Power transfer unit

Details Power transfer unit Power transfer unit

2001-12-28

2003-09-16

Estremsky, Sherry (Department: 3681)

Planetary gear transmission systems or components

Variable speed or direction transmission combined with...

C475S210000, C475S221000, C180S251000

Reexamination Certificate

active

06620069

ABSTRACT:

BACKGROUND
1. Field of the Invention
The present invention relates to the power train of a motor vehicle. More specifically, the present invention relates to a power transfer unit in the power train for distributing power to the front and rear wheels of the vehicle.
2. Description of the Prior Art
In the past, most automobiles in the United States utilized a rear wheel drive power delivery scheme. 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.
Currently in the United States, a significant portion (if not a majority) of new automobiles are front wheel drive based vehicles. In a front wheel drive vehicle, both the engine and the transmission assembly are typically transversely oriented in the vehicle. By positioning the power plant and transmission assembly transversely in the vehicle, more direct coupling of the transmission assembly to the vehicle's transaxle and front wheels can be achieved. In doing so, a front wheel differential is 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 these 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
. Such a power transfer unit
10
couples to the transversely oriented output of the transmission assembly and 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 is coupled to the output
22
of the transmission assembly by way of a splining engagement
24
. The cylindrical extension
20
itself extends off of a first gear wheel
26
or may be a sleeve to which the gear wheel
26
mounts.
From the first gear wheel
26
, power is transferred through a second and third gear wheel, respectively
32
and
34
, each supported on bearings
36
for rotation about axes
38
and
40
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 also mounted. 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
that includes 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 axis
56
along which the parallel gear set
16
engages with one another corresponds with the axis about which the output member
50
rotates. As a result of the locating of the power transfer unit
10
relative of to the output of transmission
22
, it is clear that this axis
56
may be offset from the centerline of the vehicle. As seen in
FIG. 1
b,
the axis
28
of input into the power transfer unit
10
, is vertically or elevationally offset relative to the output axis
58
about which the output member
50
rotates. This “drop” or height decrease results from the relative positioning of the first, second and third helical gears
26
,
32
and
34
of the parallel gear set
16
. The non-parallel gear set
18
is a hypoid beveled gear set in that the axis of rotation
40
of the bevel ring gear
44
does not intersect the axis
58
of rotation of the bevel gear
46
.
While prior power transfer units work sufficiently well for-their intended purposes, their construction limits the extent to which their size can be reduced (thereby making the engine bay unavailable for other components). This also limits packaging flexibility of the units themselves. Normally front differentials in transaxles are of the bevel type and require a large amount of axial space. As the transaxle package grows axially, it interferes with having equal length halfshafts and furthermore steering, suspension, and engine mount/roll restrictor placement. Additionally, current power transfer units utilize a series of helical gears, spur gears or a chain gear to initially receive power from the transmission assembly. While not seen in
FIGS. 1A and 1B
, power may then be provided to a bevel gear set and subsequently to the rear wheel drive shaft. This scheme applies a significant amount of torque to helical (or other type) gears and also imparts significant bending forces into the drive train. The latter drawback occurs because of the distance between the bevel gear set's transverse axis and the output axis of the transmission assembly.
It is therefore an object of the present invention to overcome the above and other limitations of the prior art.
It is also an object of this invention to reduce the bending forces applied to the drive train.
A further object of this invention is to increase the available packaging space in the motor vehicle's engine bay.
Another object of this invention is to provide a power transfer unit having the front differential incorporated therein.
SUMMARY OF THE INVENTION
The present invention overcomes the limitations of the prior art by integrally packaging the primary components of a power transfer unit, a non-parallel gear set, a parallel gear set, and input and output members within a common housing. With the present invention, the non-parallel gear set is located to first receive, in conjunction with input of the power transfer unit, power being transmitted from the output of the transmission assembly.
The output of the transmission assembly is coupled to the input member and to a first bevel gear ring. The first bevel gear engages a second bevel gear, such as a hypoid pinion gear, mounted to or formed with a shaft; this shaft being oriented generally perpendicularly to the rotational axis of the hypoid ring gear.
On the opposing end of the shaft is a first gear wheel, the drive sprocket wheel, in the parallel gear set of the power transfer unit. The drive sprocket wheel transfers rotation to a second gear or sprocket wheel through a transfer chain. That second sprocket wheel is mounted on a shaft whose rotational axis is generally parallel to the rotational axis about which the drive sprocket wheel rotates. On the end of this shaft is the output member that then transfers power to the rear drive shaft of the vehicle.
As mentioned above, the power transfer unit of the present invention may, in a second embodiment, include a front wheel differential. Input into the front differential is through a ring gear coupled to rotate with the first bevel gear of the non-parallel gear set. Planet gears engage the ring gear and are supported by a carrier that in turn forms or is connected to one output of the front differential. The planet gears also engage a sun gear. The sun gear is mounted to the other differential output, one output being coupled to the left front wheel half-shaft with the other output being coupled to the right front wheel half-shaft. During normal straight line driving, these gears do not turn relative to each other. Rather, the entire planetary assembly rotates. During turning of the vehicle, these gears will rotate relative to one another. By incorporating a planetary style differential with the present invention, additional packaging space becomes available in order to provide adequate space for the helical gear set without adding to the overall transaxle space requirements.
By locating the non-parallel gear set so as to receive power from

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