Mechanical Engineering


Introduction

The kWh NEO is a result of continuous research and development by the kWh team. The chassis has been designed and developed in house to suit the purpose of an Electric 2 Wheeler. The powertrain sizing has been done rightly to match the vehicle performance expectations. The exterior body is made sleek and minimalistic. Neo promises to be a perfect delivery fleet vehicle with its robust build, high performance and ease of maneuverability.

Concept design of the vehicle is as shown below :

Fig 1: Concept Design

Chassis Development

Based on the above concept design, we developed a model of the chassis using the Double Cradle Frame type structure. The chassis development happens to be a procedural activity which starts from vehicle ergonomic benchmarks, followed by concept chassis, CAD model, FEA process, refinements, design for manufacturing, joining methods and finally manufacturing.

Ergonomics

The benchmarking process was added on to the vehicle ergonomics study where we conducted a survey of the vehicles which offer rider comfort and benchmark these standards on to the NEO to offer superior ride comfort.

The following are a few outcomes from the ergonomics study implemented on the vehicle.

  • Seat height (<= 765mm)
  • Wheelbase (< 1130mm)
  • Ground clearance (<= 165mm)
  • Rake angle (23o)

Along with the above cited constraints, swing arm, battery and motor mounting was accommodated in the chassis by replicating the specific dimensions of those parts in the CAD model, and this was done while simulating the assembly to maintain a lower CG and to protect it from breaking at high vibrations.

CAD

Cited below are the various views of the chassis:

Isometric view

Front view

Top view

Side view

As pointed out earlier, this is a Double Cradle Frame type structure, which has a down tube supporting the motor controller, DC-DC converter and other minor components. This chassis has a significant advantage in its strength and rigidity compared to a single cradle type of chassis structure. While double cradle frames are heavier than single cradle frames but they are durable and robust.

After CAD design, we moved to the FEA process.

FEA

FEA Analysis is a procedure to study the behaviour of a structure upon different loading conditions and rectify the design in case of failures. In our application, the need for performing analysis is to design a chassis with a good factor of safety by maintaining high yield Strength against Maximum Internal Stress of the material used.  

Maximum Internal Stress <<< Yield Strength

By carrying out this process, it helps us understand the material behaviour upon load application and allows us to strengthen the weak points. This is a time saving process which otherwise would take us a number of iterations in prototype making and testing. By applying FEA we can reach better design optimisation levels in less time.

The modelled chassis is run through static analysis.

Fig 4: Chassis package loaded into FEA


Chassis components table


Fig 5: Boundary conditions and loads applied on the Chassis

Fig 6: Results of Von Mises Analysis

From the above set of images from the FEA process we can incur the loaded chassis package, boundary and loading conditions and the von-mises results. The inference from the results is evident through pictorial representation. In the results image, the legends range from blue to red which is the range of failure possibility. Thus this simulation proves the robustness of the chassis


Powertrain Sizing

Powertrain sizing was performed based on vehicle dynamics calculations and vehicle performance targets. This was a mathematical modeling done using spreadsheets and the results were obtained in graphical format.

Fig 8: Power vs Torque requirement

Fig 9: Torque vs Motor RPM requirement

Based upon internally evaluated powertrain sizing data, we chose a motor of 1.2kW delivering a peak torque of 80Nm and a peak RPM of 610. A suitable battery was designed and developed in house.

After designing the chassis, selection of powertrain components, we moved to exterior panels development.


Panels Development

Panel development was a challenging task as we just had a concept sketch to begin with. Vehicle concept was designed by an expert through 2D sketches. We had to retrieve the exterior aesthetic panels from this concept and set the scale. We further designed the panels according to the concept on CAD, fit the designs to the chassis scale and then fabricate the physical panels through various iterations. The panels with their CAD images are being listed below.

Fascia Panel (PL – 1)

This Panel covers the front section of the chassis and it houses a circular headlamp of 100 mm diameter and it also houses left and right turn indicators.

Front Panel Rear (PL - 2)

This Panel covers the rear section of the fascia panel and houses the key slot to power on.


Floor Board Panel (PL - 3)

This panel covers the mid-section of the chassis and covers the motor controller, it also provides the area for the rider to keep their foot comfortably.

Rear Panel (PL - 4)

This panel wraps around the rear section of the chassis below the body panels, it matches with the floor board panel and the body panels.


Body Panel Left (PL - 5)

This panel covers the rear section of the chassis above the Rear panel.


Boot Space Panel (PL - 7)

This panel sits between the right and left body panel, the bottom section of this panel extends till the battery box on the chassis. It also houses a mount for the seat hinge and houses the MCB. The boot has enough space for keeping a full size helmet.


Complete Panel Assembly

These Pictures show the rendering of the panels assembled together.

Real Images