ABSTRACT
This paper is based on the
project “Power Assisted Gear Shifting Mechanism for Automobiles”. This is a
design, fabrication and implementation project. The project provides solution
for gear shifting for the cars. The passenger cars that now ply on the road
have transmission either of manual or automatic type of gear changing. The
manual type of transmission is preferred for the perfect performance without a
loss in power but a compromise for comfort ness. In this type automatic system
of power transmission there is easiness of gear shifting but there is a
definite loss of power and mileage. The main objective of this project is to
create a mechanism to reduce the inconvenience caused when changing gears in
the car. The gear shifting here is by mere pressing of feather touch buttons
present on the dash board. The gear shifting is by hydraulic force achieved by
a simple modification to the gear box. This is a versatile pack, simple and can
be fitted to any car equipped with hydraulic power steering. The setup consists
of power steering pump, piston cylinder assembly and a set of fluid valves.
This project if implemented is a clear alternative for the Automatic
transmission because of its low cost and ease of use. Moreover the whole set up
is small and requires a very small space. This can sure be a standard fitment
if proper marketing strategy is carried out. Further, automatic clutch can be
incorporated with this unit to make it fully automatic.
PROJECT MODEL
INTRODUCTION
The
paper deals with the real time project, “Power Assisted Gear Shifting Mechanism
for Automobiles” which was done in the academic year 2004- 2005. The paper
deals with the various design aspects of the creation of this project. This
project is aimed at giving driver the convenience for gear shifting. The car
with this project will have a series of buttons in the format of 4 forward, a
reverse and a neutral. The clutch operation may or may not be put in the car
depending on the user. Currently the project has been done for the transmission
of third and reverse gears. The power
for gear shifting is got from hydraulic fluid. The power for fluid is from the
power steering pump. So a car with a power steering fitment can be easily
adaptable to this project. The project has been started as a concept and it
requires a lot more work to be done to put in a car.
PROBLEM DEFINITION
Whenever
a project is carried out there is a reason behind it. The existing cars now
pose some problems for the drivers. In the Manual Transmission cars the main
problem for the drivers is the gear shifting. But the engineering concept
behind this type of transmission paves way for higher power transmission
efficiency. More over the mileage of the car and life is also more. These cars
do not give much of comfort ness for the drivers in the terms of using the gear
lever and the clutch. Also it occupies a major area in the cabin resulting in
the space congestion. These are the problems in the Manual Transmission cars.
In the Automatic Transmission type of
cars, the gear shifting is easy. We just have to select the drive band, which
is already preset. This selection may be either of lever type or a set of
buttons. This is easy for the drivers as they don’t have to use clutch during
gear shift. But there is a compromise for power transmission and mileage. As
the gear selection is by a fluid, power is required to drive it, so the engine
performance is reduced. So the problem
here is mileage drop, power loss and also it is costly.
The need of the hour, combining the
position of both MT and AT a mechanism has to be created for better mileage and
comfortable gear shifting. This is the objective of the project. So a car with
this project provides ease of gear shift as in AT without a compromise in
mileage as in MT. the cost of the project is less as it requires a minor
alteration in the gear box.
DESIGN OF PROJECT
The
project is done as a table top on the FIAT car’s gear box. The project design
comprises of designing the following parts,
1.
Hydraulic circuit
2.
Electronic circuit
3.
Mechanical components
HYDRAULIC CIRCUIT
Hydraulic
motion is selected for gear shifting owing to its large load acceptance and
ease of adaptability in the car. Also the gear shift should be quick. The basic
components design is explained in detail.
CYLINDER DESIGN
Load
required to move the selector rod or to change the gear F=30 Kg
Pressure
built in the compressor unit
P=10 bar
To find:
Cylinder dimensions D,L=?
1. Cylinder
diameter D=?
P=F/A
(10*105)*(P/4)*D2 = 30*9.81
D=0.0194 m = 20 mm
2. Cylinder length
L =?
Cylinder length L= Stroke Length+ Piston thickness+ Clearance
L= 30+10+7 = 47 mm
L=47mm
Cylinder
diameter= 20mm Cylinder
length= 47mm
SELECTION OF PUMP
Selection of pump is based
on following characteristics:
1. Select the
actuator that is appropriate based on loads encountered.
2.
Determine the flow rate requirements. This involves the calculation of the flow
rate necessary to drive the
actuator to move the load through a specified distance within the given time.
3.
Determine the pump speed and select the prime mover. This, together with the
flow rate calculation, determines the pump size
4. Select the
pump based on application
5.
Select the system pressure. These involves in with the actuator size and
magnitude of the resistive force produced by the external load on the system.
Also involved here is the total amount of power to be delivered by the pump.
6.
Select the reservoir and associated plumping, including piping, valving,
hydraulic cylinders, motors and other miscellaneous components.
7. Calculate
the overall cost of the system.
8.
Consider factors such as noise levels, horse power loss, need for a heat
exchanger due to heat generated, pump wear, scheduled maintenance service to
provide a desired life of the total system.
