GB2421989A

GB2421989A - A differential gear with a casing that is a rotor of an electric motor

Info

Publication number: GB2421989A
Application number: GB0524599A
Authority: GB
Inventors: Terence John Tranter; David Frederick Lee
Original assignee: MODIFF Ltd
Current assignee: MODIFF Ltd
Priority date: 2004-12-03
Filing date: 2005-12-02
Publication date: 2006-07-12
Also published as: GB0426584D0; GB0524599D0

Abstract

A differential gear, e.g. for a wheelchair, mobility scooter etc, comprises a casing 10 having mounted therein a drive shaft 30 on which is located planetary bevel gears 40, 40' that are meshed with main bevel gears 50, 50 fixed to half shafts 60, 60'. On an outer face 14 of the casing 10 is mounted a plurality of permanent magnets 80, 80' which act as a rotor for an electric motor, e.g. stepping motor 84, that also includes a wound stator 82 secured to a chassis of the scooter. A contractible braking calliper 74 may be fixed to the chassis and is forced against a brake disc 70, which is attached to the casing 10 by fasteners 72, so that a braking force is applied to the scooter. A pulley 20 is attached via a one-way bearing 22 to the casing 10 so that the differential may be driven by an external source of power.

Description

A Differential Gear The present invention relates to a differential gear,

in particular, a simplified differential gear with optional integral power and braking features.

A differential gear is a means of allowing differential rotation of two or more driven means, such as wheels, from a driving means, such as a drive shaft. Many such designs are known to persons skilled in the art.

In recent years small vehicles such as wheelchairs, mobility vehicle, golf trolleys and the like have become increasingly used. In such vehicles, size, weight and reduced complexity are at a premium whilst their increasing sophistication requires that many features such as drive, braking and differential gearing are required. * * * S.

An aim of the present invention is to provide a device meeting one or more of the above objectives. *.

The present invention in its various embodiments is as set out in the appended claims. * * *

S

The present invention provides a differential gear comprising, a casing; a planetary gear, comprising a drive shaft and a planetary gear wheel rotatable about said drive shaft; and two main gear wheels each connected to a half shaft, wherein the planetary gear wheel engages the two main gear wheels, wherein in use the drive shaft is capable of driving the planetary gear wheel, the planetary gear wheel is capable of driving the main gear wheels and the main gear wheels are capable of driving their respective half shafts, wherein the planetary gear and the two main gear wheels are housed within the casing, and wherein the drive shaft is engaged with the casing such that when a rotational force is applied to the casing the casing drives the drive shaft.

The present invention also provides a differential gear comprising an outer driving casing, to which a force may be applied, a drive shaft, a planetary gear, two main gears and two half shafts, arranged so that the drive shaft is drivable by the casing and has one or more planetary gear wheels located thereon for independently driving the main gears which, in use, each serve to drive a half shaft, such that the foregoing act to provide a differential gear.

The present invention may optionally consist of the above features, optionally in association with one or more of the features of aspects of the invention (below).

The differential gear of the invention is preferably located wholly within, and is enclosed by, the casing. A single casing, such as a two part casing thereby serves to both protect the gears, and perform as a functioning part of the differential. A rotational force may be applied to the casing so as to drive the half shafts with differential gearing. : .,*

S

es.,, , The planetary gear may comprise one, two, three or four planetary gear wheels and preferably two gear wheels as these may be mounted on a single straight shaft. **. *.S.

According to one aspect of the invention power may be applied, such from a belt, by * : : means of a driving wheel directly to the casing so as to, in use, cause it to rotate. The actuating force, in the form of a torque, is applied to the casing by means of an integral driving wheel such as a pulley, notched wheel, sprocket or gear wheel feature on the casing and preferably by means of a notched wheel for engaging a driven belt.

Alternatively and preferably the driving wheel may be rotateably attached by means of a unidirectional transmission mechanism, such as a ratchet or one-way bearing, preferably by means of a one-way bearing, to the casing.

