BASICS OF THE ATV DRIVE TRAIN DESIGNING

DRIVE TRAIN-DESIGN

Objective-

The drive train includes the engine, transmission and theaxles for transmitting the power to the wheels. The drivetrain of amotor vehicle is the group of components that deliver power to

the driving wheels. This excludes the engine or motor thatgenerates the power. In contrast, the powertrain is considered asincluding both the engine or motor, and the drivetrain

SHIFTER TRANSMISSION (MANUAL GEARBOX) –

The shifter transmission has high output and power transfer.The power is more easily controlled on with the gear shifter anddesired gear can be chosen at any time. The main advantage of

the shifter transmission is that it is tried and tested in manyprevious vehicles besides it has a high output also.Therefore we have decided to use the shifter transmission. Wehave studied the transmissions of various 2-wheelers and othersmall vehicles but none of them meets our requirements as muchas the Honda CBR 250 transmission does. Therefore we havedecided to use the HONDA CBR 250 transmission. Since wehave to manage maximum speed at 60 kmph so we have

restricted our vehicle up to 3rd gear only.

Engine Specification -

Engine                                                                                               CBR 250

Displacement                                                                                    249.4 cc

Bore x stroke                                                                                    76 mm x 55 mm

Compression Ratio                                                                           10.7:1

Power                                                                                                26.2 bhp (18.7 Kw) @8500 rpm

Torque                                                                                              22.9 N-m @ 7000 rpm

Idle Speed                                                                                        1400 rpm +/- 100 rpm

Ignition                                                                                            Computer controlled digital                                                                                                                       transistorized with electric advance

Fuel                                                                                                 Petrol

Cooling                                                                                           Liquid cooled

Lubrication                                                                                     Forced and wet Sump

Lube Oil                                                                                         10W30 MB Oil

Calculations –

Formulae used:

Rw= Radius of wheel,

R = overall gear ratio,

N = Redline rpm (8500 rpm),

ηt = Transmission efficiency (85%)

fr = Rolling resistance constant,

TE = Engine torque (22.9 N-m)

Vehicle speed (V) = (2π× Rw ×N×3600/R×1000 )×0.85

(Assuming 85% efficiency ,due to transmission losses as we have used old parts)

Tractive Effort (F) = R× ηt × TE / Rw

Torque on wheel (Tw ) = R× ηt × TE

TYRES AND RIMS -

Objective -

Traction is one of the most important aspects of both steering and getting the power to the ground. The ideal tire has low weight and low internal forces. In addition, it must have strong traction on various surfaces and be capable of providing power while in puddles.

Functions-

-Supports weight

-Transmit vehicles propulsion-

-Soften impacts from roads

TYRES–

Keeping in mind all the above mentioned aspects we studied about the various types of tires available in  market and decided to use 2-Ply Duro rating tyres, tubeless tires and that have got specific tread pattern so as to provide a very strong and firm grip on all kinds of surfaces as well as sturdy enough to absorb various bumps and depressions on track. After going through the engine, transmission and some basic torque and angular velocity calculations we have finalized the diameter of front tires to 19 inches and the diameter of rear tires to 18 inches which would help us to transmit maximum power. This calculation is also in accord with the requirements of Acceleration, Hill climb, Maneuverability and Endurance events. The dimension of Front tires is finalized as 19×7 inches and Rear tires 18×9.5 where diameter is 19 inches and 18 inches and width is 7 inches and 9.5 inches respectively.

RIMS -

The Rims shall be made up of Aluminum to minimize unsprung weight. By reducing the width of the rim the inertia will be directly decreased and subsequently this will also reduce the overall weight. The diameter of all four rims will be 8 inches. To make our Design cost effective we have customised our own rims.

We selected two identical scooter rims from the scrap yard and fastened them with four 3 inch bolts which are fixed together by welding collar joint of the bolts.