GEAR TOOTH CROWNING ARRANGEMENT
FIELD
[0001] The present disclosure relates generally to parallel-axis gears and more
specifically, to a gear crowning arrangement.
BACKGROUND
[0002] Gear trains that require torque sharing among multiple pinions may be found in
the automotive industry such as in differentials and transmissions. Limited-slip
differentials which use parallel-axis gearing rely on gear meshing events, and the friction
thereof, to create the desired friction and torque bias. Gear alignment however is loosely
controlled by the fit and clearance involved between the housing and gears. These
misalignments, when combined with the high torque loads, can cause less than optimal
gear meshing events. Historically, the fluctuation within these meshing events can cause
undesirable noise.
SUMMARY
[0003] A parallel axis gear configuration constructed in accordance to one example of
the present disclosure can include a first gear having a first gear tooth that includes a lead
crowning across a face width thereof. The lead crowning can include (i) a first lead crown
defined from a centeriine to a transition point and (ii) a second lead crown defined from
the transition point to a first end point. The lead crowning can include a drop-off
magnitude that is greater at the second lead crown than the first lead crown.
[0004] According to additional features, the parallel axis gear configuration can further
include a second gear that is in meshed relationship with the first gear. The first and
second gears can be helical gears. The parallel axis gear configuration can further
include a parallel axis differential that houses the first and second gears. The first gear
can include a chemical vapor deposit coating thereon. The chemical vapor deposit can
be BALINIT® C Star coating.
[0005] A parallel axis gear configuration constructed in accordance to additional
features of the present disclosure can include a first gear having a first gear tooth that
includes a lead crowning across a face width thereof. The lead crowning can include (i)
a first lead crown defined from a centerline to a transition point and (ii) a second lead
crown defined from the transition point to a first end point. The first and second lead
crowns can have distinct magnitudes across the face width.
[0006] According to additional features, the second lead crown can include a drop-off
magnitude that is greater at the second lead crown than the first lead crown. In one
configuration, the first lead crown is zero. The parallel axis gear configuration can further
include a second gear that is in meshed relationship with the first gear. The first and
second gears can be helical gears. The parallel axis gear configuration can additionally
include a parallel axis differential that houses the first and second gears. The first gear
can include a chemical vapor deposit coating thereon. The chemical vapor deposit can
be BALINIT® C Star coating.
[0007] A parallel axis gear configuration constructed in accordance to additional
features of the present disclosure can include a first gear and a second gear received in
a housing in a meshed relationship. The first gear can include a first gear tooth that
includes a first gear tooth lead crowning across a face width thereof. The first gear tooth
lead crowning can include (i) a first lead crown defined from a centerline to a transition
point and (ii) a second lead crown defined from the transition point to a first end point.
The first gear tooth lead crowning includes a drop-off magnitude that is greater at the
second lead crown than the first lead crown. The second gear can have a second gear
tooth that includes a second gear tooth lead crowning across a face width thereof. The
second gear tooth lead crowning can include (i) a first lead crown defined from a
centerline to a transition point and (ii) a second lead crown defined from the transition
point to a first end point. The second gear tooth lead crowning includes a drop-off
magnitude that is greater at the second lead crown than the first lead crown. The second
lead crowns of the respective first and second gear tooth lead crowns align with each
other providing load intensities that inhibit micro-welding between the gears and the
housing.