According to a further aspect of the invention the driving casing (the casing) is equipped as a rotor and the device of the invention further comprises a stator so as to form an integral electric motor. The motor may be AC or DC and preferred types are where the rotor has no electrical connection to the stator, such as in a stepper motor or an induction motor. According to this aspect of the invention the motor may be used to rotate the casing and hence power the half shafts. Hence the casing may further function as part of a torque generating drive mechanism. In addition, the motor may be used to electrically brake the half shafts and in doing so may optionally act as a generator of power.

The pulley drive and integral motor features may be combined.

According to a yet further aspect of the invention the casing may be equipped with a frictional braking mechanism, such as disc or drum brake. Preferably a braking disc is attached to the casing for braking by an external caliper. Hence, the casing may further function as part of a braking mechanism.

The braking andlor pulley drive and/or integral motor features may be combined with the S p differential gear of the present invention to form a differential gear assembly. : S. * * 0 * The present invention is also advantageous in that one set of main bearings, those on each * half shaft act as bearings for the differential, any motor and any braking mechanism(s), ., only one further set of bearings being required to support any wheels or alternative power take off means. Other bearing surfaces, particularly when the device is used in a small * S * *Pe powered vehicle may be provided by bushes, such as bronze bushes. This allows for * : : *. S simple construction, light weight and compactness. The main bearings on each half shaft preferably comprise two spaced apart bearings, such as ball races, these are preferably spaced apart by more than a diameter of the half shaft and may be up to two diameters of the half shaft apart. Such an arrangement gives sufficient rigidity in normal use to allow the casing to perform its various functions effectively when used in a small vehicle. This feature is particularly significant in achieving a small air gap, and hence higher efficiency, of any integral electric motor.

The present invention is advantageous in that a single component, the casing, acts as; a protection means for the gears; a functioning component of a differential and optionally a power take off (e.g. via a pulley) feature; a braking feature and/or part of a torque generating drive mechanism. All these features only require four journalled surfaces (i.e. two on the drive shaft and one on each half shaft). This could be reduced to just three if a single planetary gear wheel is located on a suitable spigot, such as a drive shaft, on the inside wall of the casing. This reduction in complexity reduces production cost and increases efficiency.

Devices of the invention may be manufactured from metal and/or plastics, preferably engineering plastics. The casing may preferably comprise two halves attached along a centre line about the drive shaft, thus giving an optimal reduction in mechanical complexity and simplicity of construction.

A mobility vehicle (i.e. a one person, three or four wheel motorised transporter suitable for use by an invalid, or the infirm, for use on footpaths and the like) or a wheelchair may incorporate a device of the invention. a

**S. p a.

Also within the scope of the invention is an electric motor, preferably a stepper motor, equipped with a differential as described herein, the differential residing within the rotor. a of the motor.

The present invention will now be described with reference to the illustration shown in. a.

the following diagram in which; * :: a Figure 1 is a cross-section through a differential gear of a first embodiment according to the invention and, Figure 2 which is a cross-section through a stepper motor incorporating a differential gear of a second embodiment according to the invention.

Referring to figures 1 and 2, a differential gear (2) of the invention comprises outer driving casing (10) in which is located a drive shaft (30) , on which are located two planetary bevel gears (40, 40'), also inside the casing (10) are main bevel gears (50, 50'), on the ends of two half shafts (60, 60'), those gears engaging the planetary gears (50).

Pulley (20) isjournalled onto the driving casing (12) by means of a oneway bearing (22).

A central portion of the driving casing is substantially cylindrical (12) and on its outer face (14) are mounted a plurality of permanent magnets (80, 80' etc) for acting as a rotor for a stepping electric motor (84) further including a wound stator (82) separated from the rest of the device by means of a small air gap. The stator is in use secured to a chassis (not shown), the chassis being journalled to the half shafts (60, 60') at a point such as a wheel bearing (not shown).

