GB2454172A

GB2454172A - Motor assembly

Info

Publication number: GB2454172A
Application number: GB0721139A
Authority: GB
Inventors: Allan Kwan; Sam K S Lam; Jing Ning Ta
Original assignee: Johnson Electric SA
Current assignee: Johnson Electric SA
Priority date: 2007-10-29
Filing date: 2007-10-29
Publication date: 2009-05-06
Also published as: GB0721139D0

Abstract

A kitchen appliance 10 having interchangeable implement 15, has a base unit 11 accommodating a motor assembly providing coaxial outputs 16, 17 operating at two different speeds. The motor assembly comprises a motor having a motor shaft forming a high speed output 16 and a planetary gear train driven by the motor shaft and driving a low speed output 17. The gear train has a housing which has substantially the same radial dimensions as the motor allowing a more compact base unit for the appliance 10.

Description

TITLE 2454172 Motor Assembly

FIELD OF THE INVENTION

This invention relates to a motor assembly and in particular, to a motor assembly having two outputs which rotate at different speeds, especially such a motor assembly adapted for use in a kitchen appliance such as a food processor.

BACKGROUND OF THE INVENTION

In some household appliances such as a food processor, it is desirable to have two outputs which rotate at different speeds. This is often achieved by using a motor with an electronic speed control or a motor having different windings giving different output speeds of the motor. However, while this works well for speeds which are close, it is not efficient for two output speeds which are very different, as desired, for example. in a food processor where different implements are attachable or driven by a common base unit. Here, a high speed of about 10,000 rpm is required for the blender and a low speed of 200 rpm is required for the citrus juicer, for example. Such a wide variation i usually achieved by using two motors. Recently. a gearbox driven by the motor is used to step down the motor speed to drive the low speed implements. This gearbox has spur gears and takes up a large volume, about the same volume as required by a two motor design and the base unit must be large and have two separate locations for attaching the high speed and low speed implements. This arrangement can not be used in a hand held food processor. Even for bench top units, today's trend is for smaller, lighter appliances and the prior art units are too big and heavy.

SUMMARY OF THE INVENTION

In order to reduce the size of the base unit and to streamline the attachment process, it is desirable for the high speed and low speed outputs to he co-axial. A secondary desire is for the whole motor assembly including the gearbox to be very compact.

Accordingly. in one aspect thereof, the present invention provides a motor assembly for an appliance, comprising: a motor having a motor shaft; and a gear train driven by the motor shaft and having a gear shaft, wherein the motor shaft forms a high speed output, the gear shaft forms a low speed output and the motor shaft and gear shaft are co-axial.

Preferred and/or optional features are set forth in the dependent claims 2 to 16.

According to a second aspect, the present invention provides a kitchen appliance having a base unit and interchangeable implements requiring high or low rotational input, wherein the base unit has a motor assembly as described above having a high speed output coaxial with a low speed output.

Preferable and/or optional features are set forth in claims I 8 to 20.

BRIEF I)ESCRIPTION OF THE I)RAWINGS A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure I is a perspective view of a free standing food processor; Figure 2 is a sectional view of a hand held food processor; Figure 3 is a perspective view of a motor assembly for the food processor of Figure 1 or Figure 2; Figure 4 is a partial sectional view of a gear train being a part of the motor assembly of Figure 3; Figure 5 is a plan view of the gear train of Figure 4: and Figures 6 and 7 are enlarged sectional views of a coupling arrangement.

I)ETAILEI) I)ESCRIPTION OF THE PREFERRED EMBODIMENTS The food processor 10 of Figure i is a free standing or bench top food processor and has a base unit 11 accommodating a drive mechanism including an electric motor assembly. The front of the base unit 11 has a control panel 13 for selectively operating the food processor. The top surface has an implement receiving section 14 for receiving various types of implements IS of which two possible implements, a blender and a juicer, are shown schematically. The implements 15 are received by the implement receiving section 14 in a known manner. The base unit II has two co-axial outputs 16, 17 for driving implements 15. The two outputs operate at different speeds and they can be considered as a high speed output 16 or a low speed output I 7.

