Patent Description:
In process of manufacturing semiconductor devices, liquid crystal panels, LEDs, solar cells, etc., a process gas is introduced into a process chamber to perform a certain type of process, such as etching process or CVD process. The process gas that has been introduced into the process chamber is exhausted by a vacuum pump apparatus. Generally, the vacuum pump apparatus used in these manufacturing processes that require high cleanliness is so-called dry vacuum pump apparatus that does not use oil in gas flow passages. One typical example of such a dry vacuum pump apparatus is a positive-displacement vacuum pump apparatus having a pair of pump rotors in a rotor chamber which are rotated in opposite directions to deliver the gas.

The process gas may contain by-product having high sublimation temperature. When a temperature in the rotor chamber of the vacuum pump apparatus is low, the by-product may be solidified in the rotor chamber and may be deposited on the pump rotors and an inner surface of a pump casing. The solidified by-product may prevent the rotation of the pump rotors, causing the pump rotors to slow down and, in the worst case, causing shutdown of the vacuum pump apparatus. Therefore, in order to prevent solidification of the by-product, a heater is provided on an outer surface of the pump casing to heat the rotor chamber.

On the other hand, it is necessary to cool an electric motor that drives the pump rotors and gears that are fixed to rotation shafts of the pump rotors. Therefore, the vacuum pump apparatus described above usually includes a cooling system for cooling the electric motor and the gears. The cooling system is configured to cool the electric motor and the gears by, for example, circulating a cooling liquid through a cooling pipe provided in a motor housing accommodating the electric motor and a cooling pipe provided in a gear housing accommodating the gears. Such a cooling system can prevent overheating of the electric motor and the gears and can therefore achieve stable operation of the vacuum pump apparatus.

Examples of such vacuum pumps are shown in e.g. in <CIT>, and <CIT>. Furthermore, <CIT> discloses a vacuum pump according to the preamble of claim <NUM>.

The heater attached to the pump casing in the Japanese documents is sandwiched between side covers. Therefore, when the heater is to be replaced due to the end of its service life, etc., the vacuum pump apparatus should be disassembled, and as a result, the heater cannot be easily replaced.

Therefore, the present invention provides a vacuum pump apparatus capable of maintaining a high temperature in a rotor chamber of a pump casing and capable of allowing a heater to be easily attached and removed. In accordance with the invention, a vacuum pump apparatus as set forth in the claims is provided.

In an embodiment, there is provided a vacuum pump apparatus comprising: a pump casing having a rotor chamber therein; a pump rotor arranged in the rotor chamber; a rotation shaft to which the pump rotor is fixed; an electric motor coupled to the rotation shaft; a side cover forming an end surface of the rotor chamber; a housing structure located outwardly of the side cover in an axial direction of the rotation shaft; and a cartridge heater disposed in the side cover or in the pump casing and removably attached to the side cover or the pump casing, wherein the cartridge heater has a heater and a heater casing covering at least a part of the heater, and the heater casing has a slit extending from one end to other end thereof.

In an embodiment, the heater casing is made of a material having a higher coefficient of linear expansion than that of a material constituting an outer shell of the heater.

In an embodiment, the heater casing is made of one of aluminum alloy, aluminum, copper, and magnesium.

In an embodiment, the side cover or the pump casing has a hole which is open in an outer surface of the side cover or the pump casing, the hole extending linearly, and the cartridge heater has a rod shape and is arranged in the hole.

In an embodiment, the vacuum pump apparatus further comprises: a fixing mechanism configured to removably fix the cartridge heater to the side cover or the pump casing.

According to the present invention, an inside of the rotor chamber can be maintained at a high temperature by attaching the cartridge heater in the side cover or in the pump casing.

The slit formed in the heater casing can absorb thermal expansion of the heater and the heater casing. As a result, deformation of the cartridge heater due to deformation of the heater over time can be prevented, and the cartridge heater can be easily removed from the side cover or the pump casing.

The heater casing is made of a material having a higher coefficient of linear expansion than that of a material constituting the outer shell of the heater, so that a gap between the side cover or the pump casing and the heater can be filled by thermal expansion of the heater casing. Therefore, heat can be efficiently transferred from the cartridge heater to the side cover or the pump casing.

<FIG> is a cross-sectional view showing an embodiment of a vacuum pump apparatus. The vacuum pump apparatus of the embodiment described below is a positive-displacement vacuum pump apparatus. In particular, the vacuum pump apparatus shown in <FIG> is a so-called dry vacuum pump apparatus that does not use oil in its flow passages for a gas. Since a vaporized oil does not flow to an upstream side, the dry vacuum pump apparatus can be suitably used for a semiconductor-device manufacturing apparatus that requires high cleanliness.

