GEAR SET FOR A DIFFERENTIAL ASSEMBLY
FIELD OF INVENTION
[0001] The present invention relates to the field of gear sets of differential
assemblies. In particular, the invention relates to a gear set for a differential assembly capable of generating active torque bias between at least two output shafts, to allow the output shafts to rotate at different speeds.
BACKGROUND OF THE INVENTION
[0002] The subject matter discussed in the background section should not be
assumed to be prior art merely because of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may correspond to implementations of the claimed technology.
[0003] Differential bevel gears are components that are used in almost all
automotive applications and are required as soon as a vehicle axle is driven. When driving around corners, an outer wheel of a vehicle has to cover a bigger distance than an inner wheel, which also means that the outer wheel has to turn faster than the inner wheel. The differential assembly is used to achieve the required difference in speed of the outer wheel and the inner wheel.
[0004] In a conventional differential assembly, a driving torque of a transmission
shaft is symmetrically divided into two output torques of equal magnitude. This is realized by using a bevel-gear pair. A drive axle differential assembly is the version which is used in most of the vehicles. In the drive axle differential assemblies, a torque converter is additionally integrated to adjust torque bias between the output shafts. The transmission shaft and the output shafts are perpendicular to each other. The bridging of an axle angle and torque conversion are taken over by a spiral or hypoid-toothed bevel-gear pair which

typically consists of a drive-shaft pinion and a differential ring gear connected to the differential assembly.
[0005] Gear sets including bevel gears are typically used to transmit engine torque
to wheels of a vehicle, and are used to provide differential action to output shafts, i.e., axle shafts, of the vehicle. In the existing technology of differential assemblies, torque bias requirement is achieved through expensive attachments, such as Limited Slip Differentials (LSDs).
[0006] A conventional LSD includes a clutch pack arrangement for introducing
frictional bias in gear arrangements of the differential assembly. In such gear arrangements, a gear rolling contact surface of the bevel gear follows the involute gearing principle with the same tooth profile across all gear teeth. However, such attachments increase cost and complexity of the overall differential assembly.
[0007] To address the above constraints, a gear set for a differential assembly is
developed which can substantially increase the active torque bias between the output shafts of the vehicle, by efficiently utilizing available surface for rolling contact of the gears at any instance, and providing torque biasing effect by means of variation in gear geometry. The gear set of the invention prevents the requirement of complex and expensive attachments for introducing torque bias between the output shafts of the vehicle.
OBJECTS OF THE INVENTION
[0008] An object of the present invention is to provide a gear set for a differential
assembly for increasing active torque bias between output shafts of a vehicle.
[0009] Another object of the present invention is to provide a gear set for a
differential assembly that utilizes available surface for rolling contact of a gear at any instance, and provides torque biasing effect by means of variation in gear geometry.
[00010] Another object of the present invention is to provide a gear set for a
differential assembly for preventing the requirement of complex and expensive attachments for introducing torque bias between the output shafts of the vehicle.

SUMMARY OF THE INVENTION
[00011] In order to achieve the above-mentioned objects, according to an aspect of
the present invention, a gear set for a differential assembly is disclosed. According to an aspect of the present invention, the gear set includes a pair of side gears rotatably mounted in a housing of the differential assembly, and at least one pinion rotatably mounted in the housing, the at least one pinion being present in a meshing engagement with the pair of side gears.
[00012] Each side gear of the pair of side gears has a plurality of gear teeth, each
gear tooth having a gear tooth form selected from a plurality of tooth forms. The at least one pinion has a plurality of pinion teeth, each pinion tooth having a pinion tooth form corresponding to the gear tooth form of the gear teeth present in a meshing engagement thereto. Change in the gear tooth form is configured to cause a linear translation of plane of action defining contact points between the gear tooth and the pinion tooth, and generate a pre-defined amount of torque bias between the pair of side gears.
[00013] According to an embodiment of the present invention, each side gear of
the pair of side gears is a bevel gear.
[00014] According to an embodiment of the present invention, the at least one
pinion is a bevel gear.
[00015] According to an embodiment of the present invention, each tooth form of
the plurality of tooth forms has a pre-defined design parameter, and wherein change in the gear tooth form corresponds to change in the pre-defined design parameter.
[00016] According to an embodiment of the present invention, the pre-defined
design parameter corresponds to change in contact location, change in pressure angle, and addendum modification.
[00017] According to an embodiment of the present invention, number of the
plurality of tooth forms range from 2 to 5.

