The 2013 KIIT University, Baja SAE Team is creating a design for a single-passenger off-road vehicle. The vehicle design relied heavily on knowledge of engineering principles learned in the classroom, as well as past competition experiences. The main criteria considered in the design included high-performance, reliability, safety, ergonomics, manufacturability, serviceability, and cost. All of the factors are used together to make sure that the vehicle would meet all requirements, and would be able to be produced and sold at a reasonable market value. The vehicle is designed, modeled and assembled in Solid Works and Catia to assist in finding any potential assembly problems. ANSYS is used to perform the Finite Element Analysis of the vehicle components. The use of all of these variables assisted the team in designing the most competitive vehicle possible
INTRODUCTION
THE 2013 SAE-TEAM KIIT BAJA Racing design is a
continuing development of the 2012 design. Design
goals and changes made to the vehicle are primarily
determined from observations made during the 2012
competition season. Modifications to the design not only
increased the performance characteristics of the vehicle,
but are also made to facilitate the manufacturability of
the vehicle. A complete chassis and suspension
redesign took place for 2013. The main intentions of
design changes are to decrease weight of the
components while maintaining or increasing strength.
The use of sheet metal components and FRP is a key in
the design of the 2013 vehicle. Using sheet metal
allowed the team to create components with increased
strength characteristics and reduced weight. The 2013
vehicle has been redesigned to be stronger, lighter, and
have better handling characteristics.
MAIN SECTION
This section includes design consideration, data and calculations we performed in order to finalize our design.
ROLLCAGE
Design Constraints –
Spacious enough to accommodate 6’3” tall driver.
6’3” mannequin created using anthropology data.
Comfortable driving position -drifting driving posture.
Easy entrance and exit for driver.
Strictly as per BAJASAEINDIA 2013 Rulebook.
Proper mountings for shockers, wishbones, steering, rear compartments for engine and transmission etc.
Material Selection –
The material chosen for the manufacturing of the chassis was 4130 Chromoly Steel. Although thousands of steel alloys exist, only two types, 1020 and 4130, are readily available and reasonably priced. The most common carbon steel, 1020, is a basic structural steel that welds and forms very well; however it has a lower overall strength than 4130. 4130 Chromoly is known throughout the racing industry for its high strength and outstanding welding characteristics. As a result of these characteristics Chromoly was deemed the best material for the chassis.
Also to reduce weight and increase stiffness and strength two different dimensions of tubes were used.1.25” OD 0.079” thickness and 1” OD 0.079” thickness for Primary and Secondary sections. The dimensions and 1:1 PVC model are shown in in APPENDIX I. Overall length was reduced by 10% due to proper assembly of powertrain and weight was reduced from 55kg in 2012 to 39kg this year.
Analysis –
To properly approximate the loading that the vehicle will see an analysis of the impact loading seen in various types of accident was required. To properly model the impact forces, the deceleration of the after impact needs to be found. To approximate the worst case scenario that the vehicle will see, research into the forces the human body can endure was completed. It was found that human body will pass out at loads much higher than
7g.And the Crash pulse scenario standard set by industries is 0.15to 0.3sec. We considered this to be around 2.5sec.It is assumed that worst case collision will be seen when the vehicle runs into stationary object. Also rollcage analyzed at much higher forces than in real case scenario. Analysis pictures are included in APPENDIX II.
ANALYSIS TYPE FORCE MAX DEFORMATION
FRONT 5600lbf – (8G)
.110”
SIDE 2800lbf – (4G) .116”
REAR 5600lbf – (8G) .213”
ROLLOVER FRONT 1400lbf – (2G) .544”
ROLLOVER SIDE 1400lbf – (2G) .346”
SUSPENSION
Objective –
Designing a suspension which will influence significantly on comfort, safety and maneuverability.
Contributing to vehicles road holding/handling and braking for good active safety and driving pleasure.
Protect the vehicle from damage and wear from force of impact with obstacles(including landing after jumping)
Maintaining correct wheel alignment.
Objective –
The overall purpose of a suspension system is to absorb impacts from coarse irregularities such as bumps and distribute that force with least amount of discomfort to the driver. We completed this objective by doing extensive research on the front suspension arm’s geometry to help reduce as much body roll as possible. Proper camber and caster angles were provided to the front wheels. An independent rear suspension will be achieved with rear semi-trailing arms (with control arms). The shocks will be set to provide the proper dampening and spring coefficients to provide a smooth and well performing ride. Thorough analysis was done on MD ADAMS CAR. Analytical Value –
Static camber: -1.5˚ Caster: +7.2˚ Spring Constant (Front): 20N/mm Spring constant (Rear): 15N/mm Static Toe angle in front tire: (-1.0˚) toe out
Front Suspension –
For our front suspension we chose one with a double arm wishbone type suspension. It provided specious mounting position, load bearing capacity besides better camber recovery.
Front Unequal Non Parallel double wishbone suspension
The tire need to gain negative camber in a rolling situation, keeping the tire flat on the ground
View of front suspension in ADAMS Car
Rear Suspension –
An independent rear suspension system was chosen to be semi trailing link with upper and lower control arms keeping into consideration the rear loading and impact effects.
a) The trailing link along with the upper and lower control arms helps in checking camber changes to a better.
b) Since the motion of the semi-trailing link is in the same plane as that of tires which allows proper motion of the shock absorber mounted on it.
Rear 3 link trailing arm suspension
Can remove unwanted unsprung mass from the suspension.
Increases wheel travel to much extent
View of rear suspension in Lotus Software
STEERING
Objective –
1. The purpose of steering system is to provide max directional control of the vehicle and provide easy maneuverability of the vehicle.