As shown in <FIG>, the vacuum pump apparatus includes a pump casing <NUM> having a rotor chamber <NUM> therein, pump rotors <NUM> arranged in the rotor chamber <NUM>, rotation shafts <NUM> to which the pump rotors <NUM> are fixed, and electric motor <NUM> coupled to the rotation shafts <NUM>. Each pump rotor <NUM> and each rotation shaft <NUM> may be an integral structure. Although only one pump rotor <NUM> and only one rotation shaft <NUM> are depicted in <FIG>, a pair of pump rotors <NUM> are arranged in the rotor chamber <NUM>, and are secured to a pair of rotation shafts <NUM>, respectively. The electric motor <NUM> is coupled to one of the pair of rotation shafts <NUM>. In one embodiment, a pair of electric motors <NUM> may be coupled to the pair of rotation shafts <NUM>, respectively.

The pump rotors <NUM> of the present embodiment are Roots-type pump rotors, while the type of the pump rotors <NUM> is not limited to the present embodiment. In one embodiment, the pump rotors <NUM> may be screw-type pump rotors. Further, although the pump rotors <NUM> of the present embodiment are single-stage pump rotors, in one embodiment the pump rotors <NUM> may be multistage pump rotors.

The vacuum pump apparatus further includes side covers 10A and 10B located outwardly of the pump casing <NUM> in an axial direction of the rotation shafts <NUM>. The side covers 10A and 10B are provided on both sides of the pump casing <NUM> and are coupled to the pump casing <NUM>. In the present embodiment, the side covers 10A and 10B are fixed to end surfaces of the pump casing <NUM> by not-shown screws.

The rotor chamber <NUM> is formed by an inner surface of the pump casing <NUM> and inner surfaces of the side covers 10A and 10B. The pump casing <NUM> has an intake port 2a and an exhaust port 2b. The intake port 2a is coupled to a chamber (not shown) filled with gas to be delivered. In one example, the intake port 2a may be coupled to a process chamber of a semiconductor-device manufacturing apparatus, and the vacuum pump apparatus may be used for exhausting a process gas that has been introduced into the process chamber.

The vacuum pump apparatus further includes a motor housing <NUM> and a gear housing <NUM> which are housing structures located outwardly of the side covers 10A and 10B in the axial direction of the rotation shafts <NUM>. The side cover 10A is located between the pump casing <NUM> and the motor housing <NUM>, and the side cover 10B is located between the pump casing <NUM> and the gear housing <NUM>.

Each rotation shaft <NUM> is rotatably supported by a bearing <NUM> held by the side cover 10A and a bearing <NUM> held by the side cover 10B. The motor housing <NUM> accommodates a motor rotor 8A and a motor stator 8B of the electric motor <NUM> therein. The motor housing <NUM> and the gear housing <NUM> are examples of the housing structure, and the housing structures are not limited to this embodiment. For example, the housing structure may be a bearing housing that holds a bearing.

Inside the gear housing <NUM>, a pair of gears <NUM> that mesh with each other are arranged. In <FIG>, only one gear <NUM> is depicted. The electric motor <NUM> is rotated by a not-shown motor driver, and one rotation shaft <NUM> to which the electric motor <NUM> is coupled rotates the other rotation shaft <NUM> to which the electric motor <NUM> is not coupled in an opposite direction via the gears <NUM>.

In one embodiment, a pair of electric motors <NUM>, which are coupled to the pair of rotation shafts <NUM>, respectively, may be provided. The pair of electric motors <NUM> are synchronously rotated in opposite directions by a not-shown motor driver, so that the pair of rotation shafts <NUM> and the pair of pump rotors <NUM> are synchronously rotated in opposite directions. In this case, the role of the gears <NUM> is to prevent loss of the synchronous rotation of the pump rotors <NUM> due to a sudden external cause.

When the pump rotors <NUM> are rotated by the electric motor <NUM>, a gas is sucked into the pump casing <NUM> through the intake port 2a. The gas is transferred from the intake port 2a to the exhaust port 2b by the rotating pump rotor <NUM>.

