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Suspension and steering systems. Karim Wagdy. A short summary of this paper. Download Download PDF. Translate PDF.
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. 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.
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. 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. 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.
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. The steering effort passes to the wheels through a system of pivoted joints. It carries the vehicle body and transmits all the forces between the road and the body. The system consists of the wishbones, the spring and the shock absorber. The spring carries the body mass and isolates the body from road disturbances.
The task of the damper is the damping of the body and wheel oscillations. Key Terms: 1. Camber — The small angle made by the wheels of the vehicle with respect to the vertical. Kingpin Angle - The angle between the steering axis and the vertical line.
Working Principle - Tyres are the most important parts of a race car. They have to transmit all drive, brake and steering forces to the road through a very small contact patch. This makes it very important for a car to keep the tyres in optimal contact with the road at all times.
That is the task of the suspension system. The wheel and brake disc are connected to the upright by bearings. One of these six rods the inclined one is not mounted to the chassis, but to a rocker. If the wheel moves up with respect to the vehicle body, the upright pulls on the rod, which in turn causes the rocker to rotate about its pivot point. A spring- damper is connected to the bell crank on one end, and to the chassis on the other.
So by rotating the rocker, the spring-damper is compressed. The coil spring absorbs the energy from a bump by compressing, and releases it again at an uncontrolled rate.
The spring will continue to bounce until all of the energy originally put into it is dissipated. Dampers are used to control this energy dissipation. They slow down and reduce the amplitude of the wheel motion by converting kinetic energy into heat.
The anti-roll system consists of a torsion bar with a lever on each end. If the movements on each end of the bar are not exactly the same, it will be twisted. This results in a reaction force. The main rocker connects the pull rod to the two subsystems.
The geometry of this rocker determines the movement of the spring-damper and the anti-roll bar as a result of the movement of the pullrod. Two operating conditions will be explained to show how the subsystems work to control the movements of the suspension. This results in the same angular rotation of the left and right main rocker. The spring-dampers are therefore actuated equally.
Since left and right levers of the anti-roll bar are rotated to the same angle in the same direction, it will not create a reaction moment.
As a result, the outer wheel moves up with respect to the chassis, and the inner wheel will move down. This means the main rockers are rotated in opposite directions. The load on the outside spring will become higher, while the inside spring will be partially unloaded. The anti-roll bar will be twisted, which results in an opposing moment that tries to keep the vehicle body level. It takes the form of a slender arc-shaped length of spring steel of rectangular cross-section.
The centre of the arc provides location for the axle, while tie holes are provided at either end for attaching to the vehicle body. For very heavy vehicles, a leaf spring can be made from several leaves stacked on top of each other in several layers, often with progressively shorter leaves.
Leaf springs can serve locating and to some extent damping as well as springing functions. While the interleaf friction provides a damping action, it is not well controlled and results in stiction in the motion of the suspension.
For this reason manufacturers have experimented with mono-leaf springs. This lower arm system provides both lateral and longitudinal location of the wheel. The upper part of the hub is rigidly fixed to the inner part of the strut proper, the outer part of which extends upwards directly to a mounting in the body shell of the vehicle.
To be really successful, the MacPherson strut required the introduction of unibody construction, because it needs a substantial vertical space and a strong top mount, which unibodies can provide, while benefiting them by distributing stresses. The strut also usually has a steering arm built into the lower inner portion. The whole assembly is very simple and can be preassembled into a unit; also by eliminating the upper control arm, it allows for more width in the engine compartment, which is useful for smaller cars, particularly with transverse-mounted engines such as most front wheel drive vehicles have.
Overall: Simple design with wide placed anchor points providing good transverse rotational stiffness good for isolating chassis against acceleration and braking torques. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckle.
The shock absorber and coil spring mount to the wishbones to control vertical movement. Double wishbone designs allow the engineer to carefully control the motion of the wheel throughout suspension travel, controlling such parameters as angle, caster, toe pattern, roll centre height, scrub radius, scuff and more.
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