Development of the Chassis and Steering System for a Narrow Track Rapid Response Vehicle under Traffic Congestion Conditions
Development of the Chassis and Steering System for a Narrow Track Rapid Response Vehicle under Traffic Congestion Conditions.
A narrow-track rapid response vehicle is a vehicle that is a narrow track vehicle with features of a rapid response vehicle that is used in emergency cases. A good narrow-track rapid response vehicle should have good strength features to enhance its performance in harsh traffic conditions. The vehicle should also have good maneuverability features to work well in traffic congestions. To enhance these features, the vehicle should have a strong chassis to enhance the strength and a good steering system which adheres to the traffic condition requirements. To achieve the requirements, a good design approach which incorporates good choice of materials, mathematical modeling and analysis is required. This research entails the development of the chassis and steering system for a narrow-track rapid response vehicle under traffic congestion conditions.
Chassis are the load bearing frameworks in artificial objects. The chassis supports the object during its construction as well as during its function. In an automobile, the chassis is the frame below the body of the automobile where the body is mounted. Other parts like the wheels and transmission system, the engine and in some cases the seats are assembled on the chassis to form a rolling chassis. In automotive, the rolling frame or chassis is made up of the frame and the running gear (Genta & Morello, 2019). The running gear is made up of the transmission system, the engine, the differential system, suspension and the driver shaft. The underbody id then then built on the chassis to complete the automobile. The frame should be strong enough to withstand twist, shock, vibrations and all other stresses. Fatigue failures should be avoided in the design of the frame. The magnitude of the stresses applied to the chassis can be used to design the chassis and predict its lifespan. In that case the stress analysis can be used.
The steering system is a system which consists of components and linkages that allow an automobile to follow a desired path. In most cases the steering system is located on the front wheels only. A hand operated steering wheel is then used by the driver to maneuver the vehicle. The rotational motion of the steering wheel is converted by the steering system into a swiveling motion (Harrer & Pfeffer, 2017). The system allows the driver to apply only small forces when maneuvering the vehicle. The chassis are interconnected with the with the steering system to allow for the movement and maneuvering of the automobile.
On the other hand, a narrow-track vehicle is a vehicle that moves forward while leaving a narrow track on the ground. Narrow track vehicles are different from other types of vehicle in that they normally lean into turns to avoid collapse on the outside. They also have a different model dynamic which enables them to hydroplane (slide and float) (Abdullah et al., 2017). In wheeled vehicles the narrow-track vehicles may have counter steering. The dynamics of narrow track vehicles enhances their fuel efficiency through reduced pavement requirements and aerodynamic drags.
A rapid response vehicle are types of vehicles which are small and can travel at high speeds. The vehicles have the ability to travel in traffic congestions and can move at higher speeds than other vehicles enabling them to respond more easily than normal emergency vehicles. A narrow-track rapid response vehicle is a vehicle which incorporates the features of a narrow-track vehicle and those of a rapid response vehicle. The objective of this research is to develop a chassis and steering system for a narrow-track rapid response vehicle which can be used under traffic congestion conditions.
The design of the frame of a vehicle mainly focuses on the stability of the vehicle and loads. The load requirements and the stability determine the shape and volume of construction. The stability is associated with the stiffness and damping characteristics of the connections. Parts connection to the chassis must ensure torsional flexibility (Szczęśniak et al., 2014). To achieve the torsional flexibility, pivot and fixed bearings are used.
Development of chassis design
The process of chassis design is as follows;
Step 1. Load case:
All the loads, displacement constraints and supports that act on the model are determined. All the forces acting on the model at different times are determined considering that the model is subjected to different forces at different conditions. First are loads due to normal running conditions. This comprise of vehicle transverse on uneven ground and maneuvering performed by the driver. The five basic load cases are bending case, torsion case, combined bending and torsion, fore and aft loading and lateral loading.