The implements IS, when fitted to the implement receiving section 14. engage only one of the outputs 16, 17, according to the type of implement. For example, the blender would engage the high speed output 16 whereas the juicer would engage the low speed output 17. The outputs 16, 17 are co-axial and have axially spaced ends adapted to couple with selected implements for operation thereof.

The food processor 10 of Figure 2 is a hand held food processor commonly known as a stick blender. The hand held food processor has a base unit 11 which is adapted to be hand held during operation and a number of interchangeable implements 15 (only one shown, attacl�^ed to the base unit in Fig. 2). some which require a high speed operation arid some which require a slow speed operation. Known stick blenders may have a two speed motor but, as explained above, electronic speed controls only give a small percentage of variation in the output speed. Even so, the present invention can be used with a multi-speed motor to give an even greater range of selectable output speeds. The motor assembly I 2 of the hand held food processor is essentially the same as that used in the free standing food processor of Fig. I. The motor assembly 12 is shown in Figure 3. The motor assembly has an electric motor 18 and a gear train 19. The motor 18 has a motor housing 20 having an outer diameter and an axial length. The motor 1 8 has a motor shaft 21 extending axially 1 5 from a first end of the motor housing 20. Motor terminals 22 for connecting to the control panel are provided on the opposite second end.

The motor shaft 21 forms the high speed output 16. A gear shaft 31. forming the low speed output I 7. is co-axially mounted about the motor shaft 21 and is driven by the motor through the gear train 19. The motor shaft 21 and the gear shaft 31 have axially spaced ends to allow for fitting of the respective coupling members. The motor illustrated is a HVI)C motor having a permanent magnet stator and a wound rotor. A flux ring 23 is fitted to the motor housing 20 about the stator to reduce flux leakage.

The gear train 19 is accommodated within a gear housing 24. The gear housing 24 is fitted to the first end of the motor housing 20. The gear housing 24 is shown in section in Figure 4 is cup shaped having an open end which engages the motor housing 20 and a closed end which faces the outputs. A mounting flange 25 (shown in Figs. 2 & 4) is fixed to the closed end, for example, by screws, for mounting the motor assembly 12 within the base unit I I. The gear housing 24 may he fixed to the motor housing by screws or other suitable means. However, the preferred method is to use a mounting adapter 26 which is used to close the open end of the gear housing and is fixed to the end of the motor housing 20 and precisely located by engagement with an outer surface of a bearing boss 29 formed in the end of the motor housing 20.

Preferably the engagement is a press fit engagement. Engaging the bearing boss avoids relying on the outer surface of the motor housing which may not be accurate enough for alignment of the gear train with the motor shaft. The mounting adapter 26 retains a metal cover plate 27 within the gear housing24. the function of which will be described herein after. The gear housing 20 has a stepped mouth forming a location guide 28 in the form of an axially extending wall which engages a radially outer wall of the mounting adapter 26 to radially locate the gear housing 24. While the location guide is shown as a continuous wall it could be a number of discrete projections or fingers. The gear housing 24 appears as a cap forming an extension of the motor housing 20 and has the same or similar diameter or radial dimension as the motor housing 2. thus producing a radially compact motor assembly. In practise, a gear housing having a radial dimension with is flO greater than 10% more than the radial dimension of the motor would produce a useful and compact motor assembly.

The gear train 19 is more clearly shown in Figures 4 and 5. The gear train is based on a planetary gear design. A sun gear 32 is fixed to the motor shaft (not shown in Figs. 4 & 5). The sun gear 32 engages a number of planet gears 33 (preferably five as shown). The planetary gears 33 engage a stationary ring gear 34 associated with the gear housing 24. The ring gear 34 may be a separate ring fixed to the inner surface of the gear housing or it may be integrally fornied on the wall of the gear housing as a monolithic construction. The planet gears 33 are rotatably mounted on axles 35 fixed to a gear carrier 30. The gear shaft 3 I is associated with the carrier 30 by being formed integrally with the carrier as a monolithic construction. Alternatively, the gear shaft 3 I can be fixed to the gear carrier 30 by, for example, press fitting, welding, form lock deforming, etc. The cover plate 27 is located at the distal ends of the axles 35 and provides a low friction rubbing surface or thrush surface for the planet gears 33 limiting their axial movement.

