Differential assembly

Abstract

Disclosed is a differential assembly comprising a ring gear, a sun gear and a planet gear. The ring gear and sun gear are rotatable about a first axis of rotation. The planet gear is rotatably mounted on the ring gear at a position offset from the ring gear centre and is configured to orbit the first axis as the ring gear rotates. Rotation of the sun gear drives rotation of a first output member, and rotation of the planet gear drives rotation of a second output member. A universal joint arrangement may be included to decouple orbital motion of the second output member about the first axis and transfer rotational motion from the second output member to the first axis. Also disclosed is a three-gear differential that is light-weight, compact and is easier to manufacture and assemble than existing differentials.

Description

[0001] DIFFERENTIAL ASSEMBLY

[0002] The present disclosure relates generally to differential gear assemblies. More specifically, the present disclosure relates to compact differential gear assemblies configured for use with a vehicle drivetrain. More specifically, the present disclosure relates to a three-gear differential that is light-weight, compact and is easier to manufacture and assemble than existing differentials.

[0003] BACKGROUND

[0004] Differential assemblies are essential components for smooth and safe cornering in vehicles, as they enable torque distribution between two axles and allow speed differentiation of left and right wheels.

[0005] In a vehicle, the differential assembly is integrated into a drivetrain in which the engine or other prime mover provides power to the differential assembly via a drive shaft. The differential assembly splits the torque delivered by the drive shaft between two separate outputs, each of which is connected to a respective axle and wheel.

[0006] There are several basic designs of known differential assemblies, including a ring and pinion design, epicyclic design, and spur-gear design. Each design comprises numerous interworking moving parts, many of which require high precision engineering to manufacture. Modern differential assemblies are even more complex, including additional mechanical and electrical elements. Such differential assemblies are thus expensive to manufacture and may require regular maintenance and consequently have relatively high repair costs.

[0007] The manufacture and assembly of gears is amongst the most precise processes in the manufacture of a vehicle, as there can be virtually no play between the surfaces of engaging gear teeth. In addition, gear teeth must be hard and durable, requiring technologically and energetically intensive processes.

[0008] Accordingly, differential assemblies are complex mechanical components that are relatively expensive to manufacture. There is therefore a need fora simpler, more compact alternative differential assembly that may be produced efficiently and at a lower cost to conventional differential assemblies.

[0009] It is also an object to address one or more of the above-mentioned shortcomings and / or to at least provide the public with a useful alternative.

[0010] In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally to provide a contextfor discussing features of the invention. Unless specifically stated otherwise, reference to such external documents or sources of information is not to be construed as an admission that such documents or such sources of information, in any jurisdiction, are prior art or form part of the common general knowledge in the art.

[0011] SUMMARY OF THE INVENTION

[0012] The present disclosure relates to a differential assembly having a simplified construction and more compact design compared to known differential designs. The differential assembly provided herein advantageously uses a reduced number of gears compared to known differential designs.

[0013] In an aspect of the present disclosure, there is provided a differential assembly comprising:

[0014] a ring gear arranged to rotate about a first axis of rotation;

[0015] a sun gear arranged to rotate about the first axis of rotation; and

[0016] a planet gear engaging the sun gear, and rotatably mounted to the ring gear such that the planet gear orbits the first axis of rotation as the ring gear rotates;

[0017] wherein a first output member is connected to the sun gear to rotate therewith, and a second output member is connected to the planet gear to rotate therewith about a moving second axis spaced apart from the first axis of rotation.

[0018] The differential assembly may further comprise a universal joint arrangement configured to transmit a rotational motion from the second axis to the first axis without transferring orbital motion of the second axis about the first axis. The universal joint arrangement may comprise a shaft, a proximal universal joint at a first end of the shaft configured to connect to the second output member, and a distal universal joint at a second end of the shaft.

[0019] The first output member may connect, or be configured to connect, to a first axle. The first axle may connect, or be configured to connect, to a first wheel.

[0020] The distal universal joint may connect, or be configured to connect, to a second axle. The second axle may connect, or be configured to connect, to a second wheel.

