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 –