Title: Final drive assembly with differential lock
Abstract: Axle-drive unit for a motor vehicle which contains a first and a second differential (18, 19) in a driven housing (22), the two differentials (18, 19) being spur-gear-type planetary gears with parallel axes, the sun wheels (32, 43) of which are in each case connected in terms of drive to the half axles (8, 9) of the first driven axle, and planet wheels (36, 38) of the two differentials (18, 19) meshing with their common ring gear (35). The housing (22) has a machined inner surface (50) which surrounds the ring gear (35) with little clearance, the ring gear is so thin in the radial direction that it is deformed in a lobe-like manner by the radial component of the tooth forces exerted by the planet wheels (31, 36). The outer circumferential surface (60) of the ring gear is placed against the inner surface (50) of the housing (22) in a manner producing friction at least locally.
Patent Number: 6,935,983 Issued on 08/30/2005 to Pecnik
| Inventors:
|
Pecnik; Hermann (Nestelbach, AT)
|
| Assignee:
|
Magna Steyr Fahrzeugtechnik AG&Co KG (Graz, AT)
|
| Appl. No.:
|
398358 |
| Filed:
|
October 4, 2001 |
| PCT Filed:
|
October 4, 2001
|
| PCT NO:
|
PCT/AT01/00317
|
| 371 Date:
|
September 22, 2003
|
| 102(e) Date:
|
September 22, 2003
|
| PCT PUB.NO.:
|
WO02/28678 |
| PCT PUB. Date:
|
April 11, 2002 |
Foreign Application Priority Data
| Oct 04, 2000[AT] | GM733/2000 |
| Current U.S. Class: |
475/249; 475/205 |
| Intern'l Class: |
F16H 048/20 |
| Field of Search: |
475/200,204,205,249
|
References Cited [Referenced By]
U.S. Patent Documents
| 2837936 | Jun., 1958 | Fackler, Jr.
| |
| 3494226 | Feb., 1970 | Biddle.
| |
| 3528323 | Sep., 1970 | Kamlukin.
| |
| 5194058 | Mar., 1993 | Amborn et al.
| |
| Foreign Patent Documents |
| 02-248743 | Oct., 1990 | JP.
| |
Primary Examiner: Ho; Ha
Attorney, Agent or Firm: Bachman & LaPointe, P.C.
Claims
1. An axle-drive unit for a motor vehicle having a first and a second driven
axle which comprises a first and a second differential (
18,
19) in
a housing driven by an engine/transmission block (
1), the first differential
(
18) dividing the torque fed to it between a first half axle (
9)
of the first driven axle (
8,
9) and the second differential (
19),
and the second differential (
19) furthermore dividing the torque fed to
it between a second half axle (
8) of the first driven axle (
8,
9)
and a power take-off (
7) for the second driven axle (
16,
17),
the two differentials (
18,
19) being spur-gear planetary gears with
parallel axes, the sun wheels (
32,
43) of which are in each case
connected in terms of drive to the half axles (
8,
9) of the first
driven axle, and planet wheels (
36,
38) of the two differentials
(
18,
19) meshing with their common ring gear (
35), a first
planet carrier (
23) being connected in a rotationally fixed manner to the
housing and a second planet carrier (
40) being connected in terms of drive
to the power take-off (
7) for the second driven axle, wherein
a) the housing (
22) has a machined inner surface (
50) which surrounds
the ring gear (
35) with a clearance (
63),
b) the ring gear (
35) is so thin in the radial direction that it is deformed
in a lobe-like manner (
35*) by a radial component (F
R) of tooth
forces exerted by the planet wheels (
31,
36),
c) the ring gear outer circumferential surface (
60) thereby being placed
against the inner surface (
50) of the housing (
22) in a manner producing
friction at least locally, and a braking moment thereby acting on the ring gear
(
35).
2. The axle-drive unit as claimed in claim 1, wherein the housing is a driven
housing (
22) which is divided in a radial plane into two housing parts (
23,
24), wherein that part of the housing (
24) which forms the inner
surface (
50) rises above the radial plane of separation and has an undercut
(
54) between this part and a radial surface (
51).
3. The axle-drive unit as claimed in claim 2, wherein the housing part (
24)
with the inner surface (
50) has radial cooling ribs (
62) on its outside.
4. The axle-drive unit as claimed in claim 1, wherein the circumferential surface
(
60) of the ring gear (
35) has machined, raised zones (
61)
of limited axial width.