[0021] The planet gear and the sun gear may have an equal gear ratio.

[0022] The ring gear may be configured to mesh with an input gear that drives rotation of the ring gear.

[0023] The differential assembly may further comprise a housing for retaining at least the ring gear, the sun gear, and the planet gear. The housing may comprise one or more portsconfigured for the addition and removal of a lubricant, and seals configured to retain the lubricant within the housing.

[0024] In another aspect of the present disclosure, there is provided a vehicle drivetrain comprising the differential assembly as described above.

[0025] In another aspect of the present disclosure, there is provided a vehicle drivetrain comprising:

[0026] a drive shaft configured to receive torque from a prime mover;

[0027] a housing;

[0028] a differential assembly enclosed by the housing and configured to be mounted within a vehicle, the differential assembly comprising:

[0029] a ring gear rotatable about a first axis, the ring gear operatively connected to the drive shaft and configured to receive torque from the prime mover via an input gear;

[0030] a sun gear arranged to rotate about the first axis; and

[0031] a planet gear engaging the sun gear, and rotatably mounted to the ring gear such that the planet gear orbits the first axis as the ring gear rotates;

[0032] a first output member connected to the sun gear and configured to rotate therewith about the first axis;

[0033] a second output member connected to the planet gear and configured to rotate therewith about the second axis and orbit about the first axis;

[0034] a first axle connected to the first output member;

[0035] a universal joint assembly connected to the second output member at a proximal end, and connected to a second axle at a distal end, the universal joint assembly configured to translate rotational motion from the second axis to the first axis;

[0036] each of the first axle and second axle extending outwardly in opposite directions from the housing along the first axis.

[0037] This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features. Where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually described.Where components of the present technology are described herein as being 'connected', it will be understood that (unless the context clearly indicates otherwise), the components may be connected by connecting elements, or the components may be integrally formed with one another.

[0038] The term 'comprising' as used in this specification and claims means 'consisting at least in part of'. When interpreting statements in this specification and claims that include the term 'comprising', other features besides those prefaced by this term can also be present. Related terms such as 'comprise' and 'comprised' are to be interpreted in a similar manner.

[0039] It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range and any range of rational numbers within that range (for example, 1 to 6, 1.5 to 5.5 and 3.1 to 10). Therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed.

[0040] As used herein the term '(s)' following a noun means the plural and / or singular form of that noun. As used herein the term 'and / or' means 'and' or 'or', or where the context allows, both.

[0041] BRIEF DESCRIPTION OF THE FIGURES

[0042] The present disclosure will now be described by way of example only and with reference to the accompanying drawings in which:

[0043] Figure 1 shows a perspective view of a differential assembly in accordance with an embodiment of the present disclosure.

[0044] Figure 2 shows a cross-section view of a differential assembly in accordance with an embodiment of the present disclosure.

[0045] Figure 3 shows a cross-section view of a differential assembly in accordance with an embodiment of the present disclosure.

[0046] Figures 4 to 8 show side views of a differential assembly in accordance with an embodiment of the present disclosure.

[0047] DETAILED DESCRIPTION

[0048] The present disclosure relates to a novel differential assembly and its implementation in a vehicle drivetrain.

[0049] Figures 1 to 3 show aspects of an exemplary differential assembly 1 of the present disclosure. As shown in these Figures, there is provided a differential assembly 1comprising a ring gear 2 arranged to rotate about a first axis of rotation 10, a sun gear 5 arranged to rotate about the first axis of rotation 10, and a planet gear 4 engaging the sun gear 5 and rotatably mounted to the ring gear 2 such that the planet gear 4 circles the first axis of rotation 10 as the ring gear 2 rotates. A first output member 12, extending in a first direction A, is connected to the sun gear 5 to rotate therewith, and a second output member 14, extending in a second direction B opposite the first direction A, is connected to the planet gear 4 to rotate therewith about a moving second axis 16 spaced apart from the first axis of rotation 10.

