Chassis & Frames

Content: Chassis Layouts & components, Types of chassis frame

Chassis: Vehicle without body called chassis, all systems mounted on that.

1 Chassis Layouts: Rear Wheel drive, Front Wheel drive, Four wheel drive

 

 2.2 Terminologies: Wheel base, Wheel track, Ground clearance

Wheel base: The distance measured between center of front axle and center of rear axle is called wheel base.

Wheel Track: The center to center distance between two tyres on the same axle is known as track width of the vehicle.

Ground clearance: Vertical distance between the lowest portion of a vehicle and the ground is termed as ground clearance.

2.3 Layouts based on Engine location:

a)  Front engine front wheel

b)  Front engine rear wheel drive

c)  Rear engine front wheel drive

d)  Rear engine rear wheel drive

2.4 Advantages and Disadvantages of Front engine Front wheel Drive: 

Advantages:

√     Load remains distributed on the steered and driven wheels.

√     Good road holding, especially on wet road. The car is pulled not pushed.

√  Insensitive to side  wind.

√     Simple rear axle design.

√     Long wheel base making high ride comfort.

√     Short power flow.

√     Good engine cooling (radiator in front), and an electric fan can be fitted.

√     Effective heating due to short paths.

√     Exhaust system with long path.

Disadvantages:

√     Poorer drive off capacity on inclines , thus decreased climbing performance.

√     With powerful engines, due to increasing torque and vibration influence steering and also engine length.

√     With high front axle load, high steering ratio necessary.

√     Difficult to mount an engine.

      √     Chances of bending on the exhaust system.

√     Complex front axle so, inner drive shaft need a sliding cv joints.

√     Higher tire wear on front.

√     Poor braking force distribution.

Advantages and Disadvantages of Front engine Rear wheel Drive: 

Advantages:

√     Low load at front axle, so effective steering can be possible.

√     Steering ratio is low.

√     Load is distributed on steering wheel and drive wheel individually.

√     Grear dive off capacity on inclines.

√     Breaking force is uniformly distributed.

√     Simple front axle design.

√     Good engine cooling (radiator in front), and an electric fan can be fitted.

√     Effective heating due to short paths.

√     Exhaust system with long path.

Disadvantages:

√     Complex rear axle design.

√     Rear tyre wear.

√     Poor holding of vehicle on road due to pushing effect.

√     Long drive shaft causes noises and vibration, thus causes in comfort drive.

√     Power losses are high.

Advantages and Disadvantages of Four wheel Drive:

Advantages:

√     Even tyre wear.

√     More balanced axle load distribution.

√     Reduced sensitivity to side wind.

√  An increase in the drive off and climbing capacity.

√     Better acceleration in low gear.

√     Better traction on smooth surface in all road conditions.

Disadvantages:

√     Increase kerb weight of the vehicle.

√     Lower maximum speed.

√     Increased fuel consumption.

Advantages and Disadvantages of Rear Engine Drive:

 Advantages:

√     Very good drive off and climbing capacity.

√     A short power flow.

√     Light steering due to low front axle load.

√     Good braking force distribution.

√     Easy engine dismentaling.

√     A small overhung to the front is possible.

Disadvantages

√     Moderate straight running abilities.

√     Sensitivity to side winds.

√  Extreme over steering behaviour on bends.

√     Difficult to steer on ice because of low weight on front wheels.

√     Uneven tyre wear.

√     The exhaust system is difficult to design due to sort path.

√     The engine noise is problematic.

√     Complex gear shift and clutch shifting mechanism.

√     Long water path with front radiators.

√     Engine overheating.

√     The fuel tank is difficult to house in safe zones.

2.5  Frame construction & Types:

Frame is a Strong metal structure that supports various vehicle components & systems. Function: 1. To support the chassis components and the body.

            To withstand static and dynamic loads without undue deflection or distortion.

 2.5.1 Loads on Frame:

- Bending Load: Weight of the passengers, Dead weight of vehicle, Engine torque Thrust taking members between frame and back axle withstand Compressive load.

-Torsional Load: Due to road bump

Cross members, radius rod withstand torsional load. -Impact Load: Impact of wheels with obstacles. Bumpers and over riders are used to sustain impact load.

2.5.2  Frame construction:

√     It consists of longitudinal member and Cross members(x-members at center).

√     Frame is upswept at rear and front to accommodate movement of axles due to springing. It also lowers chassis height.

√     Frame is narrowed at front for steering lock and smaller turning circle.

√     Various brackets are provided for joining body on the chassis frame, for spring shackles, mounting the springs.

√     The extension of the chassis frame ahead of the front axle is called front overhang, whereas beyond the rear axle is called rear overhang.

√     For heavy commercial vehicle, Members are straight without taper towards front or un sweep at the front and rear.

√     Various cross-sections are used at side members and cross members are:

- Channel section (Trucks etc.): Used in side members. Good to resist bending.

-          Square section (Swaraj Mazda premium etc.): Used in cross members Good to resist twisting. Channel section, two welded channel section

-            Hat section : Used for cross members.

-          I section (HCV)

Good to withstand bending load.

- Tubular section( Racing car, two wheeler) Higher resisiting torque compared to square section.

√  Materials for Frame: Mild sheet steel, Carbon sheet steel, Nickel alloy steel.

Carbon(0.25-0.35%) Mg (0.35-0.75%) Si(0.30%),Nickel(3%), Phosphorous(0.05%), Sulphur(0.5%); Aluminium alloy etc.

2.5.3 Types of frame:

1.  Ladder (Flat) frame: TATA (LPT 2213) Truck

2.  Tubular Frame: Kinetic marvel, Moped, Racing car, Motor cycle

3.    Backbone Frame: Hero Honda Street, Honda CT 100 racing motor cycle, Rear engine mounted auto vehicles, VW car

4.  Unibody or Frameless:

      - Greater strength and stiffness                Lesser weight

      -Jointless construction -Less         noise and vibration -                     Cheaper construction.