Patent Description:
Conventional approaches to dissipate heat on electric motors rely on the thermal conductivity of motor components to transport heat. However, generally motor components need to provide high electrical resistance for safety and operating reasons. High electrical resistance typically comes with high thermal resistance, thus traditional cooling strategies are limited by this factor.

Liquid-cooled stators for linear motors are well-known in the art and many solutions have been proposed.

<CIT>, for example, discloses a cooled stator for a linear motor, comprising a stator having a magnetic laminated core and a cooling arrangement mounted on the stator. The cooling arrangement is made of a first and a second corrugated metal hose for flowing a cooling medium along the longitudinal direction of the stator. The first corrugate metal hose is arranged to form a serpentine flow path mainly in bores of the laminated core while the second corrugated metal hose is arranged on top of the first corrugate metal hose to form a serpentine flow path in the slots of the stator.

The cooling arrangement of <CIT> has several disadvantages. This cooling arrangement is not modular and designing and producing a cooling arrangement specific to a particular motor length may be tedious, time consuming and therefore costly since every motor with a different length needs a specific corrugated hose shape. Significant pressure drop may also occur due to the significant length and multiple turns of the cooling arrangement. This cooling arrangement has also a negative impact on the motor performance as electrically conductive cooling hose are inserted in the slots of the stator where strong magnetic fields are present.

<CIT> discloses an electric linear motor comprising a heat-generating motor part, and a modular cooling arrangement. The cooling arrangement has a meandering configuration and is secured to the motor part for removal of heat. The cooling arrangement comprises separate straight cooling pipes, and separate deflections for attachment and interconnection of the straight cooling pipes. The deflection includes two separate elbows made of plastic and a coupling section for connecting the elbows to one another, with one of the elbows made in one piece with the coupling section.

This cooling arrangement is modular at the cost of additional complexity and at the risk of cooling fluid leakage at the joints between segments.

<CIT> discloses a linear motor comprising a cooling arrangement including pipes press-fitted into slots located at the back of the lamination stack of the magnetic core, thus avoiding degrading the motor performance. Placing the cooling arrangement at the back of the lamination stack has however the drawback to significantly reduce the cooling capacity of the cooling arrangement. Further cooling arrangements for stators of electrical machines are disclosed in <CIT>, <CIT>, and <CIT>.

An aim of the present invention is therefore to propose a stator cooling assembly for a linear motor, comprising a modular cooling arrangement which overcomes the above limitations.

More particularly, an aim of the present invention is to propose a stator cooling assembly for a linear motor, comprising a modular cooling arrangement that is easy to manufacture and cost effective.

Another aim of the present invention is to propose a stator cooling assembly for a linear motor, comprising a modular cooling arrangement that produces insignificant pressure drop occurring along the cooling arrangement.

A further aim of the present invention is to propose a stator cooling assembly for a linear motor, comprising a modular cooling arrangement presenting a lower risk of leakage.

These aims are achieved by a stator cooling assembly for a linear motor with the features of claim <NUM>, comprising a stator and a modular cooling arrangement mounted on the stator. The modular cooling arrangement comprises:.

Each primary cooling unit comprises at least one heat pipe having a first portion extending along the corresponding recess of the stator, and a second portion extending along a portion of the U-shaped fluid cooling pipe. The connecting members connect the second portion of the at least one heat pipe of each primary cooling unit to the corresponding portions of the U-shaped fluid cooling pipe.

In an embodiment, the at least one heat pipe of each primary cooling unit of the central cooling arrangement is L-shaped.

In an embodiment, each primary cooling unit comprises a first and a second L-shaped heat pipe comprising each the first and second portions. The first portion of the first and second L-shaped heat pipes of each primary cooling unit extends along the recess. The second portion of the first and second L-shaped heat pipes of each primary cooling unit extends along a portion of respectively the first and second linear segments of the U-shaped fluid cooling pipe.

In an embodiment, each connecting member comprises two pipe receiving portions parallel to each other. One receiving portion receives a portion of either the first and second linear segments of the U-shaped fluid cooling pipe. The other receiving portion receives the second portion of either the first and second L-shaped heat pipes of the corresponding primary cooling unit. The pipe receiving portions are for example in the form of grooves extending across the connecting member or in the form of through-holes extending through said connecting member.

In an embodiment, each primary cooling unit comprises a primary insert having a first and a second pipe receiving portion, for example a first and a second groove, parallel to each other and receiving respective first portions of the first and second L-shaped heat pipes.

In an embodiment, the modular cooling arrangement further comprises two secondary cooling units arranged into recesses of the stator extending along both sides of the central cooling arrangement. Each secondary unit comprises a single L-shaped heat pipe having a first and a second portion extending respectively along the recess and along a portion of respective first and second linear segments.

In an embodiment, each secondary cooling unit comprises a secondary insert having a single pipe receiving portion, for example a groove, receiving the first portion of the single L-shaped heat pipe.

In an embodiment, the primary and secondary inserts of respective primary and secondary cooling units are press-fitted into the corresponding recesses of the stator.