[0050] In preferred embodiments, the differential assembly 1 is integrated with a vehicle drivetrain. In such an embodiment, the first output member 12 connects to a first axle leading to a first wheel. And the second output member 14 connects to a second axle leading to a second wheel on a laterally opposite side of the vehicle. The first and second output members (12, 14) may be integrally formed with the respective first and second axles.

[0051] Ring gear 2 is configured to mesh with and receive torque from an input gear (not shown in the Figures), the input gear itself receiving torque from a prime mover (for example, via a drive shaft and / or transmission).

[0052] Ring gear 2 comprises a toothed circular body, in which the gear teeth are configured to mesh with the input gear. As shown, gear teeth may be located on an outwardly facing surface of the circular body, but in other embodiments the teeth may be located on another surface of ring gear 2, such as an inwardly facing surface of the circular body, and the input gear configured accordingly. The gear teeth are cut to match the angle of the teeth of the input gear. The ring gear teeth shown in Figure 1 are helical, i.e., cut at an angle to the axis of rotation of ring gear 2. However, other configurations of teeth may be suitable.

[0053] Ring gear 2 is rotatably mounted on, and supported by, the first output member 12. First output member 12 may be any suitable gear shaft known in the art. Its axis of rotation defines the first axis of rotation 10, about which ring gear 2 is configured to freely rotate. Accordingly, ring gear 2 and first output member 12 are configured to rotate relative to one another in use. Differential assembly 1 may comprise a bearing 20a between ring gear 2 and the first output member 12 to reduce friction and facilitate independent rotation of the ring gear 2 and first output member 12. Similarly, bearing 20b, located between ring gear 2 and the second output member 14, may reduce friction between ring gear 2 and the second output member 14. Other components that facilitate relative rotational movement between the ring gear 2 and the first and second outputmembers 12, 14 known to those skilled in the art would also be suitable. For example, hardened steel or bushes, such as bushes used in vehicles crankshafts.

[0054] The gear ratio between the input gear and the ring gear 2 may be determined by the skilled person, in consideration of the purpose to which the differential assembly 1 is put. For example, the gear ratio between the input gear and the ring gear 2 may be determined according to requirements around torque and the performance of the differential assembly.

[0055] Planet gear 4 comprises a circular body having gear teeth on a radially exterior side thereof. The teeth of planet gear 4 are configured to mesh with teeth of sun gear 5. As with ring gear 2, the gear teeth shown in Figure 1 are helical although other configurations of teeth may be suitable.

[0056] Planet gear 4 is rotatably mounted at its centre to ring gear 2 by second output member 14. Planet gear 4 is configured to rotate about the second output member 14, which defines the second axis of rotation 16. The position of the second output member 14, and the mounting of planet gear 4, on ring gear 2 is at a point offset from the centre of the ring gear 2. Second output member 14 extends in a direction B, towards a second axle and second wheel.

[0057] The second axis of rotation 16 is thus parallel to and offset from the first axis of rotation 10. Planet gear 4, the second output member 14, and the second axis of rotation 16 all orbit the first output member 12 (and therefore the first axis of rotation 10) as the ring gear 2 rotates. In other words, rotational motion of the ring gear 2 drives orbital motion of the second axis 16 about the first axis 10.

[0058] Planet gear 4 is fixed to second output member 14 such that there is no relative rotation between the planet gear 4 and second output member 14, in use. Planet gear 4 may be connected to second output member 14 via splines or similar. In this way, the rotation of planet gear 4 directly drives rotation of the second output member 14.

[0059] As planet gear 4 is rotatably mounted at a position offset from the centre of ring gear 2, the second axis of rotation 16 circularly orbits the first axis of rotation 10. The differential assembly 1 may include mechanisms configured to transfer the rotation of the planet gear 4 to an axle or wheel, and decouple the axle or wheel from the orbital motion of the planet gear 4. A suitable mechanism is a double universal joint, as described below.