A cooling channel <NUM> is provided in the motor housing <NUM>. Similarly, a cooling channel <NUM> is provided in the gear housing <NUM>. The cooling channel <NUM> extends through an entire circumferential wall of the motor housing <NUM>, and the cooling channel <NUM> extends through an entire circumferential wall of the gear housing <NUM>. The cooling channel <NUM> and the cooling channel <NUM> are coupled to a not-shown cooling-liquid supply source. Cooling liquid is supplied from the cooling-liquid supply source to the cooling channel <NUM> and the cooling channel <NUM>. The cooling liquid flowing through the cooling channel <NUM> cools the motor housing <NUM>, so that the electric motor <NUM> and the bearings <NUM> arranged in the motor housing <NUM> can be cooled. The cooling liquid flowing through the cooling channel <NUM> cools the gear housing <NUM>, so that the gears <NUM> and the bearings <NUM> arranged in the gear housing <NUM> can be cooled.

Some of the process gases to be handled by the vacuum pump apparatus include by-product that is solidified as the temperature decreases. During the operation of the vacuum pump apparatus, the process gas is compressed in the process of being transferred from the intake port 2a to the exhaust port 2b by the pump rotors <NUM>. Therefore, an inside of the rotor chamber <NUM> becomes hot due to the heat of compression of the process gas. The side cover 10A is configured to reduce heat transfer from the pump casing <NUM> to the motor housing <NUM>, and the side cover 10B is configured to reduce heat transfer from the pump casing <NUM> to the gear housing <NUM>. Therefore, the side covers 10A and 10B can maintain the inside of the rotor chamber <NUM> at a high temperature. In particular, the side covers 10A and 10B can maintain the inside of the rotor chamber <NUM> at a high temperature while the motor housing <NUM> and the gear housing <NUM> is cooled with the cooling liquid flowing through the cooling channels <NUM> and <NUM>.

In the present embodiment, the pump casing <NUM> and the side covers 10A and 10B forming the rotor chamber <NUM> are made of cast iron. In one embodiment, the side covers 10A and 10B may be made of a material having a lower thermal conductivity than that of the cast iron.

The vacuum pump apparatus further includes cartridge heaters 70A and 70B disposed in the side covers 10A and 10B, respectively. The cartridge heaters 70A and 70B are removably attached to the side covers 10A and 10B, respectively. Details of configurations of the cartridge heaters 70A and 70B will be described later.

Since the side covers 10A and 10B have basically the same configuration, and the cartridge heaters 70A and 70B have basically the same configuration, the side cover 10A and the cartridge heater 70A will be described below. <FIG> is a side view of the side cover 10A according to the embodiment shown in <FIG>. <FIG> is a cross-sectional view taken along a line A-A of <FIG>. The side cover 10A has through-holes <NUM> through which the rotation shafts <NUM> extend. The through-holes <NUM> communicate with the rotor chamber <NUM>.

The side cover 10A has an inner wall portion <NUM> forming an end surface 31a of the rotor chamber <NUM>, an outer wall portion <NUM> located outwardly of the inner wall portion <NUM> in the axial direction of the rotation shafts <NUM>, and a plurality of spacers <NUM> sandwiched between the inner wall portion <NUM> and the outer wall portion <NUM>. The inner wall portion <NUM> and the outer wall portion <NUM> are located away from each other by the spacers <NUM>. The inner wall portion <NUM> is coupled to the pump casing <NUM> (see <FIG>), and the outer wall portion <NUM> is coupled to the motor housing <NUM>. The outer wall portion <NUM> has recesses (not shown) in which the bearings <NUM> are accommodated. A heat insulating material may be disposed between the outer wall portion <NUM> and the motor housing <NUM>.

The inner wall portion <NUM> of the side cover 10A has holes 31b opened in an outer surface of the side cover 10A (more specifically, an outer surface of the inner wall portion <NUM>). The holes 31b extend linearly. Each cartridge heater 70A has a rod shape extending linearly, and is arranged in each hole 31b. The vacuum pump apparatus of this embodiment allows the cartridge heaters 70A to be locally mounted by providing the holes 31b at desired positions where the cartridge heaters 70A are to be attached.

In this embodiment, two cartridge heaters 70A are arranged so as to sandwich the rotation shafts <NUM> (see <FIG>). In one embodiment, only one cartridge heater 70A may be provided, or three or more cartridge heaters 70A may be provided. In this embodiment, the inner wall portion <NUM> and the outer wall portion <NUM> are separated, while in one embodiment, the inner wall portion <NUM> and the outer wall portion <NUM> may be integrally formed without providing the spacers <NUM>. Further, in one embodiment, the hole 31b may be formed in an outer surface of an existing side cover of the vacuum pump apparatus, and the cartridge heater 70A may be inserted into the hole 31b.