[0008] According to other features, the parallel axis differential can house the first and
second gears. The first and second gears can both include a chemical vapor deposit
coating thereon. The chemical vapor deposit can be BALINIT® C Star coating. The first
and second gears can be helical gears. In one configuration, the first lead crown of at
least one of the first and second gear tooth lead crowning is non-zero.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The present disclosure will become more fully understood from the detailed
description and the accompanying drawings, wherein:
[0010] FIG. 1 is an exploded view of a parallel axis differential that can incorporate
pinion gears according to one example of the present disclosure;
[001 1] FIG. 2 is a perspective view of a pinion gear according to one example of prior
art;
[0012] FIG. 3 is a side view of the pinion gear of FIG. 2 ;
[0013] FIG. 4 is an exploded view of a first and second pinion gear and a first and
second side gear used in the parallel axis differential of FIG. 1;
[0014] FIG. 5 is a side view of an exemplary meshing event for corresponding pinion
gears according to one example of prior art;
[0015] FIG. 6 is a side view of a pair of meshing pinion gears having areas of scuffing
and deformation according to one example of prior art; and
[0016] FIG. 7 is a lead inspection profile of the pinion gear of FIG. 2;
[0017] FIG. 8 is a lead inspection profile of a pinion gear having lead crowning
constructed in accordance to one example of the present disclosure;
[0018] FIG. 9 is a lead inspection profile of a pinion gear having lead crowning
constructed in accordance to a second example of the present disclosure;
[0019] FIG. 10 is a lead inspection profile of a pinion gear having lead crowning
constructed in accordance to a third example of the present disclosure;
[0020] FIG. is a lead inspection profile of the pinion gear shown in FIG. 9 identifying
additional features according to the present disclosure;
[0021] FIG. 12 is a lead inspection profile of a the pinion gear of FIG. 11 and identifying
a crowning tolerance band according to one example of the present disclosure;
[0022] FIG. 3 is a load intensity distribution of a pair of mating pinion gears according
to prior art; and
[0023] FIG. 14 is a load intensity distribution of a pair of mating pinion gears
constructed in accordance to one example of the present disclosure;
DETAILED DESCRIPTION
[0024] Reference will now be made in detail to examples of the present disclosure. It
will be understood that the following examples are not intended to limit the disclosure. On
the contrary, the instant disclosure is intended to cover alternatives, modifications and
equivalents, which may be included within the spirit and scope of the disclosure. For
example, while the following discussion is directed toward crowning of meshed pinion
gears, the same principles can be applied to other meshed gears such as side gears in a
differential.
[0025] With initial reference to FIGS. 1-4, a parallel axis differential constructed in
accordance to one example of prior art is shown and generally identified at reference
numeral 10. The parallel axis differential 10 can include one or more side gears 12, a
plurality of pinion gears 14, a differential case 20, a first cover 22, a second cover 24 and
a plurality of fasteners 28. The pinion gears 14 are helical pinion gears. A gear train 30
can comprise one or more side gears 12 and a plurality of pinion gears 14. During
operation, the plurality of pinion gears 14 may engage the two side gears 12. The side
gears 12 may transmit torque from the respective pinion gears 14 to an output such as
axle shafts (not shown). Each side gear 12 may have an axis of rotation and an inner
axially aligned opening 34 through which an axle shaft may connect to the side gear 12
via a splined interconnection. Both side gears 12 may comprise heiicai teeth 36
configured to rotatably mesh with corresponding heiicai teeth 40 disposed on the pinion
gears 14.
[0026] With specific reference to FiG. 3, the pinion gear 14 can include an axial lead
42. The pinion gear 14 can include a first zone 44, a second zone 4 and a third zone
48. The second zone 46 can be centrally located on the pinion gear 14. The first and
third zones 44 and 48 can be located at opposite ends of the pinion gear 14. The pinion
gear 14 includes crowning in the lengthwise direction. The average crowning amount is
referred to as C . The average crown is defined within the second zone 46. As will
become appreciated by the discussion herein, the first zone 44 and the third zone 48 on
a pinion gear constructed according to the present disclosure will have a drop-off defined
in length and magnitude.
[0027] FIGS. 5 and 6 illustrate a pair of meshed pinion gears 14 according to prior art.
The respective teeth 40 of the meshed pinion gears 14 engage at an interface area 50.
In some examples, as illustrated in FiG. 6, the pinion gears 14 may develop scuffing 52
and/or plastic deformation 54 thereon during use.
[0028] As will become appreciated from the following discussion, the present
disclosure is directed toward a gear tooth crowning arrangement on the pinion gears 40.
The gear tooth crowning arrangement disclosed herein permits more consistent gear
meshing events which reduce the noise, vibration and handling (NVH) level of the parallel
axis differential 10. Moreover, the present disclosure can be shown to inhibit end-loading
of the gear train 30 and compensate for any misalignments.
[0029] Turning now to FiG. 7, a baseline lead profile according to one example of prior
art is shown and generally identified at reference 70. A face width 72 is horizontal or
linear along the lead profile 70. No crowning is provided on the lead profile 70.
[0030] FIG. 8 illustrates a lead profile 80 having a face width 82 that includes a first
lead crown 84 and a second lead crown 86 in accordance to the present teachings. The
first lead crown 84 is defined from a centerline 88 to a transition point 90. The second
lead crown 86 is defined from the transition point 90 to a first end point 92. In the example
shown in FIG. 8, the first lead crown 84 can be zero. Explained differently, the first lead
crown 84 can have no crowning. The second lead crown 86 can have a drop-off. The
drop-off can correspond to an area of reduced gear teeth contact with a mating gear
(having a similar lead crown drop-off). It will be appreciated in light of the disclosure that
the drop-off can be located in one or both of the first and third zones 44, 48 (FIG. 3). The
lead profile 80 can be similar between the centerline 88 and a second end point 94. In
such a configuration, while only one end may be meshed with a corresponding pinion
gear, having a similar lead crown on both ends of the pinion gear can help with assembly
as the gear may be installed into the differential case 20 with either end first.