[0060] Ring gear 2 may further comprise a counterweight 8 configured to balance the rotation of the ring gear 2 in use and offset the mass of planet gear 4. The counterweight 8 may be integrally formed with ring gear 2 as a thickened portion of its body, or alternatively as a weight connected thereto by one or more connecting elements.As shown in Figure 1, the counterweight 8 comprises a thickened segment of ring gear 2. The thickened segment is positioned diametrically opposite the planet gear 4. The counterweight 8 is sized and weighted such that rotation of the ring gear is balanced when bearing planet gear 4.

[0061] With reference to Figures 2 and 3, the counterweight 8 may comprise a weight connected to the ring gear 2, although counterweight 8 may alternatively be an integral part of ring gear 2. For example, when casting a blank from which the ring gear 2 is to be machined, the counterweight 8 would be an integral part of the casting. And after the casting has been machined, the counterweight 8 may be trimmed back to its correct weight.

[0062] Sun gear 5 comprises a circular body having gear teeth on a radially exterior side thereof. The teeth of sun gear 5 are configured to mesh with gear teeth of planet gear 4. The teeth are preferably helical, although other configurations of teeth may be suitable.

[0063] Sun gear 5 is oriented coaxially with ring gear 2 and mounted on the first output member 12. Sun gear 5 is thus configured to rotate about the first axis of rotation 10. Sun gear 5 is fixed to first output member 12 such that there is no relative rotation between the sun gear 5 and first output member 12, in use. For example, rotation of sun gear 5 may be transferred to the first output member 12 by one or more splines, which rotationally fix sun gear 5 to output member 12, although other fixing connections known in the art are suitable. In this way, the rotation of sun gear 5 directly drives the rotation of the first output member 12.

[0064] Sun gear 5 is configured to mesh with and receive torque from planet gear 4 and direct torque to the first output member 12. Accordingly, planet gear 4 and sun gear 5 are each mounted on the same side of ring gear 2. It also follows that the offset location at which the planet gear 4 is mounted on the ring gear 2 is selected such that the planet gear 4 and sun gear 5 are properly meshed.

[0065] In the embodiments shown in Figures 1 to 7, planet gear 4 and sun gear 5 have an equal gear ratio (1:1). When integrated in a vehicle drivetrain such that the first and second output members drive rotation of laterally opposite wheels (e.g., left and right wheels), an equal gear ratio between the planet gear 4 and sun gear 5 is particularly desirable. This allows the first output member (being configured to connect to a first axle and first wheel) and second output member (being configured to connect to a second axle and a second wheel) to rotate at the same rate when driving in a straight line. Altering the gear ratio away from 1:1, for example, by providing a radius disparity between the sun gear 5 and planet gear 4, may cause a vehicle to tend to pull to the side with the larger and therefore slower gear, with its correspondingly slower wheel. However, wheredifferential assembly 1 is applied in other applications, an unequal gear ratio between planet gear 4 and sun gear 5 may be desirable.

[0066] With reference to Figures 2 and 3, differential assembly 1 may further comprise a universal joint arrangement 6 in rotational communication with the second output member 14 (the second output member 14 being in direct connection with planet gear 4). The universal joint arrangement 6 is configured to transmit the rotational motion of second output member 14 about the second axis, but not its orbital motion about the first axis, to a second axle or wheel oriented along the first axis 10, i.e., co-axial with the first axle or wheel.

[0067] Universal joint arrangement 6 may comprise a double universal joint. For example, the universal joint arrangement 6 may comprise a pair of universal joints 24, 26 at proximal and distal ends of a shaft 22. Proximal end joint 24 connects with the second output member 14 (which is itself connected to planet gear 4). Distal end joint 26 connects with the second axle, leading towards the second wheel (see direction B in Figures 2 and 3). The second axle has a rotational axis substantially coaxial with the first axis 10 and the first output member 12. In this way, rotational motion about the second axis 16 is transferred whilst the orbital motion of planet gear 4 about the first axis 10 is decoupled.

