WO2018042151A1

WO2018042151A1 - Pump with bidirectional heat transfer between pump housing and control housing

Info

Publication number: WO2018042151A1
Application number: PCT/GB2017/052389
Authority: WO
Inventors: James HAYLOCK; Gary Michael George LORD
Original assignee: Edwards Limited
Priority date: 2016-09-01
Filing date: 2017-08-14
Publication date: 2018-03-08
Also published as: GB201614814D0; GB2553321A

Abstract

Electronics modules for vacuum pumps were previously separate from the pump housing. More recently they have been attached to the pump housing. Thermal breaks are usually provided between the pump and the control to allow independent thermal management of the pump and controller. However, it has been discovered that by thermally coupling the control housing to the pump housing by a thermal coupling arrangement for transferring heat from the pump housing to the control housing, the control housing forms a heat sink for the vacuum pump, and thus the control arrangement can be configured so that heating of the control housing by heat generated by the vacuum pump components allows the temperature of the control to be maintained within a thermal rating of the control during operation of the pump.

Description

PUMP WITH BIDIRECTIONAL HEAT TRANSFER BETWEEN PUMP HOUSING

AND CONTROL HOUSING

The invention relates to temperature management of a pump, such as a vacuum pump (or compressor).

Mechanical vacuum pumps and compressors are supplied with energy in order to operate. During operation waste heat is produced. This heat must be dissipated to the environment in order to avoid excessive temperatures within and on the surfaces or the pump/compressor mechanism. An electronic control is required to power and control many classes of vacuum pumps, including but not limited to turbo molecular pumps. Any electronics associated with the pump will also consume power and produce waste heat. This heat must also be dissipated to the environment.

In these vacuum pumps, the control electronics and the pumping

mechanism/motor have different operating temperature limits. For example, a thermal rating of the rotor of a pumping mechanism may be 90° C and the thermal rating of the control electronics may be 70° C. Thermal rating is the temperature at which normal operation can be sustained for extended periods without causing significant damage to the elements of the vacuum pump or failure.

Hereto therefore, the motor control electronics for turbo molecular pumps are provided in separate enclosures spaced away from the main pump body so that the thermal management of the pumping mechanism and control can occur one independent from the other. These controllers are connected to the pump through a length of cable. The cable provides a thermal separation between the pump and the controller. More recently electronics modules have been attached to the pump. A thermal break or insulation has been provided between the pump and the control to allow independent thermal management of the pump and controller.

The present invention provides a pump comprising heat dissipating components in a pump housing which forms a heat sink for the heat dissipating components, the heat dissipating components comprising a pumping mechanism, a motor for driving the pump mechanism and a bearing arrangement for supporting rotation of the pumping

mechanism; a control arrangement comprising a control for controlling the pump and a control housing which houses the control and forms a heat sink for the control; wherein the control housing is thermally coupled to the pump housing by a thermal coupling arrangement for transferring heat from the pump housing to the control housing so that the control housing forms a heat sink for the heat dissipating components, and the control arrangement is configured so that heating of the control housing by heat generated by the heat dissipating components allows the temperature of the control to be maintained within a thermal rating of the control during operation of the pump.

The control may include components which transfer electrical power from a source to the pump and components which manage or regulate parameters of the delivered electrical power and other aspects of the pump. The former components generate more heat and therefore the temperature of the control is maintained within a thermal rating of these electrical transfer components during operation of the vacuum pump. The control housing may be configured with cooling formations for increasing the surface area of the housing in contact with ambient air for cooling the control housing. The cooling formations may comprise fins.

The control housing may comprise a cooling mechanism for generating a cooling flow of air for cooling the control.

The pump housing may have a target maximum surface temperature and the thermal rating of the control may be selected to be higher than the target maximum surface temperature so that heat can be transferred to the control housing from both the pump housing and the control without exceeding the thermal rating of the control. The control thermal rating may be in the range of 65 °C to 125° C and the target maximum surface temperature of the pump housing may be 65°C or lower.

The pump housing and control housing may have respective heat transfer surfaces which are shaped to complement each other over the surface area of both of the surfaces. When mounted together the heat transfer surfaces may be in intimate contact with each other over the surface area of both of the surfaces.

