Drive motor and method for regulating a pressure in a drive motor

Abstract

Drive motor for driving a compression member of a compressor element of a compressor device for the compression of a gas, whereby the drive motor (1) has a motor housing (2) provided with a motor chamber (3), whereby a motor stator (4) is installed in the motor chamber (3) and a motor shaft (5) is mounted in the motor chamber (3) for driving the compression member (23) of the compressor device (19), whereby the motor stator (4) is provided with windings (6), and the motor housing (2) is provided with a supply channel (7) for a gas supply into the motor chamber (3), whereby the supply channel (7) is provided with a valve (8) which is configured to allow the gas supply into the motor chamber (3) when a pressure of a gas medium in the motor chamber (3) is below a predetermined threshold level (Pth).

Description

[0001] Drive motor and method for regulating a pressure in a drive motor

[0002] The present invention relates to a drive motor for driving a compression member of a compressor element of a compressor device for the compression of a gas , a compressor device for the compression of a gas comprising such a drive motor , and a method for regulating a pressure in a drive motor for driving a compression member of a compressor element of a compressor device for the compression of a gas .

[0003] More specifically, the present invention relates to a drive motor for driving a compression member of a compressor element of a compressor device for the compression of a gas , whereby the drive motor has a motor housing provided with a motor chamber , whereby a motor stator is installed in the motor chamber and a motor shaft is mounted in the motor chamber for driving the compression member of the compressor device , and whereby the motor stator is provided with windings .

[0004] Such drive motors are already known in the prior art .

[0005] These drive motors may be prone to a reduction of a pressure of a gas medium in the motor chamber .

[0006] Firstly, if the motor shaft is mounted in the motor chamber by means of liquid-lubricated bearings , liquid leaking out of the liquid-lubricated bearings needs to be evacuated and drained from the motor housing . This evacuation and drainage will lead to the reduction of the pressure of the gas medium in the motor chamber .

[0007] Secondly, if the motor chamber and a compression chamber of the compressor element are fluidly connected, the reduction of the pressure of the gas medium in the motor chamber may result from a reduction of a pressure in the compression chamber , for instance when the compressor device goes in an "unload" mode to temporarily stop a delivery of compressed gas . During this "unload" mode , a gas inlet valve of the compressor element is closed off while the drive motor is still running at a low power consumption . The "unload" mode enables the compressor device to stop and restart the delivery of the compressed gas very quickly, such that the compressor device can meet a required gas demand . When the gas inlet valve is closed off , an underpressure or vacuum will be created between the gas inlet valve and the compression chamber and in the compression chamber at an inlet for the gas .

[0008] The reduction of the pressure of the gas medium in the motor chamber can be harmful for the windings of the motor stator which are energized at a certain voltage . According to Paschen' s law, a breakdown voltage at which the drive motor is grounded or at which windings of a motor stator of the drive motor are shortened by means of an electrical breakdown in the gas medium in the motor chamber, will decrease as a result of the reduction of the pressure of the gas medium in the motor chamber . Therefore , a ris k that the breakdown voltage would decrease to the voltage at which the windings are energized and that such an electrical breakdown would occur in the gas medium in the motor chamber emerges upon the reduction of the pressure of the gas medium.

[0009] Encapsulation of the windings in an electrically insulating casting material such as an epoxy resin is known in vacuum integrated motor applications to avoid any electrical breakdown in the gas medium in the motor chamber .

[0010] However , this encapsulation of the windings is a timeconsuming and costly process , and after the encapsulation it is impossible to easily reopen and reclose the encapsulation to rework the windings . The encapsulation is also difficult to scale to large motors .

[0011] Evacuation and drainage of liquid leaking out of liquid- lubricated bearings can be avoided by replacing the liquid- lubricated bearings to grease-lubricated bearings ( also known as "greased for life ( capped) bearings" ) .

[0012] However , these grease-lubricated bearings need to be replaced once an end of lifetime of their lubricating grease has been reached .

[0013] The reduction of the pressure of the gas medium can be avoided by using a shaft seal to keep oil inside of a bearing pocket in the motor housing and seal the motor chamber and compression chamber from each other .

[0014] However , such a shaft seal will wear out over time and also result in friction losses during operation of the compressor device . The obj ective of the present invention is to provide a solution to one or more of the aforementioned and / or other disadvantages .