The bending forces are due weights along the chassis and loading in the X-Z plane. In dynamic conditions, the loading is always higher than in static loading and the inertia contributes to total loading. The dynamic loads can be up to four times the static loads. On the other hand, torsion occurs when the vehicle is subjected to
Fig. Bending and torsional forces
In reality the torsional stresses are accompanied by gravitational bending moments.
RR can be determined from moments balance as;
RR/2 x tr = RF/2 x tf
RR is equal to RF when the rear and front wheel tracks are the same. On road dynamic factor is 1.3 while off-road dynamic factor ranges from 1.5 to 1.8
Lateral loading is generated due to cornering and at the tire-ground contact. The loads are balanced by centrifugal forces. The vehicle rolls over when the inside wheel’s reaction is zero.
Longitudinal loads are generated when the vehicle accelerates and decelerates generating inertia forces. In acceleration, the weight is transferred from the front to the back while in deceleration, the weight is transferred from the back to the front.
Fig. Bending and torsional forces
RF =Mg (L-a) – Mh (dV/dt)/ L ………………………………………………… acceleration
RF =Mg (L-a) + Mh (dV/dt)/ L ………………………………………………… deceleration
Fig. Longitudinal forces
When it comes to longitudinal loading, the limiting tractive and braking forces are decided by the coefficient of friction between the tires and the road surface. Braking and tractive forces leads to bending through suspension. Inertia forces then add additional bending. On the other hand, asymmetrical loading is created when a wheel drops into a pit or strikes a raised object. The magnitude of asymmetrical loading is dependent on the speed of the vehicle, body mass, wheel mas and the suspension stiffness.
Step 2. Types of chassis
The chassis are classified on basis of different parameters like engine fitting, number of wheels fitted to the vehicle and controlling. There are five types of chassis used in vehicles depending on their application. The first type of chassis is the ladder frame car chassis. This type of chassis creates a solid base from the shape of the vehicle. The second type of chassis is the backbone frame chassis. The chassis connects the front and rear of the entire frame. The third type is the monocoque chassis. Monocoque chassis is similar to unibody chassis and utilizes molded metal from the materials sheet. The fourth type of chassis is the space or tubular chassis. The parts in this type of chassis are welded together to form a very strong frame. This type of chassis is very flexible compared to other forms of chassis. The final type of chassis is the combination type of chassis. The chassis uses a combination of other types of chassis to produce a form of frame which is best suitable for specific application.
Step 3. Determining the type of chassis which fits the application
The type of chassis used is dependent of the strength requirements, flexibility, cost, ease of production, size and the shape of the vehicle. In a narrow track rapid response vehicle, the frame should be light to offer flexibility and due to the high speeds required. The chassis should also be strong. Due to the small size of a rapid response vehicle the chassis frame design should also be easy to use and offer high stability to the vehicle. The high stability is also advantageous due to the high speeds of the vehicle. Looking into the characteristics of all the chassis and the requirements for this case, the tubular design meets the requirements. The design offers a lot of flexibility, strength and stability. This type of chassis also offers high strength against vibrations. The vehicle chassis should also offer for battery placement and the interconnection of the motor.
Tubular space frame
The space frame offers high strength and safety for application in a vehicle. The dynamic shape also offers less resistance allowing a vehicle to move at high speeds with high power efficiencies. The light weights of the frame also provide more advantages in terms of speeds and fuel efficiency. This type of chassis can also be designed according to the requirements of an application and components requirements. For the case of a narrow-track rapid response vehicle, this type of chassis is therefore suitable as it offers most of the requirements.
Step 4. Battery and in-hub motor placement
The battery of the vehicle should be placed in a strategic place such that it offers easy connection to the motors. Due to the weight of the battery, the battery should also be placed in a location where it offers more stability. Due to the movement characteristics of the vehicle, a lot of stability is required. Maneuvering in traffic congestions at high speeds and the small narrow shape means that the vehicle should be very stable to avoid toppling. The arrangements of the motor should also determine the placement of the battery. For high stability, the most efficient location of the battery is at the middle of the frame is located. The battery should also be placed on the frame nearer to the ground to move the center of gravity (COG) at the middle of the frame and closer to the ground. The vehicles stability will be high through such a design.