With the cartridge heaters 70A inserted into the holes 31b, the cartridge heaters 70A are fixed to the side cover 10A by screws <NUM>, respectively, which are fixing mechanisms. More specifically, the inner wall portion <NUM> of the side cover 10A has screw holes <NUM> communicating with the holes 31b. When each screw <NUM> is screwed into each screw hole <NUM>, a distal end of each screw <NUM> presses the cartridge heater 70A in the hole 31b against the inner wall portion <NUM>, so that positions of the cartridge heaters 70A are fixed. When each of the screws <NUM> is loosened, the cartridge heaters 70A can be removed from the holes 31b. Since the holes 31b are open in the outer surface of the side cover 10A, the cartridge heaters 70A can be removed from the side cover 10A without disassembling the vacuum pump apparatus. Therefore, if a malfunction of the cartridge heater 70A occurs, the cartridge heater 70A can be easily replaced with a new cartridge heater.

Next, the configuration of the cartridge heater 70A will be described. <FIG> is a perspective view of the cartridge heater 70A. <FIG> is a cross-sectional view taken along a line B-B of <FIG>. The cartridge heater 70A has a heater <NUM> and a heater casing <NUM> covering at least a part of the heater <NUM>. The heater <NUM> has a heating element 71a and an outer shell 71b surrounding the heating element 71a. The outer shell 71b is made of metal and has a function of transferring heat generated by the heating element 71a while protecting the heating element 71a. The cartridge heater 70A is a heating device in which the heater <NUM> is inserted inside the heater casing <NUM>. A type of the heater <NUM> is not particularly limited, while a sheathed heater, which is a kind of electric heater, can be used for the heater <NUM>. The heater <NUM> is a rod-shaped heater extending linearly.

The heater casing <NUM> is open at both ends thereof and has a cylindrical shape forming a columnar space therein. The heater casing <NUM> has a slit 72a extending from one end to other end thereof. The slit 72a extends over an entire length of the heater casing <NUM>. A cross section of the heater casing <NUM> has an annular shape opened at the slit 72a having a width s1. In this embodiment, the entire length of the heater casing <NUM> is the same as an entire length of the heater <NUM>, and the heater casing <NUM> covers the entire heater <NUM>. In one embodiment, the entire length of heater casing <NUM> may be longer than the entire length of heater <NUM>.

<FIG> is an enlarged cross-sectional view of the cartridge heater 70A inserted into the hole 31b. As shown in FIG. 6B, before the heater <NUM> generates heat, an inner diameter ϕ1 of the hole 31b of the side cover 10A is larger than an outer diameter ϕ2 of the heater casing <NUM>. Therefore, a gap is formed between the side cover 10A (more specifically, an inner wall forming the hole 31b) and the heater casing <NUM> when the cartridge heater 70A has been inserted into the hole 31b. Before the heater <NUM> generates the heat, an inner diameter ϕ3 of the heater casing <NUM> is larger than an outer diameter ϕ4 of the heater <NUM>. Therefore, a gap is formed between the heater <NUM> and the heater casing <NUM> before the heater <NUM> generates the heat.

In this embodiment, the outer shell 71b of the heater <NUM> is made of stainless steel. The stainless steel has a higher coefficient of linear expansion than that of cast iron constituting the pump casing <NUM> and the side covers 10A and 10B. The heater casing <NUM> is made of a material having a higher coefficient of linear expansion than that of the outer shell 71b of the heater <NUM>. More specifically, the heater casing <NUM> is made of metal having a higher coefficient of linear expansion than that of the outer shell 71b of the heater <NUM>. Examples of the metal having a higher coefficient of linear expansion than that of the stainless steel constituting the outer shell 71b of the heater <NUM> include aluminum alloy, aluminum, copper, magnesium, etc..

When the heater <NUM> generates the heat, the heat is transferred through the heater casing <NUM> and transferred from the side cover 10A to the rotor chamber <NUM> (see <FIG>), so that the rotor chamber <NUM> can be heated. As a result, the inside of the rotor chamber <NUM> can be maintained at a high temperature, and solidification of by-product contained in the process gas can be prevented.

