AU2004307193B2 - Variable speed electric motors - Google Patents

Description

VARIABLE SPEED ELECTRIC MOTORS Field of the invention This invention relates to variable speed electric motors.

Background of the invention Three-phase induction electric motors can provide variable speed by incorporating a controller which controls the voltage and frequency of the power to motor. Conventional 3Ph electric motors can be made to have variable speed control, even if only a single-phase power supply is available, by providing a VVVF (variable voltage variable frequency) controller circuit mounted in a box which is separate to the motor. The box for example can be located separately from the motor and connected thereto by cabling or can be mounted to the motor, e.g. on top or by the side of the motor.

It can be difficult or inconvenient to locate or mount or accommodate or protect a motor and its separate, sometimes bulky associated controller apparatus.

Summary of the invention It is an object of the present invention to provide a convenient and/or compact variable speed electric motor.

According to the present invention there is provided a variable speed electric motor including: a motor assembly having a stator and a rotor with a motor shaft mounted for rotation in bearings, so as to be rotatable within the stator of the motor; a cooling fan arranged to direct cooling air flow over or through the motor assembly; a casing enclosing the motor assembly; a controller circuit for controlling in a selectively variable manner the supply of power to the motor assembly so as to selectively control the speed of rotation of the rotor, the controller circuit including numerous components thereof which are mounted to form a controller assembly; and a controller housing in which the controller assembly is located, the controller housing being mounted within the casing of the electric motor and being located and arranged so that the cooling fan causes a cooling air flow past or through the controller housing so as to provide a cooling effect for the controller assembly therein, the controller housing comprising a metal housing mounted adjacent an endshield of the motor assembly with the motor shaft extending from the motor assembly at one side of the endshield through the endshield and extending axially through the controller housing with the components of the controller circuit located therein, the cooling fan forcing cooling air onto and over the controller housing before reaching and providing cooling effect for the motor assembly, the controller assembly including a circuit board to which the components of the controller circuit located within the controller housing are mounted with the motor shaft extending axially through the circuit board, the circuit board having at least one heat generating circuit component of the controller circuit mounted at one side of the circuit board and in abutting heat exchange relationship with the inside surface of the metal controller housing.

Preferably the cooling fan is located within the casing and is driven by the motor shaft, the controller housing being located between the fan and the motor assembly with the motor shaft extending axially from the motor assembly through the controller housing to the fan, whereby cooling air flow generated by the fan provides a cooling effect for the controller housing and for the motor assembly.

The casing preferably includes a fan cowl which encloses both the cooling fan and the controller housing, the cowl also providing an annular outlet for cooling air flow to be directed over the outside of the casing surrounding the motor assembly.

In a preferred embodiment of the electric motor, the controller circuit includes a speed input means located externally of the casing of the motor and through which a speed control signal or command is input from externally to the controller circuit. In one embodiment, the speed input means comprises a potentiometer and associated control knob which a user can turn to adjust the potentiometer and thereby provide a speed input command to the controller circuit. In an alternative embodiment, the speed input means includes a remote automatic speed controller such as a computer which is operative to input speed control signals to the controller circuit in a predetermined or programmed manner.

The circuit board has the at least one heat generating circuit component of the controller circuit mounted at one side of the circuit board and in abutting heat exchange relationship with the inside surface of the metal controller housing, with other components of the controller circuit being mounted at the opposite side of the circuit board and facing the endshield of the motor assembly.

Components of the controller assembly may be encapsulated within a resin for protecting the components against physical and/or chemical deleterious conditions, such as dirty or high-humidity, or aerosol containing, or corrosive atmospheres.

WO 2005/043720 PCTIAU2004/001495 Brief description of the drawings Possible and preferred features.of the present invention will now be described with particular reference to the accompanying drawings. However it is to be understood that the features illustrated in and described with reference to the drawings are not to be construed as limiting on the scope of the inventi8n. In the drawings: Fig. 1 is a side, partially sectional, view of an electric motor according to an embodiment of the present invention, Fig. 2 is a front view of the motor of Fig. 1, and Fig. 3 is a diagram of the functional units of a controller circuit for use in the motor of the present invention.

Detailed description of embodiments Referring to the drawings, the motor 10 depicted in Figs. 1 and 2 is a three phase induction motor having a motor assembly 11 having a stator 12 and a rotor 13 with a motor shaft 15 extending axially and mounted in bearings 16, 17 so that the rotor 13 is rotatable within the stator 12. A casing 25 encloses the motor assembly 11.

