Vehicle Chassis- Layout

Vehicle Layout

Definition-

It is the layout of the vehicle which indicates the location of the engine and drive provided to it.

Significance of vehicle layout - Vehicle layout (i.e. chassis layout) is nothing but a representation of locations of various components like engine, clutch, gearbox, transmission system, etc. One can easily identify the various advantages and disadvantages of chassis layout by just looking to its type.

Types of vehicle layout-

1.     Front engine Rear-wheel drive

2.     Front engine Front-wheel drive

3.     Rear engine Rear wheel drive

4.     All-wheel drive (Four-wheel drive)

1)    Front engine Rear wheel drive-

Layout-

Fig. Front Engine Front Wheel Drive

Explanation- 

Ø    It is the most conventional type of layout & as the name suggests, the engine is mounted at the front part while the drive is transmitted to the rear axle. e.g. Bolero XL  

Ø The drive chain in this layout is: Engine-Clutch-Gearbox-Universal joint- Propeller shaft- Differential- Rear axle-Wheels

Advantages-

1)    Balanced weight distribution in the vehicle.

2)    Simple front axle design with a steering mechanism.

3)    Accessibility to various engine components is easier.

    4) Better engine cooling by taking full benefits of natural air stream flowing across the radiator.

Disadvantages-

1) It requires a long propeller shaft to transmit the power from gearbox to differential.

2)    Higher noise transmitted from front engine to driver cabin.

3)    The rear floor houses the propeller shaft and hence rear legs space is limited.

    4) It requires larger brake pads at front wheels because of higher weight being transmitted on front wheels while declaration.

2)    Front engine Front-wheel drive-

Layout-

Fig. Front Engine Front Wheel Drive

 Explanation-

 Ø   In this layout engine is at frontal side and power is also transmitted to the front axle.

     Ø  Hence front axle becomes a live axle. The length of propeller shaft is reduced    and hence more space is available in passenger compartment.

Advantages-

1.     This type of layout is economical and compact.

2.     The height of the chassis is less.

3.     As the propeller shaft is eliminated, weight is reduced.

4.     More weight is placed at the frontal wheels hence the vehicle has very good road adhesion.

5.     This layout tends to produce understeering which is good oversteering for safety measures.

6.     Mechanical inertia is less and hence greater fuel economy.

7.     This layout performs well on slippery roads and curves.

8.     More space is available at the passenger compartment

Disadvantages-

This layout is not used in powerful vehicles because it is difficult to provide more power and speed during a turn without resulting in understeer.

3)    Rear engine Rear wheel drive-  

Layout-

Fig. Rear Engine Rear Wheel Drive

 Explanation-

Ø This type of layout eliminates the necessity of propeller shaft as the engine mounted at rear side and drive is also given to the rear side (i.e. rear axle is a live axle now). 

Advantages-

1.     It overcomes the disadvantage in front-engine front-wheel-drive while going up the slopes.

2.     While going up the slopes, driving wheels are with more weight and hence give better road traction and adhesion.

3.     Complications at the front axle are simplified and hence it is only used only for steering.

4.     This layout has lesser chassis height due to absence of propeller shaft so that frontal side of vehicle can be designed better (i.e. aerodynamically better)

5.    As the engine is at the rear side, the engine noise and heat are carried away from the passenger compartment.

     6.  The exhaust system (like silencer, exhaust pipe, etc.) of the vehicle need not cover the whole length and can be more compact. 

Disadvantages-

1.     The vehicle becomes unstable at higher speeds due to the increase in weight at the rear side.

2.     Mechanical linkage becomes complicated due to less space for engine, clutch and transmission.

3.     As the engine is at the rear side, cooling efficiency is reduced.

4.     Oversteering conditions due to lightweight at the frontal part may occur which is very sensitive to crosswinds and somewhat dangerous.  

      5.  The access in engine and transmission units for maintenance is very difficult.

4)    All (four) wheel drive-

Layout-

Fig. All (Four) wheel drive

Explanation-

Ø This kind of layout is designed to give all speed driving, especially on paced surfaces. It will provide greater driver control and reduce wheel slippage.

Ø A transfer box is located next to the gear box to divide torque equally between the front and the rear axle.

Ø Constant velocity joints are provided at the front axle because of the large angular momentum involved during steering.

Ø With the help of transfer box, front-wheel drive can be disengaged when not required.

Advantages-

1.     In emergency conditions like front wheels fall into a ditch, they can be driven out as being power-driven.

   2.  These vehicles give additional adhesion between road and wheels so that skidding reduces.

Disadvantages-

1.     Higher fuel consumption.

2.     Smooth steering is not possible due to direct and indirect loads on axles.

3.     Ground clearance is kept more to avoid any collision with road irregularities.

     4. Chassis experience more weight due to extra propeller shaft, extra differential, etc.