The heater <NUM> may be heated up to about <NUM>, which causes the heater <NUM> itself to thermally expand. When the heater <NUM> is repeatedly heated over a long period of operations, the entire heater <NUM> may be deformed. As a result, there is a problem that the heater <NUM> cannot be removed from the side cover 10A, and the heater <NUM> cannot be easily replaced when a malfunction of the cartridge heaters 70A occurs. If the inner diameter ϕ1 of the hole 31b of the inner wall portion <NUM> is enlarged in consideration of the deformation of the heater <NUM>, the heat cannot be efficiently transferred from the heater <NUM> to the side cover 10A. As a result, power consumption of the heater <NUM> may increase, and operating cost may increase.

<FIG> is an enlarged cross-sectional view of the cartridge heater 70A during heating. According to the present embodiment, the cartridge heater 70A includes the heater casing <NUM> covering the heater <NUM>. Therefore, when the heater <NUM> generates the heat, the heater <NUM> and the heater casing <NUM> thermally expand. As a result, the gap between the heater <NUM> and the heater casing <NUM> becomes smaller. More specifically, the inner diameter ϕ3 of the heater casing <NUM> becomes equal to the outer diameter ϕ4 of the heater <NUM>. The heater casing <NUM> having the slit 72a can absorb the deformation of the heater <NUM> over time. Therefore, deformation of the entire cartridge heater 70A due to the deformation of the heater <NUM> over time can be prevented, so that the cartridge heater 70A can be easily removed from the side cover 10A.

The heater casing <NUM>, which is made of the material having a higher coefficient of linear expansion than that of the outer shell 71b of the heater <NUM>, thermally expands more greatly than the heater <NUM>. The heater casing <NUM> expands until the heater casing <NUM> contacts the inner wall forming the hole 31b of the side cover 10A. More specifically, the outer diameter ϕ2 of the heater casing <NUM> becomes equal to the inner diameter ϕ1 of the hole 31b. Thus, the thermally-expanding heater casing <NUM> can fill the gap between the side cover 10A (more specifically, the inner wall forming the hole 31b) and the heater <NUM>. Therefore, the heat can be transferred efficiently from the cartridge heater 70A to the side cover 10A.

As can be seen from comparison between <FIG>, the thermal expansion of the heater casing <NUM> after contacting the hole 31b is absorbed by the slit 72a of the heater casing <NUM>. More specifically, the thermal expansion of the heater casing <NUM> is restricted by the hole 31b, while the heater casing <NUM> expands in a direction in which the slit 72a narrows. As a result, stress generated in the heater casing <NUM> is reduced, so that the deformation and breakage of the heater casing <NUM> are prevented.

When the heat generation of the heater <NUM> is stopped and the temperatures of the heater <NUM> and the heater casing <NUM> are lowered, the heater <NUM> and the heater casing <NUM> contract. As a result, the gap is formed again between the side cover 10A (more specifically, the inner wall forming the hole 31b) and the heater casing <NUM>. Therefore, the cartridge heater 70A can be easily attached to and removed from the side cover 10A.

<FIG> is a cross-sectional view showing another embodiment of the vacuum pump apparatus. <FIG> is a cross-sectional view taken along a line C-C of <FIG>. Configurations of this embodiment, which will not be particularly described, are the same as those of the embodiment described with reference to <FIG>, and duplicated descriptions will be omitted. The vacuum pump apparatus shown in <FIG> has cartridge heaters <NUM> disposed in the pump casing <NUM>. The cartridge heaters <NUM> are removably attached to the pump casing <NUM>. Details of the configuration of each of the cartridge heaters <NUM> are the same as those of the configuration of the cartridge heater 70A described with reference to <FIG>.

The cartridge heaters <NUM> are arranged at both sides of the intake port 2a and at both sides of the exhaust port 2b of the pump casing <NUM>. As shown in <FIG>, the pump casing <NUM> has holes 2c opened in an outer surface of the pump casing <NUM>. The holes 2c extend linearly. Each cartridge heater <NUM> has a rod shape extending linearly, and is arranged in each hole 2c. The vacuum pump apparatus of this embodiment allows the cartridge heaters <NUM> to be locally mounted by providing the holes 31c at desired positions where the cartridge heaters <NUM> are to be attached. In this embodiment, four cartridge heaters <NUM> are arranged so as to sandwich the intake port 2a and the exhaust port 2b of the pump casing <NUM>. In one embodiment, three or less, or five or more cartridge heaters <NUM> may be provided.