[00018] According to an embodiment of the present invention, number of the gear
teeth of each side gear of the pair of side gears and number of the pinion teeth of the at least one pinion are present as a multiple of the number of the plurality of tooth forms.
[00019] According to an embodiment of the present invention, the number of the
gear teeth of each side gear of the pair of side gears is an even number.
[00020] According to an embodiment of the present invention, the number of the
pinion teeth of the at least one pinion is more than or equal to 6.
[00021] According to an embodiment of the present invention, each side gear of
the pair of side gears is coupled with an axle shaft of a vehicle, and the at least one pinion is coupled with a transmission shaft of the vehicle.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[00022] Fig. 1A illustrates an exemplary representation of sequence of tooth form
in a side gear of a gear set, in accordance with an embodiment of the present invention.
[00023] Fig. IB illustrates an exemplary representation of sequence of tooth form
in a pinon of the gear set, in accordance with an embodiment of the present invention.
[00024] Figs. 2A to 2C illustrate exemplary representations of location of contact
patterns for different tooth forms in the pinion, in accordance with an embodiment of the present invention.
[00025] Fig. 3 illustrates an exemplary cross-sectional view of the side gears in
meshing engagement with the pinion, where a left side gear and a right side gear mesh with the pinion with different tooth forms, respectively, in accordance with an embodiment of the present invention.
[00026] Fig. 4A illustrates an exemplary representation of the left side gear in
meshing engagement with the pinion of the gear set, in accordance with an embodiment of the present invention.

[00027] Fig. 4B illustrates an exemplary representation of the right side gear in
meshing engagement with the pinion of the gear set, in accordance with an embodiment of the present invention.
[00028] Fig. 5 illustrates an exemplary graphical representation of torque bias
generated between the left side gear and the right side gear of the gear set, in accordance to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[00029] The detailed description set forth below in connection with the appended
drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. Each embodiment described in this disclosure is provided merely as an example or illustration of the present invention, and should not necessarily be construed as preferred or advantageous over other embodiments. The detailed description includes pre-defined details for the purpose of providing a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these pre-defined details.
[00030] It must also be noted that as used herein and in the appended claims, the
singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Although any systems and methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the preferred, arrangements and methods are now described.
[00031] Exemplary embodiments will now be described more fully hereinafter
with reference to the accompanying drawings, in which exemplary embodiments are shown. This disclosure may however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those of ordinary skill in the art. Moreover, all statements herein reciting embodiments of the disclosure, as well as pre-defined examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it

is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure).
[00032] The present invention relates to a gear set for a differential assembly for
generating active torque bias between at least two output shafts of a vehicle, to allow the output shafts to rotate at different speeds, while utilizing available surface for rolling contact of a gear at any instance, and providing torque biasing effect by means of variation in gear geometry. The gear set of the invention also prevents the requirement of complex and expensive attachments for introducing torque bias between the output shafts of the vehicle.
[00033] Figs. 1A and IB illustrate exemplary representations of sequence of tooth
form in a side gear (102) and a pinion (104) of a gear set, respectively. The gear set includes a pair of side gears (102-1 and 102-2) rotatably mounted in a housing of a differential assembly, and at least one pinion (104) rotatably mounted in the housing. The at least one pinion (104) is present in a meshing engagement with the pair of side gears (102). The gear set is used in the differential assembly to generate a pre-defined amount of torque bias between two output shafts coupled with the side gears (102) by splitting a torque received from a transmission shaft coupled with the at least one pinion (104).
[00034] The side gears (102) and the at least one pinion (104) may be selected from
any of straight bevel gears, spiral bevel gears, and zerol bevel gears, depending upon design requirements of the gear set. The side gears (102) or the at least one pinion (104) may be manufactured through forming process.
[00035] Each side gear (102) has a plurality of gear teeth (106), each gear tooth
(106) having a gear tooth form selected from a plurality of gear tooth forms (108-1, 108-2, 108-3, ... 108-N). The number of the gear tooth forms (108-1, 108-2, 108-3, ... 108-N) of the gear teeth (106) may be unique tooth form of 2, 3, 4, 5, etc., depending upon application and design requirements of the side gears (102). The number of the gear teeth (106) of each side gear (102) may be an even number. As shown in Fig. 1A, sequence of the gear tooth forms of the side gear (102) is selected as (108-3), (108-2), (108-1), (108-1), (108-2), and (108-3), where (108-1) represents a first gear tooth form, (108-2)