A cooling fan 20 is mounted for rotation by the motor shaft 15 by direct mounting to the shaft. The fan 20 in use directs cooling air flow over the motor assembly 11 by providing the fan 20 within a cowl 21 which is part of the casing 25. The cowl 21 is arranged to discharge cooling air flow through the annular outlet 22 along the outside surface of the cylindrical part 26 of the casing 25 which encloses the motor assembly 11.

The fan 20 could be driven indirectly by the motor shaft 15 e.g. through a gear mechanism, instead of being directly mounted as in the drawings. Alternatively the fan could be a separately powered and operated component.

In the illustrated motor, the bearing 16 is mounted by an intermediate back endshield 30 located at one end of the motor assembly 11 and the bearing 17 is mounted 4 WO 2005/043720 PCT/AU2004/001495 by the front endshield 33 forming part of the casing 25 so that the drive end 18. of the shaft 15 projects beyond the endshield 33.

A controller circuit 40 is shown schematically in Fig. 3 and in use controls in a selectively variable manner the supply of power to the motor assembly I1 so as to selectively control the speed of rotation of the rotor 13. The controller circuit 40 includes numerous components which can include, as illustrated in Fig. 3, power input conditioning components including EMC filter 65, charging circuit 66, rectifier 67, and DC link filter 68operative to produce from a single phase AC input 64 a DC power supply to the power module 70. The power module can be an integrated power module i] operative to generate a variable three phase power output for the three phase induction motor 10. The power module 70 is selectively variably controlled by a digital controller 71. DC power supply voltages for the power module 70 and digital controller 71 can be provided by the switch mode power supply 72.

'Fhe digital controller 71 operates in response to an external speed input signal on line 74. In the simplest embodiment, the speed input signal may be provided by an operator of the motor by means of an external or peripheral input means 41. In the motor of Figs. 1 and 2 the input means 41 comprises a potentiometer provided within the terminal box 42 and having for example a rotary control knob 43 which the operator turns to operate the potentiometer and thereby provide a speed input signal or speed command on line 74 to the digital controller 71. In another possible embodiment (schematically shown in the drawings), the speed input signal to the digital controller may be provided by an associated control computer running a motor control program.

For example, in an industrial process, speed changes of an electric motor performing some operation in the industrial process may be required at certain stages of the process and the invention enables such motor speed control automatically under computer WO 2005/043720 PCT/AU2004/001495 program control This can include control not only of forward speeds but also of stopping and reverse speeds.

The digital controller 71 may be susceptible to inference in its operations by electromagnetic noise, e.g. arising in the associated motor 10. Therefore, if desired, the circuit of the controller 71 may incorporate appropriate software and hardware filtering and shielding for reducing or eliminating undesirable noise that might interfere with the controller's operation.

In the motor according to the invention, the controller circuit 40 includes a number of components thereof which are mounted to form a controller assembly 50 (Fig.

o1 As many of the controller circuit components as possible are preferably mounted together to form the controller assembly 50. A controller housing 51 is provided in which the controller assembly 50 is located. The controller housing 51 is mounted within the casing 25 of the motor, namely within the cowl 21 of the casing in the particular illustrated embodiment. The controller housing 51 is located and arranged so that the fan 21 generates a cooling air flow over the controller housing 51 so as to provide a cooling effect for the controller assembly 50 therein.

The controller assembly 50 includes at least one heat generating circuit component of the controller circuit 40 mounted and located in direct heat exchange or thermal contact with the controller housing 51 so that heat generated within that circuit component is conducted to the controller housing for dissipation. In the circuit of Fig. 3, the rectifier 67 and the power module 70 are the two units with maximum heat generation and which desirably are actively cooled. Therefore, the heat generating component(s), illustrated schematically by the reference numeral 52 in Fig. 1, are located in direct heat exchange or thermal contact with the housing 51. In particular, the components 52 include a surface or surfaces in abutting heat exchange contact with an inside 6 WO 2005/043720 PCTAU2004/001495 complementary surface 53 of the housing 51 so that the housing is a heat sink for the heat generating components 52. As shown in Fig. 1, the controller housing 51 comprises a metal (or other thermally conductive) housing mounted adjacent to the endshield 30 of the motor assembly 11. The motor shaft 15 extends from the motor assembly 11 through the endshield 30 and thence axially through the controller housing 51 having the components constituting the controller assembly 50 of the controller circuit 40 located therein. Shaft 15 then extends to the cooling fan 20 so that the fan forces cooling air onto and over the housing 51 before passing the air through the outlet 22 to provide a cooling flow over the cylindrical part 26 of the casing The controller assembly 50 within the controller housing 51 includes a circuit board 55 to which the components of the controller circuit located in the housing are mounted. In this arrangement, the motor shaft 15 extends axially through the circuit board 55. The circuit board 55, for example, may be an annular board having a central hole through which the motor shaft 15 extends. As shown in Fig. 1, the heat generating components 52 can be mounted at one side of the board 55 for heat conducting direct contact with the housing 51 while other components that are not as susceptible to undesirable heat effects can be mounted to the side of the circuit board facing the endshield 30. The components on the circuit board can if desired be encapsulated in resin for protection against physical damage and contamination during assembly and during use of the motor.