With the cartridge heaters <NUM> inserted into the holes 2c, the cartridge heaters <NUM> are fixed to the pump casing <NUM> by screws <NUM>, respectively, which are fixing mechanisms. More specifically, the pump casing <NUM> has screw holes <NUM> communicating with the holes 2c. When each screw <NUM> is screwed into each screw hole <NUM>, a distal end of each screw <NUM> presses the cartridge heater <NUM> in the hole 2c against the pump casing <NUM>, so that positions of the cartridge heaters <NUM> are fixed. When each of the screws <NUM> is loosened, the cartridge heaters <NUM> can be removed from the holes 2c. Since the holes 2c are open in the outer surface of the pump casing <NUM>, the cartridge heaters <NUM> can be removed from the pump casing <NUM> without disassembling the vacuum pump apparatus. Therefore, if a malfunction of the cartridge heater <NUM> occurs, the cartridge heater <NUM> can be easily replaced with a new cartridge heater.

A relationship between an inner diameter of the hole 2c of the pump casing <NUM>, an outer diameter and an inner diameter of the heater casing <NUM> of the cartridge heater <NUM>, and an outer diameter of the heater <NUM> of the present embodiment is the same as the relationship of the inner diameter ϕ1 of the hole 31b of the side cover 10A, the outer diameter ϕ2 and the inner diameter ϕ3 of the heater casing <NUM> of the cartridge heater 70A, and the outer diameter ϕ4 of the heater <NUM> described with reference to <FIG>, and duplicated descriptions are omitted.

When the heater <NUM> generates the heat, the heat is transferred through the heater casing <NUM> and transferred from the pump casing <NUM> to the rotor chamber <NUM> (see <FIG>), so that the rotor chamber <NUM> can be heated. As a result, the inside of the rotor chamber <NUM> can be maintained at a high temperature, and solidification of by-product contained in the process gas can be prevented.

According to the present embodiment, the cartridge heater <NUM> includes the heater casing <NUM> covering the heater <NUM>. Therefore, when the heater <NUM> generates the heat, the heater <NUM> and the heater casing <NUM> thermally expand. As a result, the gap between the heater <NUM> and the heater casing <NUM> becomes smaller. More specifically, the inner diameter of the heater casing <NUM> becomes equal to the outer diameter of the heater <NUM>. The heater casing <NUM> having the slit 72a can absorb the deformation of the heater <NUM> over time. Therefore, deformation of the entire cartridge heater <NUM> due to the deformation of the heater <NUM> over time can be prevented, so that the cartridge heater <NUM> can be easily removed from the pump casing <NUM>.

The heater casing <NUM>, which is made of the material having a higher coefficient of linear expansion than that of the outer shell 71b of the heater <NUM>, thermally expands more greatly than the heater <NUM>. The heater casing <NUM> expands until the heater casing <NUM> contacts an inner wall forming the hole 2c of the pump casing <NUM>. More specifically, the outer diameter of the heater casing <NUM> becomes equal to the inner diameter of the hole 2c. Thus, the thermally-expanding heater casing <NUM> can fill the gap between the pump casing <NUM> (more specifically, the inner wall forming the hole 2c) and the heater <NUM>. Therefore, the heat can be transferred efficiently from the cartridge heater <NUM> to the pump casing <NUM>.

When the heat generation of the heater <NUM> is stopped and the temperatures of the heater <NUM> and the heater casing <NUM> are lowered, the heater <NUM> and the heater casing <NUM> contract, so that the gap is formed again between the pump casing <NUM> (more specifically, the inner wall forming the hole 2c) and the heater casing <NUM>. Therefore, the cartridge heater <NUM> can be easily attached to and removed from the pump casing <NUM>.

In one embodiment, the vacuum pump apparatus may further include the cartridge heaters 70A and 70B in the side covers 10A and 10B as well as the embodiments described with reference to <FIG>, in addition to the cartridge heaters <NUM> in the pump casing <NUM> described above.

<FIG> is a cross-sectional view showing still another embodiment of the vacuum pump apparatus. <FIG> is a side view of a side cover according to the embodiment shown in <FIG>. <FIG> is a diagram as viewed from a direction indicated by an arrow D in <FIG>. <FIG> is a perspective view of the side cover 10A shown in <FIG>. Configurations of this embodiment, which will not be particularly described, are the same as those of the embodiment described with reference to <FIG>, and duplicated description will be omitted. Side covers 10A and 10B of the vacuum pump apparatus shown in <FIG> further include narrow portions <NUM> and heater housings <NUM>. The cartridge heaters 70A and 70B are removably attached to the heater housings <NUM> of the side covers 10A and 10B, respectively. Details of the configurations of the cartridge heaters 70A and 70B are the same as those of the configurations of the cartridge heater 70A described with reference to <FIG>.