The in-hub motors should be placed depending on the power requirements of the vehicle and speeds. The motor could be placed in the front wheels only, the rear wheels only or in all the wheels. The most economical design is to place the wheels only on either of the wheels. To provide for simplicity in the design the in-hub motors can be placed in the rear wheels or the front wheels only. The motors should be inter-connected such that failure of one motor does not affect the other motor hence the vehicle can function with one motor. Moving further, the placement of the steering system should determine where the motors should be located. Considering that the steering system is technically located on the front wheels to offer easy control of the vehicle, the in-hub motors should be placed in the rear wheels to offer simplicity in the design and ease of production of the vehicle.
Fig. Design with two front wheels in-hub motors
Fig. Design with four in-hub motors
Fig. Design with two rear wheels in-hub motors
Step 5. Different concepts of tubular spaceframe for narrow track vehicle and their comparison
Looking at concept one, the chassis design is very complex. The chassis design is for the vehicle to have two front wheel and two rear wheels. This design offers little flexibility. The motors are in all wheels or the rear or front wheels only. The battery is then to be placed in the middle of the chassis below the driver and the steering system is to be on the front wheels. This design is complex and expensive because it requires a lot of material. The placement of the battery in the middle also offers a lot of stability. The light weight of the design offers for fuel efficiency as much fuel is not consumed. The design also little convergence flexibilities while maintaining the stability and safety of the vehicle. the design offers a lot of strength due to the materials used.
The concept uses a little bit of a lot of materials. The design has the vehicle using two one wheels and two rear wheels. The batter is placed below the driver offering stability for the system. The frame is strong and offers a lot of strength. The design is a little bit complex. Since the vehicle uses two rear and one front wheels, the design offers a lot of stability. The design can used two in-hub motors in all the wheels or two in hub motors in either the rear or the front wheels only.
In the concept, the narrow track vehicle has one front wheel and one rear wheel like a motorcycle. The motor can be placed on either the rear wheel or the front wheel. The design offers high maneuverability of the vehicle. the battery is placed in the middle below the driver. The frame design has low strength though it is light due to the little material used. Despite that, the frame has less stability and low safety and any mistakes by the driver can cause toppling of the vehicle.
feature Concept 1 Concept 2 Concept 3
simplicity moderate Very complex very simple
cheap Moderate costs Very expensive cheap
strength Moderate strength Very strong Little strength
Flexibility/ maneuverability Flexible Little flexibility High flexibility
safety moderate Very safe Low safety
weight moderate moderate very light
stability stable Very stable Very unstable
speeds Average Low speeds Very high speeds
Inn the selection of the design, the features has differing ranking. The features can be arranged and given scores according to their importance in a range of five. The concept with the highest scores in terms of features is then selected.
Feature Rank points Concept 2 Concept 1 Concept 3
speeds 10 1 3 5
flexibility 9 1 3 5
strength 8 5 3 2
stability 7 5 4 2
safety 6 5 3 2
weight 5 1 2 5
simplicity 4 1 3 5
Concept two score =1 x 4+1 x 5+5 x 6 + 5 x 7 + 5 x 8 + 1 x 9+ 1x 10=133
Concept one score = 3 x 4+2 x 5+3x 6 + 4 x 7 + 3 x 8 + 3 x 9+ 3x 10=149
Concept three score = 5x 4+5 x 5+2 x 6 + 2 x 7 + 2 x 8 + 5 x 9+ 5x 10=182
Concept three has the highest score hence is the most suitable for this application. The concept also offers a lot of flexibilities when it comes to the development of the steering system as it is easy to maneuver the vehicle. since the vehicle’s application requires high speeds for response team to respond quickly the design is very good.
