Continuously Variable and Geared Transmission SLTIET / MECHANICAL DEPARTMENT Page 1 1

Continuously Variable and Geared Transmission
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1. INTRODUCTION OF CVGT
In the automobile industry the transmission system is the prime consideration for any concept of the vehicle. It decides the nature of the vehicle the transmission system is designing such that it fulfills the requirement based on different factors like users, region, comfortness. Though there are various transmission systems have been invented in the last some decades. Still there are unsolved areas like higher fuel economy, higher losses, low efficiency of vehicle etc. That’s why there is still newer transmission system is require which can solve the main problems like lower fuel economy.
1.1 Concept of bike transmission: In fact the fuel economy mainly depends on the following factors 1. Transmission system 2. The way users deal with transmission system
The manufacturers can surely control the first factor by introducing first factor in developing newer transmission system But second one is not in the hand of company, because of the fuel economy value change from user to users and the way they deal with transmission system i.e. one man start the bike in first gear in full throttle. Bike reaches the maximum speed of 1st gear but he still accelerates the bike but speed not increase because of limiting speed of 1st gear. So there is total wastage of fuel after maximum speed of 1st gear. So user must change the gear but he can’t so the fuel economy is depend on the user of transmission system. We can take two most lively examples of transmission system. ? First take a case of Hero splender 110 cc motorcycles having constant mass gear transmission system with four speed gears.
So, the first issue has been solved by equipping a four speed constant mesh gear box so theoretically the fuel economy should be at a greater. But actually it is not happening. Because have not constrain second function which is the way of users deal with transmission system. When we start the bike and shift into the first gear, it is ready to be accelerated. Consider the engine speed rungs from 900 rpm (ideal speed) to 6000 rpm full throttle speed and we know that torque vs. rpm curve of any engine i.e. engine has tendency as shown in figure.
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1. Performance characteristics
Fig. 1.1 Performance characteristics of gesoline engine
The torque of lower rpm of engine increases as the speed increases and become maximums of certain engine rpm. Then as the speed still going to increase the torque rating starts decreasing, thus there is a peak value of torque at certain speed range in between lower and higher rpm of the engine speed. Now coming back into the motorbike, In first gear the gear ratio is kept high to accelerate the vehicle at higher speed from still condition. The condition is the bike in first gear, we have control over the throttle of engine i.e. rpm of the engine and our aim is to accelerate the vehicle of maximum acceleration but what happens if we actually can’t able to know when to change the gear from at which position of throttle. we can have that rpm range at which the torque value is maximum thus provides maximum transmission force on wheel. So, we have actually no control on the economy of the engine.
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2. Vehicle speed vs. Engine speed
Fig. 1.2 Vehicle speed vs. Engine speed
The speed of vehicle is has been limited due to first gear. So if you further increase the speed of the engine by giving more throttle. There will be less acceleration and more fuel consumption of the same time, as we can see into graph. The torque axis shows the same value for few different rpm values. One is of lower side and another is at higher side. It is always feasible to accelerate vehicle from the left part of peak torque curve with lower rpm, because the same torque with higher rpm of engine will consume the more fuel. This is what we can’t control into constant mesh gear box equipped motor cycle. So if there is a way we know that the speed range at which the torque is maximum and then decreases. We can change gear from first to second this phenomenon will help to perform the engine with best inputs. The same happens with second gear, thus somehow if we know the best time to change the gear we can increase the fuel economy. But in actually is it not possible , then what is possible is to introduce newer transmission system that sense the demand of speed and load condition and run the engine as it best parameter.
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3. Tractive effort vs. Speed
Fig. 1.3 Tractive effort vs. Speed
At the higher gear like in 3rd and 4th there is no issue because in 3rd and 4th gear the vehicle speed is quietly high and now not the torque on accelerator is prime consideration only speed matters. It is not require bike should get speed of 90 km/h from 60 km/h in 5 seconds. So in lower gear ratio like 3rd and 4th gear no more acceleration is required. So also there is no major change into fuel economy over the range of rpm for the 3rd and 4th gear respectively. So, the problem that decreases the fuel economy lies into first and second gear. So, somehow we have to take controls of throttle from the
gear during 1st and 2nd and again drives 3rd and 4th gear as constant gear mesh. We can switch the control from users to the throttle.