The side cover 10A of this embodiment has an inner wall portion <NUM> forming an end surface 31a of the rotor chamber <NUM>, an outer wall portion <NUM> located outwardly of the inner wall portion <NUM> in the axial direction of the rotation shafts <NUM>, and the narrow portion <NUM> located between the inner wall portion <NUM> and the outer wall portion <NUM>. The inner wall portion <NUM> is coupled to the pump casing <NUM> and the outer wall portion <NUM> is coupled to the motor housing <NUM>. The outer wall portion <NUM> has recesses 32a in which the bearings <NUM> are accommodated. A heat insulating material may be disposed between the outer wall portion <NUM> and the motor housing <NUM>.

The inner wall portion <NUM>, the outer wall portion <NUM>, and the narrow portion <NUM> are an integral structure. In this embodiment, the inner wall portion <NUM>, the outer wall portion <NUM>, and the narrow portion <NUM> are an integrally molded casting. Since the side cover 10A includes the integral structure, it is not necessary to produce multiple members separately and assemble these multiple members. As a result, manufacturing cost can be reduced.

The narrow portion <NUM> has an outer peripheral length shorter than outer peripheral lengths of the inner wall portion <NUM> and the outer wall portion <NUM>. Specifically, the narrow portion <NUM> has a cross-sectional area smaller than cross-sectional areas of the inner wall portion <NUM> and the outer wall portion <NUM>. The inner wall portion <NUM>, the outer wall portion <NUM>, and the narrow portion <NUM> are made of the same material, while the cross-sectional area of the narrow portion <NUM> is smaller than the cross-sectional areas of the inner wall portion <NUM> and the outer wall portion <NUM>. Therefore, the heat is less likely to be transferred from the inner wall portion <NUM> through the narrow portion <NUM> to the outer wall portion <NUM>. Although descriptions are omitted, the side cover 10B also basically has the same configuration as the side cover 10A. Since the side covers 10A and 10B having such narrow portions <NUM> have high heat insulating performances, the interior of the rotor chamber <NUM> can be maintained at a high temperature. Furthermore, cooling of the pump casing <NUM> by the cooling liquid flowing through the cooling channel <NUM> and the cooling channel <NUM> can be prevented.

The side cover 10A has two heater housings <NUM> having holes 35a, respectively. The two heater housings <NUM>, the inner wall portion <NUM>, the outer wall portion <NUM>, and the narrow portion <NUM> are an integral structure. Each hole 35a is open in an outer surface of the side cover 10A (more specifically, an outer surface of the heater housing <NUM>), and the cartridge heater 70A is arranged in the hole 35a. In this embodiment, two cartridge heaters 70A are arranged so as to sandwich the rotation shafts <NUM>. In one embodiment, only one cartridge heater 70A may be provided, or three or more cartridge heaters 70A may be provided.

The holes 35a extend linearly, and the cartridge heaters 70A are rod-shaped heaters extending linearly. With the cartridge heaters 70A inserted into the holes 35a, the cartridge heaters 70A are fixed to the side cover 10A by screws <NUM>, respectively, which are fixing mechanisms. More specifically, the heater housing <NUM> has screw holes <NUM> communicating with the holes 35a. When each screw <NUM> is screwed into each screw hole <NUM>, a distal end of each screw <NUM> presses the cartridge heater 70A in the hole 35a against the heater housing <NUM>, so that positions of the cartridge heaters 70A are fixed. When each of the screws <NUM> is loosened, the cartridge heaters 70A can be removed from the holes 35a. Since the holes 35a are open in the outer surface of the side cover 10A, the cartridge heaters 70A can be removed from the side covers 10A without disassembling the vacuum pump apparatus. Therefore, if the cartridge heater 70A breaks down, the cartridge heater 70A can be easily replaced with a new cartridge heater.

A relationship between an inner diameter of the hole 35a of the heater housing <NUM>, an outer diameter and an inner diameter of the heater casing <NUM> of the cartridge heater 70A, and an outer diameter of the heater <NUM> of the present embodiment is the same as the relationship of the inner diameter ϕ1 of the hole 31b of the side cover 10A, the outer diameter ϕ2 and the inner diameter ϕ3 of the heater casing <NUM> of the cartridge heater 70A, and the outer diameter ϕ4 of the heater <NUM> described with reference to <FIG>, and duplicated descriptions are omitted.