[0031] FIG. 9 illustrates a lead profile 00 having a face width 102 that includes a first
lead crown 104 and a second lead crown 106. The first lead crown 104 is defined from
a centerline 108 to a transition point 110. The second lead crown 106 is defined from the
transition point 10 to a first end point 112. In the example shown in FiG. 9, the first lead
crown 04 can be non-zero (as compared with the first lead crown 84 shown in FIG. 8).
The lead profile 100 can be similar between the centerline 108 and a second end point
114. in such a configuration, while only one end may be meshed with a corresponding
pinion gear, having a similar lead crown on both ends of the pinion gear can help with
assembly as the gear may be installed into the differential case 20 with either end first.
[0032] FIG. 10 illustrates a lead profile 120 having a face width 122 that includes a
first lead crown 124. The first lead crown 124 is defined from a centerline 128 to a first
end point 132. In the example shown in FIG. 10, the first lead crown 124 can be non¬
zero (as compared with the first lead crown 84 shown in FIG. 8). In the example shown
in FIG. 10, the first lead crown 124 can be continuous from the centerline 128 to the end
point 132. Explained further, the first lead crown 124 can be similar to the first lead crown
104 described in FIG. 9 however, the first lead crown 124 can continue to the first end
point 132 without a defined transition. The lead profile 120 can be similar between the
centerline 128 and a second end point 134. In such a configuration, while only one end
may be meshed with a corresponding pinion gear, having a similar lead crown on both
ends of the pinion gear can help with assembly as the gear may be installed into the
differential case 20 with either end first. It is appreciated however that while the lead
profile 120 is shown having both ends of the pinion crowned (such as to assist with
assembly), the pinion gear 14 may be constructed as having only one end with a lead
crown.
[0033] With reference now to FIGS. 11 and 12, additional features of the present
disclosure will be described. FIG. 1 shows features of the lead profile 80 (FIG. 8), the
lead profile 100 (FIG. 9) and the lead profile 120 (FIG. 10) together. A drop-off magnitude
M is identified between the first lead crown 124 and the second lead crown 106. In one
example, the drop-off magnitude M can be greater than a distance 150 between a
foundation line 152 and a centerline 108, 128. In one example, the drop-off magnitude
M can be a multiple of 1.5 greater than a distance 150. Other configurations are
contemplated. A drop-off distance L is identified between the transition points 90, 110
and the first end points 92, 112. The drop-off distance L can be determined based on a
given application. FIG. 12 illustrates an exemplary crowning tolerance band 170 having
an upper tolerance 172 and a lower tolerance 174. The crowning tolerance band 170
identifies an area that the lead profile can occupy while still providing the reduced NVH
levels in a given gear train.
[0034] FIG. 13 illustrates a load intensity distribution 200 for a pinion gear disposed in
a parallel axis differential according to prior art. Notably, an active face width shows
increased load intensities 202 and 204 in meshed areas consistent with a meshed
interface area 50 (FIGS. 5 and 6). The increased load intensities 202 and 204 produce
unfavorable NVH. FIG. 14 illustrates a load intensity distribution 210 for a pinion gear
having a lead crowning according to one of the examples of the present disclosure and
disposed in a parallel axis differential. Notably, an active face width shows reduced load
intensities 212 and 214 in meshed areas consistent with a meshed interface area 50. The
reduced load intensities 212 and 214 provide improved NVH characteristics. The reduced
load intensities avoids micro-welds and subsequent breaking of those micro-welds
causing NVH chatter. The micro-welds can occur in prior art examples between the pinion
teeth 40 and the housing 20.
[0035] According to other examples of the present disclosure, a chemical vapor
deposit coating may be additionally or alternatively applied to the pinion gears 14 that can
be shown to provide improved NVH qualities. One such product is a chemical vapor
deposit coating marketed by Oerlikon Balzers of Liechtenstein. One example is BALINIT®
C Star coating marketed by Oeriikon Baizers. The chemical vapor deposit coating can
reduce friction and/or pressure between the pinion gears 14 and the housing. In this
regard, the coating can reduce the propensity of the micro-welds from forming between
the pinion gears 14 and the housing 20 and the resulting stick-slip action that would
otherwise cause noise. In prior art examples, high pressure, lack of sufficient lubricant,
and similarity of material properties such as hardness, alloy content, and surface finish
are characteristics that can encourage micro-welds. The chemical vapor deposit coating,
such as identified above, separates and protects the substrate materials from contacting
each other in this operating scenario. Preventing such micro-welding and adhesive wear
has been shown to also improve the NVH performance of the differential. In other
examples, tip relief may be added in the involute profile direction (measuring from root to
tip). This further helps improve the load intensity plot in FIG. 14. Such tip relief may be
produced with specially designed hob cutters.
