FIELD OF INVENTION
This invention relates to Pseudo-Synchronized Reverse Gear Shift system.
PRIOR ART
In the known art, reverse Gear in manual transmission uses an idler gear, which
has to slide into mesh with two other spur gears sequentially in order to reverse
the direction of motion (Fig. 1). This meshing takes place in two stages as follows:
1. Idler gear meshes with the spur gear on the input shaft
2. Meshing with the spur gear projected over Low Speed Synchronizer sleeve
These two stages complete reverse gear shifting process and affects shift comfort &
quality the most. Each time when spur gear interacts, the teeth collide instead of
gently sliding into contact. This impact makes a lot of noise and also increases the
stresses on the gear teeth. When a loud is heard, clash noise from the vehicle in
reverse, it is basically the sound of reverse spur gear teeth cracking against one
another.
When the relative angular speed difference between meshing part is high, clashing
or grinding noise is accompanied by higher shift impulses raising overall required
shifting effort for engagement.
Among different problems like clashing noise, high shifting effort & frequent
reverse blocking, affecting Reverse gear shift quality, Blocking is the worst kind of
problem customer experiences. Blocking occurs when high ends of the entry
chamfer zone on the spur gear pair comes into contact & restrain each other
during meshing. This problem is highly probabilistic in nature & depends on
initial meshing configuration of spur pairs as shown in fig. 1 which indicates the
following: -
1. Chamfer angle.
2. Rake angle.
3. Entry chamfer, mating gear.
4. Entry chamfer
5. Reverse idler, spur gear.
High shift effort, clashing or gear grinding noise while shifting & frequent block
are major problems affecting reverse gear shift quality, thus Shift comfort can
broadly be defined as the measure of control set on these problems by the system
in use. Further, there problems are inherent in 'Sliding Mesh A-Synchronized
type" Reverse system which is widely used.
Few premium sedans use Fully Synchronized reverse system which offers
stringent control over these problems.
Synchronized Reverse system reduces Noise & Block practically to zero level but at
the expense of huge cost & weight impact.
Hence, the present invention i.e. Pseudo-Synchronized Reverse Gear Shift system
has been proposed to address the aforesaid problems.
OBJECTS OF THE INVENTION
An object of the present invention is to provide Pseudo-Synchronized Reverse Gear
Shift system which overcomes disadvantages associated with the prior art.
Another object of the present invention is to provide Pseudo-Synchronized Reverse
Gear Shift system for smooth shifting of reverse gears.
Further object of the present invention is to provide Pseudo-Synchronized Reverse
Gear Shift system to reduce shift force which is achievable through leverage ratio.
STATEMENT OF INVENTION
According to this invention, there is provided Pseudo-Synchronized Reverse Gear
Shift system comprising input shaft extending downward to be in constant mesh
with idler for avoiding blockage, in which output shaft is positioned adjacent to
the input shaft.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Further objects and advantages of this invention will be more apparent from the
ensuing description when read in conjunction with the accompanying drawings
and wherein:
Fig. 1 shows: Details of spur gear entry chamfer.
Fig. 2 shows: Meshing between input shaft and idler according to the present
invention.
Fig. 2A shows: provision of chamfer at notch of lever synchronizer sleeve.
Fig. 3 shows: value curve for pseudo-synchronous mechanism.
Fig. 4 shows: comparison of input shaft speed deceleration.
Fig. 5 shows: reverse blockage characteristics.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING DRAWINGS:
The present invention discloses Pseudo-Synchronized Reverse Gear Shift system
comprising combination of constant mesh reverse idler and reverse, input shaft
and lever synchronizer. Now, reference may be made to fig. 2, wherein input shaft
(2) is extended downward to be in constant mesh with idler (I), which avoids
blockage. Further, output shaft (3) is positioned adjacent to the input shaft.
pseudo reverse synchronizer is modified by providing a chamfer (C) at its notch at
an angle of 15-25 degree. The chamfer is provided on one side of the V-notch
preferably on the right hand side for limited braking. This accommodates one end
of the lever.
Constantly Meshed Reverse Idler reduces the probability of blocking by reducing
the probability of high end chamfer interactions to half when pitched against a
"Sliding Meshed System" because number of times indexing is required in PRS is
one instead of two in a conventional system; firstly with input entry and further at
sleeve entry, as shown in figure 2.