When the heater <NUM> generates the heat, the heat is transferred through the heater casing <NUM> and transferred from the heater housings <NUM> and the inner wall portion <NUM> to the rotor chamber <NUM> (see <FIG>), so that the rotor chamber <NUM> can be heated. As a result, the inside of the rotor chamber <NUM> can be maintained at a high temperature, and solidification of by-product contained in the process gas can be prevented. In particular, since the heater housings <NUM> and the inner wall portion <NUM> are integrally formed, heat conduction efficiency from the cartridge heaters 70A to the inner wall portion <NUM> is improved.

As shown in <FIG>, at least a part of each heater housing <NUM> is separated from the outer wall portion <NUM>. Although not shown, the entire heater housings <NUM> may be located away from the outer wall portion <NUM>. With such a configuration, the heat generated by the heaters <NUM> and transferred through the heater casings <NUM> is less likely to be transferred to the outer wall portion <NUM>. Therefore, this configuration can prevent heating of the motor housing <NUM> (see <FIG>), which is a housing structure coupled to the outer wall portion <NUM>, while the cartridge heaters 70A heats the rotor chamber <NUM>.

According to the present embodiment, the cartridge heater 70A includes the heater casing <NUM> covering the heater <NUM>. Therefore, when the heater <NUM> generates the heat, the heater <NUM> and the heater casing <NUM> thermally expand. As a result, the gap between the heater <NUM> and the heater casing <NUM> becomes smaller. More specifically, the inner diameter of the heater casing <NUM> becomes equal to the outer diameter of the heater <NUM>. The heater casing <NUM> having the slit 72a can absorb the deformation of the heater <NUM> over time. Therefore, deformation of the entire cartridge heater 70A due to the deformation of the heater <NUM> over time can be prevented, so that the cartridge heater 70A can be easily removed from the heater housing <NUM>.

The heater casing <NUM>, which is made of the material having a higher coefficient of linear expansion than that of the outer shell 71b of the heater <NUM>, thermally expands more greatly than the heater <NUM>. The heater casing <NUM> expands until the heater casing <NUM> contacts the inner wall forming the hole 35a of the heater housing <NUM>. More specifically, the outer diameter of the heater casing <NUM> becomes equal to the inner diameter of the hole 35a. Thus, the thermally-expanding heater casing <NUM> can fill the gap between the heater housing <NUM> (more specifically, the inner wall forming the hole 35a) and the heater <NUM>. Therefore, the heat can be transferred efficiently from the cartridge heater 70A to the heater housing <NUM>.

When the heat generation of the heater <NUM> is stopped and the temperatures of the heater <NUM> and the heater casing <NUM> are lowered, the heater <NUM> and the heater casing <NUM> contract, so that the gap is formed again between the heater housing <NUM> (more specifically, the inner wall forming the hole 35a) and the heater casing <NUM>. Therefore, the cartridge heater 70A can be easily attached to and removed from the heater housing <NUM>.

As shown in <FIG>, the cartridge heaters 70B are also disposed in the side cover 10B. The descriptions with reference to <FIG> can also be applied to the side cover 10B and the cartridge heaters 70B disposed therein, and duplicated descriptions are omitted.

In one embodiment, the vacuum pump apparatus may further include the cartridge heaters <NUM> in the pump casing <NUM> as well as the embodiments described with reference to <FIG> and <FIG>, in addition to the cartridge heaters 70A and 70B in the side covers 10A and 10B described above.

Claim 1:
A vacuum pump apparatus comprising:
a pump casing (<NUM>) having a rotor chamber (<NUM>) therein;
a pump rotor (<NUM>) arranged in the rotor chamber (<NUM>);
a rotation shaft (<NUM>) to which the pump rotor (<NUM>) is fixed;
an electric motor (<NUM>) coupled to the rotation shaft (<NUM>);
a side cover (10A, 10B) forming an end surface of the rotor chamber (<NUM>); and
a housing structure (<NUM>, <NUM>) located outwardly of the side cover (10A, 10B) in an axial direction of the rotation shaft (<NUM>);
a cartridge heater (70A, 70B; <NUM>) disposed in the side cover (10A, 10B) or in the pump casing (<NUM>) and removably attached to the side cover (10A, 10B) or the pump casing (<NUM>),
wherein the cartridge heater (70A, 70B; <NUM>) has a heater (<NUM>), characterized in that the cartridge heater has a heater casing (<NUM>) covering at least a part of the heater (<NUM>), and
the heater casing (<NUM>) has a slit (72a) extending from one end to the other end thereof.