In an embodiment, the primary and secondary inserts and the connecting members are made of metal having a thermal conductivity coefficient exceeding <NUM> W m-<NUM> K-<NUM> at <NUM> and <NUM> bar, such as aluminum or copper.

In an embodiment, the second portion of the first L-shaped heat pipe of each primary cooling unit extends along the first linear segment of the U-shape fluid cooling pipe in a first direction. The second portion of the second L-shaped heat pipe of each primary unit extends along the second linear segment of the U-shape fluid cooling pipe in a second direction opposite the first direction.

In an embodiment, the cross-section of the L-shaped heat pipes is smaller than the cross-section of the U-shaped fluid cooling pipe.

In an embodiment, the U-shaped fluid cooling pipe further comprises a third linear segment between the first and second linear segments. The third linear segment extends along a lateral side of the stator.

Another aspect of the invention relates to a primary part of a linear motor, comprising the stator cooling assembly as described above and a housing arranged to encapsulate the stator cooling assembly.

In an embodiment, spacers are mounted on mounting portions of the stator such that a top side of each spacer is in contact against a bottom side of the housing which is opposite the housing top side to keep the bottom side away from the modular cooling arrangement to avoid excessive heating of the housing.

In an embodiment, the first and second linear segments of the U-shaped fluid cooling pipe are mounted against two opposite longitudinal sides of the housing by means of the cooling members which are fixed to the opposite longitudinal sides of the housing to cool down the housing.

Another aspect of the invention relates to a linear motor comprising the primary part as described above.

The invention will be better understood with the aid of the description of several embodiments given by way of examples and illustrated by the figures, in which:.

With reference to <FIG>, the primary part <NUM> of a linear motor comprises a housing <NUM> encapsulating a stator cooling assembly <NUM>. The stator cooling assembly <NUM> comprises a stator <NUM> and a modular cooling arrangement <NUM> mounted on the stator. The modular cooling arrangement <NUM> comprises a U-shaped fluid cooling pipe <NUM> provided with a first and a second port <NUM>, <NUM> mounted on free ends of the U-shaped fluid cooling pipe <NUM> for circulating a cooling fluid around a central part of the stator. In this respect, the fluid cooling pipe <NUM> comprises a first linear segment <NUM> arranged along a first longitudinal side of the stator, a second linear segment <NUM> arranged along a second longitudinal side of the stator, opposite to the first longitudinal side and a third linear segment <NUM> arranged along a lateral side of the stator.

Referring to <FIG>, the modular cooling arrangement <NUM> further comprises a central cooling arrangement <NUM> mounted on a top side of the stator <NUM>, as shown in <FIG> and <FIG>, and surrounded by the fluid cooling pipe <NUM>.

The central cooling arrangement <NUM> comprises primary cooling units <NUM> mounted into recesses <NUM> of the stator <NUM> between mounting portions <NUM> of the stator as shown in <FIG>. The recesses <NUM> extend from the first to the second longitudinal side of the stator. In an embodiment, each primary cooling unit <NUM> comprises a primary insert <NUM> adapted to be press-fitted into the respective recesses <NUM> of the stator as well as a first and a second L-shaped heat pipe 44a, 44b mounted in the primary insert (<FIG>). To this end, each primary insert <NUM> comprises pipe receiving portions 52a, 52b for example in the form of parallel grooves, as per the modular cooling arrangement of the illustrated embodiment, extending along the insert <NUM>, or in the form of parallel through-holes extending through the insert according to a non-illustrated variant.

With reference to <FIG>, the first and second L-shaped heat pipes 44a, 44b of each primary cooling unit comprise each a first portion <NUM> and a second portion <NUM>. The first portion <NUM> of the first and second heat pipes 44a, 44b extends along respectively the first and second grooves 52a, 52b of the insert <NUM>. The second portion <NUM> of the first and second heat pipes 44a, 44b extend along a portion of respectively the first and second linear segments <NUM>, <NUM> of the U-shaped fluid cooling pipe <NUM>.

In a preferred embodiment, the second portion <NUM> of the first L-shaped heat pipe 44a of each primary cooling unit <NUM> extends along the first linear segments <NUM> in a first direction whereas the second portion <NUM> of the second L-shaped heat pipe 44b of each primary unit <NUM> extends along the second linear segment <NUM> in a second direction opposite the first direction.

With reference to <FIG>, the modular cooling arrangement <NUM> further comprises two secondary cooling units <NUM> mounted into recesses <NUM> of the stator <NUM> (<FIG>) extending along both sides of the central cooling arrangement <NUM>. In an embodiment, each secondary unit <NUM> comprises a secondary insert <NUM> with a pipe receiving portion <NUM> and a single L-shaped heat pipe <NUM>. The width of the secondary insert <NUM> is approximately half the width of the primary inserts <NUM>. The secondary insert <NUM> is press-fitted into the corresponding recess <NUM> of similar width. The single heat pipe <NUM> comprises a first portion <NUM> extending along the pipe receiving portion <NUM>, for example along a groove, and a second portion <NUM> along a portion of respective first and second segments <NUM>, <NUM> of the fluid cooling pipe <NUM> as shown in <FIG>.

