A REVERSE GEAR MECHANISM IN AN AUTOMOBILE
GEAR TRANSMISSION
FIELD OF INVENTION
The present invention relates to an automobile gear automatic manual1 manual
transmission, particularly, to a reverse gear mechanism in an automobile gear
transmission.
BACKGROUND OF THE INVENTION
It is known that an automobile transmission, particularly, a gear transmission,
includes mainly an input shaft and an output shaft. A plurality of drive gears are
mounted on the input shaft and a plurality of driven gears are mounted on the output
shaft, for providing a plurality of forward gear speed ratios and a reverse gear or
reverse speed ratio.
The input shaft of the gear transmission can be directly connected through clutch to an
engine output shaft. The drive gears are either rigidly connected or connected by hub
sleeve arrangement on the input shaft. The drive gears responsible for forward gear
ratio on the input shaft remain in meshing relationship with corresponding driven
gears on the output shaft which can be selectively engageable with the output shaft.
To achieve a particular forward gear ratio between the transmission input and output
shafts, the user can manually actuate a gear shift lever that controls the engagement of
the clutch means with the desired gears on the input shaft. To achieve a reverse gear
ratio, an idler gear is provided which can be selective engaged between an input shaft
drive gear and an output shaft driven gear to reverse the rotational direction of the
output shaft, and thus the drive wheels.
Figure 1 illustrates a configuration of reverse idler gear (lo), an idler shaft (1 1) and
reverse drive gear (12). As shown in Figure 1, the idler gear (10) is mounted on an
idler shaft (1 1) and it is free to rotate on the idler shaft (1 1). The idler gear (10) is
axially slidable on the idler shaft (11) to achieve its selective engagement and
disengagement with the reverse drive gear (12) on the input shaft. However, at the
time of engagement, the reverse idler gear (10) teeth and the reverse drive gear (12)
teeth can be at any random angle which may result in shift blockage which is a
blockage condition of the teeth of the reverse idler gear (10) and the reverse drive
gear (12) as shown Figure 2.
Figure 2 illustrate such blockage condition of the reverse idler gear (10) teeth and the
reverse drive gear (12) teeth. As shown in figure 2, the shift blockage occurs when a
reverse idler gear tooth (13) falls in-line with a reverse drive gear (14) tooth while the
reverse idler gear (10) is axially sliding towards the reverse drive gear (12). In this
situation, side face of the reverse drive gear tooth (14) obstructs or struck with the
reverse drive gear tooth (13) and results in a shift blockage as shown in Figure 2
(Detail-A). The shift blockage might also occur due to more than one tooth, for
example, two teeth of the reverse drive gear (12) fall in line with the teeth of the
reverse idler gear (10) which may result in severe shift blockage. As can be clearly
understood, such shift blockage hinder smooth operation of the reverse gear and the
user has to apply either a higher shift force or re-try the actuation of gear shift lever
after the releasing clutch-pedal to engage the reverse idler gear (10) with the reverse
drive gear (12). In addition, the blockage condition is detrimental to the long term
durability of the gear teeth and can cause higher repairing charges to the user.
As explained in previous paragraph that the blockage condition occurs because the
reverse drive gear and idler gear can be at any random angle during their engagement.
Further, as such there is no control with user to correct the same precisely. Therefore,
it is observed that the occurrence of blockage condition is frequent and the user has to
make re-attempts to operate reverse gear due to the blockage condition.
Accordingly, there is a need to provide a mechanism to reduce or eliminate the
occurrence of blockage condition between the reverse idler gear and the reverse drive
gear.
