STEERING SYSTEM

Ø  Control of front wheel (sometimes rear wheel) direction.

Ø  Transmit road feel (slight steering wheel pull caused by the road surface) to the drivers hand.

Ø  Maintain correct amount of effort  needed to turn the wheels.

Ø  Absorb most of the shock going to the steering wheel as the tire hits holes and bumps in the road.

Ø  Allow for suspension action

MANUAL STEERING SYSTEM

There are several different types of manual steering systems, which are as follows:

Ø    Worm and sector 

Ø    Worm and roller 

Ø    Cam and lever 

Ø    Worm and nut 

Ø    Rack and pinion

POWER STEERING

The development of Power Steering was led by:

Ø  The need achieve the greatest possible road safety under:

Ø   Increasing traffic density

Ø   High axle loads

Ø   Poor road conditions 

 

MODES OF ACTUATION

Ø  Hydraulic systems

Ø  Electronic systems

HYDRAULIC POWER SYSTEM

Ø  Power steering systems normally use an engine-driven pump and hydraulic system to assist steering action.

Ø  Pressure from the oil pump is used to operate a piston and cylinder assembly.

Ø  When the control valve routes oil pressure into one end of the piston, the piston slides in its cylinders.

Ø   Piston movement can then be used to help move the steering system components and front wheels of the vehicles.

ELECTRONIC POWER SYSTEM

Ø  A "steering sensor" is located on the input shaft.

Ø  The steering sensor is actually two sensors: a "torque sensor" that converts steering torque input and its direction into voltage signals, and a "rotation sensor" that converts the rotation speed and direction into voltage signals.

Ø  There is an "interface" circuit that converts the signals from the torque sensor and rotation sensor into signals that are sent to a microprocessor.

Ø   Inputs from the steering sensor are digested by a microprocessor control unit that also monitors input from the vehicle's speed sensor.

Ø  The sensor inputs are then compared to determine how much power assist is required according to a preprogrammed "force map" in the control unit's memory.

Ø  The control unit then sends out the appropriate command to the "power unit" which then supplies the electric motor with current.

Ø  The motor pushes the rack to the right or left depending on which way the voltage flows (reversing the current reverses the direction the motor spins). Increasing the current to the motor increases the amount of power assist.

CLASSIFICATION OF EPS

EPS can mainly classified in to 3 kinds depending up on the position of the motor:

Ø  Column assist type.

ØThe power assist unit, controller and the torque sensor are attached to the steering column.

ØThis system is compact and easy to mount on vehicle.

 

Ø  Pinion assist type.

ØThe power assist unit is attached to steering gears pinion shaft.

ØThe power assist unit is outside the vehicles passenger compartment, allowing assist torque to be increased greatly without raising interior noise.

Ø  Rack assist type

. 

ØThe power assist unit is attached to the steering gear rack.

ØThe power assist unit can be located freely on the rack, allowing great flexibility in layout design.