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.

BASICS OF ATV TIE ROD AND BRAKES DESIGNING

ANALYSIS OF TIE ROD :

As that of theoretical study of tie rod is done. The overall purpose if tie – rod is to transmit the motion from steering arm to steering knuckle and sustain the forced vibrations caused by bumps from tires due to uneven road surfaces the main task is to find the deformation and stresses induced in the tie rod and optimising it for various material combinations. The 3-D model is prepared for Tie-Rod of AISI 1020 material is assigned and analysis is carried out using ANSYS14.0.

                                                                                                                                                                                FEM OF TIE ROD FOR MAX. DEFORMATION        

                                                                                                                                                                   

                                                                                                                                                                                                         FEM OF TIE ROD FOR TIE ROD FOR MAX. STRESS                                                                                                                                                                                                            TIE ROD DETERMINATION :-

Tie rod length was found virtually in CATIA VSR20 by assuming the position of tie rod to be fixed on knuckle and extending wishbone axis to meet at the instantaneous centres and with the help of steering angle, geometrically we found tie rod                                                                                                                                                                                                                                                                                                                                                            

                                                                                                     

 Graph :

                                                                                                                                                                    Effect of the w/l on the Ackermann condition for the front-wheel steering vehicles:-                  

Bump and roll steer

Steer with ride travel is very common in all terrain scenarios.steer with ride travel is undesirable because if the wheel steers when it runs over a bumps or when the car rolls in a turn the car will travel on a path that a driver did not select intentionally.

Ride/Bump and roll steer are a function of the steering geometry . If the tied rod is not aimed at the instant axis of the motion of the suspension system then the steer will occur with ride because the steering and suspension are moving about different centres. If the tie rod is not of the correct length for its location then it will not continue to point at the instant axis when the suspension travelled in ride. Thus the choice of the tie rod location and length is important. If the tie rod height and angle are adjustable it is usually possible to tune most of the ride steer out of a suspension.

Curved ride/bump steer as shown in figure are to be avoided because they result in a net change in toe with ride and the steer effect changes from under steer to over steer depending on the wheel ride position. If ride steer plot is curved then a possible solution is to raise both the ends of the tie rod to move it closer to the shorter, upper A arm with the tie rod angle also be adjusted.

Braking system

Objective –

The purpose of the braking system is to increase the safety and maneuverability of the vehicle. In order to achieve maximum performance from the braking system, the brakes have been designed to lock up all four wheels at the same time. It is desired from a quad bike that it should have effective braking capability to negotiate rigid terrains.

Design –

The braking system is composed of both internal expanding drum brakes and disc brakes. The drum brakes are installed at the two front wheels and a single rotor is mounted on the rear axle to satisfy the braking requirements of our quad bike such as terrain of the track, speedlimits, driver ergonomics and other rulebook constraints.

The front drum brakes are mounted on each wheel of internal radius 2.5 inches having a brake lining width of 3 mm. The distance between the pivot point of both the brake shoes and the cam is 3.93 inches.

At the rear axle we are using disc brake due to fact that we require a effective braking at the rear. It is also to our advantagethat even if the front brakes fail in the worst case scenario, braking power is still available to the driver. The Rear brake is composed of 5 inch diameter disc and dual piston 1.5 inch diameter calliper.

FEM OF BRAKE DISK ( CUSTOMISED ) :

The role of FEA analysis in disk brake helps us to ascertain the importance of holes in the design of disks.

TYPE of Element used : PLANE 55

Since the thickness of disk is very small (4mm) when it is compared to its diameter, hence the analysis in 2-D. for this reason, the plane element is chosen in place of solid element in case of 3-D analysis.

BOUNDARY CONDITION :

The boundary condition is that the temperature of outer edge is 40C and of the inner edge also 40C.

THERMAL LOAD :

The temperature of the contact patch is assumed to be 700C. It is assumed to be annular region.

                                              

ANALYSIS OF RESULT :

By using 8 holes of 10mm diameter in the disk the temperature of the disk is reduced and more area is under reduced temperature. Hence by using holed disk the life of the disk can be improved from thermal degradation.

Calculations–

The total weight of the vehicle along with a average weight of driver ( 70 kg ) was estimated to be 260 kg. The weight distribution for the quad bike was estimated to be approximately 45:55 from the front to the rear. The static weight distribution of the vehicle is 117 kg at the front and 143 kg at the rear.

Stopping Distance (SD) = (Vmax)2/2μg

= (16.662/2 x 0.75 x 9.81 = 18.72 m

Deceleration rate (Dx) = (Vmax)2/2 SD

= 16.662/2 x 18.72 = 7.36 m/sec2

Dynamic weight transfer (ΔW) = Dxx W x Hc.g/gxl

=7.36 x 280 x 0.406 / (9.81 x 1.193) = 71.49 kg

Total Torque to drive the wheel =
TF + TR = 1656.3x0.2413 + 403.18x0.2286
= 491.83 Nm

For Front Drum brake–

Initial Data-

Driver effort                                                              25 lbs

Lever Ratio                                                               6.3:1

Coefficient of friction ()                                           0.5

Internal Radius of Drum (r)                                      2.5 inches

Width of Brake Lining (b)                                        3 mm

Pivot point to cam distance (l)                                  3.93 inches

θ1                                                                              30

Θ2                                                                             150

Braking Torque( Tb )

= μp1br2 ( cosθ1– cos Θ2 )