SUMMARY OF INVENTION
The present invention relates to a reverse gear mechanism in an automobile gear
transmission. The reverse gear mechanism comprises a reverse drive gear mounted on
a first shaft and rotatable with the first shaft; a reverse driven gear mounted on a
second shaft being placed parallel to the first shaft, and said reverse driven gear is
rotatable with the second shaft; a reverse idler gear mounted on a third shaft being
disposed between the first shaft and the second shaft; said reverse idler gear is axially
movable on the third shaft so as to engage or disengage with the reverse drive gear
The reverse gear mechanism also includes a spline section comprising plurality of
splines disposed on the third shaft; a hub coaxially mounted on the reverse idler gear;
a plurality of spring-ball assemblies disposed in the hub and adapted to cooperate with
the spline section of the third shaft so as to orient the reverse idler gear at a
predetermined angular position when the reverse idler gear is disengaged with the
reverse drive gear for preventing a shift blockage between the reverse idler gear and
reverse drive gear.
BRIEF DESCRIPTION OF FIGURES
Further aspects and advantages of the present invention will be readily understood
from the following detailed description with reference to the accompanying
figures of the drawings. The figures together with a detailed description below, are
incorporated in and form part of the specification, and serve to further illustrate
the embodiments and explain various principles and advantages but not limiting the
scope of the invention. In the accompanying drawings,
Figure 1 illustrates a configuration of reverse idler gear, an idler shaft and reverse
drive gear.
Figures 2 illustrate such blockage condition of the reverse idler gear teeth and the
reverse drive gear teeth.
Figures 3(a)-(d) and 4 illustrate a reverse gear mechanism according to an
embodiment of the present invention.
Figure 5 illustrates stages when the hub of the reverse idler gear is positioned on the
spline section in the reverse gear mechanism according to an embodiment of the
present invention.
Figures 6 (a) and 6(b) illustrate a perspective view of reverse gear mechanism
according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
While the invention is susceptible to various modifications and alternative forms,
specific embodiment thereof has been shown by way of example in the figures
and will be described in detail below. It should be understood, however that it is not
intended to limit the invention to the particular forms disclosed, but on the
contrary, the invention is to cover all modifications, equivalents, and alternative
falling within the spirit and the scope of the invention as defined by the appended
claims.
Before describing in detail the various embodiments of the present invention it
may be observed that the novelty and inventive step that are in accordance with
the present invention resides in the construction of reverse idler gear mechanism. It
is to be noted that a person skilled in the art can be motivated from the present
invention and modify the various constructions of reverse idler gear mechanism.
However, such modification should be construed within the scope and spirit of the
invention.
Accordingly, the drawings are showing only those specific details that are pertinent
to understanding the embodiments of the present invention so as not to obscure
the disclosure with details that will be readily apparent to those of ordinary skill
in the art having benefit of the description herein.
The terms "comprises", "comprising", "including" or any other variations thereof,
are intended to cover a non-exclusive inclusion, such that an assembly,
mechanism, setup, that comprises a list of components does not include only
those components but may include other components not expressly listed or
inherent to such assembly, mechanism or setup. In other words, one or more
elements in reverse idler gear mechanism or assembly proceeded by "comprises a"
does not, without more constraints, preclude the existence of other elements or
additional elements in the assembly or mechanism. The following paragraphs
explain present invention and the same may be deduced accordingly.
Accordingly, the present invention relates to a reverse gear mechanism in an
automobile gear transmission comprising: a reverse drive gear mounted on a first
shaft and rotatable with the first shaft; a reverse driven gear mounted on a second
shaft being placed parallel to the first shaft, and said reverse driven gear is rotatable
with the second shaft; a reverse idler gear mounted on a third shaft being disposed
between the first shaft and the second shaft; said reverse idler gear is axially movable
on the third shaft so as to engage or disengage with the reverse drive gear;
characterized in that, the reverse gear mechanism comprises: a spline section
comprising plurality of splines disposed on the third shaft; a hub coaxially mounted
on the reverse idler gear; a plurality of spring-ball assemblies disposed in the hub and
adapted to cooperate with the spline section of the third shaft so as to orient the
reverse idler gear at a predetermined angular position when the reverse idler gear is
disengaged with the reverse drive gear for preventing a shift blockage between the
reverse idler gear and reverse drive gear.