The above characteristics
are satisfied by the GEAR OIL PUMP and the following data are obtained from
measurement,
Do =75 mm Di =50 mm W= 25 mm N=1440 rpm
1. Flow rate Q= (P/4)*(Do2-Di2)*W*N
= (P/4)*(0.0752-0.0502)*0.050*1440
= 0.0883 m3/S = 0.00147 m3/min
= 1.47 Ltrs/min
2. Power required = Pressure*Flow rate= (10*105)*0.0883 = 88.3 kw
SELECTION OF RESERVIOR
1. Reservoir Capacity= 2.5
to 3 Times of Pump flow
= 3*1.47
= 4.41 Ltrs
=4 Ltrs
2. Size of the copper tube =6 mm(for
transmitting hydraulic fluid to valves
HydraulicCircuitDiagram
Hydraulic circuit diagram of the project
1.
Reservoir. 7.
Cylinder piston assembly
2.
Pump. 8. Limit Switch
3.
Clutch 9.
Gear Box
4.
Engine 10.
Gear selector rod
5.
Inlet Solenoid Valve 11. Spring
6.
Outlet Solenoid Valve
ELECTRONIC CIRCUIT
The electronic circuit is used for governing the hydraulic
operation. For this purpose we have used two solenoid valves (inlet and outlet)
for each gear to be shifted. The supply voltage is from battery which is 12V.
there will be six buttons 1, 2, 3, 4, R, N for gear shifting. Each actuates the
gear corresponding when pressed.
The diagram below shows the electronic circuit for various
operation of the gear shifter.
i. Engaging first gear
ii. Maintaining gear position
iii. Releasing gear-neutral position
iv. Gear changing
MECHANICAL COMPONENTS
The main mechanical component for the project is the spring.
The spring is used to counter balance the force exerted by the piston. Moreover
it is useful in the return motion of the gear selector rod during gear
disengagement. Presence of spring on the gear selector rod helps in the quick
action that is required during the gear shift.
DESIGN OF SPRINGS
We have formula for deflection
Y = 8PD3n/Gd4
Where,
Y=deflection
of spring
P=load
acting on the spring
D=Diameter
of spring
d=
Diameter of spring coil
N=no
of coils in the spring
G=modulus
of elasticity of spring material
G=2*105
N/mm2
D=3.5
Cm
d=0.4
Cm
P=30
Kg
Y=1.5
Cm
No of coils in the spring,
n=YGd4/8PD3
=
1.5*2*105*0.44*100/(8*30*9.81*3.53)
=
8 coils
WORKING
PRINCIPLE
The main driving force for the
gear shifting is by the hydraulic fluid. The gear shifting along with the
clutch operation works with the pressing of buttons. On pressing the button
corresponding to the gear, three operations take place,
1.
Engine rotation
2.
Clutch engagement
3.
Pump rotation
When the car is switched on the
engine rotates, on pressing the button clutch engages. Now electromagnetic
clutch engages the pump. Due to the pump rotation the hydraulic fluid is pumped
from reservoir to the inlet solenoid valve. Through this valve the fluid pushes
the piston in the cylinder. This motion causes the gear shifter rod to engage
the gear which is fitted to the piston. In order to avoid slippage of gear a
limit switch is used to sense the position of selector rod and cut off the
supply.
To bring the car to neutral position we
press the N button. Now the outlet solenoid valve energizes so the fluid in the
cylinder rushes back to the sump with the aid of spring tension. If the next
higher gear has to be selected, the same operation takes place on pressing the
next button.
CURRENT STATUS
Presently
we have done this project as a table top working model. This consists of
various parts which are listed below.
1)
FIAT Gearbox
2)
TOYOTA Power steering compressor
3)
Motor for driving the compressor
4)
Electro magnetic clutch
5)
Tank or reservoir for storing the
hydraulic fluid
6)
Valves for controlling the flow of
hydraulic fluid
7)
Limit switch to cut off the supply
8)
Hydraulic cylinder and piston
assembly
9)
Copper tubes for transportation of
fluid
10)
Fluid Hoses
11)
Base structure for holding the
gearbox and motor arrangement
The
current model is a simple one which is actuated by a stick switch governing the
gear selection. This set up works good for two gears. In the future there are
plans to incorporate the clutch action in the set up by using the electronic
clutch.
MERITS AND DEMERITS
A project with a novel idea does have its own merits and
demerits which are discussed below,
Merits:
¨
A clear alternative for Auto
Transmission this, is much cheaper and user friendly with more features.
¨
Leg room for passengers at front is
increased more since the removal of gear rod.
¨
Ease of operation, by the use of
feather touch buttons.
¨
A boon for the handicapped, the car
can be driven even with only one hand since buttons are used for changing
gears.
¨
No loss in mileage of the car as
the load required for gear shift is meager.
¨
Gear shift is sequential, so no
problem of wrong gear selection.
Demerits:
Since
the project is custom made, it requires a skilled technician to assemble the
set up in the car, considering the space constraints. Moreover the driver
should be well trained in using the system to avoid malfunction.
CONCLUSION
This project is an innovative
concept. It is a new dimension in the transmission system of a car. This is a
simple and versatile pack that may be fitted to any cars existing with power
steering. By implementing this smart gear shifter in cars, we can achieve more
space, smooth operation, more user friendly, less effort to change the gear and
no play. Also the project is a boon for physically challenged persons. The
present condition of the project is promising for further developments. Lots of
inputs are also got from the car specialists and academicians for its
improvement. The concept can be transformed to a real time fitment on further
development. We estimate a period of two years to see a car fitted with this
mechanism.
REFERENCE
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