2. It must be durable to sustain the harsh off-road terrain
Customer requirements –
Low cost and high sensitivity
Low turning radius.
Minimum maintenance and high durability.
Less lock to lock angle Design –
Rack and Pinion Steering geometry was chosen because of high efficiency and sudden response. Rack and Pinion Steering box of MARUTI SUZUKI ALTO is chosen and set centrally by placing universal joints and satisfied our required steering ratio, furthermore it was cost effective too. Ackermann Steering Geometry is used, here the steering arms are angled are angled to turn the inside wheel at a sharper angle than the outside wheel. This allows the inner wheel to follow a smaller radius than the outside wheel. Collapsible steering shaft is used to enhance driver safety during the collision. Why Rack & Pinion –
Simple Construction, Light Weight & Durable
Easily Available & Cost Effective
Low Maintenance, Easy To Service & Repair
Calculation Result –
Ackermann Steering geometry is considered and according to various ADAMS iterations knuckle arm of 7.5 cm was selected, which gave optimum results. Static caster = +7.2˚. Bump steer was minimized. Inner Turning Angle (θ) = 36˚ Outer Turning Angle (Φ) =26˚ Outer Wheel turning radius was found out to be 3.8m Rof = b/Sin Φ + (a-c)/2
POWERTRAIN
As all the teams are provided with same B&S engine, so lots of emphasis was done over the design of powertrain. We had to determine which type of transmission we were going to use: manual transmission (MT) or automatic transmission (AT). For BAJA vehicle we would have to utilize CVT. CVT provides us better driver comfortability (no gear shifting), infinite gear ratio, easy installation. Moreover most MTs that would fit our application are found in motorcycles and in 4-wheelers.These vehicles have very high RPM range. A MT on these vehicles is beneficial because the operator can shift into a high gear with the RPM at a higher value. Since our engine has a small range between 1750-3600rpm, the performance gained by incorporating a MT is minimal. We felt that since CVT allows the engine to run near its max torque, it would give us the ability to obtain the max power, both at low and high ranges. Performance gain of MT happens only if the operator shifts the gear at optimal RPM otherwise there is a significant loss of performance. Using CVT we will eliminate this possibility of error. And also reliability of vehicle increases (endurance events).
Driveline –
Power is transmitted to wheel in following manner.
Advantages of using Spool –
Provides continuous traction, even in muddy terrain
& reduced power loss.
No tire skidding in wet tracks.
Light Weight- as no moving parts
Low Cost
Gear Reduction Max speed
Low forward 5.682:1 28.87 Km/hr
High forward 2.734:1 59.06 Km/hr
REVERSE 7.297:1 22.48 km/hr
Sprocket: Pinion 39:14 -NA-
ENGINE CVT FNR CHAIN SPOOL
Spool Analysis -
Max. total torque acting on the spool is 619 Nm
Minimum factor of safety is 2.2
Max. Deformation 0.5713mm
SAFETY
1. Use of standard helmet, goggle, long sleeve, long pants, gloves, arm restraint, shoes & fire safety equipment's to ensure driver safety.
2. All rotating parts to be shielded so as to prevent injuries.
3. God amount of clearance available from all the members of the cockpit.
4. Point Harness Seat Belts with Seat Belt Alarm for improved safety.
5. Worst –Worst case analysis done on the space frame.
6. Use of Standard Rear View Mirrors. 7. Brake Lights reverse light & alarm. 8. Color of the vehicle was selected to be Red as it is
least prone to accidents according to a study conducted by Monash University Accident Research Centre (MUARC) and published in 2007, analyzed 855,258 accidents.
9. Considerable analysis of sub-systems such as suspension, steering, brakes which are responsible for whole system safety.
10. Roll bar padding of optimum thickness.
INNOVATION
A particle and harmful gas control device that uses electrical forces to move the particles out of the flowing gas stream and onto collector plates. The particles are given an electrical charge by forcing them to pass through a corona, a region in which gaseous ions flow. Electrons produced in CORONA effect collides with SO2
gas and form (SO₂⁻). Anions of gases are then separated by the electric field and get deposited on collector plate.
The basic circuits of the system convert 12 v DC from battery to 8KV DC using Fly-back transformer.
Construction -
Shell is to be constructed by using mild steel, plate having dimension (0.2 * 0.1) m^2. Collecting electrodes are fabricated from lighter gauge mild steel having thickness of 18 gauges.
Discharge electrodes are wire having diameter of 2.5 mm (0.1 in.) made of stainless steel.
The overall cost is affordable and can be installed in our vehicle because of less space requirement.
Its more effective than catalytic convertor as it maintains the optimum back pressure of the engine.
Our system thus by reducing pollutant from the vehicle achieves “GO GREEN “initiative.
CONCLUSION
The objective of designing a single-passenger off-road race vehicle with high safety and low production costs seems to be accomplished. The design is first conceptualized based on personal experiences and intuition. Engineering principles and design processes are then used to verify and create a vehicle with optimal performance, safety, manufacturability, and ergonomics. The design process included using Solid Works, CATIA and ANSYS software packages to model, simulate, and assist in the analysis of the completed vehicle. Actual testing was performed to verify strengths of the chassis and components. The knowledge of the various team members regarding engineering principles and their use in automotive design contributed to the vehicle changes made. The 2012-13 BAJA SAE-TEAM KIIT design has taken weak points of past designs and used them to help develop a high performance off-road vehicle.
REFERENCES
1. Society of Automotive Engineers, 2008 SAE Mini Baja Rules, http://www.sae.org.
2. 4130-Chrome Moly Material Properties, http://www.matweb.com.
3. Smith, Carroll, Engineer to Win, MBI Publishing Company, Osceola, WI 1984.
