07-08-2012, 01:26 PM
Steering gear mechanism
Steering gear mechanism.pptx (Size: 957.88 KB / Downloads: 75)
STEERING SYSTEM
Steering is the term applied to the collection of components, linkages, etc. which will allow a vehicle to follow the desired course.
An automobile is steered with the help of steering gears and linkages, which transfer the motion of the hand operated steering wheel to the pivoted front wheel hubs via steering column. The other parts that are used for steering a vehicle are steering wheel pads, steering shafts, steering boxes, steering arms and steering stabilizers. These parts are made of durable materials like stainless steel, iron, aluminum, copper, magnesium, titanium, platinum, rubber, and plastics.
REQUIREMENTS OF STEERING SYSTEM
The steering system of any vehicle should fulfill the following requirements:
It should multiply the turning effort applied on the steering wheel by the driver.
It should be to a certain extent irreversible. In other words, the shocks of the road surface encountered by the wheels should not be transmitted to the driver’s hands.
The mechanism should have self brightening effect i.e., when the driver releases the steering wheel after negotiating the turn, the wheel should try to achieve straight ahead position.
ACKERMANN’S STEERING SYSTEM
The basic aim of steering is to ensure that the wheels are pointing in the desired directions. This is typically achieved by a series of linkages, rods, pivots and gears. One of the fundamental concepts is that of caster angle- each wheel is steered with a pivot point ahead of the wheel; this makes the steering tend to be self-centering towards the direction travel.
Ackermann steering geometry
The steering linkages connecting the steering box and the wheels usually conforms to a variation of Ackermann steering geometry, to account for the fact that in a turn, the inner wheel is actually travelling a path of smaller radius than the outer wheel, so that the degree of toe suitable for driving in a straight path is not suitable for turns.
POWER STEERING
Power steering has two types of device for steering effort one type is a hydraulic device utilizing engine power. The other type utilizes an electric motor. For the former, the engine is used to drive a pump. For the latter, an independent electric motor in the front luggage compartment is used the pump. Both develop fluid pressure, and this pressure acts on a piston within the power cylinder so that the pinion assists the rack effort. The amount of this assistance depends on the extent of pressure acting on the piston. Therefore, if more steering force is required, the pressure must be raised. The variation in the fluid pressure is accomplished by a control valve which is linked to the steering main shaft.
ELECTRIC POWER STEERING (EPS OR EPAS) is designed to use an electric motor to reduce effort by providing steering assist to the driver of a vehicle. Sensors detect the motion and torque of the steering column, and a computer module applies assistive torque via an electric motor coupled directly to either the steering gear or steering column. This allows varying amounts of assistance to be applied depending on driving conditions. The system allows engineers to tailor steering-gear response to variable-rate and variable-damping suspension systems achieving an ideal blend of ride, handling, and steering for each vehicle. In the event of component failure, a mechanical linkage such as a rack and pinion serves as a back-up in a manner similar to that of hydraulic systems.