valve which activates to relieve high internal pressure in the scroll pump <NUM> when required. In this embodiment, the fluid recirculation valve 190b is a spring loaded check valve which makes use of an elastomeric ball to seal against an opening. However, it will be appreciated that in general any appropriate type of valve may be used, e.g. a check valve which makes use of a differently shaped pad to seal against the opening.

<FIG> is a schematic illustration (not to scale) showing a cross-sectional view of a scroll pump <NUM> according to another embodiment. The scroll pump <NUM> of <FIG> is the same as the one described above with reference to <FIG> except that the fluid recirculation mechanism <NUM> is in the orbiting scroll <NUM> instead of the fixed scroll <NUM>. More specifically, in this embodiment, the fluid recirculation channel 190a extends through the orbiting scroll <NUM> from the space defined between the fixed and orbiting scrolls <NUM>, <NUM> to the inlet of the scroll pump <NUM>. In particular, the fluid recirculation channel 190a extends through the second axial seal 180b and the second base <NUM> of the orbiting scroll <NUM>.

<FIG> is a schematic illustration (not to scale) showing a cross-sectional view of a scroll pump <NUM> according to yet another embodiment. The scroll pump <NUM> of <FIG> is the same as the scroll pump <NUM> described above with reference to <FIG>, except that the fixed scroll <NUM> is located on the other side of the orbiting scroll <NUM>. In other words, rather than the fixed scroll being located between the actuator <NUM> and the orbiting scroll <NUM>, in the embodiment of <FIG>, the orbiting scroll <NUM> is located between the actuator <NUM> and the fixed scroll <NUM>. In this embodiment, the drive draft <NUM> does not pass through the fixed scroll <NUM>.

<FIG> is a schematic illustration (not to scale) showing a cross-sectional view of a scroll pump <NUM> according to yet another embodiment. The scroll pump <NUM> of <FIG> is the same as the scroll pump <NUM> described above with reference to <FIG>, except that the fluid recirculation mechanism <NUM> is in the orbiting scroll <NUM> instead of the fixed scroll <NUM>. More specifically, in this embodiment, the fluid recirculation channel 190a extends through the orbiting scroll <NUM> from the space defined between the fixed and orbiting scrolls <NUM>, <NUM> to the inlet of the scroll pump <NUM>. In particular, the fluid recirculation channel 190a extends through the second axial seal 180b and the second base <NUM> of the orbiting scroll <NUM>.

<FIG> is a schematic illustration (not to scale) showing a cross-sectional view of a scroll pump <NUM> according to yet another embodiment. The scroll pump <NUM> of <FIG> is the same as the scroll pump <NUM> described above with reference to <FIG>, except that the biasing apparatus <NUM> comprises only one spring which is attached at one end to the drive shaft <NUM> and at the other end to the bearing <NUM> which mechanically couples the orbiting scroll <NUM> to the drive shaft <NUM>. In this embodiment, the biasing apparatus <NUM> (specifically the spring) is configured to apply a biasing force directly on the bearing <NUM> which mechanically couples the orbiting scroll <NUM> to the drive shaft <NUM>. The biasing force acts to push the orbiting scroll <NUM> towards the fixed scroll <NUM> to bias the fixed and orbiting scrolls <NUM>, <NUM> together.

<FIG> is a schematic illustration (not to scale) showing a further view of the scroll pump of <FIG>. As illustrated, an entrance <NUM> of the fluid recirculation channel 190a is located in the fixed scroll <NUM> and extends, through the fixed scroll <NUM>, from the space defined between the fixed and orbiting scrolls <NUM>, <NUM> to the inlet <NUM> of the scroll pump <NUM>. As illustrated, in this embodiment, the entrance <NUM> to the fluid recirculation channel 190a is located at position radially outwards of a centre line of the scroll pump <NUM> defined by the drive shaft <NUM>. More specifically, the entrance <NUM> is located at a position such that there are three turns (or wraps) of the spiral walls between the entrance and the centre line in the radial direction. However, in general, it will be appreciated that the entrance <NUM> may be located at any other appropriate location on the scroll, as long as it is able to provide the above-described functions.

In scroll pumps of the type described above, there tends to be high internal pressures in the space between the fixed and orbiting scrolls at various points in the scroll pump's operation (e.g. due to the scroll pump being exposed to varying inlet pressure, varying ambient exhaust pressure, and use of an exhaust check valve). These pressures act on the orbiting scroll, pushing back against the biasing apparatus. If the forces created by these high internal pressures overcome the biasing force provided by the biasing apparatus, the orbiting scroll can be forced away from the fixed scroll so that the spiral walls of the fixed and orbiting scrolls no longer contact the opposing surfaces of the axial seals (an effect called "lift-off"). This causes radial leakage and loss of pump performance. Thus, the biasing force provided by the biasing apparatus tends to be high to prevent the orbiting scroll lifting off. This high axial loading tends to lead to the use of large orbiting scroll bearings and a high wear rate for the axial seals. However, in the above-described scroll pumps <NUM>, the use of the fluid recirculation mechanism <NUM> to relieve the pressure in the space between the fixed and orbiting scrolls <NUM>, <NUM>, tends to advantageously avoid these above-described problems. In particular, the fluid recirculation mechanism <NUM> tends to enable the use of a biasing apparatus <NUM> which provides less biasing force on the orbiting scroll <NUM>, which in turn tends to enable smaller orbiting scroll bearings to be used and also tend to reduce wear on the axial seals 180a, 180b.

Claim 1:
A scroll pump, comprising:
an inlet and an outlet;
a fixed scroll (<NUM>) and an orbiting scroll (<NUM>) intermeshed with each other, wherein the fixed scroll and orbiting scroll define a space therebetween for pumping fluid through the scroll pump from the inlet to the outlet,
a biasing apparatus (<NUM>) configured to bias the orbiting scroll against the fixed scroll;
a fluid recirculation channel (190a) separate to the biasing apparatus (<NUM>), wherein the fluid recirculation channel (190a) extends from the space to the inlet through either the fixed scroll or the orbiting scroll; and
a fluid recirculation valve (190b) disposed in the fluid recirculation channel (190a), wherein:
when in an open state, the fluid recirculation valve (190b) is configured to permit flow of fluid from the space to the inlet through the fluid recirculation channel,
when in a closed state, the fluid recirculation valve (190b) is configured to block flow of fluid through the fluid recirculation channel, and
the fluid recirculation valve (190b) is configured to switch from the closed state to the open state when a pressure differential across the fluid recirculation valve is equal to or exceeds a certain threshold value.