Power train assembly

Details Power train assembly Power train assembly

2002-04-03

2004-04-27

Wright, Dirk (Department: 3681)

Machine element or mechanism

Gearing

Plural power paths to and/or from gearing

C074S6650GE, C180S233000

Reexamination Certificate

active

06725744

ABSTRACT:

BACKGROUND
1. Field of the Invention
The present invention generally relates to motor vehicle power train assemblies. More specifically, the present invention relates to a power train assembly having a power transfer unit located prior to a final drive unit.
2. Description of the Prior Art
Historically, automobiles in the United States have primarily utilized a rear wheel drive power delivery schemes. In adapting these rear wheel drive schemes into four wheel drive applications, a transfer case was, and often still is, positioned at the output of the transmission assembly. When engaged, the transfer case diverts a portion of the power coming from the transmission assembly from the rear wheels to the front wheels.
Today, a significant portion of new automobiles in the United States, and perhaps the world, are front wheel drive based vehicles. In a typical front wheel drive vehicle, typically both the engine and the transmission assembly are transversely oriented relative to the vehicle. By positioning the engine and transmission assembly transversely in the vehicle, a more direct coupling of the transmission assembly to the vehicle's transaxle and front wheels is achieved. In doing so, the final drive unit (where the last torque multiplication takes place) and the front wheel differential are often incorporated directly into the transmission assembly itself.
With front wheel drive vehicles themselves becoming a mature market, a recent trend in the automobile industry has been to adapt front wheel drive schemes for all or four wheel drive applications. This is accomplished by providing a power transfer unit that diverts a portion of the power from the front wheels to a rear wheel drive shaft and, subsequently, the rear wheels.
Seen in
FIGS. 1
a
and
1
b
is a typical prior art power transfer unit
10
. The power transfer unit
10
includes a housing
12
within which is located a gear set
14
comprised of a parallel gear set
16
and a non-parallel gear set
18
. The parallel gear set
16
includes a cylindrical extension
20
that operates as its input and this input
20
is coupled to the transversely oriented output
22
of the transmission assembly by way of a splined engagement
24
. The cylindrical extension
20
itself is an extension off of a gear wheel
26
or may be a sleeve to which the gear wheel
26
mounts. From the gear wheel
26
, power is transferred through a second and third gear wheel, respectively
32
and
34
. These gear wheels
32
and
34
are each supported on bearings
36
for rotation about axes
38
and
40
that are parallel to the rotational axis
28
of the first gear wheel
26
.
The non-parallel gear set
18
includes a bevel ring gear
44
that is mounted to a shaft or sleeve
42
onto which the third wheel gear
34
is mounted or formed therewith. The bevel ring gear
44
engages a bevel gear
46
mounted to another shaft
48
whose axis is generally perpendicular (and therefore non-parallel) to that of shaft
42
. Mounted to an opposing end of the shaft
48
is an output member
50
, illustrated as including a flange
52
and appropriately located bolt openings
54
. The latter features enable the output member
50
to be bolted to a rear drive shaft (not shown).
As seen in
FIG. 1
a
, the line
56
along which the gear wheels
26
,
32
and
34
of the parallel gear set
16
engage with one another generally corresponds with the axis about which the output member
50
rotates. When locating of the power transfer unit
10
relative to the output of the transmission
22
, it is clear that this line
56
may be offset from the centerline of the vehicle. Additionally and as seen in
FIG. 1
b
, the axis
28
of input into the power transfer unit
10
, is offset, vertically or elevationally in the vehicle, relative to the output axis
58
about which the output member
50
rotates. This “drop” or height decrease from the transmission assembly output
22
to the output member
50
results from the relative positioning of the first, second and third helical gears
26
,
32
and
34
of the parallel gear set
16
, in conjunction with the non-parallel gear set
18
. The non-parallel gear set
18
is a hypoid beveled gear set where the axis of rotation
40
of the bevel ring gear
44
does not intersect the axis
58
of rotation of the bevel gear
46
.
Located within the transmission assembly, and before the output
22
thereof, is a final drive unit (illustrated schematically as box
57
). The final drive unit
57
performs the last torque multiplication in the power train and is configured in any one of a number of conventional constructions well known in the art. One such construction is a planetary gear set with the input to the final drive unit being through a sun gear while the output of the final drive assembly is through a ring gear. The ring gear may be directly coupled to the transmission output
22
and therefore a large amount of torque is delivered to the power transfer unit.
Since the power transfer unit receives power after the final drive assembly
57
, the components of the power transfer unit
10
must be robust enough for high torque loads to pass there through. This adds weight and expense to the power transfer unit.
In view of the above and other limitations on the prior art, it is an object of the present invention to provide a drive train construction that permits a decrease in the weight of the system. In doing so, the present invention provides a power transfer unit located in the power train assembly prior to torque multiplication by the first drive unit.
SUMMARY OF THE INVENTION
The present invention overcomes the limitations of the prior art by packaging the power transfer unit such that it receives power from the transmission assembly before torque multiplication by the final drive unit. The present invention may therefore be seen as a power transfer unit that includes a parallel gear set that receives its input from an intermediate output of the transmission assembly. The power transfer unit includes a parallel gear set, more specifically a drive sprocket wheel that transfers rotation to an output sprocket wheel through either an intermediate transfer wheel, a transfer chain or belt. The output sprocket wheel is mounted axis is generally parallel to the axis about which the drive sprocket wheel rotates the output axis of the transmission assembly. That shaft then transfers power to a non-parallel gear set.
In the non-parallel gear set, a hypoid bevel gear is mounted to or coaxial with the same shaft as the output sprocket wheel so as to rotate therewith. The hypoid bevel gear engages a hypoid pinion gear mounted to a second shaft, this second shaft being oriented generally perpendicularly to the first shaft. On the distal end of the second shaft is the output member of the power transfer unit. This output member couples the power transfer unit to the rear drive shaft of the vehicle.
In another aspect, the present invention uses a power transfer unit, coupled to an output of the transmission assembly before the final drive unit, with a non-parallel gear set being coupled to the output of the transmission assembly. The output of the non-parallel gears set is then used as the input into a parallel gear set, if desired or required. Subsequent to the input of the power transfer unit, the output of the transmission assembly is also provided to a final drive unit. Final torque multiplication takes place in the final drive unit, which may be a planetary gear set using its sun gear as the input. From the final drive unit, power is supplied to a front differential and thereafter to the front wheels of the vehicle.
By incorporating the power transfer unit on the front transaxle before the final drive unit, the power transfer unit is subjected to less torque and can be smaller, lighter and simpler in design.
In one aspect, the present invention is therefore seen to be a drive train having a power transfer unit adapted to connect to an intermediate output portion of a transmission assembly in a primary drive line, with the powe

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