[0036] The foregoing description of the many examples has been provided for
purposes of illustration and description. It is not intended to be exhaustive or to limit the
disclosure. Individual elements or features of a particular aspect are generally not limited
to that particular example, but, where applicable, are interchangeable and can be used in
a selected example, even if not specifically shown or described. The same may also be
varied in many ways. Such variations are not to be regarded as a departure from the
disclosure, and all such modifications are intended to be included within the scope of the
disclosure.

CLAIMS
What is claimed is:
. A parallel axis gear configuration comprising:
a first gear having a first gear tooth that includes a lead crowning across a
face width thereof, the lead crowning comprising:
a first lead crown defined from a centerline to a transition point; and
a second lead crown defined from the transition point to a first end
point; and
wherein the lead crowning includes a drop-off magnitude that is greater at
the second lead crown than the first lead crown.
2 . The parallel axis gear configuration of claim 1, further comprising a second
gear that is in meshed relationship with the first gear.
3. The parallel axis gear configuration of claim 2 wherein the first and second
gears are helical gears.
4 . The parallel axis gear configuration of claim 3, further comprising:
a parallel axis differential that houses the first and second gears.
5. The parallel axis gear configuration of claim 1 wherein the first gear includes
a chemical vapor deposit coating thereon.
. The parallel axis gear configuration of claim 5 wherein the chemical vapor
deposit coating comprises BALINIT® C Star coating.
7. A parallel axis gear configuration comprising:
a first gear having a first gear tooth that includes a lead crowning across a
face width thereof, the lead crowning comprising:
a first lead crown defined from a centerline to a transition point; and
a second lead crown defined from the transition point to a first end
point; and
wherein the first and second lead crowns have a distinct magnitudes across
the face width.
8. The parallel axis gear of claim 7 wherein the second lead crown includes a
drop-off magnitude that is greater at the second lead crown than the first lead crown.
9. The parallel axis gear of claim 7 wherein the first lead crown is zero.
0. The parallel axis gear configuration of claim 7, further comprising a second
gear that is in meshed relationship with the first gear.
1. The parallel axis gear configuration of claim 0 wherein the first and second
gears are helical gears.
12. The parallel axis gear configuration of claim 7, further comprising:
a parallel axis differential that houses the first and second gears.
13. The parallel axis gear configuration of claim 7 wherein the first gear includes
a chemical vapor deposit coating thereon.
14. The parallel axis gear configuration of claim 3 wherein the chemical vapor
deposit coating comprises BALINIT® C Star coating.
15. A parallel axis gear configuration comprising:
a first gear having a first gear tooth that includes a first gear tooth lead
crowning across a face width thereof, the first gear tooth lead crowning comprising:
a first lead crown defined from a centerline to a transition point; and
a second lead crown defined from the transition point to a first end
point wherein the first gear tooth lead crowning includes a drop-off magnitude that
is greater at the second lead crown than the first lead crown; and
a second gear having a second gear tooth that includes a second gear tooth
lead crowning across a face width thereof, the second gear tooth lead crowing
comprising:
a first lead crown defined from a centerline to a transition point; and
a second lead crown defined from the transition point to a first end
point wherein the second gear tooth lead crowning includes a drop-off magnitude
that is greater at the second lead crown than the first lead crown; and
wherein the first and second gears are received in a housing in a meshed
relationship, the second lead crowns of the respective first and second gear tooth lead
crowns aligning providing load intensities that inhibit micro-welding between the gears
and the housing.
16. The parallel axis gear configuration of claim 15, wherein the housing
comprises:
a parallel axis differential that houses the first and second gears.
17. The parallel axis gear configuration of claim 15 wherein the first and second
gears both include a chemical vapor deposit coating thereon.
18. The parallel axis gear configuration of claim 17 wherein the chemical vapor
deposit coating comprises BALINIT® C Star coating.
19. The parallel axis gear configuration of claim 15 wherein the first and second
gears are helical gears.
20. The parallel axis gear configuration of claim 15 wherein the first lead crown
of at least one of the first and second gear tooth lead crowning is non-zero.