A thermal coupling medium may be located between and in contact with the heat transfer surfaces. The thermal transfer medium may comprise a thermal grease or graphite film.

A heat pump (for example a Peltier heat pump device) may be located between the heat transfer surfaces and when activated causes a differential temperature between opposing surfaces thereof to pump heat from the pump housing to the control housing. In the case of a Peltier device differential temperature is generated in response to a supplied electrical current. In this way, even if the control housing has a temperature above the pump housing heat can be pumped from the pump housing to the control housing.

One or more heat conduits may be in contact with the pump housing and control housing, and containing a fluid for receiving heat from one of the pump housing or the control housing and outputting heat to the other of the pump housing or the control housing.

In another aspect, there is provided alternatively or additionally, a pump comprising a pumping mechanism, a motor for driving the pump mechanism and a bearing arrangement for supporting rotation of the pumping mechanism, the pumping mechanism, motor and bearing arrangement being housed in a pump housing; a control arrangement comprising heat dissipating components including a control for controlling operation of the pump, the heat dissipating components being housed in a control housing which forms a heat sink for the heat dissipating components; wherein the control housing is thermally coupled to the pump housing by a thermal coupling arrangement for transferring heat from the control housing to the pump housing so that the pump housing forms a heat sink for the heat dissipating components, whereby heat from the heat dissipating components of the control arrangement can be transferred to the pump housing for raising or maintaining the temperature the pumping mechanism, motor and bearing arrangement. This latter aspect may be of use in applications where the temperature of the pump mechanism must be raised or maintained to encourage evaporation of contaminants, or prevent condensation of process deposits, within the pump. In order that the invention may be well understood, an embodiment thereof, which is given by way of example only, will now be described with reference to the

accompanying drawings, in which:

Figure 1 shows a vacuum pump comprising a pump housing and control housing;

Figure 2 shows a Peltier device for modifying the vacuum pump shown in Figure

1; and

Figure 3 shows heat flow in the vacuum pump and to atmosphere.

Referring to Figure 1, a vacuum pump 10 is shown which comprises a vacuum pumping mechanism 12 housed in a pump housing 14 and a motor 16 for driving the vacuum pump mechanism. The motor and the pumping mechanism may be provided in a single housing or in respective housing enclosures. The vacuum pumping mechanism is supported for rotation by a drive shaft 18 which is rotated when the motor rotates. In this example, the vacuum pumping mechanism comprises alternate arrays of rotor blades 20 and stator blades 22 in a turbo molecular pumping mechanism. Other examples may comprise, without restriction, a molecular drag mechanism, a roots or claw mechanism, a screw mechanism or a scroll mechanism, supported for operation by one or more drive shafts. In this example, rotation of the vacuum pumping mechanism causes gas to flow into the pump housing through inlet 24, where it compressed by the mechanism and flows out of the pump housing through outlet 26.

The drive shaft is supported by bearings 28, 30, such as rolling or magnetic bearings. The motor 16 is arranged to rotate the drive shaft 18 in response to an electrical input received from a control 32 along a control line 34 operatively connecting the control to the motor. A typical electrical motor has rotor and stator windings for commutated excitation by the control in a brushless arrangement. The motor may be AC or DC and have any number of poles greater than or equal to two. In the illustrated example of a turbo molecular mechanism the motor is required to rotate the mechanism at high rotational speeds around 10,000 rpm or higher.

The control 32 controls operation of the vacuum pump 10 and in particular the motor 16. The control may be operated by a user, for example to start, stop or control the speed of the pump, or may receive a feedback from the motor for controlling the pump, or may receive an input from a processing chamber for controlling vacuum pumping. The control receives electrical power from a source of electrical power, such as the mains, along a supply line 35.

The control 32 is housed in a control housing 36. The control comprises electronic components, such as an inverter, for driving the motor. The electronics of the control consume electrical power and produce waste heat. The electronics have an upper working temperature above which operation may be inhibited or cause failure. Therefore the heat generated must be dissipated. In this example, a cooling mechanism 38, such as a fan, generates a cooling air flow for cooling the control. In this regard, the cooling mechanism causes air flow into the housing through openings 40, over the control and out of the housing through openings 42. Additionally in this example the housing comprises cooling formations 44, such as fins, for increasing the surface area of the housing in contact with ambient air for increasing transfer of heat from the housing. In this connection, electronics enclosures are typically manufactured from extrusions or casings (castings formed from a tool). These two manufacturing methods allow complex 2D and 3D forms to be fabricated cost effectively, at least in cases where production volumes are a few hundred units or higher. One of the advantages of these manufacturing methods is that they allow cooling features, e.g. fins, to be included in the electronics enclosure.