[0068] Any suitable universal joint may be used in universal joint assembly 6. In an example, each universal joint 24, 26 comprises a pair of yokes. In the proximal end joint 24, one of the pair of yokes may be connected to the second output member 14 and the other yoke connected to the shaft 22. In the distal end joint 26, one of the pair of yokes may be connected to the axle or wheel and the other is connected to the shaft 22. A spider is positioned between each of the pairs of yokes, the spider comprising trunnions that fit into the yokes. The spider is configured to pivot within the pair of yokes. Rotation of second output member 14 about the second axis 16 drives rotation of the universal joint arrangement 6. The spider is pivotable about the trunnions as the second output member 14 rotates about the first axis 10. The proximal and distal universal joints are oriented on the shaft 22 to transmit rotational speed uniformly between the second output member 14 and the axle or wheel in use.

[0069] As shown in Figures 2 and 3, differential assembly 1 may further comprise a counterbalancing bar 30 configured to balance the universal joint arrangement 6 in use. Counterbalancing bar 30 comprises a rigid member configured at one end to wrap around a distal end portion of shaft 22 while still allowing shaft 22 to freely rotate. The wrapping portion of counterbalancing bar 30 may comprise two half round castings screwed together so as to encompass the ball bearing which is press fitted into place on the shaft 22. The opposite end of counterbalancing bar 30 is attached via brackets to the counterweight 8of the ring gear 2 (e.g., via screws or welds). A hole through both brackets and the counterbalancing bar 30 allows a bolt to pass through all three and a locknut at the other end of the bolt holds everything together.

[0070] Differential assembly 1 may be mounted to a vehicle's chassis or axle housing. Typically, the differential assembly 1 would be enclosed by a housing. The differential assembly 1 may be securely positioned to align with a drive shaft and axles for efficient torque transfer. To maintain the alignments between the meshing gears of the engine and transmission at the precision required, the transmission and differential assembly 1 may be fixed to the engine for front wheel drive engines, so they remain aligned. For rearwheel-drive engines, the transmission sits behind the engine and connects to the rear differential via a long drive shaft with two universal joints, similar to arrangement 6, to help isolate most engine vibrations and movements from reaching the rear differential. In this case, a rear wheel housing constrains the differential assembly 1 in place. This housing in turn may be fixed to the car's suspension, which in turn may be fixed to the chassis. In all cases the engine and transmission may be supported on three to four vibration absorbing mounting brackets attached to the chassis.

[0071] The housing for differential assembly 1 may be configured to enclose and support differential assembly 1 (not shown in Figures). The housing may comprise removable panels or be configured to be manually opened to be able to access differential assembly 1. Housing may be configured to retain a lubricant or comprise a mechanism for supplying lubricant to the interfaces of the movable parts of differential assembly 1. In addition, the housing may be configured to be fully sealed about input and output members, for example by gaskets and seals. The housing may further comprise plugs or similar for ease of lubricant changes. Differential assembly 1 may be further supplied with lubricant to reduce friction and wear. Differential assembly 1 may further comprise a cooling system to manage heat generated during operation.

[0072] The components of the differential assembly 1, including ring gear 2, planet gear 4 and sun gear 5, universal joint arrangement 6 and first and second output members (12, 14), may be suitably supported and retained in place within a housing by means known to the skilled person. Non exhaustive examples of such supports and retaining mechanisms are described herein, although it will be apparent to the skilled person that additional or alternative mechanisms may be used.

[0073] As shown in Figures 2 and 3, planet gear 4 and sun gear 5 may be retained on their respective output members by lock nuts (15a, 15b) and washers, or alternatively, raised bosses on the gears for quicker and easier assembly. A roller bearing may also be provided.The first output member 12 and the second output member 14, extending in opposite directions A and B respectively, may be each supported and fixed in place by thrust bearings 17 and 18. Note that while only the first axle and wheel extension is shown in Figures 2 and 3, a corresponding arrangement of parts may be provided in direction B.

[0074] On the first output member 12, between the lock nut 15a and thrust bearing 18, lies the sun gear 5 and the bearings supporting the ring gear 2. The sun gear 5 is held in place on first output member 12 by the lock nut 15a and thrust bearing 18. Tightening of lock nut 15a secures the sun gear 5, ring gear 2, and bearings against fixed collar 21.