The modular cooling arrangement <NUM> further comprises connecting members <NUM> connecting the heat pipes to the fluid cooling pipe <NUM>. More particularly, the connecting member <NUM> comprises two pipe receiving portions 32a, 32b in the form, for example, of parallel grooves. One receiving portion 32a of each connecting member <NUM> receives a portion of either the first and second linear segments <NUM>, <NUM> of the fluid cooling pipe <NUM>. The other receiving portion 32b of each connecting member <NUM> receives the second portion <NUM> of either the first and second L-shaped heat pipes 44a, 44b of the corresponding primary cooling unit <NUM> or the second portion <NUM> of the L-shaped heat pipe <NUM> of the corresponding secondary unit <NUM>.

The primary and secondary inserts <NUM>, <NUM> as well as the connecting members <NUM> are made of metal having a high thermal conductivity coefficient, preferably exceeding <NUM> W m-<NUM> K -<NUM> at <NUM> and <NUM> bar, such as aluminum or copper to maximize heat transfer.

The heat pipes of the primary and secondary cooling units <NUM>, <NUM> comprise each a working fluid which turns into vapour by absorbing heat from the primary and secondary inserts <NUM>, <NUM> which are heated by the stator when in operation. The vapour then travels from the first to the second portion of the heat pipes, whereupon the working fluid in a gaseous state is cooled down by the fluid cooling pipe <NUM>, thereby condensing the working fluid back into a liquid and releasing the latent heat. The liquid then returns from the second to the first portion of the heat pipes through capillary action to cool down the stator and to repeat a cooling cycle.

In another non illustrated embodiment, the first portion of the L-shaped heat pipes of the primary and secondary cooling units are directly fitted into the respective recesses of the stator to avoid one thermal interface.

In the embodiment of <FIG>, a top side of the housing <NUM> comprises though-holes <NUM>. During manufacturing, the housing <NUM> is fixed to the stator cooling assembly <NUM> by means of screws fitted into the through-holes <NUM> and screwed into the mounting portions <NUM> of the stator located between the stator recesses <NUM>. The bottom side of the housing top side is therefore in direct contact with the modular cooling arrangement <NUM>. After motor potting operation, these screws are removed and the housing <NUM> is thus glued onto the stator cooling assembly <NUM>. During operation, the housing top side, which is a customer interface, is therefore heated. Excessive heating may be however an issue for certain customer applications.

The embodiment illustrated in <FIG> solve the above issue. Spacers <NUM> are mounted on the mounting portions <NUM> of the stator <NUM> such that a top side of each spacer is in contact against a bottom side of the housing <NUM> which is opposite the housing top side so as to keep the bottom side away from the modular cooling arrangement to avoid excessive heating of the housing during operation.

Advantageously, the first and second linear segments <NUM>, <NUM> of the U-shaped fluid cooling pipe <NUM> are mounted against two opposite longitudinal sides of the housing <NUM> by means of the connecting members <NUM> which are fixed to the opposite longitudinal sides so as to cool down the housing.

To this end, each connecting member <NUM> is designed to have a supporting part <NUM> supporting the corresponding portions of the L-shaped heat pipes 44a, 44b and of the U-shaped fluid cooling pipe <NUM>, and a fixing part <NUM> fixed to respective longitudinal sides of the housing by means of screws <NUM>.

Claim 1:
A stator cooling assembly (<NUM>) for a linear motor, comprising a stator (<NUM>) and a modular cooling arrangement (<NUM>) mounted on the stator (<NUM>), the modular cooling arrangement (<NUM>) comprising:
a U-shaped fluid cooling pipe (<NUM>) having a first linear segment (<NUM>) extending along a first longitudinal side of the stator (<NUM>) and a second linear segment (<NUM>) extending along a second longitudinal side of the stator (<NUM>), opposite the first longitudinal side,
an inlet and an outlet port (<NUM>, <NUM>) connected to a free end of the first and second linear segments (<NUM>, <NUM>) respectively of the fluid cooling pipe (<NUM>) for circulating a cooling fluid along both longitudinal sides of the stator (<NUM>),
a central cooling arrangement (<NUM>) comprising primary cooling units (<NUM>) mounted into respective recesses (<NUM>) of the stator (<NUM>) extending across said stator from the first to the second longitudinal side, and
connecting members (<NUM>) connecting the central cooling arrangement (<NUM>) to the U-shaped fluid cooling pipe (<NUM>),
wherein each primary cooling unit (<NUM>) comprises at least one heat pipe (44a, 44b) having a first portion (<NUM>) extending along the corresponding recess (<NUM>) of the stator (<NUM>), and a second portion (<NUM>) extending along a portion of the U-shaped fluid cooling pipe (<NUM>), and wherein the connecting members (<NUM>) connect the second portion (<NUM>) of said at least one heat pipe (44a, 44b) of each primary cooling unit (<NUM>) to the corresponding portions of the U-shaped fluid cooling pipe (<NUM>).