In the preferred embodiment, the gear housing 24 including the ring gear 34, the gear carrier 30 including the gear shaft 31, and the planet gears 33 are of plastics material whereas the sun gear 32 is of a metal material, preferably a sintered metal construction. The axles 35 are of metal, preferably being steel pins interference press fitted into holes in the gear carrier 30. Thus, it will be realised that the motor shaft 21 forms the high speed output and is the inner output 16 while the outer output is the low speed output 17 being driven via the gear train 19. The distal end of the motor shaft 21 has non-round cross section for drivingly mating with the sun gear 32. The preferred non-round cross section is formed by creating two diagonally opposite flat portions. The sun gear 32 is pressed on to the motor shaft 2 I and has a corresponding shaped hole 36 to receive the motor shaft 2 1.

It should be realised that the when the motor is rotating, both the high speed output 16 and the low speed output I 7 are rotating.

The sun gear 32, the ring gear 34 and the intermeshing planet gears 33 have circumferentially inclined gear teeth. This gives the gear train a higher loading capacity and quieter operation than straight axially extending gear teeth.

When the motor shaft 21 rotates, it drives the sun gear 32 which in turn drives the planet gears 33 which are in mesh with the stationary ring gear 34. This causes the planet gears 33 to roll along the surface of the ring gear 34 rotating the gear carrier 30 and thus the gear shaft 31. i.e. causing the low speed output 17 to rotate.

The gear train 19 gives the low speed output 17 a reduction in speed compared to the high speed output 16, preferably in the range of 3. 5 to 6 meaning that one revolution of the low speed output requires 3.5 to 6 revolutions of the motor shaft (high speed output). The test motor assembly used a reduction gear ratio of 4.8: I which proved to be very adequate.

The motor shaft 21 is journalled in hearings of the motor 18. The gear shaft 31 is journalled in a bearing 37, preferably a ball bearing, supported by the gear housing 24. A circlip 38 holds the gear carrier / gear shaft combination 30, 3 I, to the bearing to prevent axial movement there between. Although the two shafts 21, 3 I are coaxial, they do not contact each other under normal operation. The motor shaft 21 simply passes through the gear housing 24 and through an axial hole 39 in the gear shaft 3 1 and carrier 30. Thus, apart from the sun gear 32, the motor shaft 21 passes right through the gear box without contact.

The implements 15, be they separate devices or beaters etc. adapted for use with the base unit of the free standing food processor or the hand held food processor, need to couple with the outputs of the base unit. One way to do this is illustrated in Figures 6 and 7 where a portion of two implements 15 are shown in sectional view, respectively coupled to the high speed output and to the low speed output.

In Fig. 6, the implement IS has a high speed coupler 41 which is adapted to mate with the high speed output I 6. It has an axially extending recess 42 which fits over the end of the motor shaft 2 I. As mentioned above, the end of the motor shaft 21 has two flat surfaces to drivingly engage the sun gear 32. These flat surfaces are also used to drivingly engage the high speed coupler 41. The cross-sectional profile of the recess 42 in the coupler 41 corresponds to the shape of the end portion of the motor shaft 21.

As the implement needs to be easily removed and replaced. the fit can be a neat sliding fit and detent means (not shown) provided to releasably hold the coupler 41 to the motor shaft 21. Such detents may be a resilient snap finger and a recess or a spring loaded ball and recess. The end of the motor shaft 21 and/or the mouth of the recess 42 in the coupler may be chamfered to assist alignment and insertion of the motor shaft into the coupler.

The arrangement for the low speed coupler 43, shown in Fig.7, is similar. The low speed coupler 43 also has an axially extending recess 44. In this case, the recess 44 is adapted to couple with the low speed output (the gear shaft 31 of the gear train). The end of the gear shaft 31 and the recess 44 have complementary shapes with the end of the gear shaft 31 and/or the mouth of the recess 44 being chamfered to assist insertion of the gear shaft into the low speed coupler 43. Recess 44 is deeper than the recess 42 in the high speed coupler to accommodate the high speed output 16 without contact with the low speed coupler 43, thus allowing unimpeded rotation of the motor shaft 21. The recess 44 is also of a larger diameter to mate with the larger diameter low speed output 17.