[0015] More specifically, the obj ective of the present invention is to provide an improved drive motor for driving a compression member of a compressor element of a compressor device for the compression of a gas and an improved method for regulating a pressure in a drive motor for driving a compression member of a compressor element of a compressor device for the compression of a gas , whereby it is avoided that internal motor parts in a motor chamber provided in a motor housing of the drive motor are damaged due to an electrical breakdown in a gas medium contained in the motor chamber .

[0016] Thereto , the present invention relates to a drive motor for driving a compression member of a compressor element of a compressor device for the compression of a gas , whereby the drive motor has a motor housing provided with a motor chamber, whereby a motor stator is installed in the motor chamber and a motor shaft is mounted in the motor chamber for driving the compression member of the compressor device , whereby the motor stator is provided with windings , with the characteristic that the motor housing is provided with a supply channel for a gas supply into the motor chamber , whereby the supply channel is provided with a valve which is configured to allow the gas supply into the motor chamber when a pressure of a gas medium in the motor chamber is below a predetermined threshold level .

[0017] The advantage of such a drive motor according to the invention is that a reduction in the pressure of the gas medium in the motor chamber can be limited or stopped by the gas supply into the motor chamber when the pressure of the gas medium in the motor chamber falls below the predetermined threshold level .

[0018] In this way, it can be avoided that the pressure of the gas medium in the motor chamber is reduced to a pressure level at which the breakdown voltage is equal to a voltage at which the windings of the motor stator are energized, whereby the drive motor would be grounded or the windings of the motor stator of the drive motor would be shortened by means of an electrical breakdown through the gas medium in the motor chamber .

[0019] In a preferred embodiment of the drive motor according to the invention, the motor housing is provided with a drive end flange for connecting the motor housing with the compressor element .

[0020] Hereby, the supply channel with the valve is preferably integrated in the drive end flange .

[0021] In this way, the supply channel with the valve can be integrated according to an axial direction in the motor housing with respect to a rotational axis of motor shaft mounted in the motor chamber . This allows for a compact radial configuration of the drive motor provided with the supply channel with the valve .

[0022] In a next preferred embodiment of the drive motor according to the invention, the motor housing is provided with a non drive end flange for connecting a head to the motor housing, whereby the supply channel with the valve is integrated in the non drive end flange or the head .

[0023] Again, in this way, the supply channel with the valve can be integrated according to an axial direction in the motor housing with respect to a rotational axis of motor shaft mounted in the motor chamber . Once again, this allows for a compact radial configuration of the drive motor provided with the supply channel with the valve .

[0024] In an alternative preferred embodiment of the drive motor according to the invention, the motor housing is provided with a j acket , whereby the supply channel with the valve is integrated in the j acket .

[0025] In this way, the supply channel with the valve can be integrated according to a radial direction in the motor housing with respect to a rotational axis of motor shaft mounted in the motor chamber .

[0026] This allows for a compact axial configuration of the drive motor provided with the supply channel with the valve . In a next preferred embodiment of the drive motor according to the invention, the supply channel is provided with a filter upstream from the valve .

[0027] The filter can prevent foreign particles to enter the motor chamber through the supply channel , which foreign particles would damage internal motor parts in the motor chamber such as the motor stator or motor bearings .

[0028] In a next preferred embodiment of the drive motor according to the invention, the supply channel is provided with a restriction for the gas supply .

[0029] The restriction can be used to regulate the gas supply through the supply channel depending on a required minimum pressure level of the gas medium in the motor chamber and losses implied by the gas supply . By regulating the gas supply, an optimal trade-off can be found between this required minimum pressure level and these losses .

[0030] In a next preferred embodiment of the drive motor according to the invention, the motor shaft is mounted in the motor chamber by means of liquid-lubricated bearings , whereby the motor housing is provided with a drainage channel system for drawing out liquid leaking out of the liquid-lubricated bearings from the motor housing by means of a vacuum source .

[0031] Thanks to the gas supply allowed by the valve through the supply channel into the motor chamber, the reduction of the pressure of the gas medium into the motor chamber by drawing the liquid out of the motor housing through the drainage channel system can be mitigated in this preferred embodiment of the drive motor .

[0032] For this reason, it becomes possible to use liquid-lubricated bearings to mount the motor shaft in the motor chamber, without a need to be concerned about the pressure of the gas medium in the motor chamber being reduced to a pressure level at which the breakdown voltage would be equal to the voltage at which the windings of the motor stator are energized .

[0033] Hereby, the drainage channel system is provided with a restriction means for restricting a fluid flow through the drainage channel system.