[0075] On the second output member 14, planet gear 4 is held in place by lock nut 15b and a fixed collar. Tightening of lock nut 15b about the second output member 14 secures planet gear 4, bearings and planet gear are pressed against a fixed collar, thereby securing the parts in place.

[0076] Sun gear 5 may be axially spaced apart from ring gear 2. Planet gear 4 may be similarly axially spaced from ring gear 2. For example, Figure 3 shows differential assembly 1 comprising a fixed collar 21 that goes around the first output member 12, which in turn runs through the ring gear 2 and sun gear 5. Fixed collar 21 is secured to the output member 12 via any suitable fixing means, including friction fit or screws. Alternative collars include steel (e.g. low carbon steel), or plastic collars.

[0077] As shown in Figures 2 and 3, the flange at the end of the axle is for connection to a vehicle wheel, and for a bearing 17 to press against, to stop the axle moving off its axis (i.e. first axis 10). Bearing 18 presses against fixed collar 21, to also stop movement.

[0078] A common problem for front wheel drive cars is the differential not being equally spaced between the two wheels it drives. The shorter and therefore lighter shaft accelerates slightly faster than a longer, heavier one. This however is solved by adjusting the weight of both shafts to make them more equivalent, e.g., by adding mass to the shorter shaft, so it is equal in weight to the longer one.

[0079] Efficiency of the differential assembly in operation is dependent on the quality of the build and alignment of parts. When driving straight forward or straight in reverse, ideally the only friction losses are between the input gear and the ring gear 2, and the main roller bearings, which is 1% + [2% x 4] = 9 % loss or 91% efficient.

[0080] When cornering however, the sun gear 5 and planet gear 4 and their bearings move just enough to cover the difference in speed between the inner and outer wheels driving the vehicle, estimated to be 25% of the speed of the vehicle at most. In this case the losses are 1% + [ 2% x 4] = 9% but because its only turning 25% of the speed, it's = 2.1 %. The total when cornering is the above 9% plus 2.1 % = 11 .1 % loss or 88.9%efficient. There may be additional losses due to the two universal joints, but this imbalance is only experienced in very sharp turns; milder turns will result in a milder loss and will reduce to zero when going straight.

[0081] Operation of differential assembly 1 will now be described with reference to its integration in a vehicle drivetrain, in which first output member 12 drives a first axle and wheel (notionally a left axle and left wheel) of a vehicle and second output member 14 drives a second axle and wheel (notionally a right axle and right wheel) of the vehicle. First and second axles are coaxial with each other and extend in opposite directions from the differential assembly 1 towards respective first and second wheels.

[0082] Ring gear 2 receives torque from an input gear in communication with a drive shaft delivering rotational power from the engine or other prime mover (not shown). Planet gear 4 and sun gear 5 are meshed. Sun gear 5 is mounted and rotationally fixed to first output member 12, and planet gear 4 is mounted on and rotationally fixed to second output member 14. Whilst ring gear 2 and sun gear 5 are coaxial and may be mounted on a single supporting shaft (e.g., first output member 12), ring gear 2 is not rotationally fixed to first output member 12. Therefore, the rotational speed of the sun gear 5 may vary from the rotational speed of ring gear 2.

[0083] The first axle and second axle are co-axial with the first axis 10. First output member 12 directly drives a first axle (optionally the first output member 12 is integrally formed with the first axle). The second output member 14 communicates with the second axle via universal joint arrangement 6 which translates rotational motion from the second axis 16 to the first axis 10. Orbital motion of the second axis 16 about the first axis 10 is thus decoupled from the second axle by the operation of the universal joint arrangement 6.

[0084] Figures 4 to 7 show ring gear 2, sun gear 5, and the planet gear 4 each having one half shaded to illustrate relative rotational motion. Figure 4 shows a starting configuration of differential assembly 1. Certain operative connections between these features, the output members and the axles, for example, are not shown, but it will be understood that operation of the differential assembly is substantially the same as the differential assembly 1 shown in Figures 1 to 3.