In the particular illustrated motor, there may be some components that are external to the easing 25. As discussed earlier, the speed input control means comprising the potentiometer and associated control knob 43 mounted within box 42 can be mounted as shown to the top of the motor for direct operator control of the speed. Also in the illustrated embodiment, a capacitor box 60 having electrolytic capacitors 61 located 7 WO 2005/043720 PCT/AU2004/001495 therein can be mounted externally because these circuit components can be relatively bulky. However, all other controller circuit components can be located internally of the motor casing 25 as described and illustrated.

The motor according to the preferred embodiment particularly described and illustrated herein can provide a compact variable speed motor even where only single phase AC supply is available. The only discernible difference from a conventional induction motor may be a slight elongation of the fan cowl 21.

Claims (8)

1. A variable speed electric motor (10) including: a motor assembly (11) having a stator (12) and a rotor (13) with a motor shaft mounted for rotation in bearings (16, 17), so as to be rotatable within the stator of the motor; a cooling fan (20) arranged to direct cooling air flow over or through the motor assembly; a casing (25) enclosing the motor assembly (11); a controller circuit (40) for controlling in a selectively variable manner the supply of power to the motor assembly (11) so as to selectively control the speed of rotation of the rotor the controller circuit including numerous components thereof which are mounted to form a controller assembly and a controller housing (51) in which the controller assembly (50) is located, the controller housing (51) being mounted within the casing (25) of the electric motor and being located and arranged so that the cooling fan (20) causes a cooling air flow past or through the controller housing (51) so as to provide a cooling effect for the controller assembly (50) therein, the controller housing (51) comprising a metal housing mounted adjacent an endshield (30) of the motor assembly (11) with the motor shaft extending from the motor assembly (11) at one side of the endshield through the endshield and extending axially through the controller housing (51) with the components of the controller circuit (40) located therein, the cooling fan (20) forcing cooling air onto and over the controller housing (51) before reaching and providing cooling effect for the motor assembly (11), the controller assembly (50) including a circuit board (55) to which the components of the controller circuit (40) located within the controller housing (51) are mounted with the motor shaft (15) extending axially through the circuit board the circuit board (55) having at least one heat generating circuit component (52) of the controller circuit (40) mounted at one side of the circuit board (55) and in abutting heat exchange relationship with the inside surface (53) of the metal controller housing (51).

2. A variable speed electric motor as claimed in claim 1 wherein components of the controller circuit (40) other than the said at least one heat generating component (52) are to the said at least one heat generating component (52) and facE the endshield (30) of the motor assembly (11).

3. A variable speed electric motor as claimed in claim I or 2 wherein the cooling fan is located within the casing (25) and is driven by the motor shaft the controller housing (51) being located between the fan (20) and the motor assembly (11) with the motor shaft (15) extending axially from the motor assembly through the controller housing (51) to the fan whereby cooling air flow generated by the fan (20) provides a cooling effect for the controller housing (51) and for the motor assembly (11).

4. A variable speed electric motor as claimed in any one of the preceding claims wherein the casing (25) includes a fan cowl (21) which encloses both the cooling fan and the controller housing the cowl (21) also providing an annular outlet (22) for cooling air flow to be directed over the outside of the casing (25) surrounding the motor assembly (11). A variable speed electric motor as claimed in any one of the preceding claims wherein the controller circuit (40) includes a speed input means (41) located externally of the casing (25) of the motor and through which a speed control signal or command (74) is input from externally to the controller circuit

6. A variable speed electric motor as claimed in claim 5 wherein the speed input means (41) comprises a potentiometer and associated control knob (43) which a user can turn to adjust the potentiometer and thereby provide the speed input command (74) to the controller circuit

7. A variable speed electric motor as claimed in claim 5 wherein the speed input means (40) includes a remote automatic speed controller (80) which is operative to input speed control signals to the controller circuit (40) in a predetermined or programmed manner.

8. A variable speed electric motor as claimed in any one of the preceding claims wherein components of the controller assembly (50) are encapsulated within a resin for protecting the components against physical and/or chemical deleterious conditions.

9. A variable speed electric motor as claimed in claim 1 and substantially as herein before described with particular reference to the accompanying drawings.