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1.2 Concept of CVT transmission:
Now take a scope of vehicle equipped with 110cc engine having continuously variable transmission systems (CVT) Again recalling the factor that mainly influence the fuel economy are 1.The transmission system 2.The way users deal with transmission system
In CVT equipped vehicles the second factor has been highly constrained. Because the drive has no independent control over the throttle position of engine. But the first main factor which highly influence on the fuel economy has been compromised due to get rid of changing gears frequently into traffic or many such reasons. So there is analytically decrease in fuel economy with CVT. There are several technical reasons that tells the cause of lower fuel economy. In CVT there are infinitely gear ratios possible over range of rpm of engine. The gear ratio is depends on the engine speed which depend on throttle position. There are no manually gear changing take place. CVT is the automatic in that, so we can place it of 1st and 2nd gears in the constant mesh gear box. Theoretically the fuel economy of CVT should be higher because as we have discovered previous that as it the control of changing gears overtaken by engine itself is the fuel economy increases. Because the engine itself understand the need of torque of specified engine speed. So the fuel economy should be higher. But it is not happening practically into vehicle due to several below reasons CVT technology is equipped with mostly centrifugal clutch in which the centrifugal force acting on rotating balls actuate the pulley position and changes the gear rotation thus to make it happen the ball should be rotated of the same speed as the engine is running. Thus the power required to rotate the balls of clutch at higher rpm is taken from the engine thus somewhat power is subtracted from to be used for main purpose. Secondly it doesn’t have manual clutch as in constant mesh geared motorcycle in which the function of manually clutch is to separate the gearbox from engine when required this can be understood by considering simple example. Consider two vehicles are going on a straight road both having same engine specification and same weight but having different transmission system one of them has constant mesh transmission system and second has CVT. Both are go frequently at same speed. There is speed 70 kmph. Now, there is a speed breaker at distance of 10m, they see on road. Now, the driver of bike having constant mesh gearbox will clutch the engine as soon as see the speed breaker ahead of 10m. so gear box and engine will be separated from each other and the engine will run of ideal speed but the vehicle is still travelling with decreasing speed without use of engine power due to inertia for next 10 meters. This saves fuel.
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But a person having a vehicle equipped with CVT has no option as like other one. He can’t clutch the engine manually. So, he is not able to run of the engine at ideal condition, because there is no separation of wheels and engine possible. Here user should be the breaking the vehicle. In other word users decreasing the rpm of vehicle and hence engine. So, in next 10m the vehicle equipped with CVT is waste the engine power and hence fuel. Hence it required more fuel compare to other vehicle which travels for 10m with ideal engine condition.
So due to lack of manual clutch here lower fuel economy and hence lower efficiency. The third reason lies of higher speed of vehicle. let’s see what happens of higher speed, when the vehicle is travelling of higher speed. The gear ratio minimum so there will be more rpm of wheels and less torque available at the wheels. But if the we decrease the throttle to decrease speed of vehicle the gear ratio will automatically change so a small region of rpm change of speed as shown into graph, through no more torque require for getting the previous speed again but this is not desirable phenomenon. Because as we compare this with gear bike in which if the vehicle is going of higher speed into fourth gear and if the speed of vehicle is decrease slightly, there is no requirement of change the gear from forth to third until the fourth gear is capable to accelerate the vehicle again. So, there constant gear ratio is maintained because no further acceleration is required for it.
Fig. 1.4 Variable gear ratio vs. Engine speed
Thus, as compare to CVT the engine will run at lower rpm and consume less fuel. But CVT is it’s best part also lies as lower engine rpm range. It is very good and smart at lower range of engine rpm.
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1.3 Concept of CVGT:
It can smartly handle the condition to accelerate the vehicle from still condition up to certain speed. Because the throttle increase so the gear ratio automatically change of optimum time and vehicle speed increase. This is the best part of CVT. It can perform the tasks of which way impossible into constant mesh gearbox causes lower fuel economy of lower gear of 1st and 2nd. So, it the control of changing gear during lower rpm up to certain limit is given to CVT and then give it return to driver at higher rpm for best fuel economy ever. So what we have done is coupled the best performance range of CVT with the constant mesh gear box, at a point at which economy of CVT start decreasing That’s why we called it CVGT continuous variable and geared transmission. That perform the both role of CVT and constant mesh gearbox within predefine engine speed. Now, what we just have to do with original data available for CVT and gear box of different two motorcycle having same all other specification. We come to know about that specified engine rpm at which the switching from CVT to geared transmission takes place and vice versa.
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2. GRAPHICAL REPRESENTATION
2.1 CVT:
Fig. 2.1 CVT Transmission
2.2 Constant mesh gear:
Fig. 2.2 Constant mesh gear box
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2.3 CVGT:
Working transmission when vehicle speed is under 35 kmph
Working transmission when vehicle speed is over 35 kmph
Fig. 2.3 CVGT Transmission concept
So as we shown into block diagram CVGT has specified switching rpm at which it switching from CVT to constant mesh gear box.