Referring to Fig. I, a side face (16) of the driving casing has a braking disc detachably attached thereto by means of fasteners(72).A contractible braking caliper (74) is engageable with the disk and is itself mounted onto the chassis (not shown).

Referring to Fig. 2, the stepper motor (84A) has a casing (96), mounted on the driving casing (10) by means of two ball bearing races (90, 90'). The casing is mountable onto a chassis by means of flanges (92, 92') equipped with mounting holes (88, 88' etc.).

The device has a motor control mechanism to control the stepper motor (84) comprising a motor control disc (94) attached to a side face (16) of the driving casing and on which are mounted permanent magnets (96) to actuate a Hall-effect sensor (98).

In use of the differential gear (2) power is transmitted at the pulley (20) to the outer driving casing (10) and from there to the ends (32,32') of the drive shaft (30) on which are rotateably mounted the planetary bevel gears (40, 40') at each end (30, 30') of the * *S*S drive shaft (30) . The planetary bevel gears (40, 40') further transmit force to main bevel * :: gears (50, 50') mounted on ends (62, 62') of half shafts (60, 60'). The half shafts (60, 60') are each journalled by two ball bearing races (64, 66, 64', 66') into the driving casing (10). The bearings (64, 66) on each half shaft (60) are set apart, at their centers by two shaft diameters.

In use, a rotating force is applied to the pulley (20) by means of a notched belt (not shown) powered by an electric motor remote from the device. Power is transmitted via the one-way bearing (22) to the driving casing (10) and from there, via the drive shaft ends (32) to the drive shaft (30). From the drive shaft (30) power is transmitted to the planetary gears (40, 40') which rotateably engage with the main gears (50, 50') to transmit force to the half shafts (60, 60') and thereby to wheels (not shown) mounted on outer ends of the shafts.

The driving casing (10) thereby rotates along with the driving pulley (20) and in normal unimpeded, straight line movement, at the same rate as both the half shafts (60, 60').

When a vehicle propelled via the device turns a corner such that differential resistance forces are present on the half shafts (60, 60') a differential rate of rotation is imparted on those shafts via the main gears from the planetary gears, in the manner of a differential gear. In this manner a very simple and compact differential drive, for example, for a small vehicle is achieved.

In use a stepper motor of figure 2 is controlled by supplying external electric power, the sequencing of the stepper motor coils is determined by conventional electrical/electronic components in association with the motor control mechanism (100). By detecting a position of the rotor (102) from actuation of the Hall-effect switch (98) as intermittently a, activated by magnets (96) on the disc (94) the sequencing of the stator coils (82) is: . achieved to achieve powered motor rotation. * *

When in motion a vehicle using the device, when coasting, or when, for example running 41 down a hill can be braked by means of the disc brake assembly (76). The braking force S..

obtained being distributed in a differential manner to the shafts (60, 60') and hence to * I. wheels.

A further means of generating a rotating force on the driving casing (10) is by means of the stepper motor (84). The stator being energised in a conventional manner, thereby creating a rotational force on the driving shell. That force may be used for propulsion, to assist propulsion, for braking or to assist braking. In a further mode of operation power may be generated from the motor during braking by means of using the current induced in the stator by the rotor.

The device of the invention may be modified a by a person skilled in the art whilst remaining within the scope of the invention. Modifications include substituting an induction motor for the stepper motor (84), use of drum brake, such as by utilising the outer face of the driving casing (10) as a mount for friction pads or as a friction surface for external pads. Where the various elements are journalled, bushes; roller, needle or ball bearings may be utilised as they may be between all abutting moving surfaces in the device. The bearing arrangement shown in the diagram is preferred. The motor control mechanism may alternatively comprise a disc, such as a disk with apertures therein, and an optical sensor to detect disc position. The disc (94) may alternatively be a multiple commutator disk of suitably arranged concentric ring segments with corresponding electrical contacts associated with wiring from the casing so as to conduct electricity from an electrically contacted ring or rings on the disc (94) sO as to sequence the coils (84) of the stator (104) thus obviating the need for control electronics to sequence the coils (84).

