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To develop a gear shifting mechanism for the SUPRA SAE vehicle. There will be factors like suspension system and steering which will govern the maneuverability and control of the vehicle during the race event. But without gear shifting mechanism and transmission the use of suspension system and steering on our vehicle is merely of any use as running of vehicle is very important criteria for completing the competition.
Since our SUPRA SAE competition carries 50 points for fuel efficiency therefore there is a intense requirement of a stable and efficient gear shifting mechanism which is capable enough of translating the gears according to the convenience of drivers to achieve the desirable torque and velocity.
Thus a good gear shift mechanism has to be implemented in SUPRA SAE vehicle.
The principle objective of SUPRA SAE-INDIA is for students to conceive, design, build and compete with a small open wheel race car.
The restrictions on the car are designed to maximize the use of the student's imagination and knowledge, and to give the students a meaningful project as well as good practice working in a team environment.
The car is to be designed to maximize its acceleration, handling and braking.
2.1 OBJECTIVE OF PROJECT
Objective of the project is to develop gear shifting mechanism.
We need to change gear shifting mechanism as per our vehicle design which uses a standard maruti 800 engine situated at rear of the vehicle.
As we are using the engine of maruti 800 which is originally mounted at front of the car, shifting rod was also from front and was smaller in length but in our vehicle, engine is mounted in rear of the vehicle and thus creating problem for shifting gears from drivers position easily and in same way as it was before in maruti 800.
3.0 BACKGROUND HISTORY
A manual transmission is also known as a manual gearbox or standard transmission which is a most common transmission used in vehicle applications.
It uses a driver-operated clutch operated by a pedal or lever for controlling torque transfer from the engine to the transmission and a gear stick which is operated with hands for selecting different gears.
In olden times, four-speed floor shifters were sometimes referred to as "four on the floor," during the time when steering column mounted shifters were more common which were also known as "three on the tree."
3.1 Types of gear shift pattern on floor-mounted shifter:
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Fig 1 A 4 speed gear lever
In many cars, gears are selected by manipulating a lever connected to the transmission by means of linkage or cables and mounted on the floor of the vehicle. This is called a gear stick, gearshift, or shifter. Moving this lever frontward, rearward, left, and right into particular positions selects specific gears marked on the gear knob. Figure 2 shows a four-speed transmission. N is the neutral position in which no gears are engaged and the engine is separated from the drive wheels. The entire horizontal line is a neutral position, even though shifter is equipped with springs so that it will come back to the N position if not moved into another gear position. The R marks is the reverse gear position used for moving the motor vehicle rearward.
This design is called the shift pattern. Due to the shift quadrants as shown above in fig 2, the basic arrangement is often called as H-pattern. The shift pattern is generally molded or printed on the gear knob.
The layout for gears 1, 2, 3 and 4 is same while location for reverse is not fixed. Location for reverse on gear knob depends on the particular transmission design; reverse may be positioned at the upper left, lower left, lower right, or at the upper right of the shift pattern.
Fig 3 five speed shift pattern
The above pattern of shifting is logically natural because it starts at the higher left and works from left to right, from top to bottom and with reverse at the end of the series toward the rear of the car.
Fig 4 Dog leg shift pattern
The name dog leg comes from the up-and-over path between first and second gears. Its use is common in race cars and sports cars.
First gear is across the dog leg which is beneficial as first gear is usually only used for moving the car and therefore it allow 2nd and 3rd gears to be aligned front and behind of each other, which ease shifting between the two.
Fig 5 Shift pattern for a six-speed transmission
Six speeds is the most usually seen transmission in single range transmissions.
4.0 GENERAL SHIFTING MECHANISM
Fig 6 Neutral Fig 7 1st gear
Fig 8 2nd gear Fig 9 3rd gear
Fig 10 4th gear Fig 11 reverse
Above figures shows the general shifting mechanism for engaging different gears.
Figures consist of an input shaft, counter shaft or lay shaft and an output shaft colored orange, grey and yellow respectively.
Shift stick is used to engage different gears through the 2 different dog clutches shown in blue and purple and reverse shown in green color.
5.0 LAYOUT OF SUPRA SAE VEHICLE
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Fig 12 ISOMETRIC VIEW
Above figures shows the isometric view of our SUPRA SAE vehicle.
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Fig 13 SIDE VIEW
Above figures shows the side view of our SUPRA SAE vehicle.
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Fig 14 TOP VIEW
Above figures shows the top view of our SUPRA SAE vehicle. All dimensions are in accordance with the vehicle.
6.0 TRANSMISSION IN OUR ENGINE
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Fig 15 Top section view
Fig 16 configuration of transmission inside the engine
The transmission provides four forward speeds and one reverse speed by means of four synchronizers, Two Hub & Sleeve and three shafts:
1. Input shaft
2. Counter shaft
3. Differential Gear
All forward gears are in constant mesh with Hub and Sleeve Input Shaft gears / Rev Synchronizer and reverse uses a sliding gear Counter Shaft gears idler gear arrangement.