[0085] Figures 5 to 7 show configurations following a 180-degree rotation of ring gear 2. Figure 5 shows a configuration following driving straight where rotation of first and second output members is equal. Figure 6 shows a configuration following a left turn where rotation of the first output member 12 is reduced, and second output member 14 is advanced. Figure 7 shows a configuration following a right turn where rotation of the first output member 12 is advanced, and second output member 14 is reduced.Figure 5 shows that rotation of ring gear 2 by 180 degrees causes rotation of both sun gear 5 and planet gear 4 also by 180 degrees. That is, relative motion of planet gear 4 and sun gear 5 is stationary relative to ring gear 2. Accordingly, the first and second axles and wheels driven by the sun gear 5 and planet gear 4, respectively, are revolving at the same rate too, as would naturally occur when a vehicle is going straight forwards or straight in reverse. So, the ratios for the ring, R; planet, P; sun, S; and wheels, W are 1: 1: 1: 1. Therefore, during straight driving, where rotation of first and second output members is equal, R=P=S=W

[0086] Figure 6 shows the configuration of differential assembly 1 during a sharp left turn, in which the ring gear 2 has rotated 180 degrees from the configuration shown in Figure 4. During a left turn the rotation of sun gear 5 (and the first output member 12, the first axle and the first wheel connected thereto) slows relative to ring gear 2. That is, the rotation of sun gear 5 (and the first output member 12, the first axle and the first wheel connected thereto) is reduced relative to ring gear 2. Rotation of planet gear 4 is concomitantly advanced relative to ring gear 2. In this example, sun gear 5 has had its rotation retarded by 90 degrees, relative to ring gear 2, and therefore only advanced by 90 degrees (180 - 90 = 90 degrees), whereas ring gear 2 has advanced 180 degrees. Because sun gear 5 is meshed with planet gear 4, the rotation of planet gear 4 has advanced by an additional 90 degrees, and therefore the total rotation of planet gear 4 is 270 degrees (180 + 90 = 270), which increases the right wheel's rotation relative to left wheel. The turning ratios of the ring gear 2, planet gear 4 and sun gear 5 in the above example are 2: 3: 1.

[0087] Figure 7 shows the configuration of differential assembly 1 during a sharp right turn, in which the ring gear 2 has rotated 180 degrees from the configuration shown in Figure 4. The converse configuration shown in Figure 6 is produced. That is, the rotation of planet gear 4 (and the second output member 14, the second axle and the second wheel connected thereto) is reduced relative to ring gear 2. And rotation of sun gear 5 is advanced relative to ring gear 2. The turning ratios of the ring gear 2, planet gear 4 and sun gear 5 in the above example are 2: 1: 3.

[0088] It will be appreciated that the total angular rotation output is equal to the angular rotational input. For example, the slowing of sun gear 5 is equal to the speeding up of planet gear 4.

[0089] It will also be appreciated that the terms "left" and "right" are illustrative only, and that differential assembly 1 may be configured such that first output member and second output member are connected to either a left or right axle and / or wheel.It will be further appreciated that the turning ratios the angles 180 and 90 degrees are provided to simply exemplify the operation of the differential assembly 1, and that retardation and advancement of the respective sun gear 5 and planet gear 4 relative to ring gear 2 during cornering could be nearly anything that is physically possible.

[0090] It will be further appreciated that the examples described herein also work in reverse.

[0091] The differential assembly 1 may be constructed to allow manual disassembly, such that parts may be removed and replaced. For example, sun gear 5 may not be permanently fixed to the first output member 12. Similarly, the bearings, lock nuts, ring gear 2 and planet gear 4 are not permanently attached to the first and / or second output members 12, 14.

[0092] Advantageously, the differential assembly 1 is able to distribute torque from an input to first and second outputs using only three gears. That is, the differential assembly may comprise only three gears between the input and the two outputs. This enables a differential assembly 1 to be configured as a compact, lightweight and cost-effective alternative to known differentials.