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2.4 Flow chart of CVGT:
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3. TECHNICAL PROOF ; ANALYSIS
The theory explain above should be proven from technical data and graphs available for two different vehicles one equipped with CVT and other equipped with constant mesh gearbox with same engine specification. The detailed data that was thankfully available for geared bike is for Hero Honda CD 100 which has following dimensions and specification.
3.1 Specifications:
Hero Honda CD 100 Specifications Primary reduction ratio 3.421 (65/19) Secondary reduction ratio 3.000 (42/14) Clutch type Wet, multiple-disc Transmission type Constant mesh, 4-speed Shift type Return Gear ratio-1st gear 3.273 (36/11) Gear ratio-2nd gear 1.765 (30/17) Gear ratio-3rd gear 1.190 (25/21) Gear ratio-4th gear 0.917 (22/24) Wheel diameter 25.984 inch.
Final drive Chain
Table 1. Hero Honda CD 100 Specifications
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The detailed data for Honda Activa which equipped continuous variable transmission (CVT) which has following dimensions and specification.
Honda Activa specifications
Displacement 109.19 cc Bore 50mm Stroke 55.6mm Compression ratio 9.5:1 Maximum power 8 bhp Maximum torque 8.74 Nm Weight of active 103 kg Table 2. Honda Activa specifications
3.2 Gear transmission graphs:
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Fig. 3.1 Gear transmissions graph
3.3 Cvt graph:
Fig. 3.2 CVT transmission graph

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4. FUEL ECONOMY ; RESULT
The fuel economy of a vehicle is evaluated by the amount of fuel consumption per 100 km traveling distance (liters/100km) or mileage per gallon fuel consumption (miles/gallon), which is currently used in the U.S. The operating fuel economy of a vehicle depends on a number of factors, including fuel consumption characteristics of the engine, gear number and ratios, vehicle resistance, vehicle speed, and operating conditions.
Fuel Economy Characteristics of Internal Combustion Engines
The fuel economy characteristic of an internal combustion engine is usually evaluated by the amount of fuel per kWh energy output, which is referred to as the specific fuel consumption (g/kWh). The typical fuel economy characteristic of a gasoline engine is shown in Figure.
The engine that we have chosen has following specifications:
Engine type Air cooled, 4-strokes, SOHC, 2 valve Weight(with oil and a full fuel tank) 98kg Cylinder arrangement Single cylinder Displacement 100 cm Bore ; stroke 50.0×56.2mm Compression ratio 9.9:1 Maximum horse power 5.5kW(7.5PS)/7000r/min Maximum torque 8.5N?m(0.9kgf?m)/4500r/min
Table 3 Engine specification
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Fig. 4.1 Fuel characteristics graph
4.1 Assumptions make:
? Both the concept has some engine specification. ? Both the vehicle has same weight. ? A frictionless has been neglected. ? The human nature toward driving vehicle has been taken ideal. ? The vehicle testing will same source. ? Fuel economy depends only on transmission system. All other factor that influences fuel economy has been underestimated because we are just comparing only transmission system. ? Drag force during higher speed has been neglected or can be taken same in both the case. ? Both transmission system running at 100% efficiency.
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4.2 Fuel economy of constant mesh gearbox vehicle:
? Fuel economy characteristic with constant mesh geared vehicle
Fig. 4.2 Constant mesh geared fuel economy
As shown into above graph the fuel economy in 1st and 2nd gear is comparatively low because the max speed is bounded by higher gear ratio and also, we apply bigger throttle so kmpl stay lower and decrease with increase the rpm of engine. In 3rd and 4th gear the gear ratio are lower so there is less digression into speed. So, linear velocity of vehicle would be higher though lower engine rpm kmpl for third and fourth gear is high but decreasing with increasing in speed due to engine characteristics. The fuel economy curve with linear speed for CVT vehicle has been shown in figure.
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4.3 Fuel economy of CVT vehicle:
? Fuel economy characteristic with CVT vehicle
Fig. 4.3 CVT fuel economy
The graph has slightly higher fuel economy at starting and remains somewhat constant throughout the vehicle speed. But at higher speed there is decrease in fuel economy. These happen because, unlike constant mesh geared transmission here into CVT as engine speed increase which cause higher fuel consumption. The gear ratio also changes which causes lower fuel consumption.