[0034] Within the context of the invention, the term "fluid" means a gas , a liquid or a mixture of a gas and a liquid . Therefore , the fluid flow may be a flow of gas medium from the motor chamber , a flow of liquid that has leaked out of the liquid- lubricated bearings or a flow of a mixture of gas medium from the motor chamber and liquid that has leaked out of the liquid-lubricated bearings .

[0035] The restriction means can be used to regulate the pressure of the gas medium in the motor chamber to a required minimum pressure level to avoid a grounding of the drive motor or an electrical breakdown between the windings of the motor stator on the one hand, and to provide a sufficient evacuation of the liquid from the bearings out of the motor housing on the other hand .

[0036] In a next preferred embodiment of the drive motor according to the invention, the valve is a non-return valve . In this way, the gas medium will not leak out of the motor chamber through the supply channel with the valve , which could lead to a loss of the gas medium to an environment of the drive motor when the pressure of the gas medium in the motor chamber would be higher than an atmospheric pressure of this environment .

[0037] The present invention also relates to a compressor device for the compression of a gas , comprising a compressor element having a compressor element housing provided with a compression chamber , whereby the compression chamber contains at least one compression member for the compression of the gas in the compression chamber , with the characteristic that the compressor device further comprises a drive motor according to any one of the embodiments as described hereabove for driving the compression member .

[0038] As the compressor device according to the invention comprises a drive motor according to any one of the already described embodiments , it is evident that this compressor device according to the invention has the same benefits as the embodiments of the drive motor according to the invention as described hereabove .

[0039] In a preferred embodiment of the compressor device according to the invention, the compressor element housing has an inlet part for supplying the gas into the compression chamber, and the motor housing of the drive motor is directly connected to the inlet part of the compressor element housing such that the motor chamber and compression chamber are fluidly connected .

[0040] Thanks to the gas supply allowed by the valve through the supply channel into the motor chamber , a reduction of the pressure level of the gas medium into the motor chamber due to an underpressure or vacuum created in the compression chamber at the inlet part of the compressor element housing, can be mitigated in this preferred embodiment of the compressor device .

[0041] For this reason, it becomes possible to directly connect the motor housing to the inlet part of the compressor element housing with a fluid connection between the motor chamber and compression chamber, without a need to be concerned about the pressure of the gas medium in the motor chamber being reduced to a pressure level at which the breakdown voltage would be equal to the voltage at which the windings of the motor stator are energized .

[0042] The present invention also relates to a method for regulating a pressure in a drive motor for driving a compression member of a compressor element of a compressor device for the compression of a gas , wherein a pressure of a gas medium in a motor chamber provided in a motor housing of the drive motor is regulated, with the characteristic that a gas supply is allowed into the motor chamber when the pressure of the gas medium in the motor chamber is below a predetermined threshold level . It is evident that this method according to the invention has similar benefits as the embodiments of the drive motor and compressor device according to the invention as described hereabove .

[0043] In a preferred embodiment of the method according to the invention, the predetermined threshold level is higher than a breakdown pressure value at which the drive motor is grounded or at which windings of a motor stator of the drive motor are shortened by means of an electrical breakdown in the gas medium in the motor chamber .

[0044] Hereby, the predetermined threshold level is preferably equal to a sum of the breakdown pressure value and a safety margin .

[0045] With the intention of better showing the characteristics of the invention, some preferred embodiments of a drive motor and a compressor device according to the invention are described hereinafter by way of example , without any limiting nature , with reference to the accompanying drawings , wherein : figure l is a graph illustrating Paschen' s law; figure 2 shows a drive motor according to the invention; figure 3 shows a compressor device according to the invention .

[0046] Figure 1 is a graph showing a dependence of a breakdown voltage VB at which an electric discharge occurs in a gas medium between two electrodes at a specific distance from each other as a function of a pressure p in the gas medium.

[0047] The breakdown voltage reaches a minimum value VB,min at an intermediate pressure p±nt of the gas medium. Therefore , at pressure levels of the gas medium higher than this intermediate pressure pint, the breakdown voltage VB decreases as the pressure of the gas medium is reduced .

[0048] Figure 2 shows a drive motor 1 according to the invention for driving a compression member of a compressor element of a compressor device for the compression of a gas .

[0049] The drive motor 1 has a motor housing 2 provided with a motor chamber 3 . A motor stator 4 is installed in the motor chamber 3 and a motor shaft 5 is mounted in the motor chamber 3 for driving the compression member of the compression device , whereby the motor stator 4 is provided with windings 6 .