Blocking is further reduced by Braking Mechanism constituted by lever
synchronizer in the system. Braking Mechanism with force amplification (Lever
Synchronizer) also reduces the shift effort required to engage Reverse gear as it
amplifies the input force value by a predefined leverage ration, rapidly reducing
relative angular speed difference between the "reverse idler" and "to-be indexed
sleeve entry chamfer" & thus reducing the effective shift impulse value.
Considerably amount of shift related, whirringlclash noise reduction takes place
as a result of decrease in relative speed of the system.
Lever synchronizer on input shaft helps synchronizing 5th speed gear cone which
is free on the input shaft and lever synchronizer system which is fured on the
input shaft by generating friction between the mating surfaces both in case of 5th
gear & reverse gear engagement eliminating the need of placing a dedicated
synchronizer for shifting reverse.
Without impacting preliminary design functionally, significant improvement over
reserve gear shift related problem can be achieved with the help of the present
Parameters for the input shaft of the modified system are kept same as that of
conventional system.
With such a configuration in the transmission, momentous shift quality gain can
be achieved.
Now, reference may be made to fig. 3 indicating Value curve for PRS with
optimized functional variance.
Testing L Validation
Simulation was carried out to validate the system for its functionality as a whole
and to analyze the behaviour of components in dynamic condition. Result is
shown in figure 4.
Noise levers were measured subjectively both by driver & the passenger.
Maximum Engine RPM at which noise becomes apparent while shifting was noted
down: higher this RPM value better is the system against clashing noise. This test
was performed on a stationary vehicle with engine running and reverse is shifted
from neutral at different but increasing engine RPM values.
Clashing noise was prominent at idle speed itself in all test vehicles with Sliding
Mesh Reverse Mechanism. However clashing noise was not observed in test
vehicles with Pseudo-Reverse Synchronizer, owing to the presence of Braking
Mechanism.
Blocking instances were evaluated on probability basis after 500 times shifting
cycle from 1st gear to reverse gear & Neutral to reverse gear. Percentage blocking
instance for different type of mechanisms are as shown in fig. 5.
Sliding Meshed reverse gear shift mechanism fared worst in terms of blocking with
an average of 16% of blocking instances where as Test Vehicle with "Sliding Mesh
A-Synchronized type" reverse shift mechanism shows inferior Reverse blockage
characteristics when pitched against "Pseudo-Synchronous type" (marked in star)
Reverse Mechanism. From the above, it is evident that, the PRS improves the
reverse blockage characteristics of the system.
Advanta~eousf eatures of the invention
1. Reduction of blockage of reverse gears
2. Smooth driving experience
3. Lower shift impulse
4. Elimination of noise
5. Easier to adopt in existing transmissions (no change required) without
adding to cost.
Pseudo-Reverse synchronizer can be used for overcoming problems related to
reverse gear shifting and bring out significant improvement over reverse gear shift
quality. Force reduction is achievable through leverage ratio. Noise is eliminated at
idle shifting, and block instance percentage has shown noteworthy improvement
over conventional sliding meshed reverse gear shift system.
It is to be noted that the present invention is susceptible to modifications,
adaptations and changes by those skilled in the art. Such variant embodiments
employing the concepts and features of this invention are intended to be within
the scope of the present invention, which is further set forth under the following
claims: -

WE CLAIM
1. Pseudo-Synchronized Reverse Gear Shift system comprising input shaft
extending downward to be in constant mesh with idler for avoiding
blockage, in which output shaft is positioned adjacent to the input shaft.
2. Pseudo-Synchronized Reverse Gear Shift system as claimed in claim 1,
wherein lever synchronizer is fured on to the input shaft.
3, Pseudo-Synchronized Reverse Gear Shift system as claimed in claim 1 or 2,
wherein the lever synchronizer sleeve is provided with a chamfer at its
notch.
4. Pseudo-Synchronized Reverse Gear Shift system as claimed in claim 3,
wherein the chamfer is provided on one side of the notch at an angle of 15-
25 degree.
5. Pseudo-Synchronized Reverse Gear Shift system as claimed in any of
preceding claims, wherein the chamfer is provided preferably on right side
for limited braking which accommodates one end of the lever.
6. Pseudo-Synchronized Reverse Gear Shift system as claimed in any of the
preceding claims, wherein the system is associated with the advantageous
features such as herein described.
7. Pseudo-Synchronized Reverse Gear Shift system substantially as herein
described with reference to the accompanying drawings.