The term casing, as used herein, may also be termed a shell or housing. * S * ,, *

II

S *S S * S * ,. cv,. * * I, * S S.

Claims

Claims A differential gear comprising a casing (10); a planetary gear,

comprising a drive shaft (30) and a planetary gear wheel (40, 40') rotatable about said drive shaft; and two main gear wheels (50, 50') each connected to a half shaft (60, 60'), wherein the planetary gear wheel engages the two main gear wheels, wherein in use the drive shaft is capable of driving the planetary gear wheel, the planetary gear wheel is capable of driving the main gear wheels and the main gear wheels are capable of driving their respective half shafts, wherein the planetary gear and the two main gear wheels are housed within the casing, and wherein the drive shaft is engaged with the casing such that, when a rotational force is applied to the casing, the casing drives the drive shaft. :.. * *
2. The differential gear as claimed in claim 1, wherein the planetary gear comprises two planetary gear wheels rotatable about the drive shaft and both planetary gear - wheels are engaged with the two main gear wheels. . :1:'
3. The differential gear of claim 1 or claim 2, constructed so that the casing is, in use, capable of being solely supportable on the half shafts or the half shafts are, in use, solely supportable by the casing.
4. The differential gear of any preceding claim, wherein the drive casing is a rotor (80, 120) of an electric motor.
5. The differential gear of claim 4, wherein the stator (82, 104) of the electric motor is directly or indirectly journalled to the rotor.
6. The differential gear of any preceding claim, wherein a driving wheel (20) is mounted on the casing for the transmission of motive power to the differential gear from an external motive power source.
7. The differential gear of claim 6 wherein the driving wheel is rotateably mounted on the casing by means of a unidirectional transmission mechanism (22).
8. The differential gear of any preceding claim, further comprising a frictional braking mechanism (76).
9. An electric motor comprising a differential gear as claimed in any one of claims 1 to 7.

9. A differential gear substantially as hereinbefore described with reference to figure I or to figure 2 of the drawings. S.

10. A mobility vehicle comprising a differential gear according to any one of the * preceding claims. .. : I. * * . * ..

11. An electric motor comprising a differential gear as claimed in any one of claims I to9. *:::: *

S ** It'

A

Amendments to the claims have been filed as follows A differential gear comprising a casing (10); a planetary gear, comprising a drive shaft (30) and a planetary gear wheel (40, 40') rotatable about said drive shaft; and two main gear wheels (5C)) each connected to a half shaft (60, 60'), wherein the planetary gear wheel engages the two main gear wheels, wherein in use the drive shaft is capable of driving the planetary gear wheel, the planetary gear wheel is capable of driving the main gear wheels and the main gear wheels are capable of driving their respective half shafts, wherein the planetary gear and the two main gear wheels are housed within the casing, and wherein the drive shaft is engaged with the casing such that, when a rotational force is applied to the casing, the casing drives the drive shaft, wherein a driving wheel (20) is mounted on the casing for the transmission of motive power to the differential gear from an external motive power source and wherein the driving wheel is rotateably mounted on the casing by means of a unidirectional transmission mechanism (22).

2. The differential gear as claimed in claim I, wherein the planetary gear comprises two planetary gear wheels rotatable about the drive shaft and both planetary gear wheels are engaged with the two main gear wheels.

3. The differential gear of claim I or claim 2, constructed so that the casing is, in use, capable of being solely supportable on the half shafts or the half shafts are, in use, solely supportable by the casing.

4. The differential gear of any preceding claim, wherein the drive casing is a rotor (80, 120) of an electric motor.

5. The differential gear of claim 4, wherein the stator (82, 104) of the electric motor is directly or indirectly joumalled to the rotor.

6. The differential gear of any preceding claim, further comprising a frictional braking mechanism (76).

7. A differential gear substantially as hereinbefore described with reference to figure I or to figure 2 of the drawings.

8. A mobility vehicle comprising a differential gear according to any one of the preceding claims.