represents a second gear tooth form, and (108-3) represents a third gear tooth form of the side gear (102). This sequence of the gear tooth forms may be repetitive in nature within the side gear (102).
[00036] As shown in Fig. IB, the pinion (104) also has a plurality of pinion teeth
(110), each pinion tooth (110) having a pinion tooth form selected from a plurality of pinion tooth forms (112-1, 112-2, 112-3, ... 112-N). The number of the pinion teeth (110) of the pinion (104) may more than or equal to 6, due to manufacturing constraints. The pinion tooth forms (112-1, 112-2, 112-3, ... 112-N) of a pinion tooth (110) corresponds to the gear tooth form (108-1, 108-2, 108-3, ... 108-N) of the gear teeth (106) present in meshing engagement thereto, to ensure proper engagement of the pinion teeth (110) with the gear teeth (106) of the side gears (102). The sequence of the pinion tooth forms of the pinion (104), is selected as (112-3), (112-2), (112-1), (112-1), (112-2), and (112-3), where (112-1) represents a first pinion tooth form, (112-2) represents a second pinion tooth form, and (112-3) represents a third pinion tooth form of the pinion (104). This sequence of the pinion tooth forms may be repetitive in nature within the pinion (104).
[00037] In an implementation, if the number of tooth forms is selected as 3, then
the number of pinion teeth (110) of the pinion (104) would be a multiple of 3, i.e., 9, 12, etc. and the number of gear teeth (106) of the side gears (102) would be a multiple of 3 and more than the number of pinion teeth (110) and an even number, i.e.,12, 18, etc. In the embodiment shown in Figs. 1A and IB, the number of pinion teeth (110) of the pinion (104) and the number of gear teeth (106) of the side gear (102) are selected as 9 and 12, respectively.
[00038] According to an embodiment of the present invention, change in the gear
tooth form (108-1, 108-2, 108-3, ... 108-N) causes a linear translation of plane of action defining contact points between the gear tooth (106) and the pinion tooth (110), and generates the pre-defined amount of torque bias between the side gears (102).
[00039] Each tooth form of the plurality of gear tooth forms (108-1, 108-2, 108-3,
... 108-N) may have a pre-defined design parameter corresponding to any of change in contact location, change in pressure angle, and addendum modification, such that change

or modification of the pre-defined design parameter of the gear tooth form results in variation of the amount of torque bias between the side gears (102).
[00040] The number of the gear teeth (106) of each side gear (102) and number of
the pinion teeth (110) of the pinion (104) may be selected as a multiple of the number of the gear tooth forms (108-1, 108-2, 108-3, ... 108-N).
[00041] Fig. 2A illustrates a contact pattern for the pinion tooth form (112-1). Here,
Rl represent a centre of contact pattern location from apex of the pinion (104). Fig. 2B illustrates a contact pattern for the pinion tooth form (112-2). Here, R2 represent the centre of contact pattern location from apex of the pinion (104). Fig. 2C illustrates a contact pattern for the pinion tooth form (112-3). Here, R3 represent the centre of contact pattern location from apex of the pinion (104).
[00042] The pre-defined amount of torque bias between the side gears (102-1, 102-
2) may be achieved by change in contact position between contact points of teeth of the left side gear (102-1) and the pinion (104), and teeth of the right side gear (102-2) and the pinion (104) of the gear set. The pre-defined amount of torque bias due to change in contact position may be achieved by simultaneous contact of two different gear tooth forms at the left and right side gears (102-1, 102-2) and the pinion (104). The contact position is defined by considering available face width and the unique tooth form selected thereof. For instance, if the available face width of the side gear (102-1) is 24 mm and the selected tooth form corresponds to the third gear tooth form (108-3), then every contact width will be of 8 mm. In this case, the centre of the contact is considered for further calculation. The contact position may be defined at any location on the face width of the side gears (102) and the pinon (104), and not necessarily be at equidistant positions.
[00043] Each of the pinion tooth form (112-1, 112-2, 112-3,... 112-N) of the pinion
teeth (110) corresponds to respective gear tooth form (108-1, 108-2, 108-3, ... 108-N) of the gear teeth (106) present in meshing engagement thereto, to ensure proper engagement of the pinion teeth (110) with the gear teeth (106), and prevent interference and slip thereof.