[0093] Further advantageously, the differential assembly 1 may be constructed without the use of crown or bevelled gears. Crown and bevel gears are considerably more difficult and costly to manufacture than the helical (or optionally spur) gears in the differential assembly described herein. This is because these crown / bevel gears are more difficult to cut due to their gear teeth and the spacing between their teeth reducing in size along their length. Unlike helical and spur teeth which are uniform through their length. This may enable manufacture of the differential assembly 1 at a lower cost compared to differential assemblies requiring such parts.

[0094] The manufacture of gears is amongst the most precise and demanding processes in the manufacture of a vehicle, as there can be virtually no play between the curved surfaces of engaging, gear teeth. Even when those surfaces are compound curves. In addition, gear teeth must be hard and durable, requiring technologically and energetically intensive processes. Hence, differential assemblies are difficult and relatively expensive to manufacture. There is therefore an advantage in reducing the number of gears in a differential assembly and providing a differential assembly comprising fewer gears. For example, comprising three gears as shown in the accompanying Figures and described above.

[0095] Unlike known differential assemblies requiring five or more gears, the differential assembly of the present invention may operate to receive torque from an input and splitthe torque to two output members via only three gears. This provides advantages in the reduction in manufacturing costs, a reduction in weight of the assembly, reduction in number of parts, reduction in complexity and an improvement in simplicity of design. In addition, the differential assembly described herein provides about half the rotating mass of the known differentials of a similar overall size. Therefore, vehicles using the differential assembly described herein may experience a slightly better acceleration and fuel economy.

[0096] * * *

[0097] To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims.

[0098] This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

Claims

WHAT IS CLAIMED IS:1 A differential assembly comprising:a ring gear arranged to rotate about a first axis of rotation;a sun gear arranged to rotate about the first axis of rotation; anda planet gear engaging the sun gear, and rotatably mounted to the ring gear such that the planet gear orbits the first axis of rotation as the ring gear rotates;wherein a first output member is connected to the sun gear to rotate therewith, and a second output member is connected to the planet gear to rotate therewith about a moving second axis spaced apart from the first axis of rotation.

2. The differential assembly of any one of the preceding claims, wherein the first output member connects to a first axle.

3. The differential assembly of claim 1 or 2, further comprising a universal joint arrangement configured to transmit a rotational motion from the second axis to the first axis without transferring orbital motion of the second axis about the first axis.

4. The differential assembly of any one of the preceding claims, wherein the universal joint arrangement comprises a shaft, a proximal universal joint at a first end of the shaft configured to connect to the second output member and a distal universal joint at a second end of the shaft.

5. The differential assembly of claim 4, wherein the distal universal joint connects to a second axle, and the second axle is configured to connect to a second wheel.

6. The differential assembly of any one of the preceding claims, wherein the planet gear and the sun gear have an equal gear ratio.

7. The differential assembly of any one of the preceding claims, wherein the ring gear is configured to mesh with an input gear that drives rotation of the ring gear.

8. The differential assembly of any one of the preceding claims, further comprising a housing for retaining at least the ring gear, the sun gear, and the planet gear, and comprising one or more ports configured for the addition and removal of a lubricant, the housing comprising seals configured to retain the lubricant within the housing.

9. A vehicle drivetrain comprising:a drive shaft configured to receive torque from a prime mover;a housing;a differential assembly enclosed by the housing and configured to be mounted within a vehicle, the differential assembly comprising:a ring gear rotatable about a first axis, the ring gear operatively connected to the drive shaft and configured to receive torque from the prime mover via an input gear;a sun gear arranged to rotate about the first axis; anda planet gear engaging the sun gear, and rotatably mounted to the ring gear such that the planet gear orbits the first axis as the ring gear rotates;a first output member connected to the sun gear and configured to rotate therewith about the first axis;a second output member connected to the planet gear and configured to rotate therewith about the second axis and orbit about the first axis;a first axle connected to the first output member;a universal joint assembly connected to the second output member at a proximal end, and connected to a second axle at a distal end, the universal joint assembly configured to translate rotational motion from the second axis to the first axis;each of the first axle and second axle extending outwardly in opposite directions from the housing along the first axis.

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