While any suitable motor construction can be used with this gear train arrangement, the preferred motor is an PMDC motor (permanent magnet direct current motor), which is speed controllable through a controller in response to input from a user via the control panel. This gives further variations in the operating speeds in both the high speed and low speed outputs.

To avoid the necessity for transforming the input voltage, the DC motor may be adapted to operate on line voltage, a so called high voltage PMI)C motor.

Rectification would still be required but this may be by using a single diode or a full wave bridge. For a longer life, the motor may be a brushless DC motor using electronic commutation. In this case, the electric commutation circuit can be combined with the speed control electronics. However, the brush type motor can use a more simple, non-electronic controller, if desired.

In the description and claims of the present application, cacti of the verbs "comprise", "include" and "have", and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items.

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 in the appended claims.

For example, the gear housing is shown fitted to the end of the motor housing but could be formed as a part of the motor housing. The mounting flange is shown as a separate piece but could be integrally formed as part of the gear housing.

Claims

CLAIMS: I. A motor assembly for an appliance, comprising: a motor having a motor shaft and a gear train driven by the motor shaft and having a gear shaft.

characterised in that the motor shaft forms a high speed output, the gear shaft forms a low speed output and the motor shaft and gear shaft are co-axial.
2. A motor assenibly according to Claim I. wl�^erein the motor has a niotor housing, the gear train has a gear housing and the motor shaft extends through at least one end of the motor housing and the gear housing.
3. A motor assembly according to Claim 2, wherein the motor housing has a radial diameter and first and second axial ends, the shaft extends from the motor housing through the first axial end and the gear housing is fitted to the motor housing on the first axial end.
4. A motor assembly according to Claim 3, wherein the gear housing has an outer radial dimension which is similar to an outer radial dimension of the motor housing.
5. A motor assembly according to Claim 2, 3 or 4, wherein the gear housing is fixed to the motor housing by a mounting adapter, the mounting adapter forming a cover for the gear housing and is fixed to a bearing boss of the motor housing.
6. A motor assembly according to any one of the preceding claims, wherein the gear train is a planetary gear train, having a sun gear fitted to the motor shaft and driving a number of planet gears in mesh with a stationary ring gear, the planet gears are rotatably mounted to a carrier associated with the gear shaft, whereby rotation of the motor shaft causes rotation of the low speed output.
7. A motor assembly according to Claim 6. wherein the carrier directly drives the gear shaft.
35. A motor assembly according to Claim 7, wherein the gear shaft is integral with the carrier.
9. A motor assembly according to Claim 8. wherein the gear shaft and carrier are a monolithic construction of plastics material.
10. A motor assembly according to any one of Claims 6 to 9. wherein the planet gears are of plastics material.
II. A motor assembly according to any one of Claims 6 to 10, wherein the ring gear is formed on an inner surface of the gear housing.
12. A motor assembly according to Claim II, wherein the ring gear is formed with the gear housing as a monolithic construction.
13. A motor assembly according to any one of Claims 6 to 12. wherein the gear housing is of plastics material.
14. A motor assembly according to any one of the preceding claims, wherein the high speed output and the low speed output have axially spaced ends.
IS. A motor assembly according to any one of the preceding claims, wherein the motor is a PMI)C motor.
I 6. A motor assembly according to any one of the preceding claims, wherein the motor is a HVI)C motor.
17. A kitchen appliance having a base unit and interchangeable implements requiring high or low rotational input, wherein the base unit has a motor assembly according to any one of the preceding claims.
18. A kitchen appliance according to Claim 17. wherein the base unit has an implement receiving section accommodating the high speed output and the low speed output, and wherein the appliance has coupling means for coupling the implements to a predetermined respective output.
19. A kitchen appliance according to Claim 17. wherein the implenients have either a high speed coupler for coupling to the high speed output only or a low speed coupler for coupling to the low speed output only.
20. A kitchen appliance according to Claim 17, wherein the kitchen appliance is a food processor.
21. A nlotor assembly, substantially as hereinbefore described with reference to the accompanying drawings.
22. A kitchen appliance, substantially as hereinbefore described with reference to the accompanying drawings.