[00044] Fig. 3 illustrates a cross-sectional view of the left side gear (102-1), the
pinion (104), and the right side gear (102-2) in assembled condition while the gear tooth form (108-1) on left side and the gear tooth form (108-3) on right side are present in contact. The contact location of the left side gear (102-2) is present at a distance Rl from apex of the gear set, and simultaneously the contact location of the right side gear (102-2) is present at a distance R3 from the apex. Such a configuration leads to generation of the pre-defined amount of torque bias between output shafts coupled with the left side gear (102-1) and the right side gear (102-2).
[00045] In the above gear set configuration, maximum mechanical leverage
achieved due to rolling contact point may be determined as below.
[00046] Considering Rl is 38 mm and R3 is 52 mm, bias ratio may be determined
as:
R3/Rl = 52/38= 1.37
[00047] In addition, the pre-defined amount of torque bias between the left side
gear (102-1) and the right side gear (102-2) may be achieved with change in pressure angle. The pre-defined amount of torque bias due to change in pressure angle may be achieved by varying the pressure angle of different tooth forms selected simultaneously at the left side gear (102-1) and the right side gear (102-2), as illustrated below in Table 1:

Tooth forms Contact location (R) Pressure Angle (P)
First Gear Tooth Form (108-1) 38 (Rl) 28° (PI)
Second Gear Tooth Form (108-2) 45 (R2) 30°(P2)

Third Gear Tooth Form (108-3) 52 (R3) 32°(P3)
Table 1
[00048] In the above gear set configuration, torque bias due to change in pressure
angle may be determined as follows.
[00049] Considering pressure angle (PI) corresponding to the first gear tooth form
(108-1) is 28° and pressure angle (P3) corresponding to the third gear tooth form (108-3) is 32°, torque bias ratio may be determined as:
Tan (P3) / Tan (PI) (i.e., ratio of tangent of pressure angle)
= Tan (32°) / Tan (28°) = 1.16
[00050] The pre-defined amount of torque bias may also be obtained with
modification of addendum of the side gears (102) and the pinion (104). Change in the addendum modification of different gear tooth form (108-1, 108-2, 108-3) may be performed in order to achieve zero backlash, or of both side of the teeth (106) in contact, to result in double multiplication of frictional bias. In an implementation, to perform the addendum modification for achieving zero backlash or both side contact, the torque bias ratio may be determined as a multiple of the frictional bias. For instance, the torque bias ratio may be determined to be twice the frictional bias.
[00051] The total torque bias be may also achieved by combining bias due to
mechanical leverage, change in pressure angle and modification in addendum of the side gears (102-1, 102-2) and the pinion (104). Maximum bias may be determined as:
Mechanical leverage + Frictional bias + bias due to addendum modification > 3
[00052] Fig. 4 A illustrates a contact sequence of the output shaft coupled with the
left side gear (102-1), where the left side gear (102-1) is in meshing engagement with the pinion (104) of the gear set. Fig. 4B illustrates a contact sequence of the output shaft coupled with the right side gear (102-2), where the right side gear (102-2) is in meshing engagement with the pinion (104) of the gear set. Contact sequence and subsequent torque

bias is in such a manner that when the first gear tooth form (108-1) of the left side gear (102-1) is in contact with the first pinion tooth form (112-1) of the pinion (104), the third gear tooth form (108-3) of the right side gear (102-2) is in contact with the third pinion tooth form (112-3) of the pinion (104). This generated a maximum positive torque bias, i.e., the output shaft coupled with the right side gear (102-2) has more torque than the output shaft coupled with the left side gear (102-1). Additionally, when the second gear tooth form (108-2) of the left side gear (102-1) is in contact with the second pinion tooth form (112-2) of the pinion (104), both output shafts have same contact pair that will lead to no torque bias therebetween.
[00053] In an implementation, if the third gear tooth form (108-3) of the left side
gear (102-1) is in contact with the third pinion tooth form (112-3) of the pinion (104), the first gear tooth form (108-1) of the right side gear (102-2) is in contact with the first pinion tooth form (112-1) of the pinion (104). This configuration generates maximum negative torque bias, i.e., the output shaft coupled with the left side gear (102-1) has more torque than the output shaft coupled with the right side gear (102-2). The sequences of meshing engagement of tooth forms (108, 112) of the side gears (102) and the pinion (104) are mentioned in Table 2 provided below.

Meshing engagement of tooth forms (108, 112)
Left side gear 1 2 3 1 2 3
(102-1) meshing
with pinion (104)
Right side gear 3 2 1 3 2 1
(102-2) meshing
with pinion (104)
Table 2
[00054] Fig. 5 illustrates a torque bias chart showing torque bias generated between
the left side gear (102-1) and the right side gear (102-2) of the gear set, in accordance with an embodiment of the present invention. Torque output of the left side gear (102-1)