In an embodiment of the present invention, the spring-ball assembly is adapted to
cooperate with the spline-section to orient the reverse idler gear in such a manner that
meshing teeth of the idler gear being positioned in angularly offset position about a
center-line defined by a line joining centers of the reverse idler gear and the reverse
drive gear, when both the gears are in the same plane.
In another embodiment of the present invention, the spline section comprises the
plurality splines extending in axial direction up to a predetermined length.
In still another embodiment of the present invention, each of the plurality of springball
assemblies comprises a ball and a spring being disposed in a slot provided in the
hub.
In yet another embodiment of the present invention, the ball of the each spring-ball
assemblies is supported on the splines of the spline section under a force of the spring
thereby orienting the reverse idler gear at a predetermined angular position.
In a further embodiment of the present invention, the diameter of ball of the spring
ball assembly is greater than the circular pitch of the splines of the spline-section.
In a further more embodiment of the present invention, the length of the splines on
the spline section is such that
- during the axial movement of the reverse idler gear towards the reverse drive
gear, the spring ball assembly loses contact immediately before the start of
engagement between the reverse idler gear and the reverse drive gear;
- during the axial movement of the reverse idler gear away from the reverse
drive gear, the spring ball assembly gains contact immediately after the start of
disengagement between the reverse idler gear and the reverse drive gear;
In another embodiment of the present invention, the angular offset of the reverse idler
gear meshing teeth with respect to the center line, is in the range of 0.2-0.3 PC for
preventing the shift blockage condition between the reverse idler gear and the reverse
drive gear, during engagement, where, PC is circular pitch of the reverse idler gear.
In still another embodiment of the present invention, the angular offset of the reverse
idler gear meshing teeth with respect to the center line is preferably 0.25 PC, where,
PC is circular pitch of the reverse idler gear.
In yet another embodiment of the present invention, the number of splines on the
spline section is double the number of teeth on the reverse idler gear.
In a further embodiment of the present invention, the splines are preferably of
triangular in cross-section.
In a further more embodiment of the present invention, the reverse idler gear is axially
moveable on the third shaft by a shift lever that is mounted on a shift arm.
In one more embodiment of the present invention, the reverse idler gear is engageable
with the reverse driven gear during the engagement with the reverse drive gear.
A still further embodiment of the present invention relates to a transmission system
comprising a reverse gear mechanism.
Figures 3(a)-(d) and Figure 6 (a)-(b), illustrate a reverse gear mechanism according to
an embodiment of the present invention. Referring to Figures 3 (a) and 6 (a)-@), the
reverse gear mechanism (1 00) comprises a reverse drive gear (1 0 1) mounted on a first
shaft (102) and a reverse driven gear (103) mounted on a second shaft (1 04) which is
parallel to the first shaft (102). The first shaft (102) is an input shaft which receives
power from engine shaft (not shown in figures) and the second shaft (104) is an
output shaft for providing a drive to wheels of automobile. The reverse gear
mechanism (100) also includes a reverse idler gear (105) mounted on a third shaft
(106) parallel to the first (102) and the second shafts (104) and being disposed
between the first shaft (102) and the second shaft (104). The third shaft (106) can also
be termed as idler shaft. The reverse idler gear (105) is axially movable on the third
shaft (106) towards and away from the reverse drive gear (101) so as to engage or
disengage with the reverse drive gear (101). It can be clearly understood that the
reverse idler gear (105) also engages with the reverse driven gear (103) while
engaging with the reverse drive gear (101) so to transmit power from the first shaft
(1 02) to the second shaft (1 04) via reverse idler gear (1 05).