[0050] The motor housing 2 is provided with a supply channel 7 for a gas supply into the motor chamber 3 . The supply channel 7 is provided with a valve 8 which is configured to allow the gas supply into the motor chamber 3 when a pressure of a gas medium in the motor chamber 3 is below a predetermined threshold level pth -

[0051] In other words , the valve 8 in supply channel 7 will open to allow a gas supply into the motor chamber 3 when the pressure of the gas medium in the motor chamber 3 is reduced below the predetermined threshold level pth - Preferably, the predetermined threshold level pth is higher than a breakdown pressure level at which the drive motor 1 is grounded or at which the windings 6 of the motor stator 4 of the drive motor 1 are shortened by means of an electrical breakdown in the gas medium in the motor chamber 3 . More preferably, the predetermined threshold level pth is equal to a sum of the breakdown pressure level and a safety margin .

[0052] This supply channel 7 and valve 8 are provided to the motor housing 2 in order to avoid that the pressure of the gas medium in the motor chamber 3 would be reduced to such an extent that a breakdown voltage ( at which the drive motor 2 would be grounded or at which the windings 6 of the motor stator 4 of the drive motor 1 would be shortened by means of an electric discharge through the gas medium in the motor chamber 3 ) would be reduced to a voltage level at which the windings 6 are energized .

[0053] Optionally, the motor housing 2 is provided with a drive end flange 9 for connecting the motor housing 2 with the compressor element .

[0054] Alternatively or additionally, the motor housing 2 can be provided with a non drive end flange 10 for connecting a head 11 to the motor housing 2 , whereby the supply channel 7 with the check valve 8 is then integrated in the non drive end flange 10 as it is the case in figure 2 .

[0055] It is not to be excluded within the context of the invention that the supply channel 7 with the valve 8 is integrated in another part of the motor housing 2 , for example in the drive end flange 9 or in a j acket 12 of the motor housing 2 between the drive end flange 9 and the non drive end flange 10 .

[0056] As an additional option, the supply channel 7 is in this case provided with a filter 13 upstream from the valve 8 .

[0057] As a further additional option, the supply channel 7 is in this case provided with a restriction 14 for the gas supply .

[0058] In addition, the motor shaft 5 is in this case preferably mounted in the motor chamber 3 by means of liquid-lubricated bearings 15 . Thereby, the motor housing 2 is provided with a drainage channel system 16 for drawing out liquid leaking out of the liquid-lubricated bearings 15 from the motor housing 2 by means of a vacuum source 17 .

[0059] More preferably, the drainage channel system 16 is provided with a restriction means 18 for restricting a fluid flow through the drainage channel system 16 . Even more preferably, this restriction means 18 can be controlled such that it regulates the pressure of the gas medium in the motor chamber 3 to a specific pressure level at which an electrical breakdown between the windings 6 or a grounding of the drive motor 1 is avoided on the one hand, and a sufficient lubrication of the liquid-lubricated bearings 15 is ensured on the other hand .

[0060] As a further additional option, the valve 8 is in this case a non-return valve , such that the gas medium in the motor chamber 3 cannot leak out of the motor chamber 3 and be lost to an environment of the drive motor 1 when the pressure of the gas medium in the motor chamber 3 is higher than an atmospheric pressure of this environment .

[0061] However , it is within the context of the invention not to be excluded that the valve in the supply channel is carried out as a regulating valve whose opening degree can be regulated based on a measured pressure of the gas medium in the motor chamber .

[0062] Figure 3 shows a compressor device 19 according to the invention for the compression of a gas , in this case a screw compressor device .

[0063] The compressor device 19 comprises a compressor element 20 , in this case a screw compressor element , having a compressor element housing 21 provided with a compression chamber 22 .

[0064] The compression chamber 22 contains at least one compression member 23 , in this case a screw rotor , for the compression of the gas in the compression chamber 22 .

[0065] The compressor device 19 further comprises the drive motor 1 as shown in figure 2 for driving the compression member 23 .

[0066] The compressor element housing 21 has an inlet part for supplying the gas into the compression chamber 22 .