A vehicles steering is used in the vehicle’s motion control. It consists of joints, linkages and all the components needed for power transfer from the steering wheel as well as the engine to the wheels. The steering also regulates the angles of the wheels in two directional axes. The requirements for the steering system is that it must be precise, smooth, compact and light (Schaedler et al, 2011). The steering system must also give a perfect feel to the driver. The main types of steering systems operating mechanism used in vehicles are;
1. Rack and pinion – It is the main steering mechanism used in cars and small trucks. The rack and pinion gear are enclosed in a metal tube with the end of the track pointing out from the tube. A rod is used to connect to each end of the track. The pinion gear is then attached to the steering shaft. When the steering wheel is turned, the gear spins moving the rack (Harrer & Pfeffer, 2017). The role of the rack and pinion in this mechanism is to convert the circular motion of the steering wheel to linear motion. Gear reduction is allowed making it easier to turn the wheel.
2. Steering box or Re-circulating ball- This mechanism is mainly used in heavy vehicles. A parallelogram linkage system is used.
The steering system can be manual or powered. The selection of the right system to use is determined by the application requirements. The speed of the vehicle and the terrain and maneuvering of the vehicle is one of the aspects which should be considered as well as the weight of the vehicle. The powering can be electrical, hydraulic or an electrical-hydraulic hybrid (Harree & Pfeffer, 2017).
In the application for a narrow-track rapid response vehicle, the steering system should be able to absorb the road shocks, should be precise and have quick response due to the high speeds application, should offer great safety and controllability and be effortless. The best system which offers most of these features is the power steering system.
Fig. steering mechanisms
A narrow track vehicle requires a flexible steering system which is small to fit in the small size of the system. The steering system should also be fuel efficient taking into consideration that the vehicle is electrical. The electrical power steering system (EPS) is therefore suitable for the application. Compared to the rest of the systems, EPS system is the most power efficient and safe (Satou et al, 2014).
Different design concepts of steering system
The steering system is manual where it is directly connected to the wheel. The steering consists of two vertical linkages connected to the wheel. The horizontal rod is then connected to the vertical links and will be used as the control for the steering system. The steering system has dumpers to absorb the shock from bumping. The design is simple and offers a lot of maneuverability due to fast reactions when force is applied. The design is also cheap and has ease of productivity.
The concepts apply hydraulic to ease the effort applied in the control. The system combines both mechanical and hydraulics. The system is connected by mechanical linkages where the hydraulic system is connected to the wheel.
Comparison of the concepts
concept Advantages Disadvantages
1 Simple system
Less complex Hard maneuvering
Requires a lot of effort
2 Easy maneuvering
Less effort required Complex
Comparing the two designs, design one offers more feature and simplicity required in our system. The design also fits well in the chassis design chosen
For the chassis, vehicle total weight = frame weight +weight of the battery +weight of other components
The total force acting on the frame =.weight of the driver + weight components (vehicle body, battery)
Abdullah, M.A., Najmi, M.M., Harun, M.H., Ramli, F.R. and Mat, S., 2017. Chassis design and analysis of narrow track vehicle. Proceedings of Innovative Research and Industrial Dialogue 2016, 1, pp.177-178.
Genta, G. and Morello, L., 2019. The automotive chassis: volume 2: system design. Springer Nature.
Harrer, M. and Pfeffer, P. eds., 2017. Steering handbook. Switzerland: Springer International Publishing.
Satou, T., Uryu, N., & Mukai, Y. (2014). U.S. Patent No. 8,659,253. Washington, DC: U.S. Patent and Trademark Office.
Schaedler, A., Hauser, H., Ruebusch, R., Cornwell, I. D., & Greenwood, C. J. (2011). U.S. Patent No. 7,992,659. Washington, DC: U.S. Patent and Trademark Office.
Szczęśniak, G., Nogowczyk, P. and Burdzik, R., 2014. Some basic tips in vehicle chassis and frame design. Journal of Measurements in Engineering, 2(4), pp.208-214.