Referring to figures 3(a)-(d) and Figure 6(a)-(b), a hub (107) provided on the reverse
idler gear (105) and co-axially mounted with the reverse idler gear (105) on the third
shaft (106). As shown in figures 3(a) and 6(a)-(b) the hub (107) is rigidly connected to
the reverse idler (105) so as to rotatable and axially movable with the reverse idler
(105) on the third shaft (106). The hub (107) can be integrally formed with the reverse
idler gear (105) or can be a separate part rigidly connected with the reverse idler gear
(105). As shown figure 3@), a spline section (108) is disposed on the third shaft. The
spline section (108) includes a plurality of splines (S) that extends longitudinally up to
a predetermined length in axial direction of the third shaft (106). The splines (S) are
provided exterior side on the third shaft (106). The spline section (108) can be formed
by known methods of forming splines. The plurality of splines (S) may be formed in
any suitable shape, size configuration and in any suitable numbers. It is preferred that
the splines (S) are triangular in cross section.
As described in the previous paragraph, the reverse idler gear (105) can be axially
slided on the third shaft (106) towards the reverse drive gear (101) so to engage with
the reverse drive gear (101) and reverse driven gear (103) for operating the reverse
gear of the automobile. In a position where reverse gear is not operated, the reverse
idler gear (105) remains disengaged with the reverse drive gear (101) and reverse
driven gear (103). In the said position where reverse gear is not operated, the hub
(107) of the reverse idler gear (105) is positioned on the spline section (108) of the
third shaft (106) according to an embodiment of the present invention.
In an embodiment, the hub (107) is provided with a means to rotate the reverse idler
gear (105) to a predetermined angular position when the hub (107) of the reverse idler
gear (105) is positioned on the spline section (108) for preventing the shift blockage
between the reverse idler gear (105) and reverse drive gear (101) during the
engagement. For this purpose, as shown in Figures 3(c) and 3(d), a plurality of springball
assemblies (109) can be disposed in the hub (107). The hub (107) is provided
with plurality of slots (1 10) for accommodating the said spring ball assemblies (109)
so that the spring (1 1 1) loaded balls (1 12) remain slightly projected outside the slots
(1 lo), towards center of the hub (107). The spring ball assemblies (109) are adapted
to cooperate with the spline section (108) of the third shaft (106) so as to orient the
reverse idler gear (105) at a predetermined angular position when the hub (107) of the
reverse idler gear (105) is positioned on the spline section (108) for preventing the
shift blockage between the reverse idler gear (105) and reverse drive gear (101)
during the engagement.
Referring to Figure 4, in an embodiment, the spring ball assemblies (109) and the
spline section (108) of the third shaft (106) are adapted to cooperate with each other
so as to orient the reverse idler gear (105) in such a manner that no teeth of the reverse
idler gear (105) falls in line with a center line (C), where, the 'center line' herein
refers to a line joining centers of the reverse idler gear (105) and the reverse drive
gear (101), when both the gears (105, 101) are in the same plane. The shift blockage
occurs when the reverse drive gear (101) teeth and reverse idler gear (105) teeth fall
along the center line (C). The tooth of the reverse idler gear (105) which is obstructed
by tooth of reverse drive gear (101) during engagement is referred herein as 'clashing
tooth' (CT). In an embodiment, the spring ball assemblies (109) and the spline section
of the third shaft are adapted to cooperate with each other so as to orient the reverse
idler gear (1 05) in such a manner that the clashing tooth (CT) of the reverse idler (1 05)
is positioned angularly offset from the center line (C).
Figure 5 illustrates stages when the hub (107) of the reverse idler gear (105) is
positioned on the spline section (108) in cooperation with the spring ball assemblies
(109). Figures 5(a) and 5(b) illustrates one spring ball assembly (109) for explanation
purpose. Figure 5(a) illustrates an unstable condition which occurs when the ball
(1 12) of the spring-ball assembly (109) is resting on crest of only one spline (S1). In
other words, the ball (1 12) of the spring ball assembly (109) cannot be supported by
crest of only one spline (S) and therefore, resulting in the unstable condition.