Operation of the vacuum pump also causes the generation of heat by the vacuum pumping mechanism (particularly the rotor and the bearings) and by the motor. In the former respect, thermal expansion of the rotor may lead to clashing of the alternate blade arrays of the rotor and stator. In the latter respect, the windings of the rotor and the core of the stator generate heat in use. In the case of the motor, there is an upper working temperature above which operation is inhibited and could lead to failure. It is therefore desirable to dissipate heat from the pump housing to maintain pump components within working temperatures. In this class of pump a shaft mounted fan is not typically used, because the motor is integrated into the pump and operates in the vacuum space and the shaft does not extend out of the vacuum space.

Conversely to the control housing, the pump housing is typically manufactured by machining solid billet, rather than extrusions or castings. Where cooling features are added to the pump housing these are realised through additional machining operations, and hence additional cost.

As discussed above the pump and control housings of the prior art are thermally insulated from each other so that they are thermally independent. In known

arrangements, the control is connected to the motor by a cable which has a length to enable the two housings to be spaced apart and thermally independent from one another. In more compact designs the control housing may be mounted to the pump housing but thermally insulated from one another by a thermally insulating medium having a high coefficient of thermal insulation. A plastics material may be used for this purpose.

The present example takes a counter-intuitive step by thermally coupling the control housing with the pump housing so that operating temperature of the housings are inter-dependent or influenced by each other. In order to protect the control, the electrical components have a thermal rating which is selected to be higher than required solely for temperatures generated by operation of the control in order that the control housing can act as a heat sink for the pump housing. In more detail, the electronic components have a control thermal rating and the pump housing has a maximum target surface temperature. The thermal rating of the control is selected to be higher than the target maximum surface temperature so that heat can be transferred to the control housing from both the pump housing and the control without exceeding the thermal rating of the control.

In one arrangement, heat is transferred from the pump housing to the control housing for cooling the pump housing, for example to maintain pump temperature within operating temperatures. In this aspect the control housing acts as a heat sink for the control (and its electrical components) and the pump housing. In another arrangement, heat is transferred from the control housing to the pump housing for heating the pump housing, for example for heating the pump prior to operation to avoid a 'cold start' . Evaporation and avoidance of condensation are known examples. In this aspect, the pump housing acts as a heat sink for the control housing.

Thermal coupling can be achieved in one or more different ways including those arrangements described below. In Figure 1, the pump housing and control housing have respective heat transfer surfaces 46, 48 which are shaped to complement each other over the surface area of the surfaces. The heat transfer surfaces may be planar surfaces for forming a planar interface between the surfaces. Alternatively, the surfaces may have interlocking or tessellating formations where one surface is a negative and the other surface is a positive. This latter arrangement increases the surface area of potential contact, although adds complication in its manufacture.

The pump housing is typically machined from a solid billet and the heat transfer surface of the pump housing is machined in an additional machining step. A planar surface is most easily machined. The control housing may be extruded or cast with the heat transfer surface as part of the manufacturing process.

The control housing is mounted to the pump housing at the heat transfer surfaces by fasteners 50 as shown in Figure 1, which may be screws or bolts. Mounting the control housing brings the heat transfer surfaces into contact over the surface area. This intimate contact between the surfaces may be sufficient in itself to allow adequate transfer of heat. There will however be a small amount of air between the surfaces and as air in an insulator it will act to reduce heat transfer. Additionally therefore, a thermal coupling medium may be located between and in contact with the heat transfer surfaces. The thermal transfer medium improves the contact between the opposing surfaces, by reducing air between the surfaces, and preferably comprises a thermal grease (0.5 to 0.05 K.cm².W^_1) or a graphite film (0.1 to 0.05 K.cm².W^_1) or other medium with a low thermal resistance. If there is a smaller area of contact it is preferable to use a medium with a lower thermal resistance. In a further alternative, a Peltier device or plate 52 (shown on its own in Figure 2) is located between the heat transfer surfaces. The Peltier device causes a differential temperature, or heat flux, between opposing surfaces 54, 56 thereof in response to a supplied electrical current. The surface 54 is located in contact with heat transfer surface 48 of the pump housing and surface 56 is located in contact with heat transfer surface 46 of the control housing when the control housing is mounted to the pump housing.