and the right side gear (102-2) at different contact sequences is shown in Fig. 5. If input torque of the pinion (104), provided by transmission shaft of the vehicle, is denoted as 2X (X being an integer and X > 0), ideal output torque of the left side gear (102-1) and the right side gear (102-2) are equal. In such scenario, when the first tooth form (108-1, 112-1) and the third tooth form (108-3, 112-3) are in contact at meshing engagement of the left side gear (102-1) and the right side gear (102-2), respectively, the output torque of the right side gear (102-2) is more than 1.5X and the output torque of the left side gear (102-1) is less than 0.5X. Therefore, pre-defined amount of torque bias of more than 3 is achieved.
[00055] When the second tooth form (108-2, 112-2) is in contact at meshing
engagement of both the left side gear (102-1) and the right side gear (102-2), there is no torque bias between the left side gear (102-1) and the right side gear (102-2).
[00056] In another implementation, when the third tooth form (108-3, 112-3) and
the first tooth form (108-1, 112-1) are in contact at meshing engagement of the left side gear (102-1) and the right side gear (102-2), respectively, the output torque of the left side gear (102-1) is more than 1.5X and the output torque of the right side gear (102-2) is less than 0.5X. Therefore, pre-defined amount of torque bias of more than 3 in the opposite direction is achieved.
[00057] Thus, the present invention provides an active torque bias gear set for a
differential assembly, for generating active torque bias between two output shafts, by utilizing available surface for rolling contact of gears at any instance, and providing torque biasing effect by means of variation in gear geometry. The gear set employs bevel gears selected from any of straight bevel gears, spiral bevel gears, and zerol bevel gears, depending upon design requirements of the gear set. The gear set of the present invention offers higher technical ascendance and economic significance, compared to the existing technology, while preventing the requirement of complex and expensive attachments for introducing torque bias between the output shafts.
[00058] In view of the present disclosure which describes the present invention, all
changes, modifications and variations within the meaning and range of equivalency are considered within the scope and spirit of the invention. It is to be understood that the

aspects and embodiment of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiment may be combined together to form a further embodiment of the disclosure.

We Claim:

1. A gear set for a differential assembly, comprising:
a pair of side gears (102-1, 102-2) rotatably mounted in a housing of the differential assembly; and
at least one pinion (104) rotatably mounted in the housing, the at least one pinion being present in a meshing engagement with the pair of side gears (102-1, 102-2),
wherein each side gear of the pair of side gears (102-1, 102-2) has a plurality of gear teeth (106), each gear tooth (106) having a gear tooth form selected from a plurality of tooth forms (108-1, 108-2, 108-3, ... 108-N), and
the at least one pinion (104) has a plurality of pinion teeth (110), each pinion tooth (110) having a pinion tooth form (112-1, 112-2, 112-3, ... 112-N) corresponding to the gear tooth form (108-1, 108-2, 108-3, ... 108-N) of the gear teeth (106) present in a meshing engagement thereto,
and wherein change in the gear tooth form (108-1, 108-2, 108-3, ... 108-N) is configured to cause a linear translation of plane of action defining contact points between the gear tooth (106) and the pinion tooth (110), and generate a pre-defined amount of torque bias between the pair of side gears (102-1, 102-2).
2. The gear set as claimed in claim 1, wherein each side gear of the pair of side gears (102-1, 102-2) is a bevel gear.
3. The gear set as claimed in claim 1, wherein the at least one pinion (104) is a bevel gear.
4. The gear set as claimed in claim 1, wherein each tooth form of the plurality of tooth forms (108-1, 108-2, 108-3, ... 108-N) has a pre-defined design parameter, and wherein change in the gear tooth form corresponds to change in the pre-defined design parameter.
5. The gear set as claimed in claim 4, wherein the pre-defined design parameter corresponds to change in contact location, change in pressure angle, and addendum modification.

6. The gear set as claimed in claim 1, wherein number of the plurality of tooth forms (108-1, 108-2, 108-3, ... 108-N)rangefrom2to5.
7. The gear set as claimed in claim 6, wherein number of the gear teeth (106) of each side gear of the pair of side gears (102-1, 102-2) and number of the pinion teeth (110) of the at least one pinion (104) are present as a multiple of the number of the plurality of tooth forms (108-1, 108-2, 108-3, ... 108-N).
8. The gear set as claimed in claim 7, wherein the number of the gear teeth (106) of each side gear of the pair of side gears (102-1, 102-2) is an even number.
9. The gear set as claimed in claim 8, wherein the number of the pinion teeth (110) of the at least one pinion (104) is more than or equal to 6.
10. The gear set as claimed in claim 1, wherein each side gear of the pair of side gears (102-1, 102-2) is coupled with an axle shaft of a vehicle, and the at least one pinion (104) is coupled with a transmission shaft of the vehicle.