See appendix a for marked no 1-18.
Fig 17 table showing different parts for gear engagement
7.0 POWER TRANSMISSION IN OUR ENGINE
Fig 18 power transmission for 1st and 2nd gear
The above figure shows the power flow from engine via 1st and 2nd gears to output shaft which drives the wheel of the vehicle.
Fig 19 power transmission for 3rd and 4th gear
The above figure shows the power flow from engine via 3rd and 4th gears to output shaft which drives the wheel of the vehicle.
Fig 20 power transmission for reverse gear
The above figure shows the engagement of reverse gear and power transmission for reverse gear.
8.0 DRIVING POSITION
Fig 21 Joint angle in a comfortable position
10 - 30
85 - 100
100 - 120
85 - 95
80 - 90
66 - 50
8.1 Positioning of driver according to the rule book of formulae SAE Fig 22 driver position
9.0 Gear selection and engagement mechanism
Gear selection and engagement is achieved by two different movements:
1. Selecting the required gear shift gate and the positioning of the gate lever.
2. Then shifting of the preferred selector gate rod into the gear engaging position.
These two operations are generally performed through the medium of the gear shifting lever and the control shaft.
Any transverse movement of the gear shift lever by the driver selects the gear shift gate and the longitudinal movement of the gear shifting lever engages the gate.
Movement of the gear shift lever is transmitted to the selection mechanism through the remote control rod. Initially the shaft is twisted to select the gate shift levers which are then followed by either a push or pull movement of the shaft to engage the correct gear.
9.1 Gear selection through gear shift guide:
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Fig 23 gear selection
9.2 GEAR SELECTION MECHANISM
The gear lever is a simple lever pivoting on a spherical bearing operating the main shaft. This shaft is effectively a long shaft that extends from the shift lever back to the selector mechanism at the back of the gearbox.
The long rod is a single rod that passes the forward\backward and rotational motion of the gear stick. It passes through the vehicle cockpit under the drivers left arm, below the fire wall and exit from below the engine connected to the transmission box with the help of a linkage.
10.0 Concept generation
We are modifying the gear shifting mechanism as this is the major problem in our vehicle for shifting of gear.
As we are using the engine of maruti 800 which was originally mounted in front of the car, shifting mechanism was also from front but in our vehicle engine is mounted in rear of the vehicle.
From here our problem starts as transmission mechanism shifts towards rear of the vehicle which was originally in front. Shifting mechanism had to be modified in accordance.
In maruti 800 shifting rod comes from front connected to engine transmission towards shift stick mounted on floor near driver's seat. In our Formula SAE engine we are using the same engine and drive train which is enclosed within. The difference is that our engine is mounted in rear while in Maruti 800 it is front mounted which makes our vehicle rear wheel drive.
The above process requires changing the gear shifting mechanism behind which will be out of the reach of the driver who will be sitting in front. Therefore, the linkages need to be changed.
10.1 OLD DESIGN
Fig 24 old design
The figure 24 is the first design or a initial design which is now modified and changed for ease and simplification. The comparison of the actual shifting mechanism in Maruti 800 with our SUPRA SAE is shown with the help of the diagram shown in fig 24.
In this old design we had shown initially the shifting mechanism which goes from gear stick to control shaft(linkage) connected via a ball joint(fulcrum), this control shaft is connected to the transmission box which thus changes gear by a rotary movement followed by a push or pull movement of control shaft.
Then initially by our concept we tried to make a design which is shown in the figure as suggested mechanism.
10.2 NEW DESIGN
Fig 26 side view
In the fig 26 the new design for gear shifting mechanism in our vehicle has been has been shown.
Before this design problem which occurred was mirrored image of gear shifting pattern which will lead to a problem in shifting for driver. As driver will not be used to such a shifting pattern it will lead to convenience in driving and will result in low performance of car during the event which is not desirable.
Fig 27 initial shifting pattern Fig 28 modified shifting pattern
Then the problem which came in preliminary design shown in fig 25 was identified and changes were made which was giving mirrored image of shifting pattern as shown in fig 27 and fig 28.
All the dimensions shown in the figure 26 are in accordance to SUPRA SAE vehicle.
Fig 29 top view
Above two figures fig 26 and fig 29 shows the latest design of the gear shifting mechanism which is implemented in our SUPRA SAE vehicle.
In the design shift lever can rotate control shaft at an angle of 10o and can move control shaft 1cm forward and backward which will thus engage gear as shown in fig 29.
Fig 29 shows that for engaging gear 1st shift stick has to be rotated at anticlockwise and then in forward direction. Shift stick will only rotate at angle of 10o both in clockwise and anti clockwise direction and move 1cm back and forth.
Finally the gear shifting mechanism is implemented on SUPRA SAE vehicle with some minor changes but the concept of design remains the same.
The problem which occurred was to develop a good gear shifting mechanism which will not give a mirror image of original shifting pattern.
Solution for the problem is achieved by understanding the problem and by working on the mechanism.