In a further aspect, one or more heat conduits, or pipes, 58 (shown schematically in Figure 1) are located in contact with the pump housing and control housing. The heat pipes contain a fluid for receiving heat from one of the pump housing or the control housing and outputting heat to the other of the pump housing or the control housing.

Figure 3 shows the transfer of heat in the system by arrows between the relevant pump components. The pump housing or enclosure 14 comprises heat dissipating parts including the motor 16, bearings 28, 30 and pumping mechanism 12. The motor includes a motor winding (not shown). Located in the control enclosure or housing 36 is the control 32, which includes one or more circuit boards 33, electronic components 35 mounted on the or each circuit board, and in this example one or more electronic components 37 mounted directly to the enclosure.

The heat flow paths formed include:

1. a path from the heat dissipating parts 12, 16, 28, 30 to the pump enclosure 14;

2. a path from the electronic components 35 to the circuit board 33 and hence to the electronics enclosure36, and a path from the electronic components 37 to the electronics enclosure 36 due to direct mounting of these components to the enclosure and/or due to use of interconnecting thermal materials;

3. a path from the pump enclosure 14 to the atmosphere or environment;

4. a path from the electronics enclosure 36 to the atmosphere or environment; and 5. in embodiments of the invention, a path from the pump enclosure 14 to the electronics enclosure 36.

Each of the parts/components has an upper temperature limit. For example the winding within the motor is limited to a temperature depending on the insulation materials used and hence the Class of insulation system achieved. Typical insulation systems provide a temperature limit of 120°C or 135°C, but other insulation systems are available with higher temperature limits.

Electronic components may be rated for operation in an ambient temperature of up to 70°C (for traditionally specified 'commercial' grade components) or 85°C (for traditionally specified 'industrial' grade components) or 125°C (for traditionally specified 'military' grade components). For modern surface mounted electronic components where the thermal connection to the circuit board is relatively strong, the ambient temperature may be taken as the temperature of the circuit board. Hence the circuit board temperature should be limited to protect the components with the lowest maximum temperature limit. If all components are rated for the 'industrial temperature range', the circuit board temperature should be limited to 85°C or less.

The pump enclosure and electronics enclosure are robust parts so do not have any restrictive temperature limit for their own protection, however, there are still two temperature constraints on these enclosure components. First, normally the housings must operate at a temperature that allows heat transfer from the heat dissipating parts to the enclosure and then to the environment to provide a temperature gradient. Otherwise a heat pump, such as a Peltier device, is employed to force heat up the temperature gradient if the enclosure temperature is between the temperature of the heat dissipating parts and the temperature of the environment. Secondly, the surfaces of the pump enclosure and electronics enclosure are often exposed to human contact. Safety standards, e.g.

EN 161010 specify maximum surface temperatures. Where temperatures may exceed the specified temperatures, guarding and / or warnings may be required. The easiest way to minimise the hazard of hot surface temperatures is often to ensure the surface

temperatures do not exceed the temperature limits presented in the relevant standard. The temperature limits differ according to the type of material and surface coatings, but as an example the limit from the current edition of EN61010 for un-coated metal surfaces is 65°C for normal operating conditions. When the control housing is at a lower temperature than the pump housing a thermal gradient is produced causing heat to be conducted from the pump housing to the control housing. The cooling mechanism 38 and the cooling formations 44 help to maintain the control housing at a lower temperature than the pump housing, although the control may in any case have a working temperature which is lower than a working temperature of the pump housing.

