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.
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.
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 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.
Load required to move the selector rod or to change the gear F=30 Kg
Pressure built in the compressor unit P=10 bar
Cylinder dimensions D,L=?
1. Cylinder diameter D=?
(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
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
= 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
= 4.41 Ltrs
2. Size of the copper tube =6 mm(for transmitting hydraulic fluid to valves
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
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
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
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
No of coils in the spring,
= 8 coils
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.
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,
¨ 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.
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.
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.