GB2413218A

GB2413218A - A PMDC electric motor

Info

Publication number: GB2413218A
Application number: GB0322213A
Authority: GB
Inventors: Stefan Bernau; Joachim Friebe
Original assignee: Johnson Electric SA
Current assignee: Johnson Electric SA
Priority date: 2003-09-23
Filing date: 2003-09-23
Publication date: 2005-10-19
Also published as: GB0322213D0

Abstract

A PMDC electric motor comprises a wound rotor 18 including a shaft 16 and a commutator, a housing 12 having an open end and supporting a permanent magnet stator, and an end cap 14 closing the open end of the housing. The end cap supports motor terminals 22 and brush gear 24, and a moulded interconnect device 26 is mounted within the end cap 14. The interconnect device contains at least one electronic component, such as a Hall effect sensor or a suppression element, and may be used to detect the speed and position of the motor.

Description

A PMDC ELECTRIC MOTOR

This invention relates to a PMDC electric motor.

According to the present invention, there is provided a PMDC electric motor comprising a wound rotor including a shaft and a commutator, a housing having an open end and supporting a permanent magnet stator, an end cap closing the open end of the housing and supporting motor terminals and brush gear, and a moulded interconnect device mounted within the end cap.

Preferably, the moulded interconnect device is in the form of a module and contains conductive tracks and at least one electronic component thereon. The electronic component may be a Hall effect sensor or may be a suppression element in the form of a capacitor, varistor or coil or any combination of such electronic I S components.

Advantageously, the moulded interconnect device has a three dimensional circuit layout.

Preferably, the moulded interconnect device is a plug-in device. Typically, the moulded interconnect device is slotted into a recess in the end cap.

Conveniently, the moulded interconnect device has terminal connections for connection to external terminals.

The moulded interconnect device may be one of a plurality of different moulded interconnect devices which can be selectively mounted in the end cap.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of the inside of an end cap of one embodiment of an electric motor according to the present invention, Figure 2 is a side view of the end cap shown in Figure 1, Figure 3 is a section taken along the line A-A of Figure 2, Figure 4 is a fragmentary view, partly in section, of a motor incorporating the end cap shown in Figures 1 to 3, Figure 5 is a perspective enlarged view of one embodiment of a moulded interconnect device mounted in the end cap, Figure 6 is an enlarged perspective view showing the method of assembly of the moulded interconnect device in the end cap, and Figure 7 is a perspective view of the assembled motor.

Referring to the drawings, there is shown therein a miniature PMDC electric motor 10 having a housing 12 and an end cap 14. A motor shaft 16 extends, at one end of the motor, through a closed end of the housing 12. The shaft 16 supports a wound rotor 18 comprising a rotor core, windings wound around the core and a commutator to which the windings are connected. The housing 12 also supports permanent magnets (not shown) which confront the rotor core across a small air gap.

The shaft 16 is journalled in bearings supported by the housing 12 and the end cap 14.

The end cap 14 also supports brush gear, in the form of brushes 20 supported by brush leaves 22, for making a sliding electrical connection with the commutator for transferring electrical power from motor terminals 24 to the rotor windings. The terminals 24 are connected to an external power supply.

A moulded interconnect device 26 is slotted into a recess 28 in the end cap 14.

The moulded interconnect device 26 is a plug-in device and can be one of a plurality of different moulded interconnect devices which can be selectively mounted in the end cap 14 to suit the requirements for the motor.

As best shown in Figure 5, the moulded interconnect device 26 shown comprises an injection moulded carrier body 30 on which conductive tracks 32 have been created and on which a Hall effect sensor 34 and a resistor 36 are mounted.

Terminal springs 38 are also mounted on the carrier body 30 and extend generally transversely to the conductive tracks 32.

Guide elements in the form of ribs 40 are provided on opposite sides of the carrier body 30 to guide the moulded interconnect device 26 into the recess 28 in the end cap 14 and to ensure very good positional accuracy of the moulded interconnect device 26. The moulded interconnect device 26 can be secured within the end cap 14 by any suitable technique, such as by adhesive, snap fitting or laser welding. The moulded interconnect device 26 shown has a three dimensional circuit layout making it possible to easily place electrical/mechanical components in a small space.

A Hall sensor magnet ring 46 is mounted on the shaft 16.

Moulded interconnect devices are relatively easy to manufacture. The manufacturing process comprises the steps of injection moulding, laser structuring, circuit metalisation and the mounting of the components (electrical and mechanical) The three dimensional nature of the carrier body 30 means that the track layout and components can be designed according to particular needs and in particular it is possible to include terminal springs on the body.

The particular moulded interconnect device described above can be used for sensing position and/or speed of the motor and a signal can be provided to external circuitry by terminals (not shown) which slidably engage the terminal springs 38 through connector slots 42 in the end cap 14, power to the motor being supplied through separate connector slots 44 to the motor terminals 22.

As an alternative to a Hall effect sensor, the moulded interconnect device 26 could include a suppression element, such as a capacitor or a varistor or a coil, mounted thereon and this could be connected across the motor terminals 22 either externally or by direct electrical contact between the motor terminals 24 and the conductive tracks 32.

The embodiments described above are given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims. t

Claims

1. A PMDC electric motor comprising a wound rotor including a shaft and a commutator, a housing having an open end and supporting a permanent magnet stator, an end cap closing the open end of the housing and supporting motor terminals and brush gear, and a moulded interconnect device mounted within the end cap.

2. A PMDC electric motor as claimed in claim 1, wherein the moulded interconnect device contains conductive tracks and at least one electronic component thereon.

3. A PMDC electric motor as claimed in claim 1 or claim 2, wherein the electronic component is a Hall effect sensor.

4. A PMDC electric motor as claimed in claim I or claim 2, wherein the electronic component is a suppression element.

5. A PMDC electric motor as claimed in any one of the preceding claims, wherein the moulded interconnect device has a three dimensional circuit layout.

6. A PMDC electric motor as claimed in any one of the preceding claims, wherein the moulded interconnect device is a plug-in device.

7. A PMDC electric motor as claimed in any one of the preceding claims' wherein the moulded interconnect device is slotted in a recess in the end cap.

8. A PMDC electric motor as claimed in any one of the preceding claims, wherein the moulded interconnect device has terminal connections for connection to external terminals.

9. A PMDC electric motor as claimed in any one of the preceding claims, wherein the moulded interconnect device is one of a plurality of different moulded interconnect devices which can be selectively mounted in the end cap.

10. A PMDC electric motor substantially as hereinbefore described with reference to the accompanying drawings.