In more detail, the electronics within the electronics enclosure can tolerate a significantly higher operating temperature (e.g. 85° C) than the target maximum surface temperature of the pump body (e.g. 65° C). The electronics enclosure can also be allowed to rise to 65 °C without any concern about compromising the cooling of the electronics. This means that it is possible for the electronics enclosure to providing adequate cooling for the electronics on the one hand and additional cooling for the pump on the other hand, without conflict between the two. The potential conflict is eliminated by ensuring that the thermal connection from the electronics to the enclosure is good enough to provide adequate cooling to the electronics (i.e. to keep the electronics temperature below the rated temperature) even when the enclosure is at the its maximum allowable temperature. This may be provided without any special measures (e.g. a simple screw connection between the electronics and the enclosure may be

sufficient). Additional thermal materials may be provided for an improved thermal connection between the electronics and the electronics enclosures so as to reduce the temperature rise of the electronics above the temperature of the enclosure.

In one variation, the arrangement uses waste heat from electronics within the electronics enclosure to heat the pump. In this variation the electronics enclosure is used to heat (not cool) the pump body. The background to this variation is that some pump classes have a heater module attached to raise the temperature locally to prevent chemicals passing through the pump from solidifying within the pump. In these cases, waste heat from the electronics is used to supplement heat from the heater module.

Claims

1. A pump comprising heat dissipating components in a pump housing which forms a heat sink for the heat dissipating components, the heat dissipating components comprising a pumping mechanism, a motor for driving the pump mechanism and a bearing arrangement for supporting rotation of the pumping mechanism; a control arrangement comprising a control for controlling the pump and a control housing which houses the control and forms a heat sink for the control; wherein the control housing is thermally coupled to the pump housing by a thermal coupling arrangement for transferring heat from the pump housing to the control housing so that the control housing forms a heat sink for the heat dissipating components, and the control arrangement is configured so that heating of the control housing by heat generated by the heat dissipating components allows the temperature of the control to be maintained within a thermal rating of the control during operation of the pump.

2. A pump as claimed in claim 1, wherein the control housing is configured with cooling formations for increasing the surface area of the housing in contact with ambient air for cooling the control housing.

3. A pump as claimed in claim 2, wherein the cooling formations comprise fins.

4. A pump as claimed in any one of the preceding claims, wherein the control

housing comprises a cooling mechanism for generating a cooling flow of air for cooling the control.

5. A pump as claimed in any one of the preceding claims, wherein the pump housing has a target maximum surface temperature and the thermal rating of the control is selected to be higher than the target maximum surface temperature so that heat can be transferred to the control housing from both the pump housing and the control without exceeding the thermal rating of the control.

6. A pump as claimed in claim 5, wherein the control thermal rating is in the range of 65° to 125° C and the target maximum surface temperature of the pump housing is 65°C or lower.

7. A pump as claimed in any of the preceding claims, wherein the pump housing and control housing have respective heat transfer surfaces which are shaped to complement each other over the surface area of both of the surfaces.

8. A pump as claimed in claim 7, wherein when mounted together the heat transfer surfaces are in intimate contact with each other over the surface area of both of the surfaces.

9. A pump as claimed in claim 8, comprising a thermal coupling medium located between and in contact with the heat transfer surfaces.

10. A pump as claimed in claim 9, wherein the thermal transfer medium comprises a thermal grease or graphite film.

11. A pump as claimed in any one of claims 7 to 10, comprising a heat pump such as a Peltier device located between the heat transfer surfaces that causes a differential temperature between opposing surfaces thereof when activated for pumping heat from the pump housing to the control housing.

12. A pump as claimed in any one of the preceding claims, comprising one or more heat conduits in contact with the pump housing and control housing, and containing a fluid for receiving heat from one of the pump housing or the control housing and outputting heat to the other of the pump housing or the control housing.

13. A pump comprising a pumping mechanism, a motor for driving the pump

mechanism and a bearing arrangement for supporting rotation of the pumping mechanism, the pumping mechanism, motor and bearing arrangement being housed in a pump housing; a control arrangement comprising heat dissipating components including a control for controlling operation of the pump, the heat dissipating components being housed in a control housing which forms a heat sink for the heat dissipating components; wherein the control housing is thermally coupled to the pump housing by a thermal coupling arrangement for transferring heat from the control housing to the pump housing so that the pump housing forms a heat sink for the heat dissipating components, whereby heat from the heat dissipating components of the control arrangement can be transferred to the pump housing for raising or maintaining the temperature the pumping mechanism, motor and bearing arrangement.

14. A pump as claimed in any of the preceding claims, wherein the pumping

mechanism is a vacuum pumping mechanism.