From the unstable condition, the spring ball assembly (109) will tend to move towards
a stable condition in which the ball (1 12) of the spring-ball assembly (109) is rested
on crests of at least two splines (S1, S2) as shown in Figure 5(b). For this purpose, the
ball (1 12) of the spring ball assembly (1 09) and the splines (S) are sized so that in the
unstable condition, the ball (1 12) of the spring ball assembly (109) is rested on the
crest of one spline (S1) and in the stable condition, the ball (1 12) of the spring ball
assembly (109) is rested on the crests of the two adjacent splines (S1, S2). It is
preferred that the diameter of ball (1 12) of the spring ball assembly (109) is slightly
greater than the circular pitch (PC) of the splines (S) of the spline-section (108).
As explained in previous paragraph, each of the spring ball assembly (109) will tend
to achieve the stable condition and apply a rotation force on the hub (107) and the
reverse idler gear (105) thereby rotating the reverse idler gear (105). For this purpose,
the spring (1 10) of the spring ball assembly (109) is constructed so as to apply
sufficient spring force to enable the spring ball assembly (109) to move fkom the
unstable condition to the stable condition. Movement of the spring ball assembly
(109) from the unstable condition to the stable condition orients the reverse idler gear
(1 05) to a predetermined angular position.
As shown in Figures 5(aa) and 5(bb), in an embodiment, movement of the spring ball
assembly (109) from the unstable condition to the stable condition orients the reverse
idler gear (105) so as to angularly offset the clashing tooth (CT) of the reverse idler
gear (105) by a predetermined angle (0) with respect to the center line (C) for
preventing the shift blockage condition between the reverse idler gear (105) and the
reverse drive gear (101), during engagement. The angular offset (0) may be in the
range of 0.2 to 0.3&, where, 0c is an angle subtended by the circular pitch (PC) at the
center of the reverse idler gear (105). The angular offset (0) of the reverse idler gear
I
clashing tooth (CT) with respect to the center line (C) is preferably 0.25 PC and for this
purpose, the number of splines (S) on the spline section (108) is double the number of
teeth on the reverse idler gear (105).
Referring to Figures 2-6, in an embodiment, the length of the splines on the spline
section (108) is such that during the axial movement of the reverse idler gear (105)
towards the reverse drive gear (101), the spring ball assembly (109) loses contact
immediately before the start of engagement between the reverse idler gear (105) and
the reverse drive gear (101); and during the axial movement of the reverse idler gear
(105) away from the reverse drive gear (101), the spring ball assembly (109) gains
contact immediately after the start of disengagement between the reverse idler gear
(105) and the reverse drive gear (101). Such construction ensures smooth and noise
free rotation of the reverse idler gear (105).
Figures 6 (a) and 6(b) illustrate a perspective view of reverse gear mechanism
according to an embodiment of the present invention. As shown in figures 6 (a) and
6(b), the reverse idler gear (105) is axially moveable on the third shaft (106) by a shift
lever (1 13) that is mounted on a shift arm (1 14).
With the reverse gear mechanism of the present invention as described above, the
engagement of the reverse idler gear and the reverse drive at any random angle can be
avoided. Further, in the present mechanism teeth of the reverse idler gear will be
always in angular offset position with respect to the center line which reduces the
chances of the shift blockage because the reverse drive gear and the reverse idler gear.
Moreover, the reverse gear mechanism of the present invention achieves 15-45%
reduction in the shift force which the user has to apply to operate the reverse gear as
compared to the existing reverse gear mechanism.