[0067] In this case , the motor housing 2 of the drive motor 1 is directly connected to the inlet part of the compressor element housing 21 such that the motor chamber 3 and compression chamber 22 are fluidly connected to each other . Because the motor chamber 3 and the compression chamber 22 are fluidly connected, a reduction of the pressure of the gas medium in the motor chamber 3 will result from a reduction of a pressure in the compression chamber 22 , for instance when the compressor device goes in "unload" mode . Nevertheless , the supply channel 7 with the valve 8 can ensure that a pressure of a gas medium in the motor chamber 3 is never reduced to a breakdown pressure level at which an electrical breakdown would occur through the gas medium in the motor chamber 3 .

[0068] The present invention is by no means limited to the embodiments described as an example and shown in the drawings , but a drive motor for a compressor device for the compression of a gas according to the invention or a compressor device comprising such a drive motor can be realised in all kinds of forms or dimensions without departing from the scope of the invention as defined in the claims .

Claims

Claims .1.- A drive motor for driving a compression member of a compressor element of a compressor device for the compression of a gas, whereby the drive motor (1) has a motor housing (2) provided with a motor chamber (3) , whereby a motor stator (4) is installed in the motor chamber (3) and a motor shaft (5) is mounted in the motor chamber (3) for driving the compression member (23) of the compressor device (19) , whereby the motor stator (4) is provided with windings (6) , characterised in that the motor housing (2) is provided with a supply channel (7) for a gas supply into the motor chamber (3) , whereby the supply channel (7) is provided with a valve (8) which is configured to allow the gas supply into the motor chamber (3) when a pressure of a gas medium in the motor chamber (3) is below a predetermined threshold level (pth) .2.- The drive motor according to claim 1, characterised in that the motor housing (2) is provided with a drive end flange (9) for connecting the motor housing (2) with the compressor element (20) .3.- The drive motor according to claim 2, characterised in that the supply channel (7) with the valve (8) is integrated in the drive end flange (9) .4.- The drive motor according to claim 1 or 2, characterised in that the motor housing (2) is provided with a non drive end flange (10) for connecting a head (11) to the motor housing (2) , whereby the supply channel (7) with the valve (8) is integrated in the non drive end flange (10) or the head ( 11 ) .5.- The drive motor according to claim 1 or 2, characterised in that the motor housing (2) is provided with a jacket (12) , whereby the supply channel (7) with the valve (8) is integrated in the jacket (12) .6.- The drive motor according to any one of the previous claims, characterised in that the supply channel (7) is provided with a filter (13) upstream from the valve (8) .7.- The drive motor according to any one of the previous claims, characterised in that the supply channel (7) is provided with a restriction (14) for the gas supply.8.- The drive motor according to any one of the previous claims, characterised in that the motor shaft (5) is mounted in the motor chamber (3) by means of liquid-lubricated bearings (15) , whereby the motor housing (2) is provided with a drainage channel system (16) for drawing out liquid leaking out of the liquid-lubricated bearings (15) from the motor housing (2) by means of a vacuum source (17) .9.- The drive motor according to claim 8, characterised in that the drainage channel system (16) is provided with arestriction means (18) for restricting a fluid flow through the drainage channel system (16) .10.- The drive motor according to any one of the previous claims, characterised in that the valve (8) is a non-return valve .11.- A compressor device for the compression of a gas, comprising a compressor element (20) having a compressor element housing (21) provided with a compression chamber (22 ) , whereby the compression chamber (22) contains at least one compression member (23) for the compression of the gas in the compression chamber (22) , characterised in that the compressor device (19) further comprises a drive motor (1) according to any one of the previous claims for driving the compression member (23) .12.- The compressor device according to claim 11, characterised in that the compressor element housing (21) has an inlet part for supplying the gas into the compression chamber (22) , and that the motor housing (2) of the drive motor (1) is directly connected to the inlet part of the compressor element housing (21) such that the motor chamber (3) and compression chamber (22) are fluidly connected.13.- A method for regulating a pressure in a drive motor for driving a compression member of a compressor element of a compressor device for the compression of a gas,wherein a pressure of a gas medium in a motor chamber (3) provided in a motor housing (2) of the drive motor (1) is regulated, characterised in that a gas supply is allowed into the motor chamber (3) when the pressure of the gas medium in the motor chamber (3) is below a predetermined threshold level (pth) •14.- The method according to claim 13, characterised in that the predetermined threshold level (pth) is higher than a breakdown pressure value at which the drive motor (1) is grounded or at which windings (6) of a motor stator (4) of the drive motor (1) are shortened by means of an electrical breakdown in the gas medium in the motor chamber (3) .15.- The method according to claim 14, characterised in that the predetermined threshold level (pth) is equal to a sum of the breakdown pressure level and a safety margin.

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