= 0.5 x 16.427 x 106 x 0.003 x (0.63)2

= 169.386 N-m

Braking Torque for both the wheels (TBF)=2 x Tb

= 2 x 169.386 = 338.772 N-m

For Rear disc brake –

Initial data –

Drive Effort (DE)                                                               80 lbs

Pedal Ratio ( RP )                                                              4.66:1

I.D of Master Cylinder ( IDmc )                                       14.043 mm

I.D of Calliper (IDc)                                                         38.23 mm

μ between Disc Pad & Rotor                                             0.4

Diameter of Rotor                                                             5 inches

Pressure developed at master cylinder(Pmc)

= DE x RP / π/4 x (IDmc)2

= 10.09 x 106 N/m

Force of friction generated by brake pad (Ffri) = 2x Fcal x μ

= 9154.56 N

Torque at Rotor(Tr) = Ffri x Reff

= 9154.56 x 0.0508

= 465 N-m

Torque at Rear wheels(TBR) = Tr

= 465 N-m

Final Result-

Deceleration Rate                                                                  7.36 ms-2

Stopping Distance                                                                 18.72 m

Stopping Time                                                                       2.25 sec

Braking Force                                                                        3437 N

Dynamic mass Transfer                                                         71.49 kg

Braking Efficiency                                                                 75%

BASICS OF ATV STEERING DESIGNING

STEERING DESIGN

Objective –
The objective of steering system is to provide max directional control of the vehicle and provide easy maneuverability of the vehicle in all type of terrains with appreciable safety and minimum effort. Typical target for a quad vehicle designer is to try and achieve the least turning radius so that the given feature aids while maneuvering in narrow tracks, also important for such a vehicle for driver’s effort is minimum. This is achieved by selecting a proper steering system (Centrepoint Steering 1:1). The next factor to take into consideration deals with the response from the road. The response from the road must be optimum such that the driver gets a suitable feel of the road but at the same time the handling is not affected due to bumps. Lastly the effect of steering system parameters on other system like the suspension system should not be adverse.

Design –

We researched and compared multiple steering systems. We need a steering system that would be easy to maintain, provide easy operation, excellent feedback, cost efficient and compatible to drivers ergonomics. Thus we have selected 4 bar linkage centralized point steering system for our Quad bike.

We have increased our front and rear track width to improve the lateral stability according to offroad conditions. Rear track width is kept slightly less than front track width to create a slight over steer in tight cornering situation which allows easier maneuverability at high speed.

                   Lateral Weight Transfer (LWT) = Lateral Acceleration * Weight *Hcg
                                                                                      g * Track Width
         
     OLD-
                   Lateral Weight transfer (LWT) = 7.41 * 260 * 0.406
                                                                            9.81* 0.838
                   OLD LWT= 95.14 Kg

   NEW:-
                   Lateral Weight transfer (LWT) =  7.41 * 280 * 0.406
                                                                            9.81* 1.2192  
                 NEW LWT= 70.34 Kg
               
                   % reduction in  Lateral Weight transfer (LWT) = 95.14 - 70.34   * 100     
                                                                                                         95.14

                  % reduction in  Lateral Weight transfer (LWT)  = 26 %

Calculations -


We have done following calculations on our steering system

Wheelbase(L)                                                         47” = 1.193 m

Front Wheel Track                                                 46” = 1.168 m

Rear Track Width                                                  44” = 1.117 m

Weight Distribution                                               45:55

Total Weight                                                          280 kg

Turning Radius                                                      2.5 m

Static Weight on Front Wheel                               126 kg

Static Weight on Rear Wheel                                154 kg

        % Ackermann Geometry = Angle of inside wheel - Angle of outside wheel
                                                        Angle of outside wheel for 200% Ackermann
                                                    
                                                    = 82.56 %

Slip Angle:                                tan\theta = p/b

For front Wheels,                     theta =  17.65


For Rear Wheels,                     theta =  23.25 

Acceleration of vehicle:

                                                   =   \alpha = V^2 / g* R

                                                   = 11.705 m/s^2

Cornering Stiffness:

                                            C.S = Lateral Force On each Wheel / Slip Angle

                                             For front, C.S=35.23 N/degree
                                             For Rear, C.S=29.96 N/degree

Under Steer Gradient(K):
                                               
                            k =( weight on front tyre / c.s front ) - ( weight on rear tyre / c.s rear )

                            K= − 0.79 (-ve sign indicates the tendency to over steer)

                                   Critical Speed(=29.13 m/s = 104.86 kmph )

Description                                                       Manually Assisted (Centralized)

Steering Box                                                   Centralized Steering System (4 Bar linkage mechanism)

Lock to Lock Turns                                          0.30 Turns

Outside Wheel Turning Angle                         22.45ْ

Inside Wheel Turning Angle                            30.90ْ

Steering Ratio                                                    1:1

% Ackermann Geometry                                 82.56%

Turning radius                                                  2.5 m

Ackermann Angle                                            10.21ْ

Under Steer Gradient                                       -0.79

Steering Mechanism –

To achieve the correct steering, two types of mechanisms are used. They are the Davis & Ackermann mechanism, Ackermann Mechanism is used generally for application are low. This type of geometry is apt for all-terrain vehicle like Our Quad where the speed seldom exceeds 60 kmph because of the terrain. This geometry ensures that all the wheels roll freely without the slip angles as the wheels are steered to track a common turn centre

Steering Arm Angle:-

The angle which the steering arm makes with the centre line can be found out geometrically by drawing the given diagram in CATIA or by practical measurement

Turning Radius –