We Claim:
1. A reverse gear mechanism (1 00) in an automobile gear transmission comprising:
a reverse drive gear (101) mounted on a first shaft (102) and rotatable with
the first shaft (1 02);
a reverse driven gear (103) mounted on a second shaft (104) being placed
parallel to the first shaft (102), and said reverse driven gear (103) is rotatable with the
second shaft (1 04);
a reverse idler gear (105) mounted on a third shaft (106) being disposed
between the first shaft (1 02) and the second shaft (1 04); said reverse idler gear (1 05)
is axially movable on the third shaft (106) so as to engage or disengage with the
reverse drive gear (1 0 1);
characterized in that, the reverse gear mechanism (1 00) comprises:
a spline section (108) comprising plurality of splines (S) disposed on the third
shaft (1 06);
a hub (1 07) coaxially mounted on the reverse idler gear (105);
a plurality of spring-ball assemblies (1 09) disposed in the hub (1 07) and adapted to
cooperate with the spline section (1 08) of the third shaft (1 06) so as to orient the
reverse idler gear (1 05) at a predetermined angular position when the reverse idler
gear (1 05) is disengaged with the reverse drive gear (1 01) for preventing a shift
blockage between the reverse idler gear (1 05) and reverse drive gear (1 01).
2. The reverse gear mechanism as claimed in claim 1, wherein the spring-ball assemblies
(1 09) being adapted to cooperate with the spline-section (1 08) to orient the reverse
idler gear (105) in such a manner that clashing tooth (CT) of the reverse idler gear
(1 05) being angularly offset by a predetermined angle (0) with respect to a center-line
(C), where in the center line (C) is defined by a line joining centers of the reverse idler
gear and the reverse drive gear, when both the gears are in the same plane.
3. The reverse gear mechanism as claimed in claim 1, wherein the spline section (108)
comprises the plurality splines (S) extending in axial direction up to a predetermined
length.
4. The reverse gear mechanism as claimed in claim 1, wherein each of the plurality of
spring-ball assemblies (1 09) comprises a ball (1 12) and a spring (1 1 1) being disposed
in a slot (1 10) provided in the hub (1 07).
5. The reverse gear mechanism as claimed in claim 4, wherein the ball (1 12) of the each
spring-ball assemblies (1 09) is supported on the splines (S) of the spline section (108)
under a force of the spring (1 1 I), thereby, orienting the reverse idler gear (105) at a
predetermined angular position (8).
6. The reverse gear mechanism as claimed in claim 5, the diameter of ball (1 12) of the
spring ball assembly (109) is greater than circular pitch (PC) of the splines (S) of the
spline-section (1 08).
7. The reverse gear mechanism as claimed in claim 3, wherein the length of the splines
(S) on the spline section (1 08) is such that
- during the axial movement of the reverse idler gear (105) towards the reverse
drive gear (101), the spring ball assemblies (109) loses contact immediately
before the start of engagement between the reverse idler gear (105) and the
reverse drive gear (1 0 1);
- during the axial movement of the reverse idler gear (105) away from the
reverse drive gear (101), the spring ball assembly (109) gains contact
immediately after the start of disengagement between the reverse idler gear
(1 05) and the reverse drive gear (1 01);
8. The reverse gear mechanism as claimed in claim 2, wherein, the angular offset (8) of
the reverse idler gear clashing tooth (CT) with respect to the center line (C), is in the
range of 0.2 to 0.3 8c for preventing the shift blockage condition between the reverse
idler gear (105) and the reverse drive gear (101), during engagement, where, 8c is an
angle subtended by circular pitch (PC) at the center of the reverse idler gear (1 05).
9. The reverse gear mechanism as claimed in claim 8, wherein the angular offset of the
reverse idler gear clashing tooth (CT) with respect to the center line (C) is preferably
0.25 8c.
10. The reverse gear mechanism as claimed in claim 1 and 9, wherein the number of
splines on the spline section (108) is double the number of teeth on the reverse idler
gear (1 05).
11. The reverse gear mechanism as claimed in claim 1, wherein the splines (S) are
preferably of triangular in cross-section.
12. The reverse gear mechanism as claimed in claim 1, wherein the reverse idler gear
(105) is axially moveable on the third shaft (106) by a shift lever (1 13) that is
mounted on a shift arm (1 14).
13. The reverse gear mechanism as claimed in claim 1, wherein the reverse idler gear
(105) is engageable with the reverse driven gear (103) during the engagement with the
reverse drive gear (101).
14. A transmission system comprising a reverse gear mechanism as claimed in claims 1-
13.