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Continuously Variable and Geared Transmission
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But if you compare both the transmission system as below,
Fig. 4.4 Combine transmission fuel economy
We can see that the fuel economy from starting to certain speed of vehicle is higher into CVT from 1st and 2nd gear of constant mesh gearbox. And alter that intersection point where both the graphs intersect, the fuel economy of CVT has lower value than 3rd and 4th gear. This happened at speed around 35kmph. Thus if you run your vehicle firstly with CVT up to some speed limit (i.e. in our case it is 35 kmph) and then move onto constant mesh gearbox. The batter efficiency you will have.
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4.4 Fuel economy with CVGT vehicle:
? Fuel economy characteristic with CVGT vehicle
Fig. 4.5 Final CVGT transmission fuel economy
Now you can see from the above graph that is for CVGT, in which we have applied the above concept which gives higher fuel economy over all the speed range of the vehicle.
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5. EXPERIMENTAL COMPONENT
5.1 COMPONENT
1) Bike Engine
Fig. 5.1 Bike petrol engine
A motorcycle engine can create an enormous amount of power, which must be delivered to the wheels of the vehicle in a controllable way. The motorcycle transmission delivers power to the rear wheel through a series of structures that include the gearset, the clutch and the drive system.
2) Pulley for engine to wheel power transmission
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When the pulleys change radii relative to another, they provide an infinite gearing number gearing ratio. Figure below shows that when the radii of pulley at the driving part small and large at the driven pulley, the rotational speed at the driven is lower which can be notice as lower gear.
Fig. 5.2 Engine attached pulley
While when the radii of pulley at the driving part large and small at the driven pulley, the rotational speed at the driven is higher which can be notice as higher gear. The drive pulley connected to the engine and the driven to the wheel of the vehicle.
3) Pulley Belt
Fig 5.3 Pulley Belt
V belt Size :- 17*11 It is transmit the power from one pulley to another pulley.
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4) Bike chassis
Fig. 5.4 Bike chassis
5) Chain drive
Fig. 5.5 Chain Drive
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6) Additional Lever
Fig. 5.6 Additional lever
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6. MODELING OF CVGT
6.1 Design of CVGT
Fig. 6.1 Modeling of CVGT
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7. WORKING MODEL
7.1 Modeling of CVGT: Building a working model of CVGT , we found some mounting problems of secondary clutch to operate thus we have modified some of the mechanisms accordingly.
So, the work being carried out is described below:
Mounting of crankshaft directly to the engine magnet. On which the primary pulley is attached for use direct engine rpm. For speed reduction of engine rpm the primary pulley size is small then secondary pulley.
For secondary pulley we have attached the second chain drive. Geared transmission chain drive is working same at is and second chain drive is attached with that
In second chain drive we attached the free hub. It is for transfer the engine power to chain drive. In that weld the spline shaft for additional lever attached.
Then the secondary pulley size is large for speed reduction. In spline shaft the pulley is attach.
The additional lever is attached in spline shaft for engage the second chain drive.
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Fig. 7.1 All component Of CVGT
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7.2 Working Method of CVGT: Start the vehicle.
We start the bike then engine run at 2000 to 3000 rpm.
We have two transmission then as per requirement we use that transmission.
In traffic area we need low speed then use secondary transmission for that we engage the lever in secondary pulley then that pulley is transmit engine rpm to secondary chain drive. No need of shifting gear.
Then we want the higher speed then disengage the lever form secondary pulley. Then shift the gear for higher fuel efficiency and higher speed.
Fig. 7.2 Assembly of CVGT
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Fig. 7.3 Working of CVGT
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8. COST ANALYSIS
Sr no. PART Cost in Rs.
1. Bike Engine 5700 2. Chain Drive 460 3. Drive Pulley 290 4. Driven Pulley 1100 5. Belt 287 6. Wheel 700 7. Additional 3000
Table 4. Cost Estimation
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9. CONCLUSION
The hybrid transmission system called CVGT which comprises of best performance range of CVT transmission and constant mesh geared transmission system. CVGT gives more fuel economy than independent transmission system either it may be CVT or constant mesh gearbox. CVGT transmission save the fuel and give better performance of the light duty vehicles.
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10. REFERENCES
? https://en.wikipedia.org/wiki/Continuously_variable_transmission ? https://en.wikipedia.org/wiki/Manual_transmission ? CVtech- [email protected] ? Reference paper ? http://www.bumperdrive.com ? U.S. patent, Continuously variable gear transmission,09/287480 , U.S. patent continuously variable and geared transmission, 09/149699.

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