Description
BACKGROUND OF THE INVENTION
The invention involves an axle-drive unit for motor vehicles having a first and
a second driven axle which contains a first and a second differential in a housing
driven by an engine/transmission block, the first differential dividing the torque
fed to it between a first half axle of the first driven axle and the second differential,
and the latter furthermore dividing the torque fed to it between a second half
axle of the first driven axle and a power take-off for the second driven axle,
the two differentials being spur-gear-type planetary gears with parallel axes,
the sun wheels of which are in each case connected in terms of drive to the half
axles of the first driven axle, and planet wheels of the two differentials meshing
with their common ring gear, the one planet carrier being connected in a rotationally
fixed manner to the housing and the other planet carrier being connected in terms
of drive to the power take-off for the second driven axle.
An axle-drive unit of this type is disclosed in AT 405 923 B. In the latter,
owing
to the particular design and arrangement of the two differentials, optimum adaptation
of the moment distribution ratio is achieved with a minimum outlay on construction.
Provided between the driven housing, which contains the two differentials, and
the power take-off for the second driven axle is a fluid friction clutch as a longitudinal
differential lock. The latter is not only extremely bulky, it also has the disadvantage
of acting only as a lock for the differential between the two axles. Locking of
the other differential, the differential between the two wheels of the first driven
axle, is not possible.
It is thus the object of the invention to achieve an at least limited locking
both of the axle differential and of the longitudinal differential with a minimum
outlay on construction.
According to the invention, this is achieved in that
a) the housing has a machined inner surface which surrounds the ring gear with
little clearance,
b) the ring gear is so thin in the radial direction that it is deformed in a
lobe-like
manner by the radial component of the tooth forces exerted by the planet wheels,
c) its outer circumferential surface thereby being placed against the inner surface
of the housing in a manner producing friction at least locally, as a result of
which a braking moment acts on the ring gear.
Locking thereby takes place without additional components between the housing
and ring gear. Moreover: the lock acts both on the axle differential of the first
driven axle and on the interaxle differential between the two driven axles. The
locking behavior also complies with the requirements: the action occurs only at
high torques, i.e. when it is actually required, but not in towing mode or during
gentle cornering. Since the tooth forces between the planet wheels and ring gear
are approximately identical in both differentials, the bending stresses over the
axial length of the ring gear are also approximately the same. In addition, in
the locked state, the housing exerts a supporting action on the ring gear limiting
the local expansion, which prevents excessive deformation of the ring gear and
tooth fractures. This is all of benefit to the service life of the ring gear.
In a preferred embodiment, the driven housing is divided in a radial plane, that
part of the housing which forms the inner surface rises above the radial plane
of separation and an undercut is provided between this part and the radial surface.
This undercut is used for decoupling screwing stresses caused by the bolts acting
on the outside of the housing parts and thermal stresses caused by heating of the
inner surface in the locking mode. That part of the housing which forms the inner
surface thereby remains dimensionally accurate. A further contribution to this
resides in the housing part with the inner surface having radial cooling ribs on
its outside. This enlarges the area for the transfer of heat to the oil or to the
surrounding transmission atmosphere.
There is great design freedom for the design of the frictional surfaces-both
of the inner surface of the housing and of the outer circumferential surface of
the ring gear. Machined, raised zones of limited axial width have proven advantageous.
The reduction in the contact area may result in a reduction in the required contact
pressure for a certain braking action and makes it easier to keep to the functionally
desired, exacting tolerances.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described and explained below with reference to figures
of an exemplary embodiment, in which:
FIG. 1 shows a diagrammatic view of the entire axle-drive unit,
FIG. 2 shows an axial section through the double differential,
FIG. 3 shows a radial section according to III-III in FIG. 2.
DETAILED DESCRIPTION
In the all-wheel-drive motor vehicle illustrated in FIG. 1, the engine is referred
to by
1, the clutch by
2, and the manual transmission by
3.
The transmission
3 ends in a driven gearwheel
4 which meshes with
a large driving gearwheel
5. The driving gearwheel
5 is already part
of the axle-drive unit
6. The latter is adjoined by a power take-off
7
for the rear axle drive and by a right and a left half axle
8,
9
for the drive of the front wheels. Located in the interior of the power take-off
7 is a pair of bevel gears
10,
11, and the torque for the
rear axle is fed via a propeller shaft
12 to a, for example, conventional
differential transmission
13, in which the half axles
16,
17
of the rear wheels are driven in a known manner via a pair of bevel gears
14,
15. A first and a second planetary gear
18,
19 are located
in the interior of the axle-drive unit
6 and will be described in greater
detail below.
The rotating part of the axle-drive unit illustrated in FIG. 2 is, starting from
the driving gearwheel
5, a driven housing
22 which contains the two
planetary gears
18,
19. The housing
22 comprises two housing
parts
23,
24 which are jointly clamped together here to the driving
gearwheel
5 by means of threaded bolts
25. The axial position of
the joint between the two housing parts can be established in accordance with external
requirements; either the two housing parts can have the same depth or one of the
housing parts is a flat cover and the other is a deep bell.
The first housing part
23 is at the same time the planet carrier of the
first differential transmission
18 and is connected fixedly to the bell-shaped
housing part
24 by means of the threaded bolts
25. The two together
thus form a rigid part which is mounted rotatably in the housing
20,
21
by means of bearings
26,
27. This first planetary gear
18
also includes planet wheels
31 which can rotate about axes
30 and
a sun wheel
32, which is connected by means of a wedge-shaped toothing
33
to the left output shaft
34 to which the half axle
9 (FIG. 1) is connected.
A ring gear
35 surrounds the planet wheels
31 of the first planetary
gear
18 and is at the same time also the ring gear of the second planetary
gear
19. It meshes with the outer planet wheels
36 of the second
planetary gear
19, which planet wheels are mounted on spindles
37
which, for their part, are fastened in the second planet carrier
40. The
first planet wheels
36 also mesh with second planet wheels
38 which
are likewise mounted on the planet carrier
40 on spindles
39.
This second planet carrier
40 is connected via a wedge-shaped toothing
41 to a hollow shaft
42 which leads into the power take-off
7
for the rear axle (FIG.
1). The inner planet wheels
38 mesh with
a sun wheel
43 which is connected via a wedge-shaped toothing
44
to the right output shaft
45. The latter leads via the right axle-drive
shaft
8 (FIG. 1) to the right front wheel.
The power flux runs as follows: the torque received by the large driving gearwheel
5 is firstly divided in the first planetary gear
18 between the sun
wheel
32, and hence the left, front axle-drive shaft
9, on the one
hand, and the hollow gear
35, on the other hand. The latter constitutes
the connection between the first and second planetary gear. The torque fed in this
manner to the second planetary gear
19 is divided via the planet wheels
36,
38 to, on the one hand, their planet carriers
40, and
hence to the power take-off
7 for the rear wheels, and, on the other hand,
to the sun wheel
43, and hence to the right half axle
8 of the front
wheel drive.
According to the invention, the housing part
24 and the ring gear
35 are designed in a particular manner. The housing part
24 has a
machined, cylindrical inner surface
50 which is extended over most of the
axial width of the ring gear
35. It furthermore has a radial surface
51
which lies approximately in the radial plane of separation. Threaded bolts
25
are furthermore provided on the outside in flanges, for the purpose of connecting
the two housing parts. A further radial surface
52 is provided on the other
housing part
23. The inner surface
50 extends into a collar
53
rising above the radial surfaces
51,
52. An undercut
54 is
provided between said collar and the radial surface
51 and is used for the
purpose of keeping thermal stresses away from the radial surface
51 and
tensile stresses away from the inner surface
50.
FIG. 3 shows the ring gear
35 in radial section. It is dimensioned in
such a manner that it is deformed under the radial component F
R of the
tooth forces F exerted by the planet wheels
31 (four in this case) to form
a lobe-shaped element
35* having convexities
55* (in this case four),
this being illustrated by hatching and in a greatly exaggerated manner. For this
purpose, the radial thickness
56 of the ring gear is selected to be of such
a small size that the circumferential surface
60 of the ring gear
35
is deformed outward theoretically by an amount
57 at the points of engagement
of the planet wheels
31; of course, the zones, lying in between, of the
ring gear
35 are displaced inward. However, this does not occur during operation
because the outwardly displaced parts of the circumferential surface
60
are previously placed against the inner surface
50 of the driven housing.
The frictional connection brought about in this manner causes an at least partial
locking of the two differentials. For the sake of completeness, it should be added
that the planet wheels
36 of the second planetary gear
19 exert the
same action on the ring gear
35.
The frictional connection can be optimized by the design of the circumferential
surface
60 and of the inner surface
50. For this purpose, use can
be made of suitable surface treatment processes. In the exemplary embodiment shown,
again FIG. 2, the axial width which is limited by two raised zones
61 is
achieved on the circumferential surface
50 of the ring gear. In order to
improve the conduction of heat, radial cooling ribs
62 are furthermore also
provided on the housing part
24 and they also reinforce the housing.
*
