Suspension and steering systems PDF

Preview

Summary

Suspension and steering systems Name: karim wagdy ID: 12p5095 Suspension system Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two. Main components of the Suspension System:  Tires  Whe...

Description

Suspension and steering systems Name: karim wagdy ID: 12p5095

Suspension system Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two.

Main components of the Suspension System:       

Tires Wheels (rims) Shock Absorbers (dampers) Springs McPherson Strut Suspension Upper Control Arms (A-arms) Lower Control Arms PAGE 1

     

Sway Bars (anti-roll bars) Torsion Bars Axle System Driveshaft Wheel Alignment Tire Pressure

PAGE 2

How does the Suspension System work? The suspension system connects your vehicle to its wheels. It is designed to counteract the forces of gravity, propulsion and inertia that are applied to your vehicle as you accelerate, slow down or stop in such a way that all four wheels remain on the ground. The tires: which are mounted on your vehicle’s wheels (or rims) - are the most important and visible components of the system. They transfer the power of the engine to the ground when your vehicle moves and they counter that motion when it stops. As you drive over a bumpy road, shocks are absorbed by the combined work of a shock absorber (or damper) , And a coil or leaf spring mounted on each wheel. PAGE 3

The spring is a device that stores energy in order to supply it later on. It is actually the spring that handles the abuse of the road by allowing the wheel to move up and down with respect to the frame of the vehicle. In return, the shock absorber softens the suspension moves entailed by the spring by “absorbing the shocks”. The shock absorber is a steel or aluminum hydraulic cylinder filled with oil and pressurized with nitrogen. As the suspension moves, a piston is forced to move through the oil-filled cylinder. The energy produced from the motion of the piston is dissipated as heat which in turn is absorbed by the oil. The McPherson strut suspension differs from a conventional shock absorber by the way the spring is positioned around the strut. The surrounding upper control arm – or Aarm or wishbone - and lower control PAGE 4

arm form a pivoting frame allowing the suspension to move up and down while keeping the tire/wheel system perpendicular to the ground at all times. These arms are an integral part of the McPherson strut which has become the most common shock absorber used in recent front wheel-drive vehicles. Sway bars or anti-roll bars control body roll motion during turns. They are made of spring steel and attached between the left and right wheels, at the front and rear of your vehicle. These bars are designed to keep your vehicle as leveled as possible under all driving conditions. For instance, when the left wheel is forced upon - as you are turning left - the sway bar pushes down on the right wheel counteracting the body roll. Steel torsion bars are also part of the suspension system. For each wheel, the torsion bar has one end attached to the frame of your vehicle while the other end is PAGE 5

attached to the moving suspension of the wheel. Torsion bars act like springs, twisting with varying load forces. The suspension response time with torsion bars is slightly faster than with springs and there is no bouncing effect. finally, it is the axle system or driveshaft that the power from the engine transmitted to the wheels and tires.

is

Signs of troubles related to the Suspension System: 

Excessive tire wear.



Poor steering control or off-center steering wheel.

PAGE 6



Excessive bouncing over road bumps.



Loss of control during sudden stops.



Excusive swerving changing lanes.



Front-end nose quick stops.



Vehicle sag in front or rear.

diving

while

during

PAGE 7

Steering system

The system allows a driver to use only light forces to steer a heavy car. The steering effort passes to the wheels through a system of pivoted joints. These are designed to allow the wheels to move up and down with the suspension without changing the steering angle. PAGE 8

They also ensure that when cornering, the inner front wheel - which has to travel around a tighter curve than the outer one - becomes more sharply angled. The joints must be adjusted very precisely, and even a little looseness in them makes the steering dangerously sloppy and inaccurate. There are two steering systems in common use - the rack and pinion and the steering box. On large cars, either system may be power assisted to reduce further the effort needed to move it, especially when the car is moving slowly.

PAGE 9

The rack-and-pinion system:

At the base of the steering column there is a small pinion (gear wheel) inside a housing. Its teeth mesh with a straight row of teeth on a rack - a long transverse bar. Turning the pinion makes the rack move from side to side. The ends of the rack are coupled to the road wheels by track rods. This system is simple, with few moving parts to become worn or displaced, so its action is precise.

A universal joint in the steering column allows it to connect with the rack without angling the steering wheel awkwardly Sideways. PAGE 10

The steering-box system: At the base of the steering column there is a worm gear inside a box. A worm is a threaded cylinder like a short bolt. Imagine turning a bolt which holding a nut on it; the nut would move along the bolt. In the same way, turning the worm moves anything fitted into its thread. Depending on the design, the moving part may be a sector (like a slice of a gear wheel), a peg or a roller connected to a fork, or a large nut. The nut system has hardened balls running inside the thread between the worm and the nut. As the nut moves, the balls roll out into a tube that takes them back to the start; it is called a recirculating-ball system. PAGE 11

The worm moves a drop arm linked by a track rod to a steering arm that moves the nearest front wheel. A central track rod reaches to the other side of the car, where it is linked to the other front wheel by another track rod and steering arm. A pivoted idler arm holds the far end of the central track rod level. Arm layouts vary. The steering-box system has many moving parts, so is less precise than the rack system, there being more room for wear and displacement.

PAGE 12

Power-assisted steering: On a heavy car, either the steering is heavy or it is inconveniently low geared - the steering wheel requiring many turns from lock to lock.

Heavy gearing can be troublesome when parking in confined spaces. Power-assisted steering overcomes the problem. The engine drives a pump that supplies oil under high pressure to the rack or the steering box.

Valves in the steering rack or box open whenever the driver turns the wheel, allowing oil into the cylinder. The oil works a

PAGE 13

piston that helps to push the steering in the appropriate direction.

As soon as the driver stops turning the wheel, the valve shuts and the pushing action of the piston stops.

The power only assists the steering - the steering wheel is still linked to the road wheels in the usual way.

So, if the power fails, the driver can still steer but the steering becomes much heavier.

PAGE 14...