Patent Application
20200023735
The present disclosure relates to front differentials and more specifically to front differentials that include disconnect clutches.
Many vehicles include all-wheel drive to increase traction. A typical light-duty all-wheel-drive powertrain includes a transversely mounted engine and transmission. The transmission is operably coupled to a power-transfer unit that selectively sends power to rear wheels of the vehicle. The power-transfer unit include may one or more clutches configured to send power to the rear wheels when engaged and to not send power when disengaged.
According to one embodiment, a front differential for use with an all-wheel-drive vehicle includes an input member, and an output member selectively engaged to power rear wheels of the vehicle. The differential also includes first and second axle hubs operably coupled to the input member by a differential mechanism. A wedge clutch is configured to selectively couple the input and output members to route power to the rear wheels. The wedge clutch has an outer race fixed to the input member, an inner race fixed to the output member, and a wedge element radially disposed between the inner and outer races and actuatable to couple the inner and outer races creating a power flow path between the input and output members.
According to another embodiment, a differential includes an input member, first and second axle hubs supported for independent rotation relative to each other and operably coupled to the input member, and an output shaft configured to connect with a power-transfer unit. The output shaft circumscribes the second axle hub and has an outer surface defining at least one groove. A side plate of the differential is fixed to the input member and defines an axially extending ring that circumscribes the output shaft. The ring defines a first cam surface. A clutch element of the differential is radially disposed between the output shaft and the ring. The clutch element includes at least one projection received in the at least one groove and a second cam surface engaging the first cam surface.
According to yet another embodiment, a wedge clutch includes an inner race, an outer race circumscribing the inner race, and a plurality of arcuate segments arranged in pairs and circumferentially disposed around the inner race such that each pair forms a section of a wedge cylinder that includes springs disposed between the sections to bias the arcuate segments of each pair towards each other. The springs bias the arcuate segments of each pair towards each other to contract the wedge cylinder onto the inner race so that the races lock in response to relative rotation between the outer race and the wedge cylinder.
Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the embodiments. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.
This disclosure presents one or more embodiments of a front differential for use with all-wheel-drive vehicles. The front differential not only distributes torque between the front driving wheels but also includes a disconnect clutch configured to couple and decouple the rear driving wheels from a vehicle powerplant, e.g., an engine.
The differential 26 includes a third output, typically in the form of an output shaft, that is connected with an input of the power-transfer unit 28. The power-transfer unit 28 receives power from the front differential 26 and routes it to the rear wheels. In this application, the power-transfer unit 28 may be a simple gearbox as the disconnect clutch for the rear wheel is disposed within the front differential 26. A rear differential 36 is connected to the power-transfer unit 28 by a driveshaft 34. Power is delivered from the rear differential 36 to the rear wheels by rear axle shafts 38 and 40.
The vehicle 20 is propelled in a front-drive mode when the disconnect clutch of the front differential 26 is open and is propelled in an all-wheel-drive mode when the disconnect clutch is closed. Providing the disconnect clutch in the front differential as opposed to the power-transfer unit may provide a smaller package and reduces the cost and complexity of the power-transfer unit 28.
The differential 50 includes axle hubs 56 and 58 that connect with the front axle shaft. The axle hubs 56, 58 may define internal splines that engage with external splines formed on the axle shafts to connect the front axle shafts to the differential 50. The axle hubs 56 and 58 may be coaxial and are supported for rotation within the ring gear 54. Power received by the ring gear 54 is conveyed to the axle hubs 56 and 58 by a differential mechanism 60 that allows speed differences between the axle hubs 56, 58. Many types of differential mechanisms are known such as box-bevel gears, various planetary arrangements, and the like. In the illustrated embodiment, the differential 50 has a planetary differential mechanism 60.
The planetary differential mechanism 60 includes a pair of planetary systems each associated with one of the front axle shafts. The axle hub 56 is fixed to a sun gear 62. The axle hub 56 and the sun gear 62 may be integrally formed as a single piece. A first set 66 of planet gears 68 are circumferentially arranged around the sun gear 62 such that the sun gear 62 meshes with each of the planet gears 68. The first set 66 is supported by a planet carrier such as a first side plate 74 that is fixed to the ring gear 54. A second set 70 of planet gears 72 are circumferentially arranged around a sun gear 64 such that the sun gear 64 meshes with each of the planet gears 72. The second set 70 is supported by a planet carrier such as the second side plate 76. The differential mechanism 60 is shown as an open differential, however, in other embodiments the differential 50 may include a limited-slip differential mechanism or a locker.
The differential 50 includes an output member configured to supply power to another component such as a power-transfer unit. In the illustrated embodiment, the output member is an output shaft 82 supported for rotation within the housing 52. The output shaft 82 may be mounted coaxially with the axle hubs 56, 58 and may define a hollow center through which the axle hub 58 extends.
A disconnect clutch 84 of the differential 50 is configured to selectively couple the input and output members creating a rear-axle power flow path through the differential 50. The illustrated disconnect clutch 84 is known as a wedge clutch. The disconnect clutch 84 includes an outer race fixed to the input member and an inner race fixed to the output member. The inner and outer races may be a component or may be a machined surface. For example, the outer race may be a component that is fixed to the input member or may be a surface formed on a component fixed to the input member, similarly, the inner race may be a component that is fixed to the output member or maybe a surface formed on the output member. A wedge element 86 is radially disposed between the inner and outer races and is configured to selectively lock the inner and outer races when the clutch is 84 engaged.
In the illustrated embodiment, the outer race is an axially extending ring 78 of the side plate 76, and the inner race is a surface 79 machined onto the outer diameter of the output shaft 82. The wedge element 86 is radially disposed between the output shaft 82 and the ring 78. The wedge element 86 is radially expandable between a contracted position in which an inner surface of the wedge element 86 is seated on the output shaft 82 and an expanded position in which the inner surface is slightly spaced from the output shaft 82. The clutch 84 is engageable when the wedge element 86 is in the contracted position and is not engageable when in the expanded position. The clutch 84 can be engaged and disengaged by moving the wedge element 86 between the expanded and contracted positions.
The inner surface of the wedge element 86 may define a plurality of axially spaced circumferential projections 88 that are received in a plurality of axially spaced circular grooves 90 defined in the outer surface of the output shaft 82. When the clutch 84 is engaged, friction between the projections 88 and the grooves 90 rotationally lock the wedge element 86 to the output shaft 82. The wedge element 86 includes a cam surface 92 that engages and cooperates with a cam surface 94 defined on the ring 78. The cam surface 94 defines a plurality of ramps 116 configured to engage with lobes 80 of the cam surface 92 to wedge the wedge element 86 between the ring 78 and the output shaft 82 responsive to the wedge element 86 and the ring 78 rotating relative to each other. The wedging action induced by the cam surfaces 92, 94 tightly clamps the wedge element 86 to the output shaft 82 creating a friction coupling. The ramps and lobes are sized so that they cannot slide over each other and cooperate to lock the wedge element 86 to the ring 78.
Referring to
The thickness of each segment 100 varies between the first and second ends 104, 106 to create the cam surface 92. The second end 106 is thicker than the first end 104 causing the outer surface 112 to slope radially outward from the first end 104 towards the second end 106. The outer surfaces 112 of each segment 100 define a portion of the cam surface 92. The above-mentioned lobes 80 are the outer-most portion of the cam surface 92 and are generally formed by the outer surfaces 112 near the second ends 106. The inner surface 111 of each segment 100 is a smooth arc having a constant radius that substantially matches that of the outer diameter of the output shaft 82.
The cam surface 94 of the ring 78 has a profile that substantially matches the cam surface 92 of the wedge element 86. The cam surface 94 includes radially extending ramps 116 and pockets 118. The matching shapes of the of the cam surfaces 92, 94 allows the wedge element 86 to nest within the ring 78 with the lobes 80 disposed in the pockets 118.
The resilient members 108 bias the wedge element 86 to the contracted position in which each of the segments 100 are in frictional contact with the output shaft 82 creating sufficient drag to rotate the wedge element 86 relative to the ring 78 if the ring gear 54 and/or the output shaft 82 is rotated. Relative rotation between the ring 78 and the wedge element 86 misaligns the cam surfaces 92, 94, i.e., the ramps 116 slide into the lobes 80, causing further radial contraction of the wedge element 86. This further radial contraction clamps the wedge element 86 onto the output shaft 82 with sufficient friction force to rotationally lock the ring 78 to the output shaft 82, which engages the clutch 84.
Referring to
Each of the slots 140 is recessed into a corresponding one of the sections 102 with the first segment 100a defining one half of the slot and the second segment 100b defining the other half of the slot. Each slot 140 includes a first portion 142, a second portion 144 that is narrower than the first portion, and a sloped portion 146 that transitions between the first and second portions 142, 144. The fingers 134 have a shape that substantially matches the slots 140. Each of fingers 134 may include a main portion 138 and a tip 141. The main portion 138 is sized to snugly fit within the first portion 142 and the tip 141 is sized to snuggly fit within the second portion 144. The fingers 134 also include angled sides 143 that match the sloped portions 146 of the slots.
Axial movement of the clutch cage 130 towards the wedge element 86 disengages the clutch 84 by driving the angled sides 143 into the sloped portion 146 to separate the segments pairs 100a and 100b of each section 102 moving the clutch element 85 to the expanded position. The amount of separation can be tuned by adjusting the width of the fingers 134 and the slots 140. The axial force required to separate the segments pairs can be adjusted by modifying the slope of the angled sides 143 and the sloped portions 146. The clutch 84 can be re-engaged by retracting the clutch cage 130 and rotating the wedge element 86 relative to the ring 78.
Referring to
The second plate 154 may be driven by a linear actuator 160 that includes an electric motor and a gear train configured to convert rotational motion of the rotor into linear movement. A linkage 162 may connect between the second plate 154 and the linear actuator 160.
The above-described actuator arrangement is but one example embodiment and is not limiting. Any actuator arrangement capable of axial displacement may be used to drive the clutch cage. For example, a ball-ramp mechanism or a hydraulically actuated position may be used.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation.
Parts List:
The following is a list of reference numbers shown in the Figures. However, it should be understood that the use of these terms is for illustrative purposes only with respect to one embodiment. And, use of reference numbers correlating a certain term that is both illustrated in the Figures and present in the claims is not intended to limit the claims to only cover the illustrated embodiment.
vehicle 20
engine 22
transmission 24
front differential 26
power transfer unit 28
axle shafts 30, 32
driveshaft 34
rear differential 36
rear axle shafts 38, 40
front differential 50
a housing 52
input member 54
axle hubs 56, 58
differential mechanism 60
sun gears 62, 64
first planetary set 66
planet gears 68
second planetary set 70
planet gears 72
first side plate 74
second side plate 76
axially extending ring 78
lobes 80
output shaft 82
disconnect clutch 84
wedge element 86
projections 88
grooves 90
cammed surface 92
first cam surface 94
segments 100
section 102
first end 104
second end 106
springs 108
cylindrical body 110
outer surface 112
inner surface 114
ramps 116
pockets 118
clutch cage 130
outer ring 132
fingers 134
end face 136
main portion 138
slots 140
tip 141
first portion 142
angled sides 143
second portion 144
sloped portion 146
clutch-cage actuator arrangement 150
first plate 152
a second plate 154
ramp 156
ramp 158
linear actuator 160
linkage 162
