Front-Wheel-Drive with Steering

Objectives

• Introduction• Parts of FWD and Its functions• Advantage and Disadvantage of FWD• FWD vs RWD• Steering Parts

Introduction

• Most automobiles today have front-wheel drive– FWD car has transaxle– Drive axles extend to front wheels out of each side

of transaxle– Each end of the drive axle is a CV joint– Transaxle can be either manual or automatic

Front wheel drive (FWD)

Front-engine longitudinally mounted/ Front-wheel drive

Front-engine transversely mounted/ Front-wheel drive

FIGURE 3-2 Transverse (a) and longitudinal (b) mounted FWD drivetrains. Note that (b) can easily be redesigned to drive a shaft to the rear wheels of a 4WD or AWD vehicle.

Parts of FWD and Its functions

Parts of FWD and Its functions

• Transmission/gearbox - uses gears and gear trains - provide speed and torque conversions from a rotating power source to another device• Transaxle- major mechanical component that combines the functionality of the transmission, the differential, and associated components of the driven axle into one integrated assembly.• Final drive-is the last in the set of components which delivers torque to the drive wheels.

Parts of FWD and Its functions

• Clutch- mechanical device that engages and disengages the power transmission, especially from driving shaft to driven shaft. • Differential -is a particular type of simple planetary gear train that has the property that the angular velocity of its carrier is the average of the angular velocities of its sun and annular gears.• Drive shafts/ drive axle and constant-velocity joints to each

wheel

FWD axle

• Drive axles for FWD commonly called half shafts

• Half shafts allow wheels to turn and have suspension movements– Half shafts consist of inner CV joint, axle shaft and

outer CV joint– Most half shafts are unequal length causing torque

steer

Drive Axle Components • Outer CV-joint – Allows wheels to steer while axle is rotating • Inner CV-joint – Allows for suspension changes while axle is rotating • Axle shaft – Transmits power from inner to outer CV-joint

CV-Joints

• Outboard joint types – Rzeppa CV joint • Inboard joint types – Double-offset joint– Tripod Tripod-type joint – Cross-groove plunge joint

CV-Joint Functions a.) Fixed joint – Does not move in and out to change shaft length – Is used as the outboard joint b.) Plunging joint – Changes in length to allow movement of the suspension – Is used as the inboard joint

Inboard Joints

• Tripod-type joint – Has longer grooves than a fixed-type joint to allow for plunging • Ball-type joint – Is similar to a Rzeppa joint but has elongated grooves in the inner race – Is commonly known as a double-offset joint

Outboard joint • Rzeppa CV joint (Ball-type)– Was named after its designer, Alfred Hans Rzeppa – Uses three to six steel balls held together by a steel cage – The balls ride in a socket to allow rotation and turning – Is used in most front-wheel-drive vehicles

FWD Wheel Bearing Styles • Double-row, angular-contact bearings (a)– Are used on most General Motors, DaimlerChrysler, and European cars – Have two rows of ball bearings located next to each other • Opposed tapered-roller bearings (b)– Are used on Fords and most Asian cars a. b.

Advantage and Disadvantage of FWD

• Advantages– More efficient drivetrain– Better fuel economy– Combined with MacPherson struts: less unsprung

weight for better handling• Transmission hump is eliminated

• A few FWD engines have been mounted longitudinally– Most transaxles mounted sideways

Advantage and Disadvantage of FWD

• Disadvantages- FWD depends on drive shafts which contain CV joints which allow the vehicles to move in all directions that have a lot of defects.- Difficulty to direct the car when we start moving with high speed.- Unbalanced car because the mass is concentrated at the forward part of the car only- Torque steer

Rear – wheel drive (RWD)

FWD VS RWD

FWD VS RWD1- Load on tires

*The biggest benefit to rear wheel drive is that it spreads the loads of the car across all four tires of a car , the rear wheel do the pushing while the front wheels are for the steering duties .

* In front wheel drive cars the front tires must perform both functions , the engine acceleration\deceleration forces act on the front wheels that’s beside the steering duties.

2- Better weight balance

*Rear wheel drive cars have the engine in the front and the drive components in the rear , but the front drive cars have every thing up front .

*So by balancing the front and rear of the car you can improve the handling, acceleration, braking and thus safety of the car .

3-Torque Steer

*Front wheel Drive cars have a problem known as Torque Steer. This occurs when the acceleration of the engine effects the cars steering . Since the driveline is connected to the steering wheels the torque of the engine applies force to the front wheels causing the car to pull to the right during acceleration.

*Rear Drive cars do not have this problem since the engine is not connected to the steering gear.

STEERING PARTS• Steering wheel

- manipulated by the driver which the rest of the steering system responds to such driver inputs.

• Steering column- the shaft on which a steering wheel in mounted and by which it is connected by the steering gear.

• Steering gear - Rack and pinion which connect steering wheel and the

• Tie